GB2243349A

GB2243349A - Hydraulic stabilizer system with means for varying roll rigidity

Info

Publication number: GB2243349A
Application number: GB9108790A
Authority: GB
Inventors: Masatsugo Yokote; Fukashi Sugasawa; Tomohiro Yamamura
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1990-04-26
Filing date: 1991-04-24
Publication date: 1991-10-30
Also published as: GB9108790D0; DE4113736A1; JPH048619A

Abstract

The stabilizer of the hydraulic stabilizer system includes a pair of hydraulic cylinders 30L, R installed between a vehicle body 16 and suspension arms 22, conduits 26A, B extending crosswise to connect upper and lower cylinder chambers U, L of the hydraulic cylinder 30L to lower and upper cylinder chambers L, V of the other hydraulic cylinder 30R, respectively, accumulators 34L, R, conduits 24A, B interconnecting the accumulators 34L, R and the conduits 26A, B, and restrictions 32L, R in the conduits 24A, B. A mechanism 36, 40 for altering the hydraulic pressure within the cylinder chambers and the hydraulic conduits is controlled by a control unit 42 in accordance with a vehicle running condition, in particular lateral acceleration. <IMAGE>

Description

HYDRAULIC STABILIZER SYSTEM WITH MEANS FOR VARYING ROLL RIGIDITY The

present invention relates in general to vehicular stabilizers and more particularly to a vehicular stabilizer system of the kind operated by fluid pressure, e.g., a hydraulic stabilizer system.

An example of a prior art hydraulic stabilizer system is disclosed in Japanese Utility Model Provisional Publication No. 60-76506. Th is prior art stabilizer system incorporates a pair of single roddouble acting hydraulic cylinders installed between a vehicle body and respective suspension arms. The hydraulic cylinders are connected by cross conduits in such a manner that an upper cylinder chamber of one hydraulic cylinder is communicated with a lower cylinder chamber of the other. The cross conduits are respectively provided with orifices or restrictions and further provided, at locations between the upper cylinder chambers and the restrictions, with spring type mechanical accumulators for pressurizing the hydraulic fluid in the conduits and the cylinders, respectively.

In the prior art hydraulic stabilizer system, the restrictions are installed in the cross conduits to restrict flow of hydraulic fluid therethrough during both rolling and bouncing. Accordingly, the stabilizer system provides a damping action even during bouncing, causing a stiff or rough riding feel and therefore a deteriorated riding comfo= of the vehicle.

Further, although the mechanical accumulators can previously and manually be adjusted in order to attain a desired roll rigidity, such adjustment cannot actually be carried out each time of variation of cornering condition, e.g., variation of lateral acceleration. Accordingly, such a prior art stabilizer system cannot attain a desired roll rigidity and therefore a desired steering characteristic through control of the roll rigidity.

In accordance with the present invention, there is provided a novel and improved stabilizer system for a vehicle having a vehicle body and a pair of suspension arms spaced from each other laterally of the vehicle body.

The stabilizer system comprises a stabilizer which includes a pair of first and second double-rod double-acting fluid cylinder installed between the vehicle body and the suspension arms, respectively, the first and second fluid cylinders having upper cylinder chambers and lower cylinder chambers, respectively, a pair of first fluid conduits connecting the upper cylinder chamber and the lower cylinder chamber of the first fluid cylinder to the lower cylinder chamber and the upper cylinder chamber of the second fluid chamber, a pair of accumulators, a pair of second fluid conduits fluidly connecting the accumulators to the first conduits, respectively, and a pair of restrictions installed in the second fluid conduits for restricting flow of fluid therethrough.

The stabilizer system further comprises fluid pressure altering means for altering fluid pressure within the stabilizer, and control means for controlling fluid pressure alterating means in accordance with a running condition of the vehicle.

The above structure can be used for solving the above noted problems inherent in the prior art system.

It is accordingly possible to provide a stabilizer system which can actively control the roll rigidity of a vehicle without deteriorating the riding comfort.

A stabilizer system of the above described character is useful for active control of the steering characteristic.

A stabilizer system of the above described character is actually quite useful from the point of view of safe driving.

The invention will be described' further, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic view of a vehicular hydraulic stabilizer system according to an embodiment of the present invention; Fig. 2 is a flowchart of operations of a controller employed in the hydraulic stabilizer system of Fig. 1; and Fig. 3 is a schematic view of a portion of a hydraulic stabilizer system according to another embodiment of the present invention.

Referring first to Fig. 1, a vehicle is generally indicated by 10 and includes, when viewed from the rear of the vehicle, left and right road steering knuckles 14 wheels 12L and 12R, a pair of and 14 on which the wheels 12L and 12R are rotatably carried, and a vehicle body 16. Installed between the respective steering knuckles 14 and 14 and the vehicle body 16 are suspension struts 18 and 18 having incorporated therein shock absorbers 18A and 18A which are axially expansible and contractible. Coil springs 20 and 20 are installed between respective retainers 18B and 18B which are in turn installed on the vehicle body 16 and the steering knuckles 14 and 14, that is, installed between the sprung and unsprung portions of the suspension struts 18 and 18. Further, installed between the steering knuckles 14 and 14 and the vehicle body 16 are lower control arms 22 and 22 which pivot up and down in response to up-and-down movement of the steering knuckles 14 and 14.

The vehicle 10 is provided with a hydraulic stabilizer system of this invention which is generally indicated by 24.

The stabilizer system 24 includes a hydraulic stabilizer 26 interposed between the left and right steering knuckles 14 and 14 and the vehicle body 16, and a control unit 28 for controlling the hydraulic pressure of the stabilizer 26 and thereby controlling the roll rigidity of the vehicle 10 during cornering.

The stabilizer 26 consists of hydraulic cylinders 30L and 30R, restrictions 32L and 32R, and spring type mechanical accumulators 34L and 34R, first hydraulic conduits 26A and 26B, and second hydraulic conduits 38A and 38B.

The hydraulic cylinders 30L and 30R are of the double rod-double acting type and each consist of a -5 11 cylinder tube 30a, a piston 30b sl idable in the cylinder tube 30a and separating the inside thereof into upper and lower cylinder chambers U and L, and a piston rod 30c secured to the piston 30b and protruding therefrom in the axially opposed directions. The piston rods 30c and 30c have upper and lower end portions projecting outward from the cylinder tubes 30L and 30R and attached at the lower ends to the lower control arms 22 and 22, respectively. The upper ends of the piston rods 30c and 30c serve as free ends. The cylinder tubes 30a and 30a are pivotally installed at the upper ends on the vehicle body 16. The hydraulic cylinders 30L and --ween - 30R are thus installed upright bet '-he sprung,and unsprung portions of the vehicle 10.

of the left wheel The upper cylinder chamber I, side hydraulic cylinder 30L is fluidly connected through the first hydraulic conduit 26A to the lower cylinder chamber L of the right Wheel side hydraulic cylinder 30R while the lower cylinder chamber L of the left wheel side hydraulic cylinder 30L is fluidly connected through a first hydraulic conduit 26B to the upper cylinder chamber U of the right wheel side hydraulic cylinder 30R. The first conduits 26A and 26B are thus arranged crosswise. The second conduits 28A and 28B are disposed between the first conduits 26A and 26B and the spring type mechanical accumulators 34L and 34R to provided communication therebetween. That is, the second hydraulic conduits 28A and 28B are connected at one ends to axially intermediate portions of the first hydraulic conduits 26A and 26B and at the other ends to the accumulators 34L and 34R, respectively. The restrictions 32L and 32R are installed in the second conduits to restrict flow of hydraulic fluid therethrough.

Each of the accumulators 34L and 34R includes a cylinder tube 34a, a piston 34b slidable within the cylinder tube 34a and defining a hydraulic cylinder chamber D and, a spring 34c of a predetermined spring constant, installed in the cylinder tube 34a on the side of the piston 34b opposite to the cylinder chamber D to act upon the piston 34b. The cylinder chambers D are communicated with the second hydraulic conduit 28A and 28B, respectively.

The control unit 28 includes a control cylinder 36, third hydraulic conduits 38A and 38B, an electric motor 40, a controller 42 and a lateral acceleration sensor 42. The control cylinder.36 is of ti e double roddouble acting type and includes a cylinder tube 36a, a piston 36b slidable within the cylinder tube 36a and separating the inside thereof into two hydraulic cylinder chambers Rl and R2, and a piston rod 36c secured to the piston 36b to protrude therefrom in the axially opposed directions. The cylinder chambers R1 and R2 are communicated through hydraulic conduits 38A and 38B with the first hydraulic conduits 26A and 261B, respectively. The piston rod 30c has axially opposed ends protruding outward of the cylinder tube 36a, an end of which serves as a free end and the other end is formed with a rack 36d meshed with a drive pinion 40a of the electric motor 40.

The controller 42 consists of a microcomputer and a motor drive circuit and is adapted to effect such operations shown in the flowchart of Fig. 2 in response to a signal G supplied thereto from the lateral acceleration sensor 42 and sup-o^; ies a motor driving signal i to the electric motor 40 for driving the same. The lateral acceleration sensor 42 produces a lateral acceleration signal in the form of a voltage signal which becomes positive or negative depending upon the directions of the inertia of the vehicle during cornering. In the meantime, though not shown, a rotation angle sensor is attached to the electric motor 40 to produce a signal representative of a rotation angle of the motor 40, i. e., the rotation angle of the drive pinion 34a or drive shaft connected thereto, for controlling the drive of the motor 40.

In the fongoing, the control cylinder 36, third hydraulic conduits 38A and 38B, and electric motor 40 constitute a hydraulic pressure altering mechanism for altering the hydraulic pressure wthin the stabilizer 26. On the other hand, the controller 42 and the lateral acceleration sensor 44 constitute a control means - for controlling the operation of the altering mechanism in accordance w-th a vehicle running condition.

The operation will now be described.

The control performed by the controller 42 will first be described with reference to Fig. 2.

At step (1), a signal G representative of a lateral acceleration is supplied from the lateral acceleration sensor 44 to the controller 42 to be read thereby. At step (2), it is judged whether the absolute value 1G1 is larger than the reference value Go. The reference value Go is a threshold value. When the judgement at step (2) is NO, it is determined that the cornering vehicle is under the condition of being subjected to a relatively small lateral acceleration. The control thus proceeds to step (3) to perform a control for holding the piston 36b of the control cylinder 36 at a neutral position, i.e., a position equidistant f-rom the opposite ends of the cylinder tube 36a. such positional control of the piston 36b is performed by supplying a motor driving signal i to the electric motor 40 for thereby driving the same until it is detected by the rotation angle sensor that the piston 36b is in the neutral position.

on the other hand, when the judgement at step (2) is YES, it is determined that the cornering vehicle is being subjected to a relatively large lateral acceleration. The control thus proceeds to step (4) to produce a motor drive signal i for moving the piston 36b of the control cylinder 36 in the direction to increase the hydraulic pressure within the cylinder chambers U and L that are being subjected to compression. In this instance, the positioning of the piston 36b is also performed on the basis of the signal produced by the rotation angle sensor. Then, at step (5), it is judged whether the control is completed. When the control is not completed, the foregoing processes are repeated.

The operation of the stabilizer system 24 will now be described.

When the vehicle is travelling on a paved road, the lateral acceleration sensor 44 produces a signal G = 0. Thus, while the control of Fig 2 is performed, the piston 36b of the control cylinder 36 is held at a neutral position for thereby holding the cylinder chambers Rl and R2 equal in volume. Due to this, the hydraulic pressure within the first and second hydraulic conduits 26A and 28A connected to one pair of upper and lower cylinder chambers U and L is equal to that within the first and second hydraulic conduits 26B and 28B for connection of another pair of upper and lower cylinder chambers U and L. Under this running condition, substantially no bound and rebound of the wheels 12L and 12R is caused, thus causing substantially no variation in length of the left and right hydraulic cylinders 30L and 30R and therefore substantially no flow of hydraulic fluid through the conduits 26A, 26B, 28A and 28B is caused.

Accordingly, substantially no damping action is caused and therefore a desired suspension characteristic can be retained.

When bound and rebound of the wheels 112L and 12R is caused due to some protrusions and recess es on the road surface during straight-ahead running, the lateral acceleration sensor 40 still produces a signal G = 0. As mentioned above, the control cylinder 36 thus causes substantially no influence. to the 2 0 hydraulic pressure with the conduits 26A, 26B, 28A and 28B. In this instance, when the running vehicle comes upon some protruded road surface portion to the both left and right wheels 12L and 12R to bound and therefore the pistons 30b and 30b of the hydraulic cylinders 30L and 30R are urged to move upward, the upper cylinder chambers U and U are both subjected to compression concurrently while the lower cylinder chambers L and L are subjected to expansion and therefore prevailed by a vacuum pressure concurrently.

3 0 By this, the hydraulic fluid within the upper cylinder chambers U and U are urged to flow through the respective first hydraulic conduits 26A and 26B into the lower cylinder chambers L and L on the opposite sides. However, since variations in volume of the upper and lower cylinder chambers U and L are equal to each other since the cylinders 30T- 1 and 30R are of the double rod type, substantially no variation in 5 hydraulic pressure within the con&uits 26A, 26B, 28A and 28B is caused. The similar case is also caused when the vehicle comes upon some recessed road surface to cause the wheels 12L and 12R to rebound and therefore the lower cylinder chambers L and L to be compressed.

That is, during either of bound or rebound of the wheels 12L and 12R, substantially no variation in hydraulic pressure within the hydraulic conduits 28A and 28B is caused, thus causing substantially no flow of hydraulic fluid through the restrictions 32L and 32R and therefore substantially no damping action thereby. Accordingly, during straightahead running of the vehicle almost all of the damping action is caused by the shock absorbers 18A and 18A. The stabilizer system 24 thus produces substantially no damping action. In this connection, the above noted prior art system produces a damping action in response to bounce of wheels during straight-ahead running, thus deteriorating the riding comfort.

Then, when the vehicle is cornering, for example, turning to the right, such a roll as indicated by the arrow A in Fig. 1, is caused, in which the left wheel 12L, when viewed from the rear of the vehicle, is urged to fall or go downward while the right wheel 12R is urged to rise or go upward. During such cornering, the sensor 44 detects a lateral acceleration to which the vehicle is subjected and supplies a signal G representative of a detected ' lateral acceleration. The signal G becomes positive or negative depending upon the direction of turning. The controller 42 performs the control of Fig. 2 and drives, when the vehicle is in a predetermined turning condition, the electric motor 40 in the direction to suppress or damp the roll (i.e., in the clockwise direction in Fig. 1). By this, the piston rod 36c is caused to move a predetermined distance in the righthand direction "all in Fig. 1.

Due to this, the cylinder c.-.amber R1 of the control cylinder 36 is compressed, thus causing the hydraulic fluid within the cylinder chamber RI to flow through the third conduit 38A into the first hydraulic conduit 26A while at the same time the ozher cylinder chamber R2 is expanded and therefore prevailed by a vacuum pressure. By this, the hydraulic Pressure within the first hydraulic conduit 26A, therefore the hydraulic pressure within the upper cylinder chamber U of the left wheel side hydraulic cylider 30L and the lower cylinder chamber L of the right wheel side hydraulic cylinder 30R are caused to increase while at the same time the hydraulic pressure within the cylinder chamber D of the accumulator 34L increases gradually. On the other hand, the hydraulic fluid within the cylinder chamber D of the accumulator 34R is gradually supplied to the first and second hydraulic conduits 26B and 28B and the lower cylinder chamber L of the left wheel side hydraulic cylinder 30 L and the upper cylinder U of the right wheel side cylinder 30R.

That is, by the effect of the restricting action by the restrictions 32L and 32R in addition to the damping action by the shock absorbers 18A and 18A, a damping action against the diving of the vehicle body 16 is caused by the left wheel side hydraulic cylinder 30L while at the same time a damping action against the rise of the vehicle body 16 is caused by the right wheel side hydraulic cylinder 30R, thus making it possible to damp or suppress the roll actively. This -ed depending upon damping action against roll is adjust variation of the lateral acceleration. When the vehicle finishes turning, the control cylinder 30 is returned to its neutral position.

When the vehicle 10 turns to the left, the stabilizer system 24 produces a damping action similar to the above, though its action is reversed with respect to the left and 'Lateral sIdes of the vehicle body 16.

From the foregoing, it will be understood that by controlling the rotation angle of the electric motor 40 and thereby controlling the position of the - of its piston 36b of the control cylinder 36 out neutral position, the hydraulic pressure within the stabilizer 26 can be varied to vary the roll rigidity depending upon variation of the lateral acceleration.

it will be further understood that stabilizer system of this invention can actively control the roll rigidity without deteriorating the riding comfort.

It will be further understood that the hydraulic stabilizer system is useful for actively controlling the steering characteristic through control of load movement laterally of the vehicle body.

It will be further understood that when the hydraulic cylinders 30L and 30R are subjected to a large shock or impact due to some protruded or recessed road surface, such a shock or impact is I efficiently absorbed by the accumulators 34L and 34R and the restrictions 32L and 32R.

It will be further understood the hydraulic stabilizer system 24 of this invention is actually quite useful for attaining safe driving of the vehicle.though simple in structure.

It will be further understood that the accumulators 34L and 34R are not limited to the spring type mechanical accumulators but can be hydropneumatic accumulators 46L, 46R as shown in Fig. 3.

It will be further understood that the working fluid of the stabilizer system 24 is not limited to hydraulic fluid but can be other incompressible fluid.

- the control It will be further understood that by the control unit 28 is not necessarily based on lateral acceleration. but another factor or parameter representative of vehicle running condition such as a steering angle, steering wheel turning speed, etc., may be used.

1

Claims

Claims:

1. A stabilizer system for a vehicle having a vehicle body and a pair of suspension arms spaced from each other laterally of the vehicle body, comprising:

a fluid stabilizer including a pair of first and second double-rod doubleacting fluid cylinders installed between the vehicle body and the suspension arms, respectively, said first and second fluid cylinders having upper cylinder chambers and lower cylinder chambers, respectively, a pair of first fluid conduits connecting said upper cylinder chamber and said lower cylinder chamber of said first fluid cylinder to said lower cylinder chamber and said upper cylinder chamber of said second fluid cylinder, a pair of accumulators, a pair of second fluid conduits fluidly connecting said accuniulators to said first conduits, respectively, and a pair of restrictions installed in said second conduits for restricting flow of fluid therethrough; fluid pressure altering means for altering fluid pressure within said stabilizer; and control means for controlling said fluid pressurd altering means in accordance with a running condition of the vehicle.

2. A stabilizer system as claimed in claim 1, wherein said fluid pressure altering means comprises a double-rod double-acting fluid cylinder having a piston rod and a pair of cylinder chambers, a pair of third fluid conduits connecting said cylinder chambers of said fluid cylinder of said pressure altering means to said first fluid conduits, respectively, and drive means for axially driving said piston rod in response tZ 1 to a variation of the running condition of the vehicle.

3. A stabilizer system as claimed in claim 2, wherein said drive means further comDrises an electric motor drivingly connected with said piston rod.

4. A stabilizer system as claimed in claim 3, wherein said electric motor comprises a drive pinion, and said pis-ton rod of said fluid cylinder of said pressure altering means is provided with a rack meshed with said drive pinion.

acceleration

5. A stabilizer system as claimed in claim3 or 4, wherein said control means comprises a lateral sensor for detecting a lateral acceleration of the vehicle and producing a signal representative thereof, and a controller responsive to said signal from said lateral acceleration sensor for producing a signal for variably driving said electric motor in response to a variation of the running condition of the vehicle.

6. A stabilizer system as claimed in claim 5, wherein said fluid cylinder of said fluid pressure altering means has a piston movable with said piston rod, said controller comprising means for judging whether the lateral acceleration detected by said lateral acceleration sensor is larger than a reference value and allowing, when it is judged that the lateral acceleration is equal to or smaller than the reference value, said piston to be held in its neutral position where said cylinder chambers of said fluid cylinder of le, said pressure altering means are equal in volume to each other and allowing, when it is judged that the lateral acceleration is larger than the reference value, said piston to be driven by said electric motor out of the neutral position.

7. A stabilizer system as claimed in any preceding claim, wherein said fluid cylinders of said stabilizer comprise cylinder tubes and piston rods, said cylinder tubes are pivotally connected at upper ends thereof to the vehicle body, said piston rods of said fluid cylinders of said stabilizer being pivotally connected at lower ends to the suspension arms, respectively.

S,/ 5 e m

8. A stabilizer/ as claimed in claim 7, wherein said piston rods have upper ends serving as free ends.

J-stem

9. A stabilizer, as claimed in any preceding claim, the vehicle including a pair of wheels and a pair of steering knuckles carrying the wheels, respectively, the suspension arms being installed between the steering knuckles and the vehicle body for up-and-down movement.

sisce.

10. A stabilizeras claimed in claim 9, wherein the vehicle further has a pair of suspension struts installed between the steering knuckles and the vehicle body, respectively.

11. A stabilizer system substantially as described with reference to either of the embodiments illustrated in the accompanying drawings.

Published 1991 at The Patent Office. Concept House, Cardiff Road. Newport, Gwent NP9 1RH. Further copies maybe obtainedfrom Sales Branch. Unit 6. Nine Mile Point Cwmfelinfach. Cross Keys. Newport, NP1 7HZ. Printed by Multiplex techniques ltd. St Mary Cray, Kent.