Power Steering Nana Shinde

8/4/2019 Power Steering Nana Shinde

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Presentation

OnSteering System

Nanasaheb S Shinde


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How Car Steering Works?


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Turning the Car

For a car to turn smoothly, each wheel must follow a different circle. Since the inside wheel

is following a circle with a smaller radius, it is actually making a tighter turn than the outside

wheel.

Ifwe draw a line perpendicular to each wheel, the lines will intersect at the center point of

the turn. The geometry of the steering linkage makes the inside wheel turn more than the

outside wheel.


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While turning, the inside wheel turn more than the outside wheel

Turning the Car


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Steering Ratio

One purpose of the steering mechanism is to provide mechanical advantage.

In a machine or mechanical device, it is the ratioof the output force to the input forceapplied to it.

This means that a relatively small applied force can produce a much greater force at the

other end of the device.

The higher the steering ratio, the easier it is to steer the vehicle.

However, higher the steering ratio, the more the steering wheel has to be turned to

achieve steering.

With a 30: 1 steering ratio, the steering wheel must turn 30 degrees to pivot the frontwheels 1 degree.

Variable Steering Ratio

"Variable steering ratio" means that the ratio is larger at one position than another.

Therefore the wheels are turned faster at certain positions than at others.

At the centeror straight-ahead position, the steering gear ratio is high, giving more

steering control.

However, as the wheels are turned, the ratio decreases so that the steering action is

much more rapid. This design is very helpful for parking and maneuvering the vehicle.


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Function of Steering System

Control of front wheel (sometimes rearwheel) direction.

T

ransmit road feel (slight steeringw

heel pu

ll cau

sed by the ro

ad su

rface)to the drivers hand.

Maintain correct amount of effort needed to turn the wheels.

Absorb most of the shock going to the steering wheel as the tire hits holes

and bumps in the road.

Allow for suspension action


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Classification of Steering Systems

Manual steering system relies on the driver to provide steering force

Power steering system uses hydraulic or electric power to help the driver applysteering force

Manual Steering Systems


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Manual Steering System

There are several different types of manual steering systems, which are asfollows:

Worm and sector

Worm and rotter

Cam and lever

Worm and nut Rack and pinion


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Worm and sector type steering system

Worm and roller type steering system

Cam and lever type steering systemWorm and nut type steering system


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Manual and Power Steering Systems Have Common

Components.

Input components:

Steering wheel

Steering column

Steering shaft


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Steering Wheel used by the driver to rotate a

steering shaft that passes through the steering

column.

Steering Shaft transfers turning motion from

the steering wheel to the steering gearbox.

Steering Column supports the steering column

and steering shaft.

Linkage Steering System (Worm Gear) Parts


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Linkage Steering System (Worm Gear) Parts

Steering Gearbox

changes turning motion

into a straight-line motion to the left or right.

Steering gear box ratios range from 15:1 to

24:1 (with 15:1, the worm gear turns 15 timesto turn the selector shaft once).

Steering linkage

connects the steering

gearbox to the steering knuckles and wheels.


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Steering Components Pitman arm-Connects the linkage to the steering gear.

Idler arm-Supports the centre link to the frame.

Centre link, drag link, or steering link-Controls sideways linkage movement. Tie-rods-Connect linkage to the steering knuckles.

Linkage Steering


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Rack-and-Pinion Steering


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Rack and Pinion

The rack-and-pini

on steering gear has bec

ome increasingly p

opu

laron smallerpassengervehicles. It is simpler, more direct acting, and may be straight

mechanical or power-assisted.

In the rack-and-pinion steering system the end of the steering gear shaft contains

a pinion gear, which meshes with a long rack.

As the steering wheel is rotated, the pinion gearon the end of the steering shaft

rotates. The pinion gear moves the rack from one side to the other. This action

pushes or pulls on the tie rods, forcing the steering knuckles orwheel spindles to

pivot on their ball joints. This turns the wheels toone side or the other so the

vehicle can be steered.

The rack-and-pinion gearset 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. For light cars

11:1, and for heavy trucks 18:1.


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POWER STEERING SYSTEM


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The need achieve the greatest possible road safety under:

Increasing traffic density

High axle loads

Poor road conditions.

Led to the development of Power Steering.

Need for Power Steering

Modes of Actuation

Hydraulic systems

Electric systems


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Hydraulic Power Steering

Power steering systems normally use an engine-driven pump and hydraulic system to assist

steering action.Pressure from the oil pump is used tooperate a piston and cylinder assembly.

When the control valve routes oil pressure intoone end of the piston, the piston slides in its

cylinders.

Piston movement can then be used to help move the steering system components and front

wheels of the vehicles.


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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, theypull 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 contains a pressure-reliefvalve to make sure that the pressure does not get too high.

The pump must be designed to provide adequate flowwhen the engine is idling. So, the pump

moves much more fluid than necessary when the engine is running at faster speeds.


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Rotary Valve

The device that senses the force on the steering wheel is called the rotary valve.

The key to the rotary valve is a torsion bar.

The top of the bar is connected to the steering wheel, and the bottom of the bar is connected

to the pinion orworm 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 bottom of the torsion bar connects to the outer part of the spool-valve assembly.

As the bar twists, it rotates the inside of the spool valve relative to the outside.

The inner part of the spool valve is also connected to the steering shaft, 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.


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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.

Working of the Rotary Valve


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Rack-and-Pinion Power Steering System

In the rack-and-pinion power-steering system, the rack has a slightly different design.Part of the rack contains a cylinderwith a piston in the middle. The piston is connected to the

rack.

There are two fluid ports, one on either side of the piston. Supplying higher-pressure fluid to

one side of the piston forces the piston to move, which in turn moves the rack, providing the

power assist.


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Power Steering Leakage

A common problem with power steering systems is fluid leakage. With pressure over 1,000

psi, leaks can develop easily around fittings, in hoses, at the gearbox seals, or at the rack-and-

pinion assembly.

In Steering gear box, leakage occurs from:-

1.Upper Pinion seal.2.Rack bush side seal.

3.Pinion side seal.


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Advantages

Preventing the wheels from transferring the load to the steering column Reducing the drivers fatigue

Low input torque and continuous steering function

Oil output directly proportional to the steering speed

Disadvantages

Design is compications and increased in cost.

Fluid leakage.


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Electronic Power Steering

(EPS)


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Electronic Power Steering


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Electronic Power Steering (EPS) is an advanced power steering system. It eliminates the need

for a power Steering pump, hoses, hydraulic fluids, and a drive belt and pulley on the engine.

As a result, electric power steering is more energy efficient.

Electronic Power Steering (EPS)


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Control block diagram for EPS system


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Working


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A "steering sensor" is located on the input shaft.

The steering sensor is actually two sensors: a "torque sensor" that converts steering

torque input and its direction intovoltage signals, and a "rotation sensor" that

converts the rotation speed and direction intovoltage signals.

There is an "interface" circuit that converts the signals from the torque sensor and

rotation sensor into signals that are sent to a microprocessor.

Inputs from the steering sensor are digested by a microprocessor control unit that

also monitors input from the vehicle's speed sensor. The sensor inputs are then compared to determine how much power assist is

required according to a preprogrammed "force map" in the control unit's memory.

The control unit then sends out the appropriate command to the "powerunit"which

then supplies the electric motorwith current.

The motor pushes the rack to the right or left depending on which way the voltage

flows (reversing the current reverses the direction the motor spins). Increasing thecurrent to the motor increases the amount of power assist.

Working


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Classifications of EPS -

EPS can mainly classified in to 3 kinds depending up on the position of the motor:

Column assist type.

Pinion assist type.

Rack assist type.


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Column-Assist Type:

The power assist unit, controller and the torque sensor are attached to the steering column.

This system is compact and easy to mount on vehicle.

An integrated pivot/mount and integrated controlleroption increase mounting flexibility.

Shafts offer long-term durability performance at much higher torsion loading.


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Pinion-Assist Type:

The power assist unit is attached to steering gears pinion shaft.

The power assist unit is outside the vehicles passenger compartment, allowing assist torque

to be increased greatly without raising interior noise.

Combined with a variable ratio steering gear, this system can suffice with a compact motor

and offer superior handling characteristics.


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Rack-Assist Type:

The power assist unit is attached to the steering gear rack.The power assist unit can be located freely on the rack, allowing great flexibility in layout

design.

The power assist units high reduction gear ratio enables very low inertia and superior driving

feel.

Electric power steering rack assist is a scalable system, suitable for midsize cars to full-size

trucks.


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Advantages of EPS overHydraulic Power

Steering:

Reduced driver fatigue.

Enhances dependability and safety.

Compact, modular design and flexible tuning capability.

Helps improve fuel economy by reducing the pressure the pump has towork against during

straight-ahead highway speed driving.

Accommodates most vehicle platforms.

Reduced steering system operating temperature.

Lower noise under all driving conditions.

EPS has got upper hand compared toHydraulic power steering because:


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Thank You

Power Steering Nana Shinde

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