Control apparatus for regulating engagement of a fluid operated torque transmitting device

Abstract: An electronically mechanized control apparatus for regulating the engagement rate or stroke time of a fluid operated torque transmitting device (14), wherein the flow rate is controlled through a coordinated control of the supply pressure and an on-off fluid restriction device. At the initiation of a shift involving engagement of the rate controlled torque transmitting device, an appropriate stroke time is determined in terms of a suitable combination of line pressure and fluid restriction to be commanded for the duration of the shift. The on-off fluid restriction device (30) comprises a first orifice (80) which always remains in the servo supply circuit and second orifice (86) which is selectively connected in parallel with the first orifice via a solenoid operated shuttle valve (84).

Description: This invention relates to control apparatus for regulating the engagement of a fluid operated automotive torque transmitting device, and more particularly, to a coordinated electronic control of supply pressure and fluid restriction. In multi-speed ratio automatic transmissions of a motor vehicle, it is often desirable to effect shifting from one speed ratio to another without the use of free-wheeling or one-way devices. This requires a coordinated timing control of both off-going and on-coming, fluid operated, torque transmitting, devices (typically a band brake or friction clutch) in order to achieve a desired amount of overlap as the transmitted torque is shifted from the off-going device to the on-coming device. Typically, the fluid pressure to the off-going device is progressively released through an orifice while fluid pressure is supplied to the on-coming device through a pressure control device such as an accumulator or a servo. Where a control of the on-coming device engagement rate or stroke time is desired, the fluid flow at the inlet or outlet of the accumulator or servo may be separately regulated. In one known system involving a servo actuated friction band device, for example, a speed-biased regulator valve is used to vary a restriction for the fluid being displaced by the servo piston. In another similar system, an electro-hydraulic valve is pulse-width-modulated at a variable duty cycle to vary a restriction for the fluid supplied to the inlet of the servo. Unfortunately, these systems are relatively expensive to implement and often exhibit some level of supply pressure sensitivity, degrading the ability of the control to achieve the desired engagement rate or stroke time. From FR-A-2 485 650 a control apparatus for a motor vehicle transmission is known by means of which the supply of fluid to a servo chamber is controlled to operate a hydraulic torque converter. EP-A-0 149 013 discloses a control apparatus for a motor vehicle transmission in accordance with the preamble of claim 1 which is used for controlling the fluid supply to a servo chamber of a fluid operated torque transmission device. The control apparatus is provided with a fluid restriction means having a first alternate fluid circuit and having a second alternate fluid circuit connected in parallel with the first fluid circuit. It is an object of the present invention to provide a control apparatus for a motor vehicle by the use of which an improved regulation of the engagement rate and stroke time of the fluid operated torque transmitting device is possible. This object is solved by a control apparatus in accordance with the features of claim 1. The present invention is directed to an improved electronic control apparatus for regulating the engagement rate or stroke time of a fluid operated torque transmitting device, wherein the flow rate is controlled through a coordinated control of the supply pressure and an on-off fluid restriction device. The control is most favourably mechanized in a transmission already incorporating an electronic control of the supply or line pressure. At the initiation of a shift involving engagement of the rate controlled torque transmitting device, an appropriate stroke time is determined and a suitable combination of line pressure and fluid restriction are commanded for the duration of the shift. In a preferred embodiment, the on-off fluid restriction device comprises a first orifice which always remains in the servo supply circuit and a second orifice which is selectively connected in parallel with the first orifice via a solenoid operated shuttle valve. The desired state of the shuttle valve is determined at the initiation of the shift, and that state is retained throughout the shift. The state of the on-off fluid restriction device essentially selects one of two servo flow rate ranges, each such range being limited by the minimum and maximum permissible values of the transmission supply or line pressure. The control unit merely initializes the restriction device to establish a flow range which can satisfy the desired stroke time of the servo, and then commands a line pressure which, when applied to the fluid restriction device, will precisely achieve the desired stroke time. The digital or on-off nature of the fluid restriction device avoids the expense of precision regulator or PWM valves, and the supply or line pressure sensitivity is drastically reduced because the line pressure is an integral part of the control. In the illustrated embodiment, the control apparatus of this invention is mechanized in connection with a wash-out type shift control arrangement substantially as set forth in US Patent No. 2,865,227. In that arrangement, the servo for an off-going band brake operates as an upshift accumulator for an on-coming friction clutch. The fluid restriction device and line pressure control of this invention operate when a subsequent clutch-to-band downshift is required by controlling the stroke time of the servo for the on-coming band brake. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 depicts a control apparatus according to this invention, sectional views of various hydraulic transmission control elements and a (computer-based) control unit for carrying out line pressure and shift controls; Figure 2 graphically depicts the ranges of servo stroke time which can be achieved by each state of the on-off fluid restriction device; Figure 3 graphically depicts the control method of this invention; and Figures 4 and 5 depict flow diagrams representative of computer program instructions executed by the (computer-based) control unit of Figure 1 in carrying out the control of this invention. Referring particularly to Figure 1, the reference numeral 10 generally designates an array of hydraulic transmission control elements for regulating the engagement and disengagement of friction clutch 12 and band brake 14 to effect shifting between a pair of forward transmission speed ratios. In a typical application, a 1:1 or direct ratio (3rd) is provided with engagement of the friction clutch 12, and an underdrive ratio (2nd) is provided with engagement of the band brake 14. Thus, a 2-3 upshift is achieved through concurrent disengagement of band brake 14 and engagement friction clutch 12, while a 3-2 downshift is achieved through concurrent disengagement of friction clutch 12 and engagement band brake 14. As explained below, this invention concerns the engagement of band brake 14 to effect a 3-2 downshift. The illustrated hydraulic transmission control elements include a (positive displacement mechanically driven) hydraulic pump 16 which acts as a source of fluid pressure, a pressure regulator valve or means 18, a (force motor controlled) line pressure bias valve 20 and limit valve 22, an (operator manipulated) manual valve 24, a (solenoid controlled) 2-3 shift valve 26, a clutch apply servo 28, a fluid restriction circuit or means 30, and a band apply servo 32. The hydraulic pump 16 receives hydraulic fluid at low pressure from a fluid reservoir 40, and supplies line pressure fluid to the hydraulic transmission control elements via output line 42. Pressure regulator valve 18 is connected to the output line 42 and serves to regulate the line pressure and torque converter feed pressure (CF) by returning a controlled portion of the line pressure to fluid reservoir 40 via line 44. The pressure regulator valve 18 is biased at one end by orificed line pressure in line 46 and at the other end by the combination of a spring 48 and a controlled bias pressure in line 50. The controlled bias pressure is supplied by the line pressure bias valve 20 which develops pressure in relation to the current supplied to electric force motor 52, the electric force motor 52 being hydraulically balanced by the pressure in bias chamber 54. Line pressure is supplied as an input to line pressure bias valve 20 via line 55 and the limit valve 22. An accumulator 56 connected to the (bias pressure) line 50 serves to stabilize the bias pressure. With the above-described valving arrangement, it will be seen that the line pressure of the transmission is electrically regulated by electric force motor 52. In the event of an interruption of electrical power to the electric force motor 52, the bias pressure in line 50 assumes a maximum value, thereby forcing maximum line pressure. The friction clutch 12 and band brake 14 are activated by clutch and band apply servos 28 and 32, respectively, which are conventional fluid servos. The apply servos 28 and 32, in turn, are connected to a fluid supply system comprising the Manual Valve 24, the 2-3 shift valve 26, and the fluid restriction circuit 30. The Manual Valve 24 develops a supply pressure D32 for the 2nd and 3rd forward speed ranges of the transmission in response to driver positioning of a transmission range selector lever 60. The D32 supply pressure, in turn, is supplied via line 62 to the 2-3 shift valve 26 and fluid restriction circuit 30 for application to the apply servos 28 and 32. The 2-3 shift valve 26 is spring-biased against a controlled bias pressure developed by a solenoid 64, the 2-3 shift valve 26 being illustrated in its activated state. In the illustrated state, the 2-3 shift valve 26 supplies D32 supply pressure to the clutch apply servo 28 via line 66 and to a release chamber 68 of band apply servo 32 via line 70. In the deactivated state, the lines 66 and 70 are exhausted via exhaust port 72. The fluid restriction circuit 30 comprises a first orifice 80 connecting the D32 supply pressure line 62 to an apply or servo chamber 82 of band apply servo 32, and a (solenoid operated) shuttle valve 84 (electromagnetic means) which is selectively activated to connect a second orifice in parallel with the first orifice 80, the second orifice being defined by the valve seat 86. The first and second orifices define variable flow orifice means. The shuttle valve 84 includes a pintle armature 88 spring-biased into engagement with the valve seat 86, and a solenoid 90 which when electrically activated lifts the pintle armature 88 off the valve seat 86 to connect the seat orifice in parallel with the first orifice 80. Thus, supply pressure fluid is supplied to the apply chamber 82 via first orifice 80 alone when solenoid 90 is deactivated, and via the parallel combination of first orifice 80 and valve seat 86 when solenoid 90 is activated. The band apply servo 32 includes a post 92 fastened to a diaphragm 94 which is axially displaceable within the servo housing. A pair of springs 96 and 98 reacting against the housing of band apply servo 32 urge the diaphragm 94 and hence the post 92 downward, as viewed in Figure 1, to release the band brake 14. The spring forces may be aided by fluid pressure in release chamber 68 or opposed by fluid pressure in apply chamber 82. Reference numeral 100 designates a (computer-based) control unit (control means) which develops suitable electrical control signals for the electric force motor 52 and the solenoids 64 and 90 in response to a variety of vehicle and powertrain parameters, represented by the input lines 102. The line pressure control of electric force motor 52 is essentially continuous during operation of the transmission, ensuring that the developed pressure is sufficient to prevent clutch slippage during steady state operation, and providing shift quality control during shifting. The control of solenoids 64 and 90, on the other hand, pertain strictly to shifting and are discrete or on-off in nature. In 2nd ratio operation, the (shift valve) solenoid 64 is deactivated so that the clutch apply servo 28 and the release chamber 68 are vented through exhaust port 72. The apply chamber 82 is maintained at D32 supply pressure via fluid restriction circuit 30, overcoming the spring bias to extend the post 92 and engage the band brake 14. When a 2-3 upshift is required, the control unit 100 activates the (shift valve) solenoid 64 to connect the D32 supply pressure to clutch apply servo 28 and the release chamber 68 of band apply servo 32 via orifice 29. This pressure balances the apply chamber pressure, allowing the springs 96 and 98 to stroke the diaphragm 94, retracting the post 92 as the apply chamber fluid is displaced through the fluid restriction circuit 30 and into the (pressure control) line 62. The pressure in the clutch apply servo 28 builds as a function of the spring rates and orifices, engaging the friction clutch 12 as the band brake 14 is released. This is a conventional band-to-clutch wash-out upshift. When a 3-2 downshift is required, the control unit 100 determines the required state of the (shuttle valve) solenoid 90, commands the appropriate line pressure signal to electric force motor 52, and deactivates the (shift valve) solenoid 64 to vent the fluid in clutch apply servo 28 and release chamber 68. The line pressure and shuttle valve commands are based on factors described below in reference to Figure 3. The combination of the line (D32) pressure and the effective orifice size of fluid restriction circuit 30 determines the fluid flow rate into apply chamber 82, which in turn, determines the stroke time of the post 92. Once the shift is complete, there is no flow through the fluid restriction circuit 30, and the state of the solenoid 90 is immaterial. Under such conditions, the solenoid 90 may be deactivated to reduce power consumption and heat dissipation. The graph of Figure 2 illustrates the relationship between the stroke time of band apply servo 32 and the transmission line pressure, with and without activation of the (shuttle valve) solenoid 90. When the (shuttle valve) solenoid 90 is deactivated and the supply pressure can only pass through first orifice 80, the relationship is given by the "1 ORIFICE" trace 110. As one would expect, increasing line pressure increases the fluid flow, thereby decreasing the stroke time; similarly, decreasing line pressure decreases the fluid flow, thereby increasing the stroke time. When the (shuttle valve) solenoid 90 is activated and the supply pressure can pass through the valve seat 86 as well as the first orifice 80, the relationship is given by the "2 ORIFICE" trace 112. The parallel combination of first orifice 80 and valve seat 86 permits increased flow, resulting in reduced stroke time for a given line pressure. There are, of course, limitations on how low and high the line pressure may be adjusted without adversely affecting other transmission controls. For example, the line pressure should not be reduced to a value which would permit unwanted slippage of another friction element, as this would likely degrade the shift quality. In view of the above, it is unlikely that the desired range of stroke times could be achieved by line pressure control alone. However, the use of the shuttle valve 84 in combination with a limited line pressure control produces a desired range of stroke times. Such a control is graphically depicted in Figure 3, where Graph C depicts the desired stroke time as a function of vehicle speed Nv, and Graphs A and B respectively depict the appropriate fluid restriction and line pressure controls. Essentially, the two states of shuttle valve 84 divide the range of desired stroke time into a lower, two orifice range (I), in which the solenoid 90 is activated, and an upper, one orifice range (II), in which the solenoid 90 is deactivated. Since the stroke time is determined as a function of vehicle speed Nv, the control unit 100 may also determine the shuttle valve solenoid state as a function of vehicle speed. For vehicle speeds less than or equal to a reference speed Nref, the solenoid 90 is activated; for vehicle speeds greater than the reference speed, the solenoid 90 is deactivated. The required line pressure may similarly be determined as a function of vehicle speed, employing a look-up table storing the information represented in Graph B. Flow diagrams, representative of computer program instructions for carrying out the control of this invention with the control apparatus depicted in Figure 1, are depicted in Figures 4 and 5. The flow diagram of Figure 4 represents a main or executive computer program which is periodically executed in the course of vehicle operation in carrying out the control of this invention. Block 230 designates a series of program instructions executed at the initiation of each period of vehicle operation for setting various terms and timer values to an initial condition. Thereafter, blocks 232-234 are executed to read the various inputs referenced in Figure 1 and to determine a desired speed ratio Rdes. The desired ratio Rdes may be determined in a conventional manner as a predefined function of engine throttle position and vehicle speed Nv. If the actual ratio Ract -- that is, Ni/No -- is equal to the desired ratio Rdes, as determined at block 238, block 244 is executed to determine the desired line pressure LPdes. In this case, the desired line pressure LPdes is determined as a function of throttle position %T and output speed No, and also is adjusted based on the desired ratio Rdes and an adaptive correction term Pad. The adaptive correction term Pad may be generated during upshifting, based on shift time, as set forth in US Patent No. 4,283,970, and incorporated herein by reference. If an upshift is required, as determined by blocks 238 and 240, blocks 242 and 244 are executed to perform suitable Upshift Logic in addition to determining the desired line pressure LPdes as described above. If a downshift is required, as determined by blocks 238 and 240, blocks 246 and 248 are executed to determine the desired line pressure LPdes and to perform the Downshift Logic. Normally, the desired line pressure is determined as a function of throttle position, output speed, the pre-shift or old ratio Rold, and the adaptive correction term Pad, as indicated at block 246, but is modified by the Downshift Logic block 248 if the shift is a 3-2 downshift. As indicated at block 248, the Downshift Logic is set forth in further detail in the flow diagram of Figure 5. In any case, block 250 is then executed to convert the desired line pressure LPdes to a solenoid duty cycle LP(DC), to output the duty cycle LP(DC) to electric force motor 52, and to output discrete solenoid states to the solenoids 64 and 90, after which the program returns to block 232 as indicated by flow diagram line 236. Referring now to the Downshift Logic flow diagram of Figure 5, block 252 is first executed to determine the required states of the various shift valve solenoids. As indicated above, the present invention concerns the (2-3 shift valve) solenoid 64, which is activated to initiate a 2-3 upshift and deactivated to initiate a 3-2 downshift. If the shift is a 3-2 downshift, as detected at block 254, blocks 256 and 258 are executed to determine the required state of (shuttle valve) solenoid 90 and the desired line pressure LPdes, both as a function of the vehicle speed Nv as described above in reference to Figure 3. Regarding the shuttle valve 84, the activated state of solenoid 90 is selected if the vehicle speed Nv is less than or equal to the reference speed Nref, while the deactivated state is selected if the vehicle speed is greater than Nref. The desired line pressure, on the other hand, is determined from a look-up table representing the data depicted in Graph B of Figure 3. As explained above, the combination of the selected shuttle valve state and the desired line pressure cooperate to produce the desired stroke time of the band apply servo 32. While illustrated in reference to a wash-out shift arrangement, it will be appreciated that the engagement rate control of the present invention will find application in the engagement of any torque transmitting device having a member which is displaced by a servo in relation to the volume of fluid directed to an apply chamber thereof. It is expected that various other modifications to the illustrated embodiment will occur to those skilled in the art as well. For example, the fluid restriction circuit 30 could be constructed to select a single high flow orifice when relatively low stroke times are required instead of the parallel combination of two low flow orifices. Moreover, some applications requiring a relatively wide range of stroke times may necessitate the use of a third selectively activated orifice in the orifice network.

Claims: A control apparatus for a motor vehicle transmission for controlling the supply of fluid to a servo chamber (82) of predetermined volume which is filled to engage a fluid operated torque transmitting device (14), the control apparatus comprising: a source (16) of fluid pressure; pressure regulating means (18) adapted to regulate the pressure of the source of fluid pressure over a predetermined pressure range in accordance with a pressure command, fluid restriction means (30) including at least two alternate fluid circuits (80,86), wherein a first alternate circuit is defined by a first orifice (80), and a second alternate fluid circuit is defined by the first orifice and a second orifice (86) connected in parallel with the first orifice; the first orifice being fed directly from the source (16) during engagement of the torque transmission device, characterized by selecting means (256, 258) for determining a fluid circuit and a fluid supply pressure within the predetermined pressure range which will achieve a desired engagement time of the fluid operated torque transmitting device; fluid restriction means including an electromagnetic means (84) for connecting the selected fluid circuit between the source of fluid pressure and the servo chamber; and control means (100) effective when it is desired to engage the fluid operated torque transmitting device to issue for the duration of the shift the selected combination of pressure and restriction commands. A control apparatus as claimed in Claim 1, wherein the desired engagement time varies as a function of a certain vehicle parameter, and the selecting means selects the fluid circuit and the fluid supply pressure in accordance with a measure of the certain parameter. A control apparatus as claimed in Claim 2, wherein the certain vehicle parameter is measured in relation to an output speed of the transmission. A control apparatus as claimed in claim 1, wherein the first and second orifice include variable flow orifice means (80,86) connecting the source of fluid pressure to the servo chamber, wherein the electromagnetic means (84) are adapted to adjust the flow of the variable flow orifice means in accordance with the restriction command; and wherein the control means (100) are adapted to issue the combination of pressure and restriction commands for filling the predetermined volume in the desired time, thereby to control an engagement rate of the fluid operated torque transmitting device. A control apparatus as claimed in Claim 4, wherein the first orifice (80) is connecting the source (16) of fluid pressure to the servo chamber (82) and the second orifice (86) is selectively connectible in parallel with the first orifice by the electromagnetic means (84). A control apparatus as claimed in Claim 4 or Claim 5, wherein the control means (100) is effective in nonshifting modes of operation for developing the pressure command for the pressure regulating means (18) in accordance with specified operating parameters, and is effective in shifting modes of operation where it is desired to engage the fluid operated torque transmitting device (14) for developing the combination of pressure and restriction commands.

Inventors: KOENIG MELISSA MEI, VUKOVICH WILLIAM JOSEPH, KOENIG, MELISSA MEI, VUKOVICH, WILLIAM JOSEPH
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1992
Main classification: F16H61
IPC codes: F16H61