Device for the suspension and for roll-stabilization of motor vehicles

[0002] The present invention relates to a device for the suspension and for roll stabilization of motor vehicles.

[0003] Active chassis systems which operate in conjunction with a hydropneumatic suspension and displace hydraulic medium from the hydropneumatic spring struts on one side of the vehicle to the hydropneumatic spring struts on the other side of the re vehicle through one or more displacement units in order to thereby influence the rolling angle of the vehicle body are conventional. In these systems, a hydropneumatic suspension replaces either a conventional vehicle suspension or its stabilizers.

[0004] A system in which a hydropneumatic suspension replaces a conventional suspension in a vehicle body is described, for example, in German Published Patent Application No. 39 36 987.

[0005] This system is characterized by the fact that it actively counteracts rolling and pitching motions of the vehicle by actively displacing hydraulic medium directly between the support elements on different sides of a vehicle or between front and rear support units in order to raise one side of the vehicle while at the same time lowering the other side or to move the front part of the vehicle in the opposite direction from the rear end accordingly. However, one disadvantage of this system is that additional stabilizers are needed to guarantee the required passive roll stiffness of the vehicle and thus safe operation of the vehicle.

[0006] German Published Patent Application No. 20 48 323 describes a device for the stabilization of the vehicle superstructure against a curve gradient in which a hydropneumatic suspension replaces the stabilizers, and a pressure medium is conveyed as a function of the cornering directly to the pistons of cylinder-piston units, in particular hydropneumatic springs, which are connected between the wheels and the vehicle superstructure, so that the cylinder-piston unit allocated to the wheel on the inside of the curve is shortened in the sense of lowering the vehicle superstructure, and the cylinder-piston unit allocated to the wheel on the outside of the curve is lengthened in the sense of raising the vehicle superstructure.

[0007] One disadvantage of the device described in German Published Patent Application No. 20 48 323 is that additional add-on springs are required, but they have a negative effect on the overall roll stiffness of the vehicle. In addition, another negative effect of both devices described above is that other passive suspension elements are present in the vehicle in addition to the active hydropneumatics, resulting in a passive roll stiffness against which an active device must work, but this is unfavorable from an energy standpoint.

[0008] It is therefore an object of the present invention to provide an active device for the suspension and for roll stabilization of motor vehicles so that additional springs and stabilizers are not necessary.

[0009] The above and other beneficial objects of the present invention are achieved by providing a device for the suspension and for roll stabilization of motor vehicles as described herein.

[0010] Through specific coordination of piston surfaces and piston ring surfaces in combination with an active displacement unit, the hydropneumatic device for the suspension and for roll stabilization of motor vehicles can yield the full required vertical and roll stiffness simultaneously. This hydropneumatic device for the suspension and for roll stabilization of motor vehicles thus provides the complete suspension of the vehicle, so that no additional springs or stabilizers are needed, which thus offers advantages with regard to cost, weight and installation space in addition to the energy benefit.

[0011] FIG. 1 is a schematic view of an active hydropneumatic suspension system.

[0012] FIG. 2 is a schematic view of an example embodiment of a device for suspension and roll stabilization of a motor vehicle according to the present invention.

[0013] FIG. 1 illustrates an active hydropneumatic suspension having a rigid axle 1 and vehicle wheels 2 and 3 mounted on this axle. Dual tires may also be used instead of vehicle wheels 2 and 3, and any other wheel suspension may be used instead of rigid axle 1. Rigid axle 1 is connected to a vehicle body 4 by articulated joints 5, 6 on the axle and articulated joints 7, 8 on the body by two spring cylinders 9 and 10. Spring cylinder 9 is coupled to rigid axle 1 with a piston rod 11 in articulated joint 5. A piston rod 12 of spring cylinder 10 engages in articulated joint 6 of rigid axle 1. Each spring cylinder 9 and 10 includes an upper spring cylinder space 13 and 15 and a lower spring cylinder space 14 and 16. Spring cylinder spaces 13 and 14 are separated by an isolating piston 17, and spring cylinder spaces 15 and 16 are separated by an isolating piston 18. A line 19 connects upper spring cylinder space 13 of spring cylinder 9 to lower spring cylinder space 16 of spring cylinder 10. In the same way, a line 20 connects upper spring cylinder space 15 of spring cylinder 10 to lower spring cylinder space 14 of spring cylinder 9. The double-chamber cylinders are cross-wired together by lines 19 and 20.

[0014] A hydraulic accumulator 23 and 24 is connected to each line 19 and 20 over lines 21 and 22. Damping elements 25 and 26 provided in lines 21 and 22 also dampen rolling motions.

[0015] An actuator 27 is connected to lines 19 and 20 over lines 28 and 29. This actuator 27 is a control device or a displacement device which makes it possible to create active rolling moments. The actuator displaces medium from one side of the vehicle to the other, thus achieving roll stabilization.

[0016] In the device illustrated in FIG. 2 for the suspension and for roll stabilization of motor vehicles, damping elements 30 and 31 and storage cylinders 32 and 33 are integrated into cross-wired lines 19 and 20.

[0017] The overall stiffness of the device for the suspension and for roll stabilization of motor vehicles is composed of the vertical and roll stiffness of rigid axle 1. The following equation represents vertical stiffness k_Hof rigid axle 1: $k_H=2·n·{\left(A_K-A_R\right)}^2·\frac{P}{V},$

[0018] and roll stiffness k_Wof rigid axle 1 is calculated according to the equation: $k_W=\frac{1}{2}·s^2·n·{\left(A_K+A_R\right)}^2·\frac{P}{V}.$

[0019] where n is the polytropic exponent, A_Kdenotes a piston area 34, 36, A_Rdenotes a piston ring area 35, 37, p is the pressure in a hydraulic accumulator 23, 24, V is the gas volume of hydraulic accumulator 23, 24 and s is the wheel base of axle 1.

[0020] The required vertical and roll stiffness of the entire device for the suspension and for roll stabilization of motor vehicles may be achieved by designing the dimensions of piston areas 34, 36 and piston ring areas 35, 37 in the following ratio: $\frac{A_K}{A_R}=\frac{2·\sqrt{k_W}+s·\sqrt{k_H}}{2·\sqrt{k_W}-s·\sqrt{k_H}}.$

[0021] 1 rigid axle 32 storage cylinder

[0022] 2 vehicle wheel 33 storage cylinder

[0023] 3 vehicle wheel 34 piston area

[0024] 4 vehicle body 35 piston ring area

[0025] 5 articulated joint 36 piston area

[0026] 6 articulated joint 37 piston ring area

[0027] 7 articulated joint

[0028] 8 articulated joint

[0029] 9 spring cylinder

[0030] 10 spring cylinder

[0031] 11 piston rod

[0032] 12 piston rod

[0033] 13 upper spring cylinder space

[0034] 14 lower spring cylinder space

[0035] 15 upper spring cylinder space

[0036] 16 lower spring cylinder space

[0037] 17 isolating piston

[0038] 18 isolating piston

[0039] 19 line

[0040] 20 line

[0041] 21 line

[0042] 22 line

[0043] 23 storage cylinder

[0044] 24 storage cylinder

[0045] 25 damping element

[0046] 26 damping element

[0047] 27 actuator

[0048] 28 line

[0049] 29 line

[0050] 30 damping element

[0051] 31 damping element

[0052] 32 storage cylinder

[0053] 33 storage cylinder

[0054] 34 piston area

[0055] 35 piston ring area

[0056] 36 piston area

[0057] 37 piston ring area