To extend the service life of the power steering, change the fluid at least once every 60-80 thousand kilometers or every 3-4 years of operation.
A sharp creaking sound when turning the steering wheel in a static position most often indicates a critical drop in pressure in the system or a malfunction vane pump, which requires immediate diagnosis of the node. Loss of hydraulic pressure makes steering difficult and dangerous, therefore, understanding the principles of operation of this mechanism is necessary for every car owner to identify problems in a timely manner. The design of the system, despite its apparent simplicity, includes precision friction pairs that are sensitive to the quality of the oil and the cleanliness of the circuit. Unlike its electric counterparts, the classic hydraulic booster creates a constant pressure, which is redistributed depending on the forces applied by the driver to the steering wheel.
The basis of operation is a closed circuit filled with a special ATF fluid, which simultaneously serves as a working fluid and a lubricant. Pumping equipment, driven by a belt from the engine crankshaft, pumps fluid under high pressure, providing instant response of the mechanism. Any airiness or moisture entering the circuit leads to cavitation and rapid wear of internal surfaces, so the tightness of the system is a priority during maintenance.
Main components of the power steering system
The power steering system consists of several key components, each of which performs a strictly defined function in the overall power steering scheme. The central element is high pressure pump, which creates the required fluid flow. It can be of the vane or rotor type, with vane designs becoming more widespread due to their high efficiency and durability when properly maintained. The pump is connected to the fluid reservoir via a low-pressure hose and to the steering mechanism via a high-pressure line.
The second most important element is distributor, which is often built directly into the steering column shaft or steering rack housing. It is this unit that doses the supply of fluid into the working cavities of the hydraulic cylinder depending on the angle of rotation of the steering wheel. Inside the distributor there is a torsion bar, which twists when the steering wheel is turned, displacing the spool and opening the channels for oil supply. Accuracy of work spool mechanism directly affects the sharpness and information content of the steering.
The third component is itself hydraulic cylinder, which can be a separate unit (in systems with a bipod) or integrated into the steering rack. The cylinder contains a piston with a rod, which, under the influence of fluid pressure, moves and pushes the rods, turning the wheels. The system also includes an expansion tank with a filter element, where the liquid is cooled and air bubbles are separated. All elements are connected by pipelines, which must withstand pressure pulsations and vibrations.
Operating principle and fluid circulation diagram
The operating cycle of the system begins with the rotation of the pump pulley, which sucks liquid from the tank and pumps it into the high-pressure line. When the steering wheel is stationary, the fluid circulates along the “idle” circuit, returning to the reservoir through the bypass valve, since the distributor spool is closed. The pressure in the system at this moment is minimal, which reduces the load on the drive belt and the pump itself. As soon as the driver begins to turn the steering wheel, the torsion bar twists and the spool moves, opening the way for oil into one of the working cavities of the cylinder.
Under the influence of pressure, the hydraulic cylinder piston moves, creating a force that is added to the mechanical force of the driver. This makes it easy to turn even heavy wheels on trucks and SUVs. Safety valve, built into the pump or distributor, prevents the creation of excess pressure that could rupture hoses or damage seals. When the limit value is reached, the valve opens and part of the liquid is discharged back to the pump inlet or into the tank.
- 🔄 Liquid is sucked out of the tank through the inlet pipe under the influence of rarefaction.
- ⚡ The pump creates pressure from 70 to 150 bar depending on engine speed.
- ⚙️ The spool distributes flows depending on the direction of rotation of the steering wheel.
- ↩️ The waste liquid is drained back into the tank for cooling and filtration.
It is important to note that the system operates in constant mode as long as the car engine is running. This distinguishes classic power steering from electrohydraulic systems, where the pump is turned on only when necessary. Constant circulation ensures that the mechanism is instantly ready for operation, but also leads to the constant consumption of part of the engine power to drive the pump. Circulation scheme must be completely sealed, since even a small leak upsets the pressure balance.
⚠️ Attention: Holding the steering wheel in the extreme position for a long time (more than 5 seconds) leads to a sharp increase in fluid temperature and overload of the pump, since pressure is released through a bypass valve inside the housing.
Design and types of power steering pumps
The pump is the heart of the system, and the efficiency of the entire unit depends on its health. Most modern cars use vane pumps, which ensure a uniform supply of liquid with minimal pulsations. The main elements of such a pump are a rotor, a stator, plates (blades) and a distribution disc. The plates move freely in the rotor slots under the influence of centrifugal force and fluid pressure, pressing tightly against the inner surface of the stator.
As the rotor rotates, the volume of the chambers between the blades changes: in the suction zone it increases, creating a vacuum, and in the discharge zone it decreases, pushing out liquid under pressure. The pump is designed with O-rings and seals to prevent leakage and fluid flow between the high and low pressure areas inside the housing. Wear of these elements leads to a drop in performance and noise.
There are also variable displacement pumps that can change the volume of the working chamber depending on the needs of the system, which saves fuel. However, in the mass segment, unregulated models with a bypass valve predominate. Pump life directly depends on the quality of the fluid used and the timeliness of its replacement. The ingress of abrasive particles causes wear on the surface of the stator and the ends of the plates, which cannot be eliminated by grinding.
Technical features of vane pumps
In vane pumps, the clearance between the ends of the vanes and the distribution discs is critical. Even a microscopic increase in this gap due to wear leads to a drop in efficiency. Modern pumps often have Teflon or composite plates, which are less sensitive to oil quality, but are afraid of overheating.
Power steering rack
An integrated steering rack with power steering is a complex mechanical-hydraulic unit, where the cylinder body is part of the rack body. A piston moves inside the cylinder, attached to the rack rod or being its extension. Fluid pressure is applied alternately to the right or left cavities of the cylinder, helping the gear to turn the rack. The piston seal is ensured by cuffs, the condition of which is determined by the absence of internal leaks.
The distributor in such systems is usually made in the form of a spool shaft connected to the input shaft of the steering column. When the shaft is turned, the spool moves relative to the housing, opening the oil supply channels. The design requires high manufacturing precision, since the gaps between the spool and the body are microns. Any dirt or metal shavings can jam the spool, leading to power failure or spontaneous steering.
A typical problem with such racks is wear of the oil seals and seals, which leads to fluid leakage outward or into the inner cover (boot). Oil getting into the boot swells it and indicates the need to overhaul the unit. Rail repair often includes replacing seals, grinding the shaft (if there is no deep groove) and adjusting the clamping nut clearance.
| System element | Function | Typical fault | Symptom |
|---|---|---|---|
| Power steering pump | Creating pressure | Wear of plates/oil seal | Howl, hum, foam in the tank |
| Steering rack | Effort Conversion | Seal leakage, backlash | Knock, oil leak, beating |
| Tank with filter | Storage and cleaning | Clogged filter | Level drop, noise |
| Hoses and pipes | Transporting liquids | Cracks, delamination | Oil stains under the car |
Power steering fluid: properties and replacement
Power steering fluid (ATF) is the working fluid of the system, transmitting energy and lubricating rubbing pairs. It must have stable viscosity characteristics over a wide temperature range, anti-foam properties and oxidation resistance. Unlike brake fluid, power steering oils are mineral or synthetic based, and mixing them is not always acceptable, although standards often overlap with transmission oils.
During operation, the liquid loses its properties: wear products, moisture and air accumulate in it. Darkening of the oil and the appearance of a burning smell indicate overheating and destruction of the additives. Fluid replacement should be done by completely replacing or pumping the system, since simple cream from the tank renews only 30-40% of the volume. Using a low-quality analogue can lead to swelling of the rubber seals and failure of the system.
- 🔴 Dexron-based fluids usually have a red color (often compatible with automatic transmissions).
- 🟢 Green color is characteristic of specific oils (for example, Pentosin), they cannot be mixed.
- 🌡️ The operating temperature of the liquid can reach 100°C and higher during active work.
☑️ Checking the condition of the power steering fluid
⚠️ Attention: If an emulsion (whitish coating) is detected in a liquid, it is necessary to urgently look for the cause of water ingress, since water causes corrosion of metal parts and destruction of rubber seals.
Diagnostics and typical faults
Diagnosis of the power steering system begins with a visual inspection for leaks and checking the fluid level. If the level constantly drops and there are no external leaks, the oil is probably leaking through the rack seals and into the anthers. Extraneous sounds during pump operation (squealing, humming) often indicate wear of the bearings or air entering the system. Air in the circuit also causes foaming of the liquid in the tank and unstable operation of the amplifier.
Heavy steering may be the result of weak drive belt tension, low fluid level, or a malfunction of the pump itself. If the steering wheel “bites” or turns jerkily, the problem may lie in a dirty distributor or a stuck spool. Pressure diagnostics using a pressure gauge connected to the line gap allows you to accurately determine the pump performance and the condition of the bypass valve.
A common malfunction is wear of the distributor torsion bar, which leads to loss of feedback and a “wobbly” steering wheel. In some cases, spontaneous rotation of the wheels is observed, which indicates a misalignment of the spool or the presence of internal leaks in the rack. Repairs often require specialized tools and clean conditions to handle precision vapors.
The main sign of a power steering malfunction is a change in the force on the steering wheel and the appearance of extraneous sounds, ignoring which leads to a complete failure of the system and an accident.
Frequently asked questions (FAQ)
Is it possible to drive if the power steering is leaking?
Highly not recommended. Loss of fluid will lead to dry friction of the pump, its rapid destruction and steering jamming, which is life-threatening. In addition, oil getting on the generator or timing belt can cause it to slip or break.
What kind of fluid should I pour into the power steering if it is not specified in the instructions?
It is necessary to select the fluid strictly according to the vehicle manufacturer’s approval or the color/type of the one already filled (if the system has not been repaired). The most commonly used fluids are ATF Dexron II/III, but European cars may require specific formulations (Pentosin and analogues).
Why does the power steering pump hum when cold?
A hum when cold is often caused by thickening of the liquid, wear of the pump shaft seal (air leakage) or the development of friction in pairs. The reason may also be a low fluid level or a clogged filter mesh in the tank.
How often should the power steering fluid be changed?
The regulations depend on the manufacturer, but on average it is recommended to replace them every 60-80 thousand kilometers or once every 3-5 years. If signs of contamination or darkening of the liquid appear, the interval should be shortened.
What happens if you pour fluid into the power steering reservoir?
When the fluid heats up, it expands and excess pressure can force oil out of the reservoir vent, causing contamination in the engine compartment and a risk of fire if it comes into contact with hot engine parts.