JPH0378284B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a suspension device installed in an automobile.

(Prior Art) Conventionally, as one type of automobile suspension device, there has been a front and rear wheel suspension in which the front wheels and rear wheels are respectively suspended on the vehicle body, as disclosed in Japanese Patent Application Laid-Open No. 57-118907. The vehicle height is adjusted by supplying and discharging fluids such as pressurized oil and compressed air to and from fluid actuators that support the vehicle body and are disposed between the wheels (front wheels and rear wheels) of each suspension and the vehicle body. A so-called hydroneumatic suspension equipped with a vehicle height adjustment device is known. In particular, in the above-mentioned example, the vehicle height is changed according to the vehicle speed by the operation of the vehicle height adjustment device.

On the other hand, it is well known that there are contradictory steering characteristics in automobiles, such as understeering characteristics and oversteering characteristics.At high speeds, understeering characteristics are stronger in order to ensure driving stability, and at low speeds, understeering characteristics are stronger. In order to improve turning maneuverability, it is optimal to weaken the understeering characteristic and make it more like an oversteering characteristic, and there is a demand for its realization.

(Object of the Invention) In view of the above-mentioned circumstances, an object of the present invention is to provide a suspension device for an automobile having a vehicle height adjustment device as described above, which utilizes changes in vehicle height caused by the vehicle height adjustment device to automatically adjust the vehicle height at high speeds. To provide a suspension device in which the understeering characteristic is strengthened in terms of speed, and the understeering characteristic is automatically weakened at low speeds to become a little oversteering characteristic.

(Structure of the Invention) The automobile suspension device according to the present invention includes:
In order to achieve the above purpose, a strut-type front wheel suspension and a rear wheel suspension that suspend the front and rear wheels, and a strut-type front wheel suspension and a rear wheel suspension that are arranged between the vehicle body and the wheels of each of the above suspensions, and that receive fluid supply and discharge. a fluid actuator for adjusting the vehicle height; and a control means for receiving a vehicle speed signal from the vehicle speed detection means and controlling the supply and discharge of fluid to the fluid actuator so as to lower the vehicle height at high speeds and raise the vehicle height at low speeds. and a vehicle height adjustment device comprising: a vehicle height adjustment device, and an inclination angle θ _R inward of the vehicle body in a reference state of the strut body of the rear wheel suspension in a reference state of the strut body of the front wheel suspension; By doing _so , the rate of change in roll center height due to wheel bumps and rebound is smaller on the rear wheel suspension side than on the front wheel suspension side. It is characterized by being configured to be large.

The present invention provides that the cornering force acting on the wheels during cornering decreases (increases) in accordance with the increase (decrease) in moving load due to vehicle body inclination during cornering, and that this moving load increases due to the roll center height. It is constructed in consideration of the fact that it increases (decrease) in accordance with the increase (decrease).

That is, the present invention reduces the vehicle height at high speeds, and by reducing the vehicle height, the rate of decrease in the roll center height of the front wheel suspension, which has a smaller rate of change in roll center height, is higher than that of the rear wheel suspension. It becomes smaller than the reduction rate of high, and therefore,
The rate of decrease in the moving load due to vehicle body tilt during turning is smaller on the front wheels than on the rear wheels, and as a result, the rate of increase in cornering force acting on the wheels is smaller on the front wheels than on the rear wheels. The front wheels will experience a relatively large side slip in the opposite direction to the turning direction, resulting in stronger understeering characteristics.On the other hand, at low speeds, the vehicle height will increase, and this increase in vehicle height will cause the roll center height to increase. The rate of increase in the roll center height of the rear wheel suspension, which has a large rate of change, is greater than the rate of increase in the roll center height of the front wheel suspension. As a result, the reduction rate of the cornering force is larger on the rear wheel side than on the front wheel side, so the rear wheel has a relatively smaller force on the side opposite to the turning direction than the front wheel. This structure causes a large side slip and weakens the understeering characteristics.

A brief explanation of the relationship between the cornering force and the moving load and the relationship between the moving load and the roll center height is as follows.

First, as is conventionally known, there is a relationship between the cornering force acting on the wheel and the vertical load as shown by the curve in FIG. When the vehicle body leans when turning, the vehicle weight is applied unevenly to the left and right wheels, and a moving load of ±△W is applied, the cornering force is the average of the cornering forces C ₁ and C ₂ of each wheel. Value (C ₁
+C ₂ )/2, but as is clear from Figure 1, this average value (C ₁ +C ₂ )/2 is the cornering force when the vehicle weight is applied equally to the left and right wheels and there is no moving load. AusC becomes smaller than ₀ .
Further, the tendency for the cornering force to decrease due to such a moving load becomes more pronounced as the moving load ΔW increases.

Next, to find the relationship between the moving load and the roll center height, refer to Figure 2 to find out the moment balance when the suspension turns, for example, the moment around the 0 point (the intersection of the vehicle center line and the ground). Think about the balance. Now, if the centrifugal force at the centripetal acceleration coefficient μ is μW, the roll center height is H, the suspension roll stiffness is k, the vehicle roll angle is φ, the wheel spacing is d, and the moving load acting on the wheels is △W, then μW・H+kφ=d・△W ∴△W=(μW・H+kφ)/d. As can be seen from this equation, the moving load ΔW acting on the wheel increases as the roll center height H increases.

(Effect of the invention) The automobile suspension device according to the present invention has the following features:
As mentioned above, it is equipped with strut-type front and rear wheel suspension and a vehicle height adjustment device that lowers the vehicle height at high speeds and raises the vehicle height at low speeds.
In addition, by setting the inclination angle inward of the vehicle body in the standard state of the rear wheel suspension to be smaller than that of the front wheel suspension, the rate of change in roll center height due to wheel bumps and rebound can be reduced. The rear wheel suspension side is larger than the suspension side.

Normally, the roll center height of the front wheel suspension and that of the rear wheel suspension are set to be the same or almost the same in a reference state (a state in which the wheels are neither bumped nor rebounded).

Now, assuming that the roll center heights of the front wheels and the rear wheels are the same or almost the same, according to the automobile suspension device according to the present invention configured as described above, at high speeds, the reduction in the vehicle height The amount of decrease in roll center height is smaller on the front wheel side than on the rear wheel side, so the roll center height is higher on the front wheel side than on the rear wheel side, and therefore the moving load is more on the front wheel side than on the rear wheel side. , the cornering force becomes smaller on the front wheel side than on the rear wheel side, resulting in stronger understeering characteristics. At low speeds, as the vehicle height increases, the roll center height becomes smaller on the front wheel side. The rear wheel side is higher than the front wheel side, and the moving load is therefore larger on the rear wheel side than on the front wheel side, so the cornering force is smaller on the rear wheel side than on the front wheel side, resulting in understeering characteristics. Since the steering wheel becomes weaker and has a tendency to oversteering, it is possible to improve both running stability at high speeds and turning maneuverability at low speeds.

Further, even if the roll center height in the standard state differs to some extent between the front wheels and the rear wheels, according to the present invention having the above configuration, the cornering force at high speeds can be increased as already described above. Since the ratio is smaller on the front wheel side than on the rear wheel side, the understeering characteristic becomes stronger, and at low speeds, the reduction rate of cornering force is larger on the rear wheel side than on the front wheel side, so the understeering characteristic becomes weaker. This results in a slight oversteering characteristic, and the above-mentioned effects are produced.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

3 to 7 show an automobile suspension device according to an embodiment of the present invention. In Figure 3, 1 is a front wheel suspension that suspends the left and right front wheels on the vehicle body, 2 is a rear wheel suspension that suspends the left and right rear wheels on the vehicle body, and both suspensions 1 and 2 are the vehicle body and wheels, respectively. (front wheel and rear wheel) strut bodies 13, 23 arranged between
It is constructed as a strut-type suspension. Note that the strut body 13,
Reference numeral 23 also serves as a fluid actuator of a vehicle height adjustment device to be described later. 3 is a strut body 1 of each suspension 1, 2 as the fluid actuator.
The vehicle height adjustment device 3 is a vehicle height adjustment device that adjusts the vehicle height by supplying and discharging pressure oil to and from the suspensions 1 and 23. The vehicle height adjustment device 3 is driven by a drive motor 31 to A hydraulic pump 33 that supplies pressure oil to the hydraulic chambers of the bodies 13 and 23 via a hydraulic circuit 32.
And, each suspension 1, 2 is connected to the hydraulic circuit 32.
and vehicle height adjustment valves 34, 34 consisting of a pair of electromagnetic 4-port 3-position switching valves interposed correspondingly to the supply position 34.
In a, pressure oil from the hydraulic pump 33 is supplied to the strut bodies 13, 23 side, and the discharge position 34
In b, on the contrary, the pressure oil in the hydraulic chambers of the strut bodies 13, 23 is discharged and recovered into the oil tank 35, and furthermore, in the neutral position 34c, the pressure oil in the hydraulic chambers of the strut bodies 13, 23 is
The supply and discharge of pressure oil to and from the hydraulic chambers is now stopped.

Further, the vehicle height adjusting device 3 includes a vehicle height detecting means 4 for detecting the vehicle height, and a vehicle speed detecting means 5 for detecting the vehicle speed. Switching position 34a of high adjustment valve 34
It is connected to a controller 6, which serves as a control means for switching and controlling 34c. The controller 6 performs feedback control based on the signal from the vehicle height detection means 4, and receives the signal from the vehicle speed detection means 5, and operates a vehicle height adjustment valve to lower the vehicle height at high speeds and increase the vehicle height at low speeds. 34 switching positions 34a to 34c are controlled to switch.

Next, the structure of the suspensions 1 and 2 will be explained with reference to FIG. 4, for example, in the case of the rear wheel suspension 2. That is, in Figure 4, 2
1 and 21 are wheel support members that rotatably support left and right wheels (rear wheels) 7L and 7R, respectively; 22 and 22 are lower arms arranged in the vehicle width direction corresponding to each wheel 7L and 7R; Each lower arm 22 is
The inner end is rotatably connected to the frame 8a of the vehicle body 8, and the outer end is rotatably connected to the lower part of the wheel support member 21, so as to restrict movement of the wheels 7L and 7R in the vehicle width direction.

Further, as described above, 23, 23 are a pair of left and right strut bodies as fluid actuators arranged vertically between the vehicle body 8 and each of the rear wheels 7L, 7R, and support the vehicle body 8. It is. As shown in FIGS. 4 and 5, each strut body 23 has a cylinder 23a having a hydraulic chamber therein, and one end (base end) connected to the cylinder 23a.
The other end (tip) faces the pressure chamber and receives the pressure.
The piston rod 2 extends outside the cylinder 23a.
3b, the lower part of the cylinder 23a is connected to the upper part of the wheel support member 21 via a bracket 24, while the piston rod 23b
The tip (upper end) of is connected to the vehicle body 8 via a mount rubber 25. Pressure oil is supplied and discharged from the hydraulic circuit 32 to the hydraulic chamber of the cylinder 23a through the passage 23c formed in the piston rod 23b, as described above, so that the piston rod 23b is connected to the cylinder 23a. The strut body 23 is configured to expand and contract to change the reference length of the strut body 23, thereby varying the vehicle height. Note that 40 is a drain passage, which leads leaked oil between the cylinder 23a and the piston rod 23b to the oil tank 35.

Furthermore, 26 and 26 are the strut bodies 2, respectively.
3 and 23, and each of the accumulators 26 has a gas chamber 26a and a hydraulic chamber 2 that oppose each other inside.
6b. The hydraulic chamber 26b is connected to the cylinder 2 of the strut body 23 via a hydraulic communication path 27.
The pressure generated in the hydraulic chamber 3a is transmitted to the hydraulic chamber 26b of the accumulator, and the pressure is transferred to the gas chamber 26 of the accumulator.
It is configured to function as a gas spring by the compressive elasticity of the gas (for example, nitrogen gas, etc.) sealed in a. Although the configuration of the front wheel suspension 1 is not particularly illustrated,
The configuration is almost the same as the rear wheel suspension 2.

Here, how to determine the roll center height in the suspensions 1 and 2 configured as described above will be explained using FIGS. 6 and 7. still,
FIG. 6 schematically shows a portion corresponding to the left wheel (front wheel) 9L in the front wheel suspension 1, and FIG. 7 schematically shows a portion corresponding to the left wheel 7L in the rear wheel suspension 2. This is what is shown. In addition, in Figures 6 and 7,
The solid line represents the reference state of the wheels 9L, 7L without bumps or rebound, and the broken line represents the bump state of the wheels 9L, 7L.

First, draw an extension line _l1 of the lower arms 12, 22 inward in the vehicle width, and draw the strut bodies 13, 23.
The strut bodies 13, 23 from the upper end vehicle body connection point.
Draw a straight line l ₂ in the direction perpendicular to , and determine the intersection P ₁ between this straight line l ₂ and the above extension line l ₁ . Next, this intersection P ₁ and the ground contact center point of wheels 9L, 7L (road surface G and wheel 9
Intersection with center line l ₃ of L, 7L) _Straight line connecting P ₂
, and the intersection point P ₃ of this straight line l ₄ and the center line of the car body l ₅
Establish. This intersection P ₃ is for each suspension 1,
2, and the ground G at the intersection _P3
The height relative to the roll center height becomes the roll center height H _F and _HR .

The roll center heights H _F and H _R of each suspension 1 and 2 are determined based on the geometry of the suspension as described above, and therefore the rate of change in the roll center height due to bumps and rebound of the wheels is It depends on the geometric shape of the suspension, for example, the inclination angles θ _F and θ _R of the strut bodies 13 and 23 inward to the vehicle body, and the smaller the inclination angles θ _F and θ _R , the higher the roll center height. The rate of change in will increase.

However, in this embodiment, the lower arm 12,
The lengths and inclination angles of the struts 22 are set to be the same, and the lengths of the strut bodies 13 and 23 are also set to be the same, but the inclination angles of the strut bodies 13 and 23 inward to the vehicle body are different. The inclination angle θ _F of the suspension strut body inward of the vehicle body is the inclination angle θ _R of the rear wheel suspension strut body inward the vehicle body.
As can be easily seen from the comparison between Fig. 6 and Fig. 7, the roll center height H _F , due to the bump and rebound of wheels 9L and 7L
The rate of change in H _R is small with front wheel suspension 1,
The rear wheel suspension 2 is configured to be larger.

Incidentally, FIG. 8 shows the change characteristics of the roll center heights H _F and _HR due to bumps and rebounds of the wheels 9L and 7L. As can be seen from this figure, near the reference state (origin of the figure), the roll center height H _F of front wheel suspension 1 and the roll center height H _R of rear wheel suspension 2 match; The rate of change in roll center height H _R is the roll center height of front wheel suspension 1.
Since the change rate of H _F is larger than the rate of change of H
H _R is higher than the roll center height H _F of front wheel suspension 1, and conversely, in bump conditions, the roll center height H _F of front wheel suspension 1 is higher than the roll center height H F of rear wheel suspension 2 _.
be higher than

In the embodiment described above, when the vehicle is traveling at high speed, the vehicle height adjustment device 3 operates to lower the vehicle height under the control of the controller 6 which receives a signal from the vehicle speed detection means 5. That is, each strut body 13, 23 of the front wheel and rear wheel suspensions 1, 2
As the pressure oil in the hydraulic chamber is discharged and collected into the oil tank 35 via the hydraulic circuit 32, each strut body 13, 23 contracts and the vehicle height is lowered accordingly.

In this case, in the front wheel and rear wheel suspensions 1 and 2, the strut bodies 13 and
23 is in the same state as when the wheels bump, so the roll center heights H _F and _HR of suspensions 1 and 2 are the same as the rate of change in the roll center heights H _F and _HR due to wheel bumps and rebounds. The roll center height H _F of the small front wheel suspension 1 is higher than the roll center height H _R of the rear wheel suspension 2. For this reason, the moving load due to the vehicle body tilt when turning becomes larger on the front wheel suspension 1 side, and the cornering force acting on the wheels decreases more on the front wheel side than on the rear wheel side depending on the size of this moving load. Therefore, the front wheels cause a relatively large side slip in the opposite direction to the turning direction, thereby increasing the understeering characteristic, and as a result, driving stability can be improved.

On the other hand, when the vehicle is running at low speed, the vehicle height adjustment device 3 operates under the control of the controller 6 to raise the vehicle height. That is, by supplying pressure oil from the hydraulic pump 33 of the vehicle height adjustment device 3 to the hydraulic chambers of each of the strut bodies 13 and 23 of the front wheel and rear wheel suspensions 1 and 2, the respective strut bodies 1
3 and 23 extend, and the vehicle height increases accordingly.

In this case, in the front wheel and rear wheel suspensions 1 and 2, the strut bodies 13 and
23 is in the same state as when the wheels rebound, so the roll center heights H _F and _HR of suspensions 1 and 2 are the same as the rate of change in the roll center heights H _F and _HR due to bumps and rebound of the wheels. The roll center height H _R of the larger rear wheel suspension 2 is higher than that of the front wheel suspension 1.
Higher than H _F. For this reason, the moving load due to the vehicle body tilt when turning becomes larger on the rear wheel suspension 2 side, and depending on the size of this moving load, the cornering force decreases more on the rear wheel side than on the front wheel side. The rear wheels cause a relatively large side slip in the direction opposite to the turning direction, weakening the understeering characteristic and giving rise to a slight oversteering characteristic, and as a result, it is possible to improve the turning maneuverability.

Moreover, the vehicle height adjustment by the vehicle height adjustment device 3 lowers the vehicle height at high speeds and increases the vehicle height at low speeds, so it is possible to reduce wind resistance at high speeds and to reduce the vehicle height when driving at low speeds on rough roads. It is also possible to prevent road surface interference.

Figure 9 shows the length l' _R of the lower arm 22 and the length of the lower arm 12 of the front wheel suspension 1 shown in Figure 6.
10 is a diagram showing the rear wheel suspension 2 set to be shorter than l' _F , and FIG. 10 shows the length l _R of the strut body 23 in the standard state in the standard state of the front wheel suspension 1 shown in FIG. 6. FIG. 3 is a diagram showing a rear wheel suspension 2 set to be longer than the length _lF of a strut body 13 in FIG.

In the embodiments shown in FIGS. 6 and 7 above, the inclination angles θ _F and θ _R of the strut body inward of the vehicle body in the standard state are set so that θ _F >θ _R , so that the bumps and rebounds of the wheels are This configuration is such that the rate of change in roll center height is greater on the rear wheel suspension side than on the front wheel suspension side, which can be easily understood from a comparison between Figures 6 and 9. Front wheel suspension lower arm 1
The length l′ _F of 3 is the lower arm 2 of the rear wheel suspension.
By setting the roll center height to be larger than the length l' _R of 3 (l' _F >l' _R ), the rate of change in the roll center height is made larger on the rear wheel suspension side than on the front wheel suspension side. Similarly, as can be easily understood from a comparison between FIG. 6 and FIG _. The length of the strut at l _R
Similarly, by setting the roll center height to be shorter (l _F < l _R ), the rate of change in the roll center height is also configured to be larger on the rear wheel suspension side than on the front wheel suspension side. I can do it.

Therefore, in the suspension device according to the present invention, not only the configuration in which θ _F > θ _R as described above but also the configuration in which l' _F >l' _R as described above and/or l _F
It is also possible to make the rate of change in roll center height different between the front wheel side and the rear wheel side by adopting a configuration in which <l _R at the same time.

It should be noted that the present invention is not limited to the above-mentioned embodiment, but includes various other modifications. For example, it is also possible to configure the strut body and the fluid actuator to be provided separately.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between cornering force and vertical load, and FIG. 2 is an explanatory diagram for explaining the balance of moments when the suspension turns. Figures 3 to 8 show embodiments of the present invention, with Figure 3 being an overall configuration diagram, Figure 4 being a configuration diagram of the rear wheel suspension, Figure 5 being a sectional view of the strut body, and Figure 6 being a sectional view of the strut body. 8 and 7 are explanatory diagrams for explaining how to determine the roll center height of the front wheel and rear wheel suspensions, respectively.
Figure 9 shows the change characteristics of roll center height.
10 and 10 are views showing a rear wheel suspension in which the length of the lower arm and the length of the strut body are different from the front wheel suspension shown in FIG. 6. 1... Front wheel suspension, 2... Rear wheel suspension, 3... Vehicle height adjustment device, 5... Vehicle speed detection means, 6... Control means, 7L, 7R... Wheels (rear wheels), 8... Vehicle body, 9L...Wheel (front wheel), 13,
23... Strut body and fluid actuator,
H _F , H _R ...Roll center height.

Claims (1)

[Scope of Claims] 1. A strut-type front wheel suspension that suspends the front wheels and a strut-type rear wheel suspension that suspends the rear wheels, the inclination angle of the strut body of the rear wheel suspension inward in the vehicle body in a reference state; is set to be smaller than the inclination angle inward of the vehicle body in the reference state of the strut body of the front wheel suspension mentioned above, so that the rate of change in roll center height due to wheel bumps and rebound is lower than that of the front wheel suspension side. The suspension side is larger than the suspension side, and a fluid actuator is provided between the vehicle body and the wheels in each of the above suspensions to adjust the vehicle height according to fluid supply/discharge control, and also to detect vehicle speed. The vehicle is characterized by being provided with control means for receiving a signal from the vehicle speed detection means and controlling the supply and discharge of fluid to the fluid actuator so as to lower the vehicle height at high speeds and raise the vehicle height at low speeds. Automobile suspension device.