Control apparatus of a variable damping force damper

1. A control apparatus of a variable damping force damper of a current control type used to suspend a vehicle body of a vehicle, comprising:

a dynamic state sensor for detecting a dynamic state of the vehicle body;

a road surface condition determination unit for determining a surface condition of a road on which the vehicle is traveling;

a target damping force setting unit for setting a target damping force of the variable damping force damper based on the dynamic state of the vehicle body detected by the dynamic state sensor, the target damping force setting unit performing an attitude control under a prescribed dynamic state of the vehicle body;

a target current setting unit for setting a target current for the variable damping force damper based on the target damping force set by the target damping force setting unit and a stroke speed of the variable damping force damper;

a first low-pass filter for cutting off high frequency components of the target current;

a second low-pass filter for cutting off high frequency components of the target current, the second low-pass filter having a different response characteristic from that of the first low-pass filter; and

a low-pass filter selection unit for selecting one of the first and second low-pass filters based on at least one of the dynamic state of the vehicle body detected by the dynamic state sensor and the road surface condition determined by the road surface condition determination unit,

the low-pass filter selection unit selecting the first low-pass filter when an irregular road surface is detected by the road surface condition determination unit or when the attitude control is not being performed, and selecting the second low-pass filter when an irregular road surface is not detected by the road surface condition determination unit and the attitude control is being performed.

2. The control apparatus of a variable damping force damper according to claim 1 , wherein the road surface condition determination unit determines the road surface condition based on at least one of an operating state of the variable damping force damper and a vertical dynamic state of the vehicle body.

3. The control apparatus of a variable damping force damper according to claim 2 , wherein the road surface condition determination unit calculates an oscillation frequency of the variable damping force damper based on the stroke speed, and determines the road surface condition based on the oscillation frequency.

4. The control apparatus of a variable damping force damper according to claim 3 , wherein the road surface condition determination unit determines that the road surface has irregularities when the stroke speed exceeds a higher threshold value within a predetermined time period from a point where the stroke speed last becomes lower than a lower threshold value or when the stroke speed becomes lower than the lower threshold value within the predetermined time period from a point where the stroke speed last exceeds the higher threshold value, and otherwise determines that the road surface is flat, the predetermined time period being a half of one cycle of a sprung mass resonance frequency.

5. The control apparatus of a variable damping force damper according to claim 4 , wherein the low-pass filter selection unit selects one of the first and second low-pass filters that has a higher response characteristic when the road surface condition determination unit determines that the road surface has irregularities.

6. The control apparatus of a variable damping force damper according to claim 4 , wherein the target damping force setting unit provides a signal that can indicate whether or not an attitude control of the vehicle is conducted to the low-pass filter selection unit, and when the road surface condition determination unit determines that the road surface is flat, the low-pass filter selection unit determines whether or not the attitude control of the vehicle body is conducted based on the signal from the target damping force setting unit and selects one of the first and second low-pass filters that has a higher response characteristic when it is determined that the attitude control of the vehicle is not conducted.

7. The control apparatus of a variable damping force damper according to claim 4 , wherein the target damping force setting unit provides a signal for indicating whether or not an attitude control of the vehicle is conducted or not to the low-pass filter selection unit, and when the road surface condition determination unit determines that the road surface is flat, the low-pass filter selection unit determines whether or not the attitude control of the vehicle body is conducted based on the signal from the target damping force setting unit and selects one of the first and second low-pass filters that has a lower response characteristic when it is determined that the attitude control of the vehicle is conducted.

8. A method for controlling a variable damping force damper of a current control type used to suspend a vehicle body of a vehicle, the method comprising the steps of:

detecting a dynamic state of the vehicle body;

determining a surface condition of a road on which the vehicle is traveling;

setting a target damping force of the variable damping force damper based on the dynamic state of the vehicle body, an attitude control being performed under a prescribed dynamic state of the vehicle body;

detecting a stroke speed of the variable damping force damper;

setting a target current for the variable damping force damper based on the target damping force and the stroke speed; and

cutting off high frequency components of the target current with a low-pass filter, wherein the step of cutting off high frequency components comprises a step of selecting one of a first low-pass filter and a second low-pass filter based on at least one of the dynamic state of the vehicle body and the road surface condition, the first and second low-pass filters having different response characteristics from each other,

wherein the first low-pass filter is selected when an irregular road surface is detected or when the attitude control is not being performed, and the second low-pass filter is selected when an irregular road surface is not detected and the attitude control is being performed.

9. The method for controlling a variable damping force damper according to claim 8 , wherein the road surface condition is determined based on at least one of an operating state of the variable damping force damper and a vertical dynamic state of the vehicle body.

10. The method for controlling a variable damping force damper according to claim 9 , wherein the step of determining a surface condition of a road comprises a step of calculating an oscillation frequency of the variable damping force damper based on the stroke speed, and determining the road surface condition based on the oscillation frequency.

11. The method for controlling a variable damping force damper according to claim 10 , wherein it is determined that the road surface has irregularities when the stroke speed exceeds a higher threshold value within a predetermined time period from a point where the stroke speed last becomes lower than a lower threshold value or when the stroke speed becomes lower than the lower threshold value within the predetermined time period from a point where the stroke speed last exceeds the higher threshold value, and otherwise it is determined that the road surface is flat, the predetermined time period being a half of one cycle of a sprung mass resonance frequency.

12. The method for controlling a variable damping force damper according to claim 11 , wherein one of the first and second low-pass filters that has a higher response characteristic is selected when it is determined that the road surface has irregularities.

13. The method for controlling a variable damping force damper according to claim 11 , further comprising a step of determining whether or not an attitude control of the vehicle is conducted, wherein the step of selecting one of a first low-pass filter and a second low-pass filter selects one of the first and second low-pass filters that has a higher response characteristic when it is determined that the road surface is flat and that the attitude control of the vehicle is not conducted.

14. The method for controlling a variable damping force damper according to claim 11 , further comprising a step of determining whether or not an attitude control of the vehicle is conducted, wherein the step of selecting one of a first low-pass filter and a second low-pass filter selects one of the first and second low-pass filters that has a lower response characteristic when it is determined that the road surface is flat and that the attitude control of the vehicle is conducted.