Power Rack-and-Pinion

Power Rack-and-Pinion

- When the rack-and-pinion is in a power-steering system, the rack has a slightly different design.

- Part of the rack contains a cylinder with 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.

Rack-and-pinion Steering

Rack-and-pinion Steering

- Rack-and-pinion steering is quickly becoming the most common type of steering on cars, small trucks, and SUVs. It is actually a pretty simple mechanism. A rack-and-pinion gear set is enclosed in a metal tube, with each end of the rack protruding from the tube. A rod, called a tie rod, connects to each end of the rack.

- The pinion gear is attached to the steering shaft. When you turn the steering wheel, the gear spins, moving the rack. The tie rod at each end of the rack connects to the steering arm on the spindle.
- The rack-and-pinion gear set 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.

- On most cars, it takes three to four complete revolutions of the steering wheel to make the wheels turn from lock to lock (from far left to far right).

- The steering ratio is the ratio of how far you turn the steering wheel to how far the wheels turn.

• For instance, if one complete revolution (360 degrees) of the steering wheel results in the
wheels of the car turning 20 degrees, then the steering ratio is 360 divided by 20, or 18:1. A higher ratio means that you have to turn the steering wheel more to get the wheels to turn a given distance. However, less effort is required because of the higher gear ratio.

- Generally, lighter, sportier cars have lower steering ratios than larger cars and trucks. The lower ratio gives the steering a quicker response -- you don't have to turn the steering wheel as much to get the wheels to turn a given distance -- which is a desirable trait in sports cars. These smaller cars are light enough that even with the lower ratio, the effort required to turn the steering wheel is not excessive.

- Some cars have variable-ratio steering, which uses a rack-and-pinion gear set that has a different tooth pitch (number of teeth per inch) in the center than it has on the outside. This makes the car respond quickly when starting a turn (the rack is near the center), and also reduces effort near the wheel's turning limits.

Steering Systems

Steering Systems

You know that when you turn the steering wheel in your car, the wheels turn. Cause and effect, right? But a lot of interesting stuff goes on between the steering wheel and the tires to make this happen.


We'll see how the two most common types of car steering systems work: rack-and-pinion and
recirculating-ball steering. Then we'll examine power steering and find out about some interesting future developments in steering systems, driven mostly by the need to increase the fuel efficiency of cars.

• But first, let's see what you have to do turn a car. It's not quite as simple as you might think!
• You might be surprised to learn that when you turn your car, your front wheels are not pointing in the same direction.

• 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. If you 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.

• There are a couple different types of steering gears. The most common are rack-and-pinion and recirculating ball.

The Bose Suspension System

The Bose Suspension System

- While there have been enhancements and improvements to both springs and shock absorbers,
the basic design of car suspensions has not undergone a significant evolution over the years.

- But all of that's about to change with the introduction of a brand-new suspension design conceived by Bose -- the same Bose known for its innovations in acoustic technologies. Some experts are going so far as to say that the Bose suspension is the biggest advance in automobile suspensions since the introduction of an all-independent design.

- The Bose system uses a linear electromagnetic motor (LEM) at each wheel in lieu of a conventional shock-and-spring setup. Amplifiers provide electricity to the motors in such a way that their power is regenerated with each compression of the system.

The main benefit of the motors is that they are not limited by the inertia inherent in
conventional fluid-based dampers. As a result, an LEM can extend and compress at a much greater speed, virtually eliminating all vibrations in the passenger cabin. The wheel's motion can be so finely controlled that the body of the car remains level regardless of what's happening at the wheel. The LEM can also counteract the body motion of the car while accelerating, braking, and cornering, giving the driver a greater sense of control.

Specialized Suspensions: Formula One Racers

Specialized Suspensions: Formula One Racers

- The Formula One racing car represents the pinnacle of automobile innovation and evolution. Lightweight, composite bodies, powerful V10 engines, and advanced aerodynamics have led to faster, safer, and more reliable cars.

- To elevate driver skill as the key differentiating factor in a race, stringent rules and requirements govern Formula One racecar design. For example, the rules regulating suspension design say that all Formula One racers must be conventionally sprung, but they don't allow computer-controlled, active suspensions. To accommodate this, the cars feature multi-link
suspensions, which use a multi-rod mechanism equivalent to a double-wishbone system.

- Recall that a double-wishbone design uses two wishbone-shaped control arms to guide each wheel's up-and-down motion. Each arm has three mounting positions -- two at the frame and one at the wheel hub -- and each joint is hinged to guide the wheel's motion.

- In all cars, the primary benefit of a double-wishbone suspension is control. The geometry of the arms and the elasticity of the joints give engineers ultimate control over the angle of the wheel and other vehicle dynamics, such as lift, squat, and dive.

- Unlike road cars, however, the shock absorbers and coil springs of a Formula One racecar don't mount directly to the control arms. Instead, they are oriented along the length of the car and are controlled remotely through a series of pushrods and bell cranks. In such an arrangement, the pushrods and bell cranks translate the up-and-down motions of the wheel to the back-and-forth movement of the spring-and-damper apparatus.

Suspension Types: Rear

Suspension Types: Rear

- Dependent Rear Suspensions
• Leaf spring - If a solid axle connects the rear wheels of a car, then the suspension is usually
quite simple -- based either on a leaf spring or a coil spring.

• In the former design, the leaf springs clamp directly to the drive axle. The ends of the leaf springs attach directly to the frame, and the shock absorber is attached at the clamp that holds the spring to the axle. For many years, American car manufacturers preferred this design because of its simplicity.

• The same basic design can be achieved with coil springs replacing the leaves. In this case, the
spring and shock absorber can be mounted as a single unit or as separate components. When
they're separate, the springs can be much smaller, which reduces the amount of space the
suspension takes up.

- Independent Rear Suspensions
• If both the front and back suspensions are independent, then all of the wheels are mounted
and sprung individually, resulting in what car advertisements tout as "four-wheel independent
suspension."

• Any suspension that can be used on the front of the car can be used on the rear, and versions of
the front independent systems previously described can be found on the rear axles.

• Of course, in the rear of the car, the steering rack -- the assembly that includes the pinion gear wheel and enables the wheels to turn from side to side --is absent. This means that rear independent suspensions can be simplified versions of front ones, although the basic principles remain the same.

Suspension Types: Front

Suspension Types: Front

- The four wheels of a car work together in two independent systems -- the two wheels connected by the front axle and the two wheels connected by the rear axle. That means that a car can and usually does have a different type of suspension on the front and back. Much is determined by whether a rigid axle binds the wheels or if the wheels are permitted to
move independently.

- The former arrangement is known as a dependent system, while the latter arrangement is known as an independent system.

- Dependent Front Suspensions

• Dependent front suspensions have a rigid front axle that connects the front wheels. Basically, this looks like a solid bar under the front of the car, kept in place by leaf springs and shock absorbers. Common on trucks, dependent front suspensions haven't been used in mainstream cars for years.

- Independent Front Suspensions

• In this setup, the front wheels are allowed to move independently. The MacPherson strut, developed by Earle S. MacPherson of General Motors in 1947, is the most widely used front-suspension system.

• The MacPherson strut combines a shock absorber and a coil spring into a single unit. This provides a more compact and lighter suspension system that can be used for front-wheel drive vehicles.
- The double-wishbone suspension, also known as an A-arm suspension, is another common type of front independent suspension. While there are several different possible configurations, this design

typically uses two wishbone-shaped arms to locate the wheel. Each wishbone, which has two
mounting positions to the frame and one at the wheel, bears a shock absorber and a coil spring to absorb vibrations.

Double-wishbone suspensions allow for more control over the camber angle of the wheel, which describes the degree to which the wheels tilt in and out. They also help minimize roll or sway and provide for a more consistent steering feel. Because of these characteristics, the double-
wishbone suspension is common on the front wheels of larger cars.