The bearing of the car steering gear is a key component in the steering system, mainly responsible for supporting the rotation of the steering shaft or steering gear, ensuring the smoothness and accuracy of the steering operation. Its core working principle is based on rolling friction replacing sliding friction, combined with specific structural design to adapt to the complex force environment of the steering system. The following is its detailed working principle and key characteristics:
1. Bearing type and structure
Common types: Deep groove ball bearings: suitable for steering column support, bearing radial and mild axial loads.
Conical roller bearings: Used for steering knuckles or gearboxes, they can simultaneously withstand radial and axial loads (such as impact during vehicle bumps).
Angular contact ball bearing: In gear type steering gear (such as circular ball type), it bears joint loads and optimizes axial stiffness.
Structural composition: Inner ring: It fits with the steering shaft or interference fit and rotates with the shaft.
Outer ring: Installed on the steering column tube or gearbox, fixed in place.
Rolling element (steel ball/roller): Rolling between the inner and outer raceway to reduce friction.
Retainer: evenly separate rolling elements to prevent direct contact.
2. Working principle
Load transmission: Radial load: When turning, the lateral force feedback from the wheels on the ground is transmitted to the outer ring of the bearing through the steering mechanism, and the rolling elements disperse the force to the inner ring, ensuring stable rotation of the steering shaft.
Axial load: The steering wheel return torque or road impact is transmitted axially through the bearing, and the tapered roller bearing or angular contact ball bearing optimizes the axial bearing capacity through contact angle design (usually 15 °~40 °).
Motion conversion: In a gear rack and pinion steering system, bearings support the small gear shaft, converting the rotational motion of the steering wheel into linear motion of the gear rack to achieve wheel steering.
3. Lubrication and sealing
Lubrication method: Long term lubricating grease (such as lithium based grease) is used to fill about 30% of the space inside the bearing, reducing rolling friction and preventing rust.
Some high-end models adopt an oil lubrication system, which continuously supplies oil through an oil pump to reduce operating temperature.
Sealing design: Contact seal (rubber lip ring): prevents dust and moisture from entering, suitable for lightly polluted environments.
Non contact labyrinth seal: achieves dust prevention and reduces frictional resistance through gap control, suitable for high-speed scenarios.
4. Materials and lifespan
Material selection: Rolling elements/raceways: High carbon chromium bearing steel (GCr15), hardness HRC60~65, surface roughness Ra ≤ 0.1 μ m.
Retainer: Engineering plastic (PA66) or brass, balancing strength and lightweight.
Factors affecting lifespan: Speed: The steering wheel speed is usually ≤ 300rpm, but extreme operations (such as turning in place) may exacerbate wear.
Temperature: Long term high load use may cause grease carbonization and requires regular maintenance (usually checked every 100000 kilometers).
5. Failure modes and diagnosis
Typical fault: Abnormal noise: Insufficient lubrication or damage to the retaining frame causing direct metal contact.
Stuck: Seal expansion or damage to the raceway increases rotational resistance.
Excessive clearance: Loss of bearing preload, resulting in loose steering (affecting handling accuracy).
Diagnostic method: Vibration analysis: detect the characteristic frequency of the bearing (such as BPF=number of rollers x speed/60).
Clearance measurement: Use a dial gauge to check if the axial/radial clearance exceeds the standard value (usually ≤ 0.05mm).
6. Technological development trends
Integrated design: Integrating bearings with sensors (such as torque sensors) to achieve precise control of electric power steering (EPS).
Ceramic rolling elements: using silicon nitride (Si ∝ N ₄) ceramic balls, reducing density (60% of steel ball weight), improving corrosion resistance and lifespan.
Maintenance free technology: By optimizing the sealing and grease formula, maintenance free throughout the entire lifecycle (target lifespan ≥ 200000 kilometers) can be achieved.
summarize
The steering bearings are optimized through rolling friction, adaptable to multi-directional loads, and precisely lubricated and sealed to ensure the high efficiency and reliability of the steering system. Its design needs to balance load capacity, frictional resistance, and life cost, and will further develop towards lightweight, intelligent, and maintenance free direction in the future.
