ppt

1. Steering systems

2. Steering system:
• The steering system converts the rotation of the
steering wheel into a swiveling movement of the
road wheels.

3. Types of steering
• Manual Steering system
– A. Rack and pinion
– B. Recirculating Ball Screw
• Power assisted Steering system
– A. Rack and pinion
– B. Recirculating Ball Screw

4. 1. The rack-and-pinion system
• At the base of the steering column there is a small pinion (gearwheel)
inside a housing.
• Its teeth mesh with a straight row of teeth on a rack - a long transverse
bar.
• Turning the pinion makes the rack move from side to side.
• The ends of the rack are coupled to the road wheels by track rods.
• This system is simple, with few moving parts to become worn or
displaced, so its action is precise.

5. Rack &Pinion Steering gear box

6. Construction & Working:
• A universal joint in the steering column allows it to connect with the rack
without angling the steering wheel awkwardly sideways.
• A rack-and-pinion gearset is enclosed in a metal tube, with each end of
the rack protruding from the tube.
• A rod, called a tie rod, connects to each end of the rack.
• The pinion gear is attached to the steering shaft.
• When you turn the steering wheel, the gear spins, moving the rack.
• The tie rod at each end of the rack connects to the steering arm on
the spindle .

7. Rack &Pinion Steering gear box

8. Rack &Pinion Steering gear box
• The rack-and-pinion gear set does two things:
– It converts the rotational motion of the steering wheel into the linear
motion needed to turn the wheels.
– It provides a gear reduction, making it easier to turn the wheels.
• On most cars, it takes three to four complete revolutions of the steering
wheel to make the wheels turn from lock to lock (from far left to far right).

9. Steering gear ratio
• The steering ratio is the ratio of how far you turn the steering
wheel to how far the wheels turn.
• For instance, if one complete revolution (360 degrees) of the
steering wheel results in the wheels of the car turning 20 degrees,
then the steering ratio is 360 divided by 20, or 18:1.
• A higher ratio means that you have to turn the steering wheel
more to get the wheels to turn a given distance.

10. 2.Recirculating-ball steering mechanism/ The
steering-box system
• At the base of the steering column there is a worm gear inside a
box. A worm is a threaded cylinder like a short bolt.
• Imagine turning a bolt which holding a nut on it; the nut would
move along the bolt. In the same way, turning the worm moves
anything fitted into its thread.
• Depending on the design, the moving part may be a sector (like a
slice of a gear wheel), a peg or a roller connected to a fork, or a
large nut.

11. Recirculating-ball steering mechanism
• The nut system has hardened balls running inside the thread
between the worm and the nut. As the nut moves, the balls roll out
into a tube that takes them back to the start, it is called a
recirculating-ball system.
• The worm moves a drop arm linked by a track rod to a steering
arm that moves the nearest front wheel.
• A central track rod reaches to the other side of the car, where it is
linked to the other front wheel by another track rod and steering
arm. A pivoted idler arm holds the far end of the central track rod
level.

13. Recirculating-ball steering mechanism

14. Recirculating-ball steering mechanism
• The balls actually serve two purposes:
– 1. They reduce friction and wear in the gear;
– 2. They reduce out of contact in the gear (when you change the
direction of the steering wheel -- without the balls in the
steering gear, the teeth would come out of contact with each
other for a moment, making the steering wheel feel loose.)

15. Recirculating-ball Steering

16. • Disadvantage:
The steering-box system has many moving parts, so is less
precise than the rack system, there being more room for wear
and displacement.
• Power steering in a recirculating-ball system works similarly
to a rack-and-pinion system. Assist is provided by supplying
higher-pressure fluid to one side of the block.

17. 3. Power-assisted steering
Need:
• On a heavy car, either the steering is heavy or it is
inconveniently low geared - the steering wheel requiring
many turns from lock to lock.
• Heavy gearing can be troublesome when parking in confined
spaces. Power-assisted steering overcomes the problem.

18. Concept:
• The engine drives a pump that supplies oil under high pressure to the rack
or the steering box.
• Valves in the steering rack or box open whenever the driver turns the
wheel, allowing oil into the cylinder. The oil works a piston that helps to
push the steering in the appropriate direction.
• As soon as the driver stops turning the wheel, the valve shuts and the
pushing action of the piston stops.
• The power only assists the steering - the steering wheel is still linked to
the road wheels in the usual way.
• So if the power fails, the driver can still steer but the steering becomes
much heavier.

19. Power-assisted steering

20. Power-assisted steering
Construction:
1.Pump
• The hydraulic power for the steering is provided by a rotary-vane pump . This pump is
driven by the car's engine via a belt and pulley.
• It contains a set of retractable vanes that spin inside an oval chamber.
• As the vanes spin, they pull hydraulic fluid from the return line at low pressure and
force it into the outlet at high pressure.
• The amount of flow provided by the pump depends on the car's engine speed. The
pump must be designed to provide adequate flow when the engine is idling. As a result,
the pump moves much more fluid than necessary when the engine is running at faster
speeds.
• The pump contains a pressure-relief valve to make sure that the pressure does not get
too high, especially at high engine speeds when so much fluid is being pumped.

21. Torsion Bar:
2.Torsion Bar:
 The key to the rotary valve is a torsion bar.
 The torsion bar is a thin rod of metal that twists when torque is applied to it.
 The top of the bar is connected to the steering wheel, and the bottom of
the bar is connected to the pinion or worm gear (which turns the wheels),
so the amount of torque in the torsion bar is equal to the amount of torque
the driver is using to turn the wheels.
 The more torque the driver uses to turn the wheels, the more the bar twists.

22. Power-assisted steering
3.Rotary /Spool Valve:
 A power-steering system should assist the driver only when he is exerting force on the
steering wheel (such as when starting a turn).
 When the driver is not exerting force (such as when driving in a straight line), the system
shouldn't provide any assist.
 The device that senses the force on the steering wheel is called the rotary valve.
• The input from the steering shaft forms the inner part of a spool-valve assembly.
• It also connects to the top end of the torsion bar.
• The bottom of the torsion bar connects to the outer part of the spool valve.
• The torsion bar also turns the output of the steering gear, connecting to either the pinion
gear or the worm gear depending on which type of steering the car has.

25. Power-assisted steering
working:
• As the bar twists, it rotates the inside of the spool valve relative to the
outside.
• Since the inner part of the spool valve is also connected to the steering shaft
(and therefore to the steering wheel), the amount of rotation between the
inner and outer parts of the spool valve depends on how much torque the
driver applies to the steering wheel.
• When the steering wheel is not being turned, both hydraulic lines provide the
same amount of pressure to the steering gear.
• But if the spool valve is turned one way or the other, ports open up to provide
high-pressure fluid to the appropriate line.

27. Power-assisted steering

28. E ND