Patent Application
20200023704
This application claims priority of Japanese Patent Application No. 2018-134868 filed in Japan on Jul. 18, 2018, the entire contents of which are incorporated herein by reference.
The present invention relates to a vehicle suspension system.
In recent years, studies and development have been made for a technique that improves comfort in riding a vehicle by providing an electromagnetic damper between a sprung member and an unsprung member of a vehicle, and controlling a drive force and a damping force generated between the sprung member and the unsprung member by the electromagnetic damper (see Japanese Patent Application Publication No. 2017-165283, for example).
For example, an electromagnetic damper described in Patent Document 1 includes an outer tube, a screw rod provided coaxially with and inside the outer tube, a nut that is screwed with the screw rod and can be displaced in the stroke direction inside the outer tube, and a motor connected with the screw rod through pulleys and a belt. In the electromagnetic damper, rotation of the motor due to extension and retraction of the electromagnetic damper induces an electromotive force, whereby a damping force is generated against the extension and retraction of the electromagnetic damper. In addition, in the electromagnetic damper, when external electric power is supplied to the motor, the screw rod rotates and generates a drive force to cause extension and retraction of the electromagnetic damper.
When the electromagnetic damper thus extends and retracts in the stroke direction, not a little frictional force is generated between the nut and the screw rod. Since the frictional force occurs in a direction that hinders the extension and retraction of the electromagnetic damper in the stroke direction, if a relatively small force acts on a tire such as when the tire rides over a slight step, for example, extension and retraction of the electromagnetic damper may be obstructed. In this case, the force acting on the tire is not damped and is directly transmitted to the vehicle body.
There is a need to provide a vehicle suspension system that can keep an impact acting on a tire from being transmitted to a vehicle body through an electromagnetic damper.
(1) In accordance with one embodiment of the present invention, a vehicle suspension system (e.g., later-mentioned suspension system 1) includes: an electromagnetic damper (e.g., later-mentioned electromagnetic damper 2) that is provided between a sprung member (e.g., later-mentioned vehicle body B) and an unsprung member (e.g., later-mentioned tire T) of a vehicle, and applies a damping force and a drive force in a stroke direction to the sprung member and the unsprung member by an electromagnetic actuator (e.g., later-mentioned motor M); an acceleration sensor (e.g., later-mentioned unsprung member acceleration sensor 52) that detects unsprung member acceleration rate/speed in the stroke direction of the unsprung member; and a controller (e.g., later-mentioned ECU 6) that controls the electromagnetic actuator, and is characterized in that the controller controls the electromagnetic actuator to generate a load in such a direction that increases a relative velocity of the sprung member with respect to the unsprung member and of an amount/magnitude corresponding to the unsprung member acceleration.
(2) In this case, the controller preferably sets the load to 0 if the unsprung member acceleration is within a dead band width including 0.
(3) In this case, the controller preferably varies the dead band width according to vehicle speed.
(4) In this case, the controller preferably limits the load so not to exceed frictional force of the electromagnetic damper.
(5) In this case, the controller preferably varies the amount of the load according to vehicle speed.
(1) The suspension system includes: an electromagnetic damper that applies a damping force and a drive force in a stroke direction to the sprung member and the unsprung member by an electromagnetic actuator; an acceleration sensor that detects unsprung member acceleration in the stroke direction of the unsprung member; and a controller that controls the electromagnetic actuator. The controller controls the electromagnetic actuator to generate a load in such a direction that increases a relative velocity of the sprung member with respect to the unsprung member and of an amount corresponding to the unsprung member acceleration. With this, when unsprung member acceleration is increased by the unsprung member overriding a step, for example, a load of a size corresponding to the unsprung member acceleration is generated in such a direction that increases the relative velocity, that is, a direction that reduces the frictional force of the electromagnetic damper. Hence, according to the suspension system of the present invention, the characteristic of the frictional force can be made equivalent to that of a smaller than actual electromagnetic damper. Accordingly, even when an impact acts on the unsprung member, the impact can be kept from being transmitted to the sprung member.
(2) The controller sets the load to 0 if the unsprung member acceleration is within a dead band width including 0. According to the suspension system of the present invention, by providing such a dead band for unsprung member acceleration, it is possible to prevent generation of load in the electromagnetic damper due to noise in the acceleration sensor or micro vibration of the unsprung member, for example. Hence, comfort in riding the vehicle can be improved.
(3) The controller varies the dead band width according to vehicle speed. Hence, the area in which to generate a load in an amount corresponding to unsprung member acceleration can be varied according to vehicle speed. This can improve comfort in riding the vehicle even more.
(4) If a load larger than frictional force is generated in the electromagnetic damper, juddering of the unsprung member may increase. Hence, in the suspension system, the load is limited so not to exceed frictional force of the electromagnetic damper. This can suppress juddering of the unsprung member.
(5) The controller varies the amount of the load according to vehicle speed. Hence, it is possible to generate an appropriate load amount corresponding to vehicle speed.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The suspension system 1 includes an electromagnetic damper 2, various sensors 51, 52 that detect states of the vehicle, an electronic control unit 6 (hereinafter abbreviated as “ECU (Electronic Control Unit) 6” that controls the electromagnetic damper 2 by using detected signals of the sensors 51, 52, and a battery 7.
The electromagnetic damper 2 includes a damper main body 20 provided between a vehicle body B which is a sprung member of the vehicle and a tire which is an unsprung member of the vehicle, a motor M as an electromagnetic actuator provided in the damper main body 20, and an inverter 4 that supplies electric power supplied from the battery 7 to the motor M.
The damper main body 20 includes an outer tube member 21, a screw rod 30 provided inside the outer tube member 21, an inner tube member 31 having one end inserted into the outer tube member 21, and a spring 38 provided between the outer tube member 21 and the inner tube member 31.
The outer tube member 21 includes a cylindrical outer tube 22 that pivotally supports the screw rod 30 therein in a rotatable manner, a motor supporting portion 24 that is provided in an outer peripheral portion of the outer tube 22 and supports the motor M, and a power transmission member 25 that transmits power generated in an output shaft S of the motor M to the screw rod 30. A bearing 23 that rotatably supports a base end portion 30a of the screw rod 30 is provided inside the base end side of the outer tube 22. An unsprung member connector 26 is provided in an outer portion of the base end side of the outer tube 22. Additionally, a flange-shaped spring seat portion 27 that extends perpendicular to the axis of the screw rod 30 is provided in an outer peripheral portion of the tip end side of the outer tube 22. The power transmission member 25 includes a first pulley provided in the output shaft S of the motor M, a second pulley provided in the base end portion 30a of the screw rod 30, and an endless belt wound around the first pulley and the second pulley.
The inner tube member 31 includes a cylindrical inner tube 32 having a portion on the tip end side inserted into the outer tube 22, and a nut 33 provided on the tip end side of the inner tube 32. A spiral screw groove that receives multiple balls 34 is formed on an outer peripheral surface of the screw rod 30. The nut 33 is screwed onto the screw rod 30 through the balls 34. Accordingly, the screw rod 30, the nut 33, and the balls 34 form a ball screw. As a result, the outer tube member 21 and the inner tube member 31 can be relatively displaced in the stroke direction. A sprung member connector 35 is provided in an outer portion of the base end side of the inner tube 32. Additionally, a flange-shaped spring seat portion 36 that extends perpendicular to the axis is provided in an outer peripheral portion of the base end side of the inner tube 32.
The spring 38 is a compression coil spring, for example, and is interposed between the spring seat portion 27 of the outer tube member 21 and the spring seat portion 36 of the inner tube member 31 in a compressed state. Accordingly, the outer tube member 21 and the inner tube member 31 are energized away from each other by the spring 38.
The motor M is a three-phase brushless motor, for example. The output shaft S of the motor M is connected to the screw rod 30 through the power transmission member 25. The inverter 4 converts DC power supplied from the battery 7 into AC power according to a motor current instruction signal transmitted from the ECU 6 and supplies it to the motor M, and converts AC power supplied from the motor M into DC power and supplies it to the battery 7.
The vehicle body which is the sprung member is connected to the sprung member connector 35 of the inner tube member 31. The tire which is the unsprung member is connected to the unsprung member connector 26 of the outer tube member 21 through an unillustrated suspension arm.
The electromagnetic damper 2 described above acts in the following manner.
First, when the outer tube member 21 and the inner tube member 31 are relatively displaced in the stroke direction, the screw rod 30 and the nut 33 are relatively displaced in the stroke direction, whereby the screw rod 30 is rotated. Rotation of the screw rod 30 is transmitted to the output shaft S of the motor M through the power transmission member 25, so that the output shaft S rotates. Similarly, when the motor M rotates, the outer tube member 21 and the inner tube member 31 are relatively displaced in the stroke direction. Thus, the relative displacement in the stroke direction of the outer tube member 21 and the inner tube member 31, that is, the extension and retraction of the electromagnetic damper 2 are linked with rotation of the motor M. When the output shaft S of the motor M rotates by the extension and retraction of the electromagnetic damper 2, an electromotive force is induced and generates a rotational resistance corresponding to the induced electromotive force, whereby a damping force against the extension and retraction of the electromagnetic damper 2 is generated. Meanwhile, when the output shaft S of the motor M is rotated by electric power supplied from the battery 7, the electromagnetic damper 2 extends and retracts by generating a drive force to the extension side and the retraction side in the stroke direction. The drive force and the damping force generated in the electromagnetic damper 2 and applied to the vehicle body and the tire are controlled by exchange of electric power between the motor M and the inverter 4.
The vehicle speed sensor 51 detects vehicle speed which is the speed of the vehicle, and transmits a signal according to the detected value to the ECU 6. The unsprung member acceleration sensor 52 is provided in the tire which is the unsprung member, detects unsprung member acceleration which is acceleration of the tire in the stroke direction of the electromagnetic damper 2, and transmits a signal according to the detected value to the ECU 6.
The ECU 6 is an onboard computer formed of a CPU, a ROM, a RAM, a data bus, an input-output interface, and other components. The ECU 6 performs various calculation processing in the CPU according to a program stored in the ROM, to thereby function as a target load calculator 61 and a motor current calculator 62 described below.
The target load calculator 61 calculates a target load which is a target of a load generated by the motor M in the electromagnetic damper 2 based on the detected signal of various sensors such as the vehicle speed sensor 51 and the unsprung member acceleration sensor 52. A specific procedure of calculating a target load in the target load calculator 61 will be described with reference to
The suspension system 1 including a tire T which is the unsprung member and the vehicle body B which is the sprung member connected by the electromagnetic damper 2, is expressed as a two-degree-of-freedom vibration system shown in
Equations of motion of the two-degree-of-freedom vibration system shown in
[Expression 1]
m
2
·{umlaut over (x)}
2
=k
d·(x1−x2)+cd·({dot over (x)}1−{dot over (x)}2)+fd·({dot over (x)}1−{dot over (x)}2)−Fm (1-1)
m
1
·{umlaut over (x)}
1
=k
d·(x2−x1)+cd·({dot over (x)}2−{dot over (x)}1)+k1·(x0−x1)+fd·({dot over (x)}2−{dot over (x)}1)+Fm (1-2)
Here, a case where the tire T rides over a step with a height δx will be considered. In this case, deflection with a displacement δSt corresponding to the height δx occurs in the tire T, so that an elastic force Ft indicated by the following equation (2) acts on the tire T.
[Expression 2]
F
1
=k
l
×δS
t (2)
Additionally, when a reference space which is the space between the reference position of the tire T and the reference position of the vehicle body B is “Sd” and displacement of the space between the tire T and the vehicle body B from the aforementioned reference space Sd, that is, the stroke amount of the electromagnetic damper 2 is “δSd,” a frictional force Fd which is a term proportional to the friction coefficient fd in the equations of motion (1-1) and (1-2) is considered to occur in an infinitesimal stroke amount δSd and become saturated at a predetermined value Fd-static, as indicated by a broken line in
For this reason, the target load calculator 61 calculates the target load such that the motor element 2d generates a load Fm proportional to the unsprung member acceleration obtained by the unsprung member acceleration sensor 52, as indicated by the following equation (3). More specifically, as indicated by the following equation (3), the target load calculator 61 calculates the target load so as to generate the load Fm in such a direction that increases the relative velocity of the vehicle body B with respect to the tire T and in such an amount corresponding to unsprung member acceleration. Since the motor element 2d generates the load Fm as indicated by the following equation (3), the characteristic of the frictional force generated in the electromagnetic damper 2 can be made linear with respect to the stroke amount δSd, as indicated by the solid line in
[Expression 3]
F
m
=G
A
·{umlaut over (x)}
1 (3)
The dead band filter 611 performs dead band filter processing on a detected signal of the unsprung member acceleration sensor 52. More specifically, the dead band filter 611 outputs value 0 if the detected value of unsprung member acceleration obtained by the unsprung member acceleration sensor 52 is within a predetermined dead band width including 0, and outputs the detected value directly if the detected value of unsprung member acceleration is out of the dead band width. Hereinafter, the value of unsprung member acceleration obtained through the dead band filter processing by the dead band filter 611 is denoted as “a1.”
Note that the dead band filter 611 varies such a dead band width according to the vehicle speed detected by the vehicle speed sensor 51. More specifically, the dead band filter 611 narrows the dead band width for a higher vehicle speed, for example.
The gain setting portion 612 sets a positive gain GA corresponding to a ratio between the unsprung member acceleration a1 and the target load Fm-cmd. The gain setting portion 612 varies the value of the gain GA according to the vehicle speed detected by the vehicle speed sensor 51, so that the target load Fm-cmd varies according to the vehicle speed. More specifically, the gain setting portion 612 increases the value of the gain GA for a higher vehicle speed, for example.
The multiplier 613 calculates a basic value Fm-bs of the target load, by multiplying the unsprung member acceleration a1 obtained through the dead band filter 611 by the gain GA set by the gain setting portion 612, as indicated by the following equation (4).
[Expression 4]
F
m-bs
=G
A·α1 (4)
The limiter 614 calculates the target load Fm-cmd by performing limit processing on the basic value Fm-bs of the target load obtained by the multiplier 613. As indicated by the above equation (4), the basic value Fm-bs of the target load is proportional to acceleration of the tire T in the stroke direction. Hence, if the basic value Fm-bs obtained by the multiplier 613 is used directly, when a large impact acts on the tire T in the stroke direction, for example, the load generated by the electromagnetic damper 2 largely exceeds the frictional force Fd. This causes the tire T to judder, whereby stable driving of the vehicle may be hindered.
For this reason, the limiter 614 calculates the target load Fm-cmd by limiting the basic value Fm-bs of the target load calculated by the multiplier 613, so that the load Fm generated by the electromagnetic damper 2 does not exceed the frictional force Fd. More specifically, the limiter 614 sets the basic value Fm-bs calculated by the multiplier 613 directly as the target load (Fm-cmd=Fm-bs) if the basic value is equal to or smaller than a predetermined positive upper limit value Fm-U and equal to or larger than a negative lower limit value Fm-L, sets the upper limit value Fm-U as the target load (Fm-cmd=Fm-U) if the basic value Fm-bs is larger than the upper limit value, and sets the lower limit value Fm-L as the target load (Fm-cmd=Fm-L) if the basic value Fm-bs is smaller than the lower limit value.
Referring back to
As shown in
When the tire T rides over a step during time t2 to t5, unsprung member acceleration increases, as shown in
Additionally, when the load of an amount proportional to unsprung member acceleration is generated in this manner, if the unsprung member acceleration varies largely during time t3 to t4, the load generated by the motor M exceeds the frictional force and may cause more juddering of the tire T. Hence, the ECU 6 performs limit processing to limit the target load Fm-cmd to a range between the predetermined upper limit value Fm-U and lower limit value Fm-L, and can thereby prevent generation of a load that exceeds the frictional force as indicated by a broken line 5b in
The suspension system 1 of the embodiment exerts the following effects.
(1) The ECU 6 controls the motor M to generate a load in such a direction that increases the relative velocity of the vehicle body B with respect to the tire T and in such an amount corresponding to unsprung member acceleration. With this, when unsprung member acceleration is increased by the tire T overriding a step, for example, the load in the amount corresponding to the unsprung member acceleration is generated in such a direction that increases the relative velocity, that is, a direction that reduces the frictional force of the electromagnetic damper 2. Hence, according to the suspension system 1, the characteristic of the frictional force can be made equivalent to that of a smaller than actual electromagnetic damper. Accordingly, even when an impact acts on the tire T, the impact can be kept from being transmitted to the vehicle body B.
(2) The ECU 6 sets the load to 0 if unsprung member acceleration is within a dead band width including 0. According to the suspension system 1, by providing such a dead band for unsprung member acceleration, it is possible to prevent generation of load in the electromagnetic damper 2 due to noise in the unsprung member acceleration sensor 52 or micro vibration of the tire T, for example. Hence, comfort in riding the vehicle can be improved.
(3) The ECU 6 varies the dead band width according to vehicle speed. Hence, the area in which to generate a load of in an amount corresponding to unsprung member acceleration can be varied according to vehicle speed. This can improve comfort in riding the vehicle even more.
(4) In the suspension system 1, a load is limited so not to exceed frictional force of the electromagnetic damper 2. This can suppress juddering of the tire T.
(5) The ECU 6 varies the amount of a load according to vehicle speed. Hence, it is possible to generate an appropriate amount of the load corresponding to vehicle speed.
While an embodiment of the present invention has been described, the invention is not limited to this. Detailed configurations may be changed appropriately within the gist of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-134868 | Jul 2018 | JP | national |
