DRIVETRAIN CREEP TORQUE CONTROL

Abstract

Vehicle (10) comprising the following: a powertrain (12); and at least one control (22) programmed to, in response to a condition with foot removed from the accelerator pedal (18) and requests for a friction torque exceeding a received threshold, while the vehicle speed (10) is approximately zero, cause a friction torque of a generally constant value to be supplied, so that commands for a torque from the drive train (12) reach a minimum value, wherein the commands are based on the torque requested by the drive train (12) and the friction torque supplied, and wherein the threshold is less than a predetermined value of the torque requested by the drive train (12) during the condition with the foot removed from the accelerator pedal (18), the amount of frictional torque supplied depends not only on the amount of frictional torque requested, but also on whether the requested frictional torque increases or decreases.

Description

TECHNICAL FIELD

[0001] This disclosure relates to controlling torque during foot-off-the-accelerator pedal conditions. BACKGROUND

[0002] Certain motor vehicles powered by conventional internal combustion engines creep under foot-off-pedal conditions. That is, when the vehicle is in gear and a driver removes their foot from the accelerator pedal (and does not apply the brake pedal), the vehicle creeps forward in response to the torque generated by the driveline (assuming the vehicle is on level ground) because the driveline is mechanically coupled to the wheels via the transmission. This torque can be referred to as creep torque.

[0003] DE 10 2009 037 182 A1 discloses a method for controlling or regulating a creep torque of a vehicle with an electric drive, in particular a hybrid or electric vehicle, in which a creep torque is generated by means of the electric drive which depends on the braking force with which the vehicle is braked.

[0004] DE 102 21 835 A1 discloses a method for controlling a starting element of a motor vehicle in creep mode. A creep torque setpoint is set at the starting element depending on the current inclination of the motor vehicle, the brake pedal pressure exerted by a driver of the motor vehicle, the distance of the motor vehicle from obstacles, and the driver type.

[0005] US 2011 / 0 136 625 A1 discloses a vehicle drive train with an engine start-stop function suitable for keeping a vehicle stationary on a downhill road after the wheel brakes have been applied and the engine has been switched off. SUMMARY

[0006] A vehicle includes a powertrain and at least one controller. The at least one controller, in response to a foot-off-the-accelerator condition and friction torque requests exceeding a received threshold while a speed of the vehicle is approximately zero, causes friction torque to be delivered at a generally constant value such that powertrain torque commands reach a minimum value. The commands are based on the powertrain requested torque and the delivered friction torque. The threshold is less than a predetermined value of the powertrain requested torque during the foot-off-the-accelerator condition.

[0007] A method for controlling driveline torque of a vehicle includes requesting a predetermined amount of driveline torque in response to a foot-off-the-accelerator condition. The method also includes providing friction torque at a generally constant amount such that driveline torque commands reach a minimum amount in response to friction torque requests that exceed a threshold amount less than the predetermined amount and are received while a speed of the vehicle is approximately zero.

[0008] A powertrain control system for a vehicle includes at least one controller that causes friction torque to be delivered at a generally constant value for a range of increasing requested friction torque values ​​to cause commanded powertrain torque values ​​to decrease to a generally constant minimum value. The range of increasing requested torque values ​​is less than a requested powertrain torque value under foot-off-the-accelerator and vehicle-stopped conditions. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a motor vehicle. Fig. 2 is a graph of requested friction torque as a function of delivered friction torque, requested powertrain torque, and commanded powertrain torque under foot-off-the-accelerator pedal conditions as vehicle speed approaches zero. Fig. 3A and Fig. 3B are plots of requested friction torque as a function of delivered friction torque, requested powertrain torque, and commanded powertrain torque under foot-off-the-accelerator pedal conditions when vehicle speed is approximately zero. Fig. Figure 4 is another plot of requested friction torque as a function of delivered friction torque, requested powertrain torque, and commanded powertrain torque under foot-off-the-accelerator conditions when vehicle speed is approximately zero. Fig. Figure 5 is a flowchart of an algorithm for controlling commanded driveline torque. DETAILED DESCRIPTION

[0009] Embodiments of the present disclosure are described herein. It should be understood, however, that the disclosed embodiments are only examples, and other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As one skilled in the art will understand, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments not explicitly illustrated or described.The illustrated combinations of features provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desirable for specific applications or implementations.

[0010] Certain alternatively powered vehicles, such as hybrid electric vehicles, generate torque at low speeds using electric motors. For example, to simulate the feel of a conventionally powered vehicle, an alternatively powered vehicle can activate the electric motor under foot-off-the-pedal conditions to cause the electric motor to generate torque and consequently cause the vehicle to creep.

[0011] In other words, an alternatively powered vehicle may request a certain amount of driveline torque under foot-off-pedal conditions. However, if a driver subsequently applies a brake pedal to overcome this creep torque, energy used to activate the electric machine may be wasted.

[0012] With reference to Fig. 1, a motor vehicle 10, such as a hybrid electric vehicle, a battery electric vehicle, etc., includes a powertrain 12 and a friction braking system 14 mechanically coupled to the wheels 16, as indicated by the solid line. The powertrain 12 may include an internal combustion engine, a transmission, an electric machine, etc., arranged, as known in the art, to independently or jointly generate / provide torque to move the wheels 16. The friction brakes 14, when applied, apply braking torque to the wheels 16. The vehicle 10 further includes an accelerator pedal and a brake pedal 18, 20, and one or more controllers 22. The powertrain 12, the friction braking system 14, and the accelerator and brake pedals 18, 20 are in communication with / under the control of the controllers 22, as indicated by the thin dashed line.The brake pedal 20 is mechanically connected to the friction braking system 14, as indicated by the solid line. The controllers 22 may include a powertrain control module, a brake control module, a vehicle system control module, etc. In other examples, the functionality discussed with reference to the controllers 22 may be implemented in a single controller. Other arrangements are, of course, also possible.

[0013] Upon request from the controllers 22, the powertrain 12 (electric machine) may generate torque to move the wheels 16. A position of the accelerator pedal 18 may determine, at least in part, the amount of requested powertrain torque. As an example, the requested powertrain torque may increase proportionally with the position of the accelerator pedal 18 when the accelerator pedal 18 is applied. A baseline amount of torque, e.g., 500 Newton meters, may be requested when the accelerator pedal 18 is not applied to replicate the creep exhibited by conventionally powered vehicles. As mentioned above, the electric machine 12 may be used to generate the baseline or creep torque.

[0014] With reference to Fig. 2, the requested driveline torque in this example is generally constant under foot-off-the-accelerator pedal conditions as vehicle speed approaches zero. Furthermore, the delivered friction torque increases proportionally with the requested friction torque. The requested friction torque is determined by a position of the brake pedal 20. For example, if the brake pedal 20 has a travel of 100° and the requested friction torque can range from 0 to 10,000 Newton-meters, at 0° (foot off the brake pedal), no friction torque would be requested, at 100°, 10,000 Newton-meters of torque would be requested, and at 50°, 5,000 Newton-meters of torque would be requested, etc.

[0015] The commanded driveline torque, in this example, is the difference between the requested driveline torque and the delivered friction torque (until a minimum value is reached). That is, the control strategy is such that the requested driveline torque is reduced 1:1 by the delivered friction torque to produce the commanded driveline torque. The commanded driveline torque decreases proportionally from 500 Newton meters to a minimum value of 20 Newton meters as the delivered friction torque increases from 0 Newton meters to 500 Newton meters. The minimum value is selected in this example to ensure that the gearing of the transmission 12 does not experience significant backlash. In other examples, the minimum value may have a different value (e.g., 35 Newton meters, 0 Newton meters, etc.) depending on design considerations and objectives.

[0016] The delivered friction torque cancels the delivered driveline torque at approximately 250 Newton meters (assuming a level incline and negligible system losses). The vehicle 10 decelerates and stops moving once the delivered friction torque exceeds 250 Newton meters. When the vehicle 10 is climbing an incline, the vehicle 10 may stop moving once the delivered friction torque exceeds a value less than 250 Newton meters. When the vehicle 10 is descending an incline, the vehicle 10 may similarly stop moving once the delivered friction torque exceeds a value greater than 250 Newton meters.

[0017] If this control strategy continues to be used even after the vehicle 10 has stopped moving, the commanded driveline torque may be greater than the minimum value. Therefore, the energy used to produce that portion of the delivered driveline torque that is greater than the minimum value is wasted, as it performs no useful function, given that the vehicle 10 has stopped moving. Certain described strategies may reduce the amount of energy used to produce such unnecessary driveline torque.

[0018] With reference to Fig. 3A, the requested driveline torque is generally constant under foot-off-the-accelerator conditions when vehicle speed is approximately zero. Furthermore, the delivered friction torque increases with the requested friction torque for certain values ​​of the requested friction torque. Otherwise, the delivered friction torque is generally constant and greater than the requested driveline torque. In this example, the delivered friction torque increases proportionally with friction torque requests up to 100 Newton meters. For friction torque requests between 100 Newton meters and 520 Newton meters, the delivered friction torque is approximately 520 Newton meters. For friction torque requests exceeding 520 Newton meters, the delivered friction torque increases proportionally with the requested friction torque. (Other examples may, of course, have different values.)

[0019] The commanded driveline torque is similar to Fig. 2 the difference between the requested driveline torque and the delivered friction torque (until a minimum value is reached): The requested driveline torque is reduced 1:1 by the delivered friction torque to produce the commanded friction torque. The commanded driveline torque decreases proportionally with friction torque requests up to 100 Newton meters. For friction torque requests exceeding 100 Newton meters, the delivered driveline torque is equal to 20 Newton meters—the minimum value in this example.

[0020] When comparing Fig. 2 and Fig. 3A reduces the strategy of Fig. 3A the range over which the commanded powertrain torque exceeds the minimum value. A threshold friction torque request value (e.g., 100 Newton meters) has been selected to be less than the requested powertrain torque (e.g., 500 Newton meters). For friction torque requests less than this threshold, the delivered friction torque increases with the requested friction torque, and consequently, the commanded powertrain torque decreases. For friction torque requests greater than the threshold, the delivered friction torque is greater than the requested powertrain torque, and consequently, the commanded powertrain torque reaches the minimum value. This avoids circumstances such as those discussed with respect to Fig. 2, under which the driveline torque continues to be delivered even when the vehicle 10 has stopped moving.

[0021] Energy that would otherwise be used to generate such driveline torque is consequently saved.

[0022] A strategy similar to that with regard to Fig. 2 can be used under conditions with the foot off the accelerator pedal when the vehicle speed is greater than zero. A transition can then be made to a strategy similar to that described with reference to Fig. 3A may be performed once the vehicle speed becomes approximately zero to reduce energy expenditure and thus improve fuel economy. Changes in the delivered friction torque and commanded driveline torque for a given requested friction torque may be filtered to conceal this transition from vehicle occupants. If a vehicle comes to a stop at a requested friction torque of 200 Newton meters, the delivered friction torque of 200 Newton meters (as determined by Fig. 2) to 520 Newton meters (as specified by Fig. 3A) according to a filter function to avoid any disturbances that may cause step or sudden changes in this parameter.

[0023] With reference to Fig. 3B shows the behavior of the delivered friction torque and the commanded driveline torque under circumstances where the requested friction torque increases to approximately 370 Newton meters, decreases to approximately 280 Newton meters, and then increases thereafter. In other words, a driver depresses the brake pedal 20 to a position past that which would cause the vehicle 10 to stop, slightly releases the brake pedal 20, and then depresses the brake pedal 20 again. If the requested friction torque is in the range such that the commanded driveline torque is equal to the minimum value and a decrease in the requested friction torque is observed (e.g., because the driver slightly releases the brake pedal 20), then the delivered friction torque decreases proportionally with the decrease in the requested friction torque. Consequently, the commanded driveline torque begins to increase from the minimum value.The vehicle 10 begins to move once the delivered driveline torque exceeds the delivered friction torque (assuming a level slope). If an increase in the requested friction torque is subsequently observed (for example, as the driver begins to depress the brake pedal 20 again), the delivered friction torque returns to that value, so that the commanded driveline torque reaches the minimum value. In short, the amount of delivered friction torque (and consequently the commanded driveline torque) depends not only on the amount of requested friction torque, but also on whether the requested friction torque is increasing or decreasing.

[0024] With reference to Fig. 4, the requested powertrain torque is generally constant under conditions with the foot off the accelerator pedal when the vehicle speed is greater than zero. In addition, the delivered friction torque increases with the requested friction torque for certain values ​​of the requested friction torque. Otherwise, the delivered friction torque is generally constant and less than the requested powertrain torque. The commanded powertrain torque, in contrast to that of Fig. 2, Fig. 3A and Fig. 3B is reduced 2 to 1 by the delivered friction torque to produce the commanded driveline torque. The commanded driveline torque decreases proportionally with friction torque demands up to X1 Newton-meters. For friction torque demands exceeding X1 Newton-meters, the delivered driveline torque is equal to Yfloor Newton-meters—the minimum value in this example.

[0025] Certain of the preceding examples used threshold values ​​of the requested friction torque of 100 Newton meters and 520 Newton meters. That is, with reference to Fig. 3A, the delivered friction torque is set to a value greater than the requested powertrain torque when the requested friction torque falls within this range. However, other vehicles or control schemes may have different threshold settings to meet vehicle expectations while still attempting to minimize energy consumption. These thresholds may be determined via testing, simulation, etc. Furthermore, while significant portions of the requested and commanded powertrain torque and delivered friction torque graphs exhibit linear behavior, other such graphs may have significant portions that exhibit non-linear behavior. In one example, the requested powertrain torque may vary under foot-off-the-accelerator conditions.If the requested friction torque falls within the range defined by the upper and lower thresholds, the delivered friction torque would not be constant under this circumstance (unlike the delivered friction torque of . Fig. 3A). Other scenarios are also possible. Furthermore, various ramp functions can be used to transition the delivered friction torque to and from the ranges defined by the thresholds. In other words, the delivered friction torque in the transition ranges does not need to have sharp corners. Such ramp functions can be selected to achieve a desired behavior or to best adapt control capabilities.

[0026] With reference to Fig.5, operation 24 determines whether a vehicle is at a standstill. For example, controllers 22 may read position data associated with accelerator pedal 18 and speed data associated with vehicle 10. If the position data indicates zero and the vehicle speed is approximately zero, controllers 22 may determine that vehicle 10 is at a standstill. If the position data indicates something other than zero or the vehicle speed is greater than zero, controllers 22 may determine that vehicle 10 is not at a standstill. If not, the algorithm returns to operation 24. If so, operation 26 determines whether the requested friction torque is less than the lower threshold or greater than the upper threshold.For example, the controllers 22 may read requested friction torque data from the friction braking system 14 to determine whether the requested friction torque is less than 100 Newton meters or greater than 520 Newton meters. If so, the delivered friction torque is set equal to the requested friction torque in operation 28. For example, the controllers 22 may command the friction braking system 14 to deliver the requested amount of torque to the wheels 16. The algorithm then returns to operation 24.

[0027] Returning to operation 26, if not, the delivered friction torque is set equal to a predetermined value so that the commanded driveline torque reaches a minimum value. For example, the controllers 22 may command the friction braking system 14 to provide 520 Newton-meters of torque to the wheels 16 (assuming the requested driveline torque is 500 Newton-meters and is to be reduced 1:1 by the delivered friction torque to produce the commanded driveline torque). As another example, the controllers 22 may command the friction braking system 14 to provide 250 Newton-meters of torque to the wheels 16 (assuming the requested driveline torque is 500 Newton-meters and is to be reduced 2:1 by the delivered friction torque to produce the commanded driveline torque).In operation 32, it is determined whether the requested friction torque is decreasing. For example, the controllers 22 may read requested friction torque data from the friction braking system 14 to determine whether the requested friction torque is decreasing. If so, the supplied friction torque is decreased in operation 34. For example, the controllers 22 may command the friction braking system 14 to decrease the torque at the wheels 16. The algorithm then returns to operation 32. If not, the algorithm returns to operation 26.

[0028] The processes, methods, or algorithms disclosed herein may be deliverable to / implemented by a processing device, controller, or computer, which may include any existing programmable electronic control unit or dedicated electronic control unit. Likewise, the processes, methods, or algorithms may be stored as data and instructions executable by a controller or computer in many forms, including, but not limited to, information permanently stored on non-writable storage media such as read-only memory devices and information modifiably stored on writable storage media such as floppy disks, magnetic tape storage, optical tape storage, CDs, RAM devices, and other magnetic and optical media.The processes, methods, or algorithms may also be implemented in an executable software object. Alternatively, the processes, methods, or algorithms may be embodied, in whole or in part, using suitable hardware components such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), state machines, controllers, or any other hardware components or devices, or a combination of hardware, software, and firmware components.

[0029] Although exemplary embodiments are described above, these embodiments are not intended to describe all possible forms encompassed by the claims. Rather, the words used in the specification are words of description rather than limitation, and it is to be understood that various changes may be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments may be combined to form further embodiments of the invention that may not be explicitly described or illustrated.Although various embodiments may have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, one of ordinary skill in the art will recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes depending on the specific application and implementation. These attributes may include, but are not limited to, cost, strength, durability, lifetime cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc.As such, embodiments that are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications. A vehicle comprising: a powertrain; and at least one controller programmed, in response to a foot-off condition and requests for friction torque exceeding a received threshold while a speed of the vehicle is approximately zero, to cause friction torque to be delivered at a generally constant value such that commands for torque from the powertrain reach a minimum value, the commands being based on the torque requested by the powertrain and the delivered friction torque, and the threshold being less than a predetermined value of the torque requested by the powertrain during the foot-off condition. B The vehicle of A, wherein the at least one controller is further programmed, in response to a request for a decrease in friction torque received while causing the friction torque to be delivered at the generally constant value, to cause the friction torque to be delivered to decrease such that the powertrain torque commands increase from the minimum value. C The vehicle of B, wherein the at least one controller is further programmed to cause the friction torque to be delivered at the generally constant value in response to a request for a received increase in friction torque to decrease the friction torque to be delivered. D The vehicle of any one of A to C, wherein the at least one controller is further programmed to cause the friction torque to be delivered to increase in response to requests for friction torque that exceed the generally constant value. E Vehicle according to one of A to D, wherein the generally constant value is greater than the predetermined value of the torque requested by the drive train. F Vehicle according to any one of A to E, wherein the generally constant value is less than the predetermined value of the torque requested by the driveline. A method for controlling driveline torque of a vehicle, comprising: in response to a foot-off-the-accelerator condition, requesting a predetermined amount of driveline torque; and in response to requests for friction torque that exceed a threshold amount that is less than the predetermined amount and are received while a speed of the vehicle is approximately zero, providing friction torque at a generally constant amount such that driveline torque commands achieve a minimum amount. H The method of G, further comprising, in response to a received request for a decrease in friction torque while delivering friction torque at the generally constant amount, decreasing the amount of delivered friction torque such that the driveline torque commands increase from the minimum amount. I The method of H, further comprising, in response to a received request for an increase in friction torque while decreasing the amount of friction torque to be delivered, delivering the friction at the generally constant amount. J The method of any one of G to I, further comprising increasing the amount of friction torque delivered in response to requests for friction torque that exceed the generally constant amount. K The method of any one of G to J, wherein the generally constant amount is greater than the predetermined amount of driveline torque. L The method of any one of G to K, wherein the generally constant amount is less than the predetermined amount of driveline torque. M Powertrain control system for a vehicle, comprising: at least one controller programmed to cause friction torque to be delivered at a generally constant value for a range of increasing requested friction torque values ​​to cause commanded powertrain torque values ​​to decrease to a generally constant minimum value, wherein the range of increasing requested torque values ​​is less than a requested powertrain torque value under foot-off-the-accelerator and vehicle-stop conditions. N The system of M, wherein the at least one controller is further programmed to cause the delivered friction torque to decrease from the generally constant value in response to decreasing requested friction torque values ​​within the range. O System according to M or N, where the generally constant minimum value is zero. P system according to one of M to O, where the generally constant value is greater than the requested driveline torque value. Q system according to one of M to P, where the generally constant value is less than the requested driveline torque value.

Claims

[1] Vehicle (10) comprising: a drive train (12); and at least one controller (22) programmed to, in response to a foot-off-the-accelerator-pedal (18) condition and friction torque requests exceeding a received threshold while a speed of the vehicle (10) is approximately zero, cause friction torque to be delivered at a generally constant value such that torque commands from the powertrain (12) reach a minimum value, wherein the commands are based on the torque requested by the driveline (12) and the friction torque delivered, and wherein the threshold is less than a predetermined value of the torque requested by the driveline (12) during the foot-off-the-accelerator-pedal (18) condition, where the amount of friction torque supplied depends not only on the amount of requested friction torque, but also on whether the requested friction torque increases or decreases. [2] The vehicle (10) of claim 1, wherein the at least one controller (22) is further programmed, in response to a request for a decrease in friction torque received while causing the friction torque to be delivered at the generally constant value, to cause the friction torque to be delivered to decrease such that the torque commands from the powertrain (12) increase from the minimum value. [3] The vehicle (10) of claim 2, wherein the at least one controller (22) is further programmed to cause the friction torque to be delivered at the generally constant value in response to a request for a received increase in friction torque that the friction torque to be delivered decrease. [4] The vehicle (10) of claim 1, wherein the at least one controller (22) is further programmed to cause the friction torque to be delivered to increase in response to requests for friction torque that exceed the generally constant value. [5] The vehicle (10) of claim 1, wherein the generally constant value is greater than the predetermined value of torque requested by the powertrain (12). [6] The vehicle (10) of claim 1, wherein the generally constant value is less than the predetermined value of torque requested by the powertrain (12).

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