Wheel suspension

A wheel suspension includes a working cylinder, a main spring in parallel with the working cylinder, and a piston rod extending from the working cylinder and having a longitudinal axis, the piston rod having fixed thereto a piston and a mount for fixing the piston rod against movement with respect to a vehicle body. The piston is mounted with freedom of axial movement in an adjusting cylinder, the piston dividing the cylinder into a space above the piston and a space below the piston, and an additional spring is located on the longitudinal axis for supporting the adjusting cylinder against the working cylinder. A shut-off element is located in a flow connection connecting the space above the piston to the space below the piston, whereby movement of the piston in the adjusting cylinder can be blocked when the vehicle rolls.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to a wheel suspension, comprising a piston-cylinder assembly with a working cylinder, a piston rod, and damping valves; a main spring connected in parallel; an additional spring, by means of which the working cylinder of the piston-cylinder assembly is supported against a vehicle body; and a piston arrangement by means of which the mounts supporting the additional spring can be adjusted relative to the vehicle body on the longitudinal axis of the piston rod.

2. Description of the Related Art

In motor vehicles, especially in the case of vehicles with high centers of gravity, there is a tendency for the wheel on the outside of the curve to undergo too much inward spring deflection when the vehicle is traveling around a curve. For many years, efforts have been made to counteract this rolling tendency around the longitudinal axis of the vehicle by taking measures to increase the transverse stability. There are also ways of stabilizing a vehicle directly by means of vibration dampers (e.g., DE 10 2004 019 991 A1); in this wheel suspension, a vibration damper is provided with a housing, a piston rod, and a main spring connected in parallel to the piston rod. In this prior art, an actuatable piston arrangement can be adjusted relative to the vehicle body to stabilize the rolling; this makes it possible to obtain a controllable or partially active motor vehicle chassis of simple design and short adjustment distances. These known wheel suspensions all suffer from the disadvantage of complicated construction and also require an appropriate external energy source to make the required distance adjustments.

SUMMARY OF THE INVENTION

An object of the invention is to create a wheel suspension which provides stabilization against rolling, which can be produced at low cost, and which, even though it does not need any external energy or an electronic position control system, can nevertheless act quickly and effectively.

To achieve this object, the piston arrangement cooperating with the piston rod is installed with freedom of axial movement in a cylinder, where a flow connection connects a space above the cylinder to a space below the cylinder of the piston arrangement, and a shut-off element is located in the flow connection.

According to another feature, a spring acts on at least one end surface of the piston arrangement. It is advantageous here for the spring to be a coil spring and/or a gas spring. It is also possible for the gas spring to be located outside the piston-cylinder assembly.

According to an essential feature, the shut-off element can be controlled externally. It is advantageous for the control of the shut-off element to be implemented by way of a sensor.

According to another embodiment, a solenoid valve is provided as the shut-off element.

According to a favorable embodiment, the piston of the piston arrangement is sealed around its outer circumference against the cylinder.

According to another embodiment, a sealing ring is held in a groove in the piston.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1ashows the suspension of a vehicle with a conventional design, whereasFIG. 1bshows a piston-cylinder assembly1according to the invention. In both designs, a main spring2is provided parallel to the assembly; the upper mount3and the lower mount4serve to attach the piston-cylinder assembly1to the vehicle. An additional spring5works together with the main spring2in such a way that the overall spring rate toward the stop end has a highly progressive course. This progressive course is important, because it is needed to provide the vehicle with appropriate support, especially when traveling around curves. According toFIG. 1a, the additional spring5with its highly progressive course does not usually go into action for comfort reasons until a free distance X has been used up. The additional spring5is preferably made of PU or elastomeric material, but a steel spring could also be readily used.

A damping system is therefore comfortable as long as it has an appropriate free distance X, but this damping system becomes uncomfortable and nonrolling when the free distance X is used up and approaches zero.

FIG. 1bshows in addition a piston arrangement6, which also provides the free distance X, but which also, when needed, allows the additional spring5to go promptly into action.

So that the piston arrangement6can go into action, it is possible, for example, for the impulse which activates the stabilizing function of the piston arrangement6to be derived from a transverse acceleration sensor in the vehicle. In the case of vehicles of modern design with an electronic stability program (ESP), the existing steering angle sensor can also be easily used to activate the piston arrangement6.

FIG. 2shows a piston-cylinder assembly1similar to that illustrated inFIG. 1b, but not showing the main spring2and the wheel or tire of the motor vehicle. The piston arrangement6has a piston7, which is permanently connected at one end to the upper mount3and at the other end to the piston rod8. The upper space9is connected by a flow connection10to the lower space11, and a shut-off element12is integrated into the flow connection10.

The piston7is enclosed by a cylinder13, which can slide in a sealed manner on the piston rod8in both the upper and lower areas. The piston7also slides on the cylinder13by way of a sealing ring17received in a circumferential groove in the piston. A spring14, which is designed as a coil spring14ain the exemplary embodiment according toFIG. 2, is located in the lower space11. One end is supported against the piston7, and the other end is supported against the bottom of the cylinder13, thus ensuring that the additional spring5is always held in contact with the damper-side stop surface15on top of the working cylinder16. The re-leveling of the additional spring5should extend at least as far as the level of the vehicle; that is, it should cover the entire inward-deflection range of the piston-cylinder assembly1.

Because the shut-off element12is open in this diagram, the hydraulic fluid16can pass through the flow connection10from the upper space9to the lower space11and vice versa, and thus the additional spring5will follow the stop surface15at least as far as the level of the vehicle.

FIG. 3shows the shut-off element12in the open state. That is, the hydraulic fluid16can flow back and forth between the upper space9and the lower space11. The free distance X, asFIG. 3shows in comparison toFIG. 2, is being used; the additional spring5goes into action at the moment that the free distance X is used up completely. The spring14is compressed by an amount equivalent to the free distance X.

It can then be derived fromFIG. 4that, as the piston rod8continues to travel inward into the piston-cylinder assembly1, the additional spring5is compressed until it becomes a solid block.

InFIG. 5, the shut-off element12has been switched to the closed position; the shut-off element12can, for example, be actuated by means of a solenoid valve, or the shut-off element12can itself be a solenoid valve, which makes it possible, by way of a known transverse acceleration sensor, for the stabilizing additional spring5to go into action as soon as the vehicle starts to travel around a curve or changes lanes. The hydraulic flow connection10from the upper space9to the lower space11is blocked in this case, and the piston7is thus arrested with respect to the cylinder13.

InFIG. 6, the additional spring or buffer5has been compressed into a solid block as a result of the inward deflection of the system. It can be seen in comparison withFIG. 4that, with the shut-off element12closed, the piston7has not been displaced in the cylinder13.

FIGS. 7-10show a piston arrangement6which is not part of a working cylinder assembly, but may be installed parallel to the working cylinder and main spring. Here the cylinder13is fixed with respect to a sprung suspension member18and the piston rod8is fixed to a housing19on which the additional spring5is mounted as a buffer between the piston rod8and the vehicle body20. The shut-off valve12is located in the cylinder13and (when open) permits the piston7to travel a free distance X before the spring5is compressed.

The shut-off element12is shown open inFIGS. 7 and 8, so that the hydraulic fluid16can flow from the upper space9to the lower space11and vice versa.

When the shut-off element12is closed, as can be seen inFIGS. 9 and 10, no hydraulic fluid flows through the flow connection10, and the piston7of the piston arrangement6is held in place, so that the additional spring5goes into action immediately. The cylinder13can, for example, be mounted either on a vertical axis or rotated with respect to the body of a vehicle.

FIGS. 11 and 12show another embodiment of a piston arrangement6, where, instead of a coil spring14aaccording toFIGS. 2-10, a gas spring14bis provided. Here, too, the piston7is located in a cylinder13, and hydraulic fluid flows through the flow connection10into the upper space9or the lower space11, as already shown in principle inFIGS. 2-10. When a gas spring14bis used, an additional space is required in the flow connection10to hold the gas. The piston rod8inFIG. 11has different diameters above and below the piston7, so that different amounts of hydraulic fluid are displaced in the two different flow directions.

FIG. 12merely shows a piston7and a piston rod8, which passes through the upper space9, so that here different surface areas of the piston7are available to act upon the hydraulic fluid in the working cylinder16. In the embodiments according toFIGS. 11 and 12as well, the shut-off valve12can be actuated as needed either electrically or magnetically, corresponding in principle to the embodiments already described.