Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
114~589
1 FEEDBACK SHAFT EXTENDING BETWEEN
SWAS~PLATE AND DISPLACEMENT CONTROL VALVE
The present invention relates to variable displacement
hydrostatic pump or motor units and controls therefor and more
particularly relates to feedback linkages forming a portion of
the displacement control means for such units.
In common usage today are hydrostatic pump or motor units
lncluding swashplates mounted for selective angular adjustment to
increase or decrease the displacements of the units between zero
and maximum displacement conditions. The swashplates of these
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units are controlled by one or more hydraulic actuators connected
to the swashplates and selectively actuatable by means of control
valves, which each include concentrically mounted first and
~econd axially shiftable valve elements that are normally posi-
tioned relative to each other such as to establish a null condi-
tion in the valve for maintaining a preselected displacement
condition in the pump or motor unit. The first valve element is
6hiftable axially relative to the second valve element in response
to a command input signal such as to cause the actuator or actu-
ators to reposition the swashplate to a new position for effecting
a predetermined change in displacement corresponding to the
magnitude of the command input signal. A feedback linkage is
connected between the swashplate and the second valve element and
aats to shift the latter to re-establish the nuli condition in
the valve once the commanded displacement change has been e~fected.
Two examples of such pump or motor units and controls therefor
are respectively disclosed in U.S. Patent No. 3,803,987 issued to
Knapp on 16 April 1974 and U.S. Patent No. 3,810,715 issued to
Week et al on 14 May 1974.
Hydrostatic pump and motor units of the general type just
described are commonly coupled together to form transmissions for
driving various machine parts and for driving ground wheels or
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114~5~39
1 tracks of vehicles. These transmissions often include a transmis-
~ion case or housing which contains a pump and motor unit set and
the associated control valves for the pump and motor units are
mounted on the exterior of the case and coupled to the swashplate
of the associated unit by a feedback linkage projecting through
the case. As the case sometimes serves also as a reservoir for
the hydraulic fluid used to operate the pump and motor units and
the displacement control actuators, it is necessary to ensure
that the interface between each control valve and the case is
adequately sealed to prevent leakage of the hydraulic fluid from
the case. U. S. Patent No. 3,857,541 shows the example of how
the control valve side of that part of the valve-to-case interface
would have to be ported and sealed for permitting control fluid
to be routed to and from the control valve.
The hydrostatic pump or motor units and controls therefor of
the type described hereinabove suffer from one or more of the
disadvantages of:
1. ~aving too much looseness in the feedback linkage
resulting in inaccurate pump or motor displacement
control.
2. Having a feedback linkage which occupies a relatively
large amount of space and/or re~uires such space for
its operation.
3. ~aving the feedback linkage connected to the control
valve such that when the control valve is mounted on
the exterior of a transmission case the installation
and/or removal of the control valve is made somewhat
difficult.
4. Having the control valve connected to the transmission
case such that a large amount of fluid drains from the
case when the control valve is disconnected for repairs.
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1141589
1 ` Summary of the Inventlon
According to the present invention there is provided an
improved feedback linkage connected between a displacement control
valve for a hydrostatic pump or motor unit and an angularly
aajustable swashplate of the unit and more specifically there is
provided such a feedback linkage which is particularly adapted
for use with hydrostatic transmissions wherein the control valve
is mounted on the exterior of a case or housing of the transmis-
sion, which serves also to hold a supply of hydraulic fluid and
wherein the pump or motor unit is located within the case or
housing.
It is an obiect of the invention to provide a feedback
linkage of simple construction which works to accurately null the
control valve in response to the swashplate arriving at a new
commanded position. This object is primarily accomplished by
constructing the feedback linkage in the form of a shaft which is
di,sposed along the pivot axis of the swashplate and connected at
one of its ends to the swashplate by an interference connection
ensuring concurrent and equal angular movement of the swashplate
and feedback shaft.
It ls a further object to provide a feedback linkage which
occupies and/or operates in a minimum of space. This object is
accomplished by constructing a feedback linkage in the manner set
forth above in discussing the previous object and also by provid-
ing a ball-and-socket connection between an end of the feedback
shaft and a shiftable element of the control valve, the connection
being located eccentrically to the pivot axis of the swashplate
and feedback shaft.
Yet another object is to provide a connection between the
control valve and feedback shaft, of the immediately preceding
object, which lends to easy installation and removal of the
control valve. This object is accomplished by the provision of
1~4~S89
1 the previously mentioned ball-and-socket connection and addition-
ally by providing the feed~ack shaft with a specially configured
end portion for piloting the feedback shaft into a mating recep-
tacle provided in the control valve such as to guide together the
respective connection portions of the valve element and feedback
shaft making up the ball-and-socket connection.
Still another object is to provide a control valve which may
be disconnected from the exterior of a transmission case contain-
ing a pump or motor unit controlled by the valve without there
being a large loss of fIuid from the case when the latter is also
serving as a hydraulic fluid reservoir. This object is accom-
plished by providing the feedback shaf~, described in one or more
of the objects above, with a drilled passage which serves as the
sole passage for conveying exhaust fluid from the control valve
to the interior of the transmission case and by providing a one-
way valve, in the form of a check ball, within the passage for
permitting fluid flow only in the direction of the transmission
case.
These and~other objects will become apparent from a reading
of the ensuing description together with the appended drawings.
Brief Description of the Drawings
Fig. 1 is a somewhat schematic perspective view of a hydro-
static transmission of a type with which the present invention is
particularly adapted for use, with certain parts of the transmis-
sion being broken away to better expose the manner of mounting
the pump swashplate.
Fig. 2 is a somewhat schematic perspective view of a portion
of the swashplate shown in Fig. 1 but with sections broken away
to expose a feedback rod connected to the swashplate and in
addition showing a portion of the control valve positioned for
movement toward the feedback rod for connection with the latter.
Fig. 3 is a schematic representation of a hydrostatic pump
and control valve therefor.
il41589
1 Description of the Preferred Embodiment
Referring now to Fig. 1, therein i9 shown a hydrostatic
transmission 10 which typifies those with which the present
invention is particularly adapted for use. The transmission 10
includes a sealed case or housing 12 which contains a reversible,
variable displacement pump 14, only partly shown. Also contained
w~thin the case 12 but not illustrated here is a fixed or a
variable displacement motor and hydraulic circuitry connecting
the pump 14 to the motor such as to form a closed loop system, as
is well known in the art. An input drive shaft 16 extends into
and is supported by the case 12 and is coupled to the pump, for
transmitting drive torque to the latter, by means of conventional
gears and shafting ~not shown2.
The pump 14 includes a swashplate 18 having axially aligned
stub shafts 20 at its opposite sides and respectively rotatably
supported by a pair of bearing caps 22 forming opposite side
portions of the transmission case 12. The swashplate 18 is thus
trunnion-mounted for angular adjustment, about an axis Y passing
centrally through the shafts 20, for the purpose of effecting
changes in the displacement of the pump and hence in the speed of
rotation of the unshown motor hydraulically coupled to the pump.
Specifically, the swashplate 18 is illustrated in a centered
position wherein it effects a zero-displacement condition in the
pump. As the angular displacement of the swashplate 18 from its
centered position increases in opposite first and second angular
directions, the fluid displaced by the pump increases in opposite
first and second directions therethrough.
As can best be seen in Fig. 1, the swashplate 18 includes
upper and lower connection brackets 24 and 26 respectively located
above and below the axis Y. Referring now to Fig. 3, it can be
seen that upper and lower, single~acting hydraulic actuators 28
and 30 are respectively connected to the brackets 24 and 26 and
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.
1 are operative when selectively actuated to effect angular adjust-
ment of the swashplate 18.
The actuators 28 and 30 are, in turn, selectively controlled
by means of an electro-hydraulic direction control valve 32,
which is mounted on the exterior of the transmission case 12 at
one of the bearing caps 22. The valve 32 may ta~e many forms but
is here ~Fig. 3~ disclosed schematically as being, for the most
part, similar to t~e valve disclosed in the aforementioned U.S.
Patent No. 3,857,541 granted to Clark on 31 December 1974, the
difference being that the valving in the instant case is particu-
larly constructed to accommodate the present invention. Specifi-
cally, the valve 32 includes a valve body 34 defining a valve
bore 36, disposed along an axis X ~Fig. 2) extending above and
orthogonally to the axis Y. The bore 36 has ri~ht and left
closed ends 38 and 40, respectively, as viewed in Fig. 3.
Communicating with the bore 36 at a central location between the
closed ends thereof is a drain passage 42. A first control port
44 communicates with the bore 36 at a location spaced axially
rightwardly from the passage 42 and is joined to the actuator 28
by a control line 46 while a second control port 48 similarly
communicates with the bore at a location spaced axially leftwardly
from the passage 42 and is joined to the actuator 30 by a control
line 50. Communicating with the boxe 36 at a location between
the first control port 44 and right end 38 is a first pressure
supply port 52 while a second pressure supply port 54 communicates
with the bore at a location between the second control port 48
and the left end 40. A branched supply line 56 joins the output
of a pump 58 with the ports 52 and 54. The pump 58 is preferably
located within the transmission case 12 and the latter preferably
serves as a fluid reservoir and has a sump portion to which an
inlet of the pump 58 is connected.
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1141S89
1 The flow of fluid between the supply, control and exhaust
ports is controlled by a first valve element in the form of a
valve spool 60 and a second valve element in the form of a valve
sleeve 62, the spool 60 being axially shiftably mounted within
the sleeve 62 and the sleeve 62 being axially shiftably mounted
in the bore 36. The sleeve 62 is provided with a first set of
ports 64 which establish constant fluid communication between the
supply port 52 and one end of a first restricted passage 66 which
supplies fluid to a first pilot pressure passage 68 having a
10 nozzle 70 at one end and having its other end in constant fluid
communication with the bore end 38. Similarly, the sleeve 62 i5
provided wi-h a second set of ports 72 which establish constant
fluid communication between the supply port 54 and one end of a
second restricted passage 74 having its other end connected to a
second pilot pressure passage 76 having a nozzle 78 at one of its
ends and having its other end in fluid communication with the
bore end 40. Located centrally between the ends of the sleeve 62
is a drain port 80 which is in continuous fluid communication
with the drain port 42. A first set of control fluid ports 82
are located in the sleeve 62 between the port 80 and the first
set of ports 64 such as to establish constant fluid communication
with the contxol port 52 while a second set of control-fluid
ports 84 are similarly located between the port 80 and the second
~et of ports 72 such as to establish constant fluid communication
with the control port 48. Thus, although the sleeve 62 shifts
with the bore 36, it in no way obstructs flow from occurring
through the drain port 42, control ports 44 and 48 or supply
ports 52 and 54.
Actual control of flow through the valve body ports just
mentioned is accomplished by the spool 60 and for this purpose
the latter includes first and second end lands 86 and B8 respec-
tively exposed to pilot fluid pressure at the bore ends 38 and
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1 40, and a set of first and second lands 90 and 92 loca~ed such as
to block the control fluid ports 82 and 84 of the sleeve when the
spool 60 bears a centered null position relative to the sleeve
62, as illustrated in Fig. 3.
Pilot pressure at the ends of the spool 60 is controlled by
means of an electric torque motor 94 for controlling the position
of a nozzle flapper 96 relative to the pilot presssure passage
nozzles 70 and 78, the latter being located on opposite sides of
the flapper 96, which is in turn located in a passage 98 which
extends in the valve body 34 orthogonally to the valve bore 36
from the exterior of the valve body to a central location between
the ends of the bore. ~oined as a continuation of the flapper is
a feedback spring 100 which extends through an opening 102 pro-
vided in the sleeve 62 and terminates in a ball enlargement
received in a groove 104 provided centrally in the spool 60
between the opposite ends of the latter.
The mode of operation o~ the torque motor 94 as regards its
control over the movement of the valve spool 60 is well known to
those skilled in the art. Suffice it to say that an electrical
command input signal received by the torque motor 94 will cause
the latter to operate in accordance with the direction and magni-
tude of the signal received to move the flapper 96 toward one or
the other of the nozzles 70 and 78 to thus further restrict flow
from the same and effect a pressure imbalance in the pilot pres-
sure passages 68 and 76 and hence a pressure imbalance across the
spool 60. The spool 60 will be shifted by this pressure imbalance
and as it shifts the feedback wire 100 will be deflected until it
substantially counterbalances the action of the electrically
induced action of the torque motor. Hence spool displacement and
direction corresponds to the direction and magnitude of the
electrical signal received by the torque motor.
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1141589
1 Once the valve spool 60 has been shifted relati~e to the
sleeve 62, fluid will flow to one and from the other of the
actuators 28 and 30~ For t.he purpose of causing the flow of
fluid to and from the actuators 28 and 30 to be blocked once the
swashplate 18 reaches a new desired position as commanded by the
input signal received by the torque motor 94, a feedback shaft
105 ~ig. 2~ is coupled between the swashplate 18 and the sleeve
62 such as to shift the latter to follow the movement of the
spool 60 to restore the null condition. Specifically, the shaft
105 is located along the pivot axis of the swashplate 18 and is
received in a hole provided centrally ir. the bearing cap 22 and
in a bore 106 extending axially through one of the stub shafts
20. The inner end of the feedback shaft 105 includes diametric-
ally opposite axial extensions 107 which define a forked connec-
tion part that is received in complimentary diametrically opposite
axially extending grooves 108 provided in the outer end portion
of the swashplate 18. The extensions 107 are each provided with
an axially extending notch 110 which permits the extensions to be
resiliently deflected to effect a tight interference connection
when the extensions 107 are forced ~nto the grooves 108 during
assembly. The outer end of the shaft 105 is provided with an
annular increased diameter surface 112 sized for reception in an
annular entrance 114 of a passage 116 provided in the housing 34
and extending to the bore 36. Fixed to the sleeve 62 and project-
ing into the passage 116 is a rod 118 having a ball end 120
disposed for being received in a aocket 122 extending into the
outer end of the shaft 105 at a location eccentric to the axis Y.
Thus, it will be appreciated that movement of the control valve
34 along the axis Y toward the shaft 105 in Fig. 2 will first
result in the shaft pilot surface 112 entering the annular en-
trance 114 of the passage 116, the entrance 114 then guiding or
piloting the housing 34 onto the shaft 105 such that the ball end
114~589
1 120 of the rod 118 is guided into the socket 122. It will be
appreciated then that angular movement of the swashplate 18 will
be transmitted to the sleeve 62 via the shaft 105 such as to
effect axial shifting movement of the sleeve.
It is here noted that the drain passage 42 shown in Fig. 3
i8 actually provided in the form of a bore which extends length-
wise through the shaft 105. Fluid is prevented from escaping
from the case 12 by way of the passage 42 by means of a check
ball 124 located in the passage 42 and biased toward an inwardly
facing valve seat 126, provided in the passage by means of a coil
- spring 128.
The operation of the invention is briefly as follows.
Pirst, if it is assumed that the swashplate 18 initially occupies
a centered, zero-displacement effecting positisn, as illustrated,
and that displacement of the swashplate 18 in the clockwise
direction, as viewed in Fig. 3, will effect displacement of fluid
through the pump 14 in a forward-driving direction, then a forward
driving condition may be effected in the transmission by activat-
ing the upper actuator 28. In order to accomplish such actuation,
the operator need only to connect a predetermined command input
signal to the torque motor 94 for causing the latter to move the
flapper 96 toward the nozzle 70 such as to further restrict the
flow therefrom and cause the pilot pressure in the passage 68 to
increasé. Th~s increase in pressure will cause the spool 60 to
shift leftwardly ~ig. 31 to connect the outlet of the pump 58 to
the actuator 28 while connecting the actuator 30 to the drain
passage 42 in the feedback shaft 105. This fluid unseats the
check ball 124 and flows into the transmission case 12.
As the actuator 28 extends, the swashplate 18, and conse-
quently the feedback shaft 105, are rotated clockwise. Throughits eccentric connection with the valve sleeve 62, the feedback
shaft lOS drives the latter leftwardly to re-establish its cen-
tered relationship to the ~pool 60 at which time the lands of the
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~141589
1 ~pool will prevent the flow of fluid to and from the actuators 28
~nd 30 thus resulting in the swashplate 18 being maintained in
ttS new position.
If it should ever become necessary to detach the control
valve 32 from the transmission case 12 for service or replacement,
for example, the operator need only to unbolt the valve 32 and
pull it away from the case to separate the ball-and-socket connec-
tion between the sleeve 62 and feedback shaft 105. Despite thefact the case 12 is full of transmission fluid, no greàt loss of
1~ fluid will occur when the valve 32 is removed because the check
ball 124 will be seated to prevent leakage from the case 12
throuqh the drain passage 42 and only a relatively small amount
of trapped fluid is present in the supply and control passages.
Thus, it will be appreciated that the feedback shaft 105
provides a simple, effective way of transmitting swashplate
movement to the valve element 62 and for transmitting exhaust
fluid from the valve 32 to the case 12.
