Vehicle Control Systems

Abstract

To improve maneuverability and stability of a vehicle without giving discomfort to a driver when a steering wheel is operated to return from a state of being turned in one direction, and is then operated to be turned in the other direction after passing through a neutral position.SOLUTION: In a vehicle control system, when a steering wheel 28 is being operated to return from a state of being turned in one direction, a controller 8 executes torque increase control so as to add forward acceleration to a vehicle 1 until the steering wheel 28 returns to a neutral position. Then, when the steering wheel 28 is being operated to be turned in the other direction after passing through the neutral position, the controller 8 ends the torque increase control so as not to add the forward acceleration to the vehicle 1.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a vehicle control system that controls the attitude of a vehicle in response to steering. [Background technology]

[0002] Conventionally, there is known a technology for controlling vehicle attitude by causing deceleration or acceleration in the vehicle in response to the operation of a steering wheel (hereinafter also simply referred to as "steering") by a driver, thereby improving the responsiveness and stability of the vehicle behavior in response to steering operations.

[0003] For example, Patent Document 1 describes a vehicle motion control in which, when the vehicle is turning, the vehicle is first decelerated when the steering wheel is turned inward, and then accelerated when the steering wheel is turned back outward. This improves the maneuverability and stability of the vehicle from entering a corner to exiting the corner. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2015 / 151565 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to realize the technology described in the above Patent Document 1, it is conceivable to perform control (torque reduction control) to reduce the driving torque generated by the driving force source of the vehicle in order to decelerate the vehicle when the steering is turned inward, and to perform control (torque increase control) to increase the driving torque generated by the driving force source in order to accelerate the vehicle when the steering is turned back. Such control can be easily realized in a vehicle (e.g., an electric vehicle) equipped with an electric motor (electric motor). This is because an electric motor can quickly increase and decrease the torque it outputs.

[0006] For example, when a vehicle travels through an S-shaped corner, first, torque reduction control is executed when the steering wheel is turned inward, and then torque increase control is executed when the steering wheel is turned back. It is considered that the torque increase control ends when the steering wheel crosses the neutral position (i.e., the steering angle is 0°) and switches to turning. Here, even after the steering wheel that has been turned back passes the neutral position, the torque increase control may not end immediately but may continue for a while due to reasons such as restrictions on sudden changes in torque. In this case, even during the steering wheel turning operation after passing the neutral position, the torque generated by the driving force source is increased by the torque increase control that has not been completed, and acceleration is continued to be applied to the vehicle. As a result, the drivability and stability of the vehicle are not improved, and the driver may feel uncomfortable.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to improve the maneuverability and stability of a vehicle in a vehicle control system that controls the vehicle posture in response to steering, when the steering wheel is turned back from one side and then turned to the other side after passing the neutral position, without giving the driver any discomfort. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a vehicle control system including a driving force source that generates a torque for driving drive wheels of a vehicle, a steering wheel operated by a driver, a steering angle sensor that detects a steering angle corresponding to the operation of the steering wheel, and a controller configured to control the torque generated by the driving force source so as to control the vehicle attitude based on the steering angle detected by the steering angle sensor, the controller comprising: When the steering wheel is turned to one side, forward deceleration is applied to the vehicle. When the steering wheel is turned back from a state in which it is turned to one side, forward acceleration is applied to the vehicle until the steering wheel returns to the neutral position, and when the steering wheel passes the neutral position and is then turned to the other side, forward acceleration is not applied to the vehicle. Based on steering wheel speed Torque generated by the driving force source Set It is configured as follows: The controller is configured to control the torque generated by the driving force source so that, when the steering wheel is turned back from a state in which the steering wheel is turned to one side, the forward acceleration applied to the vehicle becomes smaller as the steering wheel approaches the neutral position, regardless of the steering speed of the steering wheel, until the steering wheel returns to the neutral position. It is characterized by the fact that

[0009] According to the present invention configured in this manner, when the steering wheel is turned beyond the neutral position, unlike the case where torque control for applying forward acceleration is continued, it is possible to prevent forward acceleration from being applied to the vehicle due to an increase in the torque generated by the driving force source. Therefore, when the steering wheel is turned beyond the neutral position after a return operation, it is possible to improve the maneuverability and stability of the vehicle without giving an uncomfortable feeling to the driver. In addition, while suppressing the occurrence of discomfort felt by the driver, forward deceleration can be quickly applied to the vehicle during turning of the steering wheel after the steering wheel has been turned back and crossed the neutral position, thereby improving the maneuverability and stability when turning the steering wheel after crossing the neutral position, and making the vehicle behavior smoother. In addition, it is possible to prevent a sudden change in the forward acceleration when the steering wheel being turned back crosses the neutral position, and to prevent the driver from feeling uncomfortable. In addition, the vehicle attitude can be quickly controlled so as to improve the responsiveness and stability of the vehicle behavior in response to the steering operation of the driver.

[0010] In the present invention, preferably, the controller A rate of change in torque generated by the driving force source in response to an operation of the steering wheel is reduced or increased to a predetermined threshold value or less. Thus, the torque generated by the driving force source of The control unit is configured to:

[0011] In the present invention, preferably, the controller detects when the steering wheel is turned back from a state in which the steering wheel is turned to one side. And, the steering angle detected by the steering angle sensor is within a predetermined angle from the neutral position. until the steering wheel returns to the neutral position. Regardless of the steering speed of the steering wheel,The torque generated by the driving force source is controlled so that the forward acceleration applied to the vehicle decreases as the steering wheel approaches the neutral position. According to the present invention configured in this manner, it is possible to prevent a sudden change in forward acceleration when the steering wheel being turned back crosses the neutral position, thereby preventing the driver from feeling uncomfortable.

[0013] 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. According to the present invention configured in this manner, it is possible to control the torque generated by the driving force source with high responsiveness. Effect of the Invention

[0014] According to the present invention, in a vehicle control system that controls vehicle posture in response to 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 after passing the neutral position, the maneuverability and stability of the vehicle can be improved without giving an uncomfortable feeling to the driver. [Brief description of the drawings]

[0015] [Figure 1] 1 is a block diagram showing a schematic overall configuration of a vehicle according to an embodiment of the present invention; [Diagram 2] 1 is a block diagram showing an electrical configuration of a vehicle according to an embodiment of the present invention. [Diagram 3] 4 is a flowchart of a vehicle attitude control process according to an embodiment of the present invention. [Figure 4] 5 is a flowchart of an additional torque setting process according to an embodiment of the present invention. [Diagram 5] 4 is a map showing a relationship between steering speed and additional torque according to an embodiment of the present invention. [Figure 6] 4 is a map showing a relationship between a steering angle and a correction gain for an increased torque according to an embodiment of the present invention. [Figure 7] 4 is a time chart when the vehicle attitude control according to the embodiment of the present invention is executed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicle control system according to an embodiment of the present invention will now be described with reference to the accompanying drawings.

[0017] <Vehicle configuration> First, a vehicle to which a vehicle control system according to an embodiment of the present invention is applied will be described with reference to Figures 1 and 2. Figure 1 is a block diagram showing a schematic overall configuration of a vehicle according to an embodiment of the present invention, and Figure 2 is a block diagram showing an electrical configuration of the vehicle according to an embodiment of the present invention.

[0018] As shown in Fig. 1, a motor generator 20 (rotating electric machine) is mounted on the front of the vehicle body of the vehicle 1 as a prime mover (power source) for driving the left and right front wheels 2, which are drive wheels. The 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 including an elastic member (typically a spring), a suspension arm, etc.

[0019] The motor generator 20 has a function of driving the front wheels 2 (i.e., a function as a prime mover (electric motor)) and a function of being driven by the front wheels 2 to generate regenerative power (i.e., a function as a generator). Power is transmitted between the motor generator 20 and the front wheels 2 via a transmission 6, and the motor generator 20 is controlled by a controller 8 via an inverter 22. Furthermore, the motor generator 20 is connected to a battery 24, and is supplied with power from the battery 24 when generating driving power, and supplies power to the battery 24 to charge the battery 24 when regenerating power.

[0020] In the vehicle 1, the rotating shaft of the motor generator 20 and the rotating shaft of the transmission 6 are connected via a clutch 62 that can be engaged and disengaged. For example, the clutch 62 is controlled to be switched between engaged and disengaged by utilizing the hydraulic pressure of the transmission 6.

[0021] The vehicle 1 has a steering device 26 including a steering wheel (steering wheel) 28 and a steering shaft 30, a steering angle sensor 34 that detects the steering angle of the steering device 26 from the rotation angle of the steering wheel 28 and the position of a steering rack (not shown), an accelerator opening sensor 36 that detects an accelerator opening corresponding to the depression amount of the accelerator pedal, a brake depression amount sensor 38 that detects the depression amount of the brake pedal, a vehicle speed sensor 40 that detects the vehicle speed, a yaw rate sensor 42 that detects the yaw rate, and an acceleration sensor 44 that detects the acceleration. Each of these sensors outputs its detection value to the controller 8.

[0022] In addition, instead of the rotation angle of the steering wheel 28, the steering angle sensor 34 may detect various state quantities in the steering system (such as the rotation angle of the motor that adds assist torque, or the displacement of the rack in a rack and pinion) or the steered angle (tire angle) of the front wheels 2 as the steering angle.

[0023] The vehicle 1 also includes a brake control system 48 that supplies brake fluid pressure to wheel cylinders and brake calipers of braking devices (braking devices) 46 provided on each wheel. The brake control system 48 includes a hydraulic pump 50 that generates brake fluid pressure required to generate braking force in the braking devices 46 provided on each wheel. The hydraulic pump 50 is driven by power supplied from the battery 24, for example, and is capable of generating brake fluid pressure required to generate braking force in each braking device 46 even when the brake pedal is not depressed.

[0024] The brake control system 48 also includes a valve unit 52 (specifically, a solenoid valve) provided in a hydraulic pressure supply line to the brake device 46 of each wheel for controlling the hydraulic pressure supplied from the hydraulic pump 50 to the brake device 46 of each wheel. For example, the opening degree 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 the brake device 46 of each wheel. The hydraulic pressure sensor 54 is disposed, for example, at a connection between each valve unit 52 and the hydraulic pressure supply line downstream of the valve unit 52, detects the hydraulic pressure downstream of each valve unit 52, and outputs the detected value to the controller 8.

[0025] Such a brake control system 48 calculates the hydraulic pressure to be supplied independently to each wheel cylinder and brake caliper 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 in accordance with the calculated hydraulic pressure.

[0026] As shown in FIG. 2, the controller 8 according to this embodiment outputs control signals to control the motor generator 20, the clutch 62, and the hydraulic pump 50 and valve unit 52 of the brake control system 48 based on detection signals output by various driving condition sensors that detect the driving condition of the vehicle 1, in addition to the detection signals from the above-mentioned sensors 18, 34, 36, 38, 40, 42, 44, and 54.

[0027] The controller 8 includes circuits and is a controller based on a well-known microcomputer. The controller 8 includes one or more microprocessors as a central processing unit (CPU) that executes programs, a memory configured, for example, of a random access memory (RAM) or a read only memory (ROM) that stores programs and data, and an input / output bus for inputting and outputting electrical signals. The system including the steering wheel 28, the steering angle sensor 34, and the controller 8 corresponds to the vehicle control system of the present invention.

[0028] <Vehicle attitude control> The vehicle attitude control according to the embodiment of the present invention will be described below. In this embodiment, the controller 8 basically performs the following control to control the vehicle attitude (vehicle behavior) based on the steering angle detected by the steering angle sensor 34. First, when the steering wheel 28 is turned away from the neutral position (i.e., when the steering angle is increasing), the controller 8 performs torque reduction control to reduce the torque generated by the motor generator 20 so as to apply forward deceleration (i.e., deceleration that slows down the forward moving vehicle 1) to the vehicle 1. Also, when the steering wheel 28 is turned back toward the neutral position (i.e., when the steering angle is decreasing), the controller 8 performs torque increase control to increase the torque generated by the motor generator 20 so as to apply forward acceleration (i.e., acceleration that accelerates the forward moving vehicle 1) to the vehicle 1. By performing such vehicle attitude control, it is possible to improve the turning performance, maneuverability, and steering ability of the vehicle 1 from entering a corner to exiting a corner.

[0029] In the following, the torque applied in the torque reduction control, that is, the negative torque added to the torque generated by the motor generator 20 to apply forward deceleration to the vehicle 1, is referred to as the "reduced torque". In addition, the torque applied in the torque increase control, that is, the positive torque added to the torque generated by the motor generator 20 to apply forward acceleration to the vehicle 1, is referred to as the "increased torque". In addition, when the reduced torque and the increased torque are not distinguished, they are referred to as the "added torque". In the vehicle attitude control, such reduced torque or increased torque is applied. Specifically, in the vehicle attitude control, the reduced torque or increased torque is subtracted from or added to the torque (hereinafter referred to as the "basic torque") that the motor generator 20 should generate to realize acceleration according to the driving state (such as the accelerator opening) of the vehicle 1. In the following, the torque obtained by subtracting or adding the reduced torque or increased torque from or to the basic torque, that is, the torque that the motor generator 20 should ultimately generate, is referred to as the "final target torque".

[0030] Next, an overall flow of vehicle attitude control according to an embodiment of the present invention will be described with reference to Fig. 3. Fig. 3 is a flowchart of a vehicle attitude control process according to an embodiment of the present invention.

[0031] The vehicle attitude control process in Fig. 3 is started when the ignition of the vehicle 1 is turned on and the power is supplied to the controller 8, and is repeatedly executed at a predetermined period (for example, 50 ms). When the vehicle attitude control process is started, in step S1, the controller 8 acquires various sensor information related to the driving state of the vehicle 1. Specifically, the controller 8 acquires detection signals output by the various sensors described above, including the steering angle detected by the steering angle sensor 34, the accelerator opening detected by the accelerator opening sensor 36, the brake pedal depression amount detected by the brake depression amount sensor 38, the vehicle speed detected by the vehicle speed sensor 40, the yaw rate detected by the yaw rate sensor 42, the acceleration detected by the acceleration sensor 44, the hydraulic pressure detected by the hydraulic pressure sensor 54, the gear stage currently set in the transmission 6 of the vehicle 1, and the like, as information related to the driving state.

[0032] Next, in step S2, the controller 8 sets a target acceleration based on the driving state of the vehicle 1 acquired in step S1. Specifically, for example, the controller 8 selects an acceleration characteristic map corresponding to the current vehicle speed and gear stage from among acceleration characteristic maps (created in advance and stored in a memory or the like) defined for various vehicle speeds and various gear stages, and sets a target acceleration corresponding to the current accelerator opening degree with reference to the selected acceleration characteristic map.

[0033] Next, in step S3, controller 8 determines the basic torque of motor generator 20 for achieving the target acceleration determined in step S2. In this case, controller 8 determines the basic torque within the range of torque that motor generator 20 can output, based on the current vehicle speed, gear stage, road surface gradient, road surface μ, etc.

[0034] In parallel with the processing of steps S2 and S3, in step S4, the controller 8 executes an additional torque setting process described later (see FIG. 4) and sets an additional torque (reduced torque or increased torque) to be applied to the torque generated by the motor generator 20 in order to control the vehicle attitude, based on the steering speed of the steering wheel 28, etc.

[0035] Next, after executing steps S2 to S4, in step S5, the controller 8 sets a final target torque based on the basic torque set in step S3 and the additional torque set in step S4. Basically, the controller 8 calculates the final target torque by subtracting the reduced torque from the basic torque or adding the increased torque to the basic torque.

[0036] Next, in step S6, the controller 8 sets a command value (inverter command value) for the inverter 22 to realize the final target torque set in step S5. That is, the controller 8 sets an inverter command value (control signal) for generating the final target torque from the motor generator 20. Then, in step S7, the controller 8 outputs the inverter command value set in step S6 to the inverter 22. After this step S7, the controller 8 ends the vehicle attitude control process.

[0037] Next, the additional torque setting process according to the embodiment of the present invention will be described with reference to Fig. 4. Fig. 4 is a flowchart of the additional torque setting process according to the embodiment of the present invention. This additional torque setting process is executed in step S4 of the vehicle attitude control process shown in Fig. 3.

[0038] When the additional torque setting process is started, in step S11, the controller 8 acquires a steering speed based on the steering angle acquired from the steering angle sensor 34 in step S1 of the vehicle attitude control process shown in Fig. 3. Next, in step S12, the controller 8 determines whether the steering speed acquired in step S11 is equal to or greater than a predetermined value. As a result, when it is determined that the steering speed is equal to or greater than the predetermined value (step S12: Yes), the controller 8 proceeds to step S13.

[0039] On the other hand, if it is not determined that the steering speed is equal to or 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 becomes 0, and the basic torque set in step S3 of the vehicle attitude control process shown in FIG. 3 becomes the final target torque.

[0040] Next, in step S13, the controller 8 determines whether or not the steering wheel 28 is being turned. Specifically, the controller 8 determines that the steering wheel 28 is being turned when, for example, the absolute value of the steering angle acquired 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 turned back (i.e., not being turned) when, for example, the absolute value of the steering angle acquired from the steering angle sensor 34 is decreasing (i.e., the steering angle of the steering wheel 28 is approaching the neutral position). As a result, when the controller 8 determines that the steering wheel 28 is being turned (step S13: Yes), the controller 8 proceeds to step S14.

[0041] Next, in step S14, the controller 8 obtains the reduced torque based on the steering speed. Specifically, before obtaining the reduced torque, the controller 8 first sets the added deceleration corresponding to the current steering speed based on the relationship between the steering speed and the added deceleration as shown in the map of Fig. 5(A). This added deceleration is a forward deceleration to be added to the vehicle 1 in response to the steering operation in order to control the vehicle attitude in accordance with the intention of the driver's turning operation of the steering wheel 28. In Fig. 5(A), the horizontal axis indicates the steering speed, and the vertical axis indicates the added deceleration. As shown in Fig. 5(A), when the steering speed is equal to or less than a threshold value S1, the added deceleration is 0. When the steering speed exceeds the threshold value S1, as the steering speed increases, the added deceleration corresponding to this steering speed increases up to a predetermined upper limit value AD max That is, the higher the steering speed, the higher the added deceleration becomes, and the rate of increase in the amount of increase becomes smaller. max is set to a deceleration level that the driver does not feel that a control intervention has occurred even if the vehicle 1 is decelerated in response to the steering operation (for example, 0.5 m / s 2 ≒0.05G). Furthermore, when the steering speed exceeds a certain value, the additional deceleration is increased to the upper limit D max is maintained. Then, the controller 8 obtains the reduction torque based on the added deceleration thus set. Specifically, the controller 8 determines the reduction torque required to realize the added deceleration by reducing the basic torque based on the current vehicle speed, gear stage, road surface gradient, etc.

[0042] Next, in step S15, the controller 8 sets the reduction torque in the current processing cycle based on the reduction torque acquired in step S14 and a threshold value (predetermined and stored in a memory or the like) that defines an upper limit of the change rate of the reduction torque so that the change rate of the reduction torque is equal to or lower than the threshold value. After step S15, the controller 8 ends the additional torque setting process and returns to the main routine. In this case, in step S5 of the vehicle attitude control process in FIG. 3, 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.

[0043] Also, in step S13, if the controller 8 determines that the steering wheel 28 is not being turned (step S13: No), specifically, for example, if the absolute value of the steering angle acquired from the steering angle sensor 34 is decreasing (i.e., if the steering angle of the steering wheel 28 is approaching the neutral position), the controller 8 proceeds to step S16.

[0044] Next, in step S16, the controller 8 obtains the increased torque based on the steering speed. Specifically, before setting the increased torque, the controller 8 first sets the added acceleration corresponding to the current steering speed based on the relationship between the steering speed and the added acceleration shown in the map of Fig. 5(B). This added acceleration is a forward acceleration to be added to the vehicle 1 in response to the steering operation in order to control the vehicle attitude in accordance with the driver's intention of the return operation of the steering wheel 28. In Fig. 5B, the horizontal axis indicates the steering speed, and the vertical axis indicates the added acceleration. As shown in Fig. 5B, when the steering speed is equal to or less than a threshold value S2, the added acceleration is 0. When the steering speed exceeds the threshold value S2, as the steering speed increases, the added acceleration corresponding to this steering speed increases to a predetermined upper limit value AA max That is, the higher the steering speed, the higher the additional acceleration becomes, and the rate of increase in the additional acceleration becomes smaller. max is set to an acceleration level (for example, 0.5 m / s) that the driver does not feel that a control intervention has occurred even if the vehicle 1 is accelerated in response to the steering operation. 2 ≒0.05G). Furthermore, when the steering speed exceeds a certain value, the additional acceleration is increased to the upper limit AA max is maintained. Then, the controller 8 obtains the increased torque based on the added acceleration thus set. Specifically, the controller 8 determines the increased torque required to realize the added acceleration by increasing the basic torque based on the current vehicle speed, gear stage, road gradient, etc.

[0045] Next, in step S17, the controller 8 determines whether the steering angle acquired from the steering angle sensor 34 is within a predetermined angle (for example, within 30 degrees clockwise and counterclockwise) from the neutral position (i.e., steering angle 0). As a result, when the controller 8 determines that the steering angle is within the predetermined angle from the neutral position (step S17: Yes), that is, when the steering wheel being turned back has entered a range close to the neutral position, the controller 8 proceeds to step S18.

[0046] Next, in step S18, the controller 8 acquires a correction gain for correcting the increased torque. Specifically, the controller 8 acquires a correction gain corresponding to the current steering angle based on the relationship between the steering angle and the correction gain shown in the map of Fig. 6. This correction gain is a correction gain that is multiplied by the increased torque so that the forward acceleration applied to the vehicle 1 becomes smaller as the steering wheel 28 is closer to the neutral position when the steering wheel 28 is being turned back. In Fig. 6, the horizontal axis indicates the steering angle, and the vertical axis indicates the correction gain. As shown in Fig. 6, when the steering angle is a predetermined angle A1 (e.g., 30 degrees), the correction gain is 1. When the steering angle is smaller than the predetermined angle A1, the correction gain corresponding to this steering angle decreases as the steering angle approaches 0 degrees, that is, as the steering wheel 28 approaches the neutral position. When the steering angle is 0 degrees, that is, when the steering wheel 28 is in the neutral position, the correction gain is 0. Also, the rate of change of the correction gain in response to the change in steering angle (the slope of the graph shown in Fig. 6) is set to decrease as the steering angle approaches 0 degrees and the predetermined angle A1.

[0047] Next, in step S19, the controller 8 corrects the increased torque acquired in step S16 by the correction gain acquired in step S18. Specifically, the controller 8 multiplies the increased torque acquired in step S16 by the correction gain acquired in step S18. By performing this correction, when the steering wheel 28 is being turned back and the steering angle is within a predetermined angle A1 from the neutral position, the increased torque becomes smaller as the steering angle approaches 0 degrees. Then, when the steering angle reaches 0 degrees, the increased torque becomes 0.

[0048] Next, in step S20, the controller 8 sets the increased torque in the current processing cycle based on the increased torque corrected in step S19 and a threshold value (predetermined and stored in a memory, etc.) that defines an upper limit of the rate of change of the increased torque so that the rate of change of the increased torque is equal to or lower than the threshold value.

[0049] Furthermore, in step S17, if the controller 8 determines that the steering angle is not within a predetermined angle from the neutral position (step S17: No), that is, if the steering wheel being turned back is not in a range close to the neutral position, the controller 8 proceeds to step S20 without correcting the increased torque. In this case, in step S20, the controller 8 sets the increased torque in the current processing cycle based on the increased torque acquired in step S16 and a threshold value (predetermined and stored in a memory or the like) that defines an upper limit of the rate of change of the increased torque, so that the rate of change of the increased torque is equal to or less than the threshold value.

[0050] After step S20, the controller 8 ends the additional torque setting process and returns to the main routine. In this case, in step S5 of the vehicle attitude control process in Fig. 3, the controller 8 sets the final target torque based on the basic torque set in step S3 and the increased torque set in step S20.

[0051] <Action and Effects> Next, the operation and effect of the vehicle control system according to the embodiment of the present invention will be described with reference to the time chart of Fig. 7. Fig. 7 is a time chart when the vehicle attitude control according to the embodiment described above is executed. In Fig. 7, the horizontal axis indicates time. The vertical axis indicates, from the top, (a) steering angle, (b) steering speed, (c) additional torque (including reduced torque and increased torque), and (d) final target torque. In Figs. 7(c) and (d), the solid lines indicate the changes in the increased torque and the final target torque when the correction gain shown in Fig. 6 is applied to the increased torque, and the dotted lines indicate the changes in the increased torque and the final target torque when the correction gain is not applied to the increased torque.

[0052] The example of Figure 7 shows a case in which, as shown in Figure 7(a), first, the steering wheel 28 is turned clockwise (CW) from the neutral position, 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, and then the steering wheel 28 is continuously turned counterclockwise (CCW) past the neutral position, and then the rotational position of the steering wheel 28 is maintained at a certain steering angle.

[0053] As the steering wheel 28 starts to be turned clockwise (CW) from the neutral position, the clockwise (CW) steering speed (absolute value) increases. When the steering speed becomes equal to or greater than the threshold value S1 at time t1, the controller 8 performs torque reduction control to set a reduced torque based on the steering speed so as to apply forward deceleration to the vehicle 1, thereby reducing the torque generated by the motor generator 20. While the steering speed is increasing, the controller 8 increases the reduced torque (absolute value) according to the steering speed, and when the steering speed becomes constant, the controller 8 maintains the reduced torque constant. Furthermore, when the steering speed decreases, the controller 8 decreases the reduced torque (absolute value) accordingly.

[0054] Thereafter, when the steering wheel 28 is held in a turned state and the steering speed becomes less than the threshold value S1 at time t2, the controller 8 ends the torque reduction control and the added torque becomes 0. That is, the forward deceleration applied to the vehicle 1 becomes 0.

[0055] Thereafter, as the steering wheel 28 is turned from a fully turned state back toward the neutral position in a counterclockwise (CCW) direction, the counterclockwise (CCW) steering speed (absolute value) increases. When the steering speed reaches or exceeds the threshold value S2 at time t3, the controller 8 sets an increased torque based on the steering speed and performs torque increase control to increase the torque generated by the motor generator 20 so as to apply forward acceleration to the vehicle 1. While the steering speed is increasing, the controller 8 increases the increased torque (absolute value) according to the steering speed, and when the steering speed becomes constant, the controller 8 maintains the increased torque constant.

[0056] Thereafter, when the steering wheel 28 being turned back approaches the neutral position and the steering angle (absolute value) becomes equal to or smaller than A1 at time t4, the controller 8 applies a correction gain to the increased torque and performs torque increase control using the corrected increased torque. As described above, as the steering angle approaches 0 degrees, the correction gain corresponding to this steering angle becomes smaller, and the correction gain is set to be 0 when the steering angle is 0 degrees. Therefore, the controller 8 reduces the increased torque (absolute value) as the steering angle becomes smaller, and sets the increased torque to 0 when the steering angle becomes 0 degrees at time t5. As a result, when the steering wheel 28 is turned back, the forward acceleration applied to the vehicle 1 becomes smaller as the steering angle becomes smaller than A1, and when the steering angle becomes 0 degrees at time t5, the forward acceleration applied to the vehicle 1 becomes 0.

[0057] Thereafter, when the steering wheel 28 passes the neutral position and is turned counterclockwise (CCW) at time t5, the controller 8 performs torque reduction control to set a reduction torque based on the steering speed so as to add forward deceleration to the vehicle 1, and to reduce the torque generated by the motor generator 20. Here, at time t5, when the steering wheel 28 crosses the neutral position and the operation of the steering wheel 28 is switched from a return operation to a turning operation, the steering speed (absolute value) is constant at or above the threshold value S1. Therefore, when the turning operation is started at time t5, the controller 8 immediately increases the reduction torque (absolute value) according to the steering speed while limiting the rate of change of the reduction torque to a predetermined threshold value or less. Then, the controller 8 increases the reduction torque (absolute value) until it becomes a value corresponding to the steering speed. Furthermore, when the steering speed decreases, the reduction torque (absolute value) decreases accordingly. Thereafter, when the steering speed becomes less than the threshold value S1 at time t6, the controller 8 ends the torque reduction control, and the added torque becomes zero. In other words, the forward deceleration applied to the vehicle 1 becomes zero.

[0058] In this manner, in this embodiment, when the steering wheel 28 is turned back from a state in which it is turned to one side, the controller 8 performs torque increase control so as to apply forward acceleration to the vehicle 1 until the steering wheel 28 returns to the neutral position (from time t3 to t5), and thereafter, when the steering wheel 28 passes the neutral position and is turned to the other side (after time t5), the controller 8 ends the torque increase control so as not to apply forward acceleration to the vehicle 1. This makes it possible to prevent forward acceleration from being applied to the vehicle 1 due to an increase in the torque generated by the motor generator 20, unlike the case in which the torque increase control is continued as shown by the dotted lines in Figs. 7(c) and (d) when the steering wheel 28 is turned across the neutral position. Therefore, when the steering wheel 28 is turned back and turned past the neutral position, the controllability and stability of the vehicle 1 can be improved without giving a sense of incongruity to the driver.

[0059] In this embodiment, when the steering wheel 28 is turned back from a state in which it is turned to one side and then turned to the other side after passing the neutral position, the controller 8 performs torque reduction control so as to apply forward deceleration to the vehicle 1. This makes it possible to quickly apply forward deceleration to the vehicle 1 during turning operation after crossing the neutral position while suppressing the occurrence of discomfort felt by the driver, thereby improving the maneuverability and stability when turning the steering wheel 28 after crossing the neutral position, and making the behavior of the vehicle 1 smoother.

[0060] In addition, in this embodiment, when the steering wheel 28 is turned back from a state in which it is turned to one side, the controller 8 corrects the increased torque so that the forward acceleration applied to the vehicle 1 decreases as the steering wheel 28 approaches the neutral position until the steering wheel 28 returns to the neutral position. This makes it possible to prevent a sudden change in the applied torque when the steering wheel 28 being turned back crosses the neutral position, and to prevent the driver from feeling uncomfortable.

[0061] 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, so that the vehicle attitude can be quickly controlled to improve the responsiveness and stability of the vehicle behavior to the steering operation by the driver.

[0062] Furthermore, in this embodiment, the controller 8 controls the torque generated by the motor generator 20, and therefore can execute torque reduction control and torque increase control with high responsiveness.

[0063] <Modification> In the above, an embodiment in which the present invention is applied to the vehicle 1 having the motor generator 20 as a prime mover (driving force source) has been shown, but the present invention can also be applied to a vehicle having an engine as a prime mover. In this case, in order to realize additional torque in the vehicle attitude control, for example, the ignition timing of the engine may be controlled. That is, when the torque reduction control is executed, the ignition timing of the engine may be retarded from the reference ignition timing (the ignition timing according to the basic torque), and when the torque increase control is executed, the ignition timing of the engine may be advanced from the reference ignition timing.

[0064] In the above embodiment, the torque (driving torque) output by the motor generator 20 is changed to realize the additional torque in the vehicle attitude control, but in another example, the additional torque by the vehicle attitude control may be realized by changing the regenerative torque input to the motor generator 20 instead of the driving torque of the motor generator 20. For example, when the vehicle attitude control is executed while the motor generator 20 is regenerating (when the accelerator opening is 0, etc.), the regenerative torque input to the motor generator 20 to brake the vehicle 1 may be increased or decreased so that the reduced torque and increased torque by the vehicle attitude control are realized. That is, when the torque reduction control is executed, the regenerative torque (absolute value) may be increased, and when the torque increase control is executed, the regenerative torque (absolute value) may be decreased.

[0065] In the above embodiment, the controller 8 obtains the additional torque based on at least the steering angle detected by the steering angle sensor 34, but the additional torque may be obtained based on the driving conditions of the vehicle 1 other than the operation of the accelerator pedal (lateral acceleration, yaw rate, slip ratio, etc.) instead of or in addition to the steering angle. For example, the controller 8 may obtain the additional torque by setting the additional acceleration or additional deceleration based on the lateral acceleration input from the acceleration sensor 44 or the lateral jerk obtained by differentiating the lateral acceleration with respect to time. [Explanation of symbols]

[0066] 1 vehicle 2 wheels 8 Controller 20 Motor generator 22 Inverter 24 Battery 26 Steering Gear 28 Steering Wheel 34 Steering angle sensor 36 Accelerator opening sensor 40 Vehicle speed sensor 46 Brake device

Claims

1. A vehicle control system, comprising: a driving force source that generates torque for driving drive wheels of the vehicle; A steering wheel operated by a driver; a steering angle sensor for detecting a steering angle corresponding to an operation of the steering wheel; a controller configured to control a torque generated by the driving force source so as to control a vehicle attitude based on the steering angle detected by the steering angle sensor, the controller is configured to set a torque generated by the driving force source based on a steering speed of the steering wheel so as to impart a forward deceleration to the vehicle when the steering wheel is turned to one side, impart a forward acceleration to the vehicle when the steering wheel is turned back from one side until the steering wheel returns to a neutral position, and thereafter, when the steering wheel has passed the neutral position and is turned to the other side, not impart a forward acceleration to the vehicle; a control unit for controlling a torque generated by the driving force source when the steering wheel is turned back from a turned state to one side until the steering wheel returns to the neutral position, regardless of a steering speed of the steering wheel, so that the forward acceleration applied to the vehicle becomes smaller the closer the steering wheel is to the neutral position.

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

3. 3. The vehicle control system according to claim 1, wherein when the steering wheel is turned back from a state in which it is turned to one side and the steering angle detected by the steering angle sensor is within a predetermined angle from the neutral position, the controller is configured to control the torque generated by the driving force source so that the forward acceleration applied to the vehicle becomes smaller the closer the steering wheel is to the neutral position, regardless of the steering speed of the steering wheel, until the steering wheel returns to the neutral position.

4. 4. The vehicle control system according to claim 1, wherein the driving force source includes an electric motor, and the controller is configured to control a torque generated by the electric motor.

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