JP5423606B2 - Steering force control device - Google Patents

Description

  The present invention relates to a steering force control device that improves the stability of a vehicle that travels under a situation where the posture of the vehicle becomes unstable, for example, a vehicle that travels under a situation where road friction coefficients of a right front wheel and a left front wheel are different.

2. Description of the Related Art In recent years, electric power steering capable of controlling a steering force by applying a steering assist force by the force of an electric motor has been adopted in power steering of vehicles.
This electric power steering has a larger friction than the hydraulic power steering etc. due to the resistance of the electric motor, etc., and the steering is difficult to return to the neutral position. There has been proposed a technique for controlling the electric power steering so that a steering assist force is applied in the direction of returning to the initial position. According to this, when turning the vehicle, the wheel speed on the inner wheel side is small and the wheel speed on the outer wheel side is increased, so that the steering assist force is controlled to be applied in the direction of the outer wheel having a higher wheel speed.
That is, when turning left while steering leftward, a steering assist force in the right direction is added, so for example, road surfaces with different road surface friction coefficients (μ) (hereinafter referred to as μ split) between the left and right wheels of the vehicle. When braking on a road), the wheel speed of the wheel that is in contact with the low friction coefficient road surface is lower than that of the wheel that is in contact with the high friction coefficient road surface. The coefficient of friction is added to the road surface side.
However, since the braking force acts strongly on the wheels on the high friction coefficient road surface side, if the vehicle deflects to the high friction coefficient road surface side and the steering assist force is added to the high friction coefficient road surface side, the high friction coefficient Deflection of the vehicle toward the coefficient road surface side is promoted, and a so-called steering wheel state occurs in response to the driver's steering operation.
In order to solve such a problem, a steering force control device that detects a one-wheel lock during braking and applies additional torque in a direction where the wheel speed is slow (low μ road side) to suppress vehicle deflection and improve stability. (See Patent Document 1).

JP 2009-113752 A

  Therefore, in the conventional steering force control device, the vehicle deflection on the μ-split road occurs not only at the time of braking but also at the start (particularly LSD-equipped vehicle), whereas the direction is deflected to the low μ road side. However, since the brake operation is used for the one-wheel lock detection, there is a problem that it cannot cope with acceleration.

  The present invention has been made in view of such circumstances, and it is possible to avoid a situation in which the steering wheel is removed with a simple configuration at the time of acceleration of the vehicle under a situation where the vehicle posture becomes unstable. An object of the present invention is to provide a steering force control device that can improve the stability of a vehicle by adding a steering assist force.

The invention according to claim 1 is a steering means for changing the direction of the pair of left and right wheels in accordance with the operation of the driver, a steering assist means for adding a steering assist force to the operation of the steering means, and the pair of left and right A wheel speed detecting means for detecting a wheel speed of each wheel, a wheel speed difference between the pair of left and right wheels and a rate of change of the wheel speed difference from the wheel speed of each wheel detected by the wheel speed detecting means, Is generated in one of the pair of left and right wheels during acceleration of the pair of left and right wheels based on the calculation means for calculating the difference between the wheel speed difference calculated by the calculation means and the change rate of the wheel speed difference. A one-wheel idling detecting means for detecting one-wheel idling, and when the one-wheel idling detecting means detects the one-wheel idling detecting means, the steering assist means provides an additional torque sufficient to suppress the steering being taken during the one-wheel idling. Steering wheel And a additional torque control means for controlling said steering assist means to added to the operation, the one wheel idling detecting means, based on the wheel speed of each wheel detected by the wheel speed detecting means, Wheel speed state determination means for determining a state in which both the wheel speed difference between the wheels and the change rate of the wheel speed difference between the wheels are increasing, and the wheel speed state determination means between the wheels. When the state where both the wheel speed difference and the change rate of the wheel speed difference are determined is determined, it is determined whether or not the size of the wheel speed difference between the wheels exceeds a first threshold value. When the wheel speed difference first threshold value determining means and the wheel speed difference first threshold value determining means determine that the magnitude of the wheel speed difference between the wheels exceeds the first threshold value, the accelerator opening degree is An accelerator operation determination means for determining whether or not a predetermined value is exceeded; The wheel speed state determining means determines a state in which both the wheel speed difference between the wheels and the rate of change of the wheel speed difference are increasing, and the wheel speed difference first threshold determining means determines between the wheels. If the wheel speed difference between the left and right wheels is determined to be greater than a first threshold value and the accelerator operation determination means determines that the accelerator opening exceeds a predetermined value, An idle rotation judging means for judging one of the idle rotation states of one of the wheels is provided.

  According to the present invention, at the time of acceleration of the vehicle under a situation where the vehicle posture becomes unstable, it is possible to add an appropriate steering assist force that can avoid a situation where the steering wheel is taken with a simple configuration, There is an effect that a steering force control device capable of improving the stability of the vehicle can be provided.

1 is a schematic configuration diagram illustrating a configuration of a vehicle to which a steering force control device according to an embodiment of the present invention is applied. It is a flowchart which shows operation | movement of the steering force control apparatus of embodiment of this invention. It is explanatory drawing which shows the additional torque added in the electric power steering of the vehicle which starts on a [mu] split road surface by the additional torque control of the steering force control apparatus of embodiment of this invention. It is a functional block diagram of steering ECU in the steering force control device of the embodiment of the present invention.

Embodiments of the present invention will be described below.
FIG. 1 is a schematic configuration diagram showing a configuration of a vehicle 1 including a steering force control device according to an embodiment of the present invention. The vehicle 1 includes a left front wheel 11, a right front wheel 12, a left rear wheel 13, and a right rear wheel 14.

  The left front wheel 11 and the right front wheel 12 are steering wheels of the vehicle 1 and are connected to the electric power steering 22 via the tie rod 21.

The electric power steering 22 includes a steering gear box 31, a steering shaft 32, a steering wheel 33, and an electric motor 34.
A steering wheel 33 is connected to the steering gear box 31 via a steering shaft 32.
The operation of the steering wheel 33 by the driver is transmitted to the steering gear box 31 via the steering shaft 32.
Further, the tie rod 21 is operated via the steering gear box 31 to change the directions of the left front wheel 11 and the right front wheel 12.
In other words, the steering system for steering the steering wheels (the left front wheel 11 and the right front wheel 12) includes the steering gear box 31, the steering shaft 32, and the steering wheel 33.

The electric motor 34 is provided in the steering gear box 31, and the rotation of the electric motor 34 is input to the steering gear box 31 to generate a steering assist force for the operation of the steering wheel 33.
In other words, the steering assist force is applied to the steering system by the electric motor 34.

The left front wheel 11, the right front wheel 12, the left rear wheel 13 and the right rear wheel 14 are provided with brakes for applying a braking force to each wheel.
The brake 41 applies braking force to the left front wheel 11, the brake 42 applies braking force to the left front wheel 12, the brake 43 applies braking force to the left rear wheel 13, and the brake 44 applies braking force to the left rear wheel 14. Is granted.
The brakes 41, 42, 43, 44 control the braking force applied to the left front wheel 11, the right front wheel 12, the left rear wheel 13, and the right rear wheel 14 by the hydraulic pressure supplied from the brake hydraulic unit 51 mounted on the vehicle. Is done.

The left front wheel 11, the right front wheel 12, the left rear wheel 13 and the right rear wheel 14 are provided with wheel speed sensors for detecting the wheel speed of each wheel.
The wheel speed sensor 61 is a sensor for detecting the wheel speed (number of rotations) of the left front wheel 11. The wheel speed sensor 62 is a sensor for detecting the wheel speed (rotation speed) of the right front wheel 12. The wheel speed sensor 63 is a sensor for detecting the wheel speed (rotational speed) of the left rear wheel 13. The wheel speed sensor 64 is a sensor for detecting the wheel speed (number of rotations) of the right rear wheel 14.

A steering ECU 71 and a braking system ECU 72 are provided.
The steering ECU 71 has a general basic function of adding a steering assist force for reducing the driver's steering torque to the steering system by the electric motor 34 as a steering force control function.
The steering ECU 71 further applies a steering assist force to the steering system by the electric motor 34 based on the wheel speeds detected by the wheel speed sensors 61, 62, 63, 64, the control status by the braking system ECU 72, and the like. It has a function of improving the stability of the vehicle 1 when the vehicle starts on the split road surface or when the vehicle accelerates.

The braking system ECU 72 realizes an ABS (Anti-lock Bracket System) function when braking the vehicle 1 by controlling the brake hydraulic unit 51.
In the ABS function realized by the braking system ECU 72, the locked state of each wheel on the low μ road surface is determined based on each wheel speed detected by the wheel speed sensors 61, 62, 63, 64 when the vehicle 1 is suddenly braked. Then, the brake hydraulic unit 51 is controlled so that an optimal braking force is applied to the wheels by the brakes 41, 42, 43, and 44 while avoiding such a locked state.

The steering ECU 71 and the braking system ECU 72 are computers, and are composed of a storage device such as a RAM and a ROM, a central processing unit, an input / output device such as a timer and an I / O port, and various interfaces. Wheel speed sensors 61, 62, 63, 64 are connected to the steering ECU 71 and the braking system ECU 72 via the input / output device.
Further, a communication function for transmitting and receiving various data between the steering ECU 71 and the braking system ECU 72 is provided.

In the steering force control device of this embodiment, the CPU of the steering ECU 71 executes a software program stored in the storage device of the steering ECU 71 to control the steering assist force, thereby realizing posture stabilization control. .
Further, when the vehicle 1 is in a specific driving situation in which the posture of the vehicle 1 becomes unstable, posture stabilization control is performed in which the steering assist force is applied in a direction to stabilize the posture of the vehicle 1 by the electric power steering 22.
In the ABS function in the braking system ECU 72, the slip ratios of the left front wheel 11, the right front wheel 12, the left rear wheel 13 and the right rear wheel 14 are determined from the wheel speeds of the wheels detected by the wheel speed sensors 61, 62, 63, 64. And the hydraulic pressure supplied from the brake hydraulic unit 51 to the brakes 41, 42, 43, 44 is controlled so that the calculated slip ratio becomes an optimum value.

FIG. 4 is a functional block diagram of the steering ECU 71 in the steering force control apparatus of this embodiment.
As shown in the figure, the steering ECU 71 includes a one-wheel idling detection means 101, an additional torque control means 102, and an additional torque control time restriction means 103.
The one-wheel idling detection means 101 includes a calculation means 111, a wheel speed state determination means 112, a wheel speed difference first threshold value determination means 113, an accelerator operation determination means 114, and an idling determination means 115.
Further, the additional torque control means 102 includes an additional torque direction determination means 121 and an additional torque control execution means 122.

  The one-wheel idling detection means 101 is based on the wheel speed difference between the left front wheel 11 and the right front wheel 12 calculated by the calculation means 111 from the wheel speeds of the left and right pair of left front wheels 11 and right front wheels 12 and the change rate of the wheel speed difference. When the pair of left and right wheels are accelerated, one-wheel idling that may occur on either one of the pair of left and right wheels is detected.

  When the one-wheel idling detection means 101 detects that the one-wheel idling detection means 101 detects that the one-wheel idling is detected, the additional torque control means 102 generates an additional torque that is sufficient to suppress the steering taking off during one-wheel idling in response to the operation of the steering shaft 32, the steering wheel 33, and the like. The electric power steering 22 is controlled so as to be added.

  The additional torque control time restricting means 103 restricts the control of the additional torque by the electric power steering 22 that is sufficient to suppress the steering that occurs during the idling of one wheel at a certain time.

  The wheel speed state determination means 112 determines a state in which the wheel speed difference between the pair of left and right left front wheels 11 and the right front wheel 12 and the change rate of the wheel speed difference between the wheels are increasing.

  The wheel speed difference first threshold determination means 113 determines whether or not the magnitude of the wheel speed difference between the pair of left and right left front wheels 11 and right front wheels 12 exceeds a first threshold.

  The accelerator operation determination means 114 determines whether or not the accelerator opening exceeds a predetermined value.

  The idling determination means 115 determines that the wheel speed difference between the wheels and the change rate of the wheel speed difference are both increased by the wheel speed state determination means 112, and the wheel speed difference first threshold value is determined. When the determining means 113 determines that the wheel speed difference between the wheels exceeds the first threshold, and the accelerator operation determining means 114 determines that the accelerator opening exceeds a predetermined value. Then, the one-wheel idling state of any one of the pair of left and right wheels is determined.

  The additional torque direction determining means 121 determines that the wheel speed difference between the wheels and the rate of change of the wheel speed difference are both increased by the wheel speed state determining means 112, and the wheel speed difference is determined. The threshold value determining means 113 determines that the wheel speed difference between the wheels exceeds the first threshold value, and the accelerator operation determining means 114 determines that the accelerator opening exceeds a predetermined value. Then, based on the wheel speed difference between the wheels, the direction of the additional torque that suppresses the steering that occurs when one wheel idles is determined.

  The additional torque control execution means 122 determines that the one-wheel idle state is determined by the idling determination means 115, and the wheel speed difference between the wheels exceeds the first threshold by the wheel speed difference first threshold determination means 113. And when the accelerator operation determination means 114 determines that the accelerator opening exceeds a predetermined value, the steering shaft 32, the steering in the direction determined by the additional torque direction determination means 121 is determined. Control of the electric power steering 22 is executed so as to add a constant torque whose magnitude is set as an additional torque setting value in accordance with the determined direction in response to the operation of the wheel 33 or the like.

Next, the operation will be described.
FIG. 2 is a flowchart showing the operation of the steering force control apparatus of this embodiment. The operation will be described below according to this flowchart.
First, the calculation means 111 of the steering ECU 71 calculates the wheel speed difference between the left front wheel 11 and the right front wheel 12 and the rate of change of the wheel speed difference based on the detection outputs of the wheel speed sensor 61 and the wheel speed sensor 62. (Step S1).
Subsequently, the CPU of the steering ECU 71 determines whether or not the posture stabilization control is being executed based on the control flag Fw (step S2).
The control flag Fw is a flag that is set while the CPU of the steering ECU 71 is executing the posture stabilization control. Since the initial state of the steering ECU 71 of the vehicle 1 is set to a state in which the posture stabilization control is not executed, the control flag Fw is not initially set. Therefore, the process proceeds from step S2 to step S3.

In step S3, the wheel speed state determination means 112 of the steering ECU 71 determines the wheel speed of the left front wheel 11 and the right front wheel 12 based on the rate of change of the wheel speed difference between the left front wheel 11 and the right front wheel 12 calculated in step S1. It is determined whether or not both speeds are accelerating. That is, it is determined whether or not the vehicle 1 is in a starting state.
As a result, if it is determined that the wheel speeds of the left front wheel 11 and the right front wheel 12 are not accelerating, that is, if the wheel speeds of the left front wheel 11 and the right front wheel 12 are both constant, the vehicle 1 is stable. It is determined that the vehicle is traveling in the state, and the process proceeds to step S11.

On the other hand, if it is determined in step S3 that the wheel speeds of the left front wheel 11 and the right front wheel 12 are both accelerating, it is determined that the vehicle 1 is in a starting state, and then the left front wheel 11 and the right front wheel 12 It is determined whether or not the absolute value of the change rate of the wheel speed difference exceeds the left and right wheel speed difference change rate on threshold value α (step S4).
The left / right wheel speed difference change rate on threshold value α is a reference value for determining the idling state of the left front wheel 11 or the right front wheel 12. When the absolute value of the change rate of the wheel speed difference between the left front wheel 11 and the right front wheel 12 exceeds the left and right wheel speed difference change rate on threshold value α, it is determined that the left front wheel 11 or the right front wheel 12 is idling. To do.
If it is determined that the absolute value of the change rate of the wheel speed difference between the left front wheel 11 and the right front wheel 12 does not exceed the left and right wheel speed difference change rate on threshold value α, the process proceeds to step S11.

  On the other hand, if it is determined that the absolute value of the change rate of the wheel speed difference between the left front wheel 11 and the right front wheel 12 exceeds the left and right wheel speed difference change rate on threshold value α, the wheel speed state determination means 112 of the steering ECU 71 continues. It is then determined whether the sign of the wheel speed difference between the left front wheel 11 and the right front wheel 12 matches the sign of the rate of change in the wheel speed difference between the left front wheel 11 and the right front wheel 12 (step S5).

When the left front wheel 11 is used as a reference, the wheel speed difference between the wheel speed VL of the left front wheel 11 detected by the wheel speed sensor 61 and the wheel speed sensor 62 and the wheel speed VR of the right front wheel 12 is “the left front wheel 11 Wheel speed VL-wheel speed VR "of the front right wheel 12".
If the right front wheel 12 is idling, “wheel speed VL of the left front wheel 11 <wheel speed VR of the right front wheel 12”, and if the left front wheel 11 is idling, “wheel speed VL of the left front wheel 11> right front wheel 12”. Wheel speed VR ".
Therefore, if the right front wheel 12 is idling, the sign of the wheel speed difference between the left front wheel 11 and the right front wheel 12 is “negative”, and if the left front wheel 11 is idling, the wheel speed between the left front wheel 11 and the right front wheel 12 is The sign of the difference is “positive”.

Further, the sign of the change rate of the wheel speed difference between the left front wheel 11 and the right front wheel 12 is “negative” when the idling state of the right front wheel 12 further proceeds, and the idling state of the right front wheel 12 is suppressed. In the state where the wheel speed difference between the left front wheel 11 and the right front wheel 12 converges in the direction of decreasing, it becomes “positive”.
Further, if the state of the left front wheel 11 idling further advances, “positive”, the idling state of the left front wheel 11 is suppressed, and the wheel speed difference between the left front wheel 11 and the right front wheel 12 is converged in a smaller direction. “Negative” in this state.

Therefore, when the sign of the wheel speed difference between the left front wheel 11 and the right front wheel 12 matches the sign of the change rate of the wheel speed difference between the left front wheel 11 and the right front wheel 12, the right front wheel 12 is idle. In this state, it is the idling state of the right front wheel in which this state is proceeding, or the idling state of the left front wheel in which this state is proceeding while the left front wheel 11 is idling.
Further, when the sign of the wheel speed difference between the left front wheel 11 and the right front wheel 12 and the sign of the change rate of the wheel speed difference between the left front wheel 11 and the right front wheel 12 do not match, the left front wheel 11 or the right front wheel 12 Even if the wheel is idling, the idling state of the left front wheel 11 or the right front wheel 12 is suppressed, and the wheel speed difference between the left front wheel 11 and the right front wheel 12 is converged in a smaller direction.

In step S5, by determining whether the sign of the wheel speed difference between the left front wheel 11 and the right front wheel 12 matches the sign of the rate of change in the wheel speed difference between the left front wheel 11 and the right front wheel 12, It is determined whether the right front wheel idling condition or the left front wheel idling condition is maintained.
If it is determined in step S5 that the sign of the wheel speed difference between the left front wheel 11 and the right front wheel 12 does not match the sign of the rate of change in the wheel speed difference between the left front wheel 11 and the right front wheel 12, the process proceeds to step S11. On the other hand, if it is determined that the sign of the wheel speed difference between the left front wheel 11 and the right front wheel 12 matches the sign of the rate of change in the wheel speed difference between the left front wheel 11 and the right front wheel 12, the process proceeds to step S6.

In step S6, the wheel speed difference first threshold value determination means 113 of the steering ECU 71 determines that the absolute value of the wheel speed difference between the front left and right wheel speeds of the left front wheel 11 and the right front wheel 12 calculated and calculated is the left and right wheel speed difference on threshold value. It is determined whether or not β is exceeded.
The left and right wheel speed difference on threshold value β is, for example, one having higher hysteresis characteristics for determining the situation in which the left front wheel 11 or the right front wheel 12 is idling from the wheel speed difference between the left front wheel 11 and the right front wheel 12. ON threshold value.
When it is determined that the absolute value of the wheel speed difference between the front left and right wheel speeds of the left front wheel 11 and the right front wheel 12 does not exceed the left and right wheel speed difference on threshold value β, the left front wheel 11 or the right front wheel 12 is idling. Since there is no situation, the process proceeds to step S11.

On the other hand, if it is determined that the absolute value of the wheel speed difference between the front left and right wheel speeds of the left front wheel 11 and the right front wheel 12 exceeds the left and right wheel speed difference on threshold value β, the accelerator operation determination means 114 of the steering ECU 71 It is determined whether or not the accelerator opening exceeds the accelerator opening on threshold value η (step S7), and the driver's accelerator operation of the vehicle 1 is checked.
Whether or not the accelerator opening exceeds the accelerator opening on threshold value η is determined based on information about the accelerator opening acquired from the control system ECU 72 by the steering ECU 71 communicating with the control system ECU 72. Do. Further, the accelerator opening on threshold value η is an on threshold value having higher hysteresis characteristics, for example, for detecting the accelerator operation of the vehicle 1 by the driver.

As a result, if it is determined that the accelerator opening does not exceed the accelerator opening on threshold value η, it is determined that the accelerator operation of the vehicle 1 by the driver is not performed, and the process proceeds to step S11.
The process after step S11 is a process that does not execute the attitude stabilization control, and the CPU of the steering ECU 71 sets “0” to the additional torque direction variable γ that defines the direction of the additional torque. “0” is set to the timer value Timer that defines the control cycle of the stabilization control, and in the next step S13, the process proceeds to step S14 without setting the control flag Fw.
In step S14, it is determined whether or not “1” is set in the control flag Fw, that is, whether or not the control flag Fw is set. At this time, the control flag Fw is not set.
For this reason, the process proceeds to step S17, where “0” is set as the set value of the additional torque Tw that is the additional torque added by the additional torque control, the additional torque control is not performed (step S16), and this processing routine is returned from the return. Exit.

  On the other hand, if it is determined in step S7 that the accelerator opening exceeds the accelerator opening on threshold value η, the process proceeds to step S8. In step S8, the additional torque direction determining means 121 of the steering ECU 71 sets the sign corresponding to the front left and right wheel speed difference obtained by the above calculation to the additional torque direction variable γ by the sign function “sgn”. In the subsequent step S9, the CPU of the steering ECU 71 sets “0” to the timer value Timer that defines the control cycle of the posture stabilization control, and further sets the control flag Fw in the next step S10, and proceeds to step S14. .

  In step S14, it is determined whether or not “1” is set in the control flag Fw. At this time, “1” is set in the control flag Fw, that is, the control flag Fw is set. Proceeding to S15, the additional torque control executing means 122 of the steering ECU 71 sets a value obtained by multiplying the additional torque direction variable γ by the additional torque setting value Tw0, that is, a torque corresponding to the direction of the additional torque, as the additional torque Tw. To do. Subsequently, the additional torque control process of step S16 is executed, and the process routine is exited from the return.

FIG. 3 is an explanatory diagram showing the additional torque applied in the electric power steering 22 of the vehicle that starts on the μ split road surface by the additional torque control of the steering force control device of this embodiment.
The direction indicated by the arrow P is the direction of the additional torque added by the additional torque control.

  The idle rotation of the left front wheel 11 or the right front wheel 12 is detected from the wheel speed difference between the left front wheel 11 and the right front wheel 12 and the rate of change of the wheel speed difference, and the difference in driving force between the left front wheel 11 and the right front wheel 12 is detected. A constant additional torque is constant in the electric power steering 22 of the vehicle starting on the μ split road surface so as to operate the steering in the direction to suppress the generated vehicle deflection, that is, the direction in which the wheel speed is low and the direction of the high friction coefficient road surface. Add time.

  The CPU of the steering ECU 71 executes each process from step S1 in the next program cycle. In this program cycle, the calculation means 111 determines the wheel speed difference between the left front wheel 11 and the right front wheel 12 based on the detection outputs of the wheel speed sensor 61 and the wheel speed sensor 62 in step S1, and the rate of change of the wheel speed difference. Is calculated. Subsequently, the CPU of the steering ECU 71 determines whether or not the posture stabilization control is being executed by determining whether or not the control flag Fw is set (step S2). At this time, since the control flag Fw is set in step S10 of the previous program cycle, the process proceeds from step S2 to step S21.

In step S21, the steering ECU 71 determines whether or not the absolute value of the wheel speed difference between the left front wheel 11 and the right front wheel 12 is greater than the left and right wheel speed difference off threshold β1.
This left and right wheel speed difference off threshold β1 constitutes, for example, a hysteresis characteristic for detecting the wheel speed difference between the left front wheel 11 and the right front wheel 12 when the left front wheel 11 or the right front wheel 12 is idling. Is the lower off threshold.
When the absolute value of the wheel speed difference between the left front wheel 11 and the right front wheel 12 exceeds the left and right wheel speed difference off threshold value β1, the left front wheel 11 or the right front wheel 12 is idle, and the vehicle 1 is unstable. It shows that the car is running in a state.
Further, when the absolute value of the wheel speed difference between the left front wheel 11 and the right front wheel 12 does not exceed the left and right wheel speed difference off threshold value β1, the left front wheel 11 or the right front wheel 12 is not idling, and the vehicle 1 Indicates that the vehicle is running in a stable state.

  If it is determined in step S21 that the absolute value of the wheel speed difference between the left front wheel 11 and the right front wheel 12 is smaller than the left and right wheel speed difference off threshold β1, that is, the left front wheel 11 or the right front wheel 12 is not idling, and the vehicle Since 1 is traveling in a stable state, the process proceeds to step S27.

On the other hand, if it is determined in step S21 that the absolute value of the wheel speed difference between the left front wheel 11 and the right front wheel 12 is greater than the left and right wheel speed difference off threshold β1, the accelerator opening at this time is further greater than the accelerator opening off threshold η1. Is determined by the accelerator operation determination means 114 of the steering ECU 71 (step S22).
The accelerator opening OFF threshold value η1 is a lower OFF threshold value that constitutes, for example, hysteresis characteristics for determining the accelerator opening amount and the accelerator operation, and the accelerator opening amount is larger than the accelerator opening OFF threshold value η1. Then, it is determined that the accelerator operation by the driver is being performed, that is, the vehicle 1 is in an acceleration state.

  If it is determined in step S22 that the accelerator opening is smaller than the accelerator opening OFF threshold η1, the process proceeds to step S27 assuming that the accelerator operation by the driver is not being performed, that is, the vehicle 1 is not in the acceleration state.

On the other hand, if it is determined in step S22 that the accelerator opening is larger than the accelerator opening OFF threshold η1, the process proceeds to step S23.
In step S23, it is determined whether or not a timer value equal to or shorter than the flag on maximum time μ is set in the timer. The flag on maximum time μ defines a period during which the flag Fw is set, that is, a maximum time during which the additional torque control is executed.
Accordingly, if a timer value exceeding the flag on maximum time μ is set in the timer in step S23, that is, if the period during which the additional torque control is being executed exceeds the maximum time μ, the process proceeds to step S27.

When executing the determination process in step S23, the timer value “0” is set in the previous program cycle. Therefore, in step S23, it is determined that a timer value equal to or less than the flag on maximum time μ is set in the timer, and the process proceeds to step S24.
In step S24, an additional torque direction variable γ is set as a variable that defines the direction of the additional torque.
In the subsequent step S25, the control cycle Ts is added to the current timer value as a timer value for the timer.
Then, the control flag Fw is set, that is, the control flag Fw is set to “1” (step S26), and the process proceeds to the next step S14.

On the other hand, when the process proceeds to step S27 in step S21, step S22 or step S23, that is, when the vehicle 1 is traveling in a stable state, the vehicle 1 is not in an acceleration state, or a period during which additional torque control is being executed. Is greater than the maximum time μ, “0” is set to the additional torque direction variable γ in step S27.
In a succeeding step S28, "0" is set as a timer value in the timer. Then, in the next step S29, “0” is set to the control flag Fw that was set to “1”, and the process proceeds to step S14.

In step S14, the CPU of the steering ECU 71 determines whether or not the control flag Fw is “1”, that is, whether or not the control flag Fw is set. In step S21, step S22 or step S23, step S27 is performed. In other words, when the vehicle 1 is traveling in a stable state, when the vehicle 1 is not in an acceleration state, or when the period during which the additional torque control is executed exceeds the maximum time μ, the control flag Fw 1 ”is not standing.
Therefore, the process proceeds to step S17, where “0” is set as the set value of the additional torque Tw, the additional torque control is not performed (step S16), and this processing routine is exited from the return.

  On the other hand, in step S21, step S22 or step S23, the left front wheel 11 or the right front wheel 12 is idling, and the vehicle 1 is traveling in an unstable state, the vehicle 1 is in an acceleration state, or added. When the period during which torque control is being executed does not exceed the maximum time μ, the control flag Fw is set to “1”, that is, the control flag Fw is set. Therefore, the process proceeds to step S15, and the additional torque control execution means 122 of the steering ECU 71 sets a value obtained by multiplying the additional torque direction variable γ by the additional torque setting value Tw0 as the additional torque Tw. Subsequently, the additional torque control process of step S16 is executed, and the process routine is exited from the return.

In the additional torque control process in step S16 at this time, taking the case shown in FIG. 3 as an example, the direction indicated by the arrow P is the direction of the additional torque added by the additional torque control.
The idle rotation of the left front wheel 11 or the right front wheel 12 is detected from the wheel speed difference between the left front wheel 11 and the right front wheel 12 and the rate of change of the wheel speed difference, and the difference in driving force between the left front wheel 11 and the right front wheel 12 is detected. A constant additional torque is constant in the electric power steering 22 of the vehicle starting on the μ split road surface so as to operate the steering in the direction to suppress the generated vehicle deflection, that is, the direction in which the wheel speed is low and the direction of the high friction coefficient road surface. Add time.

As described above, according to this embodiment, when the vehicle starts on the μ split road surface or when the vehicle accelerates, the vehicle posture becomes unstable when the left front wheel 11 or the right front wheel 12 idles. On the other hand, the wheel speed of the left front wheel 11 detected by the wheel speed sensor 61 at the time of vehicle start or vehicle acceleration, the wheel speed of the right front wheel 12 detected by the wheel speed sensor 62, and the wheels of the left front wheel 11 and the right front wheel 12 are detected. Appropriate steering assist force is added based on the change rate of the speed difference.
For this reason, steering force control that can improve the stability of the vehicle by avoiding "steering of the steering wheel" when starting or accelerating the vehicle on the μ-split road surface without increasing the cost with a simple configuration. There is an effect that a device can be provided.

  Further, the wheel speed of the left front wheel 11 detected by the wheel speed sensor 61, the wheel speed of the right front wheel 12 detected by the wheel speed sensor 62, and the rate of change of the wheel speed difference between the left front wheel 11 and the right front wheel 12 are also included. In addition, when starting or accelerating on a μ-split road surface, when the left front wheel 11 or the right front wheel 12 is idle, the vehicle posture becomes unstable and the steering wheel operation becomes difficult. It is possible to provide a steering force control device that can improve the stability of the vehicle and the operability of the steering wheel when starting on a μ-split road surface. is there.

  In addition, in order to improve the start / acceleration on the μ split road surface, in vehicles equipped with LSD (Limited Slip Differential) which is a mechanism for suppressing either left or right idling, Steering force that achieves both start / acceleration on a μ-split road and vehicle stability can be achieved by using a larger steering wheel than a vehicle without LSD. There is an effect that a control device can be provided.

  DESCRIPTION OF SYMBOLS 11 ... Left front wheel, 12 ... Right front wheel, 22 ... Electric power steering (steering assist means), 32 ... Steering shaft (steering means), 33 ... Steering wheel (steering means), 61, 62 ... Wheel Speed sensor (wheel speed detection means), 71... Steering ECU, 101... Single wheel idling detection means, 102... Additional torque control means, 103. Wheel speed state determining means, 113... Wheel speed difference first threshold value determining means, 114... Accelerator operation determining means, 115. .

Claims (4)

Steering means for changing the direction of the pair of left and right wheels according to the operation of the driver;
Steering assist means for adding a steering assist force to the operation of the steering means;
Wheel speed detection means for detecting the wheel speed of each of the pair of left and right wheels;
Calculation means for calculating the wheel speed difference between the pair of left and right wheels and the rate of change of the wheel speed difference from the wheel speed of each wheel detected by the wheel speed detection means;
Based on the wheel speed difference calculated by the calculation means and the rate of change of the wheel speed difference, one-wheel idling that may occur on either one of the pair of left and right wheels is detected during acceleration of the pair of left and right wheels. One-wheel idling detection means
When the one-wheel idling detection means detects one-wheel idling, the steering assist means adds an additional torque to the operation of the steering means that is sufficient to suppress the steering taking off during the one-wheel idling by the steering assist means. Additional torque control means for controlling the means ,
The one-wheel idling detection means includes
Based on the wheel speed of each wheel detected by the wheel speed detecting means, it is determined whether both the wheel speed difference between the wheels and the rate of change of the wheel speed difference between the wheels are increasing. Wheel speed state determination means to perform,
When it is determined by the wheel speed state determining means that the wheel speed difference between the wheels and the rate of change of the wheel speed difference are both increasing, the magnitude of the wheel speed difference between the wheels is determined. Wheel speed difference first threshold determination means for determining whether or not the first threshold is exceeded;
When the wheel speed difference first threshold value determining means determines that the wheel speed difference between the wheels exceeds the first threshold value, it is determined whether or not the accelerator opening exceeds a predetermined value. Accelerator operation determination means for
The wheel speed state determining means determines a state in which both the wheel speed difference between the wheels and the rate of change of the wheel speed difference are increasing, and the wheel speed difference first threshold determining means determines between the wheels. If the wheel speed difference between the left and right wheels is determined to be greater than a first threshold value and the accelerator operation determination means determines that the accelerator opening exceeds a predetermined value, Idling judging means for judging one of the one-wheel idling state;
A steering force control device comprising:   2. The steering force according to claim 1, wherein the additional torque has a direction and a magnitude corresponding to the wheel speed difference, and is applied to the operation of the steering means for a predetermined time. Control device. The additional torque control means includes
The wheel speed state determining means determines a state in which both the wheel speed difference between the wheels and the rate of change of the wheel speed difference are increasing, and the wheel speed difference first threshold determining means determines between the wheels. If it is determined that the wheel speed difference of the vehicle exceeds the first threshold value and the accelerator operation determination means determines that the accelerator opening exceeds a predetermined value, the wheel speed between the wheels is determined. Based on the difference, additional torque direction determining means for determining the direction of the additional torque that suppresses the steering that occurs during the idling of one wheel;
A one-wheel idling state is determined by the idling determination means, the wheel speed difference first threshold determination means determines that the magnitude of the wheel speed difference between the wheels exceeds a first threshold, and the accelerator operation determination When the accelerator opening is determined to exceed the predetermined value by means the direction determined by the additional torque direction determining means, with respect to operation of the steering means, the size as the additional torque setpoint setting Additional torque control execution means for executing control of the steering assist means so as to add the constant torque that is made to have a magnitude corresponding to the determined direction, and
The steering force control device according to claim 1, further comprising: 4. The steering force control device according to claim 3 , further comprising additional torque control time restriction means for restricting the control of the steering assist means executed by the additional torque control execution means to a predetermined time.

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