Oil-gas shock absorber for motor vehicle suspension

Abstract

The invention relates to a hydro-pneumatic shock absorber (1) for a motor vehicle, comprising:-an oil circuit (2) comprising a cylinder (6) and a piston (7) adapted to slide in the cylinder (6); -a gas circuit (3) located upstream of the oil circuit (2), and a cushion chamber (4) located between the gas circuit (3) and the oil circuit (2), the cushion chamber (4) comprising a sealed moving wall (5) located between gas and oil, while the pressure of the gas circuit (3) is increased to raise the vehicle from a low position to a high position; characterised in that the shock absorber further comprises:-a first gas reservoir (15) at a pressure P1 and a second gas reservoir (17) at a pressure P2 lower than P1; and, by successively connecting the first and second gas reservoirs (15, 17) to the gas circuit (3) and isolating the first reservoir (15), the gas circuit (3) is brought from a pressure P0 lower than P2 at which the vehicle is in the low position to a pressure P2 at which the vehicle is in the high position.

Description

[0001] The invention relates to an oil-gas shock absorber for a motor vehicle suspension.

[0002] The present invention more particularly relates to an oil-pneumatic shock absorber which can not only play its role as a shock absorber but also adjust the ground clearance.

[0003] Motor vehicle suspensions are often equipped with a shock absorbing system to improve passenger comfort when the vehicle is in motion. The system absorbs vibrations from the vehicle chassis.

[0004] Known oil-pneumatic shock absorbers also make it possible to vary the ground clearance of the vehicle in order to meet different user requirements. For example, lowering the vehicle is advantageous in reducing frictional air resistance and thus reducing fuel consumption. Conversely, when the road is damaged, it is sometimes useful to raise the vehicle and have a greater ground clearance.

[0005] Document JP2007253921 relates to a device intended to meet this requirement. This document proposes a vehicle shock absorber system that also allows the vehicle ground clearance to be adjusted when the vehicle is in motion or when the vehicle is stationary. In this system, each of the wheel suspension members is equipped with an oil-pneumatic shock absorber.

[0006] The system comprises, on the one hand, a hydraulic circuit and, on the other hand, a compressed gas circuit, the two circuits being separated from one another by a mobile piston capable of moving in a cylindrical chamber. The hydraulic circuit comprises a damping member and means for supplying and discharging a working fluid. The compressed gas circuit also comprises means for supplying and discharging a gas.

[0007] The means for supplying and discharging working fluid comprises a first cylindrical chamber for storing the fluid and supplying the shock absorber, while the means for supplying and discharging air comprises a second cylindrical chamber supplied with air by a pump, the air being directly sucked from outside the system.

[0008] Thus, the entry of air into the supply circuit exerts thrust on the moving piston and pressure on the working fluid in the shock absorber, thereby increasing the ground clearance of the vehicle.

[0009] This solution makes it possible to obtain an economical system for varying the ground clearance of the vehicle according to the driving conditions.

[0010] However, the air used in the system is sucked from outside the system by a pump, so a high-power pump is required in order to change the air pressure in the system in real time to increase the ground clearance of the vehicle.

[0011] Additionally, a significant problem that may exist with such pneumatic systems is that the pneumatic stiffness varies between low pressures for reducing vehicle ground clearance and high pressures for increasing vehicle ground clearance.

[0012] There is therefore a need to find an economical solution which makes it possible to reduce the power of the air pump at the inlet side of the system and also limits the problem of aerodynamic stiffness variations.

[0013] To this end, the first subject of the present invention proposes a motor vehicle oil-gas shock absorber, which includes:

[0014] - an oil circuit comprising a cylinder and a piston capable of sliding in said cylinder;

[0015] - a gas circuit upstream of the oil circuit and a buffer chamber between the gas circuit and the oil circuit, the buffer chamber comprising a sealed mobile wall between the gas and the oil, the pressure in the gas circuit being increased in order to raise the vehicle from a low position to a high position;

[0016] The oil-gas shock absorber further comprises:

[0017] - a first gas reservoir at a pressure P1 and a second gas reservoir at a pressure P2 lower than P1; and the gas circuit is brought from a pressure P0 lower than P2 at which the vehicle is in the low position to a pressure P2 at which the vehicle is in the high position by connecting the first gas reservoir and the second gas reservoir successively to the gas circuit and isolating the first reservoir.

[0018] The presence of the first reservoir makes it possible to improve the response time for raising the vehicle. Specifically, the pressure in the first reservoir is higher than the pressure required for the vehicle to be in a high position. Therefore, when the first air reservoir is connected to the gas circuit, the first air reservoir supplies the gas circuit more quickly to bring it to the necessary pressure.

[0019] The second reservoir makes it possible to solve the problem of the compressibility of the circuit. Specifically, it makes it possible to increase the volume of the gas circuit upstream of the oil circuit. Thus, by increasing the volume of the compressible fluid (in this case, the gas), the apparent stiffness of the gas circuit is reduced when the circuit is at high pressure, that is, when the vehicle is in a high position.

[0020] Advantageously, the gas circuit comprises a vent valve adapted to vent gas in the circuit such that the pressure in the gas circuit decreases.

[0021] Advantageously, the gas circuit is brought from pressure P2 to pressure P0 by successively isolating the first reservoir and the second reservoir and opening the exhaust valve in order to evacuate the gas from the circuit.

[0022] However, the gas in the circuit is not completely exhausted by exhausting, because there needs to be enough gas in the circuit to maintain the pressure P0 in the gas circuit. Therefore, the exhaust valve also has a check valve calibrated so that the gas circuit is not completely emptied. Then when the pressure in the gas circuit drops to pressure P0, the check valve closes.

[0023] The transition from pressure P2 to pressure P0 in the gas circuit is intended to bring the vehicle from a high position to a low position.

[0024] Advantageously, the gas circuit comprises a first isolation valve at the first reservoir and a second isolation valve at the second reservoir; the first isolation valve and the second isolation valve being capable of isolating the first reservoir and the second reservoir from the gas circuit.

[0025] These valves allow the first and second reservoirs to be isolated from the gas circuit when necessary, while making the transition from the high position to the low position and vice versa.

[0026] Advantageously, the gas circuit comprises an intermediate valve situated between the first reservoir and the second reservoir and capable of isolating a portion of the gas circuit.

[0027] When the gas circuit is at pressure P0, the pressure in the first reservoir needs to increase from pressure P2 to pressure P1. Therefore, the part of the circuit including the first reservoir needs to be isolated from the rest of the gas circuit in order to maintain the pressure in the gas circuit.

[0028] Advantageously, the first reservoir is located between the exhaust valve and the intermediate valve, and the second reservoir is located between the intermediate valve and the buffer chamber.

[0029] Advantageously, the valve used is an electrically operated valve.

[0030] The use of electrically operated valves allows the system to be automated so that the user can transition from one position to another without having to make manual adjustments.

[0031] Advantageously, the gas circuit comprises a compressor located upstream of the first reservoir and the second reservoir.

[0032] When the vehicle is in a high position, the compressor can compress the air to the target pressure of the first reservoir as a concurrent operation. Therefore, the compressor can be operated for a long time, so that its size can be reduced.

[0033] Advantageously, the gas circuit comprises a gas inlet followed by a filter upstream of the compressor.

[0034] To increase the pressure in the circuit, the compressor draws in air from outside the circuit through the air inlet. A filter placed between the compressor and the gas inlet is able to block fine particles that may enter the circuit and thus avoid such particles from damaging or accumulating in the equipment or the gas circuit.

[0035] Another subject of the invention is also a motor vehicle comprising an oil-pneumatic shock absorber as described above.

[0036] Other characteristics and advantages of the invention will become apparent from reading the following description of a particular embodiment of the invention, provided by way of indication and not limitation, with reference to the single accompanying drawing:

[0037] [ Figure 1 ] is a block diagram of the oil-gas shock absorber according to the present invention.

[0038] The invention relates to an oil-pneumatic shock absorber 1 for a motor vehicle. The motor vehicle has a suspension on each of the wheels, and a shock absorber is mounted at each suspension to absorb vibrations of the chassis of the vehicle. The shock absorber 1 according to the invention can also change the ground clearance of the motor vehicle between a low position and a high position.

[0039] Figure 1 A single shock absorber 1 is depicted mounted on a wheel, and this figure therefore does not exclude the situation where a shock absorber is mounted on each wheel of the vehicle, ie on all four wheels.

[0040] refer to Figure 1 The oil-gas shock absorber 1 comprises an oil circuit 2 and a gas circuit 3 located upstream of the oil circuit 2. The gas used here is air.

[0041] The oil circuit 2 and the gas circuit 3 are separated from each other by a buffer chamber 4. The chamber comprises a mobile wall 5 which seals between the gas and the oil. The mobile wall 5 thus separates the oil from the gas and prevents any oil from being sucked into the gas circuit 3 and vice versa. This then prevents the pump from locking or damaging the seals. In addition, the installation of the mobile wall 5 at the shock absorber 1 makes it possible to avoid cleaning the oil in the oil circuit 2 when assembling or removing the shock absorber 1. The mobile wall 5 can be, for example, a membrane (such as [ Figure 1 ]), or a floating (or in other words, a free) piston.

[0042] The oil circuit 2 comprises a cylinder 6 and a piston 7 that can slide in the cylinder 6. The piston is also fixed to a rod 22 that projects out of the cylinder 6. When the motor vehicle is jolted, for example when the wheels of the vehicle encounter an obstacle, the oil contained in the cylinder 6 tends to be compressed by the piston 7. As a result, the oil pressure in the damping chamber 4 increases and the mobile wall 5 deforms and also compresses the gas in the gas circuit 3. In order to rebalance the oil pressure on each side of the piston 7, the oil will then pass through an orifice included in the piston 7.

[0043] Thus, the gas in the circuit, which is more easily compressed than the oil, will absorb the shocks associated with the wheel, whereas the oil passing through the orifice in the piston 7 tends to damp the pulsations.

[0044] The gas circuit 3 comprises firstly a gas inlet 8 and then a compressor 10. The gas inlet is in this case an air inlet allowing external air to enter the gas circuit 3. The compressor 10 is intended for compressing the air in the gas circuit 3 in order to increase its pressure, doing so by sucking in ambient air through the gas inlet 8.

[0045] In order to prevent particles from blocking the circuit and accumulating inside the circuit, a filter 9 is placed between the compressor 10 and the gas inlet 8. A dryer 11 is also installed downstream of the compressor in order to dry the incoming gas.

[0046] The gas circuit 3 next comprises an exhaust valve 12 located downstream of the dryer 11. The exhaust valve 12 allows the gas to be released from the gas circuit 3 in order to reduce the pressure in the gas circuit 3. The exhaust valve 12 exhausts the gas from the circuit via an exhaust port 13. Between the exhaust port 13 and the exhaust valve 12, a calibrated non-return valve 14 makes it possible to maintain a minimum amount of gas in the gas circuit 3 in order to maintain a minimum pressure in the circuit 3.

[0047] A first gas reservoir 15 capable of storing compressed gas is installed downstream of the exhaust valve 12. A first isolation valve 16 is installed at the inlet of the first reservoir 15 so that this reservoir can be isolated from the gas circuit 3.

[0048] Between the buffer chamber 4 and the first reservoir 15, the gas circuit 3 comprises a second gas reservoir 17 also capable of storing compressed gas. A second isolation valve 18 is installed at the inlet of the second reservoir 17 in order to isolate this reservoir from the gas circuit 3.

[0049] Finally, the gas circuit 3 comprises an intermediate valve 19 between the first reservoir 15 and the second reservoir 17. The intermediate valve 19 is able to isolate the downstream part of the gas circuit 3 opening into the buffer chamber 4 and comprising the second gas reservoir 17 from the upstream part comprising in particular the first gas reservoir 15.

[0050] Optionally, a separation valve 20 is installed upstream of the buffer chamber 4. The separation valve 20 is adapted to isolate the buffer chamber 4 and the oil circuit 2 from the rest of the gas circuit 3.

[0051] Preferably, the valve used is an electrically operated valve, so that the operation of the oil-gas shock absorber 1 can be performed automatically.

[0052] In a preferred embodiment, an oil circuit 3 and a damping chamber 4 are installed for each wheel of the vehicle and each associated suspension, while the gas circuit is common to all damping chambers.

[0053] The oil-gas shock absorber 1 according to the present invention can change the ground clearance of the vehicle between a low position and a high position.

[0054] The purpose of the first reservoir 15 is to improve the response time when the pressure in the gas circuit is increased to raise the vehicle. Specifically, the pressure in the first reservoir is higher than the pressure required to keep the vehicle in a high position. Therefore, the first compressed air reservoir 15 allows the circuit to quickly reach the necessary pressure. The use of the first reservoir 15 also makes it possible to limit the size and power of the compressor 10, because this compressor is not used in real time to increase the pressure of the entire gas circuit 3. In addition, when the compressor 10 is in a high position, the compressor runs as a concurrent operation, and this also makes it possible to reduce the size of the compressor 10. In other words, the compressor 10 enables pressurized air to accumulate in the first reservoir 15. And it can achieve this relatively slowly.

[0055] The second reservoir 17 serves a different purpose than the first reservoir 15. It makes it possible to solve the problem of the compressibility of the circuit, thus making it possible to reduce the apparent stiffness of the gas circuit when it is at high pressure. Specifically, the second reservoir makes it possible to increase the volume of the gas circuit upstream of the oil circuit. Thus, by increasing the volume of the compressible fluid (in this case, the gas), the apparent stiffness of the gas circuit is reduced when the circuit is at high pressure. The second reservoir 17 also makes it possible to reduce the volume of the circuit that needs to be pressurized in order to pass from a low position to a high position, and therefore makes it possible to reduce the volume of the first reservoir 15.

[0056] When the vehicle is in the low position, the first gas reservoir 15 is at a pressure P1, and the second gas reservoir 17 is at a pressure P2 which is lower than the pressure P1. As for the gas circuit 3, it is at a pressure P0. In the low position, the intermediate valve 19, the exhaust valve 12, and the first and second isolation valves 16 and 18 are closed.

[0057] Alternatively, if a separation valve 20 is installed between the buffer chamber 4 and the second reservoir, the valve is open in the high position.

[0058] Therefore, using the separation valve 20 makes it possible to reduce the volume of the working gas that is at a high pressure to keep the vehicle in a high position, and to increase the rigidity of the shock absorber 1 .

[0059] In order to automate the shock absorber, it comprises means for measuring the pressure in the first reservoir 15. Other pressure measuring means located in the second reservoir 17 or in the gas circuit 3 make it possible to optimize the control of the system. The values ​​recorded by the pressure measuring means are sent to a control device that controls the valves of the shock absorber. The control device comprises at least one processor so as to be able to command the actuator based on the pressure value.

[0060] For example, the first gas reservoir 15 is at a pressure P1 of 40 bar, and the second gas reservoir 17 is at a pressure P2 of 30 bar. The pressure in the gas circuit is, for example, a pressure P0 of 3 bar corresponding to a low position of the vehicle.

[0061] To change the vehicle from the low position to the high position, the following operations are performed in succession: The control device commands the opening of the intermediate valve 19 and the first and second isolation valves 16 and 18 to connect the first and second gas reservoirs 15 and 17 to the gas circuit 3. The gas circuit 3 is then brought to pressure P2.

[0062] Thus, when the vehicle is in the high position, the pressures of the first reservoir 15, the second reservoir 17 and the gas circuit are equalized at a pressure P2. Once the high position is reached, the control means command the intermediate valve 19 to close.

[0063] When the vehicle is in high position, the compressor is activated so as to be able to increase the pressure of the first reservoir 15 until it reaches the pressure P1. Once this pressure has been reached in the first reservoir 15, the compressor is switched off and the isolation valve 16 associated with the first reservoir 15 is closed.

[0064] For example, in the high position, the gas circuit 3 and the first gas reservoir 15 and the second gas reservoir 17 are at a pressure P2 of 30 bar. When the compressor is running, the pressure of the first reservoir 15 rises to a pressure P1 of 40 bar.

[0065] Finally, in order to change the driving height of the vehicle between the high position and the low position, the following operations are performed successively. The control device commands the closing of the second isolation valve 18 and the opening of the intermediate valve 19 and the exhaust valve 12. Thus, the pressure in the second reservoir 17 is maintained at the pressure P2, while the pressure in the gas circuit 3 is reduced to the pressure P0 by exhausting a certain proportion of gas from the circuit via the exhaust valve. The remaining proportion of gas remains in the circuit in order to maintain the gas circuit 3 at the pressure P0.

[0066] Alternatively, if a separation valve 20 is installed between the buffer chamber 4 and the second reservoir, the control means command the opening of this valve before purging the gas circuit 3 .

[0067] The hydropneumatic shock absorber 1 thus allows the ground clearance of the motor vehicle to be varied without structural modifications, so as to improve the response times when raising and lowering the vehicle, while reducing the apparent stiffness of the gas circuit at high pressures.

Claims

1. A motor vehicle oil-gas shock absorber (1), comprising: - an oil circuit (2) comprising a cylinder (6) and a piston (7) capable of sliding in said cylinder (6); - a gas circuit (3) upstream of the oil circuit (2), and a buffer chamber (4) between the gas circuit (3) and the oil circuit (2), the buffer chamber (4) comprising a sealed mobile wall (5) between the gas and the oil, the pressure in the gas circuit (3) increasing in order to raise the vehicle from a low position to a high position; Characterized in that the motor vehicle oil-gas shock absorber further comprises: - a first gas reservoir (15) at a pressure P1 and a second gas reservoir (17) at a pressure P2 lower than P1; Furthermore, the gas circuit (3) is brought from a pressure P0, which is lower than P2, at which the vehicle is in the low position, to a pressure P2 at which the vehicle is in the high position, by successively connecting the first gas reservoir and the second gas reservoir (15, 17) to the gas circuit (3) and isolating the first reservoir (15).

2. The motor vehicle oil-gas shock absorber (1) according to claim 1, characterized in that: The gas circuit (3) comprises a gas exhaust valve (12) suitable for exhausting the gas contained in the gas circuit (3).

3. The motor vehicle oil-gas shock absorber (1) according to claim 1 or 2, characterized in that: The gas circuit (3) is brought from the pressure P2 to the pressure P0 by successively isolating the first reservoir and the second reservoir (15, 17) and opening the exhaust valve (12) to exhaust gas from the circuit (3).

4. The motor vehicle oil-gas shock absorber (1) according to any one of claims 1 to 3, characterized in that The gas circuit (3) comprises a first isolation valve (16) located at the first reservoir (15) and a second isolation valve (18) located at the second reservoir (17); the first isolation valve and the second isolation valve (16, 18) are capable of isolating the first reservoir and the second reservoir (15, 17) from the gas circuit (3).

5. The motor vehicle oil-gas shock absorber (1) according to any one of claims 1 to 4, characterized in that The gas circuit (3) comprises an intermediate valve (19) which is located between the first reservoir and the second reservoir (15, 17) and is capable of isolating a part of the gas circuit (3).

6. The motor vehicle oil-gas shock absorber (1) according to any one of claims 1 to 5, characterized in that The first reservoir (15) is located between the exhaust valve (12) and the intermediate valve (19), and the second reservoir (17) is located between the intermediate valve (19) and the buffer chamber (4).

7. A motor vehicle oil-gas shock absorber (1) according to any one of claims 1 to 6, characterized in that The valves used are electrically operated valves.

8. The motor vehicle oil-gas shock absorber (1) according to any one of claims 1 to 7, characterized in that The gas circuit (3) comprises a compressor (9) located upstream of the first reservoir and the second reservoir (15, 17).

9. The motor vehicle oil-gas shock absorber (1) according to any one of claims 1 to 8, characterized in that The gas circuit (3) comprises a gas inlet (8) followed by a filter (10) located upstream of the compressor (9).

10. A motor vehicle comprising the oil-gas shock absorber (1) according to any one of claims 1 to 9.

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