Regulating valve for engagement control of friction drive devices

A clutch engagement control has a flow regulating valve to control the engagement timing of the clutch. The regulating valve responds to a flow signal to reduce the fluid flow rate through the valve after the clutch apply piston has taken up the clutch free running clearance. The regulating valve has a control area communicating with a venturi between the regulating valve and the apply piston such that a flow rate signal is present at the control area.

TECHNICAL FIELD 
This invention relates to engagement control valves for fluid operated 
friction devices. 
BACKGROUND OF THE INVENTION 
Automatic shifting transmissions use fluid operated friction devices, such 
as clutches and brakes, to establish gear ratios between the vehicle 
engine and drive wheels. The gear ratios are interchanged (upshifted or 
downshifted) to extend the usefulness of the engine operating range. 
During a ratio interchange, it is necessary to control the engagement 
timing of the on-coming friction device as well as controlling the 
disengagement point of the off-going friction drive device. 
Fluid operated disc type friction devices have a free running clearance. 
That is, when a device is disengaged, the adjacent plates do not have 
significant contact to thereby maintain the slip losses of the device at a 
minimum. Free running clearance affects the engagement timing of the 
device. The apply piston must be pressurized to move through a distance 
defined by the free running clearance prior to clutch engagement. The 
movement should occur as quickly as possible. Thus, a large flow volume is 
originally required during the engagement process. The flow volume must be 
rapidly reduced to avoid a harsh apply of the friction device which will 
affect the ratio interchange. 
Engagement timing is generally provided in current transmissions using one 
of three control methods depending upon the acceptable cost for the 
transmission. One control system incorporates one-way devices in 
combination with friction devices. These systems require duplicate 
arrangements if engine coast braking is to be available. However, the 
ratio change on and off of one-way devices is known to be quite smooth. 
A second of the control systems uses variable pressure control devices, 
such as pulse-width-modulated valves to control the on-coming and 
off-going friction devices. These pulse-width-modulated devices require an 
electronic control module or computer to affect proper control of the 
variable pressure devices. 
The third system uses a fluid accumulator and valve to control the 
on-coming friction device and a bleed orifice to control the off-going 
device. The accumulator requires additional space within the transmission 
housing as well as a valve mechanism that permits the accumulator to be 
filled when the friction device is engaging and to not interfere with the 
exhausting of the friction device during disengagement. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved pressure 
regulator valve for a friction device and engagement system. 
In one aspect of the invention, a venturi is disposed in fluid flow 
relation between a regulator valve and the piston apply chamber of a fluid 
operated friction torque transmitting device. 
In another aspect of the invention, the venturi permits fast initial 
filling of the piston apply chamber. 
In yet another aspect of the invention, the pressure at the venturi 
provides a regulating or control pressure at the regulator valve. 
In a further aspect of the invention, the regulator valve reduces fluid 
flow to the torque transmitting device as the apply pressure increases.

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 FIGS. 1 
and 2 a hydraulic engagement control system 10 incorporating a flow 
regulating valve 12, an electro-hydraulic control or ECU 14, a hydraulic 
pump 16 and a fluid operated torque transmitting device 18 which is shown 
in the form of a clutch. 
The pump 16 draws fluid from a reservoir 20 for distribution through the 
electro-hydraulic control system to various transmission components 
including the regulating valve 12. The ECU 14 includes a clutch feed 
passage 22 and a control passage 24, both of which communicate with the 
valve 12. The valve 12 includes a valve body 26 in which is formed a 
stepped valve bore 28 having a large diameter portion 30 and a small 
diameter portion 
A valve spool 34 has a pair of equal diameter spaced lands 36 and 38 
slidably disposed in the bore 30 and a smaller diameter land 40 slidably 
disposed in the bore 32. The land 40 and bore 32 cooperate to form a 
control chamber which is also available to house a bypass spring 42. The 
valve land 38 and the diameter 30 cooperate to form a control chamber 44 
which is disposed for fluid communication with the control passage 24. 
The bore 30 has communicating therewith an inlet port 46, an outlet port 48 
and an exhaust port 50. The inlet port 46 is connected with the feed 
passage 22 and the outlet port 48 is connected with an engage passage 52 
which incorporates a venturi 54 and supplies fluid to a rotating clutch 
18. 
The venturi 54 has a flow rate control passage 58 communicating therewith 
which directs fluid to and from the control chamber 32. Fluid pressure in 
the control chamber 32 acts on a control area 60 which is represented by 
the left end of the land 40 and cooperates with the spring 42 to urge the 
valve spool 34 rightward, as seen in FIGS. 1 and 2. The valve land 38 has 
a control area 62 defined by the right end of the valve land 38 which is 
acted upon by fluid pressure in the control chamber 44 to urge the valve 
spool 34 leftward, as seen in FIGS. 1 and 2. 
The clutch 18 is a conventional fluid operated friction device having a 
housing 64 to which is splined a plurality of friction discs 66. The 
housing 64 supports a piston 68 and cooperates therewith to provide an 
apply chamber 70. The clutch 18 also has a plurality of friction discs 72 
which are drivingly connected with a shaft 74 which represents an output 
member of the clutch 18. The housing 64 is the input portion of the clutch 
and is generally connected to either a torque converter or an engine for 
supplying power from the power source or engine to the rear wheels of a 
vehicle, not shown. 
As seen in FIG. 1, the ECU 14 has supplied fluid pressure through the 
control passage 24 to request the engagement of the clutch 18 which is 
presumably requiring an upshift ratio change within the transmission. The 
fluid in the control passage 24, and therefore control chamber 44, urges 
the valve spool 34 leftward to the positions shown, such that fluid flow 
in passage 22 is directed between the lands 36 and 38 to the outlet port 
48 and therefore passage 52 in which it passes through the venturi 54 to 
the supply chamber 70 of the clutch 18. 
Prior to engagement, the clutch 18 has a free running clearance such that 
the friction discs 66 and friction disc 72 are not in frictional 
engagement and therefore some movement of the piston is required within 
the supply chamber 70 before the frictional engagement can occur. This is 
known as the free running clearance and the initial movement of the piston 
68 takes up this free running clearance. During this time, the pressure 
within the apply chamber is at a low level and fluid flow through the feed 
passage 22 and engage passage 52 is at a very high rate. 
As understood by Bernoulli's theorem, the pressure at the throat of the 
venturi 54 will reduce as velocity increases, such that the fluid pressure 
in passage 58 will be quite low. Thus, the balance forces on the valve 
spool 34 permit the leftward movement of the valve spool 34 to open the 
fluid flow to the clutch 18. However, when the piston 68 begins to 
compress the friction discs 66 and 72 together, the pressure in the apply 
chamber 70 will rise quite rapidly and the piston 68 will be slowed 
considerably in its axial movement resulting in less fluid flow velocity 
through the venturi 54. Thus, the pressure in the control passage 58 will 
rise. The increased pressure in the control chamber 32 and the spring 42 
will be sufficient to balance the fluid pressure in the control chamber 44 
operating on the land 38. When this occurs, the valve spool 34 will move 
rightward to regulate the fluid flow through the regulating valve 12 
thereby permitting a controlled engagement rate of the clutch 18. 
During the clutch engagement, the pressure in control passage 24 will be 
maintained such that the clutch 18 will have full pressure imposed thereon 
to maintain the frictional integrity and drive characteristics of the 
clutch. 
When it is desired to disengage the clutch, the fluid pressure in passage 
24 will be reduced by the ECU 14, such that the valve spool 34 will move 
rightward toward the position seen in FIG. 2, at which time a controlled 
exhausting of the clutch 18 will occur. Thus, the regulator valve 12 can 
control both the engagement timing of the clutch and the disengagement 
timing of the clutch. 
From the above description, it should, at this point, be obvious to those 
skilled in the art that the single regulating valve 10 is effective to 
provide engagement timing control for a fluid operated torque transmitting 
friction device. While the system in the exemplary embodiment is disclosed 
as utilizing a rotating clutch as the torque transmitter, those skilled in 
the art will appreciate that disc type friction brakes will also benefit 
from the use of this control system.