Control valve for timed clutch engagement

A control valve assembly has a multi-land spool valve slidably disposed in a stepped valve bore. One end of the spool valve has disposed adjacent thereto a control chamber in which a control signal pressure is selectively applied while the other end has a timing chamber disposed adjacent thereto which has the signal pressure selectively applied therein when the clutch is subjected to apply pressure. The timing chamber permits rapid clutch fill and controlled pressure rise of the clutch apply fluid during clutch engagement.

BACKGROUND OF THE INVENTION 
This invention relates to hydraulic valve control systems, and more 
particularly, to hydraulic control systems having a valve mechanism for 
controlling the engagement and disengagement of a torque transmitting 
friction device. Specifically, this invention relates to such systems 
wherein the friction device has a time-pressure relationship during 
engagement. 
During the engagement of a fluid operated torque transmitting device, such 
as a clutch or brake, it is desirable to provide an engagement signal 
having a rapid fill portion and a controlled pressuring portion. This is 
generally accomplished by combining one or more valves with an accumulator 
in a friction device fill circuit. The fill time and pressure is generally 
determined by the minimum spring load on the accumulator or the minimum 
spring load plus any accumulator bias pressure that is present and the 
volume of the apply chamber for the friction device. 
The pressuring or pressure rise portion is controlled by the spring rate in 
the accumulator plus any variable bias pressures that might be present. 
These systems require at least a shift valve and an accumulator. Some 
systems also require control valving for the accumulator. The prior art 
mechanisms require space and therefore add to the size and weight of the 
system. Also, in these systems, the machining complexity and added 
structures contribute to the overall cost of the system. 
SUMMARY OF THE INVENTION 
The present invention incorporates the shift valve function and accumulator 
function in a single clutch timing control valve. This eliminates the 
complexity of accumulator timed control circuits. The timing control valve 
also eliminates the spring member normally associated with the shift 
valve, thus further reducing the cost and weight of the system. 
It is therefore an object of this invention to provide an improved torque 
transmitting friction device engagement timing valve. 
It is another object of this invention to provide an improved clutch 
engaging control mechanism, wherein a single valve element provides clutch 
apply oil and clutch engagement timing. 
It is a further object of this invention to provide an improved clutch 
engagement control, wherein a single valve element provides both an 
engagement control function and an accumulator timing function without the 
use of a spring element or a separate accumulator piston and chamber. 
These and other objects and advantages of the present invention will be 
more apparent from the following specification and drawings.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT 
Referring to the drawings, wherein like characters represent the same or 
corresponding parts throughout the several views, there is seen in FIG. 1 
a valve assembly 10, which includes a valve body 12 having a stepped valve 
bore 14, a stepped diameter valve spool 16 and a solenoid control valve 
18. 
The stepped valve bore 14 has a small diameter portion 20 and a large 
diameter portion 22. The valve spool 16 has a pair of spaced equal 
diameter lands 24 and 26 slidably disposed in the small diameter portion 
20 and a large diameter valve land 28 slidably disposed in the portion 22. 
The land 24 cooperates with the valve bore 14 to form a timing chamber 30. 
The land 26, large diameter land 28 and the valve bore 14 cooperate to 
form a control chamber 32 which has an effective cross-sectional area 
equal to the differential of the areas of valve lands 26 and 28. 
The valve land 28 and valve bore 14 cooperate to form a signal control 
chamber 34 in which an end portion 36 of the solenoid valve 18 is also 
disposed. The valve assembly 10 is disposed in fluid communication with a 
conventional electro-hydraulic control system 38 and a conventional fluid 
operated torque transmission friction device, such as a clutch 40. 
The control system 38 communicates with the valve assembly 10 through an 
actuator feed passage 42 and a clutch feed passage 44. The valve assembly 
10 communicates with the clutch 40 via a clutch apply passage 46. The 
actuator feed passage 42 is connected with the valve bore 14 intermediate 
the valve lands 26 and 28 and is also connected through a restriction 48 
and a signal passage 50 with the signal control chamber 34. 
The clutch apply passage 46 is connected with the valve bore 14 
intermediate the valve lands 24 and 26. The clutch feed passage 44 is 
connected with the valve bore 14 at a position which can be selectively 
opened and closed by the valve land 24, and as seen in FIG. 1, the valve 
land 24 is positioned to close the feed passage 44. The valve bore 14 also 
has connected thereto a pair of exhaust passages 52, 54 which are 
selectively controlled to be opened or closed by the respective valve 
lands 24 and 26. 
The valve assembly 10 also includes a timing passage 56 which is connected 
with the valve bore 14 at the timing chamber 30 and also at a position 
which is selectively open to the control chamber 32 by the position of 
valve land 26. 
The solenoid valve 18 is a conventional solenoid valve which is operable to 
open the signal control chamber 34 to an exhaust passage, not shown, and 
to close the signal control chamber 34 from exhaust in response to 
actuation of the solenoid valve 18. When the solenoid valve 18 is opened, 
the pressure in signal control chamber 34 will be essentially equal to 
exhaust. Due to the restriction 48, which limits the volume of oil that 
enters the chamber 34, a significant pressure will not be developed in the 
signal control chamber 34 when the solenoid valve 18 is open. 
The differential area of control chamber 32 is continually pressurized by 
the oil supplied to the actuator feed passage 42 from the control system 
38. 
As seen in FIG. 1, the clutch 40 is disengaged by the fluid connection 
between passage 46 and exhaust passage 54 between the valve lands 24 and 
26. The clutch feed passage 44 is blocked or closed by the valve land 24. 
The timing chamber 30 is open to the exhaust passage 52 as is the timing 
passage 56. 
Due to the differential area of the control chamber 32 and the exhausting 
of signal controlling chamber 34, the valve spool 16 is urged to its 
rightwardmost position, as seen in FIG. 1, which causes valve land 26 to 
close the timing passage 56 from the control chamber 32. This eliminates 
the need for a spring to position the valve spool 16 in the downshifted 
condition. 
When it is desirable to engage the clutch 40, the control system 38 will 
issue an electrical signal to the solenoid valve 18, thereby closing the 
signal control chamber 34 to exhaust, and permitting a controlled pressure 
rise therein as pressurized fluid flows through the restriction 48. When 
the pressure in the signal control chamber 34 is sufficient to overcome 
the force on the differential area of control chamber 32, the valve spool 
16 will begin moving leftward thereby opening the clutch feed passage 44 
to the clutch apply passage 46 while simultaneously closing the exhaust 
passages 52 and 54. 
Also, substantially simultaneous with the closing of exhaust passage 52, 
the feed passage 42 is opened to the timing passage 56 thereby permitting 
a buildup of pressure in the timing chamber 30. The restriction to fluid 
flow provided by the timing passage 56 determines the time requirement for 
the timing chamber 30 to be pressurized. During this time period, the 
clutch 40 is subjected to unrestricted fluid flow from the clutch feed 
passage 44, such that the apply chamber of the clutch can be filled with 
oil. This is the mode of operation shown in FIG. 2. 
As the fluid pressure in the timing chamber 30 increases, the valve spool 
16 will be moved rightward by the combination of forces in the timing 
chamber 30 and control chamber 32, as opposed by the force in the signal 
control chamber 34. The rightward movement of the valve spool 16 will 
cause a metering of fluid flow from the feed passage 44 to the apply 
passage 46 thereby controlling the pressure rise within the control apply 
chamber which results in a controlled clutch apply time. 
The rightward movement of the valve spool 16 may result in a closing of the 
timing passage 56, however, the fluid pressure in signal control chamber 
34 will continue to rise, such that the valve spool 16 will move slightly 
leftward thereby reopening the timing passage 56 to the actuator feed 
passage 42. The valve will assume a substantially stable position, as 
shown in FIG. 3, wherein the timing passage 56 and clutch feed passage 44 
are controlled for metered flow which thereby controls the pressure rise 
within the clutch 40. 
After a predetermined time, the clutch 40 will be fully engaged and the 
valve spool 16 will reach a point of equilibrium on which the pressure 
forces thereon are balanced. When the clutch 40 is to be disengaged, the 
solenoid 18 is controlled to the "off" state thereby exhausting the signal 
chamber 34, such that the forces on the valve spool 16 in both the timing 
chamber 30 and control chamber 32 will force the valve rightward to the 
position shown in FIG. 1. In this position, the timing chamber 30 is 
exhausted via passage 52 and the control chamber 32 remains pressurized to 
thereby maintain the clutch 40 in the disengaged position, and the valve 
spool 16 in the rightward position, shown in FIG. 1. 
The valve timing, and therefore the clutch engagement timing, can be 
affected by the size of the restriction 48, the volume of timing chamber 
30 and the flow restriction presented by the timing passage 56. The 
positioning of the valve lands 24 and 26, relative to the various passages 
controlled thereby, will also have an affect on valve timing, and 
therefore on clutch engagement timing. The effect and interaction of these 
parameters is known to the designer of hydraulic control circuits and can, 
therefore, be predetermined to accommodate the valve timing desired. 
Obviously, many modifications and variations of the present invention are 
possible in light of the above teaching. It is therefore to be understood, 
that within the scope of the appended claims, the invention may be 
practiced otherwise than as specifically described.