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Steering System

 

A steering system, is a collection of components and
linkages, which allows vehicles (car, bicycle, motorcycle) to follow a desired
course. Its main purpose, is to allow the driver guide the vehicle.

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There are two main types of steering systems:

·        
Mechanical

·        
Power

 

Mechanical:

This is a steering system in which a mechanical or manual
force is used for steering. It is also known as manual or non-power steering.

 

Power:

Power steering, also known as power-assisted steering (PAS),
helps drivers steer by augmenting steering effort of the steering wheel. It is
a system that helps in steering the wheels by using some source of power or
power of engine. It is the preferred steering system, when quick turns need to
be taken.

There are three main Power steering components – power
steering pump, power steering fluid reservoir and steering gear box.

 We have three types
of Power steering systems. They are considered types of power steering systems
because they possess all the features of a power steering system. These are:

·        
Hydraulic power steering,

·        
Fully Electric power steering (EPS) and the

·        
Electro-hydraulic power steering (EPHS)

 

Hydraulic:

A hydraulic
power system uses hydraulic pressure supplied by an engine-driven
pump to assist the motion of turning the steering wheel. It acts as a transmission system that uses
pressurized hydraulic fluid to power hydraulic machinery. The hydraulic pressure
typically comes from a generator or rotary
vane pump driven by the vehicle’s engine. A double-acting hydraulic cylinder applies a force to the
steering gear, which in turn steers the road-wheels.  It add controlled
energy to the steering mechanism, so the driver can provide less effort to turn
the steered wheels when driving at typical speeds, and reduce considerably the
physical effort necessary to turn the wheels when a vehicle is stopped or
moving slowly. Hydraulic power steering systems for cars, augment steering
effort via an actuator, a hydraulic cylinder that is part of a servo system.
These systems have a direct mechanical connection between the steering wheel
and the linkage that steers the wheels. This means that power-steering system
failure (to augment effort) still permits the vehicle to be steered using
manual effort alone.

A hydraulic drive system consists of three parts: The
generator (e.g. a hydraulic pump), driven by an electric
motor, a combustion engine or a windmill;
valves, filters, piping etc. (to guide and control the system); and the
actuator (e.g. a hydraulic motor or hydraulic cylinder) to drive the machinery.

 

Electro-hydraulic
power steering system (EPHS):

The electro-hydraulic system, (sometimes abbreviated EPHS or
EHPS) is also sometimes called ‘hybrid’ system. It uses the same hydraulic
assist technology as the standard hydraulic system, but the hydraulic pressure
comes from a pump driven by an electric motor instead of a drive belt at the
engine.

The customary drive belts and pulleys that drive a power
steering pump are replaced by a brushless motor. It is driven by an electric
motor and thus also reduces the amount of power that needs to be taken from the
engine otherwise.

 

Electric
power steering system (EPS):

In this kind of system, an electric motor replaces the
hydraulic pump and a fully electric power steering system is established. The
electric motor is either attached to the steering rack or column. The important
component is the electronic control unit because it controls the steering
dynamics.

Sensors detect the position and torque of the
steering column, and a computer module applies assistive torque via the motor,
which connects to either the steering gear or steering column. This allows
varying amounts of assistance to be applied depending on driving conditions. A
mechanical linkage between the steering wheel and the steering gear is usually
retained in EPS. This means that in the event of a failure that results in an
inability to provide assistance, the mechanical linkage serves as a backup. The
driver then encounters a situation where heavy effort is required to steer.
Depending on the driving situation and driver skill, the steering assist loss
may or may not lead to a crash.

Electric systems have an advantage in fuel efficiency
because there is no belt-driven hydraulic pump constantly running, whether
assistance is required or not. This was the main reason for their introduction.
Another major advantage is the elimination of a belt-driven engine accessory
and several high pressure hydraulic hoses between the hydraulic pump, mounted
on the engine and the steering gear, mounted on the chassis. This helps to
simplify manufacturing and maintenance.

Electric power system, is necessary for some power steering
systems, like those in the largest off-road construction vehicles. Their
systems, sometimes called ‘drive by wire’ or ‘steer by wire’, have no direct
mechanical connection to the steering linkage and thus require electrical
power. In this context, ‘wire’ refers to electrical cables that carry power and
data, not thin-wire-rope mechanical control cables.

 

Most of the cars today, have power steering systems. Very
few use mechanical steering. EPS is often preferred, for the fuel economy and
lower emission. Mechanical steering systems use the power of human muscle. In
this system, more effort is required to steer the vehicles. The only energy
source is the force the driver applies to the steering wheel. However, in power
steering, mechanical steering is always allowed to be available, in case of a
problem in the engine or in the case of a power assist system failure. EPS is
more efficient than hydraulic power steering, since the electric power steering
motor only needs to provide assistance when the steering wheel is turned,
whereas the hydraulic pump must run constantly. In EPS, the amount of
assistance is easily tuneable to the vehicle type, road speed, and even driver
preference. An added benefit is the elimination of environmental hazard posed
by leakage and disposal of hydraulic power steering fluid. In addition,
electrical assistance is not lost when the engine fails or stalls, whereas
hydraulic assistance stops working if the engine stops, making the steering
doubly heavy as the driver must now turn not only the very heavy steering
(without any help) but also the power-assistance system itself.

There are two basic steering mechanism:

·        
Rack and pinion steering and

·        
Recirculating ball steering

 

Rack and
pinion steering

 In this system a
pinion gear is attached to the steering shaft. This means that as the steering
wheel is turned it turns the pinion gear (circular) and then moves the rack
(linear). It basically uses the rotational motion of steering wheels and converts
this rotational motion into the linear motion. Alternatively, it could be
described as a circular gear called the pinion, engages the teeth on the linear
gear bar called the rack. Rotational motion is then applied to the pinion which
causes the rack to move relative to the pinion, thereby translating the
rotational motion of the pinion into linear motion. This linear motion is
required to turn the wheels. It provides a less efficient mechanical advantage
than other mechanisms, like the recirculating ball, but less backlash and
greater feedback or steering feel. In mechanical steering systems, this process
is done manually while in power steering systems, it is power-assisted, usually
by hydraulic or electrical means.

 

Recirculating
ball steering

Also known as recirculating ball and nut or worm and sector.
Here, a box with a threaded hole is fastened over a worm drive that contains
many ball bearings. These ball bearings loop around the worm drive and these
balls moves out into a recirculation channel and again gets back into the worm
drive. This block gear has teeth cut into the outside to engage the sector
shaft (also called the sector gear) which moves the pitman arm. Because the
steering wheel is connected to a shaft which rotates the worm gear inside the
block, instead of twisting further into the block, the worm gear is fixed so
that when it spins, it moves the block, which transmits the motion through the
gear to the pitman arm, causing the road-wheels to turn. When the steering
wheel is turned, the worm drive turns and forces the balls to press against the
channel inside the nut. Now the forces the nut to move along the worm drive. It
is a steering mechanism found in older automobiles, off-road trucks and some
trucks.

Finally, listed below are mechanical steering systems. They
also occur as power steering systems, with the power supply being either
hydraulic or electric or electro-hydraulic, instead of manual. These include:

·        
Worm and sector (Recirculating ball steering)

·        
Worm and roller

·        
Cam and lever

·        
Worm and nut

·        
Rack and pinion

 

Worm and
roller

This is quite similar to the worm and sector, except a
roller is supported by ball or roller bearings within the sector, mounted on
the pitman arm shaft. The sliding friction is changed to rolling friction so
that less effort is required to turn the steering wheel. This is only possible
because the sector teeth are machined on a roller. As the steering wheel turns
the worm, the roller turns with it, forcing the sector and pitman arm shaft to
rotate. Friction is reduced further by mounting the roller on bearings in a
saddle at the inner end of the pitman arm shaft. The hourglass shape of the
worm which tapers from both ends at the centre, affords better contact between
the worm and the roller in every position. This design provides a variable
steering ratio to permit faster and more efficient steering. ‘Variable steering
ratio’ means the ratio is larger at one position than another. Therefore, at
certain positions, the wheels are turned faster than at others. At the very
centre, the steering gear ratio is high, giving more steering control. When the
wheels are turned however, the ratio decreases so that the steering action is
much more rapid. This design is very helpful for parking and manoeuvring the
vehicle.

 

Cam and
lever

In the cam and lever steering gear, the worm is known as a
cam. The inner end of the pitman arm shaft has a lever that contains a tapered
stud. The stud engages in the cam so that the lever is moved back and forth
when the cam is turned back and forth. If the tapered stud is fixed in the lever
so that it can’t rotate, it creates a sliding friction between the stud and the
cam. Therefore, on some vehicles that have this type of steering gear, the stud
is mounted in bearings so that it rolls in the cam groove (threads) instead of
sliding. A cam and twin-lever steering gear is used in some large trucks. This
is essentially a cam and lever gear with two tapered studs instead of one. The
studs sometimes are fixed in the lever, or they may be mounted on bearings.

 

Worm and nut

This steering gear is made in different several
combinations. The nut is meshed and screws up and down on the worm gear. The
nut may operate the pitman arm directly through a lever or through a sector on
the pitman arm shaft. The recirculating ball is the most common type of worm
and nut steering gear. Here, the nut (that is in the form of a sleeve block) is
mounted on a continuous row of balls on the worm gear to reduce friction. The
ball nut has grooves cut into it to match the shape of the worm gear. The ball
nut is then fitted with tubular ball guides to return the balls diagonally
across the nut to recirculate them, as the nut moves up and down on the worm
gear. With this design, the nut is moved on the worm gear by rolling instead of
sliding contact. Turning the worm gear moves the nut and forces the sector and
pitman arm shaft to turn.

 

Stubhub steering system? What type
of steering system did we use?

 

Wheels

Tires are designed to not only support the weight of a
vehicle, but to absorb road shocks, transmit traction, torque and braking force
to the road and maintain and change the direction of travel

The vehicle was built to be a lightweight off-road vehicle.
This means it is suitable for use on and off paved or gravel surfaces. For this
vehicle, we went with radials. A radial tire is a particular design of tire,
where the cord plies are arranged at 90 degrees to the direction of travel, or
radially. For a regular off-road vehicle, the tires have thick, deep threads.
Knowing our buggy would not be used on very sandy terrain, we selected tires
with threads that don’t run too thick. The exposed edges of the threads dig
into soft ground, giving more traction than rolling friction alone. Since our
tires have less aggressive knobs, it means we can also have adequate traction
to enable motion on a pavement, unlike the typical off-road tires. They are
usually bigger where there is more weight in the vehicle. Hence the back tires
in our vehicle are larger. It is also larger at the back because, we designed
the vehicle to be a 2 wheel drive, with the drive axle at the back tires. In
rear-wheel drive vehicles, the engine or power source, turns a driveshaft (also
called a propeller shaft or tailshaft) which transmits rotational force to a
drive axle at the rear of the vehicle. To enable the vehicle move, the wheels
have to be big enough to not only carry the weight of the vehicle (when it is
empty or otherwise), but also move when power is transmitted to it.

 

Material sourcing and cost

 

Material of choice: Steel

Steel is fairly cheap to get, it is also very widely
recycled. It is a material that does not lose its special properties (i.e.
Strength, hardenability, weldability, ductility etc.) after being recycled.
This makes it a good choice because we have the option of using new steel or
recycled steel to reduce cost, without compromising on quality.

The other material we researched was Aluminium, but even
with corrosion, steel is harder than aluminium. Most
alloys of aluminium dent, ding or scratch more easily as
compared to steel and its alloys. Steel is strong and less
likely to warp, deform or bend under force or heat. To make our buggy, the
material will be undergo a lot of welding and we wouldn’t want our material to
deform or warp during this, or any other production process.

The price of steel and aluminium is continually
fluctuating based on global supply and demand, fuel costs and the price and
availability of iron and bauxite ore; however steel is generally cheaper (per
pound) than aluminium. There are exceptions, but aluminium will almost always
cost more because of the increase in the raw material price.

 

Costing

To get some of each part we needed at a discounted price (or
free if possible), we visited the following scrapyards:

·        
JAP city auto salvage Ltd, EMR Middlesbrough

·        
C L Prosser & Co Ltd

 

The only things we were allowed to buy were some motors but
we did not get them because they were not the appropriate ones for the vehicle.
Not to mention, motors at scrapyards can sometimes be unreliable and there was
no way we could test them on site, to make sure they worked. Moving on from
there, we contacted a well-known motorsport company that deals in dirt buggies:

·        
Rage Motorsport Ltd

 

We called to ask if they had any spare parts we could buy.
They were unfortunately unwilling to sell us anything for cheap. After that, we
called multiple steel companies and got some quotes. These included:

·        
Parson and Crosland – located on forty foot road                              £90 for 3 metres
(uncut)

·        
Brettle – located on 5A Bowes road                                                         £75

·        
Q A Weldtech Ltd                                                                                             £60

·        
Jones D K Ltd                                                                                                     £45.60
for 3 metres (cut)

 

We ended up going for the Jones D K Ltd option because it
was better value for money. In my table below, I outline the different parts we
needed to source, the quoted or estimated price (as seen online) as well as the
price we obtained them for.

Next we contacted Teesside Karting, where the owner Paul,
was more than happy to help us with the project. He gave us a chassis and a
seat, at absolutely no cost.

Materials or Parts

Estimated or Quoted Price

Actual Price

Motor

£35

 

Motor controller

£11.99

£12.99

Twist Throttle

£6.99

£13.99

Wheels (4)

£27.00

£20.00

Batteries (3)

£30.00

£30.00

Steel Piping

£45.60

£45.60

A Seat

£10.00

FREE

Sprockets (2)

£3.90

 

Steel Plate

£4.65

 

Steering wheel

£6.99

 

Stubs

£3.92

 

Jubilee Clips

£1.96

£5.82

Wiring

£11.00

£12.72

Wiring connector terminals

£1.00

 

TOTAL

£200.00

£141.12

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