Method and system for controlling a vehicle wheel axle torque and control system for the same

Abstract

Method for controlling a torque on a wheel axle (12), comprising: Compare (210) at least one torque intervention request with a predetermined minimum axle torque for a current vehicle speed and a current direction of movement of a vehicle (10); wherein the predetermined minimum axle torque decreases when the vehicle speed increases in a direction of movement selected by a driver; Calculating (212) an allocated axle torque based on an axle torque requested by the driver, the current vehicle speed, the current direction of travel, and the greater of the at least one torque intervention request and the predetermined minimum axle torque; and Applying (214, 216) the axle torque to the wheel axle (12) at least partially on the basis of the allocated axle torque.

Description

TECHNICAL FIELD

[0001] The invention relates to a method and a system for controlling a vehicle wheel axle torque and a control system therefor, in particular for preventing drive in a direction opposite to an intended direction of movement.

[0002] For example, it is known from US 2009 / 0 157 243 A1 to set the minimum torque requirement of a driver equal to the creep torque if the accelerator pedal position is greater than zero.

[0003] With regard to the further prior art, reference is made to the documents US 2008 / 0 188 997 A1 and US 2010 / 0 145 559 A1. BACKGROUND

[0004] The direction of intended movement of a vehicle is determined by the vehicle driver, typically by the position of the driver's gearshift lever. If the driver has the gearshift lever in park or neutral, no movement, either forward or reverse, is intended. If the driver has the gearshift lever in drive, low, or manual, the direction of intended movement is forward. If the driver has the gearshift lever in reverse, the direction of intended movement is reverse.

[0005] Conventional drivetrains are typically protected from movement in a direction opposite to the intended direction of movement, as a prime mover cannot produce torque while running in reverse. The transmission connects the prime mover directly to the intended direction of movement by providing a connection to the axles that supports axle torque in the intended direction of movement.

[0006] However, in hybrid or fuel cell applications with one or more electric motors, the electric motor can provide torque while rotating in either direction. Therefore, the possibility exists of propelling the vehicle in the opposite direction to its intended motion. SUMMARY

[0007] In some hybrid applications, an electronic control module (ECM) interprets the driver's accelerator pedal position and determines the driver's desired axle torque. It then allocates this against other axle torque "intervention" requests, such as vehicle overspeed protection, traction or stability control, and cruise control. A final allocated axle torque request is then sent from the ECM to a hybrid control module (HCM), which determines how to use the combination of engine, electric motors, and transmission to achieve the desired axle torque.

[0008] When a vehicle is moving in the direction of intended movement at any speed greater than a relatively slow speed, such as approximately 8.05 km / h, and the driver releases their foot from the accelerator pedal, the ECM should request negative axle torque to decelerate the vehicle. As vehicle speed approaches zero, applying negative axle torque has the potential to drive the vehicle backward, depending on the magnitude of the request. Consequently, a creep control system should apply increasing positive torque (rather than negative torque) as vehicle speed decreases below a predetermined positive threshold speed and as vehicle speed becomes negative. This minimizes vehicle rollback on hills, for example, when a driver stops a vehicle on an uphill grade and then releases the brake.

[0009] A method for controlling axle torque includes determining a driver-selected direction of travel for a vehicle, a vehicle speed, and an actual direction of travel of the vehicle. At least one torque intervention request is then compared to a predetermined minimum axle torque for the vehicle speed and the actual direction of travel. The "predetermined minimum axle torque" is also referred to as a "predetermined axle torque limit." A "torque intervention request" is a requested axle torque requested by another vehicle system that is considered by the control system to determine the torque at the vehicle wheels. Because the torque intervention request is not a driver request, it is referred to as an intervention.The other vehicle systems may include, by way of non-limiting example, a vehicle overspeed system, a traction or stability control system, a braking torque control system, or a vehicle speed limiting system. In determining the "predetermined minimum axle torque," the axle torque in the direction of intended movement is considered positive. The axle torque in the direction opposite the axle torque that would drive the vehicle in the direction of intended movement is considered negative and thus has an increasingly negative value as the speed in the direction of intended movement increases. The driver-requested axle torque may be determined by a driver-operated accelerator device, such as an accelerator pedal. The driver-selected direction of movement may be determined by a driver-operated gearshift lever.

[0010] The method includes calculating an allocated axle torque based on a driver-requested axle torque and the at least one torque intervention request if the at least one torque intervention request is greater than the predetermined minimum axle torque, but instead based on the predetermined minimum axle torque if the at least one torque intervention request is not greater than the predetermined minimum axle torque. The allocated axle torque may then be applied to the driven wheel axle(s).

[0011] The predetermined minimum axle torque may function as a creep coast system torque limit at vehicle speeds below a first threshold speed. Thus, the predetermined minimum axle torque may increase when the vehicle speed is below a predetermined threshold speed and decelerating, and also when the actual direction of travel of the vehicle is opposite the driver-selected direction of travel. Further, the predetermined minimum axle torque may decrease (i.e., have an increasing negative torque value) up to a predetermined threshold as the vehicle speed increases. The predetermined threshold may be a maximum negative axle torque limit applicable regardless of vehicle speed to prevent excessive unintended (i.e., non-driver-requested) vehicle deceleration.

[0012] The method may be particularly useful for hybrid or fuel cell vehicles that have an electric motor capable of adding axle torque to the wheel axle(s) in both directions. In such vehicles, a first controller, such as an engine control module in the case of a hybrid vehicle, may be operatively connected to the driver-operated shift lever, to the driver-operated accelerator pedal device, and to the at least one torque control system that provides the torque intervention request. The first controller includes a processor with a first algorithm that calculates the allocated axle torque, as described above. A second controller is operatively connected to the first controller and to a vehicle axle. The second controller may be a hybrid controller that controls and coordinates the engine and the electric motor / generators to apply the axle torque to the vehicle axle.The second controller receives a signal corresponding to the allocated axle torque from the first controller and has a second algorithm that determines how to set the allocated axle torque to be applied to the vehicle axle.

[0013] Consequently, the method and control system control propulsion in a direction opposite to the intended direction of movement, largely preventing it, even when the vehicle systems present torque intervention requests. The method and control system also limit negative axle torque to prevent excessive vehicle deceleration.

[0014] The above features and advantages and other features and advantages of the present invention will be readily apparent from the following detailed description of the best modes for carrying out the invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of a hybrid vehicle having a control system that prevents propulsion in a direction opposite to an intended direction of travel; Fig. Figure 2 is a graph of axle torque as a function of vehicle speed showing a predetermined axle torque limit curve that establishes a limit on negative axle torque applied to a wheel axle of a vehicle to prevent drive in a direction opposite to the intended direction, and has a minimum threshold axle torque independent of vehicle speed to prevent excessive deceleration; and Fig. 3 is a flowchart of a method for controlling the wheel torque of the vehicle. DETAILED DESCRIPTION

[0015] In the drawings, where like reference numerals refer to like components in all different views, Fig. 1 depicts a vehicle 10 that is driven when axle torque is delivered to a wheel axle 12 of a vehicle wheel 14. Only one wheel axle 12 is shown. The vehicle 10 may be a front-wheel drive, rear-wheel drive, or all-wheel drive vehicle. As shown, the vehicle 10 is a hybrid vehicle having both an engine 16 and two motor / generators 18, 20. However, the vehicle 10 may instead be an electric vehicle having motor / generators but no engine, or may be a fuel cell vehicle having only a fuel cell driving one or more electric motor / generators. The vehicle 10 may have multiple operating modes depending on the engagement of clutches or brakes in a transmission 22 and whether the engine 16 is engaged and whether the motor / generators 18, 20 are each separately controlled to function as a motor or as a generator.

[0016] The engine 16 is operatively connected to an input member 23 of the transmission 22. A speed ratio of the input member 23 to an output member 25 of the transmission 22 is determined by a speed ratio established within the transmission 22 according to the engaged clutches and brakes, and whether the engine 16 is engaged and / or the motor / generators are controlled as motors or generators. A final drive spline arrangement 27 may establish an additional speed ratio between the output member 25 and the wheel axle 12.

[0017] The vehicle 10 may have multiple operating modes, such as an electric-only operating mode in which the engine 16 is off and the vehicle 10 is powered by a motor / generator 18 functioning as a motor; a load-sharing electric-only operating mode in which the engine 16 is off and the vehicle 10 is powered by both motor / generators 18, 20 functioning as motors; a charge-sustaining series operating mode in which the engine 16 drives the motor / generator 18 to function as a generator, and the motor / generator 18 provides electrical power to the motor / generator 20 to function as a motor. Finally, the vehicle 10 may have a charge-sustaining operating mode in which the engine 16 drives the motor / generator 18 to function as a motor, and the motor / generator 20 also functions as a motor.These operating modes are coordinated by a hybrid control module (HCM) 24, referred to herein as a second controller, which includes a hybrid control processor 29 with a stored algorithm that determines how to provide wheel torque using one or more of the engine 16 and the motor / generators 18, 20. Electrical energy is stored in a battery 19 and is operably connected to the motor / generators 18, 20 through a power converter 21, which converts direct current to alternating current when power is supplied from the battery 19 to one or both of the motor / generators 18, 20 functioning as motors, and from alternating current to direct current when power is supplied to the battery 19 from one or both of the motor / generators 18, 20 functioning as generators.

[0018] The axle torque delivered to the wheel axle 12 is determined in part based on a driver-requested axle torque and torque intervention requests received from other vehicle systems, where the torque intervention requests are subject to limits imposed by a control system 26 that controls and largely prevents propulsion in a direction of travel opposite the intended direction of travel and also prevents excessive deceleration of the vehicle 10. The driver may be a vehicle operator, in which case the driver-requested axle torque is the vehicle operator-desired axle torque.

[0019] The control system 26 includes an electronic control module (ECM) 30 and the HCM 24. The ECM 30 is referred to herein as the first controller and receives a plurality of driver-controlled input signals. For example, a driver-operated shift lever 32 is selectively movable by a driver to the positions of park 34, reverse 36, neutral 38, drive 40, and low 42. In the park 34 and neutral 38 positions, the driver's intent is for the vehicle 10 to have no movement or propulsion. When the shift lever 32 is arranged in the reverse 36 position, the driver-selected direction of movement for the vehicle 10 (i.e., the "direction of intended movement") is in a reverse direction.When the shift lever 32 is in the drive position 40 or the low position 42, the driver-selected direction of movement for the vehicle is forward. The shift lever 32 is configured to provide a driver-selected direction signal 44 to the ECM 30.

[0020] A driver-operated accelerator device 46, such as an accelerator pedal, is operable to provide a driver-requested axle torque signal 48 to the ECM 30. The driver-requested axle torque signal 48 is an electrical signal representing the position of the accelerator device 46, which can be correlated to a driver-requested axle torque at the wheel axle 12. The axle torque request is the sum of the torque at all axles. In an all-wheel drive application, a 400 Nm request can be achieved with 200 Nm at both axles or 300 Nm at one axle and 100 Nm at the other axle.

[0021] A driver-activated braking device 50, such as a brake pedal, is operable to provide a driver-requested braking torque signal 52 to the ECM 30. The driver-requested braking torque signal 52 represents the position of the braking device 50, which can be correlated to a driver-requested braking torque applied to the wheel axle 12 via a braking system 54. The braking torque is an axle torque in a direction opposite the driver-requested axle torque associated with the accelerator pedal device 46.

[0022] The ECM 30 also receives a vehicle speed signal 56, such as from a speed sensor 58. The speed signal 56 indicates a speed of the output element 25 as well as the direction of rotation of the output element 25.

[0023] The ECM 30 may receive signals from one or more additional vehicle torque control systems that are not directly controlled by the vehicle driver. These systems establish requests for axle torque at the wheel axle 12 in response to vehicle operating conditions. Such axle torque requests that are not directly performed by the vehicle driver are referred to herein as "torque intervention requests." For example, a vehicle torque control system may be a vehicle overspeed system 60 that generates a vehicle overspeed system axle torque request signal 62 to request negative torque at the wheel axle 12 in response to a determination that the vehicle speed is above a predetermined maximum speed threshold.As used herein, "negative torque" is an axle torque at wheel axle 12 in a direction opposite to the axle torque at wheel axle 12, providing propulsion in the direction of intended movement. Positive torque is an axle torque at wheel axle 12, providing propulsion in the direction of intended movement.

[0024] Another vehicle torque control system may be a traction or stability control system 64 that generates a traction control system torque request signal 66. The traction control system torque request signal 66 could be correlated with a request for either positive or negative torque at the wheel axle 12, as needed to overcome wheel slip or drag.

[0025] A brake torque control system 68 is another vehicle torque control system that can be used to generate a brake torque request signal 70 correlated with a request for a negative torque to be applied to the wheel axle 12, enabling the use of regenerative braking instead of friction braking. Alternatively, the brake torque request signal can be a positive value only, limiting the driver-requested axle torque to mitigate excessive friction braking torque required by the braking system 54. That is, the brake torque control system 68 requests a maximum amount of axle torque to be applied to the wheel axle 12 to enable a braking torque correlated with the driver-requested brake torque signal 52 without exceeding predetermined mechanical limits of the braking system 54.

[0026] A vehicle speed limiting system 72 is another vehicle torque control system that can be used to generate a vehicle speed limiting torque request signal 74 correlated with a request for an amount of negative torque to be applied to the wheel axle 12 to reduce the vehicle speed. Such a system 72 can be used to reduce the vehicle speed to a crawl in the event of theft of the vehicle 10.

[0027] Other torque control systems may also be provided that send torque request signals to the ECM 30 that are not initiated by the vehicle driver to control the axle torque at the vehicle wheel axle 12.

[0028] The ECM 30 includes a processor 76 having a stored algorithm and executing a method 200 for controlling wheel axle torque in conjunction with the processor 29 in the hybrid control module 24. The method 200 is illustrated as a flowchart in Fig. 3 and is shown in relation to the vehicle 10 by Fig. 1 and a diagram 100 of the axle torque 102 (vertical axis) as a function of the vehicle speed 104 (horizontal axis) in Fig. 2, which shows a predetermined axle torque limit curve 110. The predetermined axle torque limit curve 110 of Fig. 2 indicates a predetermined axle torque limit (ie, a predetermined minimum axle torque) for a given vehicle speed and direction of travel. In Fig. 2, the axle torque in the direction of movement selected by the driver (i.e., the direction of movement intended by the driver) increases in the direction of arrow 106 from an axle torque of zero at point 109. The axle torque decreases in the direction opposite to arrow 106 and has an increasing negative value in the direction opposite to arrow 106 below point 109. The horizontal axis indicates the vehicle speed, with the vehicle speed in the intended direction of movement increasing in the direction of arrow 108 from a speed of zero at point 109. The vehicle speed increases in the direction opposite to the direction of the intended movement in the direction opposite to that of arrow 108 starting at point 109. The values ​​of the predetermined axle torque limit for each given vehicle speed and for the actual direction of movement (i.e.,The values ​​of the points that create the predetermined axle torque limit curve 110 may be stored in the ECM 30 as a lookup table. The predetermined axle torque limit curve 110 acts as a limit on torque intervention requests such that when the torque intervention requests are allocated, as limited, relative to the driver-requested axle torque, the applied axle torque prevents propulsion of the vehicle 10 in a direction opposite to the intended direction 108. Below a predetermined threshold speed 112, the predetermined axle torque limit curve 110 generally follows a standard creep coast-to-stop curve 114, as indicated at 116. The creep coast-to-stop curve 114 is shown for comparison purposes only, as the predetermined axle torque limit curve 110 is the limit actually applied under the method 200.The creep coastdown curve 114 represents a limit on the negative axle torque that can be applied at zero accelerator pedal torque and is designed to prevent axle torque in a direction opposite to the intended direction of travel, but does not account for torque intervention requirements. As shown in . Fig. 2, the predetermined axle torque limit curve 110 allows for a lower minimum torque (i.e., a greater axle torque in the direction opposite to the direction of intended movement) than the creep roll-out curve 114 at vehicle speeds above the predetermined threshold speed 112.

[0029] A minimum axle torque threshold 118, which is independent of vehicle speed, is applied as the limit of the predetermined axle torque limit curve 110 to prevent excessive deceleration. Consequently, the predetermined minimum axle torque limit cannot be less than the minimum axle torque threshold (ie, cannot have a greater negative value than the minimum threshold 118).

[0030] With reference to Fig. 3, method 200, which is executed partially by the ECM 30 and partially by the HCM 24, begins with block 202, where a driver-selected direction of movement is determined. This is determined based on signal 44, which indicates the position of the driver-operated shift lever 32. In block 204, the vehicle speed is determined. The vehicle speed may be determined based on signal 56 from speed sensor 58. In block 206, the actual direction of movement of the vehicle 10 is determined. This may also be determined from the speed signal 56, which indicates the direction of rotational movement of the output member 25.

[0031] At block 208, a driver-requested axle torque and at least one torque intervention request are received from the ECM 30. The driver-requested axle torque is received via signal 48 from the accelerator pedal device 46 and signal 52 from the driver-applied brake device 50. Generally, only one of signals 48, 52 indicates a requested axle torque value, since a vehicle driver generally does not depress both the accelerator pedal device 46 and the brake device 50 simultaneously. However, if both the accelerator pedal device 46 and the brake device 50 are depressed simultaneously, the brake device 50 request may be used to override the acceleration request from the accelerator pedal device 46.The torque intervention request is received as one or more of signals 62, 66, 70, or 74 from the vehicle overspeed system 60, the traction or stability control system 64, the brake torque control system 68, or the vehicle speed limiting system 72, respectively. Blocks 202, 204, 206, and 208 may not be executed in the order illustrated in the flowchart of FIG. Fig. 3 shown order.

[0032] Once the ECM 30 determines or receives the information in blocks 202, 204, 206, and 208, the processor 76 compares the received torque intervention request (or multiple torque intervention requests) to the predetermined axle torque limit (i.e., the value indicated by the axle torque limit curve 110) stored in a lookup table for the vehicle speed determined in block 204 and the direction of travel determined in block 206.

[0033] Next, the processor 76 calculates an allocated axle torque in block 212. The allocated axle torque is calculated according to a stored algorithm and is based on the driver requested axle torque received in block 208 and indicated by signal 48 and / or signal 52. The allocated axle torque is also based on those of the one or more torque intervention requests 62, 66, 70, 74 that are greater than the predetermined axle torque limit indicated by curve 110 for the determined vehicle speed and actual direction of travel. For any of the one or more torque intervention requests that are less than the predetermined axle torque limit for the determined vehicle speed and actual direction of travel (i.e.Finally, for any torque intervention requests for the axle torque below the predetermined axle torque limit curve 110), the predetermined minimum axle torque limit for the determined vehicle speed and actual direction of travel is used by the algorithm instead of the torque intervention request value. This helps ensure that the torque applied to the axle 12 under method 200 is not in the direction opposite the driver's intended direction of travel for the vehicle 10. Optionally, the predetermined minimum axle torque indicated by curve 110 may be limited to a value greater than the predetermined excessive deceleration threshold 118.

[0034] An example of the stored algorithm used to calculate the allocated axle torque is an algorithm that first identifies the lowest decreasing torque intervention request and the highest increasing torque intervention request. These torque intervention requests exist after being compared to and limited by the predetermined minimum axle torque limit, as described above. The torque intervention request decreases if it is a request for an axle torque lower than the current axle torque and increases if it is a request for an axle torque higher than the current axle torque. If the lowest decreasing torque intervention request is less than the driver requested axle torque, then the lowest decreasing torque intervention request is the allocated axle torque value.If the lowest decreasing torque intervention request is greater than the driver-requested axle torque and the highest increasing torque intervention request is greater than the driver-requested axle torque, then the lower of the highest increasing torque intervention request and the lowest decreasing torque intervention request is the allocated axle torque value. If neither of the above two statements is true, then the driver-requested axle torque is the allocated axle torque.

[0035] In block 214, the allocated axle torque value is sent via signal 80 to the HCM 24 for application to axle 12. In block 216, the HCM 24 determines how to coordinate control of the prime mover 16 and the motor / generators 18 and 20 to provide the allocated axle torque.

[0036] When method 200 is applied to control axle torque on vehicle 10, it is possible to apply a greater negative axle torque than previously applied by prior methods without causing a drive in the direction opposite to the direction of intended movement.

Claims

[1] A method for controlling a torque on a wheel axle (12), comprising: Comparing (210) at least one torque intervention request with a predetermined minimum axle torque for a current vehicle speed and a current direction of travel of a vehicle (10); wherein the predetermined minimum axle torque decreases as the vehicle speed increases in a driver-selected direction of travel; Calculating (212) an allocated axle torque based on a driver-requested axle torque, the current vehicle speed, the current direction of travel, and the greater of the at least one torque intervention request and the predetermined minimum axle torque; and Applying (214, 216) the axle torque to the wheel axle (12) at least partially based on the allocated axle torque. [2] The method of claim 1, wherein the predetermined minimum axle torque is limited to a value greater than a minimum axle torque threshold (118) for all vehicle speeds, thereby limiting maximum vehicle deceleration. [3] The method of claim 1, wherein the at least one torque intervention request comprises a vehicle overspeed system torque request, a traction or stability control system torque request, a brake torque control system torque request, and / or a vehicle speed limit system torque request. [4] The method of claim 1, wherein the predetermined minimum axle torque functions as a creep coast system torque limit at vehicle speeds below a threshold speed (112). [5] A method for controlling a wheel axle torque, comprising: Determining (202) a direction of movement for a vehicle (10) selected by a driver; Determining (204) a vehicle speed; Determining (206) an actual direction of movement of the vehicle (10); Comparing (210) at least one torque intervention request with a predetermined axle torque limit for the vehicle speed and the actual direction of travel; Calculating (212) an allocated axle torque; wherein the allocated axle torque is based on a driver-requested axle torque and the at least one torque intervention request when the at least one torque intervention request is greater than the predetermined axle torque limit; wherein the allocated axle torque is based on the driver-requested axle torque and the predetermined axle torque limit if the at least one torque intervention request is not greater than the predetermined axle torque limit; and Applying (214, 216) the allocated axle torque to a wheel axle (12) of the vehicle (10), thereby preventing movement of the vehicle in a direction opposite to the direction of movement selected by the driver. [6] The method of claim 5, wherein the predetermined axle torque limit increases as the vehicle speed decreases, when the vehicle speed is below a predetermined threshold speed (112), and also when the actual direction of travel of the vehicle (10) is opposite to the driver-selected direction of travel. [7] The method of claim 5, wherein the predetermined axle torque limit decreases to a predetermined threshold (118) as the vehicle speed increases when the actual direction of travel and the driver-selected direction of travel are the same. [8] The method of claim 5, wherein the predetermined axle torque limit functions as a creep coast system torque limit at vehicle speeds below a predetermined threshold speed (112). [9] A system for controlling a wheel axle torque, comprising: a driver-operated shift lever (32) operable to establish an intended direction of movement of a vehicle (10); a driver-operated accelerator pedal device (46, 50) operable to establish a desired axle torque; at least one torque control system (60, 64, 68, 72) operable to determine a torque intervention request; a first controller (30) operatively connected to the driver-operated shift lever (32), to the driver-operated accelerator pedal device (46, 50), and to the at least one torque control system (60, 64, 68, 72), the first controller (30) comprising a processor (76) having: a first algorithm that: compares the at least one torque intervention request to a predetermined minimum axle torque that decreases as the vehicle speed in the intended direction of travel increases above a predetermined threshold speed (112), that increases as the vehicle speed in the intended direction of travel decreases and below the predetermined threshold speed (112), and that increases as the vehicle speed increases in a direction of travel opposite the intended direction of travel; determines the greater of the at least one torque intervention request and the predetermined minimum axle torque; and calculates an allocated axle torque based on the desired axle torque and the greater of the at least one torque intervention request and the predetermined minimum axle torque; and a second controller (24) operatively connected to the first controller (30); wherein the second controller (24) receives a signal corresponding to the allocated axle torque from the first controller (30) and comprises: a second algorithm that determines how to set the allocated axle torque to be applied to a vehicle axle (12). [10] The control system of claim 9, wherein the predetermined minimum axle torque is limited to a value greater than a minimum axle torque threshold (118).

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