Spring-damper system with instantaneous switchable spring rate

Abstract

Spring-damper system for a wheel suspension of a motor vehicle, wherein the spring-damper system comprises a suspension spring (10) with a spring constant k T , a pressure generator (20) acting parallel to the support spring (10) and filled with a fluid, an additional spring unit (30) with an additional spring (31) having a spring constant kz, a switching device (40) with a blocking position and a release position for switching the additional spring (31) and a damper (60) acting parallel to the support spring (10), wherein the switching device (40) blocks the additional spring (31) in the blocking position and in the release position the additional spring (31) acts parallel to the support spring (10) by means of the fluid, characterized in that the pressure generator (20) has a pressure cylinder, a pressure piston (23) and a piston rod (21) extending into a pressure cylinder interior (22) of the pressure cylinder, on the side of which piston rod is arranged in the pressure cylinder interior (22), the pressure piston (23) is arranged, and the pressure piston (23) divides the pressure cylinder interior (22) into a first working chamber (221) and a second working chamber (222), wherein the pressure piston has a passage device connecting the first working chamber (221) to the second working chamber (222), and the piston rod (21) extends through the first working chamber (221), wherein the spring-damper system comprises a fluid expansion tank (50) and a first and a second fluid channel (41, 42), the switching device (40) is an electrically controllable shut-off valve with a shut-off position and a flow position, the pressure generator (20) is fluidically connected to the equalizing tank (50) by means of the first fluid channel (41) via the check valve (40), and the equalizing tank (50) is fluidically connected to the pressure generator (20) by means of the second fluid channel (42), wherein the check valve (40) blocks a fluid flow through the first fluid channel (41) in the blocking position and releases it in the flow position, wherein the blocking position of the check valve corresponds to the release position and the flow position of the check valve corresponds to the blocking position, wherein the spring-damper system comprises a gas spring unit (70), the gas spring unit being formed from a gas spring cylinder, in the gas spring cylinder interior (71) of which a gas acting as a gas spring, a gas separating piston (73) and a gas separating piston stop are arranged, the gas separating piston divides the gas spring cylinder interior into a fourth working chamber and a gas spring chamber in which the gas is arranged, and wherein the gas spring permanently presses the gas separating piston in the gas spring cylinder in the direction of the gas separating piston stop and the fourth working chamber forms the compensation tank (50) the passage device of the pressure piston (23) comprises a throttle device for throttling a fluid flow between the first and second working chambers (221, 222), the pressure generator (20) comprises a closure plate (24) which closes off the second working chamber on its side facing away from the damper piston, wherein the closure plate (24) comprises at least one passage device with a throttle device, wherein the second working chamber (222) of the pressure cylinder interior (22) is fluidly connected to a third working chamber (321) of the spring cylinder interior (32) via the throttle device, and the first and second fluid channels extend partially through the throttle device, so that a fluid flow from the second working chamber (222) to the third working chamber (321) and a fluid flow through the first and second fluid channels (41, 42) is throttled, and wherein the damper is formed by the pressure generator (20) and the gas spring unit.

Description

[0001] The invention relates to a spring-damper system for a wheel suspension of a motor vehicle, wherein the spring rate of the spring-damper system can be switched over without delay by a switching device.

[0002] Various spring-damper systems, including suspension struts and telescopic forks, are known from the prior art, in which the spring rate is adjustable. These are used primarily on motorcycles. The suspension struts usually feature a coil spring with a predetermined spring constant. The spring action of the suspension strut is adjusted depending on the vehicle load or the distance to be traveled. The simplest way to adjust the spring rate under predetermined conditions is to replace the spring with one with a different spring constant. However, manually replacing the spring is time-consuming and can only be performed with suitable tools.

[0003] The prior art also includes struts consisting of two different coil springs with different spring strengths or spring constants. Depending on the desired load or the distance to be traveled, an adapted spring constant is then set, resulting from the spring constants of the individual springs, by replacing one of the springs or mechanically locking it. The problem with this, however, is that switching between the different spring constants cannot occur immediately. A mechanical locking element must move along a path to lock the spring or another component.Due to the necessary movement of the locking element, which takes place within a switching time, a load during the switching time can cause damage to the locking element or the spring in a prior art system, for example, necessitating repair. Therefore, switching is usually only possible when the strut is unloaded and the vehicle is stationary. Furthermore, the switching process requires a switching time during which the vehicle cannot be loaded or moved.

[0004] Other spring-damper systems known from the prior art with a switchable spring constant can also be implemented using alternative spring concepts, such as an air spring. These are generally expensive and require increased installation space, energy consumption, and maintenance. Such spring-damper systems are therefore only of limited use, especially for motorcycles.

[0005] Further, partially switchable spring-damper systems are also known from the documents DE 41 04 904 A1, WO 2015 / 114536 A1, DE 10 2010 046 602 A1.

[0006] The invention is therefore based on the object of overcoming the aforementioned disadvantages and providing a cost-effective spring-damper system in which the spring constant can be switched without delay and under load.

[0007] This object is achieved by the combination of features according to patent claim 1.

[0008] According to the invention, a spring-damper system for a wheel suspension of a motor vehicle is proposed. The spring-damper system comprises a suspension spring with a spring constant k T, a pressure generator acting parallel to the suspension spring and filled with a fluid, and an additional spring unit with an additional spring having a spring constant kz. The spring-damper system further comprises a switching device with a blocking position and a release position for switching the additional spring. In addition, the spring-damper system comprises a damper acting parallel to the suspension spring. The switching device blocks the additional spring in the blocking position. In the release position, the additional spring acts parallel to the suspension spring by means of the fluid. The suspension spring and the pressure generator act in parallel in that compression or expansion of the suspension spring leads to movement at the pressure generator. Compression of the suspension spring preferably leads to movement of a piston rod of the pressure generator into a pressure cylinder of the pressure generator, and expansion of the suspension spring leads to movement of the piston rod out of the pressure generator.In this case, pressure is generated in the pressure cylinder by the compression of the suspension spring and the movement of the piston rod into the pressure generator.

[0009] The switching device does not lock the auxiliary spring mechanically, but rather by changing the flow of the fluid, so that the auxiliary spring is not or only slightly pressurized by the fluid when the switching device is in the blocking position.

[0010] The total spring constant k G1 of the spring-damper system with the switching device in the blocking position results essentially from the spring constant k T the suspension spring. If the switching device is in the release position, the additional spring acts parallel to the suspension spring, so that the total spring constant k G2 of the spring-damper system is essentially the sum of the spring constant k T and the spring constant kz. Thus, the total spring constant is: kG1=kT (switching device in blocking position) kG2=kT+kZ (switching device in release position)

[0011] An advantageous embodiment of the spring-damper system provides that it has a hollow cylinder in which at least the additional spring unit and the pressure generator are arranged in series with each other.

[0012] In an advantageous further development, the suspension spring, the auxiliary spring unit, and the pressure generator are arranged in series in the hollow cylinder, with the suspension spring being supported on the pressure cylinder, so that the pressure generator and suspension spring continue to act parallel to each other. Preferably, the piston rod of the pressure generator extends through the suspension spring and along its longitudinal axis.

[0013] According to the invention, the pressure generator comprises a pressure cylinder, a pressure piston and a piston rod extending into the interior of the pressure cylinder, on the side of which piston rod is arranged in the interior of the pressure cylinder the pressure piston is arranged. The pressure piston divides the interior of the pressure cylinder into a first working chamber and a second working chamber, with the piston rod extending through the first working chamber. The pressure piston has a passage device which allows the fluid of the pressure generator to flow from the first into the second working chamber or vice versa. The damping behavior of the pressure generator can be controlled or adjusted by means of the passage device and the volume flow of the fluid through the passage device, wherein in one embodiment in which the damper and pressure generator are designed separately from one another, the passage device orPreferably, no damping force should be built up by the pressure generator, so that the passage device essentially does not throttle or limit the volume flow. The passage device can be implemented, for example, by bores in the pressure piston, by a valve or by grooves on the outer circumference of the pressure piston. It is essential for the pressure generator that it builds up excess pressure in its pressure cylinder interior through the piston rod when the piston rod moves into the pressure cylinder interior. The pressure generator therefore does not necessarily have to have a pressure piston. This serves to guide the piston rod in the pressure cylinder interior. The pressure generated creates an increased extension force for the piston rod and, depending on the position of the switching device, fluid is displaced from the pressure cylinder interior into the additional spring unit or a fluid compensation tank.

[0014] An advantageous embodiment of the invention provides that the additional spring unit is formed from a spring cylinder, in the spring cylinder interior of which the additional spring, a separating piston and a separating piston stop are arranged. The separating piston divides the spring cylinder interior into a third working chamber and a spring chamber in which the additional spring is arranged. The additional spring presses the separating piston in the spring cylinder against the separating piston stop or in the direction of the separating piston stop. The additional spring is supported on the separating piston and a wall of the spring cylinder. If the separating piston is pressed against the separating piston stop by the additional spring, the volume of the third working chamber is minimal. The separating piston stop can be formed by another wall of the spring cylinder.

[0015] In one advantageous embodiment of the invention, the second working chamber of the pressure cylinder interior is fluidly connected to the third working chamber of the spring cylinder interior. The fluidly effective connection is formed, for example, by a fluid channel and in particular by a fluid passage between the chambers. This enables the fluid to flow from the second working chamber into the third working chamber. If the fluid in the second working chamber of the pressure generator is displaced from the pressure generator by the piston rod moving into the pressure cylinder and cannot flow into the fluid compensation tank via the first fluid channel, the fluid is displaced into the third working chamber. The fluid displaced into the third working chamber acts against the separating piston and displaces the separating piston against the additional spring force, which pressurizes the fluid.The separating piston is displaced exclusively by the displaced fluid and not by any damping force generated by the pressure generator or the damper. The separating piston is displaced in the spring cylinder against the spring force of the additional spring, whereby the additional spring acts via the separating piston, the fluid and the piston rod parallel to the suspension spring. When the suspension spring is compressed, the piston rod moves parallel to this into the pressure cylinder and displaces fluid in the pressure cylinder with the volume of the section of the piston rod that is arranged in the pressure cylinder. With the switching device in the release position, the fluid is at least partially pumped into the spring cylinder, whereby the fluid acts via the separating piston on the additional spring and compresses it. The additional spring builds up a spring force that acts via the separating piston on the fluid, building up the pressure in the working chambers and thus increasing the extension force of the piston rod.This means that the suspension spring and auxiliary spring act in parallel.

[0016] According to the invention, the spring-damper system has a fluid expansion tank, a first fluid channel, and a second fluid channel. The switching device is an electrically controllable shut-off valve with a shut-off position and a flow position, which is designed to shut off a fluid flow of the fluid with which the pressure generator is filled through the first fluid channel. The pressure generator is fluidly connected to the expansion tank by means of the first fluid channel via the shut-off valve, and the expansion tank is fluidly connected to the pressure generator by means of the second fluid channel. In the shut-off position, the shut-off valve shuts off a fluid flow through the first fluid channel and releases the fluid flow in the flow position. The shut-off position of the shut-off valve corresponds to the release position of the switching device, and the flow position of the shut-off valve corresponds to the blocking position of the switching device.The fluid channels can be formed integrally with each other, at least in sections.

[0017] An advantageous embodiment of the invention provides that the first fluid channel runs at least partially through the piston rod of the pressure generator. Preferably, it extends along the longitudinal axis of the piston rod and at least over the section of the piston rod that can penetrate the pressure cylinder. The check valve can also be arranged in the piston rod or on the piston rod. For example, the check valve could also be arranged in the pressure piston or in an end cap or end plate of the pressure generator. The first fluid channel has a first section leading from the pressure generator to the switching device and a second section leading from the switching device to the fluid expansion tank.Both the first and the second sections can extend through the piston rod, wherein the sections can run at least partially parallel to one another, so that the piston rod has two bores at least in sections. A first bore forms the first section of the first fluid channel, and the second bore forms the second section of the first fluid channel. In the aforementioned embodiment, the piston rod always has a bore that forms at least part of the fluid channel.

[0018] A further advantageous development provides that both the first fluid channel and the second fluid channel extend from the second working chamber through the piston rod.

[0019] In a further development, a first check valve arranged in the first fluid channel blocks the flow of fluid from the compensation tank into the pressure generator, so that the fluid can only flow from the pressure generator into the compensation tank via the first fluid channel. The first check valve is preferably arranged in the piston rod or at least partially formed by the piston rod. Additionally or alternatively, it is provided that a second check valve is arranged in the second fluid channel and the second check valve blocks the flow of fluid from the pressure generator into the compensation tank, so that the fluid can only flow from the compensation tank into the pressure generator via the second fluid channel.

[0020] In an advantageous variant of the invention, the first fluid channel extends from the second working chamber through the pressure piston and the piston rod to the first check valve, from the first check valve to the shut-off valve, and from the shut-off valve to the compensation container. The second fluid channel extends from the compensation container to the second check valve and from the second check valve to the first working chamber. The second check valve is preferably arranged in or on a wall of the pressure cylinder through which the piston rod extends, such that the second fluid channel at least partially passes through the wall.

[0021] In a favorable embodiment of the invention, the fluid expansion tank is formed by the hollow cylinder. The fluid expansion tank is preferably designed as a chamber of the hollow cylinder that adjoins the first working chamber of the pressure cylinder. The piston rod extends at least partially through the expansion tank. Furthermore, the suspension spring is preferably arranged at least partially in the expansion tank, so that a spring chamber for the suspension spring and the fluid expansion tank are integrally formed with one another.

[0022] Furthermore, an embodiment is advantageous in which no fluid channel extends in an outer wall located on the outside in the radial direction of the hollow cylinder or on the outside of a lateral surface of the hollow cylinder, so that the installation space of the hollow cylinder is not enlarged by the fluid channels and the outer walls are not weakened.

[0023] The volume flows through the fluid channels and the passage device of the pressure piston are preferably coordinated with one another, so that a fluid displaced by the piston rod in the pressure cylinder interior can flow through the first fluid line with the switching device in the blocking position (check valve in the flow position) into the fluid compensation tank.

[0024] According to the invention, the spring-damper system also comprises a gas spring unit. The gas spring unit is formed from a gas spring cylinder, in whose interior a gas acting as a gas spring, a gas separating piston, and a gas separating piston stop are arranged. The gas separating piston divides the interior of the gas spring cylinder into a fourth working chamber and a gas spring chamber in which the gas is arranged. The gas spring permanently presses the gas separating piston in the gas spring cylinder toward the gas separating piston stop. The fourth working chamber also forms the compensation tank. The gas is preferably nitrogen.

[0025] Furthermore, according to the invention, the passage device of the pressure piston comprises a throttle device for throttling a fluid flow between the first and second working chambers, via which the damping behavior is determined. Furthermore, the pressure generator comprises a closing plate which closes off the second working chamber on its side facing away from the damper piston, wherein the closing plate comprises at least one passage device with a throttle device. The second working chamber of the pressure cylinder interior is fluidly connected to the third working chamber of the spring cylinder interior via the throttle device. The first and second fluid channels run partially through the throttle device or are partially formed by the throttle device. A fluid flow from the second working chamber to the third working chamber and a fluid flow through the first and second fluid channels is throttled by the throttle device.The damper consists of the pressure generator and the gas spring unit. This allows the damper and auxiliary spring unit to be arranged in series, allowing both the damper and a switchable spring rate to be integrated into one side of a telescopic fork, i.e., into one fork leg.

[0026] The throttle device of the pressure piston throttles the fluid flow between the first and second working chambers, so that when the piston rod is retracted or extended, a damping force is generated by means of the throttle device of the pressure piston.

[0027] When the piston rod extends from the pressure cylinder, fluid flows from the first to the second working chamber, whereby the additionally required fluid is replaced by the volume of the section of the piston rod that extends, preferably flowing unthrottled from the additional spring unit or the fluid compensation tank through the throttle device of the end plate.

[0028] When the piston rod is retracted into the pressure cylinder, fluid flows from the second into the first working chamber, whereby the excess fluid displaced by the piston rod flows throttled from the second working chamber through the throttle device of the end plate into the additional spring unit or the fluid compensation tank.

[0029] The additional pressure generated by the damping in the pressure cylinder is supported against the gas spring regardless of the position of the switching device, so that the damping by the damper and the spring action of the additional spring are decoupled.

[0030] In a further advantageous development, the gas spring cylinder and the spring cylinder are integrally formed by an additional cylinder. In the additional cylinder, the gas spring chamber and the spring chamber are adjacent to one another. The gas spring chamber and the spring chamber can be arranged in series or side by side. For example, the additional cylinder could be U-shaped, with the gas spring chamber being formed in a first leg of the U-shaped additional cylinder and the spring chamber being formed in a second leg of the U-shaped additional cylinder.

[0031] In a further development, the gas spring chamber and the spring chamber are fluidically connected to each other. The gas spring chamber and the spring chamber thus form a common volume containing the gas, so that the gas spring acts both in the gas spring chamber and the spring chamber. The third and fourth working chambers are, in turn, connected to each other via the fluid channels, so that the third and fourth working chambers are fluidically connected for the fluid, and the gas spring and spring chambers are fluidically connected for the gas.

[0032] In an advantageous embodiment, the spring-damper system has a connecting device with which it is connected to the motor vehicle. The connecting device is preferably a clamping fist which guides a wheel axle of the motor vehicle and which is arranged on the pressure generator or the hollow cylinder in series with the pressure generator and is connected to it. At least the additional spring unit is formed or arranged in the connecting device. An embodiment in which the additional cylinder is formed by a hollow space in the connecting device, the locking device is arranged on or in the connecting device, and the fluid channels extend through the connecting device is particularly advantageous.

[0033] According to the invention, a telescopic fork, in particular for a single-track motor vehicle, with a spring-damper system according to the invention is also proposed. A single-track motor vehicle is any single-track motor vehicle such as a motorcycle. The telescopic fork preferably has two fork legs, with only one fork leg comprising a spring-damper system according to the invention. Furthermore, a fork leg is preferably formed from a hollow cylinder and a compensating cylinder, which lies tightly against the hollow cylinder and is movable relative to the hollow cylinder in the direction of a common longitudinal axis. The hollow cylinder also preferably forms the pressure cylinder and the spring cylinder. In an alternative embodiment, each fork leg comprises a spring-damper system according to the invention with a gas spring unit, in which the respective pressure generator forms a damper with the gas spring unit.

[0034] The features disclosed above can be combined as desired, as long as this is technically possible and they do not contradict each other.

[0035] Other advantageous developments of the invention are characterized in the subclaims or are presented in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. They show: Fig. 1 a schematic representation of a spring-damper system; Fig. 2 a spring-damper system in a first state; Fig. 3 a spring-damper system in a second state; Fig. 4 a spring-damper system in a third state; Fig. 5 a schematic representation of another spring-damper system; Fig. 6 a spring-damper system in a first state; Fig. 7 a spring-damper system in a second state;

[0036] The figures are schematic examples. Like reference numerals in the figures indicate like functional and / or structural features.

[0037] Fig. 1 schematically illustrates the spring-damper system for better illustration. The suspension spring 10 and the pressure generator 20 act in parallel and are each connected to a vehicle body FK and a vehicle axle FA. Also schematically shown is the damper 60, designed as a damper cylinder, which is also connected to the vehicle body FK and the vehicle axle FA and thus acts parallel to the suspension spring 10. The pressure generator 20 consists of a pressure cylinder into which a piston rod 21 extends from one side. The piston rod 21 is connected to the vehicle body FK via a connecting device on the side located outside the pressure cylinder. The pressure piston 23 is arranged on the side of the pressure piston rod 21 located inside the pressure cylinder. The pressure piston 23 divides the pressure cylinder interior 22 into a first working chamber 221, through which the piston rod 21 extends, and a second working chamber 222.The pressure piston 23 also has bores as a passage device, which enable a fluid flow between the first and second working chambers in an essentially unthrottled manner. The damping behavior of the spring-damper system is determined by the damper 60. The additional spring unit 30 or the third working chamber 321 of the additional spring unit 30 is fluidly connected to the second working chamber 222. In the spring cylinder interior 32 of the spring cylinder, which forms a housing of the additional spring unit 30, the additional spring 31 is arranged, which presses a separating piston 33 in the direction of a separating piston stop 34, which in the schematic representation of the . Fig. 1 is formed by the spring cylinder, wherein the separating piston 33 divides the spring cylinder interior 32 into the third working chamber 321 and a spring chamber 322, in which the additional spring 31 is arranged. The separating piston 33 seals the third working chamber 321 from the spring chamber 322, so that the spring chamber 322 is free of fluid. Starting from the second working chamber 222, a first flow channel 41 extends via a first check valve 43 via a 2 / 2-way valve or shut-off valve as a switching device 40 into a fluid compensation tank 50, wherein a volume flow of the fluid through the first fluid channel 41 is only possible from the second working chamber 222 into the fluid compensation tank 50 due to the first check valve 43, and wherein the switching device 40 must be in the blocking position (shut-off valve in the flow position). The switching device 40 is in Fig. 1 in the release position (lock valve in the blocking position). A second flow channel 42 extends from the fluid expansion tank 50 via a second check valve 44 into the first working chamber 221, so that a volume flow of the fluid through the second flow channel 42 is only possible from the fluid expansion tank into the first working chamber 221.

[0038] The switching position of the switching device 40, i.e. blocking position and release position, enables two operating modes of the spring-damper system.

[0039] If the switching device 40 is in the release position, i.e. as in Fig. 1, a volume flow of the fluid from the second working chamber 222 into the fluid compensation tank 50 is blocked by the switching device 40. If the piston rod 21 with the pressure piston 23 moves into the pressure cylinder, the first working chamber 221 is filled by a volume V 1enlarged and the second working chamber 222 by a volume V 2 reduced. Due to the volume V S of the section of the piston rod extending through the first working chamber 221, the second volume V 2 equal to the sum of the first volume V 1 and the volume V S (V 2 = V 1 + V S ). If the piston rod 21 with the pressure piston 23 moves into the pressure cylinder, the total volume of the first and second working chambers 221, 222 is reduced by the volume Vs of the piston rod 21. The passage device of the pressure piston 23 enables a volume flow of the fluid between the first and second working chambers 221, 222, so that the volume V 1 in the first working chamber 221 by a fluid from the volume V 2the second working chamber 222 is filled. Due to the volume Vs of the section of the piston rod 21 that extends through the first working chamber 221, the volume Vs must be displaced from the pressure cylinder. Since a volume flow into the fluid compensation tank 50 is blocked by the blocking device 40, the volume Vs is pressed into the third working chamber 321 by the flow-effective connection of the second working chamber 222 to the additional spring unit 30. The volume Vs acts against the separating piston 33 and presses it, enlarging the third working chamber 321, against the additional spring 31. The spring force exerted by the additional spring 31 via the separating piston 33 increases the pressure in the pressure cylinder and acts via the pressure piston 23 on the piston rod 21, so that it is pushed out of the pressure cylinder. The additional spring 31 thus acts parallel to the pressure generator 20 and to the suspension spring 10, so that the total spring rate or total spring constant k Gof the suspension spring 10 and the additional spring 31 results from the sum of the individual spring constants. If the piston rod 21 moves out of the pressure cylinder, so that the second working chamber 222 is enlarged and the first working chamber 221 is reduced, the displaced volume flows from the first into the second working chamber 221, 222, with the additionally required fluid with the volume Vs flowing from the third working chamber 321 into the second working chamber 222.

[0040] If the switching device 40 is in its blocking position, the excess volume Vs is displaced from the second working chamber 222 into the fluid compensation tank 50 when the piston rod 21 is retracted into the pressure cylinder and flows from the compensation tank 50 via the second fluid channel 44 into the pressure cylinder interior 22 when the piston rod 21 is extended. The additional spring 31 is not subjected to pressure, so that the spring constant kz of the additional spring 31 is not included in the total spring constant k G and this essentially results from the spring constant k T the suspension spring.

[0041] The Fig. 2 to 4 show an embodiment of a spring-damper system in different states, wherein the description of the schematically illustrated spring-damper system of the Fig. 1 applies. The spring damper system of the Fig. 2 to 4 each do not show the damper 60 and each has a hollow cylinder 1 that integrally forms the fluid expansion tank 50, the pressure cylinder, and the spring cylinder. The hollow cylinder 1 is shown in sections and in a sectional view, so that at least some of the components arranged therein are visible. The hollow cylinder 1 has a first support wall on its side facing away from the suspension spring 10, against which the additional spring 31 is supported. The additional spring 31 presses the separating piston 33 (not shown in section) against the separating piston stop 34, which is designed as a circumferential projection on an inner surface of the hollow cylinder. The separating piston stop 34 forms the end of the additional spring unit 30 and serves as a movement limiter for the separating piston 33, so that it cannot move into the pressure cylinder interior 22.The section of the hollow cylinder 1 in which the piston rod 21 extends outside the pressure cylinder interior 22 forms, at least in sections, the fluid compensation tank 50 and a spring chamber in which the suspension spring 10 is arranged. The suspension spring 10 extends at least partially in a fluid bath formed from the fluid in the fluid compensation tank 50. The pressure piston 23 is shown in section so that the passage device formed from bores is visible. The piston rod 21 is shown in partial section, with a section of the first fluid line 41 extending along the longitudinal axis of the piston rod 21 and centrally therein. The second fluid channel 43 with the second check valve 44 are integrated into an intermediate wall of the hollow cylinder 1, which has a passage for the piston rod 21 and forms a closure of the pressure cylinder.The switching device 40 and a further section of the first fluid channel 41 are shown schematically, wherein in the embodiment shown they are preferably arranged in the hollow cylinder 1 or adjacent to it in the longitudinal direction.

[0042] In Fig. 2, the switching device 40 is in its release position and the pressure generator 20 is in a fully extended position, so that the first working chamber 221 is minimal in volume. The auxiliary spring 31 is not pressurized by the fluid in this position, so that the separating piston 33 rests against the separating piston stop 34.

[0043] The pressure piston 23 with the piston rod 21 are shown in the illustration of the Fig. 2 is moved a little way into the pressure cylinder, so that the fluid in the second working chamber 222 flows through the passage device of the pressure piston 23 into the first working chamber 221 and simultaneously into the additional spring cylinder, which is indicated by the arrows in the hollow cylinder 1. In the spring cylinder, the fluid pushes the separating piston 34 downwards from its initial position, in which it rests against the separating piston stop 34, against the spring force of the additional spring 31.

[0044] Fig. Figure 4 shows a spring-damper system with the switching device 40 in the blocking position and with the piston rod 21 and the pressure piston 23 in a position in which they are moved into the pressure cylinder. Due to the blocking position of the switching device 40, the excess fluid from the second working chamber 222 with the volume Vs does not flow into the auxiliary spring unit, but rather through the first fluid channel 41 into the fluid compensation tank 50, which is indicated by the arrows in the hollow cylinder 1. The auxiliary spring 31 is not pressurized by the fluid, so that the spring constant kz of the auxiliary spring 31 does not contribute to the total spring k G of the spring-damper system.

[0045] In Fig. 5, a further embodiment of the spring-damper system according to the invention is shown schematically. The description of the spring-damper system of Fig. 1 applies analogously, but in the spring-damper system the Fig. 5, the pressure generator 20 and the damper 60 are formed integrally with each other. The pressure piston 23 has bores with a throttle device as a passage device, which allow a throttled fluid flow between the first and second working chambers 221, 222 and, in contrast to the pressure piston in Fig. 1 determine the damping behavior of the spring-damper system. The spring-damper system from Fig. 5 comprises a gas spring unit 70 formed from a gas spring cylinder. The gas spring cylinder interior 71 is filled with nitrogen and acts via the gas separation piston 73 against the fluid in the fluid compensation tank 50 which is formed by the fourth working chamber of the gas spring unit.

[0046] Starting from the second working chamber 222, a first flow channel 41 extends through a Fig. 5 not shown, as well as its throttle device, and via a 2 / 2-way valve or check valve as switching device 40 into the fluid expansion tank 50 or into the fourth working chamber of the gas spring unit. The switching device 40 must be in the blocking position (check valve in flow position) so that the fluid flow from the second working chamber 222 can only lead into the third working chamber 321. The switching device 40 is in Fig. 5 in the release position (lock valve in the blocking position). A second flow channel 42 extends from the fluid expansion tank 50 through the Fig. 5 not shown end plate 24 and its throttle device and via a second check valve 44 into the first working chamber 221, so that a volume flow of the fluid through the second flow channel 42 is only possible from the fluid compensation tank into the first working chamber 221.

[0047] By means of the flow device with throttle device of the pressure piston 23, in the embodiments of the Fig. 5 to 7, a damping of the movement of the piston rod 21 and thus a damping of the suspension spring 10 is generated. The damping force occurring when the piston rod 21 retracts into the pressure cylinder is supported by the end plate and the gas spring, but does not cause any movement of the separating piston 33.

[0048] For the spring-damper systems of the Fig. 6 and Fig. 7 the description of the Fig.5, wherein the pressure piston 23 in turn comprises a passage device with a throttle device. The end plate 24 forms the end of the pressure cylinder, wherein the throttle device of the end plate 24 allows fluid to flow unthrottled from the fluid expansion tank 50 and the third working chamber 321 into the second working chamber 222 or throttled and, depending on the position of the switching device 40, from the second working chamber 222 into the third working chamber 321 or the fluid expansion tank 50.

[0049] The pressure or damping force built up by the damping is supported on the gas spring unit 70, regardless of the position of the switching device 40, without causing any movement of the separating piston 33. The gas spring chamber 71 is fluidly connected to the spring chamber 32, so that the gas is also located in the spring chamber 32 and acts as a gas spring in both the spring chamber 32 and the gas spring chamber 71. Regardless of the position of the switching device 40, the damping force is therefore supported against the gas spring via the separating piston 33 and the gas separating piston 71, but without moving the separating piston 33, so that the damping force or damping has no influence on the spring rate kz of the additional spring, the total spring rate k G or has spring rate adjustment.

[0050] The invention is not limited to the preferred embodiments described above. Rather, a number of variants are conceivable, which utilize the presented solution even in fundamentally different designs. For example, the suspension spring could be arranged around the hollow cylinder.

Claims

[1] Spring-damper system for a wheel suspension of a motor vehicle, wherein the spring-damper system comprises a suspension spring (10) with a spring constant k T , a pressure generator (20) acting parallel to the support spring (10) and filled with a fluid, an additional spring unit (30) with an additional spring (31) having a spring constant kz, a switching device (40) with a blocking position and a release position for switching the additional spring (31) and a damper (60) acting parallel to the support spring (10), wherein the switching device (40) blocks the additional spring (31) in the blocking position and in the release position the additional spring (31) acts parallel to the support spring (10) by means of the fluid, characterized by , that the pressure generator (20) has a pressure cylinder, a pressure piston (23) and a piston rod (21) extending into a pressure cylinder interior (22) of the pressure cylinder, on the side of which piston rod is arranged in the pressure cylinder interior (22), the pressure piston (23) is arranged, and the pressure piston (23) divides the pressure cylinder interior (22) into a first working chamber (221) and a second working chamber (222), wherein the pressure piston has a passage device connecting the first working chamber (221) to the second working chamber (222), and the piston rod (21) extends through the first working chamber (221), wherein the spring-damper system comprises a fluid expansion tank (50) and a first and a second fluid channel (41, 42), the switching device (40) is an electrically controllable shut-off valve with a shut-off position and a flow position, the pressure generator (20) is fluidically connected to the equalizing tank (50) by means of the first fluid channel (41) via the check valve (40), and the equalizing tank (50) is fluidically connected to the pressure generator (20) by means of the second fluid channel (42), wherein the check valve (40) blocks a fluid flow through the first fluid channel (41) in the blocking position and releases it in the flow position, wherein the blocking position of the check valve corresponds to the release position and the flow position of the check valve corresponds to the blocking position, wherein the spring-damper system comprises a gas spring unit (70), the gas spring unit being formed from a gas spring cylinder, in the gas spring cylinder interior (71) of which a gas acting as a gas spring, a gas separating piston (73) and a gas separating piston stop are arranged, the gas separating piston divides the gas spring cylinder interior into a fourth working chamber and a gas spring chamber in which the gas is arranged, and wherein the gas spring permanently presses the gas separating piston in the gas spring cylinder in the direction of the gas separating piston stop and the fourth working chamber forms the compensation tank (50) the passage device of the pressure piston (23) comprises a throttle device for throttling a fluid flow between the first and second working chambers (221, 222), the pressure generator (20) comprises a closure plate (24) which closes off the second working chamber on its side facing away from the damper piston, wherein the closure plate (24) comprises at least one passage device with a throttle device, wherein the second working chamber (222) of the pressure cylinder interior (22) is fluidly connected to a third working chamber (321) of the spring cylinder interior (32) via the throttle device, and the first and second fluid channels extend partially through the throttle device, so that a fluid flow from the second working chamber (222) to the third working chamber (321) and a fluid flow through the first and second fluid channels (41, 42) is throttled, and wherein the damper is formed by the pressure generator (20) and the gas spring unit. [2] Spring-damper system according to the preceding claim, wherein the spring-damper system comprises a hollow cylinder (1) in which at least the additional spring unit (30) and the pressure generator (20) are arranged in series with one another. [3] Spring-damper system according to one of the preceding claims, wherein the additional spring unit (30) is formed from a spring cylinder, in the spring cylinder interior (32) of which the additional spring (31), a separating piston (33) and a separating piston stop (34) are arranged, the separating piston (33) divides the spring cylinder interior (32) into the third working chamber (321) and a spring chamber (322) in which the additional spring (31) is arranged, and wherein the additional spring (31) presses the separating piston (33) in the spring cylinder in the direction of the separating piston stop (34). [4] Spring-damper system according to the preceding claim, wherein the second working chamber (222) of the pressure cylinder interior (22) is fluidly connected to the third working chamber (321) of the spring cylinder interior (32). [5] Spring-damper system according to one of the preceding claims, wherein the first fluid channel (41) extends at least partially through the piston rod (21) of the pressure generator (20). [6] Spring-damper system according to one of the preceding claims, wherein a first check valve (43) is arranged in the first fluid channel (41) and blocks a fluid flow from the compensation tank (50) into the pressure generator (20) and / or a second check valve (44) is arranged in the second fluid channel (42) and blocks a fluid flow from the pressure generator (20) into the compensation tank (50). [7] Spring-damper system according to the preceding claim, wherein the first fluid channel (41) extends from the second working chamber (222) through the pressure piston (23) and the piston rod (21) to the first check valve (43), from the first check valve (43) to the check valve (40) and from the check valve (40) to the compensation tank (50), and the second fluid channel (42) extends from the equalizing tank (50) to the second check valve (44) and from the second check valve (44) to the first working chamber (221). [8] Spring damper system according to one of the preceding claims, wherein the gas spring cylinder and the spring cylinder are integrally formed by an auxiliary cylinder, furthermore the gas spring chamber and the spring chamber (322) are adjacent to each other in the auxiliary cylinder. [9] Spring damper system according to one of the preceding claims, wherein the gas spring chamber and the spring chamber (322) are fluidly connected to one another. [10] Spring-damper system according to one of the preceding claims, wherein the spring-damper system has a connecting device with which it can be connected to the motor vehicle, which is arranged in series with the pressure generator, wherein at least the additional spring unit is formed in the connecting device. [11] Telescopic fork, in particular for a single-track motor vehicle, with a spring-damper system according to at least one of the preceding claims.

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