Oleo-pneumatic shock absorber for motor vehicle suspension

Abstract

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

Description

[0001] Title of the invention: Oleo-pneumatic shock absorber for motor vehicle suspension

[0002] The invention relates to an oleopneumatic shock absorber for a suspension of a motor vehicle.

[0003] The invention relates more specifically to an oleopneumatic shock absorber allowing not only to play its role as a shock absorber, but also to adjust the ground clearance.

[0004] The suspension of motor vehicles is usually equipped with a shock absorber system to improve passenger comfort when the vehicle is in motion. This system absorbs vibrations from the vehicle's chassis.

[0005] Known oleopneumatic shock absorbers also allow the vehicle's ground clearance to be varied to meet different user needs. For example, lowering the vehicle is advantageous for reducing air friction resistance and thus reducing fuel consumption. Conversely, it is sometimes useful to raise the vehicle and have greater ground clearance when the road surface is damaged. Document JP2007253921 relates to a device intended to meet this need. This document presents a vehicle damping system that also allows the vehicle's ground clearance to be adjusted while it is moving or when it is stationary. In this system, each of the wheel suspension components is equipped with an oleopneumatic shock absorber.This system comprises, on one side, a hydraulic circuit and on the other, a compressed gas circuit, the two circuits being separated from each other by a movable piston inside a cylindrical chamber. The hydraulic circuit comprises a damping member and a device for supplying and discharging the working liquid. The compressed gas circuit also comprises a device for supplying and discharging the gas.

[0006] The working liquid supply and discharge device comprises a first cylindrical chamber for storing the liquid and supplying the damper, while the air supply and discharge device comprises a second cylindrical chamber supplied with air by a pump, the air being taken directly from outside the system.

[0007] Thus the entry of air into the fuel circuit causes the thrust of the moving piston and causes the thrust of the working fluid in the shock absorber, which increases the ground clearance of the vehicle

[0008] This solution provides an economical system for varying the vehicle's ground clearance depending on driving conditions.

[0009] However, the air used in the system is drawn by a pump outside the system. Therefore, high pump power is required to vary the air pressure in real time in the system to raise the vehicle's ground clearance.

[0010] Additionally, the pneumatic system as described may have significant problems with variation in pneumatic stiffness between low pressure to decrease the vehicle's ground clearance and high pressure to increase it.

[0011] Thus, there is a need to find an economical solution to reduce the power of the air pump at the system inlet as well as to limit the problems of pneumatic stiffness variation.

[0012] To this end, according to a first object, an oleopneumatic shock absorber for a motor vehicle is proposed comprising:

[0013] - an oil circuit comprising a cylinder and a piston adapted to slide in said cylinder;

[0014] - a gas circuit located upstream of said oil circuit and a buffer chamber located between said gas circuit and said oil circuit, said buffer chamber comprising a sealed movable wall between the gas and the oil, while the pressure of said gas circuit is increased to bring said vehicle from a low position to a high position; said oleopneumatic shock absorber further comprises:

[0015] - a first gas tank at a pressure PI and a second gas tank at a pressure P2 lower than PI; and said gas circuit is brought from a pressure PO lower than P2, in which said vehicle is in said low position, to the pressure P2 in which said vehicle is in said high position by successively connecting said first and second gas tanks to said gas circuit, and isolating said first tank.

[0016] The presence of the first tank improves the response time of the vehicle's raising. Indeed, the pressure of the first tank is higher than the pressure required to raise the vehicle. Therefore, when the first air tank is connected to the gas circuit, it supplies the gas circuit more quickly to bring it to the necessary pressure.

[0017] The second reservoir solves the circuit's compressibility problems. Indeed, the second reservoir increases the volume of the gas circuit upstream of the oil circuit. Thus, by increasing the volume of compressible fluid, in this case gas, the apparent stiffness of the gas circuit is reduced when the circuit is at high pressure, i.e. in the vehicle's high position. Advantageously, the gas circuit includes a purge valve adapted to evacuate the gas from the circuit, so that the pressure of the gas circuit is reduced.

[0018] Advantageously, the gas circuit is brought from pressure P2 to pressure PO by successively isolating the first and second tanks, and by opening the purge valve to evacuate the gas from the circuit.

[0019] However, the gas in the circuit is not completely evacuated by the purge, since enough gas is needed in the circuit to maintain a pressure PO in the gas circuit. Therefore, the purge valve also has a calibrated valve so as not to completely empty the gas circuit. The valve then closes when the pressure in the gas circuit has decreased to reach the pressure PO.

[0020] The purpose of changing from pressure P2 to pressure PO in the gas circuit is to move the vehicle from the high position to the low position.

[0021] Advantageously, the gas circuit comprises a first isolation valve at the first tank and a second isolation valve at the second tank; said first and second isolation valves are capable of isolating the first and second tanks from the gas circuit.

[0022] The valves allow the isolation of the first and second tanks from the gas circuit when necessary when switching from the high position to the low position and vice versa. Advantageously, the gas circuit comprises an intermediate valve between the first and second tanks capable of isolating a portion of the gas circuit.

[0023] When the gas circuit is at pressure PO, the pressure of the first tank must be increased from pressure P2 to pressure PL. Thus, the part of the circuit comprising the first tank must be isolated from the rest of the gas circuit to maintain the pressure of the gas circuit. Advantageously, the first tank is located between the purge valve and the intermediate valve and the second tank is located between the intermediate valve and the buffer chamber. Advantageously, the valves used are solenoid valves.

[0024] The use of solenoid valves allows the automation of the system so that the user can move from one position to another without the need to make manual changes.

[0025] Advantageously, the gas circuit comprises a compressor upstream of the first and second tanks.

[0026] The compressor is capable of compressing the air to the target pressure of the first tank in masked time when the vehicle is in the high position. Thus, the compressor can operate for a long period of time, thus allowing its size to be reduced. Advantageously, the gas circuit includes a gas inlet followed by a filter upstream of the compressor.

[0027] To increase the circuit pressure, the compressor will suck in air from outside the circuit through the gas inlet. The filter placed between the compressor and the gas inlet is able to block fine particles that could enter the circuit and thus prevent them from damaging or accumulating in the equipment or the gas circuit.

[0028] The invention also relates, according to another subject, to a motor vehicle comprising an oleopneumatic shock absorber as described previously.

[0029] Other features and advantages of the invention will emerge from reading the description given below of several particular embodiments of the invention, given for informational purposes but not as a limitation, with reference to the single figure:

[0030] [Fig. 1] is a block diagram of an oleopneumatic shock absorber according to the invention. The invention relates to an oleopneumatic shock absorber 1 for a motor vehicle. The motor vehicle comprises suspensions on each of the wheels and a shock absorber is installed at each suspension in order to absorb vibrations of the chassis of the vehicle. The shock absorber 1 according to the invention is also capable of varying the ground clearance of the motor vehicle between a low position and a high position.

[0031] Figure 1 shows a single shock absorber 1 installed on a wheel, this figure therefore does not exclude the case where a shock absorber is mounted on each wheel of the vehicle, i.e. four wheels.

[0032] With reference to Figure 1, the oleopneumatic 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. The oil circuit 2 and the gas circuit 3 are separated from each other by a buffer chamber 4. It comprises a movable wall 5 sealed between the gas and the oil. The movable wall 5 thus separates the oil and the gas and prevents any rise of the oil in the gas circuit 3 and vice versa. This prevents the pump from blocking or the seals from deteriorating. In addition, the installation of the movable wall 5 at the shock absorber 1 makes it possible to dispense with the need for an oil purge in the oil circuit 2 when mounting or dismounting the shock absorber 1. The movable wall 5 may for example be a membrane, as illustrated in [Fig. 1], or a floating, or in other words, free, piston.

[0033] The oil circuit 2 comprises a cylinder 6 and a piston 7 adapted to slide in the cylinder 6. Also, the piston is integral with a rod 22 which extends outside the cylinder 6. When the motor vehicle jolts, for example, when a wheel of the vehicle encounters an obstacle, the oil contained in the cylinder 6 tends to be compressed by the piston 7. And consequently, the oil pressure increases in the buffer chamber 4 and the movable wall 5 deforms and also compresses the gas in the gas circuit 3. To rebalance the oil pressure on either side of the piston 7, the oil will then pass through the orifices included in the piston 7.

[0034] Thus, the gas in the circuit, which compresses more easily than the oil, helps to absorb the shock linked to the wheel, while the oil which passes through the piston orifices 7 tends to absorb the oscillations. The gas circuit 3 firstly comprises a gas inlet 8 followed by a compressor 10. Here, the gas inlet is an air inlet allowing outside air to enter the gas circuit 3. The purpose of the compressor 10 is to compress the air in the gas circuit 3 to increase its pressure, and this by taking ambient air through the gas inlet 8.

[0035] To prevent particles from clogging the circuit and accumulating inside, a filter 9 is placed between the compressor 10 and the gas inlet 8. Downstream of the compressor, a dryer 11 is also installed to dry the incoming gas.

[0036] The gas circuit 3 then comprises a purge valve 12 downstream of the desiccator 11. The purge valve 12 allows the gas to be released from the gas circuit 3 and thus to reduce the pressure inside the gas circuit 3. The purge valve 12 evacuates the gas from the circuit via an exhaust 13. Between the exhaust 13 and the purge valve 12, a calibrated valve 14 allows a minimum quantity of gas to be kept in the gas circuit 3 to maintain a minimum pressure in the circuit 3.

[0037] A first gas tank 15 capable of storing compressed gas is installed downstream of the purge valve 12. A first isolation valve 16 is installed at the inlet of the first tank 15 to be able to isolate it from the gas circuit 3.

[0038] Between the buffer chamber 4 and the first tank 15, the gas circuit 3 comprises a second gas tank 17 capable of also storing compressed gas. A second isolation valve 18 is installed at the inlet of the second tank 17 to isolate it from the gas circuit 3.

[0039] Finally, the gas circuit 3 comprises an intermediate valve 19 between the first and second reservoirs 15 and 17. The intermediate valve 19 is capable of isolating a downstream part of the gas circuit 3 leading to the buffer chamber 4 and including the second gas reservoir 17 from an upstream part including in particular the first gas reservoir 15.

[0040] Optionally, upstream of the buffer chamber 4, a separation valve 20 is installed. The separation valve 20 is adapted to isolate the buffer chamber 4 as well as the oil circuit 2 from the rest of the gas circuit 3.

[0041] Preferably, the valves used are solenoid valves to make the control of the oleopneumatic shock absorber 1 automatic.

[0042] In a preferred embodiment, for each wheel of the vehicle, and for each of the associated suspensions, an oil circuit 3 and a buffer chamber 4 are installed, while the gas circuit is common to all the buffer chambers.

[0043] The oleopneumatic shock absorber 1 according to the invention makes it possible to vary the ground clearance of the vehicle between a low position and a high position.

[0044] The purpose of the first tank 15 is to improve the response time when the pressure in the gas circuit is increased in order to raise the vehicle. Indeed, the pressure in the first tank is higher than the pressure required to maintain the vehicle in the raised position. Thus, the first compressed air tank 15 allows the circuit to be quickly brought to the required pressure. The use of the first tank 15 also allows the size and power of the compressor 10 to be limited since it is not used in real time to increase the pressure in the entire gas circuit 3. In addition, the compressor 10 operates in masked time when the compressor is in the raised position, which also allows the size of the compressor 10 to be reduced. In other words, the compressor 10 allows pressurized air to be accumulated in the first tank 15. And it can do this relatively slowly.

[0045] The second reservoir 17 has a different purpose from the first reservoir 15. It makes it possible to solve the problems of compressibility of the circuit, thus making it possible to reduce the apparent stiffness of the gas circuit when it is at high pressure. Indeed, 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 compressible fluid, here 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 to be pressurized to move from the low position to the high position and thus to reduce the volume of the first reservoir 15.

[0046] When the vehicle is in the low position, the first gas tank 15 is at a pressure PI while the second gas tank 17 is at a pressure P2 lower than the pressure PL. The gas circuit 3, for its part, is at a pressure PO. In the low position, the intermediate valve 19, the purge valve 12, and the first and second isolation valves 16, 18 are closed.

[0047] Optionally, if a separation valve 20 is installed between the buffer chamber 4 and the second tank, then it is open in the high position.

[0048] The use of a separation valve 20 thus makes it possible to reduce the volume of useful gas at high pressure to maintain the vehicle in the high position, and to increase the stiffness of the shock absorber 1.

[0049] For automation of the shock absorber, it comprises a 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 device for controlling the valves of the shock absorber. The control device comprises at least one processor to be able to control the actuators according to the pressure values.

[0050] For example, the first gas tank 15 is at a pressure PI of 40 bars while the second gas tank 17 is at a pressure P2 of 30 bars. The pressure of the gas circuit is for example at a pressure PO of 3 bars corresponding to the low position of the vehicle.

[0051] To vary the vehicle from the low position to the high position, the following operations are carried out successively. The control device controls the opening of the intermediate valve 19, as well as the first and second isolation valves 16, 18 to connect the first and second gas tanks 15, 17 to the gas circuit 3. The gas circuit 3 is then brought to the pressure P2.

[0052] Thus, when the vehicle is in the high position, the pressures of the first tank 15, the second tank 17 and the gas circuit are balanced at a pressure P2. Once the high position is reached, the control device controls the closing of the intermediate valve 19.

[0053] When the vehicle is in the high position, the compressor is activated to be able to increase the pressure of the first tank 15 until it reaches the pressure PL Once this pressure is reached in the first tank 15, the compressor is stopped and the isolation valve 16 of the first tank 15 is closed.

[0054] For example, in the high position, the gas circuit 3 and the first and second gas tanks 15, 17 are at pressure P2 of 30 bars. When the compressor is operating, the pressure of the first tank 15 is brought to pressure PI of 40 bars.

[0055] Finally, to vary the height of the vehicle between the high position and the low position, the following operations are carried out successively. The control device controls the closing of the second isolation valve 18 as well as the opening of the intermediate valve 19 and the purge valve 12. Thus, the pressure of the second tank 17 is maintained at the pressure P2, while the pressure of the gas circuit 3 is lowered to the pressure PO by evacuating a portion of gas from the circuit through the purge valve. A residual portion of gas remains in the circuit to maintain the gas circuit 3 at a pressure PO.

[0056] Optionally, if a separation valve 20 is installed between the buffer chamber 4 and the second tank, then the control device commands the opening of this valve before purging the gas circuit 3. The oleopneumatic shock absorber 1 thus makes it possible to vary the ground clearance of a motor vehicle without making structural modifications to improve the response time for raising and lowering the vehicle while reducing the apparent stiffness of the high-pressure gas circuit.

Claims

Claims

1. Oleo-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 said cylinder (6); - a gas circuit (3) located upstream of said oil circuit (2) and a buffer chamber (4) located between said gas circuit (3) and said oil circuit (2), said buffer chamber (4) comprising a movable wall (5) sealed between the gas and the oil, while the pressure of said gas circuit (3) is increased to bring said vehicle from a low position to a high position; characterized in that it further comprises: - a first gas tank (15) at a pressure PI and a second gas tank (17) at a pressure P2 lower than PI; and in that said gas circuit (3) is brought from a pressure PO lower than P2, in which said vehicle is in said low position, to the pressure P2 in which said vehicle is in said high position by successively connecting said first and second gas tanks (15, 17) to said gas circuit (3), and isolating said first tank (15).

2. Oleo-pneumatic shock absorber (1) for a motor vehicle according to claim 1, characterized in that said gas circuit (3) comprises a purge valve (12) adapted to evacuate the gas included in the gas circuit (3).

3. Oleo-pneumatic shock absorber (1) for a motor vehicle according to claim 1 or 2, characterized in that the gas circuit (3) is brought from pressure P2 to pressure PO by successively isolating the first and second reservoirs (15, 17), and by opening the purge valve (12) to evacuate the gas from the circuit (3).

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

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

6. Oleo-pneumatic shock absorber (1) for a motor vehicle according to any one of claims 1 to 5, characterized in that the first reservoir (15) is located between the purge 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. Oleo-pneumatic shock absorber (1) for a motor vehicle according to any one of claims 1 to 6, characterized in that the valves used are solenoid valves.

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

9. Oleo-pneumatic shock absorber (1) for a motor vehicle 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) upstream of the compressor (9).

10. Motor vehicle comprising an oleopneumatic shock absorber (1) according to any one of claims 1 to 9.

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