Patent Application
20170043640
The invention relates to an arrangement of a (hydraulic) vibration damper which is assigned to a wheel of a vehicle and has a fluid-filled cylinder in which a damper piston with a piston rod is guided and a damper chamber is formed on each side of the damper piston, wherein a pressure accumulator which is constructed, in particular, in the form of a gas pressure cushion, or a different intermediate accumulator for a partial quantity of the hydraulic fluid present in the damper cylinder, is connected to the damper chamber lying opposite the piston rod, and wherein the vibration damper is mounted on the vehicle body by means of a damper mount with a rubber-elastic body which can be deformed in the shifting direction of the damper piston, in which damper mount a hydraulic pressure chamber is also formed, the pressure chamber being connected via a fluid-conducting connection to that damper chamber whose volume is reduced when the wheel is deflected in relation to the vehicle body, based on DE 196 29 959 A1 as the closest prior art.
The vibration dampers which are provided in a vehicle between its wheels and the vehicle body which is supported in the vertical direction on these wheels by means of what are referred to as supporting springs serve, during the deflection and rebounding of the respective wheel (i.e. when it moves essentially in the vertical direction in relation to the vehicle body), to damp this deflection movement (directed toward the vehicle body) or rebounding (directed away from the vehicle body). Such hydraulic vibration dampers usually comprise a (damper) cylinder in which a (damper) piston is guided so as to be shiftable in the direction of the deflection movement and rebounding movement. By means of (vertical) movements of the respective wheel in relation to the vehicle body, the piston moves in the cylinder and in doing so displaces hydraulic fluid, in particular an oil. The piston rod of the vibration damper is usually connected to the vehicle body via a rubber-elastic damper mount, while the cylinder of the vibration damper is rigidly attached to a wheel carrier which supports the wheel rotatably. In such a damper mount, the free end of the piston rod is usually connected in a fixed fashion via an attachment plate to a rubber-elastic body which is embodied in the broadest sense in a hollow-cylindrical fashion and in whose center the piston rod is located or held, while the outside of this rubber-elastic body is supported on the vehicle body.
DE 196 29 959 A1, referenced above, presents a vibration damper arrangement having a hydraulic mount, wherein the specified rubber-elastic body is supported against a hydraulic pressure chamber which is hydraulically connected to that chamber in the cylinder of the damper whose volume is reduced when the wheel is deflected in relation to the vehicle body. Therefore, not only the low-frequency vibrations of the vehicle wheels in relation to the body are to be capable of being damped within the scope of their visible deflection and rebounding movements (these are also referred to in the specialist jargon as body frequencies), but rather it is possible, on the basis of the hydraulic mount, to use such a vibration damper to also damp relatively high frequency vibrations which are applied by the underlying surface in the direction of the vehicle body via the wheels and are referred to as wheel frequencies. During the deflection of the wheel, hydraulic fluid is conveyed from the damper cylinder into the pressure chamber of the hydraulic bearing.
Further known prior art, for example, U.S. Pat. No. 8,376,100 B2, presents what is referred to as a gerotor on a hydraulic vibration damper, wherein the two damper chambers which are provided in the damper cylinder are or can be connected to one another via a hydraulic pump which is driven (preferably by electric motor). Such vibration dampers are also referred to as active vibration dampers, since the latter can be used to apply, via the driven hydraulic pump, a force between the assigned wheel and the vehicle body. With such a force the vehicle body can, for example, be lifted up in relation to the wheel, i.e. in this case the wheel can, as it were, be made to “rebound” through suitable operation of the hydraulic pump. With such active vibration dampers it is possible, for example, to perform roll stabilization of the vehicle body on a two-track, two-axle vehicle in the case of rapid cornering of the vehicle. Whereas, in fact, on such a vehicle with simple non-active (referred to as “passive”) vibration dampers the rolling torque which occurs during steady-state circular-course driving is supported only via the supporting springs and a lateral stabilizer which is usually provided and in this context virtually no forces occur in the damper mount. By means of an active vibration damper, it is possible to prevent or limit the rolling of the vehicle body in that a force is introduced or applied to the damper mount and therefore to the vehicle body via the piston rod of the vibration damper. The active vibration damper then acts as a hydraulic actuator. Such an active vibration damper can also advantageously be used to acquire energy from the damping function thereof, such as electrical energy in the case of a hydraulic pump driven by an electric motor. In contrast to conventional (passive) vibration dampers, the movement of the damper piston is damped (and therefore a relative movement between the vehicle body and the vehicle wheel), not in fact by throttle ducts connecting the two damper chambers in the damper piston, but rather via the hydraulic pump which is driven by the hydraulic fluid which overflows between the damper chambers and as a result drives its assigned motor or electric motor, which then acts as an electric generator.
Returning to the possibility that an active vibration damper can be used to “apply” relatively high forces, i.e. introduce them between the wheel and the vehicle body, it has been recognized above that when a conventional damper mounting arrangement is used on the vehicle body by a simple rubber-elastic body, the latter is at any rate deformed to a great extent by the introduction of such large forces and therefore stressed in itself and would harden as a consequence of this. However, such hardening would impede the technical vibration decoupling (with respect to relatively high frequencies) which is to be actually brought about between the vibration damper (and the wheel) and the vehicle body by means of this elastic body.
Furthermore, it has been recognized above that a hydraulic pressure chamber in the damper mount in which the vibration damper is supported on the vehicle body with intermediate connection of a rubber-elastic body which can be deformed, in particular, in the shifting direction of the damper piston, can contribute to solving the problems mentioned above if this hydraulic pressure chamber is connected in a fluid-conducting fashion to a damper chamber whose volume is reduced when the wheel is deflected in relation to the vehicle body.
It has also been recognized above that it is, however, also possible to make further improvements in this respect, for which reason it is now an object of the present invention to develop a vibration damper arrangement as an active vibration damper in such a way that the risk of hardening of the rubber-elastic body in the damper mount is minimized.
The object is achieved by the claimed invention by virtue of the fact that the damper chambers which are formed in the damper cylinder on each side of the damper piston are connected hydraulically to one another via a hydraulic pump which can be driven by a motor, and in that a spring element which acts directly or indirectly on the rubber-elastic body in the shifting direction of the damper piston is provided in the damper mount. The spring force of the spring element is directed and dimensioned such that, in the case of a stationary damper piston and equality of pressure in the two damper chambers, the forces acting on the rubber-elastic body in the shifting direction of the damper piston at least approximately cancel one another out. Advantageous refinements of the invention form the subject matter of the dependent claims.
Initially, it is therefore proposed to construct a passive vibration damper which is mounted on the vehicle body by a hydraulic mount with a rubber-elastic body, and in which vibration damper the hydraulic mount is connected to the damper chamber which is reduced in size when the wheel is deflected as a basically active vibration damper (with a hydraulic pump between the two damper chambers). Furthermore, measures are proposed by means of which the rubber-elastic body is held as free of tension as possible. With these further inventive features, specifically the spring element which acts as specified and the equilibrium of forces achieved therewith, it is ensured that the rubber-elastic body can successfully damp relatively high frequency vibrations, not only when the vibration damper acts in its customary damping function (as a non-active, passive vibration damper), but also when the active vibration damper is operated as a hydraulic actuator. Even in such an operating case, the rubber-elastic body of an active vibration damper according to the invention is not subject to additional high forces so that there is no risk of this rubber-elastic body of the vibration damper hardening during its action as a hydraulic actuator (so that relatively high frequency vibrations could then no longer be successfully damped).
As far as the terms “relatively high frequency” or the damping of “relatively high frequency vibrations” are concerned, the rubber-elastic body of the damper mount via which, for example or preferably, the piston rod of the vibration damper is supported or mounted on the vehicle body, is configured to the effect that it can be used to damp relatively high frequency or high frequency excitations, preferably above 10 Hz to 15 Hz (the range of these high frequency excitations can extend up to several thousand Hertz here). By contrast, as is customary the vibration damping between the respective vehicle wheel and the vehicle body can be carried out in the low frequency range (below this frequency range which is specified numerically) by the actual vibration damper, specifically by the unit composed of the damper cylinder and damper piston. In the case of a vibration damper according to the invention, two damper systems are therefore connected in series. On the one hand, the customary damping via the piston guided in the damper cylinder is provided in the low frequency range (less than 10 Hz-15 Hz), while for the relatively high frequency range the damping takes place via the elastic body in the damper mount, and at the same time preferably no (visible) relative movement takes place between the damper piston and the damper cylinder. And, in particular for this relatively high frequency range, the elastic body is relieved of loading by additional forces by means of the pressure which prevails in the hydraulic chamber of the damper mount and is transmitted into the pressure chamber via the fluid-conducting connection, as well as the force of the spring element, The elastic body is therefore stabilized as a result of which deformation occurring without such relief of loading, possibly owing to excessively high loading, and hardening of the elastic body which results from the latter and is undesired in respect of successful damping of relatively high frequency vibrations, are prevented.
A physical derivation as to how a spring element according to the invention is to be configured is provided at a later point with reference to the appended
Moreover, by means of suitable configuration of the cross section of the the fluid-conducting connection between the damper chamber and the hydraulic pressure chamber in the damper mount, the damping property thereof can be configured in a frequency-selective fashion. If, in fact, the fluid-conducting connection is narrow or is throttled to a great extent, at low frequencies complete pressure equalization still occurs between the pressure chamber (connected to the pressure chamber of the damper mount via the fluid-conducting connection) in the damper cylinder and the pressure chamber in the damper mount. In contrast, in the case of high frequencies the hydraulic column in the fluid-conducting connection can no longer, or at least no longer completely, follow changes in pressure owing to the inertia of the hydraulic column, and consequently a pressure difference arises between the pressure chamber of the damper mount of the damper chamber. This can be used for selective configuration of the damping properties in the damper mount with respect to specific, in particular relatively high frequencies (according to the explanation above). As a result of the fact that possibly no complete pressure equalization takes place in the relatively high frequency range, a certain degree of deformation of the rubber-elastic body can be forcibly brought about in a targeted fashion and therefore the damping properties of the rubber material of this rubber-elastic body can be used.
Returning once more to the property of a vibration damper, according to the invention, as an active vibration damper it is possible, as already explained, for hydraulic fluid to be selectively conveyed from one chamber of the vibrating damper into the other damper chamber of the damper cylinder with the hydraulic pump which can be driven by an electric machine and, as a consequence, therefore the vehicle body can be lifted or lowered selectively in relation to the respective wheel. Furthermore, the electric machine which is connected in terms of drive to the hydraulic pump can also be used as a generator with the result that electrical energy can be acquired in the case of a rebounding movement or deflection movement of the wheel which is caused by the travel of the vehicle on an underlying surface, wherein at the same time the desired damping of the deflection movement or rebounding movement of the vehicle wheel in relation to the vehicle body takes place. However, it should be noted that, owing to the inertia of the hydraulic pump and the electric machine, effective regulation of the damping is limited to relatively low frequencies, i.e. effective damping of this vibration movement can be achieved virtually only in the frequency range of the visible vertical vibrations of the wheel in relation to the vehicle body (referred to in the specialist jargon as “body frequencies”). However, no effective damping can be achieved in the region of the natural vibration frequency of the vehicle body, and therefore in the region of the relatively high frequency vibrations which are mentioned above and are also referred to as “wheel frequencies,” and the damping which can be achieved by means of a simple rubber-elastic body in the damper mount is, as has already been explained, not sufficient owing to hardening of the body. The result is that a simple active vibration damper (or a simpler active vibration damper other than the one according to the invention) with a single customary damper mount (without the pressure chamber of the present invention) exhibits significant, in particular acoustic, drawbacks which give the driver of the vehicle an uncomfortable driving sensation. These drawbacks can be avoided with a vibration damper according to the invention with a hydraulic pressure chamber in the damper mount and additional spring element according to the invention.
In addition to the elastic body, a hydraulic damping device can be integrated in the damper mount. Such a hydraulic damping device comprises a fluid-filled first working space in the elastic body as well as a second working space within the damper mount outside the elastic body and at least one throttle between these two working spaces. The two working spaces are advantageously arranged as annular spaces concentrically around the piston rod. Accordingly, an annular disk with suitable holes (which can, if appropriate, additionally be provided with valve plates) is advantageously proposed as a throttle. In this context, a gas-filled equalization space can also be provided. A diaphragm is located between the equalization space and the second working space. If the piston rod is then moved (in an oscillating fashion) owing to relatively high frequency deflection movements and rebounding movements of the wheel, the elastic body is also correspondingly made to execute relatively high frequency vibration movements compared to visible reciprocating movements of the vehicle wheel (in relation to the vehicle body). As a result, hydraulic fluid is moved through the throttle between the two working spaces, as a result of which an additional damping (additional to the effect of the rubber-elastic body) occurs.
There are various possible ways of arranging the spring element according to the invention. According to a first embodiment, the spring element can be supported directly on or with respect to the vehicle body. Alternatively, the hydraulic pressure chamber can be embodied in the spring mount itself in the manner of a hydraulic cylinder and in this sense be limited by a pressure equalization piston which can be shifted in the shifting direction of the damper piston and is supported on the rubber-elastic body via the spring element (i.e. with intermediate connection of the spring element). In this context, when the damper piston is stationary and there is equality of pressure in the two damper chambers, the shiftable pressure equalization piston can be pressed against a stop by the spring element, but this is not absolutely necessary.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
The unit composed of the hydraulic pump 9 and electric machine 10 can also be used as a generator to generate electrical energy if, as is customary, the damper piston 5 is shifted (vertically) in relation to the damper cylinder 3 in the driving mode of the vehicle during the deflection or rebounding of the wheel by vehicle movement dynamics influences or by influences of the underlying surface on the vehicle body. In this context, the damping of this deflection movement and rebounding movement which oscillate to a limited extent takes place virtually only by means of the generator mode of the electric machine 10 which is then driven by the hydraulic pump 9, for which reason, in contrast to the customary passive vibration dampers, no throttled passage openings for hydraulic fluid are provided in the damper piston 5.
As shown by
The damper mount 2 has a housing 13, wherein, for example, screw bolts via which this housing 13 and therefore the vibration damper 1 are attached to the body of the vehicle can be attached to the upper side of the housing 13. The piston rod 6 of the vibration damper 1 is mounted within the housing 13 via an elastic body 14 (for example composed of rubber) which is referred to above as a rubber-elastic body 14. This rubber-elastic body 14 is illustrated here in a simplified fashion embodied as a hollow-cylindrical disk into which the free end of the piston rod 6 is inserted or with which the piston rod 6 is fixedly connected in a way which is not illustrated in more detail here. In contrast, with its outer circumference this hollow-cylindrical rubber-elastic body 14 is fixedly connected to the inner wall of the housing 13. As is generally customary, i.e. in particular on suitable vibration dampers in the chassis of motor vehicles, relatively high frequency vibrations of the vehicle wheel which do not bring about visible shifting between the damper cylinder 3 and the damper piston 5, but would be transmitted toward the vehicle body by the piston rod 6, are to be successfully damped by means of this chassis or by means of this rubber-elastic body 14.
A cavity which is bounded by a section of the inner wall of the housing 13 and by the rubber-elastic body 14 and functions as a hydraulic pressure chamber, and is therefore also referred to as a hydraulic pressure chamber 15, is formed in the damper mount 2. The fluid-conducting connection 12 which runs in the piston rod 6 opens into this hydraulic pressure chamber 15. With the exception of this fluid-conducting connection 12, the pressure chamber 15 is formed in a fluid-tight fashion within the damper mount 2. Furthermore, a spring element 40, which is embodied as a compression spring and acts, at one end, on the side of the rubber-elastic body 14 lying opposite the pressure chamber 15 and is supported, at the other end, i.e. with its other end section, on the housing 13 of the damper mount 2 and therefore ultimately on the body of the vehicle, is provided here within the housing 13. In this context, reference is expressly made to the fact that the arrangement of the spring element 40 should be understood to be non-limiting and that other arrangements are also possible (for example, an arrangement according to
The vibration damper 1 is assumed to be located in a stationary state and firstly, for the sake of simplicity, no pressure is generated in either of the chambers 7, 8 of the vibration damper 1 by the hydraulic pump 9 either. The same hydraulic pressure then prevails in the two chambers 7, 8 of the vibration damper 1 as well as in the pressure chamber 15 of the damper mount 2 (via the fluid-conducting connection 12 through the piston rod 6). The hydraulic pressure is determined by the pilot pressure of the pressure accumulator 11 and is usually of the order of magnitude of 30 bar in the case of a single-tube damper.
When there is equality (assumed initially for the sake of simplicity) between the areas A1 and A4, specifically the area A1 of the piston 5 in the damper chamber 8 and the area A4 of the rubber-elastic body 14, lying perpendicularly with respect to the piston rod 6 or with respect to the shifting direction of the damper piston 5, in the pressure chamber 15, the forces which result from the pressure in the damper chamber 8 and in the pressure chamber 15 and act on the rubber-elastic body 14 consequently cancel one another out. There is therefore still the force which results from the pressure in the other damper chamber 7 and from this area A2 of the damper piston 3, which is reduced compared to the area A1 by the area A3 of the piston rod 6, and which via the piston rod 6 is transferred to the rubber-elastic body 14 and which is to be compensated so that the rubber-elastic body 14 is, as desired, essentially free of introduced forces or additional forces. A or the spring element 40 is provided for this, which counteracts the force resulting from the hydraulic pressure in the damping chamber 7 and acts on the rubber-elastic body 14. The rubber-elastic body 14 is therefore, at least considered in terms of steady state, free of forces acting in the shifting direction of the damper piston 5 and can consequently, as has been explained expressly above, perform its function, specifically the damping of relatively high frequency vibrations as well as possible. Only for the sake of completeness, reference will be made once more to the fact that the hydraulic pressure prevailing in the steady state in the damper chambers 7, 8 is permanently predefined by the configuration of the vibration damper 1 and is essentially independent of significantly changing peripheral conditions, with the exception of a slight change in pressure as a function of the deflection state (resulting from the change in the gas volume of the pressure accumulator 11 with changed volume expelled by the piston rod 6) and of temperature influences.
Without the equality of areas introduced here only by way of a remedy, the following relationship or the following (algebraic) equation must then apply so that, considered in the steady state, an equilibrium of forces prevails at the rubber-elastic body 14 in the shifting direction of the damper piston 5:
ΣF=0=p•A1−p•A2−p•A4+F40,
where,
If an additional hydraulic pressure is built up by the hydraulic pump 9 in one of the chambers 7 or 8 of the damper cylinder 3 and at the same time hydraulic pressure is built up in the other damper chamber (8 or 7), this results in the shifting of the damper cylinder 3 (with respect to the damper piston 5). However, the equilibrium of forces at the rubber-elastic body 14 remains essentially uninfluenced for this, i.e. there is also no additional force acting on this as a result of a build up of pressure or reduction of pressure in the damper chambers 7, 8 as long as the pressure prevailing in the damper chamber 8 is propagated into the pressure chamber 15 through the fluid-conducting connection 15. In this context, a slight time delay as a consequence of the relatively small cross section of the fluid-conducting connection 12—in relation to the effective areas in the damper chambers 7, 8 and in the pressure chamber 15—is advantageous in respect of the desired equilibrium of forces even during a relative movement between the damper piston 5 and the damper cylinder 3.
When this equilibrium of forces is present or when this equation above is at least approximately satisfied, even when the damper piston 5 is shifted by means of the hydraulic pump 9 driven by the electric machine 10 and the vibration damper 1 according to the invention therefore acts as a hydraulic actuator, the rubber-elastic body 14 remains virtually free of significant additional forces which would adversely its actual function, specifically the damping of relatively high frequency vibrations.
In the exemplary embodiment according to
A development which is possible for all the exemplary embodiments and according to which a material which damps pressure vibrations is provided at least partially in the pressure chamber 15 is not illustrated figuratively. Therefore, “relatively high frequency” pressure oscillations of the hydraulic fluid, or in the hydraulic fluid, which occur (once more) in the pressure chamber 15 and could be transmitted into the pressure chamber 15 from the damper chamber 8 via the fluid-conducting connection 12 can possibly be damped, with the result that there is no risk of the latter being introduced into the vehicle body via the housing 13 of the damper mount 2. Of course, this material must not fill the pressure chamber 15 to such an extent that it can no longer carry out its function described above of establishing an equilibrium of forces. This material which damps pressure oscillations can be, for example, a suitable foamed material with which, for example, the walls of the pressure chamber 15 are lined, as illustrated in
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2014 208 083.5 | Apr 2014 | DE | national |
This application is a continuation of PCT International Application No. PCT/EP2015/059227, filed Apr. 28, 2015, which claims priority under 35 U.S.C. §119 from German Patent Application No. 10 2014 208 083.5, filed Apr. 29, 2014, the entire disclosures of which are herein expressly incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2015/059227 | Apr 2015 | US |
| Child | 15337910 | US |
