Method for controlling creep torque in a hybrid powertrain system

Abstract

Method implemented by a controller for operating a hybrid powertrain system (20) of a vehicle, comprising: Monitoring the magnitude and direction of a vehicle speed (212); Operating the hybrid powertrain (20) to generate an amount of axle torque that responds to an initial creep torque command (214) in an operator-selected direction of movement when an operator acceleration request is zero and the magnitude and direction of the vehicle speed (212) are in the operator-selected direction of movement and are less than a speed threshold associated with vehicle creep operation; Operating the hybrid powertrain (20) to generate an amount of axle torque that responds to a creep torque command modified as a result of braking in the direction of movement selected by the operator, when the operator acceleration request is zero, an operator brake request (216) is not zero, and the magnitude and direction of the vehicle speed (212) are in the direction of movement selected by the operator and are less than the speed threshold associated with vehicle creep operation, or the direction of the vehicle speed (212) is opposite to the direction of movement selected by the operator. wherein the creep torque command (232) modified as a result of braking is determined on the basis of a relationship between an operator brake request (216) and the initial creep torque command (214), wherein the operator brake request (216) is entered into a first calibration table (222) which determines a first numerical multiplier (223), and wherein the creep torque command (232) modified as a result of braking is further determined on the basis of the magnitude and direction of the vehicle speed (212) and the direction of movement selected by the operator, wherein the magnitude and direction of the vehicle speed (212) and the direction of movement selected by the operator are entered into a second calibration table which determines a second numerical multiplier (227), wherein the second numerical multiplier (227) is set to 1 when the vehicle speed (212) is zero, or is set according to an inverse relationship to the first numerical multiplier (223) when the direction of the vehicle speed (212) is opposite to the direction of movement selected by the operator, or is set according to a transit relationship when the direction of the vehicle speed (212) is in the direction of movement selected by the operator, and wherein the initial creep torque command (214) is selected as the creep torque command (232) modified as a result of braking if the initial creep torque command (214) is less than a torque threshold (218), and a second creep torque command (229) is selected as the creep torque command (232) modified as a result of braking if the initial creep torque command (214) is greater than the torque threshold (218), wherein the creep torque command modified as a result of braking is multiplied by the second numerical multiplier (227) to determine the second creep torque command (229), wherein the creep torque command modified as a result of braking (232) is compared with the initial creep torque command (214), and the minimum of the two values ​​is selected as a preferred axle creep torque command (240). is chosen, which is applied,to control the operation of the hybrid powertrain system (20) and thus generate axle torque; and , Operating the hybrid powertrain (20) to generate an amount of axle torque in the direction of movement selected by the operator when the operator acceleration request is zero and the direction of vehicle speed (212) is opposite to the direction of movement selected by the operator.

Description

TECHNICAL AREA

[0001] This disclosure concerns control systems for hybrid powertrain systems. BACKGROUND

[0002] The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an acknowledgment of prior art.

[0003] Vehicle powertrain architectures include hybrid powertrain systems that employ multiple torque-generating devices, encompassing internal combustion engines and non-combustion torque machines that transfer mechanical torque, either directly or via a transmission, to a final drive for use as propulsion torque. Known internal combustion engines can also generate torque that can be transferred to a torque machine to produce power, which can be stored as potential energy in an onboard storage device. Internal combustion engines include multi-cylinder heat engines that can convert stored fuel into mechanical power through combustion processes, and non-combustion torque machines include multi-phase electric motors that convert electrical power into mechanical power. An electrical energy storage device, e.g.,A battery stores electrical power that can be transferred and converted into alternating current (AC) power using a power converter to operate the multiphase electric machine, which then generates mechanical power to perform work. Hybrid powertrain systems generate mechanical power that is transferred to a vehicle final drive in response to an output torque demand. Power outputs from the engine and the electric machine(s) are controlled to respond to the output torque demand. DE 10 2010 034 286 A1 relates to a vehicle creep control system that includes executing a first control scheme to determine a preferred output torque as a first function of the operator's input to the brake pedal when the actual vehicle direction of travel is a first direction and the vehicle direction selected by the operator is also a first direction. Furthermore, the vehicle creep control system includes executing a second control scheme to determine the preferred output torque as a second function of the operator's input to the brake pedal when the actual vehicle direction of travel is a second direction and the vehicle direction selected by the operator is a first direction. The object of the present invention is to provide a control method for hybrid powertrain systems which minimizes the required amount of operator input into a brake pedal and the applied mechanical braking torque by using an axle creep torque. This object is achieved by the method described below. SUMMARY

[0004] A method for operating a vehicle's hybrid powertrain system comprises monitoring the magnitude and direction of a vehicle speed and operating the hybrid powertrain to generate an amount of axle torque that responds to an initial creep torque command in an operator-selected direction of motion when an operator acceleration request is zero and the magnitude and direction of the vehicle speed are in the operator-selected direction of motion and are less than a speed threshold associated with vehicle creep operation.Furthermore, the method includes operating the hybrid powertrain to generate an amount of axle torque that responds to a creep torque command modified as a result of braking in the direction of movement selected by the operator, when the operator acceleration request is zero, an operator brake request is not zero, and the magnitude and direction of the vehicle speed are in the direction of movement selected by the operator and are less than the speed threshold associated with the vehicle creep operation, or the direction of the vehicle speed is opposite to the direction of movement selected by the operator.The creep torque command modified as a result of braking is determined based on a relationship between an operator brake request and the initial creep torque command. The operator brake request is entered into a first calibration table, which determines a first numerical multiplier. Furthermore, the creep torque command modified as a result of braking is determined based on the magnitude and direction of the vehicle speed and the direction of movement selected by the operator. The magnitude and direction of the vehicle speed and the direction of movement selected by the operator are entered into a second calibration table, which determines a second numerical multiplier.The second numerical multiplier is set to 1 if the vehicle speed is zero, or according to an inverse relationship to the first numerical multiplier if the direction of the vehicle speed is opposite to the direction of movement selected by the operator, or according to a transit relationship if the direction of the vehicle speed is in the direction of movement selected by the operator.Furthermore, the initial creep torque command is selected as the creep torque command modified by braking if the initial creep torque command is less than a torque threshold, and a second creep torque command is selected as the creep torque command modified by braking if the initial creep torque command is greater than the torque threshold. The creep torque command modified by braking is multiplied by the second numerical multiplier to determine the second creep torque command. The creep torque command modified by braking is compared to the initial creep torque command, and the minimum of the two values ​​is selected as a preferred axle creep torque command, which is applied to control the operation of the hybrid powertrain system and thus generate axle torque.The method further includes operating the hybrid powertrain to generate an amount of axle torque in the direction of movement selected by the operator when the operator acceleration request is zero and the direction of vehicle speed is opposite to the direction of movement selected by the operator.

[0005] Determining a creep torque command in an operator-selected direction of movement, setting the initial creep torque command in response to an operator brake request and in response to a change in the direction of vehicle speed relative to the operator-selected direction of movement, and operating the hybrid powertrain to generate axle torque in response to the set creep torque command. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Now, one or more embodiments will be described by way of example with reference to the accompanying drawings, in which: Fig. 1 a vehicle comprising an exemplary hybrid powertrain system coupled to a final drive and controlled by a control system, as illustrated in the disclosure; Fig. 2-1 and 2-2 an axle creep torque control routine for controlling the hybrid powertrain system of Fig. 1. Illustrate according to the revelation; Fig. 3 illustrates an operation of the exemplary hybrid powertrain system that operates without using the axle creep torque control routine when the vehicle has stopped or is moving slowly uphill in one direction, as described in the disclosure; and Fig.4 illustrates an operation of the exemplary hybrid powertrain system operating with the axle torque control routine in a vehicle that has stopped at a traffic light and is pointing uphill in a direction, according to the disclosure. DETAILED DESCRIPTION

[0007] Now, with reference to the drawings, in which the illustrations serve only to depict certain exemplary embodiments and not to limit them, it is illustrated Fig.Figure 1 schematically depicts a vehicle comprising an embodiment of a hybrid powertrain system 20 coupled to a final drive 60 and controlled by a control system 10. The exemplary vehicle is configured as a hybrid electric vehicle employing an internal combustion engine (power engine) 40, a transmission 50, and a first and second electrically actuated torque machine 35 and 36, respectively. Other hybrid electric powertrain configurations are within the scope of this disclosure and include a powertrain configuration comprising a single electrically actuated torque machine arranged in series with the power engine and the transmission, and other powertrain systems that monitor the direction and speed of rotation of an output element of the powertrain system. Reference numerals used throughout this description refer to identical components.

[0008] The vehicle can be configured to operate in an electric vehicle mode (EV mode) and a hybrid vehicle mode (HV mode). Operating the vehicle in EV mode involves generating all of the propulsive torque from one or more torque machines 35, 36, which are driven by electrical power. Operating the vehicle in HV mode involves generating the propulsive torque from the power machine 40 and the first and second torque machines 35, 36. The power machine 40 can execute control schemes for auto-start and auto-stop during operation in HV mode. The HV mode can include one or more operating states in which all of the propulsive torque is generated by the power machine 40.

[0009] The hybrid powertrain system 20 employs communication links 55, mechanical power links 57, and high-voltage electrical power links 59. The mechanical power links 57 mechanically couple components that generate, utilize, and / or transmit torque, including the power unit 40, the first and second torque units 35, 36, the transmission 50, and the final drive 60. The high-voltage electrical power links 59 electrically connect components that generate, utilize, and / or transmit high-voltage electrical power, including the energy storage system 25, a power converter module 30, and the first and second torque units 35, 36.

[0010] The electrical high-voltage power lines 59 comprise a high-voltage direct current bus 29. The communication line 55 comprises high-speed data transmission lines to effect message transmission between different components of the vehicle and may include one or more of a direct connection, a local network bus, a serial peripheral interface bus, and a high-speed communication bus 18.

[0011] The exemplary energy storage system 25 is a high-voltage battery made from a plurality of lithium-ion cells. It should be noted that the energy storage system 25 can comprise a plurality of electrical cells, ultracapacitors, and other devices designed to store electrical energy in the vehicle.

[0012] The engine 40 is preferably a multi-cylinder internal combustion engine with direct fuel injection, which converts fuel into mechanical work through a combustion process. The engine 40 is equipped with a plurality of sensing devices and actuators configured to monitor operation and supply fuel, thus forming a combustion charge to generate torque. The engine 40 can be configured to execute control schemes for automatic start and stop and control schemes for fuel cut-off (FCO) during continuous vehicle operation. The engine 40 is considered to be in an OFF state when it is not supplied with fuel and is not rotating. The engine 40 is considered to be in an FCO state when it is rotating but not supplied with fuel.

[0013] The first and second torque machines 35, 36 preferably comprise multiphase electric motors / generators electrically connected to the power converter module 30 and configured to convert electrical energy into mechanical power and vice versa, which can be stored in the energy storage system 25. The first and second torque machines 35, 36 have limitations on their power outputs in the form of minimum and maximum torques and speeds.

[0014] The power converter module 30 comprises a first and second power converter 32 and 33, each electrically connected to the first and second torque machines 35 and 36, respectively. The first and second torque machines 35 and 36 interact with their respective first and second power converters 32 and 33 to convert stored electrical energy into mechanical power and to convert mechanical power into electrical energy that can be stored in the energy storage system 25. The first and second power converters 32 and 33 serve to convert high-voltage DC electrical power into high-voltage AC electrical power and also to convert high-voltage AC electrical power into high-voltage DC electrical power.The energy storage system 25 is electrically connected via the high-voltage bus 29 to the power converter module 30, which is connected to the first and second torque machines 35, 36 to transfer electrical power between them. In one embodiment, an external connector 26 is electrically connected to the energy storage system 25 and can be connected to an external AC power source to supply electrical power for charging the energy storage system 25 during periods when the vehicle is stationary.

[0015] The transmission 50 preferably comprises one or more differential gear sets and controllable clutch components to effect torque transmission over a range of speeds between the power unit 40, the first and second torque units 35, 36, and an output element 62 coupled to the final drive 60. In one embodiment, the transmission 50 is a two-mode transmission device configurable to transmit torque in one mode with input power splitting and one mode with combined power splitting. Operating parameters associated with the mechanical power transmission include power between the power unit 40 via the transmission 50, specified by input torque and input speed, and power between the transmission 50 and the final drive 60, specified by output torque and output speed.In one embodiment, the final drive 60 may include a differential gear assembly 65 mechanically coupled to an axle 64 or half-shaft, which in turn is mechanically coupled to a wheel 66 engaged with the ground. The wheel 66 includes a controllable friction brake functionally coupled to a brake controller. The differential gear assembly 65 is coupled to the output element 62 of the hybrid powertrain system 20 and transmits output power between them. The final drive 60 transmits propulsive power between the transmission 50 and a road surface. A vehicle speed sensor 61 is configured to monitor the rotation of the output element 62 and provides data, including rotational position, speed, and direction of rotation, to the control system 10. In one embodiment, the data from the vehicle speed sensor 61 are used to determine the magnitude and direction of the vehicle speed.

[0016] The control system 10 comprises a control module 12, which is connected via signaling to an operator interface 13. The operator interface 13 comprises a plurality of human / machine interface devices through which the vehicle operator commands and controls the operation of the vehicle, including an operator acceleration request via an accelerator pedal 17, an operator braking request via a brake pedal 16, a transmission range selection via a PRNDL lever 15, or another suitable device, including a vehicle speed request, e.g., via a cruise control system 14, and vehicle operation control via an ignition key.

[0017] Although the control module 12 and the operator interface 13 are shown as separate discrete components, this representation serves to facilitate description. The functions described as being performed by the control module 12 can be combined into one or more devices, e.g., implemented in software, hardware, and / or as an application-specific integrated circuit (ASIC) and supplementary circuits that are separate from and distinct from the control module 12. Information transmission to and from the control module 12 can be accomplished using communication links 55, which include, for example, a communication bus 18. The control module 12 is preferably connected, both signal-wise and functionally, to individual components of the hybrid powertrain system 20 via the communication bus 18.The control module 12 is connected, via signal technology and / or functionally, to the detection devices of each of the energy storage system 25, the power converter module 30, the first and second torque machines 35, 36, the power machine 40 and the gearbox 50, in order to monitor and control their operation and to determine their parameters.

[0018] Control module, module, control, controller, control unit, processor and similar terms mean any or various combinations of one or more application-specific integrated circuits (ASICs), electronic circuits, central processing unit(s) (preferably a microprocessor) and associated memory and storage (read-only, programmable read-only, random access, disk, etc.) that executes one or more software or firmware programs or routines, combinational logic circuit(s), input / output circuit(s) and facilities, suitable signal conditioning and buffering circuitry and other components to provide the described functionality.Software, firmware, programs, instructions, routines, code, algorithms, and similar terms refer to any set of instructions that includes calibrations and lookup tables. The control module has a set of control routines that are executed to provide the desired functions. Routines are executed, for example, by a central processing unit, and are used to monitor inputs from sensing devices and other networked control modules, and to execute control and diagnostic routines to manage the operation of actuators. Routines can be executed at regular intervals, for example, every 100 microseconds, 3.125, 6.25, 12.5, 25, and 100 milliseconds, during continuous power machine and vehicle operation. Alternatively, routines can be executed in response to the occurrence of an event.

[0019] The control module 12 executes control routines 11 to control the operation of the power machine 40 in coordination with the first and second torque machines 35, 36 and the gearbox 50, thereby generating an output torque and output speed at the output element 62, transmitting mechanical power to the final drive 60, and generating axle torque in response to the operator's acceleration and braking requests. The axle torque is either positive (propulsion) torque or negative (regenerative braking) torque. One of the control routines 11, referred to herein as creep operation, controls the operation of the torque-generating devices, i.e.,the power machine 40 and the first and second torque machines 35, 36 to generate an amount of axle torque called creep torque, which is an amount of axle torque commanded when the operator acceleration request 17 is zero, the transmission range selection 15 is one of the drive ranges, e.g. Drive (D) or Reverse (R), and the vehicle speed is lower than a speed threshold associated with creep operation, which is at or near, for example, 5 MPH (8 km / h).

[0020] The Fig. Figures 2-1 and 2-2 schematically illustrate an axle creep torque control routine for controlling the operation of a hybrid powertrain system, as described, for example, in reference to Fig.The axle creep torque control routine is used to control a hybrid powertrain system, thereby generating propulsion torque in a manner that achieves a certain amount of creep torque, limits reverse vehicle roll when operating uphill, and limits forward vehicle roll acceleration when operating downhill, thus minimizing overall energy loss caused by axle torque cancellation initiated by the operator's brake request. In summary, the axle creep torque control routine monitors and controls vehicle operation under conditions where the vehicle speed is less than a threshold without operator input to the accelerator pedal, taking into account the magnitude and direction of the vehicle speed relative to a commanded and expected direction of vehicle speed.This operation allows the vehicle to operate in a manner that achieves a creep torque while minimizing vehicle rollback, thereby minimizing the need for operator braking force acting against the creep torque generated by the powertrain system. Table 1 is a key to understanding this. Fig. 2-1 is provided, with the numbered blocks and corresponding functions being implemented as follows. Table 1 BLOCK BLOCK CONTENTS 202 Monitor the amount and direction of Vss, Tacclr, Tbrk, PRNDL 204 Is Tacclr = 0, PRNDL = R,D,L AND Vss less than the threshold value? 206 Determine preferred axle creep torque 208 Control the drivetrain system to achieve preferred axle creep torque. 210 End

[0021] The axle creep torque control routine is executed periodically during continuous vehicle operation. Various vehicle and operator parameters are monitored, including the magnitude and direction of the vehicle speed (Vss), the transmission range selection (PRNDL), the operator acceleration request (Tacclr), and the operator braking request (Tbrk) (202). When the operator acceleration request is zero, i.e., the operator is not depressing the accelerator pedal, the vehicle speed is less than a speed threshold associated with creep operation, and the transmission range selection device is in one of the drive ranges, e.g., Drive (D) or Reverse (R) (204) (1), an axle creep torque determination routine is executed (206) to determine a preferred axle creep torque, and operation of the powertrain system is controlled to achieve the preferred axle creep torque (208).If these conditions are not met or are no longer met (204) (0), this iteration of the axle creep torque control routine ends (210).

[0022] Fig. Figure 2-2 schematically shows the axle creep torque determination routine 206 from Fig.2-1, wherein inputs are monitored that include an initial creep torque command 214, a magnitude and direction (signed) of the vehicle speed 212, an operator brake request 216, and a transmission range selection 215. The initial creep torque command 214 is a calibrated value for the axle torque determined relative to the vehicle speed when the operator acceleration request is zero. The initial creep torque command 214 is a magnitude of axle torque that achieves a vehicle speed on the order of 5-8 km / h (3-5 mph) when the vehicle is operated on a level surface. The signed vehicle speed 212 includes a magnitude and direction of the vehicle speed. The transmission range selection 215 specifies the direction of travel selected by the operator, i.e., one of Drive (D), Reverse (R), or Neutral (N).

[0023] The initial creep torque command 214 is compared with a threshold torque 218 (220), and a logic signal 221, i.e., 0 or 1, is generated. The logic signal 221 is set to "1" if the initial creep torque command 214 is greater than the threshold torque 218, and the logic signal 221 is set to "0" if the initial creep torque command 214 is less than the threshold torque 218. The logic signal 221 is applied by a subsequent logic operator 230 to select an initial creep torque command 214 or a second creep torque command 229 as a creep torque command 232 modified as a result of braking.

[0024] The operator brake request 216 is entered into a calibration table 222, which selects a first numerical multiplier 223 that lies in a range between 0 and 1 (or 0% and 100%), directly related to the magnitude of the operator brake request 216 (0% - no brake torque request and 100% - maximum brake torque request). The first numerical multiplier 223 is applied to adjust the initial creep torque command 214 by numerical multiplication (224) and thus determine a creep torque command 225 modified as a result of braking. This process reduces the amount of axle torque generated in response to the initial creep torque command 214 in response to an increase in the operator brake request 216.

[0025] The signed vehicle speed 212 is entered into calibration table 226, which selects a second numerical multiplier 227 based on the magnitude and direction of the vehicle speed and the direction of movement selected by the operator. For example, the second numerical multiplier 227 is set to 1 if the vehicle speed is zero. The second numerical multiplier 227 is set according to an inverse relationship with the minimum multiplier of calibration 222 if the vehicle speed is less than zero and the transmission range selection 215 indicates that the direction of movement selected by the operator is Drive (D), or if the vehicle speed is greater than zero and the transmission range selection 215 indicates that the direction of movement selected by the operator is Reverse (R).For example, if the minimum multiplier of calibration 222 is 0.04, the maximum value at a negative vehicle speed is 1 / 0.04, or 25. The second numerical multiplier 227 is set according to a pass-through relationship if the vehicle speed is greater than zero and the transmission range selection 215 indicates that the operator-selected direction of travel is Drive (D), or if the vehicle speed is less than zero and the transmission range selection 215 indicates that the operator-selected direction of travel is Reverse (R). For example, if the signed vehicle speed 212 is positive, the calibration table 226 provides a multiplication value of 1.0 for the second numerical multiplier 227. The creep torque command 225, modified as a result of braking, is multiplied by the second numerical multiplier 227 (228) to determine the second creep torque command 229.

[0026] One of the initial creep torque commands 214 and the second creep torque command 229 is selected as the creep torque command 232 modified as a result of braking, using the logical operator 230. This means that the initial creep torque command 214 is selected as the creep torque command 232 modified as a result of braking if the initial creep torque command 214 is less than the torque threshold 218, and the second creep torque command 229 is selected as the creep torque command 232 modified as a result of braking if the initial creep torque command 214 is greater than the torque threshold 218.The creep torque command 232, modified as a result of braking, is compared with the initial creep torque command 214, and the minimum of the two values ​​is selected as a preferred axle creep torque command 240, which is applied to control the operation of the hybrid powertrain system and thus generate axle torque. The operation of the hybrid powertrain system may include an operation in which the power unit is in the OFF state and the first and second torque units are controlled to achieve the preferred axle creep torque command 240.

[0027] Thus, under low-speed conditions, when the operator is not applying any input to the accelerator pedal and the vehicle is operating on a relatively level surface, the preferred axle creep torque command 240 is equal to or less than the initial creep torque command 214 and decreases with an increase in the operator brake request 216 as long as the vehicle is moving forward and the direction of travel selected by the operator is Drive (D). Under low-speed conditions, when the operator is not applying any input to the accelerator pedal and the vehicle is stopped or rolling backward relative to the direction of travel selected by the operator (Drive (D)), the preferred axle creep torque command 240 may increase to an amount equal to the initial creep torque command 214 to prevent the vehicle from rolling backward in response to an operator brake request.

[0028] The axle creep torque detection routine 206 provides calibration flexibility to minimize the required amount of operator input into the brake pedal and the applied mechanical braking torque, thus counteracting axle creep when the vehicle is operating on a level road surface while approaching a traffic sign. This minimizes the expenditure of electrical energy by the vehicle's mechanical brakes during vehicle creep. The axle creep torque detection routine 206 also prevents a vehicle from accelerating backward when a brake pedal is depressed by applying the signed vehicle velocity as part of the torque cancellation logic.

[0029] Fig.Figure 3 graphically illustrates the operation of the exemplary hybrid powertrain system without using the axle creep torque control routine when the vehicle is stopped or moving slowly uphill in one direction, such as at a traffic light. The plotted parameters include operator brake request (%) 316, operator acceleration request 317 (%), signed vehicle speed (km / h) 314, indicating both the direction and magnitude of the speed, and axle torque 310 (Nm), all shown on the vertical axis relative to time 320 on the horizontal axis. At time 321, the operator acceleration request 317 drops to zero, indicating that the operator has removed their foot from the accelerator pedal. The axle torque 310 decreases to achieve a commanded creep torque, and the vehicle speed 314 decreases in response.At time 322, the operator brake request 316 is applied with an amount close to 10%, thereby canceling the axle torque 310 at the commanded creep torque, as indicated by the decrease in axle torque 310. The vehicle speed 314 continues to decrease and becomes negative, i.e., the vehicle reverses its direction of travel and accelerates in reverse. This could be a backward roll of the vehicle, such as can occur when the vehicle has stopped at a traffic light and is facing uphill. At time 323, the operator brake request 316 is increased, and the vehicle speed 314 (which is negative) increases towards zero, for example, to stop the backward roll of the vehicle. The vehicle speed 314 reaches zero at time 324.

[0030] Fig.Figure 4 graphically depicts the operation of the exemplary hybrid powertrain system, which uses the axle torque control routine, in a vehicle stopped at a traffic light and facing uphill. The plotted parameters include operator brake request (%) 416, operator acceleration request 417 (%), signed vehicle speed (km / h) 414, indicating both the direction and magnitude of the speed, and axle torque 410 (Nm), all shown on the vertical axis relative to time 420 on the horizontal axis. Before time 421, the operator acceleration request 417 drops to zero and remains at zero, indicating that the operator has removed their foot from the accelerator pedal, thus initiating a creep torque request.The operator brake request 416 is at or approximately 10%, and the axle torque 410 is at a commanded creep torque, with the vehicle speed 414 at zero. The operator brake request 416 is released at time 421 and decreases to 0% at time 422, at which point the vehicle speed 414 becomes negative. The axle torque 410 increases in response to the negative vehicle speed. At time 423, the operator brake request 416 increases but does not release the axle torque 410, as they work together to stop the vehicle from rolling backward. As the vehicle speed 414 approaches zero, the axle torque 410 decreases to its initial value. The vehicle speed 414 reaches zero at time 424.

[0031] The disclosure has described certain preferred embodiments and variations thereof. Further variations and modifications may become apparent upon reading and understanding the description. It is therefore intended that the disclosure is not limited to the particular embodiment(s) considered to be the best way of carrying out this disclosure, but that the disclosure will encompass all embodiments that fall within the scope of the appended claims.

Claims

[1] A controller-implemented method for operating a hybrid powertrain system (20) of a vehicle, comprising: monitoring a magnitude and direction of a vehicle speed (212); Operating the hybrid powertrain (20) to produce an amount of axle torque responsive to an initial creep torque command (214) in an operator-selected direction of travel when an operator acceleration request is zero and the magnitude and direction of the vehicle speed (212) in the operator-selected direction of travel are less than a speed threshold associated with vehicle creep operation; Operating the hybrid powertrain (20) to produce an amount of axle torque responsive to a braking-modified creep torque command in the operator-selected direction of travel when the operator acceleration request is zero, an operator braking request (216) is not zero, and the magnitude and direction of the vehicle speed (212) in the operator-selected direction of travel are less than the speed threshold associated with vehicle creep operation, or the direction of the vehicle speed (212) is opposite the operator-selected direction of travel, wherein the braking-modified creep torque command (232) is determined based on a relationship between an operator braking request (216) and the initial creep torque command (214), wherein the operator braking request (216) is entered into a first calibration table (222) which determines a first numerical multiplier (223), and the braking-modified creep torque command (232) is further determined based on the magnitude and direction of the vehicle speed (212) and the operator-selected direction of travel, wherein the magnitude and direction of the vehicle speed (212) and the operator-selected direction of travel are entered into a second calibration table which determines a second numerical multiplier (227), wherein the second numerical multiplier (227) is set equal to 1 when the vehicle speed (212) is zero, or is set according to an inverse relationship to the first numerical multiplier (223) when the direction of the vehicle speed (212) is opposite to the direction of movement selected by the operator, or is set according to a through relationship when the direction of the vehicle speed (212) is in the direction of movement selected by the operator, and wherein the initial creep torque command (214) is selected as the braking-modified creep torque command (232) when the initial creep torque command (214) is less than a torque threshold (218), and a second creep torque command (229) is selected as the braking-modified creep torque command (232) when the initial creep torque command (214) is greater than the torque threshold (218), wherein the braking-modified creep torque command is multiplied by the second numerical multiplier (227) to determine the second creep torque command (229), wherein the braking-modified creep torque command (232) is compared to the initial creep torque command (214), and the minimum of the two values ​​is selected as a preferred axle creep torque command (240) is chosen, which is applied,to control the operation of the hybrid powertrain system (20) and thus generate axle torque; and, Operating the hybrid powertrain (20) to produce an amount of axle torque in the operator-selected direction of travel when the operator acceleration request is zero and the direction of vehicle speed (212) is opposite the operator-selected direction of travel. [2] The method of claim 1, further comprising operating the hybrid powertrain (20) to produce an amount of axle torque responsive to an initial creep torque command (214) in the operator-selected direction of travel when the operator acceleration request is zero, the magnitude and direction of vehicle speed (212) in the operator-selected direction of travel are less than the speed threshold associated with vehicle creep operation, and the operator braking request is zero. [3] The method of claim 1, wherein the speed threshold associated with vehicle creep operation comprises a speed threshold of 8 km / h. [4] The method of claim 1, further comprising operating the hybrid powertrain (20) to produce an amount of axle torque in the operator-selected direction of travel when the operator acceleration request is zero and the direction of vehicle speed (212) is opposite the operator-selected direction of travel. [5] The method of claim 1, further comprising operating the hybrid powertrain to produce an amount of axle torque responsive to a braking-modified creep torque command in the operator-selected direction of travel when the operator acceleration request is zero and the direction of vehicle speed (212) is opposite the operator-selected direction of travel. [6] The method of claim 1, wherein operating the hybrid powertrain (20) to produce an amount of axle torque responsive to a braking-modified creep torque command (232) in the operator-selected direction of travel when the operator acceleration request is zero, an operator braking request is not zero, and the magnitude and direction of the vehicle speed (212) in the operator-selected direction of travel are less than the speed threshold associated with vehicle creep operation comprises decreasing the amount of axle torque in response to an increase in the operator braking request.

Images