JPH03204328A - Controller for damping force variable shock absorber - Google Patents

Abstract

PURPOSE:To maintain good running performance of a car irrespective of road surface conditions by judging road surface conditions from the integrated value of a physical quantity which is proportional to the recessed and projecting parts of a road surface, and then changing the proportional constant of a control signal for controlling the damping forces of a shock absorber. CONSTITUTION:A physical quantity (loads etc.), which is varied as uneveness of a road surface increases, is detected by a physical quantity detecting means A and its absolute values are integrated by an integrating means B every prede termined time and an integration signal indicative of an average recessed and projecting condition of a road surface is outputted. As the integration signal becomes larger, a proportional constant changing means C decreases the propor tional constant of a control signal controlling the damping force of a shock absorber E and a control signal is generated by multiplying of a proportional constant changed to the absolute value of the physical quantity by a damping force controlling means D, and the shock absorber E is controlled by the control signal. Proper damping forces are thus generated according to the road surface condition so as to maintain good running performance of a car and make it comfortable to ride in the car irrespective of road surface conditions.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a control device for a shock absorber in which a piezo actuator or the like is installed to vary damping force, and the present invention relates to a control device for a shock absorber that has a piezo actuator or the like installed therein and has variable damping force, and is a control device that realizes stable running and a comfortable ride. Regarding.

[Prior art] Shock absorbers with variable damping force that change the generated damping force by changing the diameter of the restrictive flow path provided in the piston through the operation of a piezo actuator are in practical use, and this shock absorber is used to improve the comfort and drivability of vehicles. Various attempts have been made to increase the

Among these, for example, Japanese Patent Application Laid-open No. 64-67407,
A control device has been proposed that detects the damping force change rate of a shock absorber and switches the damping force generated by the shock absorber to a smaller (softer) side when the rate of change exceeds a predetermined threshold.

[Problems to be Solved by the Invention] However, in the proposed device, the threshold value for switching the damping force is determined regardless of the size of the unevenness of the road surface.
When the threshold value is set high, the damping force of the shock absorber is always on the large (hard) side on a good road with small irregularities, and there is a feeling of roughness at joints in the road surface. On the other hand, if the threshold value is set low, the rate of change in damping force will frequently exceed the threshold value on a rough road with large bumps, and the damping force of the shock absorber will become almost soft, impairing steering stability.

Furthermore, since the damping force is switched between ON and OFF, a shock occurs due to a sudden change in the damping force at the time of switching.

SUMMARY OF THE INVENTION The present invention has been made to solve this problem, and an object thereof is to provide a control device for a variable damping force shock absorber that generates an appropriate damping force depending on the driving road surface and realizes comfortable driving.

[Means for Solving the Problems] The configuration of the present invention will be explained with reference to FIG. a physical quantity detecting means for detecting a physical quantity whose amount of change increases as the unevenness of the road surface becomes larger; and an integrating means for integrating the absolute value of the physical quantity at predetermined time intervals and outputting an integrated signal indicating the average unevenness state of the road surface. a proportional constant changing means that decreases the proportional constant as the integrated signal outputted from the integrating means increases; and a damping force controlling means that multiplies the absolute value of the physical quantity by the proportional constant and outputs the product as the control signal. Equipped with:

[Operation] In the control device having the above configuration, on a good road, the unevenness of the road surface is small, and therefore the absolute value of the physical quantity and its integrated value show small values. The proportional constant changing means changes the proportional constant to a large value, but since the absolute value of the physical quantity is sufficiently small, the signal level of the control signal is usually low, and the damping force generated by the shock absorber is on the hard side. This maintains running stability during high-speed running.

At this time, when the unevenness of a road surface joint or the like becomes slightly larger, the absolute value of the physical quantity increases accordingly, and since the proportionality constant is large, the level of the control signal increases rapidly. As a result, the damping force generated by the shock absorber rapidly changes to a soft direction, and the shock is absorbed.

On a rough road with large irregularities, the absolute value of the physical quantity and its integrated value exhibit a large value, and the proportionality constant changing means changes the proportionality constant to a small value.

Therefore, even if the absolute value of the physical quantity is large, the signal level of the control signal is sufficiently low, and the damping force generated by the shock absorber is on the hard side. Therefore, good vibration damping is achieved and running stability is maintained.

When an extremely large vibration is input, the absolute value of the physical quantity also increases rapidly, and the level of the control signal increases rapidly even though the proportionality constant is small. As a result, the damping force generated by the shock absorber rapidly changes to a soft direction, and the shock is absorbed.

In addition, since the damping force of the control device configured as described above is continuously changed in proportion to the absolute value of the physical quantity, there is no shock due to sudden changes in damping force when switching the damping force as in the conventional case, and fine control is possible. It is possible.

[Embodiment] FIG. 2 shows the overall configuration of a control device. The control device 1 includes a CPU II, the operation of which will be described later, a RAM 13, a ROM 14, an input section 15, and an output section 16 connected to the CPU II via a common bus 12. The input section 15 receives damping force data from a damping force detection circuit 17, and the damping force detection circuit 17 receives output signals from load sensors 22 installed in each shock absorber provided at the left and right positions of the front and rear wheels. is inputting.

The input section 15 further receives output signals from a steering sensor 31, a vehicle speed sensor 32, and a brake lamp switch 33 via a waveform shaping circuit 18.

A drive voltage is outputted from the output section 16 via a drive circuit 19 to a piezo actuator 21 installed inside each shock absorber.

Figure 3 shows a cross section of the main parts of the shock absorber.

In the figure, the inner space of the cylinder 23 of the shock absorber 2 is divided into upper and lower parts by a main piston 24 to form hydraulic chambers 2a and 2b, respectively, and the main piston 24 is fixed to a piston rod 25 that is fitted through the center.
The piston rod 25 is connected to the lower end of an upwardly extending shaft 26.

The main piston 24 has a contraction-side fixed orifice 241 and an extension-side fixed orifice 2 on its outer periphery.
42 are formed and are opened and closed by plate-shaped check valves 243 and 244 provided on the upper and lower surfaces of the main piston 24, respectively. Inside the piston rod 25, there is a sub-flow passage 25 which passes through the rod center and exits downward from the side facing the upper hydraulic chamber 2a.
1 is formed, and the sub-flow passage 251 has its flow passage cross-sectional area changed by an annular groove on the outer periphery of the sprue valve 252 that operates up and down.

The lower end of the shaft 26 is shaped into a cylinder, and the piezo actuator 21 is provided inside the cylinder. The piezo actuator 21 is constructed by laminating a large number of piezoelectric ceramic plates such as PZT, and expands and contracts in response to a drive voltage supplied through a lead wire 211. A piston 212 is provided in contact with the lower end of the piezo actuator 21, and an oil-tight chamber 21.3 is formed below the piston 2]-2.
A plunger 214 faces the oil-tight chamber 213 and is movable up and down.
is arranged. This plunger 214 is connected to the spool valve 252.

The load sensor 22 is provided at the uppermost end of the cylinder at the lower end of the shaft 26, and the load sensor 22 is made by stacking piezoelectric ceramic plates with electrodes in between. emits an output signal according to the

Therefore, when the main piston 24 moves downward during the contraction operation, the sealed oil flows between the hydraulic chambers 2a and 2b through the large-diameter fixed orifice 241 on the contraction side, producing a slightly small damping force, while the main piston 24 moves upward during the extension operation, the small diameter fixed orifice 2 on the extension side
The sealed oil flows between the hydraulic chambers 2a and 2b via 42, producing a somewhat large damping force.

These damping forces can be continuously changed by operating the spool valve 252 by the piezo actuator 21 and continuously changing the flow passage cross-sectional area of the sub-flow passage 251.

That is, as shown in FIG. 4, any damping force can be generated between the characteristics x, y when the cross-sectional area of the flow path is increased and the characteristics x-1y- when the cross-sectional area of the flow path is decreased. .

Here, the length of the piezo actuator 21 changes due to thermal expansion when the ambient temperature changes.

Further, while the volume of the sealed oil increases due to thermal expansion, a considerable amount of the sealed oil leaks from the oil-tight chamber 213, and the volume decreases due to this leakage. Therefore, even if the piezo actuator is energized under the same conditions, the amount of movement of the spool valve 252 fluctuates due to the influence of ambient temperature and oil leakage, and the damping force may not be uniquely determined.

Therefore, in this embodiment, the piezo actuator 21 is caused to perform expansion and contraction operations at predetermined intervals (for example, every 10 minutes), and sealed oil is introduced into the oil-tight chamber 213 via the check valve 30. As a result, the piezo actuator 21 contracts. At times, the oil-tight chamber 2]-3 is filled with sealed oil to correct volume reduction due to oil leakage.Furthermore, even if the length of the piezo actuator 21 changes due to temperature changes, the oil-tight chamber 2-3 is filled with sealed oil.
The amount of oil sealed in the piezoelectric actuator 13 cancels out the variation, so that a damping force corresponding to the amount of current applied to the piezo actuator 21 can be obtained at all times.

FIG. 5 shows the structure of the damping force detection circuit, and the output signal of the load sensor provided in each shock absorber is received by a buffer 174 through a radio noise removal filter 171, a bypass filter 172, and a low-pass filter 173. Since the above output signal corresponds to the damping force change rate of the shock absorber 2, it is further transmitted to the integrating circuit 1 in the subsequent stage.
75, the signal becomes a signal corresponding to the damping force, passes through a bypass filter 178, is digitally converted by an A/D converter 176, and is sent to the input section 15 (FIG. 2).

In addition, in the figure, 177 is an offset voltage generation circuit.

As shown in FIG. 6, the bypass filter 178 cuts signal components of approximately 2.5 Hz or less, thereby eliminating the sprung mass resonance frequency range (approximately 11-I z ) of the output signal of the load sensor. Since the 0 system does not respond to the shock absorber, the damping force of the shock absorber remains in a hard state, and the tilting vibration is reduced.

FIG. 8 shows the configuration of the drive circuit 19. CFull above
The digital control signal outputted from the converter (FIG. 2) is converted into an analog signal by a D/A converter 191, passes through a low-pass filter 199, and is input to a comparator 192. The comparator 192 converts the control signal voltage into the buffer 196.
The voltage is compared with the voltage of the piezoelectric charge amount detection capacitor 198 fed back through the . When the control signal voltage is large, a "1" level signal is output from the comparator 192, the photocoupler 193A is turned off, and the output FET is disconnected.
194A becomes conductive, and the high voltage generated by the DC/DC converter 197 is applied to the piezo actuator 21 to charge it.

The charging current at this time is kept constant by the current feedback circuit 195A.

When the voltage of the actuator 21 increases and the feedback voltage exceeds the control signal voltage, the output signal of the comparator 192 becomes "0" level. When the comparator signal reaches the "0" level, the photocoupler 193B is turned off and the output FET 19 is disconnected.
4B becomes conductive, and the piezo actuator 21 is discharged. The discharge current is kept constant by current feedback circuit 195B.

In this way, the amount of charge accumulated in the actuator 21, that is, the amount of its extension, corresponds to the signal level of the control signal, and the damping force generated by the shock absorber 2 is continuously changed by the control signal.

As shown in FIG. 7, the low-pass filter 199 allows only signal components of approximately 40 Hz or less to pass. Thereby, it is possible to prevent a problem in which high frequency components are mixed into the drive signal to the piezo actuator 21 and cause noise.

Before explaining the operating procedure of the CPU II, the flow of signals in the control device will be explained with reference to FIG.

2. The damping force signal Fc obtained by integrating the output of the load sensor 22 of the shock absorber 2 is passed through the bypass filter 178 and converted into an absolute value in the CPU 11, and the damping force absolute value signal Fca is integrated by a certain number of values. This becomes a value signal WFc. On the other hand, the damping force absolute value signal Fca has a proportionality constant K
p is multiplied, and various correction signals ΣVi, which will be described later, are added to the control signal Vs, which is passed through the low-pass filter 199 and then output to the piezo actuator 21 of the shock absorber 2 as described above. .

Here, FIG. 10 shows an example of the time change of each of the above-mentioned signals. The amount of change in the damping force signal Fc increases according to the unevenness of the road surface, and the integrated value signal WFc obtained by integrating the absolute value signal Fca of this signal indicates the average value of the road surface unevenness, that is, the road surface condition. As shown in FIG. 11, the proportionality constant Kp linearly decreases from a positive constant value to 0 as the integrated value signal WFc increases, that is, as the road changes from a good road to a bad road. Therefore, the 3 Kp correction map in FIG. 9 is stored with correction values that change the proportionality constant Kp as shown in FIG. 11 for each integrated value signal value WFc.

Now, the processing procedure within the CPU II will be explained below with reference to FIG.

In step 101, data is initialized, and in step 102, steering, vehicle speed, and brake driving state signals are input. Next, the damping force signal Fc (FIG. 9) is input (step 103), and its absolute value Fca is calculated (step 1o4), and then integrated (step 105).

This integrated value WFc is obtained, for example, every 2 ms by moving and integrating data as follows.

WFc (n)=WFc (n-1)+Fca (n)
-Fca (n-k) Here, WFc (n) and Fca (n) respectively indicate the integrated value and the absolute value of the damping force at the time of the n-th sample.

In step 106, the proportional constant Kp is corrected by 4 to a correction value corresponding to the integrated value WFc with reference to the proportional constant correction map (FIG. 9). This gives the constant of proportionality k
As shown in FIG. 11 above, p is decreased as the integrated value WFC increases.

In step 107, the control signal Vs is calculated using the following formula.

Vs = Kp . ■2 is a correction term that takes a constant negative value when stepping on the brake or turning the steering wheel. In other words, the faster the vehicle travels, the
Alternatively, the value of the control signal Vs becomes smaller during braking or turning. As a result, the damping force of the shock absorber is corrected somewhat hard, ensuring steering stability.Mana 3 is a correction term that adjusts the damping characteristics according to the passenger's preference, and a value within a certain range of positive and negative values is selected. can.

The effect of this operation will be explained with reference to FIG.

When the driving road surface is good (left half of Fig. 14 (1))
, the damping force signal Fc is small (FIG. 145 (2)), and the integrated value WFc of its absolute value Fca is also small. Therefore, the proportionality constant Kp is large in this region ((3) in FIG. 14). Since the damping force absolute value Fca is sufficiently small in most cases, the level of the control signal Vs is low ((4>) in FIG. 14), so that the damping force generated by the shock absorber 2 is on the hard side.

In this state, the vehicle looks like a small protrusion like a seam on the road surface (see Figure 14).
1) When reaching part A), the damping force Fc becomes slightly larger. Since the proportionality constant Kp is large, a small increase in the damping force Fc causes the control signal Vs to suddenly increase, and the shock absorber 2
The generated damping force changes in the soft direction.

Therefore, stability when driving on a good road such as a highway is maintained well by the shock absorber 2 which has a hard damping force as a whole, and shocks received from road joints change the damping force to a soft side. Let it be absorbed. It is known that when driving on a good road, even the slightest shock is felt by the occupants, making it particularly effective in improving ride comfort.

6. When the vehicle reaches a rough road (the right half of FIG. 14 (1)), the damping force Fc and its absolute value Fca increase. The integrated value WFc of the absolute value Fca also increases, and the proportionality constant Kp decreases accordingly (FIG. 14 (3)). Therefore, even if the damping force absolute value Fca becomes large, the control signal Vs obtained by multiplying it by the small proportionality constant Kp does not indicate a saturated state, and the damping force generated by the shock absorber 2 is based on hardness. The damping force Fc changes in the soft direction depending on the unevenness of the road surface.

In this way, running stability is maintained even on rough roads, and excessive shock (section B in FIG. 14 (1)) is alleviated.

In this embodiment, since the damping force generated by the shock absorber is continuously changed in proportion to the damping force signal indicating the unevenness of the road surface, shocks due to sudden changes in the damping force due to damping force switching do not occur.

In the above embodiment, a sprung mass acceleration signal or the like can be used instead of the damping force signal as a physical quantity whose amount of change increases depending on the unevenness of the road surface.Physics 7 As the absolute value of the quantity, the detected value is squared. You may also use the value.

[Effects of the Invention] As described above, according to the control device for a variable damping force shock absorber according to the present invention, the road surface condition is determined based on the integrated value of the physical quantity whose amount of change increases as the unevenness of the road surface increases, and the shock absorber By changing the proportionality constant of the control signal that controls the damping force of the vehicle according to the unevenness of the road surface, it is possible to maintain good running performance and ride comfort regardless of the road surface condition.

[Brief explanation of drawings]

Figure 1 is a diagram corresponding to claims, Figure 2 is a block diagram of the overall configuration of the control device, Figure 3 is a sectional view of the main parts of the shock absorber,
Figure 4 is a characteristic diagram of the shock absorber, Figure 5 is a circuit diagram of a damping force detection circuit, Figures 6 and 7 are frequency characteristic diagrams of a bypass filter and a low-pass filter, respectively, and Figure 8 is a diagram of a drive circuit. The circuit diagram, Fig. 9 shows the signal flow, Fig. 10 shows the change over time of each signal, Fig. 11 shows the change characteristics of the proportionality constant, Fig. 12 shows the program flow chart, and Fig. Change characteristic diagram of vehicle speed correction term, 14th
The figure is a diagram showing changes in road surface shape and the like over time. 1... Control device 11... CPU 17... Damping force detection circuit 19... Drive circuit 2... Shock absorber 2a, 2b... Hydraulic chamber 21... Piezo actuator 22... Load Sensor 24... Main piston 9

Claims (1)

[Claims] A shock absorber control device capable of continuously changing the generated damping force according to the magnitude of the signal level of a control signal, comprising a physical quantity detection means for detecting a physical quantity whose amount of change increases as the unevenness of the road surface becomes larger; an integrating means for integrating the absolute value of the physical quantity at predetermined time intervals and outputting an integrated signal indicating the average unevenness of the road surface; and decreasing a proportionality constant as the integrated signal outputted from the integrating means increases. A control device for a variable damping force shock absorber, comprising: proportional constant changing means; and damping force controlling means for multiplying the absolute value of the physical quantity by the proportional constant and outputting the result as the control signal.