The first thing to remember about steering is that it is all about geometry and durability of components. Before discussing which type of steering is best for what vehicle, we need a review of existing steering systems, attendant problems, and their potential for improvement. Read also more here: http://bit.ly/steering-articles

1. Which type of steering is best for what vehicle?
Brakes and steering are the most critical parts of a car, even more than the power train. A car
rolling down hill without the engine on can be just as much of a death trap when nobody can
steer or stop it. The first thing to remember about steering is that it is all about geometry and
durability of components. Before discussing which type of steering is best for what vehicle, we
need a review of existing steering systems, attendant problems, and their potential for
improvement.
Basic steering systems
There are two major areas: linkage and steering mechanism. Arrangements will vary, but most
linkage systems consist of ball-type joints (tie rod ends, control arms), intermediate links
(Pitman arm – also called “steering arm”, drag link), threaded adjuster sleeves, and links.
Major parts of a typical front end linkage system [1]
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2. Front wheel suspension assembly - Left front wheel suspension of a Saab Quantum
IV with double wishbones, showing kingpin axis, wheel hub, disc brake, steering arm
and tie rod end [2]
There are two basic steering assemblies: recirculating ball bearings, and rack and pinion. The
recirculating ball bearing system contains an “endless belt” of ball bearings that serve to
reduce friction between the steering wheel shaft and the main linkage – Pitman arm - to the
linkage assembly.
This shaft turns
right or left
(indicated by arrows)
in accordance with where
the car is turning.
To the
linkage – tie
rods, drag
link, and
control arm
assembly
Typical recirculating ball assembly at the end of the steering shaft [3]
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3. Rack and pinion steering consists of a straight toothed bar (rack) and a gear (pinion) that rolls
the bar back and forth.
Rack and pinion concept [4]
The bar is attached to the tie rods that connect to the wheel, as depicted in the following
diagram of a typical rack and pinion assembly.
Steering mechanism – rack and pinion [5]
The main advantage of the recirculating ball assembly is that the ball bearings reduce friction
considerably. There is a steering wheel play and it is adjustable, usually by a slotted bolt with
a securing nut mounted on top of the housing. The rack and pinion, while giving the driver a
sense of directly steering the vehicle, it is not adjustable. Once the rack and pinion assembly
wears out, they have to be replaced.
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4. Power assistance methods
Hydraulic
Power steering originally was used on the SS Great Eastern in 1866 [6]. While one may not
realize, power steering for vehicles pre-dated the Model T Ford in 1909. In 1902 Frederick W.
Lanchester in the UK patented a hydraulic power steering system for cars. On 30 August 1932,
Klara Gailis filed the first U.S. patent. The cost of these systems kept them from being
attached to cars, but during World War Two, they were needed on heavy vehicles. In 1951, the
Chrysler Imperial emerged with its "Hydraguide” power steering system, the first one mass-
produced for the public.
The basic modern hydraulic system consists of:
Steering torque detector
Controlled pressure distributor case/housing containing ports and valves
Hydraulic booster pump
Tank with a working liquid, often mineral oil based
Connection hoses.
These are configured typically as indicated by the following:
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5. Typical hydraulic power steering system [7]
Fluid from the reservoir travels through pump with the rotating vanes, to the various ports as
indicated by the arrows, through the rack and back to the reservoir. The pump vane turns
either clockwise or counterclockwise to deliver pressure to the appropriate side of the rack –
chamber A or chamber B.
Chambers A
and B
lead to the rack.
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6. Pump vanes in hydraulic power steering pump [8]
Electric
While hydraulic power steering will shut off when the motor is not running (because of the
power steering pump being driven by a belt around the crankshaft pulley) electric motor assist
will operate as long as there is battery power available. This can be important if the car is
moving with the motor not running for some reason (e.g., being pushed started, towed, or is
coasting down a hill) and needs to be steered by a person. Another advantage of electric-
assist power steering is that it does not rob power from the motor and is a demand-only
system. Hydraulic systems run constantly, and during high speeds power assisted steering is
not necessary, because of the gyroscopic action and inertial motion of the wheels stabilizes the
forward thrust of the car. The power is used only when needed. Still, another advantage is that
there are no bulky hydraulic lines that can deteriorate or get in the way of other repairs.
Hydraulic systems not only are bulky, they are much heavier than electric-based ones, thus
making for a more fuel-efficient vehicle. Of course, if the electric system fails, then for not
such a strong person it is almost impossible to steer the car. With the hydraulic system, a
person often has advanced warning of failure, such as a low fluid level in the pump reservoir or
worn vee belt.
In the basic system, an electric motor is connected to the steering wheel shaft and turns in
accordance with the resistance generated from the wheels transmitted through the steering
column, i.e., the torque. A torque sensor operating through a controller tells the motor how
fast to turn. This is increasingly being done by regulating the magnetic fields in the stator of
the brushless permanent magnet (BPM) motor used to drive the rack. In addition, there is a
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7. sensor detecting wheel rotation that helps modulate the motor's signal voltage, which, through
the well-known formula E=IR (volts equals ohms multiplied by amperage) determine the
amperage, or power input to the motor. Another sensor detects engine speed; not as much
power assist is needed when the vehicle is moving faster, so the power assist unit needs to be
cut back. The more amperage supplied to the motor, the faster it turns. Voltage signals can
be negative or positive, thus causing the motor to move the rack in the proper direction.
Typical electric-assisted power steering system – basic components [9]
Hybrid systems
There are hydro-electric power steering assist systems, which use a combination of an electric
motor and fluid. The major feature is that an electric motor powers the pump driving the
hydraulic fluid, rather than the motor being the propellant. Hence, the advantage is gained of
the system being functional if the vehicle's engine stops and as long as there is battery power.
Of course, this doesn't resolve the hydraulic line and weight issues.
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8. References (Subject is indicated by URL – accessed 9 July 2011)
[1] http://autorepair.about.com/library/bl244lib.htm
[2] http://en.wikipedia.org/wiki/File:Suspension.jpg
[3] Adapted from http://en.wikipedia.org/wiki/File:RecirculatingBall.png
[4] http://en.wikipedia.org/wiki/Steering
[5] http://autorepair.about.com/library/bl244lib.htm
[6] http://en.wikipedia.org/wiki/Power_steering
[7] MarcusRösth Hydraulic Power Steering System Design in Road Vehicles - Analysis, Testing
and Enhanced Functionality, Linköping Studies in Science and Technology. Linköping Studies in
Science and Technology. Dissertations, No. 1068 Division of Fluid and Mechanical Engineering
Systems, Department of Mechanical Engineering, Linköping University, SE–581 83 Linköping,
Sweden 2007, p. 20.
[8] Ibid. pp. 21-22
[9] http://www.insightcentral.net/encyclopedia/eneps.html
[10] http://en.wikipedia.org/wiki/Power_steering
[11] http://www.autoobserver.com/2010/11/compact-cars-are-bigger-and-heavier-than-ever-
edmundscom-reports.html
[12] http://auto.howstuffworks.com/hy-wire3.htm
[13] Ibid.
[14] Ibid.
Resources (Subject is indicated by URL – accessed 2 July 2011)
http://en.wikipedia.org/wiki/Steering
http://www.usatoday.com/money/autos/2007-09-13-overloaded-cars_N.htm
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9. http://www.aa1car.com/library/steering_power_electric.htm
https://docs.google.com/viewer?url=http://www.autoshop101.com/forms/Hybrid17.pdf&embe
dded=true&chrome=true
http://www.indiacar.com/infobank/epc.htm
http://www.nsxprime.com/FAQ/Technical/eps.htm
http://www.carblogindia.com/electric-power-steering-vs-hydraulic-power-steering/
http://www.eetimes.com/design/embedded/4006457/Electric-power-steering-one-good-turn-
deserves-another
http://auto.howstuffworks.com/steering5.htm
http://en.wikipedia.org/wiki/Hydraulic_power_steering
liu.diva-portal.org/smash/get/diva2:23027/FULLTEXT01
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