Driving a modern car, especially a heavy SUV or executive sedan, would be almost impossible without additional systems that make the driver’s work easier. Power steering (Power Steering) has become a standard in the auto industry, allowing you to turn the steering wheel with one finger even at low speeds or when parking. This system is based on Pascal's simple physical law, which states that the pressure exerted on a fluid in a confined space is transmitted without change in all directions.
Understanding exactly how this mechanism functions allows you not only to correctly diagnose emerging problems, but also to significantly extend the life of expensive components. Many car enthusiasts take the operation of the amplifier for granted until they hear a characteristic howl or feel a sharp weighting of the steering wheel. Hydraulic system requires careful attention to the quality of the working fluid and the condition of the seals, since it is these factors that determine the durability of the entire unit.
In this article, we will analyze in detail the structure of a classic hydraulic booster, trace the path of the working fluid and find out why modern electro-hydraulic systems (EGUR) are gradually replacing classical solutions. You will learn which components are under the greatest load and how to avoid critical mistakes when operating a car in winter.
Main components of the power steering system
Structurally, the power steering system is a closed circuit consisting of several key elements. The heart of the mechanism is power steering pump, which creates the necessary pressure in the system. This is usually a vane type pump that is driven by a belt from the engine crankshaft. It is this that forces the fluid to circulate through the tubes, providing an instant response to turning the steering wheel.
The second most important element is the distribution mechanism, often integrated into steering rack or a separate spool assembly. It reacts to the rotation of the steering shaft and directs the flow of fluid under pressure into the desired cavity of the hydraulic cylinder. The third component is the hydraulic cylinder itself, which creates a force that pushes the rack in the direction the wheels turn.
- 🔧 Expansion tank: A reservoir for storing a supply of liquid, equipped with a filter and a pressure relief valve.
- 🔧 Highways: high-strength high and low pressure hoses that connect all components into a single system.
- 🔧 Working fluid (ATF): special oil that transmits force and lubricates rubbing pairs.
⚠️ Attention: Using a fluid that does not meet the manufacturer's specifications (for example, mixing mineral and synthetic oils) can cause the rubber seals to swell and cause rapid system failure.
Operating cycle: from idle to turning
The operating principle of power steering is based on constant oil circulation, even when the driver does not perform any actions. In neutral position, when the steering wheel is stationary, distributor configured so that the liquid circulates freely from the pump back to the tank via the “return”. The pressure in the system at this moment is minimal, which reduces the load on the drive belt and the pump itself.
The situation changes dramatically the moment the driver begins to turn the steering wheel. Torque is transmitted to the distributor torsion bar, which twists slightly. This displacement opens channels that direct high-pressure oil flow into one of the hydraulic cylinder chambers. The piston begins to move under pressure, helping the driver turn the wheels.
Warm up the engine before active driving in winter: cold, thick oil circulates less well, which can cause temporary “biting” of the steering wheel and increased wear on the pump in the first minutes of operation.
As soon as the driver stops turning the steering wheel, but keeps it in the turned position, the system goes into hold mode. Spool mechanism closes the drain, and the pressure in the working chamber is stabilized, holding the wheels in the given position. If the driver suddenly releases the steering wheel, the torsion bar will return to its original position, and the fluid will again flow in a low-pressure circle.
The role of the distributor and spool mechanism
The most complex and precise component in the entire system is the distributor. It is he who determines exactly where the liquid should go. Inside it is spool, which can move relative to the body. When the steering wheel is turned, the shaft moves the spool, allowing high-pressure oil to enter the corresponding cavity.
The sensitivity of this mechanism directly affects the “sharpness” of the steering. If the gaps in the distributor increase due to wear, the steering wheel becomes less informative and play appears. In some designs, the distributor is combined with rotary pump, which makes the unit compact, but difficult to repair.
What is reactive action in power steering?
As vehicle speed increases, the system automatically reduces the efficiency of the amplifier. This is done so that on the highway the steering wheel is not too light and the driver feels the road, ensuring directional stability.
It is important to note that the distributor also functions as a fuse. If the pressure in the system exceeds a critical level (for example, when the wheels rest against a curb), the bypass valve is activated, allowing some of the fluid to bypass. This prevents hoses from bursting and pump failure.
Pump types and their characteristics
The efficiency of the entire system depends on the performance of the pump. In the automotive industry, vane pumps are the most common type. They provide stable pressure and have high efficiency. However, there are other designs, each of which has its own operating and maintenance features.
Let's compare the main characteristics of different types of pumps to understand what you have to deal with when servicing different cars.
| Pump type | Operating principle | Resource | Features |
|---|---|---|---|
| Lamellar | Operation of blades in an oval stator | High | Low noise level, sensitive to oil purity |
| Gear | Meshing of gears | Medium | Simple design but high pressure pulsation |
| Axial piston | Piston movement parallel to the shaft | Very tall | Used in heavy equipment, complex and expensive |
Most common vane pumps require regular fluid replacement, since wear products of the plates and stator quickly contaminate the system. Abrasive particles act like sandpaper, accelerating wear of all rubbing surfaces.
Typical faults and their symptoms
Despite its reliability, the hydraulic system is subject to wear. The first sign of problems is often noise. A hum or whine when turning the steering wheel indicates that there is air in the system (cavitation) or the pump is working at its limit due to low fluid levels.
Fluid leakage is the second most common problem. O-rings and seals become tanned and lose elasticity over time. A leak can occur on the rack rod, at the joints of the tubes, or in the pump itself. Loss of tightness It is dangerous not only because the oil level drops, but also because of the risk of fire if liquid gets onto the hot outlet.
- 🚗 Heavy steering: Indicates a loose belt, low fluid level, or worn pump.
- 🚗 Jerks when rotating: often indicate air has entered the system or the distributor is dirty.
- 🚗 Oily stains under the car: a direct sign of a leak in the hoses or seals.
⚠️ Attention: Holding the steering wheel in the extreme position for a long time (more than 5 seconds) leads to a sharp jump in pressure and temperature, which can squeeze out the seals or damage the pump.
☑️ DIY power steering diagnostics
Maintenance and service life extension
To power steering served for a long time, it is necessary to follow the rules for replacing the working fluid. Although many manufacturers claim that the oil is filled for its entire service life, practice shows that its properties degrade after 60-80 thousand kilometers. Old oil loses its lubricating properties and accumulates wear products.
When replacing a fluid, it is important not just to add a new one, but to carry out the procedure of completely replacing or flushing the system, if this is provided for by the design. You should also regularly check the condition of the drive belt: overtightening it creates excessive load on the pump bearings, and weak tension leads to slipping and lack of pressure.
Regularly replacing ATF fluid and using only oil brands recommended by the manufacturer is the only way to avoid costly repairs to the steering rack and pump.
During winter operation, you should be especially careful. Sudden jerking of the steering wheel on a cold car can damage the seals due to the high viscosity of the oil. Allow the engine to warm up before actively maneuvering into a parking lot.
Why does the power steering hum after changing the fluid?
A hum after replacement often occurs due to air in the system. When adding new fluid, air enters the tank, which is then sucked in by the pump. It is necessary to smoothly turn the steering wheel from lock to lock several times (without holding it in extreme positions) with the engine running to expel air pockets.
Is it possible to drive if the power steering is leaking?
A short trip to service is possible if the fluid level is still sufficient. However, driving with a dry pump will cause it to instantly jam. In addition, oil that gets on the generator or timing belt can cause it to slip or break, which will lead to more serious damage.
What kind of fluid should I put in the power steering?
It is necessary to use only the fluid that is indicated in the vehicle’s service book (usually ATF Dexron II, III or special CHF fluids for PSA/BMW systems). Mixing different types of oils (for example, mineral and synthetic) is prohibited, as this may cause a chemical reaction and destruction of the rubber elements.