The invention relates to a pneumatic spring and damper unit, in particular for chassis of vehicles, which is arranged between the bodywork and chassis and has at least two working spaces filled with compressed air, in which the working spaces are each bounded at least partially by movable walls in the form of rolling bellows or corrugated bellows, and the rolling bellows or corrugated bellows roll at least partially on the contours of rotationally symmetrical elements (rolling contours), preferably on housing parts which are embodied as cylindrical surfaces, the working spaces being arranged one on top of the other and being connected to one another by means of throttle valves through which there can be a flow, and in which in the case of spring compression in the main load direction the volume of one working space is reduced and the volume of the other working space is increased or remains unchanged.
DE 103 11 263 B3 2004.07.29 presents a pneumatic spring with pneumatic damping, two working chambers and three rolling bellows being provided. The rolling bellows which is the largest in diameter determines here the spring rate of the pneumatic spring over the spring travel and is arranged between an upper and a lower pot-shaped housing part. The two further bellows which compensate one another in their effective spring force are arranged between the lower pot-shaped housing part and a rolling tube which is attached within the upper pot-shaped housing part and projects into the lower pot-shaped housing part. Air can flow between the two working spaces via throttle bores in the cylindrical walls of the rolling tube. In this embodiment, the two lower bellows which are arranged in mirror-inverted fashion permit axial guidance of the pneumatic spring, which largely reduces the friction during the spring travel. However, in this system the volume of the two working chambers is decreased in the case of spring compression and increased again in the case of spring extension. As a result of the decrease in the two volumes in the case of spring compression, the pressure, and thus the gas density, increase in the two working chambers, but the dynamic difference in pressure at the throttle valves disadvantageously does not increase. This in turn brings about a level of energy conversion which is only slightly increased even at a relatively high pressure, i.e. relatively little dissipation and thus less damping work.
U.S. Pat. No. 5,180,145 discloses a damper which operates in particular with an electrorheological fluid and has an upper and a lower working space which are each bounded by rolling bellows. The damper permits a relatively large degree of travel despite the reduced overall height, and in an embodiment which is disclosed in said document it can also be combined with a simple pneumatic spring whose single working space is also partially bounded toward the outside by a rolling bellows. However, the combination of dampers and springs which operate with respectively different media increases the complexity and thus the cost of the component. In addition, the recycling of, in particular, electrorheological fluids gives rise to possible problems in the life cycle management.
DE 34 36 664 A1 discloses a diaphragm pneumatic spring which also provides suspension and damping and has two working chambers of different sizes, which are each bounded toward the outside partially by rolling bellows. The rolling bellows are supported and roll here on external cylinder surfaces of housing parts which are axially movable and embodied as hollow pistons. The working chambers which are of different sizes are divided by a wall which is provided with throttle openings. Air can flow from one working chamber into the other through the throttle openings, the resulting dissipation producing the damping work. However, in the basic design of the diaphragm pneumatic spring, in which the housing parts which are embodied as hollow pistons are connected to a central rod which is guided in a dividing wall, said diaphragm pneumatic spring is subject to considerable friction losses in this guidance. As a result, inter alia, a minimum force is necessary which has to be reached in order to counteract a spring movement/spring effect at all. Below such a minimum force, all the vibrations are transmitted in an undamped and unsprung fashion. A further embodiment which is shown there, in which the rigid connecting rod which is guided in the dividing wall is replaced by an external frame is virtually unusable in cardanic suspensions, in particular of vehicles, due to its overall size.
The German laid-open patent application DE 24 06 835 discloses a spring and damping device in which two working spaces, specifically a damper space and a spring space, are connected to one another via throttle valves. The two working spaces are bounded at least partially by movable walls in the form of corrugated bellows or rolling bellows and can therefore accommodate different volumes. In contrast to the pneumatic spring disclosed in DE 103 11 263 B3 2004.07.29, in the case of spring compression the volume of the spring space is reduced here and the volume of the damper space increased, and the reverse respectively applies in the case of spring extension. Inherent to such a system is the fact that the damping effect/damping work increases as the load increases, while normal hydraulic damping is designed for just one load stage and changes (decreases) acutely if, for example, the load is increased. However, if the load increases in the spring and damping device disclosed in the German laid-open patent application DE 24 06 835, the gas pressure in the spring space and in the damping space rises and leads, owing to the associated increase in the gas density, to an increase in the dynamic pressure difference at the throttle valves. This in turn brings about an increased conversion of energy, i.e. increased dissipation and thus greater damping work. A disadvantage here is also a perceptible degree of friction in the system of all the embodiments presented, as a result of which, inter alia, a minimum force becomes necessary to activate the spring-damper system.
DE 101 15 980 discloses a gas spring-damper unit with a piston which can be displaced in a cylinder housing, is sealed with respect to the latter and divides two working spaces. In this context, the suspension space or spring damper space which lies on the front side of the piston becomes smaller in the case of spring compression. The damper space which is located on the rear side of the piston and includes the piston rod is increased in the case of spring compression, and vice versa. The damper space is partially bounded toward the outside by a rolling bellows. The throttle valves which are located in the piston are configured here in such a way that a different flow resistance is present depending on the throughflow direction, and the location of the changeover from laminar flow to turbulent flow is adapted. The problem of friction is also not sufficiently solved here by the guidance of the piston in the cylinder.
The same applies to the device disclosed in DE 199 32 717 A1. Here too, there is a gas spring-damper unit with a sealed piston which can be displaced in a cylinder housing and divides two working spaces. The suspension space or spring damper space located on the front side of the piston becomes smaller in the case of spring compression, while the damper space which is located on the rear side of the piston and contains the piston rod becomes larger in the case of spring compression, and vice versa. The damper space is partially bounded toward the outside by a rolling bellows. The throttle valves which are located in the piston are configured here as valves which are loaded with spring disks, the spring disks and valve cross sections being embodied as a function of the throughflow direction.
However, all the solutions known in the prior art are subject to the disadvantage that transverse forces acting on the pneumatic springs or pneumatic dampers, i.e. chassis forces which are normal to the axis of the pneumatic springs, cannot be transmitted since there is either no sufficient axial guidance or else damage could occur to the components. Pneumatic springs or pneumatic dampers of conventional design are therefore not able to perform a wheel guidance function within a chassis. Essentially for this reason, and of course also due to their overall size, pneumatic dampers have hardly been used hitherto in McPherson struts.
For the invention, the object has therefore been to make available a pneumatic spring and damper unit whose installation space is small and which is also suitable, for example, for a passenger car, which can be installed without additional structural expenditure in the installation space of conventional spring and damping devices, which does not have any friction—in particular has no dry friction—which can lead to acoustic problems or requires a minimum force to activate the spring-damper system, and which pneumatic spring and damper unit also operates with just one medium, can be configured for different load situations by simple measures and is in particular capable of absorbing transverse forces, thus making wheel guidance possible.
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