What does the pinion-and-rack pair do in a rack and pinion steering gear?

Converts the rotary motion of the steering wheel into linear motion of the rack

Locks the steering when the vehicle is parked

Multiplies torque using a worm and nut with recirculating balls

Converts linear motion of the rack into higher engine speed

Why is the rack and pinion gear not used in heavy vehicles?

It passes road shocks (kickback) to the driver and is unsuitable for heavy loads, so a recirculating-ball box is used

It has too many joints and is too costly

It cannot give a steering ratio above 5:1

It needs a hydraulic pump to turn at all

Which statement correctly compares engine load in HPS and EPS?

The HPS pump runs continuously and uses fuel, while EPS draws current only when steering

Both draw power continuously from the engine

EPS pump runs continuously, HPS draws current only when steering

Neither system loads the engine

How does an EPS system produce assistance?

A torque sensor signal goes to the ECU, which drives an electric motor on the column or rack

A rotary valve directs fluid to either side of the rack piston

A vacuum booster multiplies the driver's effort

A vane pump driven by the engine raises oil pressure

Practice · 4+4 marks

Manual and power steering systems

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.

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?

Rack and pinion steering

 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

✓ Answer checked by Claude Opus 5.5 (high effort)

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