Control system for sequentially actuating fluid actuators

The heretofore known transmission control systems providing automatic sequential engagement of the fluid clutches have valves directly controlled by the operator and are not readily convertible to be pilot operated. The present invention has a selector valve (31) movable between first and second positions for communicating a supply line (19) with first and second fluid clutches (11,12) respectively. A fluid actuated valve (44) is moved to a first position communicating a third fluid clutch (13) with a drain line (18) when the fluid pressure in a fluid chamber (61) thereof drops below a preselected value and to a second position communicating the supply line (19) with the third fluid clutch (13) when the fluid pressure in the fluid chamber (61) exceeds the preselected value. A dump valve (76) drops the fluid pressure in the chamber (61) below the preselected value in response to a momentary pressure drop in the supply line (19) upon moving the selector valve (31) between the first and second positions. An orifice (81) delays filling of the fluid chamber (61) until the selected one of the first and second clutches (11,12) is engaged. The elements of the control system are fluid actuated and are, in effect, pilot operated.

TECHNICAL FIELD 
This invention relates generally to a control system and more particularly 
to a transmission control system which prevents the engagement of a fluid 
actuated clutch until one of a pair of fluid actuated clutches has been 
engaged. 
BACKGROUND ART 
Some hydraulic controls for power shift transmissions automatically provide 
for the sequential engagement of specific clutches after the transmission 
is shifted from one speed to another. For example, the system disclosed in 
U.S. Pat. No. 3,091,976 which issued to Johnson et al. on June 4, 1963 
causes the speed clutches to be fully engaged before either one of the 
directional clutches is engaged so that the directional clutches absorb 
the shock of transmitting power through the transmission. With that system 
both the selector valve and directional control valve are directly 
controlled by the operator through a mechanical linkage. However, the 
control system of many of the industrial vehicles are being designed to 
incorporate pilot control circuits to control the shifting of the main 
control valves. Those pilot control circuits can be either totally 
hydraulic or a combination of electrical and hydraulic components. In 
either case, while the sequential engagement system taught by the 
above-noted patent has functioned satisfactory in the direct operator 
controlled arrangement in which it is used, that specific system is not 
readily convertible to a pilot operated control circuit. 
The present invention is directed to overcoming one or more of the problems 
as set forth above. 
DISCLOSURE OF THE INVENTION 
In one aspect of the present invention a control system adapted for 
sequentially actuating first, second and third fluid actuators has a pump 
and a drain line connected to a tank, a supply line connected to the pump, 
and a selector valve connected to the supply line and to the first and 
second fluid actuators. The selector valve is movable between a first 
position at which the supply line is communicated with the first fluid 
actuator and a second position at which the supply line is communicated 
with the second fluid actuator. A fluid actuated valve is connected to the 
supply line, the drain line and the third fluid actuator and has a valve 
element movable between a first position at which the third fluid actuator 
is communicated with the drain line and a second position at which the 
supply line is communicated with the third fluid actuator, a spring 
biasing the valve element to the first position, and a fluid chamber at 
one end of the valve element. The valve element is moved to the second 
position in response to fluid pressure in the fluid chamber exceeding a 
preselected value and to the first position in response to the fluid 
pressure in the fluid chamber dropping below the preselected value. A 
means is provided for dumping the fluid in the fluid chamber of the fluid 
actuated valve to the drain line for dropping the fluid pressure in the 
fluid chamber below the preselected value responsive to shifting the 
selector valve between the first and second positions. An orifice 
connecting the supply line to the fluid chamber delays the filling of the 
fluid chamber with fluid until the selected one of the first and second 
fluid actuators is filled with fluid. 
The control system of the present invention provides a system in which one 
of a pair of fluid actuated clutches is engaged prior to engagement of a 
third fluid actuated clutch so that the third clutch always absorbs the 
shock of transmitting power through the transmission when the transmission 
is shifted. The valves utilized to control the engagement and 
disengagement of the fluid actuated clutches are fluid actuated valves and 
are controlled by directing pressurized fluid thereto from the control 
system by selectively operable valves. The components of the system 
causing the selected one of the pair of clutches to be engaged prior to 
the engagement of the third clutch utilizes the characteristic of many 
power shift transmissions wherein the fluid pressure in the control system 
drops drastically due to the filling of the fluid actuated clutches each 
time the transmission is shifted.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawing, a control system is generally indicated by 
the reference numeral 10 and is adapted to control a plurality of fluid 
actuators 11, 12, 13 and 14 which can be, for example, fluid actuated 
clutches in a power shift transmission, not shown. In this particular 
embodiment, fluid actuators 11 and 12 represent first and second speed 
clutches while fluid actuators 13,14 represent forward and reverse 
clutches respectively of the transmission. The fluid actuated clutches 
11-14 are engaged when pressurized fluid is directed thereto and are 
disengaged when the fluid is exhausted or vented therefrom. 
The control system 10 includes a tank 16, a pump 17 and a drain line 18 
connected to the tank 16, a supply line 19 connected to the pump 17 and a 
relief valve 21 positioned between the supply line 19 and drain line 18. 
The relief valve 21 limits the fluid pressure in the supply line 19 to a 
preselected maximum and includes a spool 22 slidably positioned within a 
bore 23 defining a fluid chamber 24 at one end of the spool 22. The 
chamber 24 is connected to the supply line 19 such that as the pressure in 
the supply line 19 increases the spool 22 is moved leftwardly against the 
bias of a spring 26 positioned between the spool 22 and a plug 27 fixedly 
positioned within the bore 23. The spool 22 moves leftwardly until metered 
communication is established between the supply and drain lines 19,18 and 
the force acting against the end of the spool 22 by the fluid pressure in 
the chamber 24 equals the biasing force of the spring 26. 
A selector valve 31 is connected to the supply line 19, drain line 18 and 
to the fluid actuated clutches 11,12. The selector valve 31 includes a 
valve spool 32 slidably positioned within a bore 33 and is movable between 
first and second positions. At the first position the supply line 19 is 
communicated with the fluid actuated clutch 11 through an annular groove 
34 on the valve spool 32 while the fluid actuated clutch 12 is 
communicated with the drain line 18 through an annular groove 36 on the 
valve spool 32. At the second position the supply line 19 is communicated 
with the fluid actuated clutch 12 through annular groove 36 while the 
fluid actuated clutch 11 is communicated with the drain line 18 through 
the annular groove 34. A spring 37 is positioned within a fluid chamber 38 
at one end of the valve spool 32 and biases the valve spool 32 to the 
first position against a plug 39 fixedly positioned within the bore 33. 
Another fluid chamber 41 is formed between the valve spool 32 and the plug 
39 and is continuously connected to the supply line 19. 
The fluid chamber 38 is connected to the supply line 19 through an orifice 
42. A solenoid actuated valve 43 is connected to the fluid chamber 38 and 
to the drain line 18 and is movable between a first position at which the 
fluid chamber 38 is blocked from communication with the drain line 18 and 
a second position at which the fluid chamber 38 is communicated with the 
drain line 18. 
With the solenoid valve 43 in the disengaged or first position as shown 
both chambers 38 and 41 are subjected to the same fluid pressure from the 
supply line 19 and the spring 37 effectively biases the valve spool 32 to 
the first position. Moving the solenoid valve 43 to the second position 
reduces the fluid pressure in the chamber 38. The chamber 41 remains 
pressurized thereby causing the valve spool 32 to be shifted to the right 
to the second position. 
A pair of fluid actuated valves 44,46 are connected to the fluid actuators 
13,14 respectively, the supply line 19 through an orifice 47 and to the 
drain line 18. Inasmuch as the fluid actuated valves 44,46 are identical 
only the fluid actuated valve 44 will be described in detail with primed 
reference numerals applied to counterpart elements of the valve 46. The 
valve 44 includes a valve spool 48 slidably positioned in a bore 49. The 
valve spool 48 is movable between a first position at which the fluid 
actuated clutch 13 is in communication with the drain line 18 through an 
annular groove 51 on the valve spool 48 and a second position at which the 
fluid actuated clutch 13 is communicated with the supply line 19. A 
passageway 52 in the valve spool 48 connects the annular groove 51 with a 
reduced diameter portion 53 which is positioned in a chamber 54 
surrounding the reduced diameter portion 53. A spring 56 is positioned in 
the chamber 54 and biases the valve spool 48 to the first position. 
A control means 57 for moving the valve spool 48 to the second position 
against the bias of the spring 56 includes a selector piston 58 slidably 
positioned within a bore 59 defining a fluid chamber 61. A spring 62 is 
positioned between the selector piston 58 and an annular collar 63 which 
functions as a stop for establishing the first position of the valve spool 
48. A load piston 64 is slidably positioned within a fluid chamber 66 of 
the selector piston 58. The chamber 66 is connected to an annular groove 
67 in the exterior of the selector piston 58 through a radial port 68. A 
load spring 69 has one end in abutment with the load piston 64 and extends 
through the annular collar 63 with its other end abutting the valve spool 
48. At the position shown the annular groove 67 and hence the chamber 66 
is vented to the drain line 18. An orifice 71 connects the bore 59 with 
the fluid actuated clutch 13. 
For an understanding of the present invention it will suffice to note that 
the valve spool 48 is moved to the second position in response to fluid 
pressure in the fluid chamber 61 exceeding a preselected value and to the 
first position in response to the fluid pressure in the fluid chamber 61 
dropping below the preselected value. When the fluid pressure in the fluid 
chamber 61 exceeds the preselected value the selector piston 58 is moved 
to the right until it abuts the annular collar 63. Annular groove 67 will 
thus move out of communication with the drain line 18 but will remain in 
communication with the orifice 71. Simultaneously therewith the load 
piston 64 will move rightwardly to permit load spring 69 to overcome the 
opposed biasing force of the spring 56 to move the valve spool 48 to the 
second position to initiate filling of the fluid actuated clutch 13 with 
fluid. Upon filling of the fluid actuated clutch 13, fluid pressure will 
be transmitted through the passage 52 to the chamber 54 thereby providing 
additional force biasing the valve spool 48 to the left. At the same time, 
however, the pressurized fluid passes through the orifice 71 and into the 
control chamber 66. The pressurization of the control chamber 66 will 
function to urge load piston 64 rightwardly to modulate movement of the 
valve spool 48 against the biasing force of the spring 56 and the force 
generated by the fluid pressure in chamber 54 as the fluid pressure in the 
fluid actuated clutch 13 increases. 
Each of a pair of solenoid actuated control valves 72,73 is connected to 
the control chambers 61,61' of the respective valves 44,46 and to the 
drain line 18. The solenoid valves 72,73 are each movable between a first 
position at which the respective fluid chamber 61,61' is vented to the 
drain line 18 and a second position at which the respective fluid chamber 
61,61' is blocked from communication with the drain line 18. 
Means 74 and 75 are provided for dumping the fluid chambers 61,61' of the 
fluid actuated valves 44,46 to the drain line 18 for dropping the fluid 
pressure in the fluid chambers 61,61' below the preselected value 
responsive to shifting the selector valve 31 between the first and second 
positions. 
Since the dumping means 74,75 are structurally identical, only the means 74 
will be described with primed numerals being applied to counterpart 
elements of the means 75. The dumping means 74 includes a fluid actuated 
dump valve 76 connected to the fluid chamber 61 of the fluid actuated 
valve 44 and the drain line 18. The dump valve 76 includes a dump spool 77 
slidably positioned within the bore 33,23. The dump spool 77 is movable 
between a first position at which the fluid chamber 61 is vented to the 
drain line 18 and a second position at which the fluid chamber 61 is 
blocked from communication with the drain line 18. A spring 78 biases the 
dump spool 77 to the first position at which the dump spool 77 is in 
abutment with the plug 39,27 forming a fluid chamber 79. The fluid chamber 
79 is connected to the supply line 19. The dump spool 77 is moved to the 
second position in response to pressurized fluid in the fluid chamber 79 
exceeding the preselected value and to the first position in response to 
the fluid pressure in the fluid chamber 79 dropping below the preselected 
value. 
A pair of orifices 81,81' connect the fluid chambers 61,61' of the fluid 
actuated valves 44,46 to the supply line 19 with the orifices 81,81' being 
of a size sufficient for delaying the filling of the fluid chambers 61,61' 
with fluid until the selected one of the fluid clutches 11,12 is filled 
with fluid upon movement of the valve spool 32 of selector valve 31 
between the first and second positions. 
INDUSTRIAL APPLICABILITY 
The control system 10 is illustrated with the components at the positions 
which they would assume when the pump 17 is not operating. Operating the 
pump 17 introduces fluid into the supply line 19 and thus into fluid 
chambers 24, 38, 40 41, 61,61' and 79,79'. When the pressure in the supply 
line 19 exceeds the preselected value the dump spools 76,76' will move to 
their second position blocking communication between the chambers 61,61' 
and the drain line 18. However, with solenoid valves 72 and 73 in the 
first position shown, the chambers 61,61' remain vented to the drain line 
18 so that the valve spools 48,48' of the valves 44 and 46 remain at their 
first positions. Also, with solenoid valve 43 in the first position shown 
fluid pressure in chamber 41 and 38 equalizes so that the selector valve 
31 remains at its first position. Eventually the fluid pressure in the 
supply line 19 reaches the maximum value as established by the relief 
valve 21. The output capacity of the pump 17 is such that the maximum 
pressure value can be obtained even though fluid is being bled from the 
supply line 18 through one or more of the orifices 81,81' and 42. 
To shift the transmission to, for example, forward drive the solenoid valve 
72 is moved to its second position by an appropriate electrical signal. 
With fluid chamber 61 of valve 44 now totally blocked from communication 
with the drain line 18 fluid pressure builds therein above the preselected 
value shifting the valve spool 48 to its second position to direct 
pressurized fluid to the fluid clutch 13. The orifice 47 prevents the 
fluid pressure in the supply line 19 from dropping below the preselected 
value so that dump spools 76 remain at their second positions. 
To shift the transmission from the first forward speed to the second 
forward speed the solenoid valve 43 is moved to its second position. The 
volumetric relationship of the pump 17 and each of the clutches 11, 12 is 
such that during the initial filling of one of the fluid clutches the 
fluid pressure in the supply line 19 momentarily drops below the 
preselected value. The momentarily pressure drop causes both dump valves 
76,76' to move to their first positions. This immediately dumps the fluid 
from chamber 61 of the valve 44 to the drain line 18 causing the valve 
spool 48 to shift to the first position at which the fluid actuated clutch 
13 becomes disengaged. When the fluid clutch 12 is filled the fluid 
pressure in the supply line 19 again rises above the preselected value 
causing the dump valves 76,76' to move back to their first positions 
blocking communication between the fluid chambers 61,61' and the drain 
line 18. The orifice 81 is sized to delay filling of the chamber 61 until 
the fluid clutch 12 is fully engaged. Subsequently the valve spool 48 will 
be moved to its second position to again reengage the fluid clutch 13. 
In view of the foregoing it is readily apparent that the structure of the 
present invention provides an improved control system for sequentially 
actuating fluid actuators which includes fluid actuated components which 
are in effect pilot operated. 
Other aspects, objects and advantages of this invention can be obtained 
from a study of the drawings, the disclosure and the appended claims.