Note: Descriptions are shown in the official language in which they were submitted.
1~9S~62;2
~ack~round o~ the Invention
.
The present invention is directed toward numerous
features within a drive train of a type having a transmission
unit which is capable of providing a generally continuous
positive coupling within the drive train. Such a transmission
unit ls preferably embodied within a hydrostatic unit in~
cluding at least one hydraulic translating means such as a
pump or motor capable of variable displacement. Again, it is
pref`erable that both the pump and motor be capable of variable
displacement.
- The present invention is also directed toward
.
broadening the operating capabilities of such a transmission
unit by combining it in series with a multiple speed range
transmission.
I The present invention is particularly concerned with
i automatically synchronizing operation of the two transmission
units to achieve a smooth transition of torque transmitting
capacity and operating speeds for the drive train.
1~ :
The present invention is also concerned with providing
20~ automatic speed controls for a transmission unit of t~Stype
first noted above. Preferably, the means for synchronizing ~-
operation of the two transmission units as well as means for ; ;~
accomplishing the speed control functions referred to above
are embodied in hydraulic controls as described in greater ~ ;~
detail below. However, it will be apparent from the following
description that the same or similar fllnctions can be achieved
through other control elements such~as electronic control
, ,:,-~
circuits.
Substantial efforts have been expended and are still
~ 30 being undertaken in an attempt to more effectively use the
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numerous advantages afforded by hydrostatic transmissions.
Generally, hydrostatic transmissions present spe~ial problems
in control since displacement of both the pump and motor must
be varied in exact sequence in order to achieve efflcient
operation and to provide suitable regulation over torque
transmitting capacity and operating speed of the ~rive train.
For example, in such a hydrostatic transmlsslon, the pump is
commonly set at zero displacement with the motor being at or
near its maximum displacement when the drive train is in a
neutral condition.
For acceleration of the vehicle, displacement of the
~ pump may first be varied toward a maximum value while the motor
- remains at its maximum displacement in order to develop maxi-
mum torque transmitting capacity for initially accelerating
the vehicle. After the pump reaches maxlmum displacement,
displacement of the motor may be gradually reduced to further
accelerate the vehicle.
Usually, as the motor approaches minimum displacement,
the full operating range of the hydrostatic transmission is
realized according to the presently available prior a~-un~ess ~ -~
the transmission includes relatively sophisticated developments
such as multiple pumps ~or extending the torque transmitting
capacity of the hydrostatic transmission. However~ such
solutions tend to make the transmissions very complex while
~; even further increasing difficulties in properly sequencing
operation of the variable displacement components therein.
'
Accordingly, it is desirable to provide a relatively
. .
simple and easily controlled means for expanding the torque
;' transmitting capacity of a hydrostatic transmission unit in
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order to better adapt hydrostatic transmissions for use in a -~
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wide variety of vehicles. In particular, hydrostatic trans-
missions wlth expanded torque transmittin~ capacity would be
useful in material handling machines such as earth moving
vehicles where a single prime mover is employed both to supp]y
motive power for the vehicle as well as to operate one or more
implements which may also have substantial instantaneous power ~
requirements relative to the maximum output capabllity of the ~;
prime mover.
An improved hydrostatic transmission would be particu-
larly useful in such machinery for numerous reasons. For
example~ material handling vehicles must be adapted both for -~
transport operation at relative high speeds as well as low ;
speed, high torque operation of the vehicle together with
intermittent operation of its implements. At such times~ the
vehicle may be subjected to frequent changes of direction and ~-
continuous accelerating and/or decelerating operation. A
;`
hydrostatic transmission unit is very suitable for such appli-
cations particularly if automatic controls are provided to `
maximize use of the available power from the single prime mover.
A hydrostatic transmission could also be adap~ëd ~or
,: :. :
relieving the engine and increasing output torque during lug
conditions by selectively and automatically reducing vehicle
speed. In addition, a hydrostatic transmission would enable
available power from a prime mover to be more precisely pro-
portioned between what is required for motive power to the
vehicle as well as supplying preferential power requirements
of various implements mounted on or assoclated with the vehicle.
Examples of presently available hydrostatic trans-
missions for use in such vehicles are set forth, for example~
in United States Patent No. 3,302,390 to Christenson and
United States Patent No. 3,47~,225 to Cryder et al~ the last
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noted patent being ass~gned to the asslgnee of the present in~entlon. The
Christenson patent discloses a transmission which is adapted for operation
of track-type vehicles whereas the present invention is partlcularly intended
for use with wheeled vehicles since it provides only a single primary drive
train. However, it will be apparent that numerous features of the present
invention could also be used, for example, with track~type vehicles includ- ;
ing dual primary drive trains.
Other examples of prior art in the area of hydrostatic transmissions
~. include United States Patents Mos. 3,187,509; 3,212,263; 3,236,049; 3,238,724;
3,247~669; 3,273,344; 3,285,000; 3,324,797; 3,331,480 and 3,411,297. -~
Summary of the Present Invention ;
The present application is divided out of copending Canadian
Application No. 256,384, filed July 6, 1976, and according to the invention .;
to which the present application is specifically directed there is provided
. a control system for regulating opera~ion of a hydrostatic transmission unit
including a hydraulic translating means having infinitely variable displace-
ment and a hydraulically actuated pilot means for regulating displacement of
the translating means, the control system comprising a flow control valve
: which is arranged to receive fluid from a source of fluid under pressure and ~.
producing a generally constant volume flow, a speed control valve in communi-
, cation with the flow control valve to receive the generally constant volume ~
flow, the speed control valve including manually operable means for producing .~: .
a fluid signal having a pressure representative of a desired output speed of :
the hydrostatic transmission, and a modulating valve assembly including a ~
modulating valve, a first pressure regulating valve communicating the speed . ~.
I control valve with the modulating valve and a second pressure regulating .
.:i valve communicating the modulating valve with.a valve means in communication
~ with the pilot means, the modulating valve being responsive to modulated
fluid pressure communicated therefrom toward the pilot means as well as means
providing an opposed biasing force, and.the modulating valve being operable
respectively with the pressure regulating valves in order to modulate the
rate of fluid flow from the flow control valve toward the pilot valve, in .
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,
use, during accelerating operation of the hydrostatic transm~ssion and for
modulating the rate of fluid flow from the pilot valve toward the speed con-
trol valve, in use during decelerating operation of the hydrostatic trans-
mission unit.
Brief ~escription of the D _win~s
Figure 1 is a partlally schematic representation oE a drive train
including a hydrostatic transmission unit and a multiple speed range trans- ;
` mission unit toge~her with a hydraulic circuit for controlling operation of
the two transmission units as well as for supplying necessary fluid to the
hydrostatic transmission unit.
Figure 2 is a schematic representation oE a control group of
elements within the hydraulic circuit for regulating operatlon of the two
transmission units. ;
' Figure 3 illustrates the composite arrangement of Figures 4-12 to ~
provide a more detailed representation, with parts in section, of the control ~ ~ -
assembly of Figure 2.
Figure 4, within the composition figure, includes a safety reset
''1 valve.
Figure 5, within the composition igure, includes a speed control
valve and a moduIating orifice valve.
~' Figure 6, within the composition figure, includes a directional
valve and a fluid accumulator.
Figure 7, within the composition figure, includes a range selector
~J valve.
i Figure 8, within the composition figure, includes an override
~l speed control valve assembly.
~ 1 , . .~1 Figure 9, within the composition figure, includes an underspeed ~ ~ -
control valve. ~-
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~ig. 10, within the composition figure~ includes an
overspeed control valve and a brake pressure control valve.
Fig. 11, within the composition figure, includes a
portion of the displacement actuator for the hydrostatic motor ;~
together with a pilot motor for operating the motor actuator.
Fig. 12, within the composition ~igure, includes a
pilot motor and associated actuator for the hydrostatic pump
unit.
Fig. 13 is a graphical representation illustrating
accelerating and~or decelerating response of the combined
transmlssion units of the present invention to a control signal.
Description of the Preferred Embodiment
In view of the relative complexity of the present
invention and the drive train embodying the invention, the fol-
lowing description is presented under the following divisions:
1) The drive train and associated hydraulic supply j`~
and controls of Fig. 1.
2) ~A summary of the hydraulic control assembly
illustrated in Fig. 2 and composite Figs. 4-12.
~! 20 3) ;Detailed description of the control asse~ly
having reference to composite Figs. 4-12
4) Description of the preferred mode of operation.
Generally, it will be noted that the present invention ;
is described with reference to a drive train includ1ng a hydro-
static transmission unit and a multiple speed range transmission
unit under the regulation of a control assembly comprising a
numher of hydraulic valve components forming a hydraulic control
circuit. However, it is emphasized again that numerous varia-
-~ tions are possible within the scope of the present invention.
Further, it will be clearly apparent from the
following description that the various control valve assembly
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.
components described below for regulatlng operation of the two
transmission units, as illustrated in Figs. 2-12, may readily
be replaced by other control elements capable of performing the
same or similar functions. In this connection, it will be
particularly obvious that the novel control functions of the
present invention may also be accomplished, for example, by
means of an electranic control circuit.
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1) The drive traln and assocLated~
and controls Or Fl
Referring now to Flg. 1, a drive train 20 is schematlc-
ally represented as including a prime mover or engine 22 wlth
a hydrostatlc transmlssion unit 24 and a multiple speed range
transmlssion unlt 26 being arranged in series between the prlme ~;
mover 22 and a primary output shaft 28 suitable ~or providlng
moti~e power ln a vehicle (not shown). ~he prime m~ver 22 is also
directly coupled ln driving relation with a pump 30 representa-
tive o~ an implement (not shown) having intermlttent power require- c
ments which are substantial relative to available power from the
prime mover 22.
If the drive t,rain 20 is employed for example, in a
loader vehicle, the implement pump 30 could be employed to ~ ;
operate a bucket or other material handling means arranged upon
lift arms of the loader vehicle (not shown). The actual identity
o~ the implement is not of importance to the present invention
except to note that power requirements o~ the implement together
with motive power requirements for the vehicle may in combination
'l~ 20 exceed the available power ~rom the prime mover 22, Accordingly,
it is desirable to efficiently employ power from the prime
mover 22 and to closely regulate operation o~ the drive train
so that both motive and implement power may be available when
required. -
The hydrostatic transmission unit 24 is o~ a type
including at least one variable displacement translating device
such as the pump indicated at 32 and the motor indicated at
34. The hydrostatic pump and motor are interconnected by means
of a hydrostatic loop comprising lines or manifolds 36 and 38 ~ ;~
` 30 which are suitably adapted ~or high pressure operation o~ the
hydrostatic transmission.
.; ~
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One embodimen~ of such a pump and motor within a
hydrostatic transmission unit is shown in U.S. Patent No.
3,381,472 invented by C. Brown, et al and issued April 29,
1969. For purposes of this disclosure, it is sufficient to
understand that the pump and motor units 32 and 34 are
respectively rotated about their trunnion mountings 40 in
order to selectively change or vary their displacement. The
pump 32 is rotated by means o~ a hydraulic servo actuator 42
while the motor 34 is rotated by operation of another servo
actuator 44. Within the preferred embodiment of the present
lnvention9 the motor actuator 44 is pre~erably arranged to
have its piston 46 fixed with its housing or cylinder 48
being coupled for movement with the motor 3LI in order to
; facilltate operation o~ a pilot means 50 in a manner described
in greater detail below.
The hydrostatic transmission 24 is illustrated in a
neutral control condition with the pump 32 being positioned
', for minimum or zero displacement and the motor 34 being ;~'
-' arranged at or near a position of ma~imum displacement.
~ecause of the closed loop mode o~ operation"-b-ët~een
the hydrostatic pump 32 and motor 34, little ~luid is lost from
the transmission so that only a limited amount of make-up fluid
need be added to the hydrostatic circuit. Accordingly, a con-
ventional relief and replenishing valve group 52 is provided
in communication with the hydrostatic lines 36 and 38 in
order to assure an ample fluid supply and to maintain a suitable
temperature range for fluid within the hydrostatic transmission
components. The relief and replenishing valve group is adapted
, for operation at high pressure while being capable of removing
or addlng fluid to either of the hydrostatic lines 36 and
38 depending upon 'cheir relative pressurization.
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~ luid under pressure which i5 supplied to the trans-
mission units as well as being employed to regulate their opera- .
tion in a manner described below, is delivered by means of a
pump 54 which is also driven by the prime mover 22. The pump
54 is of a proportional type supplying ou~put flow in proportion
to operating speed of the prime mover 22. The pump 54 draws
fluid from a reservoir 56 and di.rects it through a filter 58
toward a venturi orifice unit 60 including conventional thermal
compensating means 62. Pressure taps, 64, 66 and 68 are in .
respective communication with the venturi inlet conduit 70, the
venturi throat 72, and the outlet conduit 74 for control purposes, ~ : .
described in greater detail below. Fluid from the outlet conduit .
74 is delivered to a flow control valve 76 having a spring-
loaded spool 78 forming a restrictive orifice 80 which com-
municates the conduit 74 with another conduit 82. Operation of .;
the spring-loaded spool 78 provides generally constant volume
flow, of for example, 7.5 gallons per minute, to the conduit
"
; 82. As the spool 78 is shifted rightwardly by increased flow - :
:~ from the conduit 74, excess fluid is communicated into another ~ :
s. . ~ :
;~ 20 conduit 84 which is in communication with a variable flow
relief valve 86. The variable relief valve 86 maintains a
selected supply pressure within the conduit 811 for purposes
described below while communicating excess fluid into one of a .
~ pair of conduits 88 and 90 which are in respective communication
.. with the relief and replenishing valve group 52.
~ Excess or high temperature fluid from the relief and
:~. replenishing valve group 52 is also communicated through the
-1 conduit 90 to~a pressure-responsive cooler by-pass and relief
valve 92 which selectively directs the fluid either through a
30 cooler 94 or a by-pass conduit 96 to a jet pump 98. The jet
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pump 98 also draws fluid from the multlple speed range trans-
mission 26 through a conduit 100 wlth fluid passing through
the jet pump 98 from the supplemental cooler 94 where the
fluid temperature has been reduced to a suitable temperature
range before the fluid is returned to the reservoir 56.
The varlous portions of the hydraulic supply and
control circuit of Fig. 1, as described immediately above,
combine to permit the separate pump 54 to supply the various
fluid requirements for operation and regulation of the drive
train. One suitable embodiment is described in U.S. Patent
3,877,224, invented by G. WO Johnson and issued April 15,
1975.
The hydraulic circuit of Fig. 1 also includes a
control valve assembly 102 which is in respective communi-
cation with the conduits described above and indicated
respectively at 64, 66, 68, 82, 84, and 88. The valve
assembly 102 is effective to communicate fluid signal through
conduits 210 and 228 ~or operating the pump's servo 246 and
actuator 42. The valve assembly 102 is also operable to
develop fluid signals in additional conduits 108 and il~ wKich
are in communication with the pilot motor or the valve 50
which in turn operates the actuator l14 for the hydrostatic
; motor 34. The various components within the control valve
assembly 102 together with its mode of operation are descrlbed
below with reference to Fig. 2 and composite Figs. 4-12. ;~
2~ Summary of the hydraulic control assembly
illustrated in Fig. 2 and in composite F'igs. 4-12.
Before proceeding with a detailed description of
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the constructlon and operatlon for the various valve
components within the control valve assembly, the
various functional purposes of the valve components may be
summarized as follows. The relative location of the valve
components within the control valve assembly may be best
seen in Fig. 2 while the cletailed construction of each
valve component is illustrated within the composite Figs.
4-12. The venturi unit 60, the flow control valve 76
and the hydrostatic motor actuator 44 wh1ch were described
above in connection with Fig. 1, whlle not strictly a
part of the control valve assembly, are nevertheless
included within Fig. 2 and composite Figs. 4-12 in order
to better indicate the path of fluid flow into and through
:
the control valve assembly 102.
As an initial element within the control valve
assembly 102~ a speed control valve 112 is manually `~
operable by an operator to indicate a desired rate of ~.
operation for the drive train of Fig. 1 or its vehicle.
~he speed control valve accomplishes its function.b~
generating a signal, preferably a differential pressure
signal within a pair of conduits, as described in
greater detail below, which varies for regulating
operation of the hydrostatic transmission unit and the
. ...
multiple speed range transmission unit after first being
modified and controlled by other valve components within
the control valve assembly.
A modulating valve 114 acts upon the variable
- signal generated by the speed control valve in order -
;~ to regulate both the rate of increase for the signal,
corresponding to acceleration of the drive train, as
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well as the rate of decrease for the signal which corres-
ponds to deceleration of the drive train. The modulating
valve 114 accomplishes hoth of these purposes by means
of a common modulating orifice valvewhich will be described
in greater detail below.
The rnodulated variable sienal generated by the
speed control valve 112 and ad~usted by the madulating
valve 114 is applied to the pilot control valves for
the hydrostatic motor and pump actuators through a
directional valve 116. The directional valve 116 pre- ~-
ferably performs three basic functions. Initially, it
establishes the direction of operation for the drive
train by regulating the manner in which the modulated
signal is communicated to the pilot control valves.
Secondly, the directional valve includes means (described
below) for closely regulating the sequence in which dis-
placement variation of the hydrostatic pump and motor
is to take place. Thirdly~ the directional valve 116
establishes a selected rate of deceleration when the
direction of operation is changed, that rate of decelera-
tion being independent from the normal rate of deceleration
established by the modulating valve 114.
A range selector valve 118 operates in response to
the modulated variable signal from the speed control
'i ~ valve for autornatically establishing one of the multiple
speed ranges within the multiple speed range transmission
unit 26 (See Fig. 1). Operation o~' the range selector `-
valve for causing a shift between speed ranges is
regulated by an accumulator 120 which also receives - ~ -
the modulated signal from the speed control valve 112
~ 30 and the modulating valve 114.
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The accumulator 120 also serves to absorb unde-
sirable pressure surges in the modulated variable
signal from the speed control valve 112 and the modu-
lating valve 114, particularly during directional
changes initiated by the directional valve 116 and
speed range shifts initiated by the range selector
valve 118 and accompanied by response of the pilot
control valve 50 to reset displacement of the hydro-
static motor.
In connection with operation of the range selector
valve 118, it is also important to note that the pilot ~-
control valve 50 for the motor actuator includes means
responsive to shiftlng of the range selector valve for
resetting displacement of the hydrostatic motor in
order to permit its continued response to the modulated
signal for further acceleration or deceleration in the
new speed range. Preferably, resetting of the hydro~
static motor is accomplished without affecting the `~
modulated signal from the speed control valve 112 and
3 20 the modulating va~ve 114 in order to permit smoother
operation of the hydrostatic transmission unit in con- ;-
junction with the multiple speed range transmission ~i
unit ~See Fig. 1).
A safety control valve 122 preferably operates
in conjunction with the speed control valve 112 and ~;
prevents development of a variable signal after ;~
~tart-up of the prime mover 22 (See Fig. 1) until
the manual control element of the speed control
valve 112 is first returned to a neutral setting.
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Thus, the sarety control valve 122 assures that the con~,rol
valve assembly 102 is properly condltioned to lnitiate accelera-
ting opera-tion of the transmission a~'ter start up.
A number of components within the control valve
assembly 102 perform a generally common function of regulating
operating speed of the prime mover 22 (see ~'ig. 1), particularly
below or above a preselected operating speed range. Initially,
an underspeed control valve 124 functions to adJust the modulated
variable signal from the speed control valve 112 and the modu-
lating valve 114 when the operating speed of' the prime mover 22
is below a preselected level. Thus, when the transmission is
operating under lug conditions, its torque load is reduced in
order to permit the operating speed of the prime mover to return
to a satisfactory range.
An override speed control valve 126 acts upon themodulated variable signal from the speed control valve and the
~, modulating valve 114 in substantially the same manner as the
: underspeed control valve but under manual control in order to
enable an operator to selectively reduce the operating speed
` 20 of the drive train. The particular manner in which thi~
:~:
function is accomplished does not require resetting of the ~;
speed control valve so that a preselected speed setting may be
maintained within the speed control valve. Additionally, the
override speed control valve 126 permits a feedback function
discussed immediately below in connection with a speed limiting ;
control valve 128.
The speed limiting control valve 128 performs the
basic function of generating a signal for the purpose of applying -
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a brake within the drive train whenever the operating speed
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of the prime mover 22 exceeds a preselected maximum value~ ThusJ
when the prime mover 22 tends to be driven ln operation through
the drive train, for example, when a vehicle is travelling down-
hill, the operating speed ls automatically limited at generally
the setting established by the speed control valve 112,
The speed limiting conkrol valve 128 per~orms an
additional function in conJunction with the manually operable
override speed control valve 126. Normally, overspeeding of
the prime mover 22 occurs when an operator is attempting to
reduce operating speed o~ the drive train or vehicle through
; manipulation of the override speed control valve 125. Accord-
ingly, the speed limltlng control valve is designed to generate
a ~eedback signal which resists manual operation o~ the over-
ride control valve 126 in order to indicate to the operator the -
- 15 degree of engagement for the brakes within the drive train. Thus,
the override speed control valve 126 may be freely adjusted by
its manually controlled element to employ dynamic braking capacity
~, within the hydrostatic transmission unit for reducing speed of
` the drive train. However, when the speed limiting control valve -
initiates engagement of the supplemental brakes within the drive
train, the degree of engagement for the supplemental brakes is ; ~
thus signalled to the operator so that he is aware o~ thelr use `~ ;
in deceleratin~ the drlve train. The feedbaclc signal generated
. b~ the speed limiting control valve is ad~usted in response to
3 25 engagement pressure of the brake as well as operating speed o~
the prime mover and output operating speed Or the drive train in
order to provide a true indication to the operator as to the amount
of supplemental braking provided by the brakes. ~
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~ Lnally, the brake pre~ssure control valve
129 functions in response to the brake engagement
signal from the speed limiting control valve lZ8 in
order to selectively pressurize or engage the brake
within the drive train. Pre~erably, the brake pressure
control valve 129 is adapted to communicate actuating
pressure for the brake from one of the hydrostatic
~ manifolds, whlchever is at a higher pressure
;- It may be seen from the above summary that
the underspeed control valve 124, the override speed
control valve 126 and the speed limiting control valve ~-~
128 function in combination to automatically regulate
operating speeds for the drive -train. Operation of the
underspeed control valve 124 is relatively conventional.
. . . .
However, the valve components 126 and 128 novelly permit
the employment of dynamic braking capacity of the
hydrostatic transmission to the fullest extent possible,
:,
thereafter computing the amount of supplemental braking
capacity required to maintain operation of the prim~.S
mover within acceptable limits. This computing function
extends further to generation of the feedback signal
discussed above in order to signal the operator as to
the amount of supplemental braking capacity being employed
within the drive train. These functions for the valve
components 126 and 128 may readily be accomplished by
means other than the hydraulic valves illustrated and
described. The use of an electronic control circuit is
particularly suggested for this purpose.
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3) D _ iled description of the control valve -~
assembly 102 ;.~ ~ :
A complete representationr including cross-sectîonal
. views of the various valve components in the control valve `
: 5 assembly 102, is provided by composite Figs. 4-12. Fluid ~:
is supplied a~ a constant volume flow rate from the venturi
.~ :
.` 60 through the flow control valve 76 ~Fig. 1) to the con- .~
.. :; . ' : :- :
~. trol valve assembly 102 through the conduit 82. ..
:` Pressurized fluid necessary for operation of the hy- ; ;;:~ 10 draulic actuators which vary displacement of the pump 32 .
and motor 34 and which engages the clutches of the multiple
speed range transmission unit enters the control val~e ~;~.;.
;~ assembly through the conduit 84O .
Fluid in conduit 82 is communicated to the speed con-
trol valve 112. The valve ].12 produces a differential pres~
j sure signal for actuating or regulating other components in .~;
the control assembly 102. When a manual control spool 130 e~
l is in a neutral position within the valve 112, fluid passes . .
~ freely into another signal conduit 132 for passage through . ~
~ 20 the valve 126 and 124 before returning to the relief and ~.
:~ replenishing circuit, as illustrated in Fig. 1. . ~
' t'~
The valve 112 is illustrated in greater detail in
:j composite Fig. 5. Fluid enters the valve 112 from the con- .. ~
. duit 82 and flows through an annular groove 134 and a pair .~
~ 25 of metering slots 136 on the spool 130, an annular recess .~ .
:, .,
137 in the valve 112 and then into the conduit 132. When ~. . :
:. the spool 130 is shifted righ~wardly, the slots 136 restrict
flow thereacross 50 that pressure rises in the conduit 82. .~ ~ .
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5762Z
i~ passage 138 :In the valve 112 communicates the
conduit 82 with conduit 140 through a check valve 142 for
communication to the valves 126 and 124 for a purpose described
below.
When the spool 130 of the speed control valve 112 is
shifted leftwardly, low pressure signal fluid from the conduit
i 132 is directed to a conduit 144 in communication with the end
of a spool 146 (See ~'ig. 4) reciprocably located in the safety
control valve 122. The reset runction of the valve 122 is
initiated when the spool 146 is thus shifted upwardly against
a spring 148. Pressure from the conduit 88 in a branch conduit
150 and passage 152 is thereby communicated across a groove 154
in the spool 146 to a conduit 156 which releases the parking
brake 158 and delivers pressurized fluid to the pilot stage of
relief and replenishing valve 52 via a conduit 157, ( also see
- Fig. 1). Thus, the conduit 157 serves to vent the relief and
replenishing valve group at the same time that the parking brake
158 is applied. In addition, communication between conduits
160 and 162 is blocked for a purpose described below.
As the spool 130 of the valve 112 is shifte~-~igh~t-
wardly toward its maximum speed control position, it blocks
conduit 144 which remains pressurized by fluid from the groove
154 flowing through an orifice 164 in order to maintain the
spool 146 shifted upwardly against the spring 148. If a
malfunction should occur within the control system~ causing a
lowering of pressure in the conduit 144~ the spring 148 would
then move the æpool 146 downwardly toward its vent position
3 while fluid in the conduit 144 generally escapes past the lands
adjacent groove 166 to a drain conduit 168 to provide a timed
delay before groove 154 communicates drain conduit 168 with -
A conduit 156 so that the parking brake is allowed to engage.
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The time clelay ~eature i5 provlded to prevent mlnor pressure
rluctuations ~rom affectlng operation of the safety control
valve 122. A check valve 170 prevents excess pressure from
escaping the conduit 144 into the conduit 150. ~;
When the spool 130 of the valve 112 is moved com-
pletely to the left, the conduit 144 is communicated to a drain
- conduit 172 which enables the spool 146 to be moved downwardly ~;
by the spring 148, thus venting the transmission and applying -'
the parking brake.
When fluid pressure enters the conduit 82, it also
flows into the modulating valve 114 through a branch conduit i~
174 while lower pressure signal fluid in the conduit 132 is
directed to that valve through a conduit 176 by operation of
the valve 112 as described above. ,
,'~ The pressure of rluid entering the modulating valve
... .. .
114 is initially ad,justed by a pressure regulating reducing
: '.: !
~ valve 178 and communicated to a passageway 180. Fluid under
.: . ... , - ~ .
pressure in the passage 180 is communicated into a chamber
182 in a modulating orifice valve spool 184 and another passage
~ 20 186. The passage 186 communicates with a spring chamb^er~l~8 ;,~
; for a second pressure regulating reducing valve 190 which is
thereby responsive to pressure established by the first pressure
regulating valve 1'78 in the passage 180. Fluid from the
chamber 182 passes through modulating ori~ices 192 into a
passage 194 and then across the pressure regulating valve 190
into a high pressure signal conduit 196.
' A branch conduit 198 directs high pressure signal ~ ;
,~ fluid from the conduit 196 into a chamber 200 located on the
left end of the modulating spool 184. At the same time, low
. ~:pressure signal fluid from the conduit 176 biases the modu~
, lating spool 184 so that it is thus responsive to the same -
; differential pressure applied to the pilot operated actuators
A
~.; ,~ ~ .
7i~
42 and L14 f`or the hydrostatlc pump and motor, as will be described
in greater detail below, the dlfrerentia:L pressure thus being
a function of output speed of the drive train.
The valve 114 modulates or adjusts pressure ln the
conduit 196 by regulating the flow rate into and out of the
spring-loaded pump pilot cylinder 211 and accumulator 120.
Spring characteristics within the accumulator 120 and pilot
cylinder 211 are selected so that, as pressure in the conduit
196 increases~ the pump pilot cylinder 211 moves first, the
accumulator 120 moving second ln unison with the motor actuator
44. Thus, increased pressure in the conduit 196 results in an
increase in output speed for the drive train.
In summary, the steady-state pressure level in the
conduit 196 is determined by the instant setting for the valve
112 while the valve 114 modulates the transition or rate of
pressure change in the conduit 196 from one level to another.
Because of the opposed arrangement of the pressure
regulating valves 178 and 190, they operate in conjunction with
the single modulating valve spool lg4 to regulate fluid flow
in either direction between conduits 174 and 196, thus `eg~ab~ishing
the rates of both acceleration and deceleration for the hydro-
; static transmission. The pressure regulating valves 178 and
.
190 operate in conjunction with the modulating valve spool 184
to establish a fixed pressure drop regardless of pressure
fluctuations caused primarily by manual operation of the spool
-~ control valve 112 so that the instantaneous rate of acceleration
or deceleration is the same at any given speed of operation.
The novel construction of the modulating valve assembly
. , . ~
114 also permits three separate and independent adjustments -
~ 30 corresponding to acceleration rate, deceleration rate and the
: ', ''
:~ :
. .
57~ii2Z
characteristl.c rate chan~e f`or the modulatlrlg valve 184 - for
example, by adjusting or changing the blas:Lng force acting on
each of the regulating valves 178 and 190 and the modulating
valve spool 184 by means of their respective springs 202, 204,
and 206.
The conduit 196 communicates high pressure signal
fluid to a directional control valve 116 which determines the ;~
direction o~ travel for the drive train by varying the direction
in which displacement of the hydrostatic pump 32 occurs. ~-~
Low pressure signal ~luid is also communicated to
-;
the valve 116 through the conduit 132.
The position of a manually adjustable spool 208 ,~
determines the direction of travel for the drive train. For
~, ~... .
forward operation, the spool 208 is shifted to the position
illustrated in the composite Fig. 6. High pressure signal
fluid in the conduit 196 is then communicated through conduit
210 to one end of a pilot control cylinder 211 for regulating ~
the pump actuator 42 (also see Fig. 1). The cylinder 211 ~-
ncludes a piston 213 acted upon by opposed centering springs :
215 and 216. .~.s ~ `
. ~ With the spool 146 of the safety control valve 122
shifted upwardly, the conduit 162 is blocked from the conduit
160 to permit pressurization of the conduits 210 and 162 (see
Fig. 4).
- The directional valve 116 (see Fig. 6) also contains `
; a sequencing spool 212 which shifts to direct pressurized fluid
`~ to the pilot valve 50 for the hydrostatic motor 34. The motor ~
.j 34 is, of course, not reversible like the hydrostatic pump 32. ~ ~;
When the spool 208 ~shifts (to the position shown) to pressurize
the conduit 210, it also communicates high pressure signal -
.. , ~ .
~.' '
A
-''
~35~6;~2
rluld through a passage 214 ~o the sequerlcing valve spool 212.
Fluid flow through a passage 218 in the spool 212 shi~ts the
spool upwardly against the centering spring assembly 220. The
passage 214 is thus communicaked with a condult 222 which leads
. . . ~ ~ .,
to the pilot control valve 50 for the hydrostatic motor, the
accumulator 120 and the range selector valve 118 (see F'ig. 7). :
: When the spool 208 is shifted downwardlyf corresponding ~ ~
: to reverse operation, pressurized fluid in the conduit 196 is ~ .
transmitted through an axial passage 226 in the spool to a
conduit 228. Pressurization of the conduit 228 transmits ~luid
to the opposite end of the pump pilot cylinder 211 in order to
shift the pump 32 in the opposite direction. However, since ,
~:; the conduit 228 is in communication with a passage 230 leading ~ -
to the sequencing valve spool 212, high pressure signal fluid
is also communicated to a chamber 232 at the top of the spool :`
: 212 by means of a passage 234. The spool 212 is thus shifted ~ ;
.. : so that the passage 230 communicates with the conduit 222 for
the motor pilot valve 50.
'
. Regardless of the direction in which the spool 208: :~
is shifted, pressure in either passage 214 or 230 is al~o~
-' ~
3 ~ ~ dlrected to a passage 236 and a chamber 238 to act upon a spool , :~
240 containing variable ori~ices 242. :;
During the deceleration portion of a forward-reverse
shift which is initiated by the directional spool 208, the ~
spool 212 maintains its position until pressure acting on either .~ :
~,: end of the spool diminishes. Thus, fluid escaping from the
, pump pilot cylinder in conduit 210 must flow through the
`! variable orifices 242 thence to the low pilot pressure conduit
: 132. The variable orifices 242 are controlled by vehicle
speed, as represented by pressure in the passage 236g in order
:
. ~ .~ , ,
-
:. ~,3
-.~; :. . ~
~57g~
to provide a programmed rate of deceleratlon only during
directional shifts. The sequencing spool 212 subsequently ~ ;
shifts back to its centered position so that subsequent
acceleration, in reverse, is again regulated by the modu-
lating valve assembly 114.
As indicated above, conduit 210 communicates pres-
surized fluid to the pump pilot cylinder 211, which acts
upon a servo actuator valve 246 (see Fig. 12) so that a
,
servo-coupled valve spool 244 is shifted to direct fluid from
~ 10 the conduit 84 to the actuator cylinder 247. The cylinder
;~ 247 is part of the actuator 42 for the hydrostatic pump 32.
c
As pressure increases in the conduit 210, the piston
;` 213 moves rightwardly against the spring 215 and fluid
pressure from the conduit 228 which is connected to the low
pressure pilot signal conduit 132. As the piston 213 is ;
, shifted rightwardly, the spool 244 also moves rightwardly.
, ~ Fluid pressure is directed from the conduit 84 through the ~ ~
passage 217 to the chamber 219 in order to move the piston 221 - ~ -
leftwardly. The cyllnder 211 is thus moved leftwardly in
order to adjust pump displacement. The piston 213 is ~ëreby
shlfted leftwardly in order to block the conduit 84 from the
passage 217 and limit leftward movement of the cylinder 211. -
.3
., ~ The servo actuator functions in a similar manner in reverse.
For example~ pressure in the conduit 228 is then increased
ln order to shift the piston 213 against the spring 216 and the ~-~
relatlvely low signal pressure from the conduit 210. ~;
As the high pressure signal fluid is increased by the
speed control valve 112, displacement of the pump is first
varied. As the~pump approaches maximum~displacement, further `;
~ ~ 30 pressure increases are communicated across the sequencing spool
'.
- A ::: _~Y
~
. .~., ., .
;, ~
~ ~ 57 ~ ~Z
212 to shift a spool 248 Or the motor pi].ot valve 50 (see Fig.
11) which in turn directs fluid from the conduit 84 to the
motor actuating cylinder in order to change displacement of
the motor, as descrlbed in greater detail below.
The range selector valve 118 (see Fig. 7) functions
automatically to shift speed ranges as the motor approaches
minimum displacement or maximum speed. Low pressure signal
fluid in the conduit 132 is communicated to a chamber 250 of ~ ;
the accumulator 120 (see Fig. 6). That chamber is also com-
municated to a conduit 252 by means of an orifice 254. The
conduit 252 leads to a chamber 256 at the left end of a spool
258, as seen in Fig. 7, reciprocabIy located in the range
selector valve 118. An orifice 260 in a drain passage 262
permits pressurization of the chamber 256 which shifts the spool ~:
258 rightwardly to the position shown.
Once the spool 258 is moved rightwardly, pressure is
communicated from the conduit 222 into a conduit 264 across a
,. . .
groove 266 formed on the spool 258. Also, with the spool in
that position, fluid under pressure from the conduit 84 is
directed to a conduit 268 across a groove 270 on the spao~l 258
in order to direct fluid under pressure to engage a low range
.. , ,. ~
., j .
clutch 272 of the multiple speed range transmission 26 (also
see Fig. l). Supply fluid from the conduit 84 is also directed
to a chamber 274 and acts between a slug 276 and the spool 258 .
in order to assist in maintaining 258 in its rightwardly -~
shifted position.
As the speed control valve spool is moved further
toward the right, increasing signal fluid pressure develops
: ~.
in the conduit 222 which is communicated to the accumulator
120 and the motor pilot valve 50. As the pressure in the
- -:
.. . ~
'.' ;-:
-- A
:.... ~ .
.; . ~ .. . .. . . , ~ . . . . . .
~L~S~ 2
conduit 222 increases, it shirts a piston 278 upwardly in the
accumulator 120 against a spring 279 (see Fig. 6). The piston
moves upwardly until the chamber 250 is communicated with a
~..... ..
conduit 280 by orifices 282 in order to pressurize a chamber
284 at the right end of the spool 258. Pressure in the chamber
284 acts upon the spool 258 and shifts it to the left. rrhis
occurs because the piston 278 in the accumulator 120 moves
upwardly to ~lock the line 252, thereby allowing fluid pressure
in the chamber 256 to escape through the drain line 262. -
When the spool 258 shifts leftwardly, the conduit
268 is communicated to a drain conduit 286 across the groove
270 while a conduit 288 is communicated with the fluid supply
conduit 84 aoross a groove 290 on the spool 258. Thus, the
low range clutch 272 is deactuated and a high range clutch
2g2 is simultaneously engaged. Also, fluid pressure from the
conduit 84 is communi¢ated to a passage 294 in the spool 258
in order to work against a slug 296 and assist in holding the ;
, .! ,. : ~
;ij spool 258 in its leftwardly shifted position. The chamber 274
is simultaneously vented to a drain line 298.
Accordingly 9 to summarize accelerating operab~n,~ -~
- . ~ ~ -: .
the multiple speed range transmission is lnitially in a low
speed range and, as speed increases, the i.ncreasing differential ;~
~ . -- .
pre sure in the signal conduits first shifts the pump pilot -~
valve to increase the pump 32 from zero toward maximum dis-
placement. After the pump reaches maximum displacement, `
further increases in the differential pressure begin to shift
the motor 34 from maximum displacement toward a minimum
O
displacement condition.
In order to further increase operating speed,
~-~ 30 increasing di;fferentlal pressure shifts the multiple speed
;. i
' ~:
., '
,,
A
~S76~Z
range transmisslon unit ~rom low to high ~ange operation as
descrlbed above, while at the same time shifting the motor
displacement back toward maximum displacement as described
belo~. After the high ran~e clutch 292 is engaged, further ;
increases in differential press~re again cause the motor to
shift from maxirnum toward minimum displacement.
Rapid shifting of the motor from the minimum to
maximum displacement is accomplished as follows: The motor
pilot valve 50 and hydraulic actuator 44 are shown in detail
on Fig. 11. As stated, high pressure signal fluid is com- -
municated through the conduits 222 and 264, leading to the left
end of the pilot valve 50. Low pressure signal fluid is
directed to the right end of the pilot valve through the ;
conduits 132 and 110. The conduits 222 and 108 connect with a
chamber 300, formed in a piston 302 by means of a passage 304
in the pilot valve, a passage 308 formed in the spool 248 and
a passage 306 formed in the piston 302. The conduit 264 is in
similar communication with a chamber 310 formed in the spool
248. Pressure in the chamber 300 acts against the left end of
a plunger 312. The plunger 312 also has its right end ~n~con-
tact with the spool 248. The combination of forces developed
in the chambers 300 and 310 is counteracted on the opposite end
of the spool 248 by low pressure signal fluid communicated from
the conduit 110 and acting in a chamber 314 formed between a
piston 316 and the spool 248. Rightward travel of the piston
316 is limited by a fixed pin 318. The spool 248 is also
urged leftwardly by a spring pack 320 located at the right end
of the spool 248 (see Fig. 2).
Increasing pressure in the chambers 300 and 310
30 eventually causes the spool 248 to move rightwardly so that ~~
~ ~7
,...
.: :., . . . - - ., .~ :. . -
` ~(3 5~iZZ :`
actuator supply fluid from the conduit 84 i5 directed to a
chamber 322 in the motor actuator 44. The motor actuator
piston rod 46 moves to the left (see Fig. 11) and changes dis-
placement of the motor 34. The spring 320 is thus compressed
to balance a higher pressure in chambers 300 and 310. When
the forces on the spool 248 are balanced, the spool returns to
its center position, shown in Fig. 11, and the motor ceases to
change position. This incremental operation occurs for every
incremental increase of signal fluid pressure, until the hydro-
static motor ls shifted to a minimum displacement setting, in
order to provlde maximum output speed in a given~speed range.
At the same time increasing fluid signal pressure in
~`~ the conduit 222 is communicated into the bottom of the accumu- -
lator 120 as the hydrostatic motor 34 is shifted toward mlnimum
displacement~ the passages 282 in the accumulator piston 278 `
begin to enter into communication with the conduit 280 through
an orifice 324. Thus~ the accumulator provides precise timing
-7 for directing low pressure signal fluid into the conduit 280 ~ ~ `
i .;~ in order to shift the range selector valve spool 258 leftwardlyfor disengagement of the low speed clutch 272 and engag~7~ent ~f
the high speed clutch 292. This function was also described
i above. However, at the same time, the conduit 264 which
previously contained high pressure signal fluid is communicated
with tne low pressure signal fluid conduit 132 by means of the
groove 266 formed on the right end of the spool 258. The
I resulting reduction of pressure in the conduit 264 is also
immediately reflected within the chamber 310 in the pilot
valve 50 so that substantially constant pressure within the
chamber 314 shifts the spool 248 leftwardly. Thus, the pilot ;
valve 50 directs actuating fluid pressure from the conduit 84 ~ ~
:
,
.
1~7~
into a chamber 326 at the head end of the motor actuator 4LI
in order to rapidly shift the motor back toward a position
of maximum disp:Lacement.
After the motor is rapidly shifted back toward
its position of maximum displacement as described above, the
pilot valve 50 continues to respond to further incremental
increases in the differential signal pressure to again shift
the motor toward a condition of minimum displacement ln order
to provide acceleration in the high speed range.
It is particularly important to note that the
motor 34 is shifted back to its position of maximum displace- ~
ment by means independent of pressure in the signal conduits ~ ;
222 and 132. Rather, the motor is merely shifted by
effectively reducing pressurization in the chamber 310 of
the motor pilot valve 50. Pressure escaping from the chamber
310 may be absorbed within the accumulator 120 so that it
does not affect any other portion of the control valve `
assembly. Consequently, a shift from low to high operating ~
:: :
~- speed range does not result in uneven operation for the
drive train since it is not necessary to generate a coh~en-
i~, tional underspeed signal when the drive train is shifted ~ `~
,
into its high operating speed range.
The remaining portion of the description for the
~, control valve assembly 102 is directed toward the valve
~ components 124, 126, 128 and 129 which function to auto-
i matically regulate the differential signal pressure within
.
the control assembly 102 and thus operating speed limits for
the drive train.
.:,' ,
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~';~'', .
: . , 0~
., , -30-
.''` ~
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One embodiment o:f the underspeed control valve 124
i5 shown in above-referenced United States Patent No. 3g477~225~
The construction and mode of operati.on for the underspeed .-
control valve 124 is described below. High pressure fluid
from the conduit 140 is in communication with a passage 328 -~
in the valve 124. It is also important to note that the conduit ;.
140 is in communication with the high pressure fluid signal
conduit 222 by means of a check valve 330 (see composite Fig.
5 and Fig. 2). Generally, the underspeed control valve
functions in response to operation of the prime mover 22 below ~::
a predetermined minimum value in order to communicate the .:; :
conduit 140 and accordingly the high pressure signal conduit .
222 with the low pressure signal conduit 132 and its downstream ~:~
conduit 88. The underspeed control valve performs this function
in response to a fluid signal received from the venturi unit
60 through the venturi signal conduits 64 and 66. Note that the
.. ~ .
pressure differential between those two conduits is represen-
tative of operating speed for the prime mover 22. ;~
;: The underspeed control valve 124 includes a metering ` .~.
spool 332 for regulating fluid communication from the ~nduit
140 and:passage 328 into another branched passage 334 in
: communication with the low pressure conduits 132 and 88. Fluid ~:
,~.
: pressure from the venturi signal conduit 64 is communicated
through a passage 336 to act against the left end o~ the spool
332. Similarly, fluld from the venturi signal oonduit 66 is ~:~
communicated through a passage 338 into a spring chamber at
the right end of the spool 332.
During relatively high speed operation of the prime
:~ mover, pressure in the signal conduit 66 is relatively low so
. ~ 30: that the spool 332 remains shifted toward the right, in the ;~ - :
,:~ ,.
:': ~ :'
; :
~7~
positlon ill~lstrated in ~ig 9, by press~lre from ~he signal
conduit 64. ~lowever, as operating speed of the prime mover
decreases below a predetermined minimum value, pressure in the
conduit 66 increases in relation to pressure within the conduit
64. Accordingly, fluid pressure in the chamber 340 combines
with force of the spring 342 to shift the spool 332 leftwardly
and relieve some of the fluid pressure from the conduit 140 and
accordingly, from the high pressure signal conduit 222, thus
allowing the pump or motor to effectively reduce the output
speed of the vehicle. This, of course, reduces torque :Loading
on the prime mover 22. When operating speed of the prime mover
recovers, pressure in the venturi signal conduit 66 diminished,
permitting the spool 332 to be shifted rightwardly so that a
differential pressure may again be developed within the conduit ~ ~
- 222. ~;
The override speed control valve 126 also receives ~
... ;~: ~, .
high pressure fluid through the conduit 140 from the speed
. i~
control valve 112. Low pressure signal fluid is also communi~
cated across the valve 126 by means of the conduit 132 as noted
above.
The purpose of the override speed control valve 126
is to permit an operator to selectively reduce operating speed
of the drive train (see Fig. 1) without necessarily adjusting
or resetting a speed control valve 112. This feature is of
course of particular value in material handling vehicles where
an operator isbusy manipulating implements as well as regu-
lating the operating speed and the direction of the vehicle. ~
Accordingly, the override speed control valve 126 permits him ~ `
. . .
to establish a desired operating speed by means of the speed ;-
control valve 112 and to maintain that sekting while inter-
mittently reducing operating speed through use of the valve 126. `~
~'''` .
~:.
: . .
.-,
:
~()576'~;2
The operator may selectively reduce operating speed
by manually shifting a control rod 344 le~twardly to compress ~`
a spring 3l16 (see ~ig. 8). Compression Or the sprlng 346 acts
through an adapter 348 and a piston 350 against a pivoted lever
352. Resulting movement of the lever 352 urges a spool 354
rightwardly against its spring 356 in order to communicate
relatively high pressure fluid from the conduit 140 to the low
pressure conduit 132. As noted above, t;his permits high pressure
signal fluid from the conduit 222 to escape through the check
valve 330, thereby reducing the differential pressure in the
signal conduits 132 and 222 in order to reduce operati.ng speed
of the drive train.
During operation of the override speed control valve
126 in the manner described above, the prime mover is often
subjected to overspeed conditions while attempting to provide
necessary dynamic braking through the hydrostatic transmission.
This condition occurs for example when the vehicle is operating
;i at a high rate of speed or when the vehicle is traveling down- -
. hill. At such times, the dynamic braking capacity of the prime
mover and hydrostatic transmission may be insufficient~
decelerate the vehicle at the desired rate. Accordingly, the
present invention contemplates supplemental brakes which are
automatically operated to supply additional braking capacity
in response to operating conditions within the drive train.
In order to prevent such overspeeding, the speed
limiting control valve 128 (see Fig. 10~ is selectively operable
,
in a manner described immediately below to cause variable en- :
- gagement of brake 360 within the drive train 20. The brake 360
.: ::
is schematically represented on Fig. 10 in conjunction with the
- 30 brake pressure control valve 129.
- ~ .
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.;
A ~ -
.~:
.. . .. . ~ .. . . .
~L~S7~
The speed limi~ing control valve receives a low
pressure signal from the venl;uri signal conduit 66 through
branched conduits 362 and 364. The valve 128 also receives ~:
an inlet pressure signal from the venturi unit 60 by means of
the signal conduit 64. It is a~ain important to note that the :~.
signal received from the signal conduits 64 and 66, in combina-
tion, provide an indication of operating speed for the prime
mover 22, as described above. An override spool 366, normally ~
urged into the position illustrated by a spring 368, iS acted ~ -
upon by fluid pressure from each of the conduits 6LI and 66.
Under normal operating conditions where the prime mover is
within an acceptable speed range, relative pressure in the signal
conduits 64 and 66 iS not surficient to urge the spool 366 up~
wardly. ~lowever, when operating speed of the prime mover
increases above a predetermined maximum value, as described
above, relative pressure in the signal conduit 64 increases and
acts against the spring 368 to shift the spool 366 upwardly in
order to permit variable fluid communication from the actuator .
conduit 84 into the brake supply conduit 370. Thus, conduit
~: ~
370 is normally pressurized, except for a condition o~ ~vérspeed ~ :
of the prime mover. Under this condition, the brake pressure
control valve 129 iS responsive to variable pressure in the
:. conduit 370 fo~ correspondingly engaging the brake 360.
.~ Returning again to the speed limiting control valve
128, the conduit 370 has a branch conduit 372 for communicating
. the actuating brake fluid pressure from the conduit 370 through
the branch conduit 372 into a passage 374 in the override speed
. control valve 126 (also see composite Fig. 8). Brake actuating
,: ~
:. ~
.. ':'~ '; '
;; :
. ~ _~3
:
~C~57GZ~
pressure ln the passage 3'74 acts through a piston 376 which
ls thus urged against the lever 352 in parallel with the manual
control rod 344. Rightward movement of the piston 376 is
limited by a pin 378 only for the purpose of preventing rapid
oscillation of the plston 376 in response to pressure f'luctu-
ations in the passage 3711.
The fluid signal communicated to the override speed
control valve 126 through the conduit 372 is only a portion
of a feedback signal generated by the speed limiting control
valve 128 to provide an indication to the operator of the a-
mount of engagement for the drive train brake 360. An additional ~'
fluid pressure signal is communicated from the speed limlting
control valve to the override speed control valve through a
conduit 380.
In order to develop the feedback signal within the
conduit 380, fluid from the signal conduit 68 is communicated
to a passage 382 of the speed limiting control valve 128. A
first regulating spool 384, including a set of variable orifices
386 and a single orifice 387, functions in substantiaII'~the
same manner as the spool 366 in response to differential pressure
in the conduits 64 and 66. For example, when the prime mover
22 is operating within an acceptable speed range, pressure in
the venturi signal conduit 64 is not suf'ficient relative to :~
pressure in the conduit 66 to urge the spool 384 upwardly
against its spring 389.
However, as operating speed of the prime mover increases
above a predetermined maximum level, relative pressure is
:, ~
:'
..,'
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:; :
_.. . . ~. . . . .. .. .. . . ...
~0~7ti2~
increased within the signal conduit 6l~ which serves to shif't the
spool 384 upwardly so that the orifices 386 begin to communicate
a variable feedback signal into the passage 388 and the conduit
38Q, as further described below.
In addition, the orifice 387 provides selective
communicat:lon between the passage 382 and the conduit 222. ~;
The passage 382 is always pressurized to a relatively higher
degree than the cond.uit 222. The purpose of the orifice 387
is to increase pressure in the conduit 222 during overspeed
conditions of the prime mover. ~or example, if the operator
sets the speed control valve 112 at a selected level, pressure
in the conduit 222 will tend to approach a corresponding -:
setting during normal operation. However~ pressurized fluid
communicated from the passage 382 through the orifice 387
also increases the pressure level in the conduit 222. This .
additional pressurization in the conduit 222 serves as an ~-~
artificial signal corresponding to a further increase in
output speed of the hydrostatic transmission in order to reduce
the overspeed condition of the prime mover. '~
: . ,
` 20 The feedback signal in the passage 388 is also acted
. upon by a second regulating spool 390 which is responsive to
~ high pressure signal fluid from the conduit 222 and low pressure
:~, signal fluid from the conduit 132. The differential pressure ~ ;~
.. ~ "
~ between these two conduits is of course proportional to output . ~ .:, speed of the drive train so that the spool 390 is operable for :~
further adjusting the feedback signal in the passage 388 in ~
proportion to operating speed of the drive train or vehicle. -
''' .:'~ ~
~ : .
:, ~
3s- i ::;;
~57~;2Z
In operation, the spool 3go :Ls normally urged up~ardly
by its spring 392. Low pressure signal fluid fro~ the conduit
132 acts upon the spool 390 ln con~unction with its spring 392.
High signal pressure from the conduit 222 acts upon the other
end of the spool 390 in a chamber 394. Accordingly, a pressure
differential between the conduits 222 and 132 is sufficient to
shift the spool 390 downwardly against its spring in order to
provide variable communication ~or the passage 388 with a drain
passage 396 through a slot 391.
Thus, the feedback signal supplied into the conduit
380 is proportional both to operating speed of the prime mover
as well as output speed of the drive train which, in combination
with the signal in the branch conduit 372, provides a true
indication as to the amount of braking effort that is instantly
- provided by both the drive train brake 360 and the prime rnover.
The feedback signal from the conduit 380 is communi-
cated to a passage 398 in the override speed control valve 126 -
and a chamber 400 in order to act upon the spool 354 through a
slug 402. Thus, by means of the lever 352 and the sp~ol.~354~,
.
~ 20 the feedback signal within the chamber 400 serves to resist .`
:'
manipulation of the control rod 344 in proportion to engagement
of the brake 360. Any hydraulic delays or fluctuations in the ;~
system are compensated for by a check valve 40LI and a restrictive ~:
orifice 406 arranged in parallel between the passage 398 and ~ ;
the chamber 400.
From the immediately preceding description, it may ~ :
be seen that the override speed control valve 126 and the speed
limiting control valve 128 automatically function in combination
to compute the amount of braking capacity required in addition :
3~
.
~C~57~'~2
:
to -the dynamic capacity o~ the drive train in order to maintain ~
operating speed of the prime mover within acceptable limlts. The ~;
speed limiting control valve f'urther functions to automatically
apply the supplemental brake within the drive train while
delivering a feedback signal to the override speed control valve
as an indication to the operator of the amount of engagement for
the drive train brake.
The bralce pressure control valve 129 merely functions
ln response to a fluid signal ~rom khe speed limiting control
valve 128 in the conduit 370 in order to proportionally apply
the brake 360. It is noted that the brake 360 is of a type
being no~mally disengaged. A regulating spool 408 is normally
shifted downwardly by pressure in conduit 370 acting against
spring 410. Thus, any pressure in passage 412 is blocked ~rom
:
the brake 360. As the signal from the conduit 370 decreases,
due to overspeed o~ the prime mover, the spring 410 shifts the
spool 408 upwardly to allow communication between the passage ~
~ 412 and the brake 360. Any pressure communicated to the brake ~;
- 360 also acts upon the spool 408 in opposition to the spring
~-: 20 410 by means of an interconnecting passage 414. Fluid from the
passage 414 acts upon a slug 416 which is accordingly urged
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downwardly against the spool 408. The brake 360 is then dis-
engaged by variable communication with a drain passage 418.
. .
The brake pressure control valve 129 also includes a
shuttle valve 420 which is automatically shifted in order to
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supply actuating fluid to the passage 412 from one of a pair
of conduits 422 and 424. Preferably, the conduits 422 and 424
are in respective communication with the manifolds 36 and 38
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for the hydrosta~ic transmission (also see Fig. 1). Since
either of the mani~olds may be filled with high pr~ssure fluid
depending upon the direction of operation for the transmission,
the shuttle valve spool 420 serves to assure that the relatively -
high pressure side of the hydrostatic transmission is in com-
munication with the passage 412 in order to assure adequate
pressure for engaging the bralce 360.
4) Detailed descriptlon of the preferred mode of
~- ' .
It is believed that the mode o~ operation for the
control valve assembly 102 is clearly set forth in the above
description. However, the mode of operation for the various
valve components within the control assembly 102 is briefly
summarized below in order to assure a better understanding of
their combined operation.
Initially, the speed control valve 112 is manually -;~
operable to develop a relatively high pressure in the conduit
~ 174 relative to the low pressure signal conduit 132. The ~`
.I signal ~rom the conduit 174 is modulated during either accelera-
ting or decelerating operation of the transmission to provide
a variable high pressure signal in the conduit 196.
The directional valve 116 responds to the differential
, pressure in the conduits 196 and 132 for performing three
functions. Initially, the directional valve determines the
direction of operation for the pump actuator 42 (see Fig. 1) ~-
in order to determine forward or reverse operation of the drive
train. Secondly, the directional valve establishes the sequence
in wnich displacement of the hydrostatic pump 32 and motor 34
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takes place. Finally, the directional valve includes a third
valve component for modulating a decreasing differential pressure
in the conduits 196 and 132 in order to regulate deceleration
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Or the hydrostatic transm:Lssion only during a direction change
As the transmission passes through a neutral condition, the
modulating valve 114 thereafter functions to again regulate the - -
rate of acceleration for the transmission.
The range selector valve 118 functlons to automatically
shift a multiple speed range transmisslon unit 26 (Fig. 1) into a
different speed range as the hydrostatic transmission approaches
a select limit of displacement. Concurrently, the pilot control
valve 50 for the hydrostatic motor actuator 48 responds to the
di.fferential pressure signal in conduits 196 or 222 and the low
pressure signal conduit 132. The function of the range selector
valve 118 and the automatic response of the pilot control valve
50 is timed by operation of the accumulator 120.
Before operation of the transmission can be initiated,
however~ it is first necessary that the safety control valve
122 be positioned to disengage a parking brake 158 (see Fig. 4
and also to block communication between the conduits 160 and
162 so that differential pressurization may be developed within
the low pressure signal conduit 132 and the high pressure signal
~ 20 conduit 222 or 196. The safety control valve 122, of co~se;
; provides these functions when the speed control valve 112 is
first returned to a neutral position so that the transmission
units may thereafter be accelerated in proper sequence.
As noted above, the underspeed control valve 124
` functions in a generally conventional fashion to decrease the
differential signal in the conduits 132 and 196 when the prime
mover is operating beneath a predetermined minimum speed level.
The override speed control valve 126 provides a means
- for selectively accomplishing the same purpose in order to de-
celerate the drive train at any time desired by the operator.
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Any corresponding overspeed condlt:Lons of the prlme
mover are sensed by the speed limiting control valve 12~ which
accordingly causes engagement of a brake 360 within the drive
train in order to supplement dynamic braking capacity of the
hydrostatic transmission unit. The speed limiting control
valve 128 further communicates a feedback signal to the over-
ride speed control valve 126 which is proportional to actual
engagement of the brake 360, actual operating speed of the prime
mover and actual output speed of the drive train in order to
provide a true indication to the operator as to the combined
degree of braking from the brake 360, and the prime moyer through
the drive train.
The graph of Fig. 13 also clarifies the manner in
~; ~
which the combined hydrostatic and multiple speed range trans-
mission units function in combination~ Referring now to Fig.
13, the curve indicated at 502 represents the angle of displacement
for the pump 32 (regardless of operating direction) while the
;. curve 504 represents the angle of displacement for the motor 34
(also see Fig. 1). At zero speed Or the transmission, for
20 example, during start up conditions with the speed cont~l v~alve ~ ;
112 being in neutral, the pump is at minimum displacement while
the motor is at maximum displacement. As the operating speed
of the drive train is increased through manipulation of the
speed control valve 112, the pump 32 is first shifted from
minimum toward maximum displacement. As it reaches maximum
displacement as indicated at 506, the motor 34 begins to ex-
perience displacement variation from its maximum condition
toward a minimum. As displacement of the motor 34 approaches a
conditlon of minimum displacement indicated at 508 on the graph,
; 30 the range selector valve 118 (see Fig. 2) automatically shifts - -
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the mliltiple speed range transmlsslon un:Lt into a di~ferent
speed range. Simultaneously, displacement of the motor i5
shif'ted or reset back toward its condition of maximum dis-
placement. Resetting of the motor 34 occurs between points
508 and 510 on the graph. Thereafter, the motor agaln continues
to experience gradually decreasing displacement in order to
provide acceleration within the higher speed range setting
established by the range selector valve.
The above procedure graphically represented in Fig.
13 may be performed in opposite relation ~or decelerating opera-
tion of the drive train. Thus, the graph of Pig. 13 indicates
that the shift between speed ranges, indicated between the
points 508 and 510, may take place at any point selected along ~ ;
the curve in order to establish the most desirable torque trans-
mitting characteristics within the drive train. This feature
is particularly facilitated by the automatic and simultaneous
conditioning of the multiple speed range transmission and the
hydrostatic motor in response to a single differential signal. ;~
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