JP4461895B2 - Steering device - Google Patents

Description

  The present invention belongs to a technical field of a steering device that varies a steering gear ratio in accordance with a vehicle speed.

In the conventional steering apparatus, the steering gear ratio is changed in accordance with a change in tire air pressure to suppress the steering characteristic from becoming an understeer tendency or an oversteer tendency (see, for example, Patent Document 1).
JP 7-52622 A

  However, since changes in tire pressure affect the two parameters of "steady steering characteristics" and "turning response", the conventional technology that changes only the steering gear ratio changes the steady steering characteristics associated with changes in tire pressure. Although the fluctuation can be suppressed, there is a problem that it cannot cope with the fluctuation of the turning response.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a steering device that can suppress a change in turning response due to a change in tire air pressure.

In order to achieve the above object, the present invention provides:
A variable gear ratio actuator that varies a steering gear ratio that is a ratio of a steering angle of a steering operation means to a steering wheel turning angle of a vehicle;
Tire pressure detecting means for detecting the tire pressure of each wheel;
Variable gear ratio control means for outputting a control command to the variable gear ratio actuator based on a turning angle control amount corresponding to a steering angle;
With respect to the variable gear ratio actuator, differential steer control means for outputting a control command based on a differential steer control amount set to a larger value as the steering angular velocity of the steering is higher ,
With
When the vehicle rear wheel load is smaller than a predetermined value at which the tire cornering power changes from an increasing tendency to a decreasing tendency as the tire air pressure increases , the differential steering control means When the air pressure is lower than the reference air pressure, the differential steering control amount is reduced as compared with the case where the tire air pressure is the reference air pressure .

  In the steering device of the present invention, when the vehicle responsiveness changes due to the tire air pressure, it can be corrected to keep the motion characteristics of the vehicle constant, and the fluctuation of the turning responsiveness accompanying the change in the tire air pressure Can be suppressed.

Hereinafter, the best mode for carrying out the present invention will be described based on Reference Example 1 and Example 1 .

Reference example 1

First, the configuration will be described.
FIG. 1 is a system block diagram of a vehicle to which the steering device of Reference Example 1 is applied. This vehicle has a front wheel load and a rear wheel load that exceed predetermined values. This is the FR vehicle that was adopted. Further, the steering device of Reference Example 1 can also be applied to vehicles of a hybrid system combining an engine and a motor or an electric motor system.

As shown in FIG. 1, the steering device of Reference Example 1 includes a column shaft 2, a front wheel steering mechanism 3, front wheels (steering wheels) 4 and 4, rear wheels 5 and 5, and a variable gear ratio actuator 6. And a variable gear ratio controller 7, a steering angle sensor 8, a vehicle speed sensor 9, and tire pressure sensors (tire pressure detection means) 10a to 10d.

  The front wheel steering mechanism 3 converts the rotation input to the column shaft 2 from the steering wheel (steering operation means) 1 into a lateral movement of the vehicle by a rack and pinion and steers the front wheels 4 and 4.

  The steered actuator 6 includes, for example, a DC brushless motor (hereinafter referred to as a motor) equipped with a speed reducer. In FIG. 1, an upper column shaft 2 a with a steering wheel 1 attached to the upper end position and a front wheel steered mechanism 3 It arrange | positions in the position between the lower column shaft 2b connected. This variable gear ratio actuator 6 decelerates the rotation input via the upper column shaft 2a by the steering gear ratio and outputs it to the lower column shaft 2b, whereby the steering wheel 1 with respect to the front wheel turning angle δ. The steering gear ratio (θ / δ), which is the ratio of the steering angle θ, is changed.

  The steering angle sensor 8 detects the steering angle θ of the steering wheel 1 and outputs the steering angle information to the variable gear ratio controller 7. For example, the vehicle speed sensor 9 detects the vehicle speed (vehicle body speed) from the rotational speeds of the front wheels 4, 4 and the rear wheels 5, 5 and outputs vehicle speed information to the variable gear ratio controller 7.

  The tire pressure sensors 10a to 10d detect tire pressures of the front wheels 4, 4 and rear wheels 5, 5, and output tire pressure information of the front wheels 4, 4 and tire pressure information of the rear wheels 5, 5 by radio signals. . The variable gear ratio controller 7 receives the outputs of the tire pressure sensors 10a to 10d by the receiver.

  The variable gear ratio controller 7 calculates a target steering gear ratio according to the vehicle speed, calculates a target value of the turning angle control amount according to the target steering gear ratio and the steering angle, and A control command is output based on the calculated turning angle control amount (corresponding to variable gear ratio control means).

  Further, the variable gear ratio controller 7 calculates the target value of the differential steering control amount from the steering steering speed-differential steering control angle setting map shown in FIG. 3 according to the steering angular speed obtained from the steering angle, and the variable gear ratio. A control command is output to the actuator 6 based on the calculated differential steer control amount (corresponding to differential steer control means).

  As shown in FIG. 3, the differential steer control amount is set so as to increase as the steering angular speed increases until the steering angular speed reaches a predetermined speed, so that the responsiveness of the variable gear ratio actuator 6 is enhanced. Further, when the steering angular velocity exceeds a predetermined speed, the constant value is set regardless of the steering angular velocity, and the sudden change in the vehicle behavior is suppressed.

  The characteristic of the target steering gear ratio is performed by changing a plurality of steering gear ratio maps set in advance according to the vehicle speed. In the steering gear ratio map, the steering gear ratio (ratio of the steering angle of the steering wheel 1 to the steering angle of the front wheels 4 and 4) is reduced in the low to medium speed range to make the steering response quick, and the steering gear in the high speed range. By increasing the ratio and slowing down the steering response, it is set to achieve both a light and good steering feeling in the low to medium speed range and a gentle and stable steering feeling in the high speed range. .

  Here, the variable gear ratio controller 7 corrects the target steering gear ratio according to the front wheel tire pressure information obtained from the tire pressure sensors 10a and 10b. Specifically, when the front tire pressure is higher than the design value (reference tire pressure), the target steering gear ratio is increased and the steering response is corrected more slowly than when the front tire pressure is equal to the design value. To do. On the other hand, when the front tire pressure is lower than the design value, the target steering gear ratio is made smaller than when the front tire pressure is equal to the design value, and the steering response is corrected to the quick side.

  Further, the variable gear ratio controller 7 performs differential steer control amount change control for correcting the differential steer control amount (differential steering control angle) according to the rear wheel tire air pressure information obtained from the tire air pressure sensors 10c and 10d.

Next, the operation will be described.
[Differential steer control amount change control processing]
FIG. 2 is a flowchart showing the flow of the differential steer control amount change control process executed by the variable gear ratio controller 7 of Reference Example 1. Each step will be described below.

  In step S1, it is determined whether variable gear ratio steering control is being performed. If yes, then go to step S2, if no, go to return.

  In step S2, tire pressure information of the rear wheels 5 and 5 is received from the tire pressure sensors 10c and 10d, and the process proceeds to step S3.

  In step S3, it is determined whether or not the tire air pressure of the rear wheels 5 and 5 is a design value. If YES, the process proceeds to step S4. If NO, the process proceeds to step S5.

  In step S4, a process of returning the differential steering control amount to the normal state is performed, and the process proceeds to return.

  In step S5, it is determined whether or not the tire air pressure of the rear wheels 5 and 5 is larger than the design value. If YES, the process proceeds to step S6, and if NO, the process proceeds to step S7.

  In step S6, a process for reducing the differential steer control amount is performed, and the process proceeds to return.

  In step S7, a process of increasing the differential steering control amount is performed, and the process proceeds to return.

[Differential steer control amount change control operation]
That is, when the tire air pressure of the rear wheels 5 and 5 is larger than the design value, in the flowchart of FIG. 2, the flow proceeds from step S 1 → step S 2 → step S 3 → step S 5 → step S 6. A process for reducing the differential steering control amount is performed.

  Therefore, when the tire air pressure of the rear wheels 5 and 5 becomes higher than the design value, the tire cornering power of the rear wheels 5 and 5 is increased and the turning response is increased, but the differential steering control amount is decreased. As a result, the turn responsiveness is lowered and the change in vehicle behavior can be reduced.

  When the tire pressures of the rear wheels 5 and 5 are below the design value, the flow proceeds from step S1 to step S2 to step S3 to step S5 to step S7 in the flowchart of FIG. As shown in FIG. 4, a process for increasing the differential steering control amount is performed.

  Therefore, when the tire air pressure of the rear wheels 5 and 5 is lower than the design value, the tire cornering power of the rear wheels 5 and 5 is decreased and the turning response is decreased, whereas the differential steering control amount is increased. As a result, the turn responsiveness is improved and the change in vehicle behavior can be reduced.

[Relationship between tire pressure and tire cornering power]
The relationship between currently analyzed tire pressure and cornering power will be described.

  FIG. 4 is a diagram showing the relationship between wheel load and tire cornering power (CP). As shown in FIG. 4, when the wheel load is larger than a predetermined value, such as front and rear wheels of an FR vehicle and front wheels of an FF vehicle. As the tire pressure increases, the CP value also increases. On the other hand, when the wheel load is smaller than a predetermined value like the rear wheel of the FF vehicle, the CP value decreases as the tire air pressure increases. The wheel load at this change point is set as a predetermined value.

[Relationship between vehicle behavior and tire cornering power]
FIG. 5 is a diagram showing the relationship between the vehicle behavior and the CP value. As shown in FIG. 5, the stability factor decreases as the front wheel tire cornering power FrCP increases, and the oversteer tendency sharply increases. On the other hand, the yaw resonance frequency increases as the tire cornering power RrCP of the rear wheel decreases, and the responsiveness increases rapidly.

  That is, it can be seen that the steady steering characteristic (stability factor) is greatly influenced by the tire cornering power FrCP of the front wheels, and the turning response (yaw resonance frequency) is largely influenced by the tire cornering power RrCP of the rear wheels.

[Problems of conventional technology]
In a conventional steering device, for example, the technique described in Japanese Patent Application Laid-Open No. 7-52622, the steering gear ratio is changed in accordance with the change in tire air pressure to suppress the change in vehicle behavior.

  However, as described above, changes in tire air pressure affect the two parameters of "steady steering characteristics" and "turning response", so the conventional technology that changes only the steering gear ratio results in changes in tire air pressure. Although it can cope with the fluctuations in the steady steering characteristics, it cannot cope with the fluctuations in turning response. As a specific example, it was impossible to reduce responsiveness while reducing understeer.

[Steering gear ratio / differential steer control amount correction for FR vehicles]
On the other hand, in the steering device of Reference Example 1, by correcting the steering gear ratio, it is possible to cope with fluctuations in the steady steering characteristics accompanying changes in the tire air pressure of the front wheels 4 and 4, and by correcting the differential steering control amount. Thus, it is possible to cope with fluctuations in turning responsiveness associated with changes in tire air pressure of the rear wheels 5 and 5.

  That is, the steering gear ratio is corrected in accordance with the change in the tire pressure of the front wheels 4 and 4, and at the same time, the differential steering control amount is corrected in accordance with the change in the tire pressure of the rear wheels 5 and 5, thereby changing the steady steering characteristic. And fluctuations in turning responsiveness can be suppressed, and fluctuations in vehicle motion characteristics associated with changes in tire air pressure can be suppressed.

FIG. 6 shows a method for correcting the steering gear ratio and the differential steer control amount in accordance with changes in the front wheel air pressure and the rear wheel air pressure in the reference example 1 device.

  When both the front tire pressure and the rear tire pressure are lower than the design values, the steering gear ratio is decreased to correct the steering response to the quick side, and the differential steering control amount is increased. Therefore, it is possible to suppress both understeer accompanying a decrease in front wheel tire cornering power and a decrease in turning response due to a decrease in rear wheel tire cornering power.

  When both the front tire pressure and the rear tire pressure are higher than the design values, the steering gear ratio is increased to correct the steering response to the slow side, and the differential steering control amount is reduced. Therefore, it is possible to suppress both oversteering accompanying an increase in front wheel tire cornering power and an increase in turning responsiveness accompanying an increase in rear wheel tire cornering power.

  If the front tire pressure is lower than the design value and the rear tire pressure is higher than the design value, the steering gear ratio is reduced to correct the steering response to the quick side, and the differential steering control amount is reduced. Therefore, it is possible to suppress both the understeer accompanying the decrease in the front tire cornering power and the increase in turning response due to the increase in the rear tire cornering power.

  When the front tire pressure is higher than the design value and the rear tire pressure is lower than the design value, the steering gear ratio is increased to correct the steering response to the slow side, and the differential steering control amount is increased. Therefore, it is possible to suppress both oversteer accompanying an increase in front wheel tire cornering power and a decrease in turning response due to a decrease in rear wheel tire cornering power.

Next, the effect will be described.
In the steering device of Reference Example 1, the effects listed below are obtained.

  (1) The variable gear ratio actuator 6 for changing the steering gear ratio, which is the ratio of the steering angle of the steering wheel 1 to the steered wheel turning angle of the vehicle, and the tire pressures of the front wheels 4, 4 and the rear wheels 5, 5 are detected. A control command is output to the variable gear ratio actuator 6 based on the steering angle control amount according to the steering angle and a control command is output based on the differential steering control amount according to the steering angular velocity. A variable gear ratio controller 7. The variable gear ratio controller 7 changes the differential steer control amount in response to changes in tire air pressure, so that when the vehicle responsiveness changes due to tire air pressure, it corrects it. The motion characteristics of the vehicle can be kept constant.

  (2) In an FR vehicle with a rear wheel load equal to or greater than a predetermined value, the variable gear ratio controller 7 controls the differential steering when the tire air pressure of the rear wheels 5 and 5 is lower than the reference air pressure than when the tire air pressure is the reference air pressure. Since the amount is increased, a decrease in turning response due to a decrease in rear wheel cornering power can be suppressed, and a change in vehicle behavior can be suppressed.

  (3) In an FR vehicle with a rear wheel load equal to or greater than a predetermined value, the variable gear ratio controller 7 performs differential steer control when the tire air pressure of the rear wheels 5 and 5 is higher than the reference air pressure than when the tire air pressure is the reference air pressure. Since the amount is reduced, an increase in turn response with an increase in rear wheel cornering power is suppressed, and fluctuations in vehicle behavior can be suppressed.

  (4) The variable gear ratio controller 7 increases the steering gear ratio when the tire pressure of the front wheels 4 and 4 is higher than the reference air pressure than when the tire air pressure is the reference air pressure. When the air pressure is lower than the air pressure, the steering gear ratio is made smaller than when the tire air pressure is the reference air pressure, so that both fluctuations in steady steering characteristics and fluctuations in turning response can be suppressed.

The steering device of the first embodiment is different from the reference example 1 in that it corresponds to a vehicle having a rear wheel load smaller than a predetermined value, for example, an FF vehicle employing a front engine / front drive driving system. Further, the steering device of the first embodiment can be applied to a hybrid system combining an engine and a motor, an electric motor system, or the like. Since the configuration is the same as that of the reference example 1 shown in FIG. 1, the description of the configuration is omitted.

Next, the operation will be described.
[Differential steer control amount change control processing]
FIG. 7 is a flowchart showing the flow of the differential steer control amount change control process executed by the variable gear ratio controller 7 of the first embodiment. Each step will be described below. Since steps S11 to S15 perform the same processing as steps S1 to S5 in FIG. 2, only different steps will be described.

  In step S16, a process for increasing the differential steering control amount is performed, and the process proceeds to return.

  In step S17, a process for decreasing the differential steering control amount is performed, and the process proceeds to return.

[Differential steer control amount change control operation]
That is, when the tire air pressure of the rear wheels 5 and 5 is larger than the design value, the flow proceeds from step S11 to step S12 to step S13 to step S15 to step S16 in the flowchart of FIG. Processing for increasing the differential steering control amount is performed.

  Therefore, when the tire air pressure of the rear wheels 5 and 5 becomes higher than the design value, the tire cornering power of the rear wheels 5 and 5 decreases and the turning response decreases, whereas the differential steering control amount is increased. As a result, turning response can be improved and changes in vehicle behavior can be reduced.

  When the tire air pressure of the rear wheels 5 and 5 is less than the design value, the flow proceeds from step S11 to step S12 to step S13 to step S15 to step S17 in the flowchart of FIG. As shown in FIG. 5, processing for reducing the differential steering control amount is performed.

  Therefore, when the tire air pressure of the rear wheels 5 and 5 is lower than the design value, the tire cornering power of the rear wheels 5 and 5 is increased and the turning response is increased, while the differential steering control amount is decreased. As a result, the turn responsiveness can be reduced and the change in vehicle behavior can be reduced.

[Correction of steering gear ratio and differential steering control in FF vehicles]
As described above, when the wheel load is small like the rear wheel of an FF vehicle, the CP value decreases and the turn response decreases as the tire air pressure increases, contrary to the FR vehicle. End up. Therefore, in the FF vehicle, when the tire pressure of the rear wheels 5 and 5 is higher than the design value, the differential steering control amount is increased and the turning response is improved, while the tire pressure of the rear wheels 5 and 5 is higher than the design value. If it is low, the differential steering control amount is decreased and the turning response is lowered.

FIG. 8 shows a method for correcting the steering gear ratio and the differential steer control amount in accordance with changes in the front wheel pressure and the rear wheel air pressure in the first embodiment.

  When both the front tire pressure and the rear tire pressure are lower than the design value, the steering gear ratio is reduced to correct the steering response to the quick side, thereby reducing the differential steering control amount. Therefore, it is possible to suppress both the understeer accompanying the decrease in the front wheel tire cornering power and the increase in turning response due to the increase in the rear wheel tire cornering power.

  When both the front tire pressure and the rear tire pressure are higher than the design values, the steering gear ratio is increased to correct the steering response to the slow side, and the differential steering control amount is increased. Therefore, it is possible to suppress both oversteer accompanying an increase in front wheel tire cornering power and a decrease in turning response due to a decrease in rear wheel tire cornering power.

  When the front tire pressure is lower than the design value and the rear tire pressure is higher than the design value, the steering gear ratio is reduced to correct the steering response to the quick side, and the differential steering control amount is increased. Therefore, it is possible to suppress both understeer accompanying a decrease in front wheel tire cornering power and a decrease in turning response due to a decrease in rear wheel tire cornering power.

  If the front tire pressure is higher than the design value and the rear tire pressure is lower than the design value, the steering gear ratio is increased to correct the steering response to the slow side, and the differential steering control amount is reduced. Therefore, it is possible to suppress both oversteering accompanying an increase in front wheel tire cornering power and an increase in turning responsiveness accompanying an increase in rear wheel tire cornering power.

Next, the effect will be described.
In the steering device of the first embodiment, the effects listed below are obtained in addition to the effects (1) and (4) of the reference example 1.

  (5) In an FF vehicle in which the rear wheel load is smaller than a predetermined value, the variable gear ratio controller 7 performs differential steer control when the tire air pressure of the rear wheels 5 and 5 is lower than the reference air pressure than when the tire air pressure is the reference air pressure. Since the amount is reduced, an increase in turning response due to an increase in rear wheel cornering power is suppressed, and changes in vehicle behavior can be suppressed.

  (6) In an FF vehicle in which the rear wheel load is smaller than a predetermined value, the variable gear ratio controller 7 performs differential steer control when the tire air pressure of the rear wheels 5 and 5 is higher than the reference air pressure than when the tire air pressure is the reference air pressure. Since the amount is increased, an increase in turning response due to a decrease in rear wheel cornering power is suppressed, a decrease in turning response due to a decrease in rear wheel cornering power is suppressed, and a change in vehicle behavior can be suppressed.

It is a system block diagram of a vehicle to which the steering device of Reference Example 1 is applied. 7 is a flowchart showing a flow of differential steer control amount change control processing executed by the variable gear ratio controller 7 of Reference Example 1. It is a setting map of steering steering speed-differential steering control angle which shows the correction method of differential steer control amount. It is a figure which shows the relationship between wheel load and tire cornering power. It is a figure which shows the relationship between a vehicle behavior and CP value. It is a figure which shows the correction method of the steering gear ratio and differential steer control amount according to the change of the front-wheel air pressure and the rear-wheel air pressure in the reference example 1 apparatus. 6 is a flowchart showing a flow of differential steer control amount change control processing executed by the variable gear ratio controller 7 of the first embodiment. It is a figure which shows the correction method of the steering gear ratio and differential steer control amount according to the change of the front wheel air pressure and the rear wheel air pressure in Example 1 apparatus.

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Column shaft 2a Upper column shaft 2b Lower column shaft 3 Front wheel steering mechanism 4 Front wheel 5 Rear wheel 6 Variable gear ratio actuator 7 Variable gear ratio controller 8 Steering angle sensor 9 Wheel speed sensor 10 Tire pressure sensor

Claims (3)

A variable gear ratio actuator that varies a steering gear ratio that is a ratio of a steering angle of a steering operation means to a steering wheel turning angle of a vehicle;
Tire pressure detecting means for detecting the tire pressure of each wheel;
Variable gear ratio control means for outputting a control command to the variable gear ratio actuator based on a turning angle control amount corresponding to a steering angle;
With respect to the variable gear ratio actuator, differential steer control means for outputting a control command based on a differential steer control amount set to a larger value as the steering angular velocity of the steering is higher ,
With
When the vehicle rear wheel load is smaller than a predetermined value at which the tire cornering power changes from an increasing tendency to a decreasing tendency as the tire air pressure increases , the differential steering control means When the tire pressure is lower than the reference air pressure, the differential steering control amount is decreased as compared with the case where the tire air pressure is the reference air pressure . A variable gear ratio actuator that varies a steering gear ratio that is a ratio of a steering angle of a steering operation means to a steering wheel turning angle of a vehicle;
Tire pressure detecting means for detecting the tire pressure of each wheel;
Variable gear ratio control means for outputting a control command to the variable gear ratio actuator based on a turning angle control amount corresponding to a steering angle;
With respect to the variable gear ratio actuator, differential steer control means for outputting a control command based on a differential steer control amount set to a larger value as the steering angular velocity of the steering is higher,
With
When the vehicle rear wheel load is smaller than a predetermined value at which the tire cornering power changes from an increasing tendency to a decreasing tendency as the tire air pressure increases, the differential steering control means When the tire pressure is higher than the reference air pressure, the steering control device increases the differential steering control amount as compared with the case where the tire air pressure is the reference air pressure . The steering apparatus according to claim 1 or 2,
The variable gear ratio control means increases the steering gear ratio when the tire pressure of the front wheels is higher than the reference air pressure than when the tire air pressure is the reference air pressure, and when the tire pressure of the front wheels is lower than the reference air pressure, There steering apparatus according to claim to Rukoto small steering gear ratio than that of the reference air pressure.

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