--- title: "Manual and power steering systems" subject: "Automotive Technology" chapter: 6 key: "semester_5/automotive_technology:manual-and-power-steering" source: https://www.bctengineer.com/q/semester_5/automotive_technology/manual-and-power-steering site: BCT Engineering --- # Manual and power steering systems Automotive Technology · Chapter 6: Suspension and Steering - Asked in: year not given, 4+4 marks - Video: [Every Car Steering System Explained | Hydraulic, Electric & Steer-By-Wire](https://www.youtube.com/watch?v=3JO3VnRHqY0) — The Engineers Post - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/automotive_technology/manual-and-power-steering - Whole chapter: https://www.bctengineer.com/md/semester_5/automotive_technology/chapter-6 ## Question Explain the layout of a rack and pinion steering gear with a sketch. How does a hydraulic power steering system differ from an electric power steering (EPS) system? ## Short answer Rack and pinion steering meshes a pinion with a toothed rack, converting rotary to linear motion to turn wheels via tie rods. Hydraulic power steering (HPS) uses an engine-driven pump and fluid to assist via a rack piston; electric power steering (EPS) uses an electric motor and torque sensor, providing variable assist and higher efficiency. ## Answer #### Rack and pinion steering ```text Steering wheel | Steering column (universal joints) | [Pinion]---meshes--- [Rack] | | tie-rod tie-rod | | steering arm steering arm | | left wheel right wheel ``` - Turning the steering wheel rotates a small **pinion** gear that meshes with a toothed **rack**; the rotary motion becomes linear motion of the rack. - The rack moves the **tie rods** (with ball joints), which turn the steering arms on the stub axles of the wheels. - The steering ratio (steering wheel angle to road wheel angle) is typically 14:1 to 20:1. - **Advantages:** simple, compact, direct feel, low cost, few joints. It is used in nearly all cars and many SUVs. - **Limitations:** it passes road shocks back to the driver (kickback) and is unsuitable for heavy vehicles (a recirculating-ball box is used there). #### Hydraulic and electric power steering Power steering reduces the driver's effort at low speed and when parking. | Point | Hydraulic power steering (HPS) | Electric power steering (EPS) | |---|---|---| | Source of power | Engine-driven vane pump, fluid | Electric motor on the column or rack | | Fluid | Hydraulic oil, reservoir, hoses | None | | Operation | Rotary valve directs fluid to either side of the rack piston | Torque sensor signals the ECU, which drives the motor | | Engine load | Pump runs continuously, uses fuel | Draws current only when steering | | Efficiency | Lower | Higher; saves about 3 % fuel | | Tuning | Fixed assistance | Varies with speed; lane assist and park assist possible | | Maintenance | Leaks, fluid change | Almost none | | Use | Heavy vehicles | Modern cars, EVs | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does the pinion-and-rack pair do in a rack and pinion steering gear? A. Locks the steering when the vehicle is parked B. Multiplies torque using a worm and nut with recirculating balls C. Converts the rotary motion of the steering wheel into linear motion of the rack D. Converts linear motion of the rack into higher engine speed Answer: C. The small pinion turns with the steering wheel and meshes with the toothed rack, so the rack moves linearly and pushes the tie rods. (Key point: Rack and pinion action) 2. Why is the rack and pinion gear not used in heavy vehicles? A. It has too many joints and is too costly B. It cannot give a steering ratio above 5:1 C. It needs a hydraulic pump to turn at all D. It passes road shocks (kickback) to the driver and is unsuitable for heavy loads, so a recirculating-ball box is used Answer: D. Its direct feel returns road shocks to the driver and it is not suited to heavy vehicles, where the recirculating-ball box is used. (Key point: Limitation) 3. Which statement correctly compares engine load in HPS and EPS? A. Both draw power continuously from the engine B. EPS pump runs continuously, HPS draws current only when steering C. The HPS pump runs continuously and uses fuel, while EPS draws current only when steering D. Neither system loads the engine Answer: C. The engine-driven pump of HPS runs all the time, but the EPS motor takes current only while the driver steers, giving a small fuel saving. (Key point: HPS vs EPA engine load) 4. How does an EPS system produce assistance? A. A rotary valve directs fluid to either side of the rack piston B. A vacuum booster multiplies the driver's effort C. A vane pump driven by the engine raises oil pressure D. A torque sensor signal goes to the ECU, which drives an electric motor on the column or rack Answer: D. EPS senses the driver's torque, and the ECU drives the motor; this allows speed-variable assistance, lane assist and park assist. 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