Patent Publication Number: US-2022234571-A1

Title: Vehicle control system

Description:
TECHNICAL FIELD 
     The present disclosure relates to a control system for a vehicle, which controls attitude of the vehicle according to steering. 
     BACKGROUND OF THE DISCLOSURE 
     Conventionally, a technique is known for controlling attitude of a vehicle by causing deceleration or acceleration in the vehicle according to a driver&#39;s operation of a steering wheel to improve the response and the stability of the vehicle behavior with respect to the steering operation. 
     For example, WO2015/151565A1 discloses a motion control for a vehicle, in case of the vehicle turning, which decelerates the vehicle when the steering wheel is first turned in one direction, and accelerates the vehicle when the steering wheel is then returned. Thus, the maneuverability and the stability of the vehicle from an entry into a corner to an escape from the corner are improved. 
     In order to achieve the technique disclosed in WO2015/151565A1, when a turning operation of the steering wheel is carried out, a control (torque decreasing control) for reducing a driving torque generated by a driving force source of the vehicle is performed in order to add deceleration to the vehicle, and when a returning operation of the steering wheel is carried out, a control (torque increasing control) for increasing the driving torque generated by the driving force source is performed in order to add acceleration to the vehicle. Such a control can easily be achieved in a vehicle provided with an electric motor (for example, an electric vehicle). This is because the electric motor can promptly increase and decrease the output torque. 
     For example, in case of the vehicle traveling an S-shaped corner, the torque decreasing control is performed when the turning operation of the steering wheel is first carried out, the torque increasing control is performed when the returning operation of the steering wheel is then carried out, and the torque increasing control is ended when the steering wheel is then changed to the turning operation crossing the neutral position (that is, the steering angle is 0°). Here, even after the steering wheel passes through the neutral position after the returning operation, the torque increasing control may not be ended immediately but may be continued for a while because of a restriction, etc. of a rapid change in the torque. In this case, also during the turning operation of the steering wheel after passing through the neutral position, the torque generated by the driving force source is increased by the unfinished torque increasing control, and therefore, acceleration continues being added to the vehicle. As a result, the improvements in the maneuverability and the stability of the vehicle cannot be obtained, and it may give discomfort to the driver. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure is made in view of solving the problem described above, and one purpose thereof is to provide a control system for a vehicle, capable of controlling attitude of the vehicle according to steering, which improves maneuverability and stability of the vehicle without giving discomfort to a driver, when a returning operation is carried out from a state where a steering wheel is turned in one direction, and a turning operation is again carried out in the other direction after the steering wheel passes through a neutral position. 
     According to one aspect of the present disclosure, a control system for a vehicle is provided, which includes a driving force source configured to generate torque for driving drive wheels of the vehicle, a steering wheel configured to be operated by a driver, a steering angle sensor configured to detect a steering angle corresponding to operation of the steering wheel, and a controller configured to, based on the steering angle detected by the steering angle sensor, reduce the torque generated by the driving force source to add deceleration to the vehicle when the steering wheel is being turned in one direction, and increase the torque generated by the driving force source to add acceleration to the vehicle when the steering wheel is being turned back in the other, returning direction. The controller controls the torque generated by the driving force source, when the steering wheel is being turned in the returning direction from a state where the steering wheel is turned in the one direction, so as to add forward acceleration to the vehicle until the steering wheel returns to a neutral position, and when the steering wheel is then being turned in the other direction after passing through the neutral position, so as not to add the forward acceleration to the vehicle. 
     According to this configuration, when the turning operation of the steering wheel is carried out after crossing the neutral position, the forward acceleration being added to the vehicle by the increase in the torque generated by the driving force source can be prevented, unlike the case where the torque control for adding the forward acceleration is continued. Therefore, the maneuverability and the stability of the vehicle when the steering wheel passes through the neutral position after the returning operation and the turning operation is then carried out, can be improved, without giving discomfort to the driver. 
     The controller may perform a control for reducing the torque generated by the driving force source so as to add forward deceleration to the vehicle, when the steering wheel is turned in the returning direction from a state where the steering wheel is turned in the one direction, and the steering wheel is then being turned in the other direction after passing through the neutral position. 
     According to this configuration, the forward deceleration can promptly be added to the vehicle during the turning operation of the once returned steering wheel after passing through the neutral position, while suppressing discomfort given to the driver. Therefore, the maneuverability and the stability when the turning operation of the steering wheel is carried out after passing through the neutral position, can be improved to smoothen the behavior of the vehicle. 
     The controller may control the torque generated by the driving force source so that the forward acceleration added to the vehicle becomes smaller as the steering wheel becomes closer to the neutral position, when the steering wheel is being turned in the returning direction from a state where the steering wheel is turned in the one direction, until the steering wheel returns to the neutral position. 
     According to this configuration, the rapid change in the forward acceleration when the returning steering wheel passes through the neutral position can be avoided to prevent discomfort being given to the driver. 
     The driving force source may be comprised of an electric motor, and the controller may control torque generated by the electric motor. 
     According to this configuration, the torque generated by the driving force source can be controlled with the high response. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram schematically illustrating the overall configuration of a vehicle according to one embodiment of the present disclosure. 
         FIG. 2  is a block diagram illustrating an electric configuration of the vehicle according to this embodiment. 
         FIG. 3  is a flowchart of a vehicle attitude control processing according to this embodiment. 
         FIG. 4  is a flowchart of an additional torque setting processing according to this embodiment. 
         FIGS. 5A and 5B  are maps each illustrating a relationship between a steering speed and an additional torque, according to this embodiment. 
         FIG. 6  is a map illustrating a relationship between a steering angle and a correction gain for an increasing torque, according to this embodiment. 
         FIG. 7  is a time chart when performing the vehicle attitude control according to this embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Hereinafter, a control system for a vehicle according to one embodiment of the present disclosure is described with reference to the accompanying drawings. 
     &lt;Configuration of Vehicle&gt; 
     First, referring to  FIGS. 1 and 2 , the vehicle to which the control system for the vehicle according to this embodiment is applied is described.  FIG. 1  is a block diagram schematically illustrating the entire configuration of the vehicle according to this embodiment.  FIG. 2  is a block diagram illustrating the electric configuration of the vehicle according to this embodiment. 
     As illustrated in  FIG. 1 , a motor generator  20  (rotary electric machine) is mounted on a front part of a vehicle  1  as a motor (driving force source) which drives left and right front wheels  2  which are driving wheels. The vehicle  1  is configured as a so-called front-engine, front-wheel drive (FF) vehicle. Each wheel of the vehicle  1  is suspended from the vehicle body via a suspension  70  comprised of an elastic member (typically, a spring) and a suspension arm. 
     The motor generator  20  has a function to drive the front wheels  2  (that is, function as a prime motor (electric motor)) and a function to be driven by the front wheels  2  and to regenerate power (that is, function as a power generator). In the motor generator  20 , a force is transmitted between the front wheels  2  via a transmission  6 , and the motor generator  20  is controlled by a controller  8  via an inverter  22 . Further, the motor generator  20  is connected to a battery  24 . Electric power is supplied to the motor generator  20  from the battery  24  when the motor generator  20  generates a driving force, and the motor generator  20  supplies the power to the battery  24  and charges the battery  24  when it regenerates. 
     Further, in the vehicle  1 , a rotation shaft of the motor generator  20  and a rotation shaft of the transmission  6  are coupled to each other via a clutch  62  which can engage and disengage. For example, switching between engagement and disengagement of the clutch  62  is controlled using oil pressure of the transmission  6 . 
     The vehicle  1  includes a steering device  26  having a steering wheel  28  and a steering column  30 , a steering angle sensor  34  which detects a steering angle in the steering device  26  based on a turning angle of the steering wheel  28  and the position of a steering rack (not illustrated), an accelerator opening sensor  36  which detects an accelerator opening equivalent to a stepping amount of an accelerator pedal, a brake stepping amount sensor  38  which detects a stepping amount of a brake pedal, a vehicle speed sensor  40  which detects a traveling speed of the vehicle, a yaw rate sensor  42  which detects a yaw rate, and an acceleration sensor  44  which detects acceleration of the vehicle. These sensors output respective detection values to the controller  8 . 
     Note that the steering angle sensor  34  may detect, as the steering angle, various properties of the steering system (a rotation angle of the motor which adds assisting torque, a displacement of a rack in a rack-and-pinion mechanism, etc.), and a steered angle (tire angle) of the front wheels  2 , instead of the turning angle of the steering wheel  28 . 
     Further, the vehicle  1  is provided with a brake control system  48  which supplies brake fluid pressure to a wheel cylinder and a brake caliper of a brake device (brake mechanism)  46  provided to each wheel. The brake control system  48  is provided with a hydraulic pump  50  which generates brake fluid pressure required for generating a braking force at the brake device  46  provided to each wheel. The hydraulic pump  50  is driven, for example, by the power supplied from the battery  24 , and even if the brake pedal is not stepped on, it can generate the brake fluid pressure required for generating the braking force in each brake device  46 . 
     Further, the brake control system  48  is provided with a valve unit  52  (in detail, a solenoid valve) which is provided to a hydraulic pressure supply line to the brake device  46  of each wheel and controls the hydraulic pressure supplied to the brake device  46  of each wheel from the hydraulic pump  50 . For example, the opening of the valve unit  52  is changed by adjusting the power from the battery  24  to the valve unit  52 . The brake control system  48  is also provided with a hydraulic pressure sensor  54  which detects the hydraulic pressure supplied to the brake device  46  of each wheel from the hydraulic pump  50 . The hydraulic pressure sensor  54  is disposed, for example, at a connecting part between each valve unit  52  and the hydraulic pressure supply line downstream thereof, detects the hydraulic pressure downstream of each valve unit  52 , and outputs a detection value to the controller  8 . 
     Such a brake control system  48  calculates the hydraulic pressure supplied independently to the wheel cylinder and the brake caliper of each wheel based on a braking force command value and the detection value from the hydraulic pressure sensor  54  which are inputted from the controller  8 , and controls a rotational speed of the hydraulic pump  50  and the opening of the valve unit  52  according to the hydraulic pressures. 
     As illustrated in  FIG. 2 , the controller  8  according to this embodiment outputs control signals in order to perform controls of the motor generator  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 outputted from various kinds of operating state sensors which detect the operating state of the vehicle  1 , in addition to the detection signals of the sensors  18 ,  34   36 ,  38 ,  40 ,  42 ,  44 , and  54  which are described above. 
     The controller  8  is comprised of a circuitry, and is a controller based on a well-known microcomputer. The controller  8  includes one or more microprocessors (e.g., a CPU (Central Processing Unit)) which executes a program, memory which is comprised of, for example, RAM (Random Access Memory) and/or ROM (Read Only Memory) and stores the program and data, and an input/output bus which performs input/output of electric signals. Note that the system including the steering wheel  28 , the steering angle sensor  34 , and the controller  8  is an example of a “control system for a vehicle” in the present disclosure. 
     &lt;Vehicle Attitude Control&gt; 
     Below, a vehicle attitude control according to this embodiment of the present disclosure is described. In this embodiment, fundamentally, the controller  8  performs the following control in order to control the vehicle attitude (vehicle behavior) based on the steering angle detected by the steering angle sensor  34 . First, when the turning operation is carried out so that the steering wheel  28  separates from the neutral position (i.e., when the steering angle increases) by being turned in one direction, the controller  8  performs the torque decreasing control for reducing the torque generated by the motor generator  20  so that forward deceleration (i.e., deceleration to decelerate the vehicle  1  which moves forward) is added to the vehicle  1 . Further, when a returning operation is carried out so that the steering wheel  28  approaches the neutral position (i.e., when the steering angle decreases) by being turned in the other, returning direction, the controller  8  performs the torque increasing control for increasing the torque generated by the motor generator  20  so as to add forward acceleration (i.e., acceleration to accelerate the vehicle  1  which moves forward) to the vehicle  1 . By performing such a vehicle attitude control, the turnability and the steering stability of the vehicle  1  from an entry into a corner to an escape from the corner can be improved. 
     Note that, below, the torque which is applied to the torque decreasing control (i.e., the negative torque which is added to the torque generated by the motor generator  20  in order to add the forward deceleration to vehicle  1 ) is referred to as the “reducing torque.” Further, the torque which is applied to the torque increasing control (i.e., the positive torque which is added to the torque generated by the motor generator  20  in order to add the forward acceleration to the vehicle  1 ) is referred to as the “increasing torque.” Further, when the reducing torque and the increasing torque are used without being distinguished from each other, each is referred to as the “additional torque.” Such a reducing torque or increasing torque is applied to the vehicle attitude control. In detail, in the vehicle attitude control, the reducing torque or the increasing torque is subtracted or added from/to the torque to be generated by the motor generator  20  (hereinafter, referred to as the “basic torque”) in order to achieve acceleration according to the operating state of the vehicle  1  (the accelerator opening, etc.). Below, the torque after the reducing torque or the increasing torque is thus subtracted from or added to the basic torque (i.e., the torque to be finally generated by the motor generator  20 ) is referred to as the “final target torque.” 
     Next, referring to  FIG. 3 , the overall flow of the vehicle attitude control according to this embodiment is described.  FIG. 3  is a flowchart of the vehicle attitude control processing according to this embodiment. 
     The vehicle attitude control processing 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 it is repeatedly performed at a given period (for example, 50 ms). Once the vehicle attitude control processing is started, at Step S 1 , the controller  8  acquires the various sensor information on the operating state of the vehicle  1 . In detail, the controller  8  acquires, as the information on the operating state, the detection signals outputted from the various sensors described above which includes the steering angle detected by the steering angle sensor  34 , the accelerator opening detected by the accelerator opening sensor  36 , the brake pedal stepping amount detected by the brake stepping amount sensor  38 , the traveling speed or 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 , and the gear stage currently set to the transmission  6  of the vehicle  1 . 
     Next, at Step S 2 , the controller  8  sets the target acceleration based on the operating state of the vehicle  1  acquired at Step S 1 . In detail, for example, the controller  8  selects an acceleration characteristics map corresponding to the current traveling speed and the current gear stage from the acceleration characteristics maps (created beforehand and stored in the memory, etc.) in which various traveling speeds and various gear stages are defined, and sets a target acceleration corresponding to the current accelerator opening with reference to the selected acceleration characteristics map. 
     Next, at Step S 3 , the controller  8  determines the basic torque of the motor generator  20  for achieving the target acceleration determined at Step S 2 . In this case, the controller  8  determines the basic torque within a range of the torque outputtable from the motor generator  20 , based on the current traveling speed, gear stage, road surface gradient, road surface μ, etc. 
     Further, in parallel to the processings at Steps S 2  and S 3 , at Step S 4 , the controller  8  performs an additional torque setting processing which will be described later (see  FIG. 4 ), and based on the steering speed etc. of the steering wheel  28 , it sets the additional torque (the reducing torque or the increasing torque) to be applied to the torque generated by the motor generator  20  in order to control the vehicle attitude. 
     Next, after Steps S 2  to S 4 , at Step S 5 , the controller  8  sets the final target torque based on the basic torque set at Step S 3  and the additional torque set at Step S 4 . Fundamentally, the controller  8  calculates the final target torque by subtracting the reducing torque from the basic torque, or adding the increasing torque to the basic torque. 
     Next, at Step S 6 , the controller  8  sets a command value for the inverter  22  (inverter command value) for achieving the final target torque set at Step S 5 . That is, the controller  8  sets the inverter command value (control signal) for causing the motor generator  20  to generate the final target torque. Then, at Step S 7 , the controller  8  outputs the inverter command value set at Step S 6  to the inverter  22 . After Step S 7 , the controller  8  ends the vehicle attitude control processing. 
     Next, referring to  FIG. 4 , the additional torque setting processing according to this embodiment is described.  FIG. 4  is a flowchart of the additional torque setting processing according to this embodiment. This additional torque setting processing is performed at Step S 4  of the vehicle attitude control processing illustrated in  FIG. 3 . 
     When the additional torque setting processing is started, at Step S 11 , the controller  8  acquires the steering speed based on the steering angle acquired from the steering angle sensor  34  at Step S 1  of the vehicle attitude control processing illustrated in  FIG. 3 . Next, at Step S 12 , the controller  8  determines whether the steering speed acquired at Step S 11  is above a given value. As a result, if the controller  8  determines that the steering speed is above the given value (Step S 12 : YES), it shifts to Step S 13 . 
     On the other hand, if the controller  8  does not determine that the steering speed is above the given value (Step S 12 : NO), it ends the additional torque setting processing and returns to the main routine. In this case, the additional torque becomes 0, and the basic torque set at Step S 3  of the vehicle attitude control processing illustrated in  FIG. 3  becomes the final target torque. 
     Next, at Step S 13 , the controller  8  determines whether the steering wheel  28  is under the turning operation. In detail, for example, when the absolute value of the steering angle acquired from the steering angle sensor  34  is increasing (i.e., when the steering angle of the steering wheel  28  is separating from the neutral position), the controller  8  determines that the steering wheel  28  is under the turning operation. On the other hand, for example, when the absolute value of the steering angle acquired from the steering angle sensor  34  is decreasing (i.e., when the steering angle of the steering wheel  28  is approaching the neutral position), the controller  8  determines that the steering wheel  28  is under the returning operation (that is, it is not under the turning operation). As a result, if the controller  8  determines that the steering wheel  28  is under the turning operation (Step S 13 : YES), it shifts to Step S 14 . 
     Next, at Step S 14 , the controller  8  acquires the reducing torque based on the steering speed. In detail, before acquiring the reducing torque, the controller  8  first sets the additional deceleration corresponding to the current steering speed based on the relationship between the steering speed and the additional deceleration as illustrated in the map of  FIG. 5A . This additional deceleration is a forward deceleration to be added to the vehicle  1  according to the steering operation in order to control the vehicle attitude in accordance with the driver&#39;s intention of the turning operation of the steering wheel  28 . In  FIG. 5A , the horizontal axis indicates the steering speed, and the vertical axis indicates the additional deceleration. As illustrated in  FIG. 5A , when the steering speed is below a threshold S 1 , the additional deceleration is 0. When the steering speed exceeds the threshold S 1 , the additional deceleration corresponding to this steering speed gradually approaches a given upper limit AD max  as the steering speed increases. That is, as the steering speed increases, the additional deceleration increases, and an increasing rate of the amount of increase become smaller. This upper limit AD max  is set to such a deceleration that, even if the deceleration is added to the vehicle  1  according to the steering operation, the driver does not sense a control intervention (for example, 0.5 m/s 2 ≈0.05G). Further, when the steering speed becomes above the given value, the additional deceleration is maintained at the upper limit AD max . Then, the controller  8  acquires the reducing torque based on the additional deceleration set in this way. In detail, the controller  8  determines the reducing torque required for achieving the additional deceleration by the reduction of the basic torque, based on the current traveling speed, gear stage, road surface gradient, etc. 
     Next, at Step S 15 , based on the reducing torque acquired at Step S 14  and a threshold (defined beforehand and stored in the memory, etc.) which defines an upper limit of a rate of change in the reducing torque, the controller  8  sets the reducing torque in this processing cycle so that the rate of change in the reducing torque becomes below the threshold. After Step S 15 , the controller  8  ends the additional torque setting processing, and returns to the main routine. In this case, at Step S 5  of the vehicle attitude control processing in  FIG. 3 , the controller  8  sets the final target torque based on the basic torque set at Step S 3  and the reducing torque set at Step S 15 . 
     Further, at Step S 13 , if the controller  8  determines that the steering wheel  28  is not under the turning operation (Step S 13 : NO), in detail, if the absolute value of the steering angle acquired from the steering angle sensor  34  is decreasing (i.e., when the steering angle of the steering wheel  28  is approaching the neutral position), the controller  8  shifts to Step S 16 . 
     Next, at Step S 16 , the controller  8  acquires the increasing torque based on the steering speed. In detail, the controller  8  first sets the additional acceleration corresponding to the current steering speed based on the relation between the steering speed and the additional acceleration which are illustrated in the map of  FIG. 5B , before setting the increasing torque. This additional acceleration is the forward acceleration to be added to the vehicle  1  according to the steering operation, in order to control the vehicle attitude in accordance with the driver&#39;s intention of the returning operation of the steering wheel  28 . In  FIG. 5B , the horizontal axis indicates the steering speed and the vertical axis indicates the additional acceleration. As illustrated in  FIG. 5B , the additional acceleration is 0 when the steering speed is below a threshold S 2 . When the steering speed exceeds the threshold S 2 , the additional acceleration corresponding to this steering speed gradually approaches a given upper limit AA max  as the steering speed increases. That is, as the steering speed increases, the additional acceleration increases and an increasing rate of the amount of increase thereof becomes smaller. This upper limit AA max  is set to such an acceleration that the driver does not sense the control intervention even if the acceleration is added to the vehicle  1  according to the steering operation (for example, 0.5 m/s 2 ≈0.05G). Further, the additional acceleration is maintained at the upper limit AA max , when the steering speed becomes above the given value. Then, the controller  8  acquires the increasing torque based on the additional acceleration set in this way. In detail, the controller  8  determines the increasing torque required for achieving the additional acceleration with the increase in the basic torque, based on the current traveling speed, gear stage, road surface gradient, etc. 
     Next, at Step S 17 , the controller  8  determines whether the steering angle acquired from the steering angle sensor  34  is below the given angle (for example, below 30° clockwise and counterclockwise) from the neutral position (that is, the steering angle is 0°). As a result, if the controller  8  determines that the steering angle is below the given angle from the neutral position (Step S 17 : YES), that is, if the steering wheel which is under the returning operation comes in a range near the neutral position, the controller  8  shifts to Step S 18 . 
     Next, at Step S 18 , the controller  8  acquires the correction gain for correcting the increasing torque. In detail, the controller  8  acquires the correction gain corresponding to the current steering angle based on the relation between the steering angle and the correction gain illustrated in the map of  FIG. 6 . This correction gain is a correction gain to be multiplied by the increasing torque, when the steering wheel  28  is under the returning operation, so that the forward acceleration to be added to the vehicle  1  becomes smaller as the steering wheel  28  is closer to the neutral position. In  FIG. 6 , the horizontal axis indicates the steering angle, and the vertical axis indicates the correction gain. As illustrated in  FIG. 6 , when the steering angle is a given angle A 1  (for example, 30°), the correction gain is 1. When the steering angle is smaller than the given angle A 1 , the correction gain corresponding to this steering angle becomes smaller as the steering angle approaches 0° (that is, as the steering wheel  28  is closer to the neutral position). When the steering angle is 0° (i.e., when the steering wheel  28  is at the neutral position), the correction gain becomes 0. Further, the rate of change in the correction gain according to the change in the steering angle (the slope of the graph illustrated in  FIG. 6 ) becomes smaller as the steering angle approaches 0° and the given angle A 1 . 
     Next, at Step S 19 , the controller  8  corrects the increasing torque acquired at Step S 16  by using the correction gain acquired at Step S 18 . In detail, the controller  8  multiplies the correction gain acquired at Step S 18  by the increasing torque acquired at Step S 16 . By correcting in this way, when the steering wheel  28  is under the returning operation, the increasing torque becomes smaller as the steering angle is closer to 0° if the steering angle is below the given angle A 1  from the neutral position. Then, the increasing torque becomes 0 when the steering angle reaches 0°. 
     Next, at Step S 20 , based on the increasing torque corrected at Step S 19  and a threshold (defined beforehand and stored in the memory, etc.) which defines the upper limit of a rate of change in the increasing torque, the controller  8  sets the increasing torque in this processing cycle so that the rate of change in the increasing torque becomes below the threshold. 
     Further, at Step S 17 , if the controller  8  determines that the steering angle is not below the given angle from the neutral position (Step S 17 : NO), that is, if the steering wheel which is under the returning operation is not within the range near the neutral position, it shifts to Step S 20 , without correcting the increasing torque. In this case, at Step S 20 , based on the increasing torque acquired at Step S 16  and the threshold which defines the upper limit of the change rate in the increasing torque, the controller  8  sets the increasing torque in this processing cycle so that the rate of change in the increasing torque becomes below the threshold. 
     After Step S 20 , the controller  8  ends the additional torque setting processing, and returns to the main routine. In this case, at Step S 5  of the vehicle attitude control processing in  FIG. 3 , the controller  8  sets the final target torque based on the basic torque set at Step S 3  and the increasing torque set at Step S 20 . 
     &lt;Operation and Effects&gt; 
     Next, referring to a time chart in  FIG. 7 , operation and effects of the control system for the vehicle according to this embodiment are described.  FIG. 7  is a time chart when performing the vehicle attitude control according to this embodiment described above. In  FIG. 7 , the horizontal axis indicates time. Further, the vertical axis indicates (a) steering angle, (b) the steering speed, (c) the additional torque (including the reducing torque and the increasing torque), and (d) the final target torque, sequentially from the top. In the graphs (c) and (d) of  FIG. 7 , a solid line illustrates the changes in the increasing torque and the final target torque when applying the correction gain illustrated in  FIG. 6  to the increasing torque, and a broken line illustrates the changes in the increasing torque and the final target torque when not applying the correction gain to the increasing torque. 
     As illustrated in the graph (a) of  FIG. 7 , the turning operation of the steering wheel  28  is first carried out clockwise (CW) from the neutral position, the rotational position of the steering wheel  28  is then held at a certain steering angle, the returning operation is then carried out until the steering wheel  28  returns to the neutral position, the turning operation is then continuously carried out counterclockwise (CCW) even after the steering wheel  28  passes through the neutral position, and the rotational position of the steering wheel  28  is then held at a certain steering angle. 
     In connection with the turning operation of the steering wheel  28  being started in the CW direction from the neutral position, the steering speed (absolute value) in the CW direction increases. When the steering speed becomes above the threshold S 1  at time t 1 , the controller  8  sets the reducing torque based on the steering speed so as to add the forward deceleration to the vehicle  1 , and performs the torque decreasing control for reducing the torque generated by the motor generator  20 . Then, the controller  8  increases the reducing torque (absolute value) according to the steering speed while the steering speed increases, and when the steering speed becomes constant, it maintains the reducing torque. Further, when the steering speed decreases, it decreases the reducing torque (absolute value) accordingly. 
     Then, when the steering speed becomes below the threshold S 1  at time t 2  by the steering wheel  28  being held after the turning operation, the controller  8  ends the torque decreasing control and the additional torque becomes 0. That is, the forward deceleration added to the vehicle  1  becomes 0. 
     Then, in connection with the returning operation being carried out counterclockwise (CCW) toward the neutral position from the state where the steering wheel  28  is turned in the CW direction, the steering speed (absolute value) in the CCW direction increases. When the steering speed becomes above the threshold S 2  at time t 3 , the controller  8  sets the increasing torque based on the steering speed so that the forward acceleration is added to the vehicle  1 , and performs the torque increasing control for increasing the torque generated by the motor generator  20 . Then, the controller  8  increases the increasing torque (absolute value) according to the steering speed, while the steering speed increases, and when the steering speed becomes constant, it maintains the increasing torque. 
     Then, when the steering wheel  28  under the returning operation approaches the neutral position and the steering angle (absolute value) becomes below the given angle A 1  at time t 4 , the controller  8  applies the correction gain to the increasing torque, and performs the torque increasing control with the corrected increasing torque. As described above, the correction gain corresponding to this steering angle is set so that it becomes smaller as the steering angle approaches 0°, and it becomes 0 when the steering angle is 0°. Therefore, the controller  8  decreases the increasing torque (absolute value) as the steering angle becomes smaller, and sets the increasing torque to 0 when and the steering angle becomes 0° at time t 5 . Thus, when the steering wheel  28  is under the returning operation, the forward acceleration added to the vehicle  1  becomes smaller as the steering angle becomes smaller than the given angle A 1 , and the forward acceleration added to the vehicle  1  becomes 0 when the steering angle becomes 0° at time t 5 . 
     Then, when the steering wheel  28  is turned continuously to counterclockwise (CCW) even after passing through the neutral position at time t 5 , the controller  8  sets the reducing torque based on the steering speed so as to add the forward deceleration to the vehicle  1 , and performs the torque decreasing control for reducing the torque generated by the motor generator  20 . Here, when the operation of the steering wheel  28  is changed from the returning operation to the turning operation by the steering wheel  28  passing through the neutral position at time t 5 , the steering speed (absolute value) becomes constant above the threshold S 1 . Therefore, when the turning operation is started at time t 5 , the controller  8  promptly increases the reducing torque (absolute value) according to the steering speed, while restricting the rate of change in the reducing torque to below the given threshold. Then, the controller  8  increases the reducing torque (absolute value) until the torque becomes the value corresponding to the steering speed. When the steering speed further decreases, the controller  8  decreases the reducing torque (absolute value) accordingly. Then, when the steering speed becomes below the threshold S 1  at time t 6 , the controller  8  ends the torque decreasing control and the additional torque becomes 0. That is, the forward deceleration added to the vehicle  1  becomes 0. 
     Thus, in this embodiment, when the steering wheel  28  is under the returning operation from the state where it is turned in one direction, the controller  8  performs the torque increasing control so as to add the forward acceleration to the vehicle  1  until the steering wheel  28  returns to the neutral position (from time t 3  to time t 5 ), and when the steering wheel  28  is then turned to the other side after passing through the neutral position (at and after time t 5 ), it ends the torque increasing control so as not to add the forward acceleration to the vehicle  1 . Therefore, when the turning operation of the steering wheel  28  is carried out after crossing the neutral position, it can be prevented that the forward acceleration is added to the vehicle  1  by the increase in the torque generated by the motor generator  20 , unlike the case where the torque increasing control is continued as illustrated by the broken lines in the graphs (c) and (d) of  FIG. 7 . Therefore, when the steering wheel  28  passes through the neutral position after the returning operation and the turning operation is then carried out, the maneuverability and the stability of the vehicle  1  can be improved, without giving discomfort to the driver. 
     In this embodiment, when the returning operation is carried out from the state where the steering wheel  28  passes through the neutral position and the turning operation is then carried out to the other side, the controller  8  performs the torque decreasing control so as to add the forward deceleration to the vehicle  1 . Therefore, the forward deceleration can promptly be added to the vehicle  1  during the turning operation after passing through the neutral position, while suppressing discomfort given to the driver. Further, the maneuverability and the stability when the turning operation of the steering wheel  28  is carried out after passing through the neutral position can be improved to smoothen the behavior of the vehicle  1 . 
     Further, in this embodiment, when the steering wheel  28  is returned after the turning operation, the controller  8  corrects the increasing torque so that the forward acceleration added to the vehicle  1  becomes smaller as the steering wheel  28  gets closer to the neutral position until the steering wheel  28  returns to the neutral position. Therefore, the rapid change in the additional torque when the returning steering wheel  28  passes through the neutral position can be avoided to prevent discomfort being given to the driver. 
     Further, since in this embodiment the controller  8  sets the additional torque at least based on the steering angle detected by the steering angle sensor  34 , the vehicle attitude can promptly be controlled so that the response and the stability of the vehicle behavior with respect to the driver&#39;s steering operation are improved. 
     Further, since in this embodiment the controller  8  controls the torque generated by the motor generator  20 , it can perform the torque decreasing control and the torque increasing control with the high response. 
     &lt;Modifications&gt; 
     Although in the above embodiment of the present disclosure is applied to the vehicle  1  having the motor generator  20  as the prime motor (driving force source), the present disclosure can also be applied to vehicles having an engine as the prime motor. In this case, for example, the ignition timing of the engine may be controlled in order to achieve the additional torque in the vehicle attitude control. That is, when performing the torque decreasing control, the ignition timing of the engine may be retarded from a reference ignition timing (an ignition timing according to the basic torque), and when performing the torque increasing control, the ignition timing may be advanced from the reference ignition timing. 
     Further, although in the above embodiment the torque outputted from the motor generator  20  (driving torque) is changed in order to achieve the additional torque in the vehicle attitude control, in another example, the additional torque by the vehicle attitude control may be achieved by changing regenerated torque inputted into the motor generator  20 , instead of the driving torque of the motor generator  20 . For example, when performing the vehicle attitude control while the motor generator  20  regenerates (e.g., while the accelerator opening is 0), the regenerated torque inputted into the motor generator  20  for braking the vehicle  1  may be increased or decreased so that the reducing torque or the increasing torque by the vehicle attitude control is achieved. That is, when performing the torque decreasing control, the regenerated torque (absolute value) may be increased, and when performing the torque increasing control, the regenerated torque (absolute value) may be decreased. 
     Further, although in the above embodiment the controller  8  acquires the additional torque at least based on the steering angle detected by the steering angle sensor  34 , the additional torque may be acquired based on, instead of or in addition to the steering angle, operating states of the vehicle  1  other than the operation of the accelerator pedal (e.g., a lateral acceleration, a yaw rate, a slip ratio, etc.). For example, the controller  8  may set the additional acceleration or the additional deceleration based on a lateral acceleration inputted from the acceleration sensor  44 , and a lateral jerk which can be obtained by differentiating the lateral acceleration with respect to time, and acquire the additional torque. 
     It should be understood that the embodiments herein are illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof, are therefore intended to be embraced by the claims. 
     DESCRIPTION OF REFERENCE CHARACTERS 
     
         
         
           
               1  Vehicle 
               2  Wheel 
               8  Controller 
               20  Motor Generator 
               22  Inverter 
               24  Battery 
               26  Steering Device 
               28  Steering Wheel 
               34  Steering Angle Sensor 
               36  Accelerator Opening Sensor 
               40  Vehicle Speed Sensor 
               46  Brake Device