Vehicle control system

Abstract

When the steering wheel is turned back from a state in which the steering wheel is turned in one direction and then turned in the other direction through a neutral position, the driver does not feel uncomfortable and the vehicle's maneuverability and stability are improved. In a vehicle control system, a controller (8) performs torque increase control to add forward acceleration to the vehicle (1) when the steering wheel (28) is turned back from a state in which the steering wheel is turned in one direction until the steering wheel (28) returns to a neutral position. Then, when the steering wheel (28) is turned in the other direction through a neutral position, the torque increase control is terminated so that no forward acceleration is added to the vehicle (1).

Description

Technical Field

[0001] The present invention relates to a vehicle control system for controlling the posture of the vehicle according to steering. Background Art

[0002] Conventionally, there is known a technique for controlling the vehicle posture by decelerating or accelerating the vehicle in response to the driver's operation of a steering wheel (hereinafter sometimes simply referred to as "steering wheel") to improve the responsiveness and stability of the vehicle behavior to the steering wheel operation.

[0003] For example, Patent Document 1 describes the following vehicle motion control: When the vehicle is turning, the vehicle is first decelerated when the steering wheel is turned, and then accelerated when the steering wheel is turned back. This is done to improve the vehicle's maneuverability and stability from entering a curve to exiting it.

[0004] Patent Document 1: International Publication No. 2015 / 151565 Summary of the Invention

[0005] Problems to be solved by the invention

[0006] When implementing the technology described in Patent Document 1, it is considered that when the steering wheel is turned, the driving torque generated by the vehicle's driving force source is reduced to decelerate the vehicle (torque reduction control), and when the steering wheel is turned back, the driving torque generated by the driving force source is increased to accelerate the vehicle (torque increase control). This control is easily implemented in vehicles equipped with electric motors (e.g., electric vehicles) because electric motors can quickly increase and decrease output torque.

[0007] For example, when a vehicle is traveling on an S-shaped curve, torque reduction control is initially executed when the steering wheel is turned, and then torque increase control is executed when the steering wheel is returned. Then, when the steering wheel reaches a neutral position (i.e., a steering angle of 0°) and is switched to a turning operation, the torque increase control ends. Even after the steering wheel, which is being returned to the neutral position, passes through the neutral position, there is a possibility that the torque increase control may not end immediately but may continue for a period of time due to limitations on rapid changes in torque. In this case, even when the steering wheel is turned after passing the neutral position, the torque generated by the driving force source increases due to the unfinished torque increase control, resulting in continued additional acceleration of the vehicle. As a result, the vehicle's maneuverability and stability cannot be improved, and there is a possibility of causing discomfort to the driver.

[0008] The present invention is completed to solve the above-mentioned problems, and its purpose is to improve the vehicle's maneuverability and stability without causing discomfort to the driver when the steering wheel is turned back from a state of being turned to one side and then turned to the other side through a neutral position in a control system of a vehicle that controls the vehicle's posture according to steering.

[0009] Solutions for solving problems

[0010] In order to achieve the above-mentioned purpose, the present invention is characterized in that it has: a driving force source, which generates torque for driving the driving wheels of the vehicle; a steering wheel, which is operated by the driver; a steering angle sensor, which detects the steering angle corresponding to the operation of the steering wheel; and a controller, which controls the torque generated by the driving force source in order to control the vehicle posture based on the steering angle detected by the steering angle sensor, and the controller is configured to add forward acceleration to the vehicle when the steering wheel is turned back from a state where it is turned to one side until the steering wheel returns to a neutral position, and then when the steering wheel is turned to the other side after passing the neutral position, the torque generated by the driving force source is controlled so that no forward acceleration is added to the vehicle.

[0011] According to the present invention thus constructed, when the steering wheel is turned past its neutral position, unlike when torque control for adding forward acceleration is continued, the increase in torque generated by the driving force source can be prevented from causing additional forward acceleration to the vehicle. Therefore, when the steering wheel is turned past its neutral position after a return operation, the driver does not experience discomfort, and the vehicle's maneuverability and stability are improved.

[0012] In the present invention, preferably, the controller is configured to control the torque generated by the driving force source to be reduced so as to add forward deceleration to the vehicle when the steering wheel is turned back from a state in which the steering wheel is turned to one side and then turned to the other side through a neutral position.

[0013] The present invention thus constructed can suppress driver discomfort and rapidly apply forward deceleration to the vehicle during a steering operation after the steering wheel has reached a neutral position. This improves maneuverability and stability during a steering operation after the steering wheel has reached a neutral position, resulting in smoother vehicle behavior.

[0014] In the present invention, it is preferred that the controller is configured to control the torque generated by the driving force source in such a manner that the closer the steering wheel approaches the neutral position, the smaller the forward acceleration applied to the vehicle when the steering wheel is turned back from a state in which the steering wheel is turned to one side until the steering wheel returns to the neutral position.

[0015] According to the present invention thus constituted, it is possible to prevent a sudden change in forward acceleration when the steering wheel undergoes a return operation and reaches a neutral position, thereby preventing the driver from feeling uncomfortable.

[0016] In the present invention, it is preferable that the controller is configured to set the torque generated by the driving force source based on at least a steering angle detected by a steering angle sensor.

[0017] According to the present invention thus constituted, the vehicle posture can be quickly controlled to improve the responsiveness and stability of the vehicle behavior with respect to the driver's steering wheel operation.

[0018] In a preferred example of the present invention, the driving force source includes an electric motor, and the controller is configured to control the torque generated by the electric motor.

[0019] According to the present invention thus constituted, it is possible to control the torque generated by the driving force source with high responsiveness.

[0020] In a preferred example of the present invention, the controller is configured to reduce the driving torque generated by the driving force source in order to add deceleration to the vehicle when the steering wheel is turned, based on the steering angle detected by the steering angle sensor, and to increase the driving torque generated by the driving force source in order to add acceleration to the vehicle when the steering wheel is returned.

[0021] Effects of the Invention

[0022] According to the present invention, in a control system for a vehicle that controls the vehicle posture based on steering, when the steering wheel is turned back from a state in which it is turned to one side and then turned to the other side through a neutral position, it will not cause discomfort to the driver and the vehicle's maneuverability and stability can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a block diagram schematically showing the overall configuration of a vehicle according to an embodiment of the present invention.

[0024] Figure 2 This is a block diagram showing the electrical configuration of a vehicle according to an embodiment of the present invention.

[0025] Figure 3 This is a flowchart of a vehicle posture control process according to an embodiment of the present invention.

[0026] Figure 4 This is a flowchart of the additional torque setting process according to the embodiment of the present invention.

[0027] Figure 5 This is a map showing the relationship between the steering speed and the additional torque according to the embodiment of the present invention.

[0028] Figure 6 This is a map showing the relationship between the steering angle and the correction gain for the increase torque according to the embodiment of the present invention.

[0029] Figure 7 This is a time chart when the vehicle posture control according to the embodiment of the present invention is executed.

[0030] Description of Reference Numerals

[0031] 1: Vehicle; 2: Wheel; 8: Controller; 20: Electric motor; 22: Inverter; 24: Battery; 26: Steering device; 28: Steering wheel; 34: Steering angle sensor; 36: Accelerator opening sensor; 40: Vehicle speed sensor; 46: Braking device DETAILED DESCRIPTION

[0032] Hereinafter, a vehicle control system according to an embodiment of the present invention will be described with reference to the drawings.

[0033] <Vehicle Structure>

[0034] First, refer to Figure 1 and Figure 2 A vehicle to which the vehicle control system according to the embodiment of the present invention is applied will be described. Figure 1 is a block diagram schematically showing the overall structure of a vehicle according to an embodiment of the present invention. Figure 2 This is a block diagram showing the electrical configuration of a vehicle according to an embodiment of the present invention.

[0035] like Figure 1 As shown, a motor 20 (rotating electric machine) is mounted on the front portion of a vehicle 1 as a prime mover (driving force source) for driving left and right front wheels 2, which serve as driving wheels. This vehicle 1 is configured as a so-called FF vehicle. Each wheel of the vehicle 1 is suspended from the vehicle body via a suspension 70 comprising elastic members (typically springs) and suspension arms.

[0036] The electric generator 20 has the function of driving the front wheels 2 (that is, functioning as a prime mover (electric motor)) and the function of being driven by the front wheels 2 to generate regenerative power (that is, functioning as a generator). The electric generator 20 transmits power to the front wheels 2 via the transmission 6 and is controlled by the controller 8 via the inverter 22. The electric generator 20 is connected to the battery 24 and supplies power from the battery 24 when generating driving power. When performing regeneration, the electric generator 20 supplies power to the battery 24 to charge the battery 24.

[0037] In the vehicle 1, the rotating shaft of the motor generator 20 and the rotating shaft of the transmission 6 are connected via a discontinuous clutch 62. For example, the clutch 62 is controlled to switch between engagement and release by the oil pressure of the transmission 6.

[0038] The vehicle 1 includes a steering system 26 comprising a steering wheel (steering wheel) 28, a steering wheel shaft 30, and the like; a steering angle sensor 34 that detects the steering angle of the steering system 26 based on the rotation angle of the steering wheel 28 and the position of a steering wheel rack (not shown); an accelerator position sensor 36 that detects the accelerator position corresponding to the amount of accelerator pedal depression; a brake pedal position sensor 38 that detects the amount of brake pedal depression; a vehicle speed sensor 40 that detects vehicle speed; a yaw rate sensor 42 that detects yaw rate; and an acceleration sensor 44 that detects acceleration. Each of these sensors outputs its detection value to the controller 8.

[0039] In addition, the steering angle sensor 34 can also detect various state quantities in the steering system (the rotation angle of the motor with additional auxiliary torque, the displacement of the rack in the gear rack mechanism, etc.) and the turning angle (tire angle) of the front wheel 2 as the steering angle, instead of detecting the rotation angle of the steering wheel 28.

[0040] Vehicle 1 also includes a brake control system 48 that supplies brake fluid pressure to the wheel cylinders and calipers of braking devices 46 provided at each wheel. Braking control system 48 includes a hydraulic pump 50 that generates the brake fluid pressure required to generate braking force in braking devices 46 provided at each wheel. Hydraulic pump 50 is driven, for example, by electricity supplied from battery 24 and can generate the brake fluid pressure required to generate braking force in braking devices 46 even when the brake pedal is not depressed.

[0041] The brake control system 48 also includes a valve unit 52 (specifically, a solenoid valve) disposed in the hydraulic supply line to each wheel's brake device 46. This valve unit 52 controls the hydraulic pressure supplied from the hydraulic pump 50 to each wheel's brake device 46. For example, the opening of the valve unit 52 is changed by adjusting the amount of power supplied from the battery 24 to the valve unit 52. The brake control system 48 also includes a hydraulic pressure sensor 54 for detecting the hydraulic pressure supplied from the hydraulic pump 50 to each wheel's brake device 46. The hydraulic pressure sensor 54 is, for example, disposed at the connection between each valve unit 52 and the hydraulic pressure supply line downstream thereof. It detects the hydraulic pressure downstream of each valve unit 52 and outputs the detected value to the controller 8.

[0042] Such a brake control system 48 calculates the hydraulic pressures supplied independently to the wheel cylinders and brake calipers of each wheel based on the braking force command value input from the controller 8 and the detection value of the hydraulic pressure sensor 54, and controls the rotation speed of the hydraulic pump 50 and the opening degree of the valve unit 52 according to these hydraulic pressures.

[0043] like Figure 2 As shown, the controller 8 based on this embodiment outputs control signals for controlling the electric motor 20, the clutch 62, and the hydraulic pump 50 and the valve unit 52 of the brake control system 48 based on the detection signals output by various driving state sensors that detect the driving state of the vehicle 1, in addition to the detection signals based on the above-mentioned sensors 18, 34, 36, 38, 40, 42, 44, and 54.

[0044] Controller 8 is constructed using circuitry and is based on a well-known microcomputer. It includes one or more microprocessors (CPUs) that execute programs, memory such as RAM (Random Access Memory) and ROM (Read Only Memory) that stores programs and data, and an input / output bus for inputting and outputting electrical signals. The system comprising steering wheel 28, steering angle sensor 34, and controller 8 corresponds to the vehicle control system in the present invention.

[0045] <Vehicle Posture Control>

[0046] The following describes vehicle posture control according to an embodiment of the present invention. In this embodiment, controller 8 fundamentally performs the following control to control vehicle posture (vehicle behavior) based on the steering angle detected by steering angle sensor 34. First, when the steering wheel 28 is turned away from its neutral position (i.e., when the steering angle is increasing), controller 8 performs torque reduction control to reduce the torque generated by electric motor 20, thereby applying forward deceleration to vehicle 1 (i.e., deceleration that slows the vehicle 1 as it moves forward). Furthermore, when the steering wheel 28 is returned closer to its neutral position (i.e., when the steering angle is decreasing), controller 8 performs torque increase control to increase the torque generated by electric motor 20, thereby applying forward acceleration to vehicle 1 (i.e., acceleration that accelerates the vehicle 1 as it moves forward). This vehicle posture control improves the turning performance, handling stability, and steering controllability of vehicle 1 from entering a curve to exiting it.

[0047] In addition, the torque applied during torque reduction control, that is, the negative torque added to the torque generated by the electric motor 20 to add forward deceleration to the vehicle 1, will be referred to as "reduction torque" hereinafter. Furthermore, the torque applied during torque increase control, that is, the positive torque added to the torque generated by the electric motor 20 to add forward acceleration to the vehicle 1, will be referred to as "increase torque." Furthermore, when these reduction torque and increase torque are used interchangeably, they will be referred to as "additional torque." Such reduction torque or increase torque is applied during vehicle posture control. Specifically, during vehicle posture control, the reduction torque or increase torque is subtracted from or added to the torque that the electric motor 20 should generate in order to achieve acceleration corresponding to the driving state of the vehicle 1 (accelerator opening, etc.) (hereinafter referred to as "base torque"). Hereinafter, the torque resulting from such subtraction or addition of the reduction torque or increase torque to the base torque, that is, the torque that the electric motor 20 should ultimately generate, will be referred to as the "final target torque."

[0048] Next, refer to Figure 3 The overall flow of vehicle posture control according to the embodiment of the present invention will be described. Figure 3 This is a flowchart of a vehicle posture control process according to an embodiment of the present invention.

[0049] Figure 3 The vehicle posture control process is initiated when the ignition of vehicle 1 is turned on and power is supplied to controller 8. It is repeatedly executed at a predetermined interval (e.g., 50 ms). When the vehicle posture control process begins, in step S1, controller 8 acquires various sensor information related to the driving state of vehicle 1. Specifically, controller 8 acquires detection signals output by the various sensors as information related to the driving state, including the steering angle detected by steering angle sensor 34, the accelerator position detected by accelerator position sensor 36, the brake pedal depression amount detected by brake depression amount sensor 38, the vehicle speed detected by vehicle speed sensor 40, the yaw rate detected by yaw rate sensor 42, the acceleration detected by acceleration sensor 44, the hydraulic pressure detected by hydraulic pressure sensor 54, and the gear currently set for transmission 6 of vehicle 1.

[0050] Next, in step S2, controller 8 sets a target acceleration based on the driving state of vehicle 1 acquired in step S1. Specifically, for example, controller 8 selects an acceleration characteristic map corresponding to the current vehicle speed and gear position from acceleration characteristic maps (previously created and stored in memory, etc.) specified for various vehicle speeds and various gear positions, and sets a target acceleration corresponding to the current accelerator opening by referring to the selected acceleration characteristic map.

[0051] Next, in step S3, controller 8 determines the base torque of electric motor 20 for achieving the target acceleration determined in step S2. In this case, controller 8 determines the base torque within the range of torque that electric motor 20 can output based on the current vehicle speed, gear stage, road grade, road surface μ, and other factors.

[0052] In addition, in parallel with the processing of steps S2 and S3, in step S4, the controller 8 executes the additional torque setting processing described later (see Figure 4 ), based on the steering speed of the steering wheel 28, etc., an additional torque (reducing torque or increasing torque) to be applied to the torque generated by the electric generator 20 in order to control the vehicle posture is set.

[0053] Next, after executing steps S2 to S4, in step S5, controller 8 sets a final target torque based on the base torque set in step S3 and the additional torque set in step S4. Basically, controller 8 calculates the final target torque by subtracting the reduction torque from the base torque or adding the additional torque to the base torque.

[0054] Next, in step S6, controller 8 sets a command value (inverter command value) for inverter 22 to achieve the final target torque set in step S5. In other words, controller 8 sets an inverter command value (control signal) to cause motor generator 20 to generate the final target torque. Then, in step S7, controller 8 outputs the inverter command value set in step S6 to inverter 22. After step S7, controller 8 terminates the vehicle posture control process.

[0055] Next, refer to Figure 4 The additional torque setting process according to the embodiment of the present invention will be described. Figure 4 This is a flowchart of the additional torque setting process according to the embodiment of the present invention. Figure 3 The vehicle posture control process shown is executed in step S4.

[0056] When the additional torque setting process starts, in step S11, the controller 8 sets the additional torque setting process based on the Figure 3 In step S1 of the vehicle posture control process shown, the steering speed is obtained from the steering angle acquired by the steering angle sensor 34. Next, in step S12, the controller 8 determines whether the steering speed acquired in step S11 is greater than or equal to a predetermined value. If the controller 8 determines that the steering speed is greater than or equal to the predetermined value (step S12: Yes), the process proceeds to step S13.

[0057] On the other hand, if it is not determined that the steering speed is greater than the predetermined value (step S12: No), the controller 8 ends the additional torque setting process and returns to the main routine. In this case, the additional torque is 0. Figure 3 The basic torque set in step S3 of the vehicle posture control process shown becomes the final target torque.

[0058] Next, in step S13, the controller 8 determines whether the steering wheel 28 is being turned. Specifically, the controller 8 determines that the steering wheel 28 is being turned if, for example, the absolute value of the steering angle obtained from the steering angle sensor 34 is increasing (i.e., the steering angle of the steering wheel 28 is moving away from the neutral position). On the other hand, the controller 8 determines that the steering wheel 28 is being returned (i.e., not being turned) if, for example, the absolute value of the steering angle obtained from the steering angle sensor 34 is decreasing (i.e., the steering angle of the steering wheel 28 is approaching the neutral position). If the controller 8 determines that the steering wheel 28 is being turned (step S13: "YES"), the process proceeds to step S14.

[0059] Next, in step S14, the controller 8 obtains the reduction torque based on the steering speed. Specifically, before obtaining the reduction torque, the controller 8 first obtains the reduction torque based on the following example: Figure 5 The relationship between the steering speed and the additional deceleration shown in the map (A) is used to set the additional deceleration corresponding to the current steering speed. The additional deceleration is the forward deceleration that should be added to the vehicle 1 in response to the steering wheel operation in order to control the vehicle posture according to the driver's intention to turn the steering wheel 28.

[0060] exist Figure 5 In (A), the horizontal axis represents the steering speed and the vertical axis represents the additional deceleration. Figure 5 As shown in (A), when the steering speed is below the threshold value S1, the additional deceleration is 0. When the steering speed exceeds the threshold value S1, as the steering speed increases, the additional deceleration corresponding to the steering speed gradually approaches the prescribed upper limit value AD. max That is, as the steering speed increases, the additional deceleration increases, and the rate of increase in the amount of increase becomes smaller. max The deceleration is set to a level that does not make the driver feel that there is control intervention even if the vehicle 1 is decelerated by the steering wheel operation (for example, 0.5 m / s 2 ≈0.05G). When the steering speed becomes greater than a predetermined value, the additional deceleration is maintained at the upper limit AD. max .

[0061] The controller 8 then acquires the reduction torque based on the additional deceleration thus set. Specifically, the controller 8 determines the reduction torque required to achieve the additional deceleration by reducing the base torque based on the current vehicle speed, gear stage, road gradient, and the like.

[0062] Next, in step S15, the controller 8 sets the reduction torque in this processing cycle based on the reduction torque acquired in step S14 and a threshold value (predetermined and stored in a memory, etc.) that determines the upper limit of the rate of change of the reduction torque so that the rate of change of the reduction torque is below the threshold value. After step S15, the controller 8 ends the additional torque setting process and returns to the main routine. In this case, Figure 3 In step S5 of the vehicle posture control process, the controller 8 sets the final target torque based on the basic torque set in step S3 and the reduction torque set in step S15.

[0063] In addition, in step S13, when the controller 8 determines that the steering wheel 28 is not being turned (step S13: "No"), specifically, for example, when the absolute value of the steering angle obtained from the steering angle sensor 34 is decreasing (that is, the steering angle of the steering wheel 28 is approaching the neutral position), the controller 8 enters step S16.

[0064] Next, in step S16, the controller 8 obtains the increase torque based on the steering speed. Specifically, before setting the increase torque, the controller 8 first obtains the increase torque based on the steering speed. Figure 5 The relationship between steering speed and additional acceleration shown in the map (B) is used to set the additional acceleration corresponding to the current steering speed. This additional acceleration is the forward acceleration that should be added to the vehicle 1 in response to the steering wheel operation in order to control the vehicle posture according to the driver's intention to return the steering wheel 28.

[0065] exist Figure 5 In (B), the horizontal axis represents the steering speed and the vertical axis represents the additional acceleration. Figure 5 As shown in (B), when the steering speed is below the threshold value S2, the additional acceleration is 0. When the steering speed exceeds the threshold value S2, as the steering speed increases, the additional acceleration corresponding to the steering speed gradually approaches the prescribed upper limit value AA. max That is, as the steering speed increases, the additional acceleration increases, and the rate of increase in the amount of increase becomes smaller. max The acceleration is set to a level that does not make the driver feel that there is control intervention even if the vehicle 1 is accelerated by the steering wheel operation (for example, 0.5 m / s 2 ≈0.05G). When the steering speed becomes greater than a predetermined value, the additional acceleration is maintained at the upper limit value AA. max .

[0066] The controller 8 then obtains the additional torque based on the additional acceleration thus set. Specifically, the controller 8 determines the additional torque required to achieve the additional acceleration by increasing the basic torque based on the current vehicle speed, gear stage, road gradient, and the like.

[0067] Next, in step S17, the controller 8 determines whether the steering angle obtained from the steering angle sensor 34 is within a predetermined angle (e.g., within 30 degrees clockwise and counterclockwise) from the neutral position (i.e., steering angle 0). If the controller 8 determines that the steering angle is within the predetermined angle from the neutral position (step S17: "YES"), that is, if the steering wheel being turned is within a range close to the neutral position, the process proceeds to step S18.

[0068] Next, in step S18, the controller 8 obtains a correction gain for correcting the increase torque. Specifically, the controller 8 obtains a correction gain for correcting the increase torque based on Figure 6 The correction gain corresponding to the current steering angle is obtained from the relationship between the steering angle and the correction gain shown in the map. This correction gain is a correction gain that multiplies the additional torque so that the forward acceleration applied to the vehicle 1 decreases as the steering wheel 28 approaches the neutral position when the steering wheel 28 is turned back.

[0069] exist Figure 6 In the figure, the horizontal axis represents the steering angle and the vertical axis represents the correction gain. Figure 6 As shown in FIG. 1 , when the steering angle is a predetermined angle A1 (e.g., 30 degrees), the correction gain is 1. When the steering angle is less than the predetermined angle A1, as the steering angle approaches 0 degrees, that is, as the steering wheel 28 approaches the neutral position, the correction gain corresponding to the steering angle decreases. Furthermore, when the steering angle is 0 degrees, that is, when the steering wheel 28 is in the neutral position, the correction gain is 0. In addition, the rate of change of the correction gain corresponding to the change in the steering angle ( Figure 6 The slope of the graph shown) is smaller.

[0070] Next, in step S19, controller 8 corrects the boost torque obtained in step S16 using the correction gain obtained in step S18. Specifically, controller 8 multiplies the boost torque obtained in step S16 by the correction gain obtained in step S18. This correction ensures that, when the steering wheel 28 is turned back, the boost torque decreases as the steering angle approaches 0 degrees, provided the steering angle is within a predetermined angle A1 from the neutral position. Furthermore, when the steering angle reaches 0 degrees, the boost torque becomes zero.

[0071] Next, in step S20, the controller 8 sets the increase torque in this processing cycle based on the increase torque corrected in step S19 and a threshold value (predetermined and stored in a memory, etc.) that determines the upper limit of the rate of change of the increase torque, so that the rate of change of the increase torque is below the threshold value.

[0072] If, in step S17, the controller 8 determines that the steering angle is not within the predetermined angle from the neutral position (step S17: No), that is, if the steering wheel being returned has not entered a range close to the neutral position, the controller 8 does not perform correction of the incremental torque and proceeds to step S20. In this case, in step S20, the controller 8 sets the incremental torque for the current processing cycle based on the incremental torque acquired in step S16 and a threshold value (predetermined and stored in memory, etc.) that determines the upper limit of the rate of change of the incremental torque, so that the rate of change of the incremental torque is below the threshold value.

[0073] After step S20, the controller 8 ends the additional torque setting process and returns to the main routine. Figure 3 In step S5 of the vehicle posture control process, the controller 8 sets the final target torque based on the basic torque set in step S3 and the increase torque set in step S20.

[0074] <Functions and Effects>

[0075] Next, refer to Figure 7 The operation and effects of the vehicle control system according to the embodiment of the present invention are explained with reference to a timing chart. Figure 7 This is a time chart when the vehicle posture control based on the present embodiment is performed. Figure 7 In the figure, the horizontal axis represents time. In addition, the vertical axis represents (a) steering angle, (b) steering speed, (c) additional torque (including torque reduction and torque increase), and (d) final target torque. Figure 7 In (c) and (d), the solid line indicates that Figure 6 The illustrated correction gain shows changes in the increased torque and the final target torque when the increased torque is applied, and the dotted line shows changes in the increased torque and the final target torque when the correction gain is not applied.

[0076] Figure 7 The example shows the following situation: Figure 7As shown in (a), first, the steering wheel 28 is turned clockwise (CW) from the neutral position, and then the rotational position of the steering wheel 28 is maintained at a certain steering angle. Then, the steering wheel 28 is turned back until it returns to the neutral position. Then, the steering wheel 28 is continuously turned counterclockwise (CCW) through the neutral position, and then the rotational position of the steering wheel 28 is maintained at a certain steering angle.

[0077] As the steering wheel 28 is turned clockwise (CW) from the neutral position, the clockwise (CW) steering speed (absolute value) increases. When the steering speed is greater than a threshold value S1 at time t1, the controller 8 sets a reduction torque based on the steering speed and performs torque reduction control to reduce the torque generated by the electric motor 20, thereby adding forward deceleration to the vehicle 1. While the steering speed is increasing, the controller 8 increases the reduction torque (absolute value) in accordance with the steering speed. Then, when the steering speed becomes constant, the reduction torque is maintained constant. Furthermore, as the steering speed decreases, the reduction torque (absolute value) decreases accordingly.

[0078] Thereafter, the steering wheel 28 is kept turned, and when the steering speed becomes less than the threshold value S1 at time t2, the controller 8 ends the torque reduction control and the additional torque becomes 0. That is, the forward deceleration added to the vehicle 1 becomes zero.

[0079] Thereafter, as the steering wheel 28 is turned counterclockwise (CCW) toward the neutral position from the steered state, the counterclockwise (CCW) steering speed (absolute value) increases. When the steering speed exceeds threshold value S2 at time t3, controller 8 sets the boost torque based on the steering speed and performs torque boost control to increase the torque generated by the electric motor 20, thereby adding forward acceleration to vehicle 1. While the steering speed is increasing, controller 8 increases the boost torque (absolute value) in accordance with the steering speed. Then, when the steering speed becomes constant, controller 8 maintains the boost torque constant.

[0080] Afterward, the steering wheel 28, which has been returned, approaches a neutral position. When the steering angle (absolute value) is less than A1 at time t4, the controller 8 applies a correction gain to the incremental torque and performs torque increase control using the corrected incremental torque. As described above, the controller 8 is configured such that as the steering angle approaches 0 degrees, the correction gain corresponding to that steering angle decreases, reaching 0 at the steering angle of 0 degrees. Therefore, the controller 8 decreases the incremental torque (absolute value) as the steering angle decreases, and at time t5, when the steering angle is 0 degrees, the incremental torque is set to 0. Thus, when the steering wheel 28 is returned, the forward acceleration applied to the vehicle 1 decreases as the steering angle decreases below A1, reaching 0 at the steering angle of 0 degrees at time t5.

[0081] Subsequently, at time t5, when the steering wheel 28 passes through the neutral position and is turned counterclockwise (CCW), the controller 8 sets the reduction torque based on the steering speed and performs torque reduction control to reduce the torque generated by the electric motor 20, thereby adding forward deceleration to the vehicle 1. At time t5, when the steering wheel 28 transitions from the neutral position and the steering wheel 28 is switched from a return operation to a turning operation, the steering speed (absolute value) is constant and equal to or greater than a threshold value S1. Therefore, when the turning operation begins at time t5, the controller 8 immediately increases the reduction torque (absolute value) in accordance with the steering speed, while limiting the rate of change of the reduction torque to below a predetermined threshold value. The controller 8 then increases the reduction torque (absolute value) until it reaches a value corresponding to the steering speed. As the steering speed decreases, the reduction torque (absolute value) decreases accordingly. Subsequently, at time t6, when the steering speed falls below the threshold value S1, the controller 8 terminates the torque reduction control, and the additional torque becomes zero. In other words, the forward deceleration added to the vehicle 1 becomes zero.

[0082] Thus, in this embodiment, when the steering wheel 28 is turned back from the state in which it is turned in one direction, the controller 8 performs torque increase control until the steering wheel 28 returns to the neutral position (from time t3 to t5) so as to add forward acceleration to the vehicle 1. Then, when the steering wheel 28 is turned in the other direction after passing the neutral position (after time t5), the controller 8 terminates the torque increase control so as not to add forward acceleration to the vehicle 1. Figure 7 Continuing the torque increase control as indicated by the dashed lines in (c) and (d) prevents the increase in torque generated by the motor 20 from adding forward acceleration to the vehicle 1. Therefore, when the steering wheel 28 passes through the neutral position after the steering operation and is then turned, the driver does not feel uncomfortable, and the maneuverability and stability of the vehicle 1 can be improved.

[0083] Furthermore, in this embodiment, when the steering wheel 28 is turned back from a state in which the steering wheel is turned in one direction and then turned in the other direction through the neutral position, the controller 8 performs torque reduction control to apply forward deceleration to the vehicle 1. This can suppress any discomfort caused to the driver, quickly apply forward deceleration to the vehicle 1 during the turning operation after crossing the neutral position, and improve maneuverability and stability during the turning operation of the steering wheel 28 after crossing the neutral position, thereby smoothing the behavior of the vehicle 1.

[0084] Furthermore, in this embodiment, when the steering wheel 28 is returned from being turned in one direction, the controller 8 corrects the added torque so that the closer the steering wheel 28 approaches the neutral position, the smaller the forward acceleration applied to the vehicle 1. This prevents a sudden change in the added torque when the steering wheel 28 crosses the neutral position, thus preventing any discomfort to the driver.

[0085] Furthermore, in this embodiment, the controller 8 sets the additional torque based on at least the steering angle detected by the steering angle sensor 34 , and thus can quickly control the vehicle posture to improve the responsiveness and stability of the vehicle behavior to the driver's steering wheel operation.

[0086] Furthermore, in the present embodiment, the controller 8 controls the torque generated by the motor generator 20 , and therefore can execute the torque reduction control and the torque increase control with high responsiveness.

[0087] <Modification>

[0088] While the above description illustrates an embodiment in which the present invention is applied to a vehicle 1 having an electric motor 20 as a prime mover (driving force source), the present invention can also be applied to a vehicle having an engine as a prime mover. In this case, to achieve additional torque during vehicle posture control, for example, the engine's ignition timing can be controlled. Specifically, when executing torque reduction control, the engine's ignition timing can be retarded relative to a base ignition timing (the ignition timing corresponding to the base torque), while when executing torque increase control, the engine's ignition timing can be advanced relative to the base ignition timing.

[0089] Furthermore, in the above-described embodiment, the torque (driving torque) output by the electric motor 20 is varied to achieve additional torque during vehicle posture control. However, in other examples, the regenerative torque input to the electric motor 20 can be varied instead of the driving torque of the electric motor 20 to achieve additional torque during vehicle posture control. For example, when vehicle posture control is executed while the electric motor 20 is regenerating (e.g., when the accelerator opening is 0), the regenerative torque input to the electric motor 20 to brake the vehicle 1 can be increased or decreased to achieve torque reduction and torque increase during vehicle posture control. Specifically, when torque reduction control is executed, the regenerative torque (absolute value) can be increased, while when torque increase control is executed, the regenerative torque (absolute value) can be decreased.

[0090] Furthermore, in the above-described embodiment, the controller 8 obtains the additional torque based on at least the steering angle detected by the steering angle sensor 34. However, the additional torque may be obtained based on the driving conditions of the vehicle 1 (lateral acceleration, yaw rate, slip rate, etc.) other than accelerator pedal operation, in place of the steering angle, or in addition to the steering angle. For example, the controller 8 may obtain the additional torque by setting the additional acceleration or deceleration based on the lateral acceleration input from the acceleration sensor 44 or the lateral jerk obtained by time-differentiating the lateral acceleration.

Claims

1. A vehicle control system, characterized in that: have: a driving force source for generating torque for driving driving wheels of the vehicle; a steering wheel, operated by the driver; a steering angle sensor for detecting a steering angle corresponding to an operation of the steering wheel; as well as a controller that controls the torque generated by the driving force source in order to control the vehicle posture based on the steering angle detected by the steering angle sensor, The controller is configured to apply forward deceleration to the vehicle when the steering wheel is turned in one direction, apply forward acceleration to the vehicle when the steering wheel is turned back from the state in which the steering wheel was turned in one direction until the steering wheel returns to a neutral position, and then set the torque generated by the driving force source based on the steering speed of the steering wheel so as not to apply forward acceleration to the vehicle when the steering wheel is turned in the other direction after passing the neutral position. The controller is configured to control the torque generated by the driving force source in such a manner that the closer the steering wheel approaches the neutral position, the smaller the forward acceleration applied to the vehicle, regardless of the steering speed of the steering wheel, when the steering wheel is turned back from a state in which the steering wheel is turned in one direction until the steering wheel returns to a neutral position.

2. The vehicle control system according to claim 1, characterized in that: The controller is configured to control the torque generated by the driving force source so that a rate of change of torque when the torque generated by the driving force source is reduced or increased in response to an operation of the steering wheel is equal to or less than a predetermined threshold value.

3. The vehicle control system according to claim 1, characterized in that: The controller is configured to control the torque generated by the driving force source in such a manner that the closer the steering wheel approaches the neutral position, the smaller the forward acceleration applied to the vehicle is, regardless of the steering speed of the steering wheel, until the steering wheel returns to the neutral position when the steering wheel is turned back from a state in which the steering wheel is turned in one direction and the steering angle detected by the steering angle sensor is within a specified angle from the neutral position.

4. The vehicle control system according to claim 2, characterized in that: The controller is configured to control the torque generated by the driving force source in such a manner that the closer the steering wheel approaches the neutral position, the smaller the forward acceleration applied to the vehicle is, regardless of the steering speed of the steering wheel, until the steering wheel returns to the neutral position when the steering wheel is turned back from a state in which the steering wheel is turned in one direction and the steering angle detected by the steering angle sensor is within a specified angle from the neutral position.

5. The vehicle control system according to any one of claims 1 to 4, characterized in that: The driving force source includes an electric motor, and the controller controls the torque generated by the electric motor.

6. The vehicle control system according to any one of claims 1 to 4, characterized in that: The controller is configured to reduce the driving torque generated by the driving force source in order to add deceleration to the vehicle when the steering wheel is turned, based on the steering angle detected by the steering angle sensor, and to increase the driving torque generated by the driving force source in order to add acceleration to the vehicle when the steering wheel is returned.

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