Note: Descriptions are shown in the official language in which they were submitted.
DOWNSHIFT INHIBITOR CIRCUIT
BACKGROUND OF THE INVENTION
The field of art to which this invention pertains includes pres-
surized fluid control systems for multiple speed ratio powershift
transmissions. More particularly, the control system is adapted to ;
automatically shift the transmission from a higher speed ratio to a
lower speed ratio at a first predetermined vehicle ground speed and
thereafter shift back to said higher speed ratio at a second higher
predetermined vehicle ground speed. It is the function of the downshift
lQ inhibitor circuit to prevent downshifting of the transmission during ;~
vehicle full throttle directional reversals.
In front end loader applications, for example, during bucket load-
ing at the pile portion of the work cycle, the vehicle is required to
'crowd the pile as well as pry or lift with the bucket. The pile is
normally approached in second gear from a travel portion of the work
cycle, with initial crowding and bucket work being done in second gear.
During the second gear operation, in compar;son with first gear opera-
tion, less torque is available at the driving wheels which has a de-
sirable effect of minimizing wheel spin. However, when additional
hydraulic demands are placed on the engine, as a result of prying or
bucket lifting operations, insufficient power remains for transmission
to the driving wheels for effectively crowding the pile. Therefore, at
this time, the operator must normally shift to first gear and, upon
loading the bucket and backing out of the pile, he must then manually
shift to second gear. In order to relieve the operator from excessive
shifting between first and second gears, it is very desirable to have an
automatic shift system so that, when the vehicle ground speed drops to a
first predetermined speed, the transmission is automatically downshifted
from second to first gear which in turn is followed by an automatic
upshift when the vehicle ground speed thereafter exceeds a second higher
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l predetermined speed, A transmission shift control system that
provides this automatic function is set forth in the applicant's
co-pending Canadian ~pplication Serial No. 299,025,filed on 15
March 1978.
For the same vehicle speed, during full throttle oper-
ation, it is desirable to perform the directional reversal of the
vehicle in second rather than in first gear because of the
inherent lower rotational speeds of both the forward and reverse
clutch components in second gear operation. Full throttle shifts
into and out of first gear are ~uite harsh, therefore, a princi-
pal object of this invention is to provide means for prohibiting
downshifts from second to first gear while the vehicle undergoes
full throttle directional reversals. The description of my co-
pending application is fully repeated hereinafter-to assure full
understanding of its structure and function which are considered
necessary to fully understand the function and appreciate the
bene~fits of my downshift inhibitor or delay circuit.
Prior art patents wherein shift operation is effected by
electro-hydraulic means responsive to operating parameters include
U.S. Patent Nos. 3,732,755 to Beig et al; 3,403,587 to DeCastelet;
and 3,665,779 to Mori. Furthermore, a downshift inhibitor for a
powershift transmission is also shown in U.S. Patent No. 3,937,107
to Lentz.
In order to meet the objective of prohibiting trans-
mission downshifts from second to first while the vehicle under-
goes full throttle or rapid directional reversal, the transmission
control system is provided with a downshift inhibitor or delay
circuit which is activated only when the vehicle travels in the
second gear speed range. The downshift inhibitor or delay
circuit is interposed in the electronic speed sensing system
between the electronic speed switch and the solenoid valve and
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1 basically takes the form of a timer circuit that is energized
upon the initiation of a vehicle directional reversal while the
vehicle travels in the second gear speed range.
The timer circuit itself delays the downshift of the
transmission for a predetermined length of time which is suffi-
cient for the vehicle to reverse and accelerate, at full throttle,
to the normal second gear speed range. This delay is re~uired in
order to inhibit full throttle downshifts, and the delay is of
sufficient duration that the vehicle goes through the normal cycle
of slowdown, stop and acceleration in second gear until the ground
speed exceeds a second higher predetermined speed, before the -
delay time runs out.
Thus,it should be understood that during full throttle
directional reversal, the reversal itself is accomplished in
second gear and that there is full use of the downshift inhibitor
or delay circuit in that the electronic speed switch provldes a
signal for shifting the transmission to its first speed setting
which, however, is delayed by the timer circuit with the result
that the transmission itself remains in second gear.
During part throttle or slower directional reversal, the
predetermined time delay runs out and the transmission shifts to
first gear, with this downshift not being objectionable.
The features and advantages of the present invention
will be more readily understood by persons skilled in the art
when following the detailed description in conjunction with the
several drawings.
FIG. 1 shows diagrammatically and schematically a trans-
mission control system in conjunction with a multiple speed ratio
powershift transmission.
FIG. 2 is a top plan view of the sandwich valve of the
transmission control system, with portions thereof being broken
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1 away for the sake of clarity.
FIG. 3 is an enlarged sectional view, taken along line
3-3 of FIG. 2, of a valve embodied in the control system.
FIG. 4 is an enlarged sectional view, taken along line
4-4 of FIG. 2, of a further valve embodied in the control system,
with the valve spool being in the open or unshifted position.
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FIG. 5 shows the valve of FIG. 4 with the valve spool being in the
closed or shifted position.
FIG. 6 is a schematic diagram showing the shift inhibitor circuit
of this invention added to the transmission control system. ~ -;
FIG. 7 is a schematic flow diagram depicting the sequence of events
during a full throttle vehicle directional revarsal.
FIG. 8 is a further schematic diagram depicting the sequence of
events during a part throttle vehicle directional reversal.
Referring now the drawings, specifically to FIG. 1, there is shown
a transmission control system 10 in combination with a multiple speed
ratio powershift transmission 12 and its associated transmission control
cover 14.
Transm;ssion 12 includes an input shaft 16, an output shaft 18, a
fluid operated directional control clutch 20 which conditions the trans-
mission for forward drive when engaged, and a fluid operated directional
control clutch 22 which cond;tions the transmission for reverse drive
when engaged. In addition, a plurality of fluid operated speed ratio
clutches 24, 26, 28, and 30, when engaged, condition the transmission
for drive in first, second, third, and fourth speed ratios, respectively.
A more detailed description of a transmission of this type may be found
in U.S. Patent No. 3,126,752 issued in the name of R. H. Bolster on
31 March 1964.
Control cover 14 has a plurality of valves housed therein which
among others generally include a conventional pressure regulating valve
for limiting the maximum pressure in the control system, a conventional
directional control valve 45, and a conventional speed control valve 43.
These valves control the flow of pressurized fluid that operates the
various fluid actuated clutches and lubricates the gears and bearings
associated with transmission 12 in a manner well known in the art. More
detailed showings of similar transmission control covers and their
associated valves may be found in U.S. Patent No. 3,334,703 to Zeller
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and in U.S. Patent No. 3,559,780 to Erdman. A prime mover (not shown)
is used to drive one or more charge or auxiliary pumps of any well known
construction, one of which is schematically shown at 32. In order to
selectively pressurize control cover 14, pump 32 draws and pressurizes
fluid from a fluid supply reservoir or sump 34 from which fluid is drawn
through a conduit 36, with conduit 40 linking pump 32 with control cover
14.
Transmission 12 is often used in the drive l;nes of construction
machinery, a specific example thereof being front end loader applica-
tions, with the speed control shifting and the directional control
shifting being performed by the operator generally through manual hand
control levers (not shown) connected with speed control valve lever 44
and directional control valve lever 46, respectively, in control cover
14. In front end loader operation, for example, the operator is gener-
ally occupied with manually hand-manipulating both steering and hy-
draulic bucket control functions, and, therefore, it is inconvenient for
him to have to manually hand shift back and forth between first and
second gears, for example, in addition to hand shifting between the
forward and reverse during a loading-unloading operation. It should, of
course, be recognized that in front end loader operation, there is
extensive short duration reciprocation of the front end loader in con-
junction with the loading and unloading operations.
In order to relieve the operator from constantly shifting between
first and second gears, when speed control lever 44 is in second gear
location, transmission control system 10 allows transmission 12 to
operate in second gear until ground speed drops to a first predeterm;ned
speed whereupon transmission 12 automati~ally shifts back to first gear
and stays in first gear until ground speed exceeds a second higher
predetermined speed, at which time it automatically shifts back into
second gear.
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In order to accomplish this objective, transmission control system --
10 is provided with an automatic shift system 38, the best mode of which
includes an electronic speed sensing system 48 in association with a
downshi~t valve means 52 which in turn is interposed between transmis-
sion control cover 14 and electronic transmission casing 42. Electronic -~ -
speed sensing system 48 basically includes a signal generator 56, an
electronic speed switch 58 and a solenoid valve 60. Signal generator 56
is mounted on transmission first clutch shaft 54, with the latter being
drivingly connected to the output shaft and therefore rotating at a
speed proportional to road speed. Signal generator 56, which produces
an electronic pulse signal proportional to road speed, may take the form
of a model ESG signal generator (style ESG0) manufactured by Synchro-
Start Products, Inc. of Skokie, Illinois. Signal generator 56 in turn
is electrically connected to an electronic speed switch 58 which may
consist of a model ESSB-lAT electronic speed switch also manufactured by
Synchro-Start Products, Inc. of Skokie, Illinois. Electronic speed
switch 58 is also electrically connected to both a DC power supply 59
and a solenoid valve 60 which may take the form of Model No. 8-3A-3-24
Solenoid Valve manufactured by Fluid Power Systems Division of AMBAC
Industries, Inc. of Wheeling, Illinois.
Solenoid valve 60 is also hydraulically interconnected with control
cover 14 via conduit 64, as well as having a vent conduit 66 and being
further hydraulically interconnected with a second speed clutch valve 62
(FIG. 2) in valve means 52 via conduit 68 and piston-cylinder actuator-
transfer valve 70.
As previously noted, control cover 14 serves to control the hy-
draulic pressures for actuating the speed ratio and directional control
clutches via speed control and directional control valves 43 and 45,
respectively, with these valves forming no part of the present invention.
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As best seen in FIG. 1, downshift valve means 52, which includes
sandwich valve 53, is interposed between control cover 14 and transmis-
sion casing 42, with the actual structure of downshift valve means 52
being best seen in FIG. 2. Valve 53, which takes the form of a center-
cored generally rectangular plate, includes a plurality of bores or
apertures that serve to channel hydraulic pressure to the various
clutches, with apertures 72, 73 permitting hydraulic interconnection
with forward and reverse clutches 20~ 22, respectively. Similarly,
apertures 74, 75, 76, and 77 are hydraulically interconnected with
lQ first, second, third, and fourth speed ratio clutches 24, 26, 28, and
30, respectively. It should be understood that apertures 72-77 are
connected with appropriate portions of valves 43 and/or 45 and via
hydraulic lines (not shown) with their respective clutches in a manner
well known in the art.
FIGS. 2 and 3 show second speed clutch valve 62 slidably mounted
within bore 78 of sandwich valve 53, with bore 78 intersecting bore 75.
Slidably disposed in bore 78 is a spool 80 which is normally biased to
the position shown by means of the helical spring 82 and is movable, in
a position opposing the biasing of spring 82, by means of piston and
cylinder type fluid actuator valve 70. The portion of bore 78 remote
from bore 75 is also connected to a vent conduit 84. Valve bore 78
includes a relieved portion 79 which allows the venting of the residual
fluid pressure within aperture exit portion 75b via vent conduit 84
while spool 80 closes aperture entrance portion 75a. Actuator-transfer
valve 70 is threaded into a portion of bore 78 and includes a body 86
having a longitudinally extending bore 88 therein. Communicating with
bore 88 are longitudinally spaced ports 90 and 92, as well as end port
94. Port 90 of valve 70 is connected to the second speed ratio clutch
pressure supply in control cover 14 by means of conduit 96, while port
92 is connected to port 98 of a first speed clutch valve 100 via conduit
102. Conduit 68 connects port 94 with solenoid valve 60.
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Slidably disposed in valve bore 88 is a spool 106 whose spaced land
portions 108, 110 define a groove 112 which serves to selectively inter-
connec~ ports 90 and 92 upon the movement of spool 106 in response to a
control pressure from solenoid valve 60. Land portion 108 also serves
to separate portions 89 and 91 of valve bore 88 when spool 106 is in the
position shown in FIGS. 2 and 3. In addition, spool 106 includes a
stalk portion 114 which abuts and serves to move spool 80 in opposition
to spring 82. It should be understood that the interconnection of
conduits 90 and 92, via the movement of spool 106, simultaneously closes
second speed aperture 75 in sandwich valve 53 to fluid flow from control
cover 14, thereby shutting off the flow of pressurized fluid to second
speed ratio clutch 26 and consequently disengaging same.
The structure of first speed clutch valve 100 is substantially
similar to that of second speed clutch valve 62 and includes a spool 120
reciprocable in bore 118 of sandwich valve 53, with bore 118 perpendicu-
larly intersecting bore 74. Spool 120 is normally biased to the positon
shown by means of helical spring 122 and is movable in opposition thereto
as a result of fluid pressure from second speed clutch valve 62 which
enters through conduit 102 and port 98. Valve bore 11~ also includes a
relieved portion 124 which allows fluid pressure to enter aperture exit
portion 74b while spool 120 closes aperture entrance portion 74a to
direct fluid flow from control cover 14, as shown in FIG. 5, thereby
consequently engaging first speed ratio clutch 24 via the pressurized
fluid that normally actuates second speed ratio clutch 26.
In normal second speed ratio operation, pressurized fluid for
second speed ratio clutch 26 passes vertically through aperture 75 of
sandwich valve 53. In addition to being controlled by speed control
valve 43, the second ratio clutch pressure is also controlled by actu-
ator valve 70 and second speed clutch valve 62. Actuator-transfer valve
70 in turn is, of course, controlled by solenoid valve 60. Once vehicle
ground speed drops to a first predetermined speed, for example, 1 mile
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per hour, this predetermined first speed is sensed by electronic speed
switch 58 that supplies a signal which activates solenoid valve 60.
Actuation of valve 60 permits a control pressure from control cover 14
to reciprocate valve 70 and second speed clutch valve 62. As previously
noted, clutch valve spool 80 shuts off a flow of pressurized fluid to
second speed ratio clutch 26 whereas the movement of actuator valve
spool 106 channels the second clutch valve pressure in conduit 96 into
the previously unpressurized first speed clutch valve 100. As best seen
in FIG. 5, first speed clutch valve spool 120 closes off aperture por-
tion 74a of first speed aperture 74, thereby blocking off communication
with the control cover while simultaneously permitting the pressurized
fluid from valve 70 to enter aperture portion 74b which thereafter en-
gages first speed ratio clutch 24. Thus, second speed ratio clutch
pressure is used to activate first speed ratio clutch 24 and effect a
downshift.
When the vehicle ground speed exceeds a second higher predetermined
speed, for example, 2-l/2 miles per hour, a signal is removed from
electronic speed switch 58 to deactivate solenoid valve 60, thereby
cutting off the flow of second speed rat~o clutch pressure into first
clutch valve lO0 and at the same time, opening second speed ratio aper-
ture 75 so as to permit engagement of second speed ratio clutch 26 which
effects an upshift. The downshift and consequent upshift are fully
automatic and completely free the operator from the burden of manual
control in regard thereto. It should be understood that electronic
speed switch 58 can be set for varying first and second predetermined
ground speeds. Furthermore, automatic shift system 38 can, of course,
also be utilized with other than only first and second speed ratios if
so desired. In addition, if desired by the operator, shift system 38
can be disconnected via override switch 50 preferably located in the
vehicle cab.
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In order to prevent downshifting of the transmission during full
throttle or rapid directional reversals, added to previously described
automatic shift system 38, is a downshift inhibitor or delay circuit 130
which is interposed in electronic speed sensing system 48 between elec-
tronic speed switch 50 and solenoid valve 60, as shown in Fig. 6.
Circuit 130 which is encased within dashed line area 132, is shown in a
position just prior to a directional reversal of the vehicle and basically
takes the form of a timer circuit that is energized by initiating a
directional reversal when traveling in second gear only.
Associated with circuit 130, but inherent in electronic speed
switch 58, is normally closed switch 134, located between terminals 136
and 138, and normally opened switch 140 located between terminals 136
and 142. It should be noted, however, that switches 134 and 140 are
shown as open and closed, respectively, since switches 134 and 140 are
in these positions at a time just prior to a directional reversal.
During vehicle slowdown, switches 134 and 140 assume closed and open
positions, respectively, at or below a first predetermined speed and
remain in these positions until the vehicle accelerates to and above the
second predetermined speed, whereupon their positions become open and
closed, respectively. Thus, it should be understood that FIG. 6 shows
circuit 130 in a position just prior to a directional reversal of the
vehicle with switches 134, 140 being shown in the operative positions
they occupy when the vehicle is above the second predetermined speed.
Also connected with speed switch terminal 138 is solenoid valve
terminal 144, with solenoid terminal 146 being connected with power
supply 59 and speed switch terminal 148. In addition, power supply 59
is also connected with speed switch terminal 150. As previously shown
in Fig. 1, interposed in the connection between speed switch terminal
138 and solenoid terminal 146 is override switch 50 that is preferably
located in the vehicle cab. -
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Connected with speed switch terminal 142 is a normally open switch152 that is remotely mounted in the vehicle operator-actuated transmis-
sion control (not shown), with switch 152 being momentarily activated
every time the vehicle operator performs a directional reversal via
directional control valve lever 46 (Fig. 1). Switch 152 ;s ;nterposed
between speed switch terminal 142 and a f;rst relay 154. A second relay
and timer 156 branches off from the connect;on between speed switch
terminal 138 and solenoid term;nal 144.
Second relay and timer 156 controls a normally closed switch 158
lQ that is located between first relay 154 and neutral s~art switch 152.
In a similar manner, first relay 154 controls a normally open first
switch 160 that is located in a line connected to speed switch terminal
150 and whose other end is connected to the line between neutral start
switch 152 and second relay and timer switch 158. First relay 154
further controls a normally open second switch 162 that is located
between second relay and timer 156 and speed switch terminal 138.
Furthermore, first relay 154 also controls a normally closed third
switch 164 that is located between speed switch terminal 138 and sol-
enoid valve terminal 144. First relay 154 may take the form of Model
R10-E1-Y4-V700-4PDT, while second relay and timer 156 may take the form
of Model CUH-42-30010-DPDT, both of which are manufactured by the Potter
& Brumfield Division of AMF Inc., of Princeton, Indiana.
It is the function of circuit 130 to prohibit downshifts from
second to first gear while undergoing full throttle directional re-
versal. It is desirable to perform the directional reversal in second
rather than in first gear due to the inherent lower rotational speeds of
both the forward and reverse clutches in second gear operation for the
same vehicle speed. A downshift into first clutch 24 during full throttle
directional reversal is quite harsh and is thus uncomfortable for the
operator as well as being hard on the vehicle itself.
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Inhibitor circuit 130 is a timer circuit which is energized upon
vehicle directional reversal initiated by the operator when traveling in
second gear only. The timer portion of second relay and timer 156 is
activated when electronic speed switch 58 is reset, which occurs when
vehicle ground speed drops to a first predetermined speed. The trans-
mission downshift is delayed for a predetermined length of time which is
long enough for the vehicle to reverse and accelerate, at full throttle,
to the normal second gear range. The delay is needed to inhibit full
throttle downshifts, and the delay is of sufficient duration that the
machine goes through the normal cycle of slowdown, stop and acceleration
in second gear until the ground speed exceeds a second higher predeter-
mined speed, before the delay time runs out.
The sequence of events that occur during a full throttle or rapid
directional reversal is best understood by a perusal of the flow diagram
shown in Fig. 7 which diagrammatically shows a complete full throttle
directional reversal in second gear. During the predetermined delay
time there occurs a slowdown from a first predetermined ground speed in
one direction to a stop and then an acceleration in the other direction
to a second predetermined ground speed.
Circuit 130 is energized when a directional reversal is made in
second gear by the operator. As a result of the reversal, switch 152
closes momentarily thereby activating first relay 154 and as a result
thereof reversing first relay switches 160, 162 and 164. Switch 160
locks in the circuit to first relay 154, whereafter switch 152 again
opens.
When the vehicle speed falls below the first predetermined speed,
speed switch 58 closes switch 134 and opens switch 140. Since switch ;
162 is still closed as a result of the directional reversal, the timer
portion of second relay and timer 156 is activated. However, during
full throttle actuation, the predetermined time before the second relay
is actuated, is long enough for the vehicle to change directions and
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accelerate above the second predetermined speed thereby inhibiting the
shift to first gear. After the predetermined time has elapsed, second
relay 156 is activated and in turn reverses second relay switch 158
thereby causing it to open. The opening of switch 158 deactivates first
relay 154 and returns first relay switches 160, 162 and 164 to their
normal state. The opening of switch 162 deactivates second relay 156
which subsequently returns second relay switch 158 to its normally
closed state. It should be understood that at this time circuit 130 has
completely cycled through its sequence and all switches are again in
their normally open or closed states.
Thus, it should be understood that during full throttle directional
reversal, the reversal itself is accomplished in second gear. There is
full use of circu;t 130 in that speed switch 58 shifts to its first
speed setting, however, the transmission itself remains in second gear.
Fig. 8 takes the form of a flow diagram that depicts a part throttle
or slower directional reversal. In comparison with Fig. 7, it will be
seen that the first three block diagrams are identical, and, during a
predetermined time, the timer portion of second relay and timer 156 goes
through the same sequence cycle as previously described with reference
to FIG. 7 and all switches in circuit 130 again return to their normal
state. However, at this time, since the speed of the vehicle is still
below the second predetermined speed, switch 134 is closed, and after
the de-energizing of the timer circuit portion of 156 and the closing of
switch 164, solenoid 60 is energized thus causing the transmission to
downshift to first gear. Thereafter, the vehicle slows down, comes to a
stop and accelerates in the other direction. Once it exceeds the second
predetermined speed, the settings of switches 134 and 140 are reversed
thereby causing the transmission to be shifted to second gear. Thus, on
a part throttle or slower directional reversal, the predetermined time
uelay runs out and the transmission shifts to first gear, with this
downshift not being objectionable. Again, there is full use of circuit
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130, however, at part throttle, the predetermined time of second relay
and timer 156 is exceeded and the transmission shifts to first gear. It
should be understood that the actual shift of the transmission into
first gear may take place at, before, or slightly after the vehicle has
actually made its reversal, this fact being indicated by the dashed
lines in the FIG. 8 diagram. It should be noted that the predetermined
time lines in FIGS. 7 and 8 represent the same time span, although the
FIG. 8 line is broken due to space constraints.
In case the operator undertakes to reverse the direction of the
vehicle after first completely stopping the vehicle and thereafter
initiating the directional reversal, downshift inhibitor circuit 130 is
not activated since with this operational sequence, at directional
reversal time, electronic speed switch 5~3 is in the first gear position,
with circuit 130 being activated only when the vehicle travels in the
second gear speed range. It should, of course, be understood that
circuit 130 can also be utilized with other than only first and second
speed ratios if so desired.
From the foregoing, it is believed that those familiar with the art
will readily recognize and appreciate the novel concepts and features of
the present invention. Obviously, while the invention has been described
in relation to only a single embodiment, numerous variations, changes
and substitutions of equivalents will present themselves to persons
skilled in the art and may be made without necessarily departing from
the scope and principles of this invention. As a result, the embodiment
described herein is subject to various modifications, changes and the
like, without departing from the scope and spirit of the invention, with
the scope thereof being determined solely by reference to the claims
appended hereto.
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