Suspension device

Abstract

A suspension device (1) comprises: four dampers (D) that are interposed between the body (B) and the wheels (Wfr, Wfl, Wrr, Wrl) of a four-wheeled vehicle (V), that each have a damping force adjustment unit (14), and that can adjust damping force in accordance with a current supplied to the damping force adjustment unit (14); and a controller (C) that includes a plurality of drivers (2) that are provided corresponding to respective damping force adjustment units (14) installed in the dampers (D) and are each capable of supplying a current to the corresponding damping force adjustment unit (14) in response to the input of a PWM signal, and that inputs a PWM signal to each of the drivers (2). The controller (C) shifts the phases of the PWM signals from one another when inputting the PWM signals to the drivers (2).

Description

Suspension device

[0001] The present invention relates to a suspension device.

[0002] A conventional suspension device, as disclosed in, for example, JP2002-067650A and JP2009-299700A, includes shock absorbers that are installed between the body of a four-wheel vehicle and each of its four wheels and have solenoid valves that adjust the damping force, thereby enabling damping force adjustment; four drivers that supply current to the solenoid valves in each shock absorber; and a controller that inputs a PWM signal to the drivers.

[0003] When the controller inputs a PWM signal to the driver, the driver energizes the solenoid valve at the on-duty ratio indicated by the PWM signal, allowing the suspension device to control the damping force generated by each shock absorber and improve the ride comfort of the vehicle.

[0004] JP2002-067650AJP2009-299700A

[0005] In the suspension device described above, a switch that energizes a solenoid in a driver is on while the PWM signal commands it to be on, and the switch is off while the PWM signal commands it to be off, causing ripples in the current input from the power supply to each driver. Since ripples in the current cause heat generation and loss, a smoothing capacitor is generally provided between the power supply and the driver to smooth out the ripples in the current.

[0006] On the other hand, in a conventional suspension system, as shown in FIG. 8, the controller inputs PWM signals to each driver with the same cycle and phase, and the switches that energize the solenoids in each drive circuit are all turned on simultaneously, resulting in large ripples in the current input to the smoothing capacitor.

[0007] As described above, in the conventional suspension device, a large current ripple occurs, and therefore the capacity of the smoothing capacitor must be increased in accordance with the magnitude of the current ripple, resulting in a problem of increased costs.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a suspension device that can reduce current ripple and reduce costs.

[0009] In order to achieve the above-mentioned object, the suspension device of the present invention comprises four shock absorbers interposed between the body and each wheel of a four-wheel vehicle, each having a damping force adjustment unit and capable of adjusting the damping force in accordance with the current supplied to the damping force adjustment unit, and a controller including a plurality of drivers provided corresponding to each of the damping force adjustment units installed in each shock absorber and capable of supplying current to the corresponding damping force adjustment unit in response to an input of a PWM signal, and inputting the PWM signal to each driver, and the controller shifts the phase of each PWM signal before inputting it to each driver.

[0010] With a suspension device configured in this manner, PWM signals are input to each driver with a phase shift, so that although the effective voltage at each damping force adjustment unit does not change, the difference between the maximum current and the minimum current becomes smaller, thereby reducing current ripple.

[0011] FIG. 1 is a diagram showing a suspension apparatus according to an embodiment mounted on a four-wheel vehicle. FIG. 2 is a diagram showing a suspension apparatus according to an embodiment. FIG. 3 is a schematic cross-sectional view of a shock absorber. FIG. 4 is a diagram showing a configuration of a driver of the suspension apparatus according to an embodiment. FIG. 5 is a diagram showing a configuration of a controller of the suspension apparatus according to an embodiment. FIG. 6 is a diagram explaining the phase and current ripple of a PWM signal input to each driver of the suspension apparatus according to an embodiment. FIG. 7 is a diagram explaining the phase and current ripple of a PWM signal input to each driver of the suspension apparatus according to an embodiment when the shock absorber is a passive damper. FIG. 8 is a diagram explaining the phase and current ripple of a PWM signal input to each driver of a conventional suspension apparatus.

[0012] The present invention will be described below based on the embodiment shown in the drawings. As shown in Figures 1 and 2, a suspension device 1 in one embodiment is configured to include four shock absorbers D respectively interposed between a vehicle body B of a four-wheel vehicle V and each of four wheels Wfr, Wfl, Wrr, and Wrl, and a controller C including four drivers 2 capable of supplying current to damping force adjusters 14 installed in each of the shock absorbers D, and controlling the damping force by inputting a PWM signal to the drivers 2. In this embodiment, the controller C controls the damping force generated by the four shock absorbers D.

[0013] First, a description will be given of the shock absorber D in the suspension device 1. As shown in Fig. 3, the shock absorber D comprises a cylindrical cylinder 6, a piston 7 slidably inserted into the cylinder 6, a rod 8 inserted into the cylinder 6 so as to be movable in the axial direction and connected to the piston 7, an extension-side chamber R1 and a compression-side chamber R2 which are partitioned by the piston 7 within the cylinder 6 and filled with a liquid such as hydraulic oil, an intermediate cylinder 9 which covers the outer periphery of the cylinder 6 and forms an annular gap between it and the cylinder 6, and an outer cylinder 1 which covers the outer periphery of the intermediate cylinder 9 and forms an annular reservoir R filled with gas and liquid between it and the intermediate cylinder 9. 0, a rectifying passage 11 that communicates between the expansion-side chamber R1 and the compression-side chamber R2 and allows only the flow of liquid from the compression-side chamber R2 to the expansion-side chamber R1 with almost no resistance, a suction passage 12 that communicates between the compression-side chamber R2 and the reservoir R and allows the flow of liquid from the reservoir R to the compression-side chamber R2 with almost no resistance, a damping passage 13 that communicates between the expansion-side chamber R1 and the reservoir R via a gap between the cylinder 6 and the intermediate tube 9, and a damping force adjusting unit 14 that can adjust the damping force generated by the shock absorber D in accordance with the supplied current.

[0014] In this embodiment, as shown in the figure, the damping force adjustment unit 14 is a solenoid valve that includes a valve body 14a provided midway through the damping passage 13, a spring 14b that biases the valve body 14a so as to block the damping passage 13, and a solenoid 14c that generates a thrust force that counteracts the spring 14b when current is applied, and the valve opening pressure can be changed according to the amount of current supplied to the solenoid 14c.

[0015] When the pressure in the expansion-side chamber R1 upstream of the damping passage 13 acting on the valve body 14a exceeds the relief pressure (valve-opening pressure), this pressure and the force of the solenoid 14c pressing on the valve body 14a overcome the force of the spring 14b biasing the valve body 14a, and the valve body 14a compresses the spring 14b, causing the damping force adjustment unit 14 to open the damping passage 13.

[0016] Furthermore, in the damping force adjusting unit 14, increasing the amount of current supplied to the solenoid 14c increases the thrust generated by the solenoid 14c. Therefore, the damping force adjusting unit 14 minimizes the valve opening pressure when the amount of current supplied to the solenoid 14c is maximized, and conversely, maximizes the valve opening pressure when no current is supplied to the solenoid 14c. Note that the damping force adjusting unit 14 may be configured to maximize the valve opening pressure when the amount of current to the solenoid 14c is maximized.

[0017] As described above, the damping force adjustment unit 14 is equipped with a solenoid 14c, and the valve opening pressure can be adjusted by the amount of electricity supplied to the solenoid 14c, but it may also be configured so that the thrust generated by the solenoid 14c acts on the valve body 14a, allowing the flow path area to be adjusted.

[0018] In this way, the damping force adjustment unit 14 only needs to be able to adjust the damping force generated by the shock absorber D by changing the resistance to the flow of liquid passing through the damping passage 13 in accordance with the supply of current from the driver 2 described later, so in addition to a solenoid valve, it may be a valve that uses a stepping motor, or if the liquid filled in the shock absorber D is an electrorheological fluid, magnetorheological fluid, or electromagnetic rheological fluid, it may be equipped with a device that can adjust the resistance to the flow of liquid passing through the damping passage 13 by applying an electric field or magnetic field to the liquid passing through the damping passage 13.

[0019] In the shock absorber D configured in this manner, when the shock absorber D is extended, that is, when the rod 8 moves upward relative to the cylinder 6 in FIG. 2, the liquid moves from the expansion-side chamber R1, which is compressed by the piston 7 rising in the cylinder 6, to the reservoir R via the damping passage 13 and the damping force adjustment unit 14.

[0020] Therefore, the pressure in the expansion-side chamber R1 rises and becomes equal to the valve-opening pressure of the damping force adjusting unit 14. Furthermore, during the extension operation of the shock absorber D, liquid is supplied from the reservoir R via the suction passage 12 to the compression-side chamber R2, the volume of which is expanded by the piston 7 rising in the cylinder 6, and the pressure in the compression-side chamber R2 becomes approximately equal to the pressure in the reservoir R. Therefore, the pressure in the expansion-side chamber R1 becomes higher than the pressure in the compression-side chamber R2 by the valve-opening pressure of the damping force adjusting unit 14, and the shock absorber D generates a damping force that hinders the extension operation. Furthermore, since the valve-opening pressure of the damping force adjusting unit 14 changes depending on the amount of current supplied to the solenoid 14c, the damping force during the extension operation of the shock absorber D can be adjusted in level depending on the amount of current supplied to the solenoid 14c.

[0021] 3 relative to the cylinder 6, liquid moves from the compression-side chamber R2, which is compressed by the piston 7 descending in the cylinder 6, to the expanding extension-side chamber R1 via the rectifying passage 11. When the shock absorber D contracts, an excess of liquid corresponding to the volume of the rod 8 entering the cylinder 6 is created in the cylinder 6, and the excess liquid is discharged from the cylinder 6 to the reservoir R via the damping passage 13 and the damping force adjuster 14. Therefore, the pressures in the extension-side chamber R1 and the compression-side chamber R2 in the cylinder 6 both rise and become equal to the valve-opening pressure of the damping force adjuster 14. However, because the pressure-receiving area of ​​the piston 7 facing the compression-side chamber R2 is larger than the pressure-receiving area of ​​the piston 7 facing the extension-side chamber R1 by the cross-sectional area of ​​the rod 8, the shock absorber D generates a damping force that suppresses contraction. Since the valve opening pressure of the damping force adjusting section 14 varies depending on the amount of current supplied to the solenoid 14c, the damping force during the contraction operation of the shock absorber D can be adjusted according to the amount of current supplied to the solenoid 14c.

[0022] The configuration of the shock absorber D is merely an example and is not limited to the above-described configuration. Any configuration may be used as long as the damping force adjuster 14 is capable of applying resistance to the flow of liquid to generate a damping force that inhibits the extension and contraction of the shock absorber D. Therefore, the shock absorber D of the present embodiment is configured as a uniflow type that includes a reservoir R and in which liquid circulates one-way through the expansion-side chamber R1, the compression-side chamber R2, and the reservoir R in that order. However, the shock absorber D may be configured as a biflow type in which liquid flows back and forth between the expansion-side chamber R1 and the compression-side chamber R2 during expansion and contraction. When the shock absorber D is configured as a biflow type, if a damping passage connecting the expansion-side chamber R1 and the compression-side chamber R2 allows the flow of liquid from the expansion-side chamber R1 to the compression-side chamber R2 and the flow of liquid from the compression-side chamber R2 to the expansion-side chamber R1, a damping force adjuster may be provided in the damping passage. Furthermore, when the shock absorber D is configured as a bi-flow type and is provided with an extension side damping passage that allows liquid to flow only from the extension side chamber R1 to the compression side chamber R2 and a compression side damping passage that allows liquid to flow only from the compression side chamber R2 to the extension side chamber R1, the shock absorber D may be provided with a damping force adjustment unit in both the extension side damping passage and the compression side damping passage, or may be provided with a damping force adjustment unit in only one of the extension side damping passage and the compression side damping passage.

[0023] In the shock absorber D configured in this manner, the cylinders 6 are attached to the knuckles or suspension arms that hold the wheels Wfr, Wfl, Wrr, and Wrl, and are connected to the wheels Wfr, Wfl, Wrr, and Wrl, and the rods 8 are connected to the vehicle body B, and are interposed between the vehicle body B and the wheels Wfr, Wfl, Wrr, and Wrl of the four-wheel vehicle V. The shock absorber D expands and contracts due to vibrations input from the road surface while the four-wheel vehicle V is traveling, and generates a damping force that suppresses vibrations of the vehicle body B.

[0024] 5, the controller C includes four drivers 2 capable of supplying current to the damping force adjusting units 14 installed in the shock absorbers D, and a control unit 3 that controls the damping force by inputting a PWM signal to the drivers 2. The controller C of this embodiment is housed in a single housing 20 and installed in the passenger compartment of the four-wheel vehicle V.

[0025] 4, in this embodiment, the driver 2 is provided with a switch 2a that receives power from the power source 4 and switches between energizing and de-energizing the solenoid 14c in the damping force adjustment unit 14, and is configured as a drive circuit that can supply current to the damping force adjustment unit 14. When the switch 2a is turned on, the driver 2 energizes the solenoid 14c, and when the switch 2a is turned off, the driver 2 stops energizing the solenoid 14c.

[0026] The switch 2a in the driver 2 is a transistor that is placed between the power supply 4 and ground GND and closer to the power supply than the solenoid 14c, and has a base to which a PWM signal is input. When the PWM signal is a high signal, the switch 2a turns on to ground the solenoid 14c and supply current to the solenoid 14c, and when the PWM signal is a low signal, the switch 2a turns off to disconnect the solenoid 14c from ground GND and prevent current from flowing to the solenoid 14c. The switch 2a is specifically a P-channel MOSFET, and is a high-side switch that is placed closer to the power supply than the solenoid 14c, which is the load. This makes it possible to easily detect a ground fault by detecting the current flowing through the switch 2a, and by turning off the switch when a ground fault is detected, safety can be improved.

[0027] As shown in FIG. 4, the suspension device 1 is provided with one driver 2 for each damping force adjustment section 14 of each shock absorber D, and in this embodiment, since there are a total of four damping force adjustment sections 14, four drivers 2 are provided.

[0028] Each driver 2 is adapted to receive power from one power supply 4 and is connected in parallel to the power supply 4. Specifically, the power supply 4 and each driver 2 are connected via a power supply line 41 having one end connected to the power supply 4 and four branch supply lines 42 connecting the other end of the power supply line 41 to each driver 2.

[0029] Further, a low-pass filter 30 is provided in the middle of the power supply line 41, which is configured by connecting two smoothing capacitors 31, 32 and one coil 33 in a π configuration. The low-pass filter 30 reduces high-frequency ripples in the current supplied from the power supply 4 to each driver 2, thereby reducing radiation noise. In this embodiment, the low-pass filter 30 is also housed in the housing 20 together with each driver 2.

[0030] As shown in Figure 5, the control unit 3 in the controller C includes a sensor unit 3a that detects vibrations of the body B of the four-wheel vehicle V, a damping force calculation unit 3b that calculates a target damping force based on the vibration information detected by the sensor unit 3a, a current control unit 3c that controls the current supplied to the damping force adjustment unit 14 in each shock absorber D based on the target damping force calculated by the damping force calculation unit 3b, and a communication unit 3d that is capable of wireless communication with the mobile terminal 50.

[0031] Although not shown as hardware, the control unit 3 in the controller C includes a CPU (Central Processing Unit), memory, an interface, and a bus that connects these devices so that they can communicate with each other. The CPU realizes the arithmetic processing of the control unit 3 in the controller C by executing an operating system and other programs.

[0032] Each component of the control unit 3 will be described in detail below. In this embodiment, the sensor unit 3a is an inertial measurement device that detects angular velocities about the three axes of the vehicle body B (front-rear, left-right, and up-down), i.e., three angular velocities in the roll, pitch, and yaw directions of the vehicle body B, and accelerations about the three axes of the vehicle body B (front-rear, left-right, and up-down), as vibration information of the vehicle body B. The sensor unit 3a is housed in a housing 20 and installed together with the housing 20 on the vehicle body B. Note that the sensor unit 3a only needs to detect vibration information of the vehicle body B required for the control unit 3 to control the damping force. Therefore, for example, if the control unit 3 requires only the acceleration of the vehicle body B in the up-down direction, the sensor unit 3a may detect only the acceleration of the vehicle body B in the up-down direction. Note that the control unit 3 does not need to include the sensor unit 3a if it can obtain vibration information of the vehicle body B from an ECU (Electronic Control Unit) (not shown) mounted on the four-wheeled vehicle V.

[0033] The housing 20 is box-shaped and houses therein a low-pass filter 30 together with the control unit 3 and driver 2 of the controller C. The sensor unit 3a is housed in the housing 20 so that the detection axis of acceleration in the front-to-rear direction coincides with the front-to-rear direction of the housing 20, the detection axis of acceleration in the left-to-right direction coincides with the left-to-right direction of the housing 20, the detection axis of acceleration in the up-to-down direction coincides with the up-to-down direction of the housing 20, the direction of the detected angular velocity in the roll direction coincides with the direction of rotation about the axis of the front-to-rear direction of the housing 20, the direction of the detected angular velocity in the pitch direction coincides with the direction of rotation about the axis of the left-to-right direction of the housing 20, and the direction of the detected angular velocity in the yaw direction coincides with the direction of rotation about the axis of the up-to-down direction of the housing 20.

[0034] Therefore, when the housing 20 is installed near the center of the vehicle body inside the vehicle cabin with its front / back, left / right, and top / bottom aligned with the front / back, left / right, and top / bottom of the vehicle body B, the sensor unit 3a can detect three angular velocities in the roll direction, pitch direction, and yaw direction at the installation position where the housing 20 is installed relative to the vehicle body B, and accelerations in the three axes of the vehicle body B, front / back, left / right, and top / bottom.

[0035] The communication unit 3d is equipped with an antenna unit (not shown) and is capable of two-way communication with the mobile terminal 50. In this embodiment, wireless communication conforming to the IEEE802.15 standard is performed, but as long as communication with the mobile terminal 50 is possible, in addition to wireless communication conforming to the above standard, wireless LAN (Local Area Network) communication conforming to the IEEE802.11 standard may also be performed.

[0036] The mobile terminal 50 is a highly portable terminal such as a smartphone or tablet PC, and although not shown, includes a housing, an inertial measurement unit (IMU) housed within the housing and capable of detecting triaxial angular velocity and triaxial acceleration, a touch panel installed on the housing for displaying images and receiving input from an operator, a transceiver housed within the housing as a communication unit capable of wireless communication with external devices, a memory housed within the housing as a storage unit, a processing unit housed within the housing for controlling each unit constituting the mobile terminal by executing a program, a GPS (Global Positioning System) receiver, and a bus for communicatively connecting these units, thereby enabling the mobile terminal 50 to obtain its own location information. Note that the IMU in the mobile terminal 50 may not detect triaxial angular velocity but may detect only triaxial acceleration.

[0037] The mobile terminal 50 and the controller C can exchange information with each other via the communication unit 3 d. When an application program for setting parameters of the control unit 3 is started by an operator, the mobile terminal 50 becomes capable of communicating with the controller C, and can set parameters used to control the damping force in the control unit 3.

[0038] The damping force calculation unit 3b calculates the vertical accelerations directly above the four wheels Wfr, Wfl, Wrr, and Wrl of the vehicle body B from the three angular velocities and three accelerations of the vehicle body B detected by the sensor unit 3a, and then calculates the target damping force from the vertical accelerations of the four locations on the vehicle body B.

[0039] Specifically, the damping force calculation unit 3b calculates the vertical accelerations directly above the four wheels Wfr, Wfl, Wrr, and Wrl of the vehicle body B from the three angular velocities and three accelerations detected by the sensor unit 3a at the installation position of the vehicle body B. Since the detection axes for detecting the three-axial accelerations of the sensor unit 3a may not completely coincide with the front-rear, left-right, and up-down directions of the vehicle body B and the sensor unit 3a may not be installed on the vehicle body B so as to coincide with the center of gravity of the vehicle body B, the damping force calculation unit 3b corrects the three angular velocities and accelerations detected by the sensor unit 3a to calculate the vertical accelerations directly above the four wheels Wfr, Wfl, Wrr, and Wrl of the vehicle body B, and calculates the three angular velocities and accelerations at the center of gravity position of the vehicle body B.

[0040] Furthermore, the damping force calculation unit 3b corrects the three angular velocities and accelerations detected by the sensor unit 3a to obtain three angular velocities and accelerations at the center of gravity of the vehicle body B, and then calculates the vertical accelerations directly above the four wheels Wfr, Wfl, Wrr, and Wrl of the vehicle body B from these obtained angular velocities and accelerations.

[0041] Specifically, the damping force calculation unit 3b simply calculates the vertical acceleration directly above the four wheels Wfr, Wfl, Wrr, and Wrl of the vehicle body B from information on the tread and wheelbase of the four-wheel vehicle V and the center of gravity position of the vehicle body B.

[0042] After determining the vertical acceleration directly above the wheels Wfr, Wfl, Wrr, and Wrl in this manner, in this embodiment, in order to perform skyhook control, the damping force calculation unit 3b integrates or filters the vertical acceleration directly above the four wheels Wfr, Wfl, Wrr, and Wrl to determine the vertical velocity of the vehicle body B directly above the vertical acceleration directly above the four wheels Wfr, Wfl, Wrr, and Wrl. Furthermore, the damping force calculation unit 3b multiplies the vertical velocity directly above the four wheels Wfr, Wfl, Wrr, and Wrl of the vehicle body B by each skyhook damping coefficient to determine the skyhook damping force that should be generated by each of the four shock absorbers D interposed between the vertical acceleration directly above each wheel Wfr, Wfl, Wrr, and Wrl and the vehicle body B.

[0043] In addition, the damping force calculation unit control unit 3b multiplies the angular velocity in the roll direction of the vehicle body B at the center of gravity position of the vehicle body B by the roll suppression gain to obtain a roll suppression force that suppresses the roll, and multiplies the angular velocity in the pitch direction by the pitch suppression gain to obtain a pitch suppression force that suppresses the pitch.

[0044] Furthermore, the damping force calculation unit 3b adds the roll suppression force and pitch suppression force to be output by each of the four shock absorbers D to the skyhook damping force for each vertical acceleration directly above each wheel Wfr, Wfl, Wrr, and Wrl of the vehicle body B to calculate a damping force for ride comfort based on ride comfort control aimed at improving ride comfort in the four-wheel vehicle V.

[0045] In addition to the damping force for ride comfort, the damping force calculation unit 3b multiplies the longitudinal acceleration of the center of gravity position of the vehicle body B by a longitudinal acceleration gain to obtain a longitudinal attitude change suppression force aimed at suppressing nose dive and squat of the vehicle body B during sudden acceleration or sudden braking, and multiplies the lateral acceleration of the center of gravity position of the vehicle body B by a lateral acceleration gain to obtain a lateral attitude change suppression force aimed at suppressing roll of the vehicle body B during cornering, and adds up the longitudinal attitude change suppression force and lateral attitude change suppression force to be output by each of the four shock absorbers D to obtain a damping force for driving performance based on driving performance improvement control aimed at stabilizing the posture of the vehicle body B of the four-wheel vehicle V.

[0046] The damping force calculation unit 3b then performs a high select process to select the larger absolute value of the damping force for ride comfort and the damping force for running stability, and calculates the larger absolute value as the composite damping force. Note that, in calculating the composite damping force, the damping force calculation unit 3b may add the damping force for ride comfort and the damping force for running stability in a predetermined ratio.

[0047] Finally, the damping force calculation unit 3b multiplies the composite damping force by a speed gain proportional to the traveling speed of the four-wheeled vehicle V to calculate the target damping force to be generated by the four shock absorbers D. The speed gain is calculated by multiplying the speed of the four-wheeled vehicle V by a speed sensitivity coefficient, and is a gain that increases in value in proportion to the traveling speed. The controller C obtains the speed of the four-wheeled vehicle V from the mobile terminal 50. As described above, the mobile terminal 50 is equipped with a GPS receiver (not shown), which detects the position information of the mobile terminal 50 itself at a predetermined sampling period. The mobile terminal 50 calculates the travel distance from the current position information and the position information obtained in the previous sampling period, and divides the calculated travel distance by the sampling period to calculate the traveling speed of the mobile terminal itself. The mobile terminal 50 performs wireless communication according to the above-mentioned standard, and therefore can only communicate with the controller C over short distances. Therefore, when the mobile terminal 50 is traveling together with the four-wheeled vehicle V, it can transmit the speed information of the four-wheeled vehicle V to the controller C via wireless communication. In this way, when the mobile terminal 50 and the controller C are able to communicate wirelessly, the mobile terminal 50 continuously transmits speed information of the four-wheel vehicle V to the controller C, and when the controller C receives an input of the speed of the four-wheel vehicle V from the mobile terminal 50, it multiplies the speed by a speed sensitivity coefficient to determine a speed gain, and multiplies the speed gain by the composite damping force to determine a target damping force. Thus, the controller C of this embodiment can obtain speed information of the four-wheel vehicle V and determine a target damping force appropriate for the speed, even without being connected to the CAN bus of the four-wheel vehicle V. Note that if the speed can be obtained from the four-wheel vehicle V, the controller C does not need to receive speed input from the mobile terminal 50, and if it is not necessary to make the target damping force sensitive to the speed, the controller C does not need to receive speed input.

[0048] The target damping forces of the four shock absorbers D thus determined are input to a current control unit 3c which inputs a PWM signal from the damping force calculation unit 3b to the driver 2 which supplies current to the damping force adjustment unit 14 of each shock absorber D, and controls the current supplied to the damping force adjustment unit 14. The current control unit 3c inputs a PWM signal to the driver 2 and supplies current to the solenoid 14c in the damping force adjustment unit 14 of each shock absorber D so that the damping force generated by each shock absorber D matches the target damping force.

[0049] The current control unit 3c calculates the amount of current to be supplied from each driver 2 to the solenoid 14c based on the target damping force obtained from the damping force calculation unit 3b, generates a PWM signal with an on-duty ratio corresponding to the amount of current, and inputs the generated PWM signal to the corresponding driver 2. Specifically, the current control unit 3c includes a signal generation unit 3c1 that generates a PWM signal from the target damping force obtained from the damping force calculation unit 3b, a signal output unit 3c2 that outputs the generated PWM signal to the four drivers 2 corresponding to each solenoid 14c via four channels 3c3, and a current detection unit 3c4 that detects the current flowing through each solenoid 14c.

[0050] The signal generating unit 3c1 stores in advance a map that indicates the relationship between the damping force generated by the shock absorber D and the amount of current supplied to the solenoid 14c of the damping force adjusting unit 14, and calculates the amount of current to be supplied to the solenoid 14c of the damping force adjusting unit 14 by map calculation from the target damping force input from the damping force calculating unit 3b. Note that the signal generating unit 3c1 calculates the amount of current using the map, but if the relationship between the target damping force and the amount of current can be expressed as a function, the amount of current may also be calculated using the function.

[0051] Furthermore, signal generating unit 3c1 determines the deviation between the determined amount of current and the actual amount of current supplied to solenoid 14c, performs PI compensation or PID compensation on the deviation to determine a target current, and generates a PWM signal for driver 2 to supply current to solenoid 14c of damping force adjusting unit 14 in accordance with the target current. In other words, current control unit 3c controls damping force adjusting unit 14 by current feedback control.

[0052] When the signal generating unit 3c1 generates a PWM signal to be input to each driver 2, the signal output unit 3c2 outputs a PWM signal with the same control period for each driver 2 but with a shifted phase of the PWM signal, as shown in Figure 6, thereby shifting the input timing of the PWM signal to each driver 2.

[0053] Specifically, the signal output unit 3c2 outputs PWM signals from four channels 3c3 corresponding to the four drivers 2, with the phases shifted by 90 degrees, which is 360 degrees divided by 4. Therefore, for example, as shown in Fig. 6, the signal output unit 3c2 outputs a PWM signal to the driver 2 for the shock absorber D of the front left wheel Wfl after ¼ of the period of the PWM signal delayed by 90 degrees from the PWM signal input to the driver 2 for the shock absorber D of the front right wheel Wfr, outputs a PWM signal to the driver 2 for the shock absorber D of the front right wheel Wrr after ½ of the period delayed by 180 degrees, and further outputs a PWM signal to the driver 2 for the shock absorber D of the rear left wheel Wrl after ¾ of the period delayed by 270 degrees. In this way, the controller 3 inputs PWM signals with a phase shift of 90 degrees to the four drivers 2 in sequence.

[0054] Although the on-duty ratios of the four PWM signals input to each driver 2 differ depending on the target damping force calculated by the damping force calculation unit 3b, the period of the PWM signal consisting of a set of high and low signals is the same, so the input timing of the high signal differs for all drivers 2, and the switch 2a in each driver 2 switches from off to on in turn every 1 / 4 of the period of the PWM signal, so the timing at which the switch 2a in each driver 2 switches from off to on differs.

[0055] As described above, in a conventional suspension device in which all of the PWM signals input by the controller C to each driver 2 are in phase and the switches 2 a in all of the drivers 2 are turned on simultaneously, current is supplied to the solenoids simultaneously when the switches 2 a are turned on, as shown in FIG. 8, resulting in large current ripples.

[0056] In contrast, the suspension device 1 of this embodiment comprises four shock absorbers D interposed between the body B of the four-wheel vehicle V and each of the wheels Wfr, Wfl, Wrr, and Wrl, each having a damping force adjustment unit 14 and capable of adjusting the damping force in accordance with the current supplied to the damping force adjustment unit 14, and a controller C including a plurality of drivers 2 provided corresponding to each of the damping force adjustment units 14 installed in each of the shock absorbers D and capable of supplying current to the corresponding damping force adjustment unit 14 in response to an input of a PWM signal, and which inputs the PWM signal to each of the drivers 2, and the controller C shifts the phase of each PWM signal before inputting it to each of the drivers 2.

[0057] In the suspension device 1 configured in this manner, as shown in FIG. 6, the PWM signals are input to each driver 2 with a phase shift, so although the effective voltage in each damping force adjuster 14 does not change, the difference between the maximum and minimum currents in the power supply line 41 becomes smaller, thereby reducing current ripple.

[0058] Therefore, according to the suspension device 1 of this embodiment, the current ripple can be reduced compared to conventional suspension devices, and therefore the capacitance of the smoothing capacitors 31, 32 provided between the power supply 4 and the driver 2 can be reduced, thereby reducing costs.

[0059] Note that, as long as controller C shifts the phase of each PWM signal before inputting it to each driver 2, the phase shift angle is not limited to 90 degrees, but controller C in suspension apparatus 1 of the present embodiment inputs PWM signals to each driver 2 with a phase shift in increments of 360 degrees divided by the number of installed drivers 2. With suspension apparatus 1 configured in this manner, by inputting PWM signals to each driver 2 with a phase shift in increments of 360 degrees divided by the number of installed drivers 2, it is possible to lengthen and equalize the time difference at which each driver 2 starts to pass current to damping force adjuster 14, thereby minimizing current ripple and minimizing the capacitance of smoothing capacitors 31, 32, thereby further reducing costs.

[0060] In this embodiment, four drivers 2 are provided, and therefore, by outputting PWM signals to the four drivers 2 in sequence with a phase shift of 90 degrees (360 degrees divided by 4), it is possible to uniformly vary over time the timing at which the drivers 2 start to flow current to the damping force adjusters 14. Note that if two damping force adjusters 14, one for adjusting the extension side damping force and one for adjusting the compression side damping force, are provided for one shock absorber D and two drivers 2 are provided for one shock absorber D, eight drivers 2 are provided for four shock absorbers D. In this case, the controller C outputs PWM signals to the eight drivers 2 in sequence with a phase shift of 45 degrees (360 degrees divided by 8, the number of installed drivers 2), it is possible to uniformly vary over time the timing at which the drivers 2 start to flow current to the damping force adjusters 14.

[0061] The configuration of the current control unit 3c is just one example, and the current control unit 3c may be configured as an analog circuit as long as it can output a PWM signal to the driver 2 so as to generate a damping force in the shock absorber D in accordance with the target damping force calculated by the damping force calculation unit 3b.

[0062] As described above, the damping force calculation unit 3b in the control unit 3 uses various parameters, such as the skyhook damping coefficient, roll suppression gain, pitch suppression gain, longitudinal acceleration gain, lateral acceleration gain, and speed sensitivity coefficient, to determine the target damping force. As described above, the parameters are set in advance and used for control, and are used to calculate the target damping force. In this embodiment, the control unit 3 executes ride comfort control aimed at improving ride comfort and driving performance improvement control aimed at improving driving performance, and the parameters used for these controls can be set using the mobile terminal 50.

[0063] More specifically, the mobile terminal 50 is able to set the various parameters described above by executing a setting application program that sets the parameters of the control unit 3. When the mobile terminal 50 executes the setting application program, it displays an operation screen on a display unit (not shown) that allows the user to set various parameters, saves the parameter values ​​set by the user's operation, and transmits the set parameter values ​​to the controller C via wireless communication with the controller C. When the controller C receives the parameter values ​​from the mobile terminal 50 via the communication unit 3d, it executes a process of overwriting each parameter used to calculate the target damping force with the value set by the user. In this way, the suspension system 1 does not require complicated work such as connecting a dedicated device to the controller C to set parameters, and the parameters used by the controller C to control the shock absorber D can be set very easily by using a general-purpose mobile terminal 50. It should be noted that, in the suspension device 1 of the present embodiment, it is possible to set parameters using the portable terminal 50, but the controller C may be provided with operation buttons that allow setting operations and a display screen that displays parameter information, or, instead of the portable terminal 50, an operation device that can be connected to the controller C when setting parameters may be used, which has operation buttons that accept parameter setting operations and a display screen that displays parameter information.

[0064] Furthermore, when the controller C does not perform the above control and causes the shock absorber D to function as a passive damper that generates a predetermined damping force in response to the extension / contraction speed, the controller C allows the damping coefficient of the shock absorber D to be set as a parameter using the mobile terminal 50. When the controller C causes the shock absorber D to function as a passive damper, the damping force calculation unit 3b does not calculate the target damping force, and the current control unit 3c generates a PWM signal to input to the driver 2 so that a constant amount of current corresponding to the damping coefficient is supplied from the driver 2 to the solenoid 14c.

[0065] When the shock absorbers D are made to function as passive dampers in this way, if the damping coefficients of the left and right shock absorbers D on the front side of the four-wheel vehicle V are different, or if the damping coefficients of the left and right shock absorbers D on the rear side of the four-wheel vehicle V are different, the vibration of the vehicle body B while the vehicle is traveling will cause the vehicle height on the left and right sides of the vehicle body B to be higher on the side where the shock absorbers D with higher damping coefficients are installed than on the side where the shock absorbers D with lower damping coefficients are installed, causing the vehicle body B to tilt to the left or right. Therefore, when the shock absorbers D are made to function as passive dampers, the damping coefficients of the shock absorbers D lined up on the left and right sides of the vehicle body B cannot be set individually, and the damping coefficients of the shock absorbers D lined up on the left and right sides of the vehicle body B are always set to the same. Note that even if the damping coefficients of the shock absorbers D lined up in the front-rear direction of the vehicle body B are different, the vehicle body B will not tilt in the left or right direction, so the controller C allows such damping coefficient settings.

[0066] When the shock absorbers D are caused to function as passive dampers in this way, the damping coefficients of the shock absorbers D aligned in the left-right direction of the vehicle body B are always equal in the suspension device 1 of this embodiment. In this embodiment, the current control unit 3c detects the current actually flowing in each solenoid 14c and performs current feedback control. Since the actual current flowing in the solenoid 14c also fluctuates, even if the damping coefficient of each shock absorber D in passive damping is the same, the PWM signals input to each driver 2 are not necessarily equal. However, the PWM signal input to the driver 2 that supplies current to the damping force adjustment unit 14 of the shock absorber D on the front right wheel Wfr of the vehicle body B and the PWM signal input to the driver 2 that supplies current to the damping force adjustment unit 14 of the shock absorber D on the front left wheel Wfl of the vehicle body B are approximately equal, and the PWM signal input to the driver 2 that supplies current to the damping force adjustment unit 14 of the shock absorber D on the rear right wheel Wrr of the vehicle body B and the PWM signal input to the driver 2 that supplies current to the damping force adjustment unit 14 of the shock absorber D on the rear left wheel Wrl of the vehicle body B are approximately equal.

[0067] When the shock absorbers D are caused to function as passive dampers in this manner, the on-duty ratios of the PWM signals given to the two drivers 2 corresponding to the left and right shock absorbers D on the front side of the vehicle body B are approximately equal, and the on-duty ratios of the PWM signals given to the two drivers 2 corresponding to the left and right shock absorbers D on the rear side of the vehicle body B are approximately equal. Therefore, as shown in FIG. 7, the signal output unit 3c2 outputs signals to each driver 2 with a phase difference of approximately 180 degrees so that the PWM signal of the driver 2 corresponding to the front right wheel Wfr and the PWM signal of the driver 2 corresponding to the front left wheel Wfl are in opposite phases, and outputs signals to each driver 2 with a phase difference of approximately 180 degrees so that the PWM signal of the driver 2 corresponding to the rear right wheel Wrr and the PWM signal of the driver 2 corresponding to the rear left wheel Wrl are in opposite phases.

[0068] In this way, the time during which a high signal in the PWM signal of the driver 2 corresponding to the front right wheel Wfr overlaps with a high signal in the PWM signal of the driver 2 corresponding to the front left wheel Wfl is shortened, and the time during which a high signal in the PWM signal of the driver 2 corresponding to the rear right wheel Wrr overlaps with a high signal in the PWM signal of the driver 2 corresponding to the rear left wheel Wrl is shortened. Therefore, when the shock absorber D is made to function as a passive damper, the current ripple can be efficiently reduced and the capacity of the smoothing capacitors 31, 32 can be minimized, thereby further reducing costs.

[0069] In addition, since the suspension apparatus 1 of this embodiment is provided with four drivers 2, the control unit 3 in the controller C inputs PWM signals to each driver 2 in turn, with a phase shift of approximately 90 degrees. Therefore, in this case, the PWM signal is first input to the driver 2 corresponding to the front right wheel Wfr, and then, after the input of the PWM signal to the first driver 2, the PWM signal is input to the driver 2 corresponding to the rear right wheel Wrr with a phase shift of approximately 90 degrees and a time of ¼ of the PWM signal period has elapsed, and further, after the input of the PWM signal to the first driver 2, the PWM signal is input to the driver 2 corresponding to the front left wheel Wfl with a phase shift of approximately 180 degrees and a time of ½ of the PWM signal period has elapsed, and further, after the input of the PWM signal to the first driver 2, the PWM signal is input to the driver 2 corresponding to the rear left wheel Wrl with a phase shift of approximately 270 degrees and a time of ¾ of the PWM signal period has elapsed.

[0070] In this way, the controller C inputs PWM signals to each driver 2 in turn with a phase shift of 90 degrees, inputs PWM signals to the drivers 2 corresponding to the front left and right wheels Wfl, Wfr with a phase shift of approximately 180 degrees, and inputs PWM signals to the drivers 2 corresponding to the rear left and right wheels Wrl, Wrr with a phase shift of approximately 180 degrees. In this way, the time during which a high signal in the PWM signal of the driver 2 corresponding to the front right wheel Wfr overlaps with a high signal in the PWM signal of the driver 2 corresponding to the front left wheel Wfl is shortened, and the time during which a high signal in the PWM signal of the driver 2 corresponding to the rear right wheel Wrr overlaps with a high signal in the PWM signal of the driver 2 corresponding to the rear left wheel Wrl is shortened. Not only does this shorten the time during which a high signal in the PWM signal of the driver 2 corresponding to the rear right wheel Wrr overlaps with a high signal in the PWM signal of the driver 2 corresponding to the rear left wheel Wrl, but it also makes it possible to uniformly lengthen and decrease the time difference at which all drivers 2 start to flow current to the damping force adjuster 14, thereby further reducing current ripple.

[0071] Furthermore, when PWM signals are input to each driver 2 in order with a phase shift, and PWM signals are input to the drivers 2 corresponding to the left and right front wheels Wfl, Wfr with a phase shift of approximately 180 degrees, and PWM signals are input to the drivers 2 corresponding to the left and right rear wheels Wrl, Wrr with a phase shift of approximately 180 degrees, as long as these conditions are met, the order in which the PWM signals are input to each driver 2 can be changed as desired. Furthermore, the phase difference between the PWM signals input to the drivers 2 of the left and right front wheels Wfl, Wfr and the PWM signals input to the drivers 2 of the left and right rear wheels Wrl, Wrr may be a phase angle other than 90 degrees or 270 degrees.

[0072] Furthermore, even when the shock absorber D is made to function as a passive damper, if a PWM signal is input to the driver 2 corresponding to the left and right front wheels Wfl, Wfr without a 180 degree phase shift, and if a PWM signal is input to the driver 2 corresponding to the left and right rear wheels Wrl, Wrr without a 180 degree phase shift, the current ripple can be reduced as long as the phases of the PWM signals input to each driver 2 are shifted.

[0073] 7, the controller C of this embodiment inputs PWM signals to the drivers 2 corresponding to the shock absorbers C of the left and right front wheels Wfl, Wfr of the vehicle body B so that their high signals do not overlap, and inputs PWM signals to the drivers 2 corresponding to the shock absorbers D of the left and right rear wheels Wrl, Wrr of the vehicle body B so that their high signals do not overlap. With the suspension device 1 configured in this manner, the high signal in the PWM signal of the driver 2 corresponding to the front right wheel Wfr does not overlap with the high signal in the PWM signal of the driver 2 corresponding to the front left wheel Wfl, and the high signal in the PWM signal of the driver 2 corresponding to the rear right wheel Wrr does not overlap with the high signal in the PWM signal of the driver 2 corresponding to the rear left wheel Wrl. Therefore, when the shock absorbers D are made to function as passive dampers, current ripple can be efficiently reduced and the capacitance of the smoothing capacitors 31, 32 can be minimized, thereby further reducing costs.

[0074] Although the preferred embodiment of the present invention has been described in detail, modifications, variations and changes can be made thereto without departing from the scope of the appended claims.

[0075] 1...Suspension device, 2...Driver, 14...Damping force adjustment unit, B...Vehicle body, C...Controller, D...Shock absorber, V...Four-wheel vehicle, Wfr, Wfl, Wrr, Wrl...Wheels

Claims

1. A suspension device comprising: four shock absorbers interposed between the body and each wheel of a four-wheel vehicle, each having a damping force adjustment unit and capable of adjusting damping force in accordance with the current supplied to the damping force adjustment unit; and a controller including a plurality of drivers provided corresponding to each of the damping force adjustment units installed in each shock absorber and capable of supplying current to the corresponding damping force adjustment unit in response to an input of a PWM signal, and which inputs a PWM signal to each of the drivers, wherein the controller shifts the phase of each PWM signal before inputting it to each of the drivers.

2. A suspension device according to claim 1, wherein said controller inputs PWM signals to each of said drivers with a phase shift of a phase angle calculated by dividing 360 degrees by the number of said drivers installed.

3. A suspension device according to claim 1, wherein the controller inputs PWM signals with a phase difference of approximately 180 degrees to each of the drivers corresponding to the left and right shock absorbers on the front side of the vehicle body, and inputs PWM signals with a phase difference of approximately 180 degrees to each of the drivers corresponding to the left and right shock absorbers on the rear side of the vehicle body.

4. A suspension device as claimed in claim 1, wherein the controller inputs PWM signals to the drivers corresponding to the left and right shock absorbers on the front side of the vehicle body so that their high signals do not overlap, and inputs PWM signals to the drivers corresponding to the left and right shock absorbers on the rear side of the vehicle body so that their high signals do not overlap.

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