VEHICLE DRIVE SYSTEM FOR CONTROLLING A TORQUE CONVERTER CLUTCH

Abstract

Vehicle propulsion system (12) comprising: a drive machine (14) with an output shaft (28); a torque converter (30) with a compressor (34) coupled to the output shaft (28) of the drive machine (14), a turbine (36) fluidly coupled to the compressor (34) and a torque converter coupling (16) for selective mechanical coupling of the compressor (34) to the turbine (36); a continuously variable transmission (CVT) (20) coupled to the turbine (36) of the torque converter (30); and a control unit (44) that is programmed to: Receiving signals indicating the operating status of the vehicle propulsion system (12), including an accelerator pedal position signal; Determine whether the received signals, including the accelerator pedal position signal, indicate a reduction in the ratio in the CVT (20); Determine whether the torque converter clutch (16) should be opened based on a determination of the upcoming reduction in gear ratio; and Opening the torque converter clutch (16) in response to a determination to open the torque converter clutch (16); characterized by the fact that the control unit (44) is further programmed to: to determine whether a desired ratio stage change is a stage change that exceeds a predetermined threshold, and whether the rotational speed of the drive machine (14) is below a predetermined rotational speed; and to determine that the torque converter clutch (16) should be opened when the stage change exceeds the predetermined threshold and the speed of the drive machine (14) is below the predetermined speed.

Description

TECHNICAL AREA

[0001] The present disclosure relates to a vehicle drive system for controlling a torque converter clutch according to the preamble of claim 1 or claim 7, as is known essentially from DE 10 2016 121 849 A1.

[0002] Regarding the further state of the art, reference is made at this point to the publications DE 698 02 882 T2, US 5 226 393 A, DE 197 22 495 A1 and DE 11 2009 002 281 T5. INTRODUCTION

[0003] A continuously variable transmission (CVT) is a type of vehicle transmission capable of varying the input / output speed ratio across a range between a minimum (understeer) and a maximum (oversteer) ratio, thus allowing for an infinitely variable selection of engine operation. This can achieve a preferred balance of fuel consumption and engine power in response to an output torque demand. Unlike conventionally driven transmissions, which use one or more planetary gear sets and multiple rotary and friction clutches to achieve a discrete gear ratio, a CVT uses a variable-diameter pulley system to achieve the infinitely variable selection of torque ratios.

[0004] The pulley system, commonly referred to as a variator assembly, can transition continuously within a calibrated range of torque ratios. A typical belt or chain variator assembly includes two variator pulleys connected to each other by an endless rotating drive element, such as a chain or belt. The endless rotating drive element runs within a variable-width gap defined by tapered pulley faces. One of the variator pulleys receives engine torque via a crankshaft, torque converter, and drive gear set, thus acting as the drive / primary pulley. The other pulley is connected to a CVT output shaft via additional gear sets, thus acting as a driven / secondary pulley.

[0005] To change the CVT torque ratio and transmit torque to the drivetrain, a clamping force (applied by hydraulic pressure) can be applied to the variator pulleys via one or both pulley actuators. The clamping force effectively clamps the pulley halves together, changing the width of the gap between the pulley surfaces. Varying the gap, i.e., the effective radius, causes the rotating drive element to run higher or lower within the gap. This, in turn, changes the effective diameters of the variator pulleys and can alter the CVT torque ratio.

[0006] One control strategy for a vehicle drive system that includes a CVT is to configure the system to achieve optimal fuel economy. In a coasting situation, this might involve running the engine at low speed. Furthermore, a hydraulic pump that provides the hydraulic pressure used to control the CVT's speed ratio can be configured with low flow and low pressure to reduce the amount of energy required to operate the pump, which can further improve fuel economy. Generally, it is also desirable to reduce the overall size and / or flow rate of these pumps to minimize the energy required to operate them and further improve fuel economy. However, this can create problems if the driver requires additional power.A driver can indicate a power request by pressing an accelerator pedal, and the position of this pedal can then be used by the control system to configure the vehicle's drive system to provide the requested power.

[0007] In response to a driver request for additional torque, particularly when starting from a coasting configuration, the control system can request this additional torque by requesting the engine to operate at a higher RPM and also ordering a CVT reconfiguration to a lower gear ratio. However, the CVT's ability to rapidly reduce the gear ratio (as with a power reduction) may be diminished because the engine, which provides the power to operate the CVT hydraulic control pump and propel the vehicle, may have started from a low engine speed, and the power required to increase the flow to the CVT hydraulic control pump is not immediately available. It takes time for the engine speed to increase sufficiently to provide enough power to allow for a reduction in the gear ratio.To achieve the higher engine speed, however, it may be necessary to reduce the gear ratio. This combination of factors can lead to a delayed response to the driver's demand for higher torque.

[0008] Furthermore, this problem can be exacerbated when the vehicle's drive system is operated at higher altitudes. At higher altitudes, the available power of an engine can be reduced. This reduction in available engine power, and thus a diminished ability to quickly achieve a lower gear ratio, can further increase the lag in response to the driver's demand for higher torque.

[0009] The invention is therefore based on the objective of providing a solution to the problem described. SUMMARY

[0010] This problem is solved with a vehicle drive system having the features of claim 1 or claim 7.

[0011] In another exemplary aspect, the received signals include a drive capacity signal, which indicates the ability of the drive machine to provide torque, and in which determining whether the converter clutch is to be opened is further based on the drive capacity signal.

[0012] In another exemplary aspect, the control system is further programmed to determine whether the power of the drive motor is below a predetermined threshold, and the determination of whether the converter clutch should be opened is still based on whether the power of the drive motor is below the predetermined threshold.

[0013] In another exemplary aspect, the drive machine includes a motor, the received signals include a speed signal indicating the motor's speed, and the control system determines, based on determining that the drive machine's power is below a predetermined threshold, whether the motor speed is below a predetermined motor speed.

[0014] In another exemplary aspect, the received signals include a signal indicating the altitude of the vehicle's propulsion system, and the control system determines whether the capacity of the propulsion machine is below a predetermined threshold, based on determining whether the altitude is above a predetermined height.

[0015] In another exemplary aspect, the CVT includes a hydraulic pump that can be operated in a variety of modes, the mode in which the hydraulic pump is operated indicating the rate at which the CVT is able to change the gear ratio.

[0016] In another exemplary aspect, the control is further programmed to: calculate an estimated time until the end of the switching process based on the received signals, to determine when to apply the torque converter clutch based on the estimated time until the end of the switching process, and to apply the torque converter clutch in response to a determination of the torque converter clutch.

[0017] This significantly increases the speed at which a vehicle drive system with a continuously variable transmission (CVT) can downshift, thereby improving the vehicle's acceleration during downshifts. It also enhances the ability to integrate highly efficient engine operating modes and the operation, structure, and size of the CVT hydraulic pump without compromising the downshifting process, and improves the responsiveness of the vehicle drive system to driver input. This further enhances the driving experience, as the vehicle drive system can react noticeably faster to driver input, resulting in smoother and more refined shifting.

[0018] The above-mentioned features and advantages, as well as further features and advantages of the invention, are readily apparent from the following detailed description, including the claims and embodiments, when taken together with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present disclosure becomes more understandable with the aid of the detailed description and the accompanying drawings, in which the following applies: Fig. 1 is a schematic view of a motor vehicle incorporating a vehicle propulsion system according to the present disclosure; Fig. Figure 2 is a graphic illustrating exemplary signals of a vehicle drive control system according to the present disclosure; Fig. Figure 3 is another graphic illustrating exemplary signals of a vehicle drive control system according to the present disclosure; Fig. Figure 4 is a graphic 400 of signals from the vehicle propulsion system illustrating an improved response by an exemplary embodiment of the present disclosure; Fig. Figure 5 is a graphic illustrating signals of a vehicle drive control system according to a further exemplary embodiment of the present disclosure; and Fig. Figure 6 is a flowchart of an exemplary process according to the present disclosure. DETAILED DESCRIPTION

[0020] Referring to the drawings, in which identical reference numbers correspond to identical or similar components in the various figures, shows Fig. 1 A schematic representation of a motor vehicle, usually denoted by 10. The motor vehicle 10 can be any type of vehicle, such as a car, a truck, a van, an off-road vehicle, etc.

[0021] The motor vehicle 10 includes a drive system 12 configured to propel the motor vehicle 10. The drive system 12 may include a drive engine 14, a torque converter clutch 16, a forward drive clutch or shift mechanism 18, a continuously variable transmission (CVT) 20, and an axle drive unit 22. The drive engine 14 could, for example, be an internal combustion engine, an electric motor, or a hybrid. The drive engine 14 can be an engine capable of propelling the motor vehicle 10 and includes a crankshaft 24 configured to move a plurality of pistons (not shown) within a plurality of piston cylinders 26. The crankshaft 24 is configured to move each individual piston within its own cylinder 26.

[0022] Although the drive engine 14 is shown inclusively with four cylinders 26, the drive engine 14 can, for example, include any number of cylinders 26, such as two, three, four, six, or eight. Each cylinder 26 is configured to undergo a combustion event to propel the motor vehicle 10. The drive engine 14 has an output shaft 28 configured to transmit the torque to the torque converter clutch 16.

[0023] The torque converter coupling 16 is connected to the output shaft 28 and includes a torque converter 30 and a torque converter lock-up coupling 32. The torque converter 30 has an impeller (or pump) 34 and a turbine 36, which are usually separated by a stator (not shown). The impeller 34 is attached to the motor output shaft 28. The impeller 34 is configured to form a fluid coupling with the turbine 36 under certain conditions, as is known in the art. The torque converter lock-up coupling 32 is configured to increase the torque transmission capability between the impeller 34 and the turbine 36 in order to transmit torque and rotation between the impeller 34 and the turbine 36.

[0024] The turbine 36 is connected to the forward drive coupling / shifting device 18, which may include a friction clutch, a binary clutch, or a Sprague device. The forward drive coupling / shifting device 18 couples the drive motor 14 and the CVT 20 in the forward direction. The CVT 20 is configured to selectively change a gear ratio between the output shaft 28 and a transmission output shaft 38. The forward drive coupling / shifting device 18 is configured to selectively connect the turbine 36 to the CVT 20. The CVT 20 is connected to the final drive 22 to drive a set of wheels 40 of the motor vehicle 10. Although commonly referred to as a CVT 20, the CVT 20 may, for example, be a continuously variable transmission or an infinitely variable transmission.

[0025] A control system 44 can be used to control the engine 14 and / or the CVT 20. In some variations, the control system 44 includes, for example, an engine control unit 46 and a transmission control module 48. The engine 14 and the CVT 20 can be equipped with a variety of actuators and sensor devices for monitoring operation, and—in the case of the engine 14—with a fuel supply to provide torque through combustion in response to a torque demand from the driver. The sensors associated with the engine 14 or the CVT 20 can be configured to send feedback to the control system 44.

[0026] Fig. Figure 200 illustrates exemplary signals of a vehicle drive control system according to the present disclosure. Figure 200 illustrates the torque converter clutch mode 202, the engine speed 204, the turbine speed 206, the actual CVT ratio 208, the desired CVT ratio 210, an estimated time to the end of the shift operation 212, and a shift state machine 214. A first vertical dashed line 216 indicates the start of a downshift, and a second vertical dashed line 218 indicates the end of the downshift, both of which are also indicated accordingly by the shift state machine 214. Prior to the start of the downshift at 216, the torque converter clutch is in a coast-down lock mode at 220.

[0027] In response to a request to transition from the current ratio at 222 to a lower target ratio 224, a determination that the current ratio 222 deviates from the lower target ratio by more than a certain value (which can be referred to as "step-through"), and a determination that the engine speed is below a predetermined engine speed 226, an exemplary embodiment can open and unlock the torque converter clutch to transition to a "TCC-off" mode 228. Additionally, an exemplary embodiment can determine an estimated time until the end of the shifting process 230.

[0028] Disengaging, opening, or unlocking the torque converter clutch decouples the engine from the torque converter turbine, making it possible to increase the engine speed 204 more quickly to a speed that delivers higher torque. The turbine speed 206 can follow the engine speed via the fluid coupling in the torque converter. Additionally, the torque converter's fluid coupling enables torque multiplication, thus improving torque output. With the engine's ability to increase speed more quickly and deliver higher torque, the power available to the CVT hydraulic pump increases more rapidly, which in turn allows for a faster transition from the initial ratio to the target ratio than would otherwise be possible.In other words, opening the torque converter clutch in this way allows for a faster increase in engine speed, resulting in a faster rise in engine torque, a torque multiplication via the torque converter, and also more power for the CVT's hydraulic control system to enable improved transmission behavior.

[0029] As the CVT ratio 208 approaches the target ratio and the resulting estimated time to the end of the shift exceeds a "zero time line" 232, the torque converter clutch can then enter an engagement mode, which may, for example, correspond to a slip control mode at the end of the shift 218. Since the torque converter clutch is applied controllably, the turbine speed controllably approaches the engine speed until they are substantially the same, and the torque converter can then be switched to a locked mode. In an exemplary embodiment, the estimated shift time and the resulting determination of when to switch to a torque converter clutch or slip operation can be coordinated with and / or respond to the CVT ratio control.The point at which the torque converter clutch actually switches between disengagement mode and an engaged state can be set and / or calibrated based on a variety of known factors. Preferably, the torque converter clutch can be placed into an engaged state shortly before the actual end of the shifting process to compensate for the inherent delays in the hydraulic and / or mechanical system.

[0030] Fig. Figure 300 illustrates exemplary signals during the transition between a torque converter clutch disengagement mode and a torque converter clutch engagement mode for a vehicle drive system control system according to the present disclosure. Figure 300 includes a torque converter clutch mode 302, an engine speed 304, a desired engine speed 306, a projected turbine speed 308, an instantaneous turbine acceleration 310, the CVT ratio 312, and the target CVT ratio 314.In this way, once the torque converter clutch enters engagement mode, control over the slip rate of the torque converter clutch can depend on the actual turbine acceleration 310 and the actual or current ratio 316 at a given time 318. Knowing the target ratio, the final turbine acceleration at the end of the shifting process 320 can be predicted, and the system can be calibrated and controlled to achieve a desired engine acceleration (or a desired engine start-up rate 322). In this way, the engine acceleration rate can be controlled accurately and reliably.

[0031] A similar type of controllable transition from a torque converter clutch engagement mode to a locked mode is described in US 10,046,750 B1. Differences between the method of controlling the CVT during the transition described by the previous reference are that the previous reference describes a transition during a ratio increase as opposed to a ratio decrease, and that the control is based on predicted conditions rather than actual measured conditions.

[0032] Fig. Figure 400 is a graph of vehicle drive system signals illustrating an improved response by an exemplary embodiment of the present disclosure. Graph 400 illustrates the engine speed 402 and the CVT ratio 404 when the torque converter clutch remains locked during a transmission loss, and the engine speed 406 and the CVT ratio 408 when the torque converter is unlocked. The in Fig. The four illustrated signals correspond to data recorded from an actual vehicle at an altitude of approximately 7,000 feet above sea level. In this case, the switching time is reduced by about one and a half seconds under the same, somewhat extreme altitude conditions.

[0033] In an exemplary embodiment, where altitude significantly affects the power available from the engine, the control system can be calibrated and / or adjusted to open the torque converter clutch more frequently. For example, the control system can respond not only to accelerator pedal input and engine speed, but also to engine power to determine when and whether to open the torque converter clutch during a change in the CVT ratio (which can be affected by altitude). In an exemplary embodiment, an ambient air pressure sensor can provide a signal indicating altitude. In some vehicle propulsion systems, an engine control unit can also calculate a variable corresponding to the engine's "percentage capability" under current conditions.This “percent capability variable” can also be a reliable indicator of whether and when the torque converter clutch should be unlocked during downshifting.

[0034] Graphic 400 of Fig. Figure 4 illustrates that not only does the engine speed increase more quickly and the gear change occur faster, but the vehicle also accelerates more quickly. Figure 400 illustrates the vehicle speed 410 when the torque converter clutch remains locked throughout the entire gear ratio change and the vehicle speed 412 when the torque converter clutch is opened according to an exemplary embodiment of the present disclosure. The vehicle speed 412 is significantly higher than the vehicle speed 410.

[0035] Fig. Figure 5 is a diagram 500 illustrating signals from a vehicle drive control system according to a further exemplary embodiment of the present disclosure. In addition to or as an alternative to determining whether the torque converter clutch should be opened in response to an engine speed, the decision can be based on the ability of the CVT system to provide a desired gear ratio. The diagram 500 includes an accelerator pedal position 502, an engine speed 504, a turbine speed 506, a desired gear ratio 508, a pump-limited gear ratio 510, and a torque converter clutch mode (state machine) 512. Since the accelerator pedal position 502 indicates a driver request to increase the output torque of the vehicle drive system, a desired gear ratio 508 can be determined.Initially, the CVT may be able to follow the actual gear ratio 508, but current conditions may limit its ability to continue following the desired gear ratio 508. In an exemplary embodiment, this limitation may relate to the conditions and / or configuration of the pump that provides the hydraulic flow and pressure required to control the CVT's gear ratio. This may be known and determined as a pump-limited gear ratio 510. When the difference between the pump-limited gear ratio 510 and the desired gear ratio 508 reaches or exceeds a predetermined threshold 514, the controller may cause the torque converter to open, as indicated by the torque converter clutch mode signal 512.In response, the motor speed 504 can increase more rapidly and deviate from the turbine speed 506, which in turn allows the motor to reach a state providing higher torque more quickly, which in turn can improve the pump's ability to provide hydraulic flow and pressure, allowing the ratio to follow the desired gear ratio 508 more closely, as indicated by changing the limited gear ratio 510 closer to the desired gear ratio 508.

[0036] In one exemplary embodiment, the CVT pump's ability to effect a change in the gear ratio may be limited depending on the CVT pump's operating mode. For example, some CVT pumps may operate in a reduced flow / pressure mode and a full flow / pressure mode. In this configuration, an exemplary embodiment may determine whether the pump's performance is limited or not, depending on whether the pump is operating in the reduced flow / pressure mode. During reduced flow / pressure operation, the CVT's ability to follow the desired gear ratio may be limited, and an exemplary controller may disengage the torque converter clutch when it detects that the pump is not operating in a reduced flow / pressure mode.Other conditions and / or signals can also be used without restriction to determine whether limiting the transmission ratio without restriction is possible, and the operation of the torque converter clutch can then be calibrated accordingly.

[0037] Fig.Figure 6 illustrates a flowchart 600 of an exemplary procedure according to an exemplary embodiment of the present disclosure. The procedure begins at step 602 and proceeds to step 604. In step 604, the states of the vehicle propulsion system are acquired, calculated, determined, and / or measured. These conditions may include, for example, the driver's accelerator pedal position, engine speed, CVT ratio, CVT ratio control pump configuration, altitude, engine power, etc., without limitation. The procedure then proceeds to step 606. In step 606, the procedure determines whether a reduction in the CVT ratio is requested. For example, a control unit for a vehicle propulsion system may determine, based on the information acquired in step 604, whether a step reduction of the CVT ratio is required.If the procedure determines in step 606 that a reduction in the stage ratio of the CVT ratio is requested, the procedure proceeds to step 608. In step 608, the procedure determines, based on the information gathered in step 604, whether the conditions indicate that the torque converter clutch should be opened. If, in step 608, the procedure determines that the torque converter clutch should be opened, the procedure proceeds to step 610, in which the procedure opens the torque converter clutch.

[0038] The procedure then proceeds to step 612. In step 612, the procedure determines whether the ratio change is substantially complete. If the procedure determines in step 612 that the ratio change is substantially complete, the procedure engages the torque converter clutch. For example, the torque converter clutch can be controlled to transition into a slip mode and then into a locked mode. The procedure then proceeds to step 616, at which point the procedure ends. If the procedure determines in step 606 that no reduction in the stage ratio is requested, or if the procedure determines in step 608 that the conditions indicate the torque converter clutch should not be disengaged, the procedure proceeds to step 616, at which point the procedure ends.

Claims

[1] Vehicle propulsion system (12) comprising: a drive machine (14) with an output shaft (28); a torque converter (30) with a compressor (34) coupled to the output shaft (28) of the drive machine (14), a turbine (36) fluidly coupled to the compressor (34) and a torque converter coupling (16) for selective mechanical coupling of the compressor (34) to the turbine (36); a continuously variable transmission (CVT) (20) coupled to the turbine (36) of the torque converter (30); and a control unit (44) that is programmed to: Receiving signals indicating the operating status of the vehicle propulsion system (12), including an accelerator pedal position signal; Determine whether the received signals, including the accelerator pedal position signal, indicate a reduction in the ratio in the CVT (20); Determine whether the torque converter clutch (16) should be opened based on a determination of the upcoming reduction in gear ratio; and Opening the torque converter clutch (16) in response to a determination to open the torque converter clutch (16); characterized by , that the control unit (44) is further programmed to: to determine whether a desired ratio stage change is a stage change that exceeds a predetermined threshold, and whether the rotational speed of the drive machine (14) is below a predetermined rotational speed; and to determine that the torque converter clutch (16) should be opened when the stage change exceeds the predetermined threshold and the speed of the drive machine (14) is below the predetermined speed. [2] Vehicle drive system (12) according to claim 1, wherein the received signals comprise a capacitance signal of the drive machine (14) indicating the ability of the drive machine (14) to provide torque, and wherein determining whether the torque converter clutch (16) is to be opened is further based on the capacitance signal of the drive machine (14). [3] Vehicle drive system (12) according to claim 2, wherein the control unit (44) is further programmed to determine whether the capacity of the drive machine (14) to provide torque is below a predetermined threshold, and wherein the determination of whether the torque converter clutch (16) is to be opened is further based on whether the capacity of the drive machine (14) to provide torque is below the predetermined threshold. [4] Vehicle propulsion system (12) according to claim 3, wherein the drive machine (14) comprises a motor and the received signals comprise a motor speed signal indicating a speed of the motor, and wherein the control unit (44) determines whether the power of the drive machine (14) is below a predetermined threshold, based on determining whether the motor speed is below a predetermined motor speed. [5] Vehicle propulsion system (12) according to claim 3, wherein the received signals include a signal indicating the height of the vehicle propulsion system (12), and wherein the control unit (44) determines whether the capacity of the drive machine (14) is below a predetermined threshold, based on determining whether the height is above a predetermined height. [6] Vehicle propulsion system (12) according to claim 1, wherein the control unit (44) is further programmed to: to calculate an estimated time until the end of the switching process based on the received signals; to determine when to engage the torque converter clutch (16) based on the estimated time until the end of the shifting process; and to apply the torque converter clutch (16) in response to a determination to engage the torque converter clutch (16). [7] Vehicle propulsion system (12) comprising: a drive machine (14) with an output shaft (28); a torque converter (30) with a compressor (34) coupled to the output shaft (28) of the drive machine (14), a turbine (36) fluidly coupled to the compressor (34) and a torque converter coupling (16) for selective mechanical coupling of the compressor (34) to the turbine (36); a continuously variable automatic transmission (CVT) (20) coupled to the turbine of the torque converter (30); and a control unit (44) that is programmed to: Receiving signals indicating the operating status of the vehicle propulsion system (12), including an accelerator pedal position signal; Determine whether the received signals, including the accelerator pedal position signal, indicate a reduction in the ratio in the CVT (20); Determine whether the torque converter clutch (16) should be opened based on a determination of the upcoming reduction in gear ratio; and Opening the torque converter clutch (16) in response to a determination to open the torque converter clutch (16); characterized by, that the received signals indicate the rate at which the CVT (20) can change the ratio, and wherein determining whether the torque converter clutch (16) should be opened is based on whether a difference between the rate at which the CVT can change the ratio and a desired rate exceeds a predetermined threshold. [8] Vehicle drive system (12) according to claim 7, wherein the CVT (20) comprises a hydraulic pump which can be operated in a plurality of modes, and wherein the mode in which the hydraulic pump operates specifies the rate at which the CVT (20) is able to change the ratio,

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