Exploring Vehicle Steering Systems

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

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 the 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 gearbox. 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)
• 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 adds 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. The 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 is two basic steering mechanism:

• Rack and pinion steering
• 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 opinion, engages the teeth on the linear gear bar called the rack. Rotational motion is then applied to the opinion 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 move 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's 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's 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 a 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 center, 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 maneuvering 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 car 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 are 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 meshes 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?

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 the 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.

The 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 aluminum. Most alloys of an aluminum 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 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 aluminum 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 aluminum. There are exceptions, but aluminum 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
• CL 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 meters (uncut)
• Brettle – located on 5A Bowes road £75
• Q A Weldtech Ltd £60
• Jones D K Ltd £45.60 for 3 meters (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.