Accumulator and relay valve

An accumulator and relay valve is operable to isolate a fluid operated electric switch from the transient pressure pulses present at the output of a pulse-width-modulated pressure control valve. The accumulator and relay valve is further operable to control a minimum pressure level that is communicated from the pressure control valve to the switch.

BACKGROUND OF THE INVENTION 
This invention relates to hydraulic control mechanisms, and more 
particularly, to such control mechanisms including a pulse-width-modulated 
valve and an electrical switch. Specifically, this invention relates to 
control mechanisms for isolating the pressure oscillations of a 
pulse-width-modulated valve from the switch. 
Electronic controls are being utilized in many power transmissions to 
control the actuation of fluid operated friction devices, such as clutches 
and brakes. In a number of the electronically controlled transmissions, 
the fluid pressure levels in the various fluid operated friction devices 
are controlled by pulse-width-modulated solenoid valves. These solenoid 
valves operate at a substantially constant A/C frequency in the range of 
60 to 70 Hz. By changing the duty cycle by controlling the percentage of 
time that the solenoid is in the "on" state vs. the percentage of the time 
that the solenoid is in the "off" state, the apply pressure of the fluid 
operated devices can be modulated at any desired pressure level between 
zero and a maximum system pressure. These control systems have been found 
to be cost effective in controlling fluid operated friction devices, 
however, they do present a side effect of inducing high frequency noise or 
hydraulic pressure pulsations into the fluid circuit. 
These control devices also utilize pressure operated electrical switches 
which provide various diagnostic and control functions. It is preferable 
to use a low cost pressure operated electrical switches. However, low cost 
switches do not have structural advantages which will prevent the pressure 
pulsations from acting on the switch. Thus, the switches undergo 
significantly more off/on signals than are necessary during normal 
transmission operation. 
SUMMARY OF THE INVENTION 
The present invention provides an accumulator and relay control mechanism 
for both reducing the magnitude of the pressure pulsations acting on the 
electrical switch and also establishing an accumulator for the on-coming 
fluid operated friction device. This is accomplished through the use of a 
valve which is installed in a hydraulic circuit in parallel flow relation 
with a pressure switch. The valve will act as a relay valve, such that 
when the friction device is disengaged, the pressure operated electrical 
switch is coupled to exhaust and when the friction device is engaged, the 
switch is connected to the apply pressure. 
During application of the friction device, the pressure operated switch 
will remain connected to exhaust until the apply pressure is increased 
above the switch opening pressure setting. At the higher the pressure 
levels, the switch is subjected to the output pressure of a 
pulse-width-modulated valve through an accumulator chamber and a control 
passage which greatly reduces the magnitude of the pressure pulsations. 
During the transition of connecting the electrical switch from exhaust to 
high pressure, a spool valve in the accumulator and relay control 
mechanism provides a control zone, wherein the switch is connected to both 
the pressure output from the pulse-width-modulated valve and to exhaust 
through a highly restricted passage provided by the diametral clearance of 
the valve spool in the valve bore. 
The use of the present invention has been found to be effective in reducing 
the number of state changes or on/off signals of the pressure switch from 
approximately 8500 per hour to 200 per hour during a typical driving 
schedule. Due to the reduction of on/off signals, the overall life span of 
the electrical pressure switch is improved and the switch function can be 
provided with a low cost component. 
It is therefore an object of this invention to provide an improved 
accumulator and relay valve in combination with a transmission control 
system, wherein an electrical switch is operatively connected with the 
valve which provides protection from pressure pulsations within a 
hydraulic control circuit. 
It is another object of this invention to provide an accumulator and relay 
valve in a fluid operated friction device apply circuit, wherein a 
pulse-width-modulated valve is operable to provide engagement pressure and 
a pressure operated electrical switch is operative to provide an 
indication of the presence of engagement pressure, and further wherein the 
electrical switch is effectively isolated from the apply pressure prior to 
a minimum pressure value being established, and also wherein the pressure 
pulsations generated at the pulse-width-modulated valve are greatly 
reduced prior to being introduced to the electrical switch. 
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 diagrammatic representation of a hydraulic control system including a 
pump 10 which draws fluid from a reservoir 12 for delivery to a 
conventional power transmission control system 14, which incorporates a 
plurality of control valves and elements 16, a pulse-width-modulated 
solenoid valve 18 and an accumulator and relay valve 20. 
The control 14 can, of course, incorporate a number of 
pulse-width-modulated solenoids and other accumulator and relay valves 
similar to valve 20. The solenoid valve 18 is selectively operable to 
provide an output pressure in a passage 24 which is delivered to a 
conventional fluid operated friction device 26 and an accumulator port 28 
incorporated in the valve 20. The fluid operated friction device 26 is a 
conventional multi-disc arrangement which has a conventional fluid 
operated piston, not shown, selectively pressurized by pressure in passage 
24 to control the engagement and disengagement of conventional disc 
members, not shown, to thereby control the establishment of the torque 
transmission path. The friction device 26 may be either a clutch or a 
brake. 
As is well known, the solenoid valve 18 is controlled electronically, 
generally by a conventional microprocessor, which can be incorporated into 
the control 14, to cause rapid opening and closing of a pressure port to 
alternately connect the passage 24 between a pressure passage and an 
exhaust passage. By controlling the duty cycle of the solenoid valve 18, 
the pressure within the passage 24 is controlled. As the "on" time of the 
solenoid increases as a percentage of the total duty cycle, the pressure 
in passage 24 increases. This type of pressure control function is well 
known. Due to the rapid opening and closing of the solenoid valve 18, 
pressure pulsations are introduced into the passage 24. These pulsations 
are often termed "noise". 
The friction device 26, as previously mentioned, incorporates a piston 
member which has associated therewith an apply chamber which is 
sufficiently large to dampen pulsations such that the piston does not 
respond to the pressure pulsations. It is desirable, generally for 
diagnostic purposes, to employ an electrical switch which is actuated when 
the friction device 26 is operated. With the present invention, a switch 
30 is provided. The switch 30 is a conventional fluid pressure operated 
electrical switch having a fluid connection or pressure passage 32 which 
is connected to a switch port 34 of the valve 20. 
The valve 20 includes a valve body 36 in which is formed a valve bore 38. A 
valve spool 40, having a pair of spaced valve lands 42 and 44, is slidably 
disposed in the valve bore 38. The valve land 42 cooperates with the valve 
bore 38 to form an accumulator chamber 46 which is in fluid communication 
with the accumulator port 28. 
The valve 20 also includes a spring 48 which is compressed between the 
valve land 44 and a washer spring 50 which in turn is maintained in the 
valve bore 38 by a spring seat 52 and a pin 54. The valve spool 40 has an 
extension 56 which extends from the valve land 44 toward the washer spring 
50. The extension 56 has a substantially circular end portion 58 which is 
aligned with and slightly larger than a circular opening or aperture 60 
formed in the washer spring 50. 
The spring seat 52 has a central opening or restriction 62 which is aligned 
with the aperture 60. The function of these components will be discussed 
later. The valve spool 40 has a longitudinal passage 64 and a restricted 
radial passage 66. The longitudinal passage 64 extends from one side of 
valve land 42 to a location between the valve lands 42 and 44 where it is 
intersected by the passage 66. 
In the "at rest" or spring set position shown, the valve land 44 is 
operable to close the switch port 34 to the space between the valve lands 
42 and 44 and to permit fluid communication between the switch port 34 and 
an exhaust port 68. The valve spool 40 is maintained in this position 
until the fluid pressure in passage 24, and therefore in accumulator 
chamber 46, is sufficient to overcome the force in the spring 48. When the 
pressure level in the accumulator chamber 46 reaches a predetermined 
value, the valve spool 40 will begin to move rightward, as seen in the 
drawings, against the spring 48. 
As the fluid pressure in the accumulator chamber 46 continues to increase, 
the valve spool 40 will continue to move until the position shown in FIG. 
2 is reached. At this location, it is seen that the valve land 44, which 
is slightly wider than the switch port 34, is covering the switch port 34. 
Due to the diametral clearance between the valve bore 38 and the valve 
land 44, controlled communication between the fluid admitted at the 
restricted passage 66, the switch port 34 and the exhaust port 68 is 
provided. This will permit a slow or controlled buildup of pressure at the 
switch port 34 and therefore in the pressure passage 32. 
As the fluid pressure in the accumulator chamber 46 continues to increase, 
the valve spool 40 will move to the position shown in FIG. 3. In this 
position, the switch 30 is subjected to the maximum pressure found in the 
accumulator chamber 46. However, due to the volume of the accumulator 
chamber 46 and the restricted passage 66, the noise introduced by the 
solenoid valve 18 is substantially isolated from the pressure switch. 
It should be noted at this point, that the spring 48 is designed to have 
characteristics which will prevent the valve spool 40 from reaching the 
position shown in FIG. 2, prior to the pressure level in the chamber 46 
being greater than the switch opening pressure required in passage 32 to 
actuate the switch 30. Thus, once the valve land 44 has established full 
communication between the fluid pressure at passage 66 and the switch port 
34, the pressure switch will open and will remain open because the 
pressure pulsations or noise will not be sufficient to permit the pressure 
level to decrease below the level required to activate the switch 30. 
In some control systems, the valve spool 40 may have substantial momentum 
as the end of the stroke, as represented by FIG. 3, is approached. The 
washer spring 50 is provided to absorb much of this momentum and to dampen 
any energy vibrations that may occur, as the end of the stroke is 
approached. The washer spring 50 will be abutted by the end portion 58 of 
extension 56 and will be deflected from the position in FIG. 2 to that 
shown in FIG. 3. 
Along with providing mechanical damping, some hydraulic damping can also be 
provided by the restriction 62. As the end portion 58 abuts the washer 
spring 50, it will close the opening 60 thereby preventing any fluid 
trapped between the washer spring 60 and spring seat 52 from flowing to 
the exhaust port 68. As the washer spring 50 is deflected, the fluid found 
therein will be forced to pass through the restriction 62 which is aided 
by the position of pin 54. This will provide some fluid damping along with 
the mechanical spring damping. When the friction device 26 is disengaged 
by the exhausting of pressure in the passage 24, the valve spool 40 will 
return to the position shown in FIG. 1 in preparation for the next apply 
signal of the friction device 26. 
It should be appreciated that the switch 30 will be actuated only once 
during the apply signal of the friction device 26. In prior art devices 
where the switch 30 is not isolated, a considerable number of switch 
signals occur during each application signal of the friction device due to 
the pressure oscillations. The present invention will therefore greatly 
increase the life span of the switch 30 and significantly reduce the cost 
required to produce the switch.