CD b 0912004

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M. S. Ramaiah School of Advanced Studies 1

POWER STEERING

SHAILENDRA A

CDB0912004

Module Code: AEL 2515Module Title: Control systems Engineering.

Module Leader: K Vishwanath Reddy

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Head Maximum Score

Technical Content 5

Grasp and Understanding 5

Delivery – Technical and

General Aspects

5

Handling Questions 5

Total 20

Marking

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Introduction

• It is the system used for directional change of an

automobile

• It connects rotary motion of steering wheel into angular

moment to turn vehicle into particular direction

• This system is connected with front wheels of vehicles and

back wheels in some heavy vehicles making it 4 wheel

steering

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Types of powered steering

• Hydraulic powered steering

• Electronic powered steering

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Hydraulic powered steering

Hydraulic power steering (HPS) system uses high pressure

fluids for assisting the steering movement which uses the

engine's power as a drive source

Figure 1 Hydraulic Power steering

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•Electronic powered steering uses an electric motor to drive

steering linkage directly.

•The power steering mechanism is therefore independent of

engine speed, resulting in significant energy saving.

Electronic powered steering

Figure 2 Electronic powered steering

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Steering system components

•Steering wheel- column and shaft - driver inputs

• Steering gear - changes direction - rotating steering motion

into linear motion

• Steering linkage - connects steering gear to steering arms

• Ball joints - allows movement of steering components and

suspension

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HPS vs EPS

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Steering gear systems

• Recirculating ball

• Rack and pinion

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Recirculating ball type

• Uses balls on a worm gear

• Has a pitman arm

• Balls inside the gear ride inside guide paths

• Uses a Parallelogram Linkage

steering arm system

• Pitman arm moves steering tie rods

Figure 3 Recirculating ball

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Rack and pinion

• Fewer moving parts than the recirculating ball

• Smaller and more compact

Figure 4 Rack and Pinion

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• Steering ratio is a measurement of how many turns that a

steering wheel takes to go from a full lock to the other full

lock

•Basically how many turns from all the way from left to right

• Also measured from the center (straight) to a full lock turn

• Fast ratio is 2-3 turns lock to lock

•Slow is about 4 or 5 times lock to lock

• 15:1 ratio – wheels move 15deg for 1 degree of steering

wheel movement

Steering ratio

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Ackerman Steering Geometry

• Basic layout for

passenger cars, trucks,

and ag tractors

• δo = outer steering angle

and δi = inner steeringangle

• R= turn radius

• L= wheelbase and

t=distance between tires

δo δi

L

t

R

Figure 1.1.

Pivoting

Spindle

Turn

Center

Center of

Gravity

δo δi

Figure 5 Ackerman Steering geometry

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Block Diagram

CAN

Figure 6 Block Diagram

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Components

•MDPSCM(Motor Driven Power Steering Control module)

• Motor

• Steering Angle sensor

• Steering Torque sensor

• Steering Column

• Power source

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Steering Column

Figure 7 Steering Shaft

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Motor Specification

Nominal current - 78A

Nominal Torque - 3.7NM

Nominal Speed – 1000RPM

Type used : Brushless Motor

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Working

Working of EPS

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Working

• Driver steers the steering wheel

• Torsion bar detects the distortion of tyre and steering column

• Torque sensor detects the distortion of torsion bar

• The light is radiated from the element through light gun on to

the disks

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Working

Working of EPS- Light detection

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•The shadow generated by light transmitted is detected bylinear array( receiving element)

• At this time the distorted amount of torsion bar makes the

difference in the shadow on to the disks

• The linear array detects the shadow to detect whether it is left

turn or right turn

Working

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Working- MDPSCM

Working of EPS- Data sharing

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• Averaging the detected values of the torque senor, the average

is sent to the MDPSCM

• MDPSCM controls the motor current based on the calculated

values

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Calibration

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Over heat mechanism/Advanced system

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Type of region

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Vehicle equipped with ABS

Vehicle speed from right wheel speed sensor

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Vehicle without ABS

Vehicle speed from Engine ECM

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Diagnostic Codes

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Figure 7

Mechanical system

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• Jh- assembly rotary inertia of steering wheel and input shaft

• Jm is the equivalent rotary inertia of power motor armature shaft

and reducer driving gear

• Jr is the equivalent rotary inertia of steering mechanism and front

tire

• θh- Steering wheel angle

• θp- steering pinion angle

• θm- power armature shaft angle

• θf-Front tyre angle

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• Th- Input torque of steering wheel

• Ts- Measured value of torque sensor

• Tm- Input torque of power motor

• Ta- Actual assisting torque

• Tr- Steering resistive torque equivalent to steering shaft

• Ks- Rigidity co efficient of twisting rod

• Ka- Motor electromagnetic torque coefficient

• Bh- Damping coefficient of steering input shaft

• Bm- Damping coefficient of motor armature shaft

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• Br- Equivalent damping coefficient of steering mechanism and

front tyre

• G1- Reduction ratio from motor to steering shaft

•G2- Reduction ratio from steering pinion to front wheel

• I- Motor current

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EPS differential equations

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EPS differential equations

• The motor current is proportional to the measured value of

torque sensor. It is given by

I = KTs = KKs (θ h - θ p)

• But taking into account the effects of the motor inertia,

damping and friction, a compensatory current is added to

the motor current.

• The compensated current is modeled as:

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Transfer function

Under normal driving condition, the steering system keeps

transferring the impression of the contact conditions between

the tires and road to the hand wheel, then the driver feels the

force feedback.

This is what called road feeling. It is considered to be a very

important factor because it acts directly on the driver’s hands

and the driver determines his/her actions based on

this force.

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Transfer function

• For studying the road feeling, we propose a method that a

steering wheel is set in a fixed mode

• The mode corresponds to the actual driving conditions that

the driver is holding the steering wheel tightly

• When the wheel set with a fixed mode, the mathematical

model of the hand wheel as

Th = Ts = - Ksθ p

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From equation 7

The transfer function from the steering resistance torque to

the steering wheel torque can be obtained as

Transfer function

C i

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Conclusion

• Hydraulic power steering is a primitive technology used

for decades and has improved a lot with time.

• Hydraulic power steering are speed sensitive and work

better than the older hydraulic power steering.

• Electric Power Steering gives better response at different

speeds as compared to Hydraulic Power Steering

• Electric Power Steering is better than Hydraulic Power

steering in terms of maintenance, mileage and simplicity

and widely used nowadays in all automobiles based on

applications

R f

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References

• XueWu Ji, XiaoPing Ma, KuiYuan Chen, Experimental study on EPS system

performance, Journal of Jiangsu University (National Science Edition),

25(2):116-119, 2004.

• http://www.csuohio.edu/engineering/ece/research/theses/2010/Kandula%20Pr

asanth%20Babu.pdf

• http://am.delphi.com/pdf/techpapers/1999-01-0399.PDF

• http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=5203081&url=http%3

A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D5203

081

• http://liu.diva-portal.org/smash/record.jsf?pid=diva2:23027

• http://www.jofcis.com/publishedpapers/2012_8_1_65_72.pdf

•http://tos.pp.fi/koukku/892403.pdf

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Thank You

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CD b 0912004