Hydropneumatic strut and wheel suspension with a hydropneumatic strut

Abstract

A hydropneumatic strut (1), a wheel suspension with a hydropneumatic strut (1), and a land, road, or rail vehicle with such a strut (1) or wheel suspension. The strut (1) has a hydraulic shock absorber (2) which is operatively connected to a vehicle spring (3), and a pneumatic spring element (4) by which, at least temporarily under load, an additional spring force acting parallel to the direction of movement of the vehicle spring (3) can be generated. The described solution is characterized in that the pneumatic spring element (4) has a spring pressure chamber (6) filled with air and / or gas, the internal pressure of which is adjustable and / or changeable, the spring pressure chamber (6) is arranged inside a piston rod (8) connected to a working piston (7) of the vibration damper, and a volume of the spring pressure chamber changes when the working piston moves, so that forces resulting from a change in the internal pressure in the spring pressure chamber (6) act parallel to forces initiated by the vehicle spring (3).

Description

[0001] The invention relates to a hydropneumatic spring strut and a wheel suspension for a vehicle with a hydropneumatic spring strut. The hydropneumatic spring strut has a hydraulic shock absorber operatively connected to a vehicle spring to dampen a movement of the vehicle spring, and a pneumatic spring element that, at least temporarily, generates an additional spring force acting parallel to a spring force generated by the vehicle spring when subjected to a load.

[0002] In general, a suspension strut, also known as a spring-damper unit, is a component in vehicle chassis for wheel guidance and damping. A suspension strut, in particular, combines a shock absorber and a vehicle spring. Typically, suspension struts only transmit forces along their longitudinal axis and are pivotably mounted at both ends. Suspension struts are used, among other things, in double wishbone or trailing arm axles and offer the primary advantage of allowing the shock absorber and vehicle spring to be integrated into a single component.

[0003] In conventional vehicles, struts form the connection between the wheel suspension and the body or vehicle structure. The shock absorber reduces the vibrations of the body mass caused by the compression and rebound of the vehicle springs due to uneven road surfaces. It slows these vibrations down, thus contributing to driving safety and playing a key role in ride comfort.

[0004] The primary function of a shock absorber in a suspension strut is to reduce the speed of the spring's movement. The shock absorber also dampens vibrations along the length of the strut caused by the wheels moving over uneven surfaces.

[0005] A suspension strut is therefore a chassis component that contributes to increasing the comfort of vehicle occupants and passengers, improving driving safety, and protecting the load. The primary function of a suspension strut is to compensate for road surface irregularities while minimizing body acceleration, thus contributing significantly to good vehicle handling and thus to overall driving safety.

[0006] In conventional suspension struts, the kinetic energy introduced via the vehicle spring is converted into heat in the shock absorber through fluid friction. For this purpose, a working piston of the shock absorber moves back and forth in an oil-filled cylinder. In order to provide suitable resistance to the working piston during its various movements, valves are also provided that adjust the flow through the cylinder interior, particularly through different pressure chambers, which may include a low-pressure chamber and a high-pressure chamber, as required. Typically, the movement of the working piston is decelerated so sharply that the spring vibration is reduced immediately, for example, when driving over an obstacle.

[0007] Due to increasing demands for driving comfort and safety, vehicle chassis are becoming increasingly complex, which regularly requires precise tuning of the characteristics, particularly in the shock absorbers and vehicle springs used in suspension struts. In many cases, coil springs are used as vehicle springs; these are characterized by low inherent friction, making vibration reduction in the shock absorbers crucial for driving safety. Gas-filled shock absorbers are now commonly used as shock absorbers, especially in series-produced vehicles. This type of shock absorber contains an additional gas cushion within the shock absorber; the compressed gas primarily serves to prevent the release of gases dissolved in the oil. This is intended to prevent unwanted changes in the flow behavior and thus the damper characteristic curve.

[0008] In this context, DE 198 57 595 A1 discloses a self-pumping hydropneumatic spring strut with internal level control, as used particularly for motor vehicles. The spring strut has a shock absorber with a working cylinder filled with oil and a pressurized gas cushion arranged in a high-pressure chamber, which acts as a spring. The working cylinder is divided into two working chambers by a working piston carried by a hollow piston rod. A piston pump is provided, driven by the movement of the vehicle spring, which pumps oil from a low-pressure chamber into the working chamber connected to a high-pressure chamber. The pump cylinder of the piston pump is formed by a hollow piston rod, into which a hollow pump rod, attached to the working cylinder and carrying a suction valve at its front end, immerses.Furthermore, a control opening is provided, which can be closed depending on the position of the working piston in the working cylinder and which connects the working chamber connected to the high-pressure chamber with a control channel having a throttle and opening into the low-pressure chamber. The technical solution described features three spring-loaded check valves: an inlet, an outlet, and a drain valve. While the inlet and outlet valves are required for the pumping action of the piston pump, the drain valve is necessary for the throttled discharge of the damping medium when the vehicle body is relieved of load. Since different valves are required, and the shock absorber is designed as a multi-tube shock absorber with high demands on sealing elements and manufacturing tolerances, a comparatively large amount of effort is required for the production and provision of these valves, as well as for assembly and thus for the manufacture of a spring strut.

[0009] Furthermore, DE 39 10 119 A1 describes a hydropneumatic suspension system with at least one shock and vibration damper comprising a cylinder-piston unit with a gas reservoir that interacts with a damping valve having throttle valves. The throttle valves, in turn, comprise valve elements that are preloaded by springs in a closing direction of the valve elements. The preload of the springs can be varied by an adjusting element that acts jointly on these springs in the closing or opening direction of the valve elements. Load-dependent adjustment of the damping can be achieved because the adjusting element is driven by the pressure present in the gas reservoir.

[0010] Furthermore, DE 34 14 257 A1 discloses a device for controlling the spring stiffness of a road vehicle, which is combined with a control of the shock absorber stiffness. Both controls are implemented using a single control valve. The trigger signals for the control valve are determined by an electronic device that receives its signals from sensors mounted on the vehicle that measure spring travel, acceleration, vehicle speed, steering angle, or similar. In particular, a travel sensor is used that records the shock absorber compression and sends a signal based on this measured value to the electronic device, thereby achieving changes in spring stiffness.

[0011] Furthermore, in the case of state-of-the-art struts, the stiffness is ultimately determined essentially by the selection and design of the spring element, which is often designed as a coil spring. The stiffness or hardness of a spring is determined by the so-called spring rate, which is a measure of how strongly a spring compresses or rebounds when a force is applied. The stiffness of a spring has a significant influence on the movements of a vehicle body or structure, as well as on driving comfort and safety.

[0012] Hard springs result in comparatively high frequencies at which the body or vehicle structure vibrates, meaning the vehicle only drops slightly even when loaded and exhibits only slight lean when cornering. If the spring stiffness is too high, however, a vehicle loses considerable ride comfort and driving safety is reduced, as relatively short, hard impacts affect vehicle occupants and cargo. In addition, road grip is reduced. In contrast, the use of soft springs results in increased ride comfort due to the lower body frequencies, but reduces the possible payload and leads to a less precise driving feel. If the spring stiffness is too soft, the chassis can bottom out, which in turn can lead to loss of control.

[0013] When designing suspension struts, it is therefore essential to ensure an optimal balance between handling and ride comfort when used in a vehicle's chassis. The design and adjustment of a spring-damper system is therefore very complex, and a multitude of different parameters must be taken into account. Such design work can only be carried out by specialized experts. A challenge for the design is that vehicles are used for a wide range of purposes, and it is often not yet clear at the time of manufacture which suspension strut design will be suitable, or perhaps even nearly optimal, for the vehicle's subsequent operation.In this context, it is desirable for a spring strut to be designed in such a way that it is suitable for a variety of applications without the need to adapt or replace individual components, in particular the spring element or the shock absorber.

[0014] Based on the solutions for spring struts known from the prior art and the problems described above, the object of the invention is to provide a spring strut and a wheel suspension for road and land vehicles that are suitable for different vehicles and various purposes, without the need for additional adjustments or modifications during use. Using comparatively simple means and conventional design principles, it should be possible to adjust the suspension properties of a spring strut to at least a near-optimal level, in particular to match the properties of the spring element used to the damping properties. In this way, an at least near-optimal balance between ride comfort and handling of a vehicle should be achievable for different purposes of a vehicle.The specified technical solution should advantageously operate at least largely automatically and enable rapid response to changing conditions during vehicle operation without requiring special modifications to a suspension strut. The specified technical solution should particularly advantageously enable the stiffness of a suspension strut to be quickly and as needed to changing driving situations.

[0015] The above-described object is achieved with a spring strut according to claim 1, a vehicle wheel suspension according to claim 10, and a land, road, or rail vehicle according to claim 13. Advantageous embodiments of the invention are the subject of the dependent claims and are explained in more detail in the following description with partial reference to the figures.

[0016] The invention relates to a hydropneumatic spring strut for a vehicle wheel suspension, comprising a hydraulic shock absorber arranged parallel to a vehicle spring and, according to a specific development, connected to two spring plates between which the vehicle spring is arranged, and comprising a pneumatic spring element, by means of which, at least temporarily, an additional spring force acting parallel to the direction of movement of the vehicle spring can be generated when a load is applied. Thus, in addition to a vehicle spring of the spring strut, which represents a main spring for absorbing movements caused by the vehicle body or a vehicle superstructure, an additional spring is provided, which, at least temporarily, when a load is applied or force is introduced into the vehicle spring, generates an additional spring force acting parallel to the direction of movement of this vehicle spring and the spring force emanating from this main spring.The spring element provided in addition to the vehicle spring or main spring is designed as a pneumatic spring element that uses air and / or a gas as a spring medium to absorb introduced forces. The pneumatic spring element has a spring pressure chamber filled with air and / or gas, the filling of which with air or gas and / or internal pressure is adjustable and / or changeable, wherein the spring pressure chamber is arranged inside a piston rod connected to a working piston of the shock absorber and a volume of the spring pressure chamber changes when the working piston moves. According to the invention, the spring pressure chamber, which can be advantageously filled with air and / or a gas, particularly during operation, is located inside a piston rod of the shock absorber, which is designed at least partially as a hollow piston rod.The shock absorber's working piston, which separates the shock absorber's working cylinder into two working chambers with different and / or changing pressure levels, is also arranged on this piston rod. The spring pressure chamber, in which pressurized air or gas is advantageously stored, is thus located directly inside the shock absorber, making this arrangement a particularly space-saving variant of a spring strut with an additional pneumatic spring element. With the help of the pneumatic spring element provided according to the invention, an additional spring force parallel to the direction of movement as well as the spring force of the vehicle spring is generated when a load leads to movement of the vehicle spring and thus of the shock absorber's working piston. The spring stiffness of the spring strut can be changed by changing the internal pressure prevailing in the spring pressure chamber or by filling the spring pressure chamber with air or gas.According to the invention, an actuating unit is provided with which the filling of the spring pressure chamber with air or gas can be specifically varied depending on a load, in particular of the vehicle spring. For example, it is conceivable to adapt the spring stiffness of the spring strut as needed to the mass of a vehicle body or vehicle structure, even under heavy load. A comparatively short-term, automated adjustment of the spring stiffness is particularly advantageous when the vehicle mass changes, for example in the case of a commercial vehicle due to a change in the payload. By appropriately changing the spring stiffness of the spring strut, it is possible to keep the natural frequency of the vehicle body at least virtually constant, even when the mass changes. In this way, a stable, safe, and more comfortable driving behavior of a vehicle can be achieved, regardless of the vehicle's load condition.The invention thus ensures, on the one hand, satisfactory driving comfort for vehicle occupants and passengers and, on the other hand, also improves the protection of cargo and stressed vehicle components.

[0017] In a particular embodiment of the invention, the vehicle spring comprises a coil spring, an air spring bellows, a torsion spring, or a meander spring. It is always essential that the spring used and the shock absorber act and / or absorb forces in parallel directions. In this context, a very special embodiment of the invention provides for the vehicle spring to be arranged at least partially adjacent to the shock absorber.

[0018] Regardless of the specific design of the vehicle spring, the vehicle spring is the main spring element of the strut, which absorbs the movements carried out by a vehicle body or vehicle structure in the vertical direction.

[0019] These linear movements of the vehicle spring are transmitted to the working piston of the shock absorber due to the movement of a vehicle body or vehicle structure, which then also performs a linear movement within the shock absorber cylinder. The movement of the working piston within the cylinder is braked by hydraulic oil, which is also located in the cylinder, whereby the braking effect can be specifically influenced using suitable valves that allow the hydraulic oil to flow as needed. According to a special development of the invention, in this context, the shock absorber is designed as a so-called monotube shock absorber, in which suitable valves that influence the flow within the shock absorber cylinder are integrated directly into the working piston. The valves integrated into the working piston ensure a targeted flow of hydraulic oil between the working chambers of the cylinder.The response of the valves depends on the strength and speed of the vehicle spring's deflection, as well as its direction of movement, taking into account whether the shock absorber is currently subjected to a tensile or compressive load. Alternatively, it is conceivable that the valves are located in the shock absorber head or in an external hydraulic circuit.

[0020] It is conceivable that the internal pressure prevailing in the spring pressure chamber can be changed by means of the actuating unit through the targeted introduction or release of air or gas. Preferably, a change in the filling of the spring pressure chamber with air or gas for changing the internal pressure by the actuating unit is coupled to a movement of the vehicle body and / or the vehicle body. The actuating unit thus directs air or gas into or out of the spring pressure chamber depending on a movement of the vehicle body. It is conceivable in this case that the actuating unit is connected via mechanically acting transmission elements to the suspension points of the vibration damper and / or the parts of the vibration damper that can move relative to one another in order to transmit suitable drive forces.Furthermore, it is conceivable that suitable intermediate elements, such as gears, gear wheels and / or drive shafts, are provided in order to use the forces introduced into the chassis to drive the actuating unit.

[0021] According to a specific development, it is further provided that the actuating unit has at least one pump or compressor unit and at least one valve, via which air and / or gas, in particular from the surroundings of the spring strut, can be introduced into the spring pressure chamber and discharged therefrom in a targeted and demand-based manner. According to a particular embodiment of the invention, the actuating unit has a hydraulically driven pump or compressor unit, wherein the movements and forces introduced into the vehicle spring, or the pressures acting in the working cylinder, are transmitted to one or more hydraulic cylinders, which in turn drive or represent the pump or compressor.With regard to the previously described embodiments, it is of course conceivable that suitable intermediate elements, such as drive shafts, gears, transmissions and / or storage elements are provided in order to transmit or provide the forces required to drive the actuating unit.

[0022] Alternatively or in addition, it is conceivable for the actuating unit to specifically vary the internal pressure of the spring pressure chamber to change the spring characteristic of the strut using mechanically acting elements. Preferably, a pump or compressor unit with a drive is provided, into which mechanical forces can be introduced so that these can ultimately transmit the required drive forces to the pump or compressor.

[0023] What is important in each case is that the tensile or compressive forces introduced into the spring strut are used to change the internal pressure within the spring pressure chamber and thus the spring stiffness of the spring strut as needed with the help of an actuating unit. The actuating unit feeds air or gas into the spring pressure chamber as needed to increase the internal pressure or releases air or gas from it to reduce the internal pressure. If the vehicle spring is moved, this also causes the working piston of the shock absorber and thus also the movable piston rod, in which the spring pressure chamber is at least partially located, to move. Depending on the internal pressure prevailing in the spring pressure chamber at the time the piston rod is moved, the piston rod and the working piston of the shock absorber arranged on it are counteracted by more or less force.

[0024] In a specific development of the invention, the spring pressure chamber is arranged between piston rods arranged so as to be movable relative to one another, or the spring pressure chamber is at least partially delimited by these two piston rods. One of these piston rods is connected to the working piston of the shock absorber, is movably mounted, and is moved when the vehicle spring also moves. For ease of differentiation, this piston rod is referred to as the movable piston rod.

[0025] The other piston rod is immovable or fixed relative to the shock absorber cylinder and is therefore referred to as the fixed piston rod. During movement of the shock absorber's working piston, the movable piston rod, in which the spring pressure chamber is located, moves relative to the fixed piston rod, so that the volume of the spring pressure chamber increases or decreases depending on the direction of movement. Preferably, the two piston rods are arranged and sealed against each other in an airtight or gas-tight manner such that the movable piston rod slides over the fixed piston rod, with a seal being formed between an inner surface of the spring pressure chamber and an outer surface or outer surface of the fixed piston rod.

[0026] In a particularly specific development of the invention, a sliding element is located within the spring pressure chamber. This sliding element is movably arranged within the spring pressure chamber, divides the spring pressure chamber into a suspension chamber and a pumping chamber, and is sealed airtight or gas-tight on its outer surface relative to the inner surface of the spring pressure chamber. The movable sliding element is thus arranged within the piston rod connected to the working piston of the shock absorber, which is movable relative to the shock absorber cylinder.

[0027] The pump chamber formed by the sliding element can preferably be filled with air or gas, for example, through a flow channel located within a piston rod fixed relative to the shock absorber cylinder. It is also conceivable for air or gas to be released from the pump chamber in a controlled manner, for example, when a predetermined maximum pressure in the pump chamber is exceeded.

[0028] Furthermore, it is preferably conceivable that a pumping mechanism is provided to specifically pump air or gas, in particular ambient air, into the suspension chamber or to discharge it from it. According to a special development, the pumping mechanism sucks in ambient air as soon as the vehicle spring is pulled apart and pumps this air into the suspension chamber in a state that is at least slightly compressed compared to its original state. After several corresponding movement cycles of the vehicle spring, a pressure that is significantly higher than the ambient pressure builds up in the suspension chamber of the spring pressure chamber. If an operating state is now reached in which, due to compression of the vehicle spring, the volume of the spring pressure chamber is reduced by a value that is greater than the volume of the pumping chamber, the sliding element strikes the fixed piston rod, so that the sliding element is displaced further towards the suspension chamber.Due to this movement of the sliding element, the volume of the suspension chamber is also reduced and the air or gas located in the suspension chamber is compressed.

[0029] According to a particular development of the invention, a flow channel runs through the fixed piston rod, through which, with the aid of the actuating unit, air or gas can be directed into or out of the spring pressure chamber. Preferably, a valve is arranged at the end of the flow channel, which can be designed as a specifically controllable control valve or as a pressure relief valve. If a pressure relief valve is used, air or gas is specifically diverted from the spring pressure chamber through the flow channel when a maximum internal pressure is reached within the spring pressure chamber. Alternatively, the internal pressure of the spring pressure chamber can be changed by active, particularly preferably regulated, adjustment using a control or regulating valve.

[0030] In general, it is conceivable that air or gas is taken from the environment to fill the spring pressure chamber. Alternatively, or in addition, it is conceivable to use a special working medium, which is stored at least temporarily in a reservoir, to at least partially fill the spring pressure chamber. Furthermore, it is conceivable that the actuating unit provided according to the invention is fluidically coupled to an air and / or gas reservoir, so that air or gas, which can be used by the actuating unit for the targeted filling of the spring pressure chamber, can be stored in this reservoir.

[0031] Furthermore, the invention also relates to a wheel suspension of a land, road, or rail vehicle with a hydropneumatic spring strut constructed according to at least one of the previously described embodiments. The use of a spring strut constructed according to the invention for a wheel suspension is particularly advantageous in order to be able to specifically adjust the stiffness of the spring strut and thus to be able to adapt to the possibly variable mass of a vehicle body. The wheel suspension according to the invention is advantageously further developed such that the filling of the spring pressure chamber with air or gas by the actuating unit takes place as a function of a movement of a vehicle body or a vehicle body.It is particularly advantageous if such a strut is used in commercial vehicles, such as trucks or buses, whose mass can vary considerably depending on the load. Their use in motorcycles, especially two-wheelers, is also particularly advantageous, as the ratio of unladen weight to operating weight varies considerably due to their low weight compared to the payload.

[0032] By implementing the invention, it is possible to advantageously increase the ride comfort and safety of the occupants, passengers, and / or the cargo carried. Such a wheel suspension is therefore preferably further developed by coupling a pump or compressor mechanism of the actuating unit for conveying air or gas at least indirectly to a vehicle body or chassis.

[0033] In this context, coupling means that movements performed by a vehicle body or vehicle structure and introduced into the vehicle spring of the strut are used to drive the actuating unit in a suitable manner and to vary or adjust the internal pressure of the spring pressure chamber, and thus the spring stiffness of the strut, as required. In this respect, the invention also relates to a land, road, or rail vehicle with a strut or wheel suspension as previously described in connection with the invention and / or at least one of the exemplary embodiments.

[0034] In the following, the invention is explained in more detail, without limiting the general inventive concept, using specific embodiments with reference to the figures. In the figures: Fig. 1: schematic cross-sectional view of a hydropneumatic spring strut designed according to the invention to explain the functional principle Fig. 2: schematic cross-sectional view of a hydropneumatic spring strut designed according to the invention with an external pump unit, Fig. 3: Functional diagrams of hydro-pneumatic circuits for the implementation of the invention with a) with a pump unit for single-stage compression of air and b) with a pump unit for two-stage compression of air Fig. 4: schematic cross-sectional view of a spring strut designed according to the invention during compression and Fig. 5: Schematic cross-sectional view of a spring strut designed according to the invention during rebound.

[0035] Fig. 1 shows a schematic cross-sectional view of a hydropneumatic spring strut 1 designed according to the invention. Fig. The general principle underlying the invention will be explained in more detail using the representation chosen in Figure 1.

[0036] The hydropneumatic spring strut 1 shown is suitable for wheel guidance and suspension in motor vehicles, including cars, motorcycles, and tractors. The spring strut 1 is connected to a vehicle body or body via the damper eyes 22.

[0037] The main components of the hydropneumatic suspension strut 1 are a vehicle spring 3 and a vibration damper 2, which dampens vibrations caused by the spring due to movements of the vehicle body or a vehicle body. Fig. 1, the vehicle spring 3 is designed as a coil spring. However, the type of spring 3 is generally irrelevant for the implementation of the invention. Depending on the chassis design, a torsion spring, a meander spring, or even an air spring bellows of an air suspension system could be used as the vehicle or main spring 3.

[0038] Essential for the Fig. A special feature of the hydropneumatic spring strut 1 shown schematically in Figure 1 is that, in addition to the vehicle spring 3, which forms the actual main spring, and the vibration damper 2, a pneumatic spring element 4 is provided, the spring stiffness of which can be specifically varied. This technical measure makes it possible, for example, to adapt the spring stiffness of the hydropneumatic spring strut 1 to the mass of a vehicle body, a vehicle body, or a load in order to ultimately keep the body's natural frequency constant and thus ensure a more stable, safe, and comfortable ride regardless of the vehicle's load. This is particularly important for motorcycles, where the load accounts for a particularly large proportion of the total weight.

[0039] The Fig. The additional pneumatic spring element 4 shown in Figure 1 has an air-filled spring pressure chamber 6, which is arranged within a piston rod 8 of the vibration damper 2 and whose internal pressure can be specifically varied using a pump or compressor unit 5 and suitably arranged and designed valves. By changing the internal pressure prevailing in the spring pressure chamber 6 or the air filling, it is possible to change the spring stiffness of the pneumatic spring element 4 and thus ultimately of the entire spring strut 1 as required. With regard to the design of the pump unit 5, it is conceivable that it is mechanically, hydraulically and / or pneumatically coupled to the piston 7 of the vibration damper 2.It is also conceivable that at least one sensor for detecting the internal pressure of the damper cylinder 15 and / or movements of the piston 7 is provided in the region of the cylinder 15 of the vibration damper 2 and that the pump unit 5 is controlled taking into account the measured values ​​detected by the at least one sensor.

[0040] In order to achieve a change in the internal pressure of the spring pressure chamber 6, ambient air can be sucked in, compressed, and finally pumped into the spring pressure chamber 6 with the aid of the pump unit 5. The pump unit 5 can basically be designed as an external pump unit 5 or as an internal pump unit 5, which is integrated, for example, into the vibration damper 2 and / or the spring strut 1. A reduction in pressure generally takes place via a flow channel between the spring pressure chamber 6 and the environment, whereby it is generally conceivable that the pressure reduction occurs in an uncontrolled manner, for example via a design-related leak, or in a controlled manner using suitable elements that influence the flow resistance, such as valves. Both an uncontrolled and a controlled pressure reduction are conceivable when implementing a hydropneumatic spring strut designed according to the invention. According to a very special embodiment, it is conceivable, as in Fig. As schematically indicated in Figure 1, a pressure relief valve 11 is arranged at the inlet of the spring pressure chamber, which securely closes the inlet once the desired internal pressure in the spring pressure chamber 6 has been reached. If the internal pressure exceeds a predetermined value, the pressure relief valve 11 opens and air flows out of the spring pressure chamber 6. A change in the internal pressure prevailing in the spring pressure chamber 6 ultimately causes a change in the spring stiffness of the pneumatic spring element 4.

[0041] In addition, Fig. 2 shows a schematic cross-sectional view of a hydropneumatic spring strut 1 according to the invention with an external pump unit 5 for generating the internal pressure required in the spring pressure chamber 6. Fig. In the embodiment shown in Figure 2, the internal pressure of the spring pressure chamber 6 can again be adjusted as required so that the spring stiffness of the additional pneumatic spring element 4 assumes the desired value, so that ultimately not only the spring stiffness of the additional pneumatic spring element 4, but also of the entire spring strut 1 can be changed as required.

[0042] According to the invention, the spring pressure chamber 6 is arranged inside a piston rod 8, which is connected to a working piston 7 movable in the cylinder 15 of the vibration damper 2. The air required to increase the pressure in the spring pressure chamber 6 is sucked in from the environment via an intake valve 12 and then introduced into the spring pressure chamber 6 by means of the pump unit 5 through a check valve 11 at the inlet of the spring pressure chamber 6.

[0043] The Fig. The external pump unit 5 shown in Figure 2 has a hydraulic-pneumatic mechanism for moving a double-acting piston 19, 20 of the pump unit 5. This mechanism is designed such that hydraulic fluid, which is displaced in the cylinder 15 of the vibration damper 2 due to a movement of the working piston 7, flows into the hydraulic cylinder 16 of the pump unit 5, thereby causing the hydraulic piston 19 of the pump unit 5 to move in the direction of the pneumatic cylinder 17. As the hydraulic fluid flows into the hydraulic cylinder 16 of the pump unit 5, the hydraulic piston 19 is moved together with the pneumatic piston 20 of the pump unit 5 in this operating state in such a way that the air present in the pneumatic cylinder 17 of the pump unit 5 is compressed and conveyed via the inlet valve 11 into the spring pressure chamber 6 of the pneumatic spring element 4.

[0044] As soon as the working piston 7 moves in the opposite direction, hydraulic fluid flows out of the hydraulic cylinder 16 of the pump unit 5, the pneumatic piston 20 of the pump unit 5 also moves in the opposite direction and there is a relaxation in the pneumatic cylinder 17 so that air is again sucked in from the environment into the pneumatic cylinder 17. What is important here is that the stroke of the working piston 7 and thus the resulting stroke of the pistons 16, 17 of the pump unit 5 as well as ultimately the air filling and the internal pressure of the spring pressure chamber 6, i.e. the spring stiffness of the pneumatic spring element 4, depend on the spring travel of the vehicle or main spring 3, which is influenced by the weight of the moving vehicle body.

[0045] In the following, the function of the Fig. 2 shown external pump unit 5 Fig. 3, which shows two functional diagrams of hydro-pneumatic circuits for implementing the invention, in which Fig. 3a) a hydro-pneumatic circuit diagram with a pump unit 5 for single-stage compression of air and in Fig. 3b) with a pump unit for two-stage compression of air.

[0046] According to the Fig. In the embodiment shown in Figure 3a), a pump unit 5 with a hydraulically-pneumatically coupled mechanism is provided, which enables single-stage compression of the intake air. A movement of the vehicle spring 3 of a hydropneumatic suspension strut 1 designed according to the invention simultaneously leads to a movement of the working piston 7 arranged within the cylinder 15 of the vibration damper 2, so that hydraulic fluid is pumped from the cylinder 15 of the vibration damper 2 into the hydraulic cylinder 16 of the pump unit 5. Here, the inflowing hydraulic fluid causes a pressure increase, so that the piston 19 is moved toward the pneumatic cylinder 17. As a result of this movement, the air in the pneumatic cylinder 17 is compressed by the moving pneumatic piston 20 of the pump unit 5 and expelled toward the spring pressure chamber 6 of the additional pneumatic spring element 4.

[0047] During the reverse movement of the working piston 7, hydraulic fluid flows from the hydraulic cylinder 16 back into the cylinder 15 of the vibration damper 2, and the hydraulic piston 19 with the coupled pneumatic piston 20 move in such a way that the pneumatic cylinder 17 of the pump unit 5 is depressurized. Due to this depressurization, ambient air is drawn into the pneumatic cylinder 17 via an intake valve 12.

[0048] Furthermore, Fig. 3b) shows a further functional diagram of a pump unit 5 with a hydro-pneumatically coupled mechanism, as can be used for a spring strut 1 designed according to the invention. In contrast to the Fig. 3a) is used with the pump unit 5 according to Fig. 3b) a two-stage compression of the air drawn in from the environment is realized. The two-stage compression or expansion is achieved by two pump units 5a, 5b connected in series, each of which has a hydro-pneumatically coupled mechanism.

[0049] Regardless of the number of selected pump units 5 or the compressor stages connected in series, the internal pressure or the air filling in the spring pressure chamber 5 can be adjusted as required, thus allowing the spring stiffness of the additional pneumatic spring element 4 of a spring strut 1 designed according to the invention to be specifically modified. In general, it is conceivable that at least one of the pump units 5 used is mechanically and / or hydraulically coupled to the working piston 7 of the vibration damper 2, or that the internal pressure in the spring pressure chamber 6, and thus the spring stiffness of the additionally provided pneumatic spring element 4, is adjusted depending on the occurring load cases by using suitable sensors and actuators.Regardless of the selected coupling or control of the at least one pump unit 5, the pump unit 5 can be designed as an external unit which is arranged outside the actual spring strut 1, in particular outside the housing 18 of the vibration damper 2, or can be integrated into the spring strut 1 and / or arranged in the housing 18 of the vibration damper 2.

[0050] Furthermore, the Fig. 4 and Fig. 5 shows a particular embodiment of a hydropneumatic spring strut 1 designed according to the invention with a vibration damper 2, a vehicle spring 3 designed as a main spring, and an additional pneumatic spring element 4, the spring stiffness of which can be specifically adjusted. Fig. 4 or Fig. The spring struts 1 shown in Figure 5 are in different operating states. The connection of the spring struts 1 shown to a vehicle body or vehicle body is again achieved via the damper eyes 22.

[0051] What is essential about the illustrated embodiment of a spring strut 1 designed according to the invention is that the pump unit 5 for the targeted filling of the spring pressure chamber 6 with air is integrated into the spring strut 1. The vehicle spring 3 of the spring strut 1 is in the Fig. 4 and Fig. 5 is only indicated schematically, since the invention can fundamentally be implemented with different types of springs. Thus, depending on the structural design of a chassis and / or the hydropneumatic spring strut 1 used, designed according to the invention, it is generally conceivable that a coil spring, torsion spring, meander spring, or even an air spring bellows is used as the vehicle spring 3, which forms the main spring.

[0052] Fig. Figure 4 shows a spring strut 1 designed according to the invention in an operating state in which the vehicle or main spring 3 is compressed. This causes the spring 3 and the working piston 7 in the vibration damper 2 to move, to the left as shown. Due to this movement of the working piston 7, hydraulic fluid flows, on the one hand, through the damping valves 21 of the vibration damper 2 (not shown in this view for the sake of clarity), and, on the other hand, into the hydraulic cylinder 16 of the first pump unit 5a, in which the air in the pneumatic cylinder 17 of the first pump unit 5a is compressed by the movement of the pneumatic piston 20 coupled to the hydraulic piston 19.At the same time, hydraulic fluid flows into the hydraulic cylinder 17 of a second pump unit 5b in such a way that the hydraulic piston 19 and the pneumatic piston 20 of the second pump unit 5b coupled thereto are moved to the right, so that there is a relaxation in the pneumatic cylinder 17 of the second pump unit 5b and, after opening a check valve 13 at the inlet of the pneumatic cylinder 17 of the second pump unit 5b, compressed air is sucked in from the pneumatic cylinder 17 of the first pump unit 5a.

[0053] The spring pressure chamber 6 of the pneumatic spring element 4 is arranged within a piston rod 8, which is connected to the working piston 7 of the vibration damper 2. During the Fig. During the compression process shown in Figure 4, the spring pressure chamber 6 is tightly closed by means of a suitably adjusted valve 11, resulting in a pressure increase within the spring pressure chamber 6 and the pneumatic spring element 4 generating an additional spring force that is aligned with the spring force emanating from the vehicle spring 3. By changing the amount of air in the spring pressure chamber 6, the spring stiffness of the additional pneumatic spring element 4 and thus of the hydropneumatic spring strut 1 according to the invention can be specifically adjusted.

[0054] In Fig. 5 is compared to Fig. 4 shows the identically constructed hydropneumatic spring strut 1, but in a different operating state, namely during a rebound process of the vehicle spring 3 intended as the main spring and a corresponding movement of the working piston 7.

[0055] In this operating state, the working piston 7 of the vibration damper 2 moves to the right in the view shown. The pistons 19, 20 of the two pump units 5a, 5b also move in the opposite direction compared to the position shown in Fig. 4, in the opposite direction, so that air is now sucked into the pneumatic cylinder 17 of the first pump unit 5a via an intake valve 12, and the air in the pneumatic cylinder 17 of the second pump unit 5b is compressed. This air compressed in the pneumatic cylinder 17 of the second pump unit 5b is expelled via an outlet valve 14 and introduced into the spring pressure chamber 6 through the open check valve 11 at the inlet of the spring pressure chamber 6. In this way, the amount of air in the spring pressure chamber 6 is increased.

[0056] Since the spring travel of the vehicle spring 3 and thus also the stroke of the working piston 7 of the vibration damper 2 depend on the load on the vehicle spring 3, in particular the weight-dependent movements of a vehicle body or a vehicle body, the Fig. 4 and Fig. The spring pressure chamber 6 shown in Figure 5 is constantly filled with air as needed by the two pump units 5a, 5b, so that the spring stiffness of the additional pneumatic spring element 4 continually adapts to changing loads. The technical solution according to the invention thus increases the driving comfort and safety of a vehicle due to optimized suspension behavior.

[0057] According to a special training of the Fig. 4 and Fig.In the embodiments shown in Fig. 5, a pressure relief valve 23 is provided, via which air can be released from the spring pressure chamber 6 when a maximum intended pressure in the spring pressure chamber 6 is reached. List of reference symbols 1 hydropneumatic shock absorber 2 vibration dampers 3 Vehicle spring (main spring) 4 pneumatic spring element (additional spring) 5 Pump unit a) first pumping unit b) second pump unit 6 spring pressure chamber 7 Working piston of the vibration damper 8 movable piston rod 9 Flow channel 10 fixed piston rod 11 Check valve on the spring pressure chamber 12 intake valve 13 Inlet valve 14 Exhaust valve 15 cylinders of the vibration damper 16 hydraulic cylinders of the pump unit 17 Pneumatic cylinder of the pump unit 18 Vibration damper housing 19 Hydraulic piston of the pump unit 20 pneumatic pistons of the pump unit 21 damping valves 22 Damper eye 23 Pressure relief valve

Claims

[1] Hydropneumatic spring strut (1) for a vehicle wheel suspension with a hydraulic vibration damper (2) which is operatively connected to a vehicle spring (3) for damping a movement of the vehicle spring (3), and with a pneumatic spring element (4) by means of which an additional spring force acting parallel to the direction of movement of the vehicle spring (3) can be generated at least temporarily under a load, wherein the pneumatic spring element (4) has a spring pressure chamber (6) filled with air and / or gas, the internal pressure of which is adjustable and / or variable, and the spring pressure chamber (6) is arranged inside a piston rod (8) connected to a working piston (7) of the vibration damper, characterized bythat a volume of the spring pressure chamber changes when the working piston moves, so that forces resulting from a change in the internal pressure in the spring pressure chamber (6) act parallel to forces initiated by the vehicle spring (3) and that a filling of the spring pressure chamber (6) with air or gas can be changed in a controlled manner by an actuating unit depending on the load. [2] Hydropneumatic spring strut according to claim 1, characterized by that the vehicle spring (3) comprises a coil spring, a torsion spring, a meander spring or an air spring bellows. [3] Hydropneumatic spring strut according to claim 1 or 2, characterized by that the vibration damper (4) is designed as a single-tube damper. [4] Hydropneumatic spring strut according to one of claims 1 to 3 characterized by that a change in the filling of the spring pressure chamber with air or gas by the actuating unit is coupled to a movement of the vehicle spring. [5] Hydropneumatic spring strut according to one of claims 1 to 4, characterized by that the actuating unit for changing the filling of the spring pressure chamber (6) with air or gas is at least indirectly mechanically coupled to the vehicle spring (3). [6] Hydropneumatic spring strut according to one of claims 1 to 5, characterized by that the actuating unit has a pump unit (5) and at least one valve. [7] Hydropneumatic spring strut according to one of claims 1 to 6, characterized by that the actuating unit has a hydraulically driven pump unit (5) for changing the filling of the spring pressure chamber (6) with air or gas. [8] Hydropneumatic spring strut according to one of the preceding claims, characterized by that the spring pressure chamber (6) is delimited at least in sections by two piston rods (8, 10) which are movable relative to one another. [9] Hydropneumatic spring strut according to one of claims 1 to 8, characterized by that air or gas can be conducted into or out of the spring pressure chamber (6) through a flow channel (9) which runs through a piston rod (10), relative to which the piston rod (8) connected to the working piston (7) is movable. [10] Wheel suspension of a road or rail vehicle with a hydropneumatic spring strut (1) according to at least one of the preceding claims. [11] Wheel suspension according to claim 10, characterized by that the filling of the spring pressure chamber (6) with air or gas by the actuating unit takes place as a function of a movement of a vehicle body or a vehicle body. [12] Wheel suspension according to claim 10 or 11, characterized by that a pump or compressor mechanism of the actuating unit is at least indirectly coupled to a vehicle body or a vehicle body. [13] Land, road or rail vehicle with a spring strut according to one of claims 1 to 9 or a wheel suspension according to one of claims 10 to 12.

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