Multiple ratio automatic transmission and torque converter with bypass clutch

Abstract: A control system for engaging and releasing a torque converter bypass clutch and for varying the torque capacity of the clutch by adjusting the torque converter torus chamber pressure in accordance with changing operating variables, the bypass clutch including a clutch release pressure chamber that is maintained at a calibrated pressure threshold valve whereby pressure clutch capacity control is achieved by controlling pressure differential in the converter.

Description: The invention relates to multiple ratio torque converter transmissions for automotive vehicles and to electronic-hydraulic controls for effecting engagement and release of a converter clutch. Multiple ratio planetary transmissions situated in an automotive vehicle driveline typically include a hydrokinetic torque converter situated between torque input planetary gearing of the transmission and a throttle-controlled internal combustion engine. The gearing comprises two simple planetary gear units arranged in a manner similar to the gearing arrangement of the well known Simpson gear set. Located between the turbine of the torque converter and the input elements of the Simpson gearing is a third simple planetary gear unit with a friction clutch adapted to connect two elements of the third gear unit together for rotation in unison. A friction brake also is used for anchoring a reaction element of the planetary gear unit. An overrunning coupling establishes one-way torque flow between two elements of the gearing. The brake is arranged in series relationship with respect to the clutch. A second overrunning coupling in a gear unit of the Simpson gearing is used for the purpose of establishing a non-synchronous ratio shift. Forward engagement is achieved by engaging a forward clutch on a shift from neutral to the drive state. Similarly, a separate reverse engagement clutch is used to establish a torque flow path for reverse. In each instance, turbine speed is used as a feedback signal to initiate the start of the forward or reverse engagement. Ratio changes between the first ratio and the second ratio on an upshift, as well as a downshift from the second ratio to the first ratio, are achieved in our improved transmission by controlling the engagement of an overrunning clutch. The overrunning clutch is arranged in series relationship with respect to a friction brake as a reaction torque flow path for the friction brake associated with the intermediate ratio is established and disestablished. The braking of the friction brake is accomplished with a closed loop control so that harshness is avoided as the overrunning elements of the reaction torque flow path engage. This is in contrast to prior art arrangements, such as that shown in U.S. Patent No. 5,157,608, where a non-synchronous shift using overrunning couplings is achieved without the cushioning effect made available by the present invention as the associated friction brake is actuated. This invention includes a controller for a torque converter clutch assembly that has a single converter feed passage and a single converter flow return passage. Such converter clutch assemblies are distinguishable from converter clutch assemblies of the kind shown, for example, in U.S. Patent No. 5,305,663 where a converter bypass clutch feed passage acts in co-operation with two other feed passages, one acting as a flow return and the other acting as a flow delivery to the torus circuit of the converter. In the case of the converter shown in the `663 patent, continuous flow is achieved through the converter regardless of whether the clutch is engaged or released. Portions of the clutch control strategy of the present invention are common to the teachings of U.S. Patent No. 5,029,087, issued to Ronald T. Cowan, Roger L. Huffmaster and Pramod K. Jain. As in the case of the converter control of the '087 patent, our present invention includes a controller for continuously monitoring the actual converter slip and comparing that actual value to a desired value. Any error that is detected by the controller will result in calculation of a new target slip. During the engagement time of the converter clutch, the error will continuously change and the magnitude of that error will be monitored continuously. In each instance, a new target slip is calculated. This process continues until the actual slip approaches the target value. This strategy has been adapted to the so-called two pass converter system described above. In the prior art teachings discussed here, the converter is a three pass system that accommodates continuous flow through the converter regardless of the behaviour of the clutch. Notwithstanding the fact that the converter of our present invention has only two flow paths, one toward the converter and the other from the converter, the converter oil flow is capable of maintaining sufficient heat dissipation because of an improved converter flow arrangement in the converter circuit with a converter clutch modulator valve that provides the converter oil flow. The converter oil flow is divided into two components, one part of which is directed to a thermostat bypass valve into a lubrication system as the other flow component enters the transmission oil cooler. The controller for the converter uses features that are common to the electronically controlled bypass clutch strategy of U.S. Patent No. 5,303,616 where the percentage of shift completion is used as an input parameter for controlling the engagement of a bypass clutch for a converter, particularly, during ratio changes. The converter control valve system with which the control strategy is used is capable of accurately adjusting the pressure differential across a converter clutch piston in the converter torus cavity. This involves the use of a single converter pressure modulator solenoid valve or a pressure modulator solenoid valve plus a pressure modulator valve, which directly controls the torus cavity pressure. In contrast, two pressure modulators plus a pressure modulator solenoid valve are required in prior art designs in which the release side of the converter clutch piston is controlled as well as the torus cavity pressure. This feature simplifies the converter control valve system of the present invention. The valve system embodying the present invention also uses a simplified accumulator valve to create a controlled back pressure on the release side of the converter clutch piston thereby simplifying the control of pressure differential across the converter clutch piston as converter clutch torque capacity is regulated. The converter clutch control makes it feasible to operate the converter clutch in each ratio using closed loop feedback control. Inertia torque changes during shifts are moderated in this way, thereby reducing shift harshness. The ability to apply the converter clutch in all gear ratios contributes to improved fuel economy. EP-A-0 707 165 describes a control system according to the preamble of claim 1 for engaging and releasing a torque converter bypass clutch and for varying the torque capacity of the clutch by adjusting the torque converter torus chamber pressure in accordance with changing operating variables. The bypass clutch includes a clutch release pressure chamber that is maintained at a calibrated pressure by a threshold valve whereby pressure clutch capacity control is achieved by controlling pressure differential in the converter. The present invention provides an alternative to the control system described in EP-A-0 707 165 and reference should be made thereto for background information relating to the implementation of the present invention. The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a geared planetary transmission adapted to be controlled by an improved control system embodying the present invention; Figure 2 is a schematic representation of the gearing elements of Figure 1; Figure 3 is a schematic representation of the overall signal flow path for the electronic controller as the transmission control strategy executes control algorithms based on input information from the driver and from the engine itself; Figure 4 is a chart that shows the clutch and brake engagement-and-release pattern for the clutches and brakes illustrated schematically in Figure 2 as the transmission changes ratio; Figures 5a and 5b, taken together, show a circuit diagram for the invention; Figure 6 is an enlarged view of the converter control valve assembly that is shown in the circuit diagram of Figure 5a; Figure 7 is an enlarged view of the thermostatic bypass valve and cooler limit valve which are indicated in the circuit diagram of Figure 5a; Figure 8 is a plot of the thermostatic valve transfer function for the valve assembly of Figure 7; Figure 9 is an enlarged view of the converter clutch accumulator valve which is part of the control valve circuit of Figure 5b; Figure 10 is an enlarged view of the converter pressure modulator valve which is part of the circuit diagram of Figure 5b; Figure 10a and 10b are enlarged views of the differential diameter lands of the valve spool of the valve system of Figure 10; and Figure 11 is a plot of the converter pressure modulator valve system characteristics showing the relationship between pulse-width modulated pressure developed by valve 332 and both duty cycle and converter clutch modulator pressure. Transmission Hardware Overview: Transmission Torque Flow The transmission gearing contains an overdrive planetary gear set connected in series with a Simpson set. Figure 1 shows the various clutches and bands with conventional abbreviations. Figure 2 shows, in schematic form, the torque flow paths for the transmission. Torque Flow 1 st Gear In DRIVE The engine torque is transmitted to the housing of the torque converter pump or impeller 22. The converter impeller is a centrifugal pump which accelerates the fluid inside the torque converter towards the blades of turbine 24. The accelerated oil is then decelerated over the turbine blades. The oil at the turbine exit is redirected over the converter reactor back into the impeller, thereby achieving a torque multiplication effect. From the input shaft 26, the torque is transmitted to overrunning coupling OWC1, which effects a torque reaction in the rotational direction of the engine. The coupling OWC1 overruns in the opposite direction. The engaged clutch CL3 carries torque from the centre shaft to the first of two simple planetary gear units of a Simpson gear set. The torque is delivered to the ring gear 30 and then is split into two components. One part is delivered over the planetary carrier 32 to the output shaft 34, which turns in the same rotational direction as the ring gear 30. The sun gear 36 carries the remaining part of the torque in the opposite direction to the rear gear set of the Simpson planetary gear set. The planetary carrier 38 of the rear planetary gear set is held by overrunning coupling OWC2. The torque delivered to the sun gear 42 is then transmitted over the planetaries to the ring gear 40, which reduces the velocity and multiplies the torque to the output shaft. This arrangement provides a 2.474 gear ratio. In coast mode, OWC1 and OWC2 overrun and free wheeling is in effect. The converter clutch 44 stays open until no torque multiplication occurs. It then can be locked. Torque Flow: 2 nd Gear In DRIVE The torque flow is the same as in 1 st gear except that B2 is applied. With the engagement of B2, the sun gear speed is reduced to zero. The brake band (B2) then serves as a reaction element for the front planetary gear set and generates an output torque multiplication of 1.474 by holding 0.474 times engine torque as a reaction to the output. The output of the rear planetary gearset is zero since the sun gear 42 has zero speed (see Figure 2). The converter clutch 44 can be locked or unlocked in 2 nd gear depending on the driving condition. Torque Flow 3 rd Gear In DRIVE, Overdrive Cancel Switch = OFF In 3 rd gear, B2 is released and CL2 is applied. The transition from 2 nd to 3 rd gear must be synchronised since no reaction element is available to hold the CL2 drum when B2 is released. The converter clutch can be locked or unlocked depending on the driving condition. The torque input to CL2 and CL3 is split depending on the gear ratio. CL2 carries 0.321 times engine torque and CL3 carries 0.679 times engine torque. The torque flow to CL2 is the same as in 1 st or 2 nd gear. With the overdrive cancel switch turned off, the coast clutch (CL1) is disengaged - i.e., electronically released - and free wheeling takes place since OWC1 overruns in coast mode (see Figure 2). This is the direct gear with a gear ratio of one. Since the gear change from 2 nd to 3 rd and from 3 rd to 2 nd has to be synchronised, more complex control functions are implemented for these gear changes. Torque Flow 3 rd Gear in DRIVE, Overdrive Cancel Switch = ON When the overdrive cancel (ODC) switch is ON, CL1 is hydraulically applied and engine braking takes place in coast mode. CL1 is electronically controlled and hydraulically actuated along with B1 (see Figure 2). Torque Flow 4 th Gear In DRIVE In 4 th gear, B1 is applied and carries -.25 times engine torque as a reaction to the output. B1 decelerates the sun gear of the overdrive planetary gear set to zero speed and generates a gear ratio of .75. Engagement of CL1 is hydraulically inhibited and OWC1 overruns. Since B1 carries 0.25 times engine torque and since the overdrive planetary gear set is an input to the Simpson set, CL2 and CL3 are holding the 0.75 th fraction of engine torque. The gear ratio is 0.75. The converter clutch can be locked or unlocked based on the driving condition (see Figure 2.) Torque Flow 1 st Gear In MANUAL Position In MANUAL1, the torque flow is the same as in 1 st gear in drive position except B3 and CL1 are applied to generate engine braking in coast mode. The converter clutch is hydraulically inhibited and cannot be applied electronically. B3 prevents overrunning of OWC2, and CL1 prevents overrunning of OWC1. The gear ratio is 2.474 (see Figure 2). Torque Flow: 2 nd Gear In MANUAL2 Position In MANUAL2, the torque flow is the same as in 2 nd gear in drive position except CL1 is applied to achieve engine braking in coast mode. CL1 prevents overrunning of OWC1 in power OFF condition. Converter Clutch Control System The converter clutch control system has a dedicated hydraulic control system as well as a unique control strategy. The converter clutch is electronically controlled and can be engaged in each gear. Usually, the converter clutch will be locked starting in second gear, and it stays locked. By monitoring engine speed `N' and the turbine speed "NT", the state of the converter clutch or the amount of slip is determined. In order to be able to lock the converter clutch in each gear, the converter clutch must be modulated during a shift. It is then necessary to partially open the torque converter clutch during upshifts and downshifts in order to take advantage of the damping effect of the torque converter during a shift. The control system is able to adjust for the desired amount of differential speed during an upshift event or a downshift event. This requires a control system which is capable of adjusting capacity of the converter clutch. Converter clutch control systems for some known transmissions are partially electronically controlled (ON/OFF-solenoid) and are only capable of controlling the converter clutch in either "ON" or "OFF" states. This restricts the converter clutch operation only to operation in fourth or third gear. The converter clutch control system of the present invention can be operated as a simple ON/OFF system since the clutch capacity can be varied from 0% to 100%. It can also be operated, however, as a "full" modulated clutch with continuous slip under all operating conditions. The converter clutch can be controlled as a PWM-solenoid controlled converter clutch with a converter pressure modulator valve disposed between the PWM-solenoid and the converter clutch control valve as seen in Figures 5a-5b. The converter clutch control strategy will be described for each configuration. A brief description of the strategy has been set forth previously. The cooling system with a thermostat bypass valve system also will be described. Following hardware components are part of the converter clutch control system of hardware configurations 1 and 2, as well as the cooling and thermostat bypass valve control system: Pressure Build-up: main regulator valve 104 in bore 208 solenoid 1 pressure regulator 158 in bore 201 VFS variable force solenoid 18 in bore 203 PWM solenoid 20 in bore 200 converter limit valve 94 (blow-off valve) Shift Valve Configuration: converter clutch control valve 98 in bore 200 shift solenoid (SS4) 16 in bore 201 thermostat bypass valve 93 in bore 216 cooler limit valve 92 in bore 216 converter clutch accumulator valve 86 in bore 216. The following are the control parameters for the complete control system of hardware configurations 1 and 2, including the control strategy: Control Strategy: NE = engine speed NT = turbine speed SLIP_ACT = actual slip = (NE-NT) ERR_TO = difference between actual slip and desired slip. SLIP_ERR_PID = total PID slip error SLIP_DES = desired slip for converter clutch SLIP_TCAP = total slip desired K_CONV = torque converter coefficient TCAP_CON = torque being carried by the torque converter TQ_IALPHA = torque value to hold inertia torque TQ_BAR = engine torque TCAP_REQ = requested torque capacity BCSDC = percentage of duty cycle GR_DS = desired gear GR_CM = commanded gear FLG_SS_4 = shift solenoid flag 4 PCSFTCMPT = percentage shift complete SLIP_TARGET = target slip value Pressures: CDC/MOD = converter discharge/modulation pressure CC/PACC = converter charge/accumulator pressure SS4 = shift solenoid 4 pressure SOL1 = shift solenoid 1 pressure. PWM Solenoid-Controlled Converter Clutch With a Converter Pressure Modulator Valve Disposed Between the PWM Solenoid and the Converter Clutch Control Valve In Figures 5a and 5b, we show an alternate torque converter clutch control system to that described in EP-A-0 707 165 that includes a converter clutch control valve 320, an additional converter pressure modulator valve system 322, a modified converter clutch accumulator valve 324, and a solenoid regulator valve 326. Figure 6 shows the converter control valve 320 and the cooler limit valve at 330 in enlarged form. Figure 7 shows a detailed view of the cooler limit valve. The converter clutch accumulator valve 324 is shown in enlarged form in Figure 9. The converter pressure modulator valve system 322 is shown in enlarged form in Figure 10. A pulse-width modulated solenoid valve 332 receives a PWM signal from the microcomputer controller 334 through signal lines 336. The pulse-width modulated valve 332 modulates SOL1 pressure in passage 338 and distributes a modulated pressure output through passage 340 to the converter pressure modulator valve 322. Line pressure in passage 342 is distributed to the converter pressure modulator valve system 322 from the manual valve 344. Passage 342 is pressurised when the manual valve is in the D, 3, 2 or 1 positions. As indicated in Figure 10, the valve system 322 comprises a valve spool having differential diameter lands and larger landing shown at 344 and the larger landing shown at 346. Valve spring 348 urges the valve spool in a downward direction. The upper end of the valve chamber in which the valve spool is disposed is exhausted, as shown at 350. The modulated pressure output of the valve system 322 is distributed to passage 352, which extends to the converter control valve 320. The modulated pressure in passage 352 acts on the differential area of lands 344 and 346 to complement the force of the spring 348. Pulse-width modulated pressure in passage 340 is distributed to a pilot valve 354, this valve is a single diameter valve, and acts on the lower end of the valve spool of the converter pressure modulator valve. The diameter of the pilot valve is less than the diameter of either land 344 or land 346. Exhaust port 356 is located directly adjacent land 346 and the output pressure port is located directly adjacent land 344. The converter control valve 320 comprises a valve spool 358 which has three lands 360, 362 and 364. Valve spool 358 is urged in a downward direction, as viewed in Figure 6, by valve spring 366. When it is in the position shown in Figure 6, valve spool 358 is seated on a valve plug 368 which is held in place by a wire retainer 370. Modulated pressure in passage 352 acts on the lower end of the valve spool to produce a force that oppose the force of the spring 366. Converter charge pressure in passage 372 communicates with converter clutch pressure passage 374 through the space between valve lands 360 and 362, thereby pressurising the converter clutch release side. Passage 376 communicates with the apply side of the converter clutch. It is pressurised by converter charge pressure from the release side of the converter clutch when the converter control valve 320 is in the downward position. The line pressure developed by pump 380 communicates with the main regulator valve through passage 382. Regulated output pressure is distributed to passage 372. Cooler flow in passage 384 is established as communication takes place between passage 372 and passage 376, depending on whether the converter clutch control valve 320 is in the upward or downward position. Modulated converter clutch pressure is established as passage 352 communicates with the converter clutch control valve 320, thus moving the control valve to its upward position. This connects the output passage 352 of the converter clutch apply side 376 and establishes converter clutch capacity. The output pressure of the converter clutch accumulator valve is distributed through passage 386, which communicates with the clutch release pressure in passage 374 through the space between lands 366 and 362. The pressure on the release side of the converter clutch is maintained at a constant value by the converter clutch accumulator valve 324 when the converter clutch is engaged. The input to the converter clutch accumulator valve is the converter charge pressure in passage 372. The feedback pressure path 388, together with the valve spring force of spring 390 and exhaust port 392, establishes a constant pressure in passage 386. The converter clutch control valve spool is urged in a downward direction during reverse drive operation and during operation in manual low as selected by the manual valve. Thermostatic valve 328, includes an internal spring, shown at 394. The thermostatic valve transfer function for Figure 7 is plotted in Figure 8. The converter clutch accumulator valve is a pressure limiting valve with a feedback control. It is capable of maintaining a constant back pressure on the release side of the converter clutch regardless of a variable flow input. The ability to provide a constant back pressure with variable flow input enhances the converter clutch operation by achieving a constant back pressure on the clutch release side. The converter pressure modulator valve system is capable of accommodating high leakage oil flow, including leakage flow, out of the converter clutch apply side when the transmission oil temperatures are elevated. It is capable of maintaining the necessary apply pressure on the converter clutch apply side when the converter is commanded to be unlocked. The single diameter valve element 354 of the converter pressure modulator valve assembly makes it possible to calibrate the valve system for various engine applications without changing major hardware components (i.e., valve body machining) since it introduces a separate valve area that can be changed as desired for calibration purposes. The valve 354 thus acts as a pilot valve for the modulator valve. Figure 11 shows the converter clutch modulated pressure transfer function in a plot of PWM pressure against converter clutch modulated pressure. The converter clutch modulator pressure transfer function acts an amplifier for the PWM pressure developed by the PWM solenoid valve 332. The left-hand side of the plot of Figure 11 shows the PWM pressure transfer function with respect to the duty cycle of the PWM solenoid valve 332. It is plotted with two different input pressures; i.e., six bar maximum and four bar minimum. The relationship of PWM pressure versus converter clutch modulator pressure is shown in the transfer function plotted in Figure 11. The slopes of the pressures plotted in Figure 11 can be changed by changing a pilot valve diameter and by changing the spring load to adapt the system for various engine applications. The control strategy known as a torque feedforward system, which is illustrated in Figure 5d of previously referenced EP-A-0 707 165, can be calibrated to accommodate the modification illustrated in the present Figure 5. The structure of the state model control block called "inverse valve model" can be adjusted in accordance with the slopes of the plots shown in Figure 11. The control block in Figure 5d of previously referenced EP-A-0 707 165 that is called "inverse PWM model" can be adjusted according to the maximum six bar input pressure described with reference to present Figure 5.

Claims: An automatic control for a hydrokinetic, multiple ratio transmission for delivering torque from an engine to a driven member (34) comprising a hydrokinetic torque converter and multiple ratio gearing, said torque converter having an impeller (22) driven by said engine and a turbine (24) connected to a torque input element of said gearing, a torque output portion of said gearing being connected to said driven member (34); said transmission including fluid pressure-operated clutch and brake means for establishing and disestablishing torque ratio changes in said gearing; said automatic control system comprising; a pressure source, a control valve system connecting said pressure source to said clutch and brake means; a pressure-operated torque converter torque bypass clutch (44) in said converter, said bypass clutch (44) establishing a friction torque flow path between said turbine (24) and said impeller (22) when it is engaged, said bypass clutch (44) comprising a clutch piston in said converter and defining in said converter a bypass clutch release pressure chamber and a bypass clutch apply pressure chamber; said clutch piston being engaged with a torque transmitting capacity that is dependent upon pressure differential across said clutch piston; a bypass clutch apply pressure passage (376) communicating with said converter, a bypass clutch release pressure passage (374) communicating with said release pressure chamber; main pressure regulator valve means (378) in said valve system for regulating control pressure in said valve system; accumulator valve means (324) in said valve system communicating with said main pressure regulator valve means (378) for establishing an accumulator threshold pressure in said release chamber; a converter fluid cooler and transmission lubrication circuit including converter cooler and lubrication portions; converter clutch control valve means (320), movable between first and second positions, communicating with said apply pressure passage (376) for delivering pressure in said apply pressure passage to said cooler and lubrication circuit when it assumes said first position; characterized by a converter pressure modulator valve means (322) communicating with said main pressure regulator valve means (378) for modulating said control pressure to produce a converter clutch apply pressure in said bypass clutch apply pressure passage (376) when said converter clutch control valve means (320) assumes said second position for varying pressure differential across said clutch piston; A converter pressure solenoid valve means (332) in said valve system communicating with said modulator valve means (322) for establishing a pilot pressure on said modulator valve means (322); and electronic control means (334) responsive to operating variables for energising said solenoid valve means (332) whereby said bypass clutch capacity is controlled to effect smooth engagement and release. An automatic control as claimed in claim 1, wherein said operating variables include engine speed, turbine speed and vehicle speed, said solenoid control means (334) responding to said variables to effect a controlled reduction in bypass clutch capacity during changes in ratio in said gearing. An automatic control as claimed in claim 1 or 2, wherein said valve system includes a converter clutch accumulator valve means (324) communicating with said main pressure regulator valve means (378) for establishing a constant converter clutch release pressure, said converter clutch accumulator bypass clutch pressure release chamber through said converter clutch control valve means (320).

Inventors: CROONEN WERNER, KIRCHHOFFER JOHANN, MARTIN THOMAS, REICHERT ERIC, WAGNER THOMAS, WICKLER WOLFGANG, CROONEN, WERNER, KIRCHHOFFER, JOHANN, MARTIN, THOMAS, REICHERT, ERIC, WAGNER, THOMAS, WICKLER, WOLFGANG
Applicants: FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, FORD FRANCE S.A., FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1997
Main classification: F16H61
IPC codes: F16H59, F16H61