Vehicle suspension device

A vehicle suspension device includes a suspension device main body configured to support a wheel of a vehicle to a vehicle body of the vehicle; a varying device configured to cause an upper connecting portion stiffness and a lower connecting portion stiffness to be variable, the upper connecting portion stiffness being a stiffness between a vertically upper portion of the suspension device main body and the vehicle body, and the lower connecting portion stiffness being a stiffness between a vertically lower portion of the suspension device main body and the vehicle body; and a control device configured to control the varying device at a time of braking of the vehicle to perform control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased, compared to at a time of non-braking of the vehicle.

FIELD

The present invention relates to a vehicle suspension device.

BACKGROUND

As a conventional vehicle suspension device, for example, in Patent Literature 1, a suspension stiffness control device which can adjust the stiffness of a suspension provided in a vehicle is disclosed. The suspension stiffness control device strengthens the suspension stiffness as an accelerator opening degree or a brake pedal pressing amount is increased. Accordingly, the suspension stiffness control device can secure stability to suppress compliance steering at the time of acceleration while securing turning performance to obtain compliance steering at the normal time.

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

However, in the suspension stiffness control device described in Patent Literature 1 as described above, for example, there is still room for improvement in terms of more appropriate reduction in vibration.

The present invention has been made taking the forgoing circumstances into consideration, and an object thereof is to provide a vehicle suspension device capable of appropriately reducing vibration.

Solution to Problem

In order to achieve the above mentioned object, a vehicle suspension device according to the present invention includes a suspension device main body configured to support a wheel of a vehicle to a vehicle body of the vehicle; a varying device configured to cause an upper connecting portion stiffness and a lower connecting portion stiffness to be variable, the upper connecting portion stiffness being a stiffness between a vertically upper portion of the suspension device main body and the vehicle body, and the lower connecting portion stiffness being a stiffness between a vertically lower portion of the suspension device main body and the vehicle body; and a control device configured to control the varying device at a time of braking of the vehicle to perform control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased, compared to at a time of non-braking of the vehicle.

Further, in the vehicle suspension device, it is possible to configure that the varying device causes at least the upper connecting portion stiffness in a front-back direction of the vehicle and the lower connecting portion stiffness in the front-back direction of the vehicle to be variable.

Further, in the vehicle suspension device, it is possible to configure that the control device changes the upper connecting portion stiffness and the lower connecting portion stiffness so that a front-back force compliance of a spindle of the wheel at the time of braking of the vehicle is equal to a front-back force compliance of the spindle at the time of non-braking of the vehicle.

Further, in the vehicle suspension device, it is possible to configure that the control device prohibits the control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased in a case where an absolute value of a braking force of the vehicle is equal to or greater than a predetermined value set in advance.

Further, in the vehicle suspension device, it is possible to configure that the control device continuously changes the upper connecting portion stiffness and the lower connecting portion stiffness according to a change in the braking force of the vehicle.

Further, in the vehicle suspension device, it is possible to configure that the control device causes the upper connecting portion stiffness to be relatively increased and the lower connecting portion stiffness to be relatively decreased at a time of sudden-braking at which the absolute value of the braking force of the vehicle is equal to or greater than the predetermined value set in advance, compared to at a time of smooth-braking at which the absolute value of the braking force of the vehicle is smaller than the predetermined value.

Further, in the vehicle suspension device, it is possible to configure that the control device causes the upper connecting portion stiffness to be relatively increased and causes the lower connecting portion stiffness to be relatively decreased at a time of sudden-braking at which the absolute value of the braking force of the vehicle is equal to or greater than the predetermined value set in advance, compared to at the time of non-braking of the vehicle.

Advantageous Effects of Invention

The vehicle suspension device according to the present invention exhibits an effect in which vibration can be appropriately reduced.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. The present invention is not limited by the embodiments. In addition, the constituent elements in the following embodiments include elements that can be replaced or are easily replaced by those skilled in the art or substantially the same elements.

FIG. 1is a schematic view illustrating the schematic configuration of a vehicle suspension device according to a first embodiment.FIG. 2is a diagram illustrating an example of the relation between the displacement and the force of a rubber bushing.FIG. 3is a schematic view simply illustrating a suspension in a side view.FIG. 4is a schematic view illustrating the relation of unsprung forces of a braking torque.FIGS. 5 and 6are schematic views illustrating the relation between a principal elastic axis height and a spindle front-back displacement.FIG. 7is a diagram illustrating an example of the relation between the principal elastic axis height and unsprung vibration.FIG. 8is a diagram illustrating an example of the relation between the front-back stiffness of an upper support, the front-back stiffness of a lower arm bushing, and the principal elastic axis height.FIG. 9is a diagram illustrating an example of a combination of the front-back stiffness in which the front-back force compliance at a spindle position is constant.FIG. 10is a flowchart illustrating an example of control by an ECU of the vehicle suspension device.

A vehicle suspension device1according to this embodiment is provided to correspond to each of wheels3of a vehicle2as illustrated inFIG. 1. The vehicle suspension device1is configured to include a suspension5as a suspension device main body which supports the wheels3of the vehicle2to a vehicle body4of the vehicle2, and an upper connecting portion6, an intermediate connecting portion7, and a lower connecting portion8, which connect the suspension5to the vehicle body4. In the vehicle suspension device1, the upper connecting portion6, the intermediate connecting portion7, and the lower connecting portion8are provided in this order from above in the vertical direction with respect to the suspension5. In addition, the vehicle suspension device1of this embodiment is a vibration reducing device which reduces unsprung vibration at the time of braking due to the principal elastic axis height of the suspension5. The vehicle suspension device1which is provided in each of the wheels3is described to be also used as a control device (ECU50), which will be described later, but may also be provided separately without being limited to the description.

Here, the principal elastic axis of the suspension5is typically referred to as three virtual orthogonal axes in which, when a force is applied along a specific axial direction, the direction of the force and the direction of an elastic displacement of the force application point are coincident with each other and a plane including the force application point undergoes only linear displacement and does not cause angular displacement, in other words, the center of elastic restoration. The principal elastic axis of the suspension5is typically determined by the characteristics of the suspension5, and is determined according to, for example, the strength or the arrangement of the springs of the suspension5, the stiffness (spring constant) of the bushing of each part, and the like. In addition, unsprung vibration is typically unsprung vibration of the vehicle2, that is, vibration that occurs on the wheels3side rather than the suspension5.

Specifically, the suspension5is intervened between the wheels3and the vehicle body4to support the wheels3to the vehicle body4and reduces impact or vibration that is transmitted from the road surface to the vehicle body4via the wheels3. The suspension5is configured to include a coil spring9, a shock absorber10, an upper arm11, a lower arm12, a knuckle13, and the like and supports the wheels3to be steerable and rotatable relative to the vehicle body4.

The coil spring9elastically supports unsprung parts to sprung parts, that is, to the vehicle body4, to support the weight of the sprung parts of the vehicle2, and allows vibration or impact from the road surface not to be transmitted to the vehicle body4through the wheels3. The shock absorber10has a piston rod14to which the coil spring9is attached, and attenuates vertical vibration of the vehicle body4due to the coil spring9. The shock absorber10is disposed along the vertical direction so that the vertically upper end portion of the piston rod14is connected to the vehicle body4via the upper connecting portion6, and the vertically lower end portion of a cylinder15is connected to the lower arm12via a joint portion16such as a ball joint. The upper arm11and the lower arm12are suspension arms that support the shock absorber10, the knuckle13, and the like, and the upper arm11is disposed on the upper side in the vertical direction and the lower arm12is disposed on the lower side in the vertical direction. One end portion (outer end portion in the vehicle width direction) of the upper arm11is connected to the upper end portion of the knuckle13via a joint portion17such as a ball joint, and the other end (inner end portion in the vehicle width direction) thereof is connected to the vehicle body4via the intermediate connecting portion7. One end portion (outer end portion in the vehicle width direction) of the lower arm12is connected to the lower end portion of the knuckle13via a joint portion18such as a ball joint, and the other end (inner end portion in the vehicle width direction) thereof is connected to the vehicle body4via the lower connecting portion8. The knuckle13is a non-rotating part, and is a wheel support member which supports the wheels3to rotate about a spindle19as the rotation center. In addition, the knuckle13is provided with a caliper and the like of a braking device which generates a braking force for the vehicle2.

The upper connecting portion6connects a vertically upper portion of the suspension5to the vehicle body4. Here, as described above, the upper connecting portion6connects the piston rod14of the shock absorber10as the vertically upper portion of the suspension5to the vehicle body4. The upper connecting portion6is configured to include an upper support60as an upper intervening member which is intervened between the vertically upper end portion of the piston rod14and the vehicle body4. The upper connecting portion6connects the piston rod14to the vehicle body4via the upper support60. The upper support60elastically supports the vertically upper end portion of the piston rod14to the vehicle body4.

The intermediate connecting portion7connects a vertically intermediate portion of the suspension5to the vehicle body4. Here, as described above, the intermediate connecting portion7connects the upper arm11as the vertically intermediate portion of the suspension5to the vehicle body4. The intermediate connecting portion7is configured to include an upper arm bushing70as an intermediate intervening member which is intervened between one end portion (end portion on the opposite side to the knuckle13) of the upper arm11and the vehicle body4. The intermediate connecting portion7connects the upper arm11to the vehicle body4via the upper arm bushing70. The upper arm bushing70elastically supports one end portion of the upper arm11to the vehicle body4.

The lower connecting portion8connects a vertically lower portion of the suspension5to the vehicle body4. Here, as described above, the lower connecting portion8connects the lower arm12as the vertically lower portion of the suspension5to the vehicle body4. The lower connecting portion8is configured to include a lower arm bushing80as a lower intervening member which is intervened between one end portion (end portion on the opposite side to the knuckle13) of the lower arm12and the vehicle body4. The lower connecting portion8connects the lower arm12to the vehicle body4via the lower arm bushing80. The lower arm bushing80elastically supports one end portion of the lower arm12to the vehicle body4.

The upper support60, the upper arm bushing70, and the lower arm bushing80are configured to include, for example, so-called rubber bushings made of an elastomer such as rubber. The upper support60, the upper arm bushing70, and the lower arm bushing80function as so-called compliance bushings which absorb vibration and the like in the vehicle front-back direction by allowing displacement while suppressing backlash of the upper connecting portion6, the intermediate connecting portion7, and the lower connecting portion8. Accordingly, the upper support60, the upper arm bushing70, and the lower arm bushing80reduce, for example, action resistance between members having different movable axes and secures driving stability and ride quality. The stiffness (spring constants) of the upper connecting portion6, the intermediate connecting portion7, and the lower connecting portion8are respectively determined according to the stiffness of the upper support60, the upper arm bushing70, and the lower arm bushing80.

Here, in the vehicle suspension device1, for example, if the stiffness of the upper support60is increased due to the suspension design for the purpose of mainly enhancing driving stability including straight line stability, as the counteraction, there is concern that ride quality performance may deteriorate. Focusing on the phenomenon at the time of braking of the vehicle2, in this case, in the vehicle suspension device1, there is concern that vibration caused by a change in the braking torque may increase, and thus there is concern that unnecessary vibration may be transmitted to a driver through steering. In addition, in the vehicle suspension device1, for example, if the stiffness of the lower arm bushing80is increased to reduce a brake vibration phenomenon at the time of braking, there is concern that harshness characteristics (performance of reducing vibration in the vehicle front-back direction, so-called harshness, input via the wheels3in a case where the vehicle2climbs over projections on the road surface while traveling and the like) may deteriorate as the counteraction. Here, the rubber bushings used in the upper support60, the lower arm bushing80, and the like have characteristics in that the relation between the displacement and the force is non-linear as illustrated inFIG. 2. Therefore, in the vehicle suspension device1, if the stiffness of the bushing is simply increased to reduce brake vibration at the time of braking of the vehicle2, the stiffness in a normal use range at the time of non-braking of the vehicle2and the like is also increased, and thus there is concern that various counteractions as described above may occur.

Here, the vehicle suspension device1of this embodiment controls the upper connecting portion stiffness and the lower connecting portion stiffness between the vehicle body4and the suspension5to have a predetermined relation according to the braking state of the vehicle2so as to change the geometry of the suspension5through control, for example, when a braking torque is added, thereby reducing unsprung vibration in the vehicle front-back direction.

Specifically, the vehicle suspension device1includes a varying device30which causes the upper connecting portion stiffness and the lower connecting portion stiffness to vary, and the ECU50as the control device which controls the varying device30. The upper connecting portion stiffness is the stiffness between the vertically upper portion of the suspension5, that is, the vertically upper end portion of the piston rod14and the vehicle body4, and typically, is the stiffness of the upper connecting portion6. That is, the upper connecting portion stiffness corresponds to the stiffness of the upper support60. On the other hand, the lower connecting portion stiffness is the stiffness between the vertically lower portion of the suspension5, that is, the lower arm12and the vehicle body4, and typically, is the stiffness of the lower connecting portion8. That is, the lower connecting portion stiffness corresponds to the stiffness of the lower arm bushing80.

Thus, in the vehicle suspension device1, objects to control stiffness are the upper support60and the lower arm bushing80. For example, in a case where a plurality of lower arms12and the like are provided in the vehicle front-back direction, the corresponding object to control stiffness is the lower arm bushing80of the lower arm12which mainly receives a load. For example, in a case where a lower arm No1on the front side and a lower arm No2on the rear side in the vehicle front-back direction are provided to form a pair as the lower arms12, the object to control stiffness is the lower arm bushing80of the lower arm No2which mainly receives a load.

The varying device30causes the upper connecting portion stiffness and the lower connecting portion stiffness to vary. The varying device30of this embodiment is configured to include an upper varying mechanism31which causes the upper connecting portion stiffness to vary by causing the stiffness of the upper support60to vary and a lower varying mechanism32which causes the lower connecting portion stiffness to vary by causing the stiffness of the lower arm bushing80to vary. The upper varying mechanism31and the lower varying mechanism32cause at least the upper connecting portion stiffness and the lower connecting portion stiffness in the front-back direction of the vehicle2to vary.

The upper varying mechanism31of this embodiment changes the temperature of the upper support60by applying a current to the upper support60via a variable resistor or the like to change the stiffness of the upper support60, thereby changing the upper connecting portion stiffness. The stiffness of the upper support60is relatively decreased, for example, in a case where the temperature of the upper support60is relatively high. Here, the upper varying mechanism31can change the stiffness of the upper support60, furthermore, the upper connecting portion stiffness to two levels including a relatively great value and a relatively small value. As in the upper varying mechanism31, for example, the lower varying mechanism32of this embodiment changes the temperature of the lower arm bushing80by applying a current to the lower arm bushing80via a variable resistor or the like to change the stiffness of the lower arm bushing80, thereby changing the lower connecting portion stiffness. Here, the lower varying mechanism32can change the stiffness of the lower arm bushing80, furthermore, the lower connecting portion stiffness to two levels including a relatively great value and a relatively small value. In addition, the upper varying mechanism31and the lower varying mechanism32may have a configuration in which the stiffness of the upper support60and the lower arm bushing80are changed by using, for example, a magnetic fluid or the like and thus the upper connecting portion stiffness and the lower connecting portion stiffness are changed, other than the above configuration.

The ECU50controls the driving of each part in the vehicle2, and is configured to include an electronic circuit having a well-known microcomputer as a main component, which includes a CPU, a ROM, a RAM, and an interface. The ECU50is electrically connected to various sensors and detectors which are mounted in places of the vehicle2such as a brake sensor51which detects ON/OFF of a braking operation by the driver and each of wheel speed sensors52which detects a wheel speed as a rotational speed of each of the wheels3, and receives an electronic signal corresponding to the detection result. Each of the wheel speed sensors52is used as a sensor which detects and estimates a braking force (or deceleration) of the vehicle2as described later. The ECU50executes a stored control program on the basis of various input signals and various maps input from various sensors and outputs a drive signal to each part of the vehicle2including the vehicle suspension device1, thereby controlling the driving of the parts.

The ECU50of this embodiment controls the upper varying mechanism31and the lower varying mechanism32of the varying device30according to the braking state of the vehicle2to control the upper connecting portion stiffness and the lower connecting portion stiffness to vary.

Specifically, the ECU50controls the upper varying mechanism31and the lower varying mechanism32at the time of braking of the vehicle to perform control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased compared to at the time of non-braking of the vehicle2. Here, the ECU50controls the upper varying mechanism31and the lower varying mechanism32at the time of smooth-braking during the braking of the vehicle2to perform control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased compared to at the time of non-braking of the vehicle2. On the other hand, the ECU50prohibits the control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased at the time of sudden-braking during the braking of the vehicle2. Accordingly, for example, the vehicle suspension device1achieves both driving stability (straight line stability) and reduction in brake vibration while suppressing a feeling of strangeness of the driver due to a change in harshness characteristics, thereby appropriately reducing unsprung vibration.

Here, the time of non-braking of the vehicle2is a state where no braking force of the vehicle2is generated and a state where the deceleration of the vehicle2is 0. On the other hand, the time of smooth-braking during the braking of the vehicle2is a braking state where the absolute value of the braking force of the vehicle2is relatively small and a state where the absolute value of the deceleration of the vehicle2is relatively small. Typically, the time of smooth-braking of the vehicle2mentioned here is a state where a braking force and a deceleration by which brake vibration occurs are applied and is determined according to, for example, the specification of the vehicle2, the braking device, and the like. Specifically, the time of smooth-braking of the vehicle2is, for example, a smooth-braking range in which the deceleration of the vehicle2is from 0 G at the initial braking stage to about 0.3 G, more specifically, a smooth-braking range in which the deceleration causes brake vibration to be maximized, for example, is from 0 G to near 0.2 G. In addition, the time of sudden-braking during the braking of the vehicle2is a state where the absolute value of the braking force of the vehicle2is equal to or greater than a predetermined value set in advance and is a sudden-braking range in which the deceleration of the vehicle2is equal to or greater than a predetermined value set in advance.

As the ECU50controls the upper varying mechanism31, the upper support60is controlled so that the front-back stiffness of the vehicle2is relatively decreased at the time of smooth-braking of the vehicle2compared to at the time of non-braking of the vehicle2. In addition, as the above-described control is prohibited at the time of sudden-braking of the vehicle2, in the upper support60, the front-back stiffness of the vehicle2is relatively increased compared to at the time of smooth-braking of the vehicle2. Accordingly, the upper connecting portion stiffness is relatively decreased at the time of smooth-braking of the vehicle2compared to at the time of non-braking of the vehicle2, and is relatively increased at the time of sudden-braking of the vehicle2compared to at the time of smooth-braking of the vehicle2. On the other hand, as the ECU50controls the lower varying mechanism32, the lower arm bushing80is controlled so that the front-back stiffness of the vehicle2is relatively increased at the time of smooth-braking of the vehicle2compared to at the time of non-braking of the vehicle2. In addition, as the above-described control is prohibited at the time of sudden-braking of the vehicle2, in the lower arm bushing80, the front-back stiffness of the vehicle2is relatively decreased compared to at the time of smooth-braking of the vehicle2. Accordingly, the lower connecting portion stiffness is relatively increased at the time of smooth-braking of the vehicle2compared to at the time of non-braking of the vehicle2, and is relatively decreased at the time of sudden-braking of the vehicle2compared to at the time of smooth-braking of the vehicle2.

As the ECU50controls the upper varying mechanism31and the lower varying mechanism32as described above, the vehicle suspension device1allows the stiffness of the upper support60and the lower arm bushing80to vary according to the braking state of the vehicle2. In addition, the vehicle suspension device1allows the upper connecting portion stiffness and the lower connecting portion stiffness to vary and thus can reduce brake vibration by using a change in the principal elastic axis height of the suspension5with bushing stiffness control.

FIG. 3is a schematic view of the arrangement of the suspension5in a side view. InFIG. 3, “H” is the principal elastic axis height, “B” is the vehicle height, “Ks” is the spring characteristics of the shock absorber, “KZ” is the vertical stiffness of the principal elastic axis, “KX” is the front-back stiffness of the principal elastic axis, “X” is the front-back displacement of the spindle19(the position of unsprung center of gravity), “Z” is the vertical displacement of the spindle19(the position of unsprung center of gravity), “α” is the inclination of the shock absorber with respect to the vertical direction, “β” is the inclination of the principal elastic axis with respect to the horizontal direction, “T” is the torque input at the time of braking, “F” is the input from the road surface (input at the time of harshness). In addition, the height H of the principal elastic axis corresponds to a relative distance along the vertical direction from a reference point on the wheels3side (for example, the spindle19) to a reference point on the principal elastic axis. The vehicle height B corresponds to a relative distance along the vertical direction from a reference point on the wheels3side (for example, the spindle19) to a reference point on the vehicle body4side (for example, mounting bolts on the vehicle body4side of the lower arm bushing80). Hereinafter, description will be provided based on the model illustrated inFIG. 3.

Although an input from the road surface is considered at the time of harshness of vehicle2, an input of the braking torque of the braking device serves as an input source at the time of braking of the vehicle2. The relation between unsprung forces due to the braking torque is considered, for example, as illustrated inFIG. 4from torque inputs exerted on each of a rotating part (tire) of the wheel3and a non-rotating part (the knuckle13). That is, the inputs exerted on the rotating part of the wheel3include a braking torque input T to the rotating part, a front-back braking force FXexerted on the ground surface between the tire of the wheel3and the road surface, and a reaction force −FXof the front-back braking force exerted on the ground surface. In addition, inFIG. 4, “r0” is the relative distance between the spindle19and the ground surface along the vertical direction. The inputs exerted on the non-rotating part of the wheel3include a braking torque input −T to the non-rotating part, and a front-back reaction force FXfrom the rotating part to the non-rotating part. When synthesizing the inputs, the unsprung force due to the braking torque becomes an unsprung front-back input FXat the ground surface between the tire of the wheel3and the road surface.

Next, unsprung vibration will be described with reference toFIGS. 5 and 6based on the relation between the geometry of the suspension5and the braking torque input. As inFIGS. 5 and 6, a displacement amount of the position of the spindle19(hereinafter, may be referred to as a “spindle position”) with respect to the vehicle front-back direction varies depending on the principal elastic axis height in a case where the same level of force (for example, the front-back input FXdescribed above) is applied to the ground surface. InFIG. 5, the principal elastic axis height is relatively high and is positioned on the upper side in the vertical direction with respect to the spindle position in this figure. On the other hand, inFIG. 6, the principal elastic axis height is relatively low and is positioned on the lower side in the vertical direction with respect to the spindle position in this figure. In addition, inFIGS. 5 and 6, “KX” is the front-back stiffness of the principal elastic axis, “KW′” is the wind-up stiffness (the stiffness when the knuckle13rotates about the spindle19).

When the principal elastic axis height is relatively high as illustrated inFIG. 5, a displacement amount L11of the spindle position becomes a value obtained by adding a displacement amount L12of a translational component of the exerted force and a displacement amount L13of a rotational component. On the other hand, when the principal elastic axis height is relatively low as illustrated inFIG. 6, a displacement amount L21of the spindle position has a tendency to be relatively decreased as much as a displacement amount L22of the translational component of the exerted force and a displacement amount L23of the rotational component cancel each other. Therefore, the unsprung front-back vibration at the time of braking is reduced as the principal elastic axis height becomes lower and the displacement amount of the spindle19is reduced as illustrated inFIG. 7.FIG. 7illustrates a change in the unsprung front-back vibration when the principal elastic axis height is changed by changing the characteristics of the suspension5and illustrates that the unsprung front-back vibration is relatively increased in a case where the principal elastic axis height is relatively high and the unsprung front-back vibration is relatively decreased in a case where the principal elastic axis height is relatively low.

The vehicle suspension device1of this embodiment can change the stiffness of the upper support60and the lower arm bushing80according to the braking state as the characteristics of the suspension5by controlling the upper varying mechanism31and the lower varying mechanism32using the ECU50as described above to change the upper connecting portion stiffness and the lower connecting portion stiffness, thereby changing the principal elastic axis height. As illustrated inFIG. 8, the principal elastic axis height has a tendency to decrease with a decrease in the upper connecting portion stiffness (the stiffness of the upper support60) and to decrease with an increase in the lower connecting portion stiffness (the stiffness of the lower arm bushing80).

When the principal elastic axis height is changed by changing the stiffness of the upper support60and the lower arm bushing80according to the braking state through the control of the ECU50, the upper varying mechanism31, and the lower varying mechanism32of this embodiment, the upper connecting portion stiffness and the lower connecting portion stiffness are controlled so that a front-back force compliance corresponding to the displacement amount of the spindle position when a front-back force is applied to the spindle position is maintained constant.FIG. 9illustrates an example of a combination of the front-back stiffness (the upper connecting portion stiffness) of the upper support60and the front-back stiffness (the lower connecting portion stiffness) of the lower arm bushing80in which the front-back force compliance at the spindle position is constant. The front-back force compliance is changed according to the front-back stiffness of the upper support60and the front-back stiffness of the lower arm bushing80. InFIG. 9, the solid line L indicates an assembly of combinations of the front-back stiffness of the upper support60and the front-back stiffness of the lower arm bushing80in which the front-back force compliance is constant at a predetermined value. Accordingly, the vehicle suspension device1can suppress an influence on harshness characteristics.

On the basis of the above description, the ECU50of this embodiment controls the upper varying mechanism31and the lower varying mechanism32at the time of smooth-braking of the vehicle2to perform the control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased compared to at the time of non-braking of the vehicle2. Accordingly, as illustrated inFIG. 8, in the vehicle suspension device1, the principal elastic axis height changes from an operation point P1which represents the principal elastic axis height at the time of non-braking of the vehicle2to an operation point P2which represents the principal elastic axis height at the time of smooth-braking, thereby reducing the principal elastic axis height.

In this case, the ECU50changes the upper connecting portion stiffness and the lower connecting portion stiffness so that the front-back force compliance of the spindle19at the time of braking of the vehicle2, here, at the time of smooth-braking thereof is equal to the front-back force compliance of the spindle19at the time of non-braking of the vehicle2. That is, as illustrated inFIG. 9, the front-back stiffness of the upper support60and the lower arm bushing80are controlled so that the combination of the front-back stiffness of the upper support60and the front-back stiffness of the lower arm bushing80at the operation point P1and the combination of the front-back stiffness of the upper support60and the front-back stiffness of the lower arm bushing80at the operation point P2are both positioned on the solid line L. Accordingly, the vehicle suspension device1can reduce the principal elastic axis height while maintaining the front-back force compliance in a constant level at the time of smooth-braking of the vehicle2.

Moreover, the ECU50prohibits the control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased at the time of sudden-braking during the braking of the vehicle2. Accordingly, in the upper support60, the front-back stiffness of the vehicle2is relatively increased at the time of sudden-braking of the vehicle2compared to at the time of smooth-braking thereof, and in the lower arm bushing80, the front-back stiffness of the vehicle2is relatively decreased at the time of sudden-braking of the vehicle2compared to at the time of smooth-braking thereof. As a result, in the vehicle suspension device1, the operation point P2illustrated inFIGS. 8 and 9returns to the operation point P1.

As the ECU50controls the upper varying mechanism31and the lower varying mechanism32, the vehicle suspension device1configured as described above achieves a state in which the upper connecting portion stiffness is relatively high and the lower connecting portion stiffness is relatively low in the normal use range such as at the time of non-braking of the vehicle2(see the operation point P1ofFIGS. 8 and 9). Accordingly, in the vehicle suspension device1, the principal elastic axis height of the suspension5is relatively high in the normal use range such as at the time of non-braking of the vehicle2, thereby securing driving stability.

Moreover, in the vehicle suspension device1, in the smooth-braking range such as at the time of smooth-braking of the vehicle2, when the braking torque is added, the ECU50controls the upper varying mechanism31and the lower varying mechanism32as described above so that the upper connecting portion stiffness is relatively decreased and the lower connecting portion stiffness is relatively increased (see the operation point P2inFIG. 8), thereby changing the geometry of the suspension5. At this time, in the vehicle suspension device1, the front-back stiffness of the upper support60and the lower arm bushing80are changed while the front-back force compliance of the spindle19is substantially constant (see the operation point P2ofFIG. 9). Accordingly, in the vehicle suspension device1, for example, not only the principal elastic axis height is changed by simply increasing the lower connecting portion stiffness at the time of smooth-braking, but also the upper connecting portion stiffness is decreased according to the increase in the lower connecting portion stiffness, thereby decreasing the principal elastic axis height while maintaining the front-back force compliance in a constant level. As a result, in the vehicle suspension device1, brake vibration is reduced by decreasing the principal elastic axis height, and then the front-back force compliance is held to be constant, thereby suppressing an influence on harshness characteristics.

Furthermore, in the vehicle suspension device1, in the sudden-braking range such as at the time of sudden-braking of the vehicle2at which the braking force of the vehicle2is relatively increased, the ECU50prohibits the control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased such that the upper connecting portion stiffness is relatively increased and the lower connecting portion stiffness is relatively decreased, and thus both the stiffness return to values equal to those in the normal use range (see the operation point P2ofFIGS. 8 and 9). Accordingly, the vehicle suspension device1increases the principal elastic axis height at the time of sudden-braking of the vehicle2at which an influence on brake vibration or harshness characteristics and the like may not be considered, thereby enhancing driving stability.

Next, an example of the control by the ECU50will be described with reference to the flowchart ofFIG. 10. The control routine is repeatedly performed in every control cycle of several milliseconds to tens of milliseconds.

First, the ECU50determines whether or not the braking operation by the driver is performed on the basis of the detection result by the brake sensor51and the like (ST1).

When it is determined that the braking operation by the driver is performed (Yes in ST1), the ECU50determines whether or not the vehicle2undergoes the smooth-braking on the basis of the detection result by each of the wheel speed sensors52(ST2) and the like. The ECU50can determine whether or not the vehicle2undergoes the smooth-braking on the basis of whether or not the braking force (or the deceleration) of the vehicle2which is estimated on the basis of the wheel speed of each of the wheels3detected by each of the wheel speed sensors52and the change rate thereof is equal to or smaller than a predetermined value (for example, a value corresponding to 0.2 G) set in advance. In addition, the ECU50may detect the braking force (or the deceleration) of the vehicle2on the basis of various sensors and methods without being limited to the above description.

When it is determined that the vehicle2undergoes the smooth-braking (Yes in ST2), the ECU50decreases the stiffness of the upper support60and increases the stiffness of the lower arm bushing80by controlling the upper varying mechanism31and the lower varying mechanism32such that the upper connecting portion stiffness is relatively decreased and the lower connecting portion stiffness is relatively increased (ST3). Then, the ECU50ends the current control cycle and proceeds to the subsequent control cycle.

When it is determined that the braking operation by the driver is not performed in ST1(No in ST1), and when it is determined that the vehicle2does not undergo the smooth-braking (No in ST2), the ECU50increases the stiffness of the upper support60and decreases the stiffness of the lower arm bushing80by controlling the upper varying mechanism31and the lower varying mechanism32such that the upper connecting portion stiffness is relatively increased and the lower connecting portion stiffness is relatively decreased (ST4). Then, the ECU50ends the current control cycle and proceeds to the subsequent control cycle.

The vehicle suspension device1according to the embodiment described above includes the suspension5, the varying device30, and the ECU50. The suspension5supports the wheels3of the vehicle2to the vehicle body4of the corresponding vehicle2. The varying device30allows the upper connecting portion stiffness which is the stiffness between the vertically upper portion of the suspension5and the vehicle body4and the lower connecting portion stiffness which is the stiffness between the vertically lower portion of the suspension5and the vehicle body4to vary. The ECU50controls the varying device30at the time of braking of the vehicle2to perform the control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased compared to at the time of non-braking of the vehicle2.

Therefore, in the vehicle suspension device1, the upper connecting portion stiffness (the front-back stiffness of the upper support60) is decreased at the time of braking of the vehicle2compared to at the time of non-braking, the lower connecting portion stiffness (the front-back stiffness of the lower arm bushing80) is increased, thereby decreasing the principal elastic axis height of the suspension5while holding a change in the front-back force compliance at a low level. As a result, the vehicle suspension device1achieves both driving stability enhancement and a reduction in brake vibration while suppressing a feeling of strangeness of the driver due to a change in harshness characteristics, thereby appropriately reducing unsprung vibration.

In the above description, the ECU50prohibits the control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased at the time of sudden-braking of the vehicle2, and may perform this control even at the time of sudden-braking of the vehicle2without being limited thereto.

FIG. 11is a schematic view illustrating the schematic configuration of a vehicle suspension device according to a second embodiment.FIG. 12is a schematic view illustrating an operation of the vehicle suspension device.FIG. 13is a diagram illustrating an example of the relation between the displacement and the force of the upper support and the lower arm bushing.FIG. 14is a diagram illustrating an example of a control map of the vehicle suspension device.FIG. 15is a flowchart illustrating an example of control by the ECU of the vehicle suspension device.FIG. 16is a schematic view illustrating the schematic configuration of a vehicle suspension device according to a modified example. The vehicle suspension device according to the second embodiment is different from that of the first embodiment in control contents by a control device. The repeated description of configurations, actions, and effects which are common to the above-described embodiment will not be provided as much as possible.

A vehicle suspension device201of this embodiment illustrated inFIGS. 11 and 12is configured so that the varying device30includes an upper varying mechanism231and a lower varying mechanism232instead of the upper varying mechanism31and the lower varying mechanism32of the first embodiment (seeFIG. 1). The upper support60and the lower arm bushing80have substantially the same configuration, and the upper varying mechanism231and the lower varying mechanism232have substantially the same configuration. Therefore,FIGS. 11 and 12collectively illustrate both the configurations. In the following description, the common configuration of the upper support60and the lower arm bushing80and the common configuration of the upper varying mechanism231and the lower varying mechanism232will be described to be common as much as possible.

The upper varying mechanism231and the lower varying mechanism232are configured to linearly change the stiffness of the upper support60and the stiffness of the lower arm bushing80respectively between a relatively great value and a relatively small value.FIGS. 11 and 12illustrate the configurations of cases where the center axis lines of the cylindrical members of the upper support60and the lower arm bushing80are disposed along the front-back direction of the vehicle2.

The upper support60is configured to include an outer cylinder61, an inner cylinder62, an elastic body63, and the like, and the lower arm bushing80is configured to include an outer cylinder81, an inner cylinder82, an elastic body83, and the like. The outer cylinders61and81and the inner cylinders62and82are cylindrical members that extend along the front-back direction of the vehicle body4. The inner cylinders62and82are respectively inserted into the outer cylinders61and81. Any one of the outer cylinder61and the inner cylinder62is provided on the piston rod14side and the other is provided on the vehicle body4side. Here, for example, the outer cylinder61is provided to a bracket on the vehicle body4side, and the inner cylinder62is provided on the piston rod14side. Any one of the outer cylinder81and the inner cylinder82is provided on the lower arm12side and the other is provided on the vehicle body4side. Here, for example, the outer cylinder81is provided to a bracket on the lower arm12side, and the inner cylinder82is provided on the vehicle body4side. The elastic bodies63and83are made of an elastomer such as rubber and are provided in a cylindrical shape so as to be respectively intervened between the outer cylinders61and81and the inner cylinders62and82in the radial direction. That is, the elastic bodies63and83are respectively disposed on the inner circumferential sides of the outer cylinders61and81and on the outer circumferential sides of the inner cylinders62and82. In the upper support60and the lower arm bushing80, the outer cylinders61and81and the inner cylinders62and82are relatively displaced along the axial direction (the front-back direction) at the time of braking.

In addition, in the upper support60and the lower arm bushing80, protruding edge portions61a,81a,61b, and81bhaving an annular shape are respectively provided on both front-back end surfaces of the outer cylinders61and81, and stopper portions62a,82a,62b, and82bhaving a disk shape are respectively provided on both front-back end surfaces of the inner cylinders62and82. Here, the stopper portions62a,82a,62b, and82bare configured to be movable relative to the inner cylinders62and82along the front-back direction. Furthermore, in the upper support60and the lower arm bushing80, protruding edge portions63a,83a,63b, and83bhaving an annular shape are respectively provided on both front-back end surfaces of the elastic bodies63and83. In the upper support60and the lower arm bushing80, the outer cylinders61and81, the inner cylinders62and82, and the elastic bodies63and83may be assembled in the following positional relation. That is, in the upper support60and the lower arm bushing80, the stopper portions62aand82aand the protruding edge portions61aand81arespectively oppose each other at predetermined intervals in the front-back direction, and the stopper portions62band82band the protruding edge portions61band81brespectively oppose each other at predetermined intervals. In the upper support60and the lower arm bushing80, the protruding edge portions63aand83aare respectively positioned between the stopper portions62aand82aand the protruding edge portions61aand81a, and the protruding edge portions63band83bare respectively positioned between the stopper portions62band83band the protruding edge portions61band81b. In the upper support60and the lower arm bushing80, by controlling the intervals between the stopper portions62aand82aand the protruding edge portions61aand81a, the intervals between the stopper portions62band82band the protruding edge portions61band81b, and the like, the crushing amounts of the protruding edge portions63a,83a,63b, and83bare adjusted, and the bushing stiffness use ranges and bushing characteristics are adjusted.

The upper varying mechanism231and the lower varying mechanism232are configured to include motors and the like to move the stopper portions62a,82a,62b, and82balong the front-back direction. The upper varying mechanism231and the lower varying mechanism232move the stopper portions62a,82a,62b, and82balong the front-back direction by power generated by the motor. Accordingly, the upper varying mechanism231and the lower varying mechanism232allow the intervals between the stopper portions62aand82aand the protruding edge portions61aand81aand the intervals between the stopper portions62band82band the protruding edge portions61band81B to vary, and thus can change the crushing amounts of the protruding edge portions63a,83a,63b, and83b. Therefore, as illustrated inFIG. 13, the upper varying mechanism231and the lower varying mechanism232can linearly change the stiffness of the upper support60and the stiffness of the lower arm bushing80from A to B, and furthermore, can linearly change the upper connecting portion stiffness and the lower connecting portion stiffness between a relatively great value and a relatively small value.

For example, as illustrated inFIG. 11, the upper varying mechanism231and the lower varying mechanism232relatively increase the intervals between the stopper portions62aand82aand the protruding edge portions61aand81aand the intervals between the stopper portions62band82band the protruding edge portions61band81B to decrease the crushing amounts of the protruding edge portions63a,83a,63b, and83bsuch that the upper connecting portion stiffness and the lower connecting portion stiffness can be relatively decreased. On the other hand, for example, as illustrated inFIG. 12, the upper varying mechanism231and the lower varying mechanism232relatively decrease the intervals between the stopper portions62aand82aand the protruding edge portions61aand81aand the intervals between the stopper portions62band82band the protruding edge portions61band81B to increase the crushing amounts of the protruding edge portions63a,83a,63b, and83bsuch that the upper connecting portion stiffness and the lower connecting portion stiffness can be relatively increased.

The ECU50controls the upper varying mechanism231and the lower varying mechanism232of the varying device30according to the braking state of the vehicle2to control the upper connecting portion stiffness and the lower connecting portion stiffness to vary. The ECU50of this embodiment controls the upper varying mechanism231and the lower varying mechanism232on the basis of the braking force (or the deceleration of the vehicle2) of the vehicle2to linearly change the upper connecting portion stiffness and the lower connecting portion stiffness. Typically, the ECU50controls the upper varying mechanism231and the lower varying mechanism232according to the change in the braking force (or the deceleration of the vehicle2) of the vehicle2to continuously change the upper connecting portion stiffness and the lower connecting portion stiffness.

Specifically, the ECU50controls the upper varying mechanism231and the lower varying mechanism232at the time of braking of the vehicle to perform the control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased compared to at the time of non-braking of the vehicle2. Here, the ECU50controls the upper varying mechanism31and the lower varying mechanism32at the time of smooth-braking during the braking of the vehicle2to perform the control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased compared to at the time of non-braking of the vehicle2. On the other hand, the ECU50prohibits the control which causes the upper connecting portion stiffness to be relatively decreased and causes the lower connecting portion stiffness to be relatively increased at the time of sudden-braking during the braking of the vehicle2, and thus causes the upper connecting portion stiffness to be relatively increased and causes the lower connecting portion stiffness to be relatively decreased compared to at the time of smooth-braking. Accordingly, for example, the vehicle suspension device1achieves both driving stability (straight line stability) and reduction in brake vibration while suppressing a feeling of strangeness of the driver due to a change in harshness characteristics, thereby appropriately reducing unsprung vibration.

Here, the ECU50controls the upper varying mechanism231and the lower varying mechanism232on the basis of, for example, the control map exemplified inFIG. 14to change the upper connecting portion stiffness and the lower connecting portion stiffness according to the braking force of the vehicle2. The control map exemplified inFIG. 14is a map in which a combination of the upper connecting portion stiffness and the lower connecting portion stiffness in which the front-back force compliance at the spindle position is constant, and the braking force of the vehicle2are associated with each other. The control map exemplified inFIG. 14is produced in advance according to actual vehicle evaluations and the like, and is stored in a storage unit of the ECU50. The ECU50estimates the braking force (or the deceleration) of the vehicle2on the basis of the wheel speed of each of the wheels3detected by each of the wheel speed sensors52and the like, and calculates the upper connecting portion stiffness and the lower connecting portion stiffness corresponding to the estimated braking force on the basis of the control map exemplified inFIG. 14. The ECU50controls the upper varying mechanism231and the lower varying mechanism232to achieve the calculated upper connecting portion stiffness and lower connecting portion stiffness.

In this embodiment, the ECU50calculates the upper connecting portion stiffness and the lower connecting portion stiffness by using the control map exemplified inFIG. 14in the description. However, this embodiment is not limited thereto. For example, the ECU50may calculate the upper connecting portion stiffness and the lower connecting portion stiffness on the basis of a mathematical model corresponding to the control map exemplified inFIG. 14.

As the ECU50controls the upper varying mechanism231and the lower varying mechanism232, the vehicle suspension device201configured as described above achieves a state in which the upper connecting portion stiffness is relatively increased and the lower connecting portion stiffness is relatively decreased in the normal use range such as at the time of non-braking of the vehicle2(see the operation point P1ofFIG. 14). Accordingly, in the vehicle suspension device1, the principal elastic axis height of the suspension5is relatively high in the normal use range such as at the time of non-braking of the vehicle2, thereby securing driving stability.

Moreover, in the vehicle suspension device201, in the smooth-braking range such as at the time of smooth-braking of the vehicle2, when the braking torque is added, the ECU50controls the upper varying mechanism231and the lower varying mechanism232according to the braking force of the vehicle2so that the upper connecting portion stiffness is relatively decreased and the lower connecting portion stiffness is relatively increased (see the operation point P2inFIG. 14) according to the braking force, thereby changing the geometry of the suspension5. At this time, in the vehicle suspension device201, the front-back stiffness of the upper support60and the lower arm bushing80are changed while the front-back force compliance of the spindle19is substantially constant (see the operation point P2ofFIG. 14). Accordingly, in the vehicle suspension device201, for example, not only the principal elastic axis height is changed by simply increasing the lower connecting portion stiffness at the time of smooth-braking, but also the upper connecting portion stiffness is decreased according to the increase in the lower connecting portion stiffness, thereby decreasing the principal elastic axis height while maintaining the front-back force compliance in a constant level. As a result, in the vehicle suspension device201, brake vibration is reduced by decreasing the principal elastic axis height, and then the front-back force compliance is held to be constant, thereby suppressing an influence on harshness characteristics.

Furthermore, in the vehicle suspension device201, in the sudden-braking range such as at the time of sudden-braking of the vehicle2at which the braking force of the vehicle2is relatively increased, the ECU50controls the upper varying mechanism231and the lower varying mechanism232according to the braking force of the vehicle2so that the upper connecting portion stiffness is relatively increased and the lower connecting portion stiffness is relatively decreased according to the braking force (see an operation point P3ofFIG. 14). At this time, the vehicle suspension device201controls the upper connecting portion stiffness and the lower connecting portion stiffness to have values corresponding to the braking force of the vehicle2. Accordingly, the vehicle suspension device201increases the principal elastic axis height at the time of sudden-braking of the vehicle2at which an influence on brake vibration and the like may not be considered, thereby enhancing driving stability. At this time, in the vehicle suspension device1, since the upper connecting portion stiffness and the lower connecting portion stiffness are continuously changed and controlled according to the change in the braking force and the principal elastic axis height is controlled, both a reduction in brake vibration and driving stability can be achieved with higher accuracy according to the change in the braking force. In addition, in the vehicle suspension device201, the principal elastic axis height can be controlled by maintaining the front-back force compliance in a constant level even at this time, and thus an influence on harshness characteristics can be suppressed.

Next, an example of the control by the ECU50will be described with reference to the flowchart ofFIG. 15.

First, the ECU50determines whether or not the braking operation by the driver is performed on the basis of the detection result by the brake sensor51and the like (ST201).

When it is determined that the braking operation by the driver is performed (Yes in ST201), the ECU50detects the braking force (or the deceleration) of the vehicle2on the basis of the detection result by each of the wheel speed sensors52(ST202) and the like.

The ECU50changes the stiffness of the upper support60and the lower arm bushing80by controlling the upper varying mechanism231and the lower varying mechanism232to change the upper connecting portion stiffness and the lower connecting portion stiffness so that an appropriate principal elastic axis height for the braking force of the vehicle2detected in ST202is achieved (ST203). Then, the ECU50ends the current control cycle and proceeds to the subsequent control cycle.

When it is determined that the braking operation by the driver is not performed in ST201(No in ST201), the ECU50increases the stiffness of the upper support60and decreases the stiffness of the lower arm bushing80by controlling the upper varying mechanism231and the lower varying mechanism232such that the upper connecting portion stiffness is relatively increased and the lower connecting portion stiffness is relatively decreased (ST204). Then, the ECU50ends the current control cycle and proceeds to the subsequent control cycle.

In the vehicle suspension device201according to the embodiment described above, the upper connecting portion stiffness (the front-back stiffness of the upper support60) is decreased at the time of smooth-braking of the vehicle2compared to at the time of non-braking and the lower connecting portion stiffness (the front-back stiffness of the lower arm bushing80) is increased, thereby decreasing the principal elastic axis height of the suspension5while holding a change in the front-back force compliance at a low level. As a result, the vehicle suspension device201achieves both driving stability enhancement and a reduction in brake vibration while suppressing a feeling of strangeness of the driver due to a change in harshness characteristics, thereby appropriately reducing unsprung vibration.

In the vehicle suspension device201, the ECU50changes the upper connecting portion stiffness and the lower connecting portion stiffness on the basis of the braking force of the vehicle2. Therefore, the vehicle suspension device201can achieve both driving stability enhancement and a reduction in brake vibration with higher accuracy while suppressing a feeling of strangeness of the driver due to a change in harshness characteristics.

The vehicle suspension device according to the above-described embodiment of the present invention is not limited to the above-described embodiment and can be modified in various forms in a range described in the appended claims.

FIG. 16illustrates the schematic view of the schematic configuration of a vehicle suspension device301according to the modified example. The vehicle suspension device301is configured so that the varying device30includes an upper varying mechanism331and a lower varying mechanism332instead of the upper varying mechanism231and the lower varying mechanism232of the second embodiment (seeFIG. 11). The upper varying mechanism331and the lower varying mechanism332are configured to linearly change the stiffness of the upper support60and the stiffness of the lower arm bushing80between a relatively great value and a relatively small value.FIG. 16illustrates the configuration of case where the center axis lines of the cylindrical members of the upper support60and the lower arm bushing80are disposed to intersect with the front-back direction of the vehicle2.

The upper support60is configured to include the outer cylinder61, the inner cylinder62, the elastic body63, and the like, and the lower arm bushing80is configured to include the outer cylinder81, the inner cylinder82, the elastic body83, and the like. Here, the outer cylinders61and81and the inner cylinders62and82are cylindrical members that extend along a direction intersecting the front-back direction of the vehicle body4. The inner cylinders62and82are respectively inserted into the outer cylinders61and81. The elastic bodies63and83are made of an elastomer such as rubber, and are respectively disposed on the inner circumferential sides of the outer cylinders61and81and on the outer circumferential sides of the inner cylinders62and82. In the upper support60and the lower arm bushing80, the outer cylinders61and81and the inner cylinders62and82are relatively displaced along the radial direction at the time of braking. In the upper support60and the lower arm bushing80, the elastic bodies63and83are respectively provided with pairs of recesses (bored cavity parts)64and84and pairs of recesses65and85.

The upper varying mechanism331and the lower varying mechanism332are configured to include insertion members66and86provided in the recesses64and84. The insertion members66and86are formed by members and shapes which can be changed in size. In the upper support60and the lower arm bushing80, the ECU50adjusts the sizes and the like of the insertion members66and86by controlling the upper varying mechanism331and the lower varying mechanism332, and thus the bushing stiffness use ranges and bushing characteristics are adjusted. Therefore, the upper varying mechanism331and the lower varying mechanism332can linearly change the sizes of the insertion members66and86to linearly change the stiffness of the upper support60and the stiffness of the lower arm bushing80, respectively. Furthermore, the upper connecting portion stiffness and the lower connecting portion stiffness can be linearly changed between a relatively great value and a relatively small value.

Even in this case, the vehicle suspension device301can achieve both driving stability enhancement and a reduction in brake vibration with higher accuracy while suppressing a feeling of strangeness of the driver due to a change in harshness characteristics.

In addition, the ECU50may have a configuration in which driving stability is enhanced by causing the upper connecting portion stiffness to be relatively increased and causing the lower connecting portion stiffness to be relatively decreased at the time of sudden-braking at which the absolute value of the braking force of the vehicle2is equal to or greater than a predetermined value set in advance compared to at the time of non-braking of the vehicle2.

In addition, the suspension device main body described above is not limited to the above-described configuration and, for example, may have a configuration in which the upper arm11is not provided and the vertically lower end portion of the cylinder15is connected to the upper end portion of the knuckle13via a joint portion such as a ball joint.

In the above description, the control device of the vehicle suspension device is described as the ECU which controls each part of the vehicle, but without being limited thereto, for example, the control device of the vehicle suspension device may be configured separately from the ECU so as to transmit and receive information such as detection signals, drive signals and control commands with the ECU.

In addition, the varying device described above is not limited to the above-described configuration.

REFERENCE SIGNS LIST

1,201,301VEHICLE SUSPENSION DEVICE