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Hydropneumatic suspension: the principle of operation

Hydropneumatic suspension is an automotive unit that consists of elastic elements interacting with each other by means of hydraulic and pneumatic force. The modern system of this design is known under the name Hydractive. The third generation provides automatic adjustment of characteristics, which makes the node active, depending on the road and other transport conditions. Consider the features and characteristics of this unit.

History of creation

For the first time hydropneumatic suspension "Citroen" appeared in 1954. It is on this brand of the car that a more modern system, in comparison with analogues, has been tried. Over the past period, designers have been actively revising this site, making drastic changes to it.

In modern times, the third generation of this type of active suspension is being used. The design makes it possible to minimize the impact of the human factor. A similar system under license is also used by companies, Rolls-Royce and Mercedes.

Advantages

The main advantage of the hydropneumatic suspension is the smooth operation and minimal impact transmission to the car body. In addition, it is possible to adjust the ride height. The last generation of the system under consideration is capable of adapting to the driving style. High efficiency quenches the vibrations even when driving fast on rough roads or sharp corners.

Manufacturers with an official right to release the system in question often combine it with analogues such as "McPherson". Complexity of design and high price cause that this unit is used mainly on expensive cars.

For example, the hydropneumatic suspension "Citroen C5" aggregates with a multi-link block in the rear, and in front is combined with "McPherson". This combination makes it cheaper and easier to maintain. The main development of the node goes in two directions: the expansion of the functional and the increase in the reliability index.

Device

Hydropneumatic suspension of the last generation consists of the following elements:

  • Front suspension brackets;
  • Hydropneumatic cylinders on the rear axle;
  • Hydraulic and electronic unit;
  • Reservoir for working fluid.

Each part fulfills its function, but, in some cases, there may still be a contour of the hydraulic power steering.

The combined hydroelectric unit (BBB) provides a stable system pressure and liquid level. Additional devices include:

  • Electric motor;
  • pump;
  • piston;
  • Electronic management;
  • Shutoff and safety valve.

The container with liquid is placed above the BBB. The front pillar combines hydropneumatics and a cylinder, and between them is a damper valve, responsible for reducing the oscillations of the body of the car.

Working element and cylinder

Hydropneumatic suspension is equipped with a detail, which is a metal sphere, inside of which there is a multilayered membrane. Above it the space is filled with liquefied nitrogen, and in the lower part there is a special liquid. Consequently, the liquid gives pressure, and the gas serves as the main elastic element.

The last modification of the considered node is equipped with one elastic piece for each wheel and a pair of spheres on the axis of the car. Additional elastic elements significantly increase the range of stiffness correction, and the spheres of gray color used in the system have a working resource of at least 200 thousand kilometers.

Hydraulic cylinder serves to accumulate fluid intended for elastic elements. In addition, it performs the function of a body height regulator relative to the track. The part consists of a rod, a piston connected to the suspension arm. The front and rear cylinders are identical in design, but the rear specimens are placed at an angle.

Stiffness regulator

This part is designed to change the rigidity of the suspension. The regulator consists of an amortization and an electromagnetic valve, a spool and an additional sphere. To achieve ultimate softness, the unit allows the maximum internal volume of the gas to be pumped. In this case, the solenoid valve is disconnected from the power supply.

When the solenoid valve is activated, the hydropneumatic suspension switches to hard mode. In this case, the rear cylinders, additional spheres and racks are isolated from each other.

The input additional devices of the system include sensors, mode switches. On the node type Hydractive 3 there are sensors for measuring the height of the body and the angle of the rudder. Another indicator monitors the speed and rotation of the steering wheel. The mode switch forcibly sets the height of the machine and the rigidity of the suspension.

Electronic control unit

The computer serves to receive and process signals from input devices. Then it gives a signal to the suspension devices. The electronic control unit normally functions in tandem with the engine monitoring system and anti-lock brakes.

The actuators of the hydropneumatic suspension Citroen include an electric pump motor, headlight corrector, valves. The electric motor controls the speed of rotation, the pressure in the system and the productivity of the pump. In the last generation of the node under consideration, four electromagnetic valves are used, two of which regulate the rear axle, and the remaining pair - the front analog. Advantageously, these elements are placed in the liquid level regulators.

Principle of operation of hydropneumatic suspension

The node under consideration serves for automatic control of the ground clearance, adjustment of rigidity and forced change of these indicators. Correction of clearance is taking into account the speed of movement, driving style and road coverage. For example, at a speed of more than 110 km / h the clearance is automatically reduced by 15 millimeters. On a bad road and low speed (60 km / h or less), this parameter increases by 20 mm. It is worth noting that the height is maintained regardless of the load.

This possibility exists because of the special fluid circulating in the circuit of the system. This makes it possible to maintain a given level of the body of the car when driving on a rough road.

The work of the hydropneumatic suspension category "+" is characterized by the fact that it provides for automatic adjustment of the stiffness depending on the acceleration during bends, with sudden braking and straight movement. The control unit takes into account the vehicle speed, steering parameters and other aspects that change during the ride.

The system automatically controls the electromagnetic stiffness valve in automatic mode, increasing or decreasing this value. Hardness can vary on a particular wheel or on all elements. The designers also provided manual control of the change in ground clearance.

Repair and service

Hydropneumatic suspension, the device of which is discussed above, is quite expensive. Consequently, its repair will also cost "a pretty penny." Below are the estimated prices for repair of certain elements of the system:

  • Repair of hydraulic shock absorber - from two thousand rubles.
  • Replacement of the stiffener - from 4,5 thousand.
  • A similar procedure for the anterior sphere is 700 rubles and more.
  • The cost of the liquid used in the third generation is not less than 600 rubles.

The final cost depends on the assembly of the unit and the year of manufacture of the machine. It is worth noting that the failure of one of the parts often leads to the failure of other elements. As you can see, the service will have to be spent, but it's worth it.

Hydropneumatic suspension "Citroen C5": reviews

As the owners confirm, the main advantage of the Citroën C5 is the availability of the described suspension. And, no matter how it is criticized by competitors, it allows you to keep the car confidently and smoothly on virtually any road surface. The considered unit allows to adjust the clearance from 15 to 20 millimeters in the direction of reduction or increase. And it happens in automatic mode.

Among the other advantages, users note a smooth ride, easy disassembly of wheels and durability of the unit. To the negative features consumers attribute the high cost of repairs. In addition, when moving almost no holes and potholes are noticed, which leads to more intensive wear of the suspension

Conclusion

Hydropneumatic suspension is undoubtedly a breakthrough in the automotive industry. It automatically allows you to adjust a whole range of parameters. Apparently, it's not for nothing that a license for its use was acquired by such giants of the automobile industry as Rolls-Royce, Maserati and Mercedes. However, the first variations came up with Paul Mage (the French designer).

The starting test of the innovative node occurred on the Citroen Traction Avant in 1954. The company is still successfully using this system, constantly updating and updating it. With the advancement of progress, radical improvements are possible, but one of the best in its class is the third generation Hydropive hydropneumatic suspension.

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