Unit 3. The different types of steering gears are as follows:

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Benjamin Paul
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1 Steering Gears One of the important human interface systems in the automobile is the steering gear. The steering gear is a device for converting the rotary motion of the steering wheel into straight line motion of the linkage. The steering gears are enclosed in a box, called the steering gear box. The steering wheel is connected directly to the steering linkage it would require a great effort to move the front wheels. Therefore to assist the driver, a reduction system is used. The different types of steering gears are as follows: 1. Worm and sector steering gear. 2. Worm and roller steering gear. 3. Cam and double lever steering gear. 4. Worm and ball bearing nut steering gear. 5. Cam and roller steering gear. 6. Cam and peg steering gear. 7. Recirculating ball nut steering gear. 8. Rack and pinion steering gear. Under steer and Over steer Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of 1

2 a vehicle to steering. Simply put, oversteer is what occurs when a car turns (steers) by more than (over) the amount commanded by the driver. Conversely, understeer is what occurs when a car steers less than (under) the amount commanded by the driver. Automotive engineers define understeer and oversteer based on changes in steering angle associated with changes in lateral acceleration over a sequence of steady-state circular turning tests. Car and motorsport enthusiasts often use the terminology more generally in magazines and blogs to describe vehicle response to steering in all kinds of maneuvers. Understeer: the car does not turn enough and leaves the road 2

Oversteer: the car turns more sharply than intended and could get into a spin Wheel Alignment: Wheel alignment, sometimes referred to as breaking or tracking, is part of standard automobile

3 Oversteer: the car turns more sharply than intended and could get into a spin Wheel Alignment: Wheel alignment, sometimes referred to as breaking or tracking, is part of standard automobile maintenance that consists of adjusting the angles of the wheels so that they are set to the car maker's specification. The purpose of these adjustments is to reduce tire wear, and to ensure that vehicle travel is straight and true (without "pulling" to one side). Alignment angles can also be altered beyond the maker's specifications to obtain a specific handling characteristic. Motorsport and off-road applications may call for angles to be adjusted well beyond "normal" for a variety of reasons. WHAT IS CAMBER, TOE, CASTER, AND OFFSET? Maintaining proper alignment is fundamental to preserving both your car s safety and its tread life. Wheel alignments ensure that all four wheels are consistent with each other and are optimized for maximum contact with the surface of the road. The way a wheel is oriented on your car is broken down to three major components; camber, caster, and toe. 3

4 Camber The most widely discussed and controversial of the three elements is camber. Camber angle is the measure in degrees of the difference between the wheels vertical alignment perpendicular to the surface. If a wheel is perfectly perpendicular to the surface, its camber would be 0 degrees. Camber is described as negative when the top of the tires begin to tilt inward towards the fender wells. Consequently, when the top of the tires begin to tilt away from the vehicle it is considered positive. Negative camber is becoming increasingly more popular because of its visual appeal. The real advantages to negative camber are seen in the handling characteristics. An aggressive driver will enjoy the benefits of increased grip during heavy cornering with negative camber. During straight acceleration however, negative camber will reduce the contact surface between the tires and road surface. Regrettably, negative camber generates what is referred to as camber thrust. When both tires are angled negatively they push against each other, which is fine as long as both tires are in contact with the road surface. When one tire loses grip, the other tire no longer has an opposing force being applied to it and as a result the vehicle is thrust towards the wheel with no traction. Zero camber will result in more even tire wear over time, but may rob performance during cornering. Ultimately, optimal camber will depend upon your driving style and conditions the vehicle is being driven in. 4

Caster Caster is a bit harder to conceptualize, but it s defined as the angle created by the steering pivot point from the front to back of the vehicle.

This can also increase steering effort as well. Most road vehicles have what is called cross-caster.

5 Caster Caster is a bit harder to conceptualize, but it s defined as the angle created by the steering pivot point from the front to back of the vehicle. Caster is positive if the line is angled forward, and negative if backward. Typically, positive caster will make the vehicle more stable at high speeds, and will increase tire lean when cornering. This can also increase steering effort as well. Most road vehicles have what is called cross-caster. Cross castered vehicles have slightly different caster and camber, which cause it to drift slightly to the right while rolling. This is a safety feature so that un-manned vehicles or drivers who lose steering control will drift toward the side of the road instead of into oncoming traffic. Toe Perhaps the easiest concept to visualize is toe. Toe represents the angle derived from pointing the tires inward or outward from a top-down view much like looking down at your toes and angling them inward or outward. Correct toe is paramount to even tread wear and extended tire life. If the tires are pointed inward or outward, they will scrub against the surface of the road and cause wear along the edges. Sometimes however, tread life can be sacrificed for performance or stability Positive toe occurs when the front of both tires begins to face each other. Positive toe permits both wheels to constantly generate force against one another, which reduces turning ability. 5

6 However, positive tow creates straighter driving characteristics. Typically, rear wheel drive vehicles have slightly positive tow in the rear due to rolling resistance causing outward drag in the suspension arms. The slight positive toe straightens out the wheels at speed, effectively evening them out and preventing excessive tire wear. Negative toe is often used in front wheel drive vehicles for the opposite reason. Their suspension arms pull slightly inward, so a slight negative toe will compensate for the drag and level out the wheels at speed. Negative toe increases a cars cornering ability. When the vehicle begins to turn inward towards a corner, the inner wheel will be angled more aggressively. Since its turning radius is smaller than the outer wheel due to the angle, it will pull the car in that direction. Negative toe decreases straight line stability as a result. Any slight change in direction will cause the car to hint towards one direction or the other. Conclusion Vehicles are designed with manufacturer s settings for a reason. Countless hours of research and development go into designing suspension components and typically those numbers are the best to go with. Attempting to differ from the norm may result in dangerous conditions, especially for public road vehicles. As a tuner, your needs and desires may differ from the norm. In this case, be sure to exercise caution when modifying your suspension and to consult professionals prior to any major modifications. Bear in mind the differing results caused by altering your camber, caster and toe, and to remember that performance often comes at the cost of economy. Power Steering There are a couple of key components in power steering in addition to the rack-and pinion or recirculating-ball mechanism. 6

Pump The hydraulic power for the steering is provided by a rotary-vane pump (see diagram below). This pump is driven by the car's engine via a belt and pulley.

7 Pump The hydraulic power for the steering is provided by a rotary-vane pump (see diagram below). This pump is driven by the car's engine via a belt and pulley. It contains a set of retractable vanes that spin inside an oval chamber. As the vanes spin, they pull hydraulic fluid from the return line at low pressure and force it into the outlet at high pressure. The amount of flow provided by the pump depends on the car's engine speed. The pump must be designed to provide adequate flow when the engine is idling. As a result, the pump moves much more fluid than necessary when the engine is running at faster speeds. The pump contains a pressure-relief valve to make sure that the pressure does not get too high, especially at high engine speeds when so much fluid is being pumped. Rotary Valve A power-steering system should assist the driver only when he is exerting force on the steering wheel (such as when starting a turn). When the driver is not exerting force (such as when driving in a straight line), the system shouldn't provide any assist. The device that senses the force on the steering wheel is called the rotary valve. The key to the rotary valve is a torsion bar. The torsion bar is a thin rod of metal that twists when torque is applied to it. The top of the bar is connected to the steering wheel, and the bottom of the bar is connected to the pinion or worm gear (which turns the wheels), so the amount of torque in the torsion bar is equal to the amount of torque the driver is using to turn the wheels. The more torque the driver uses to turn the wheels, the more the bar twists. The input from the steering shaft forms the inner part of a spool-valve assembly. It also connects to the top end of the torsion bar. The bottom of the torsion bar connects to the outer part of the spool valve. The torsion bar also turns the output of the steering gear, connecting to either the pinion gear or the worm gear depending on which type of steering the car has. 7

8 As the bar twists, it rotates the inside of the spool valve relative to the outside. Since the inner part of the spool valve is also connected to the steering shaft (and therefore to the steering wheel), the amount of rotation between the inner and outer parts of the spool valve depends on how much torque the driver applies to the steering wheel. When the steering wheel is not being turned, both hydraulic lines provide the same amount of pressure to the steering gear. But if the spool valve is turned one way or the other, ports open up to provide high-pressure fluid to the appropriate line. It turns out that this type of power-steering system is pretty inefficient. The Future of Power Steering Since the power-steering pump on most cars today runs constantly, pumping fluid all the time, it wastes horsepower. This wasted power translates into wasted fuel. You can expect to see several innovations that will improve fuel economy. One of the coolest ideas on the drawing board is the "steer-by-wire" or "drive-by-wire" system. These systems would completely eliminate the mechanical connection between the steering wheel and the steering, replacing it with a purely electronic control system. Essentially, the steering wheel would work like the one you can buy for your home computer to play games. It would contain sensors that tell the car what the driver is doing with the wheel, and have some motors in it to provide the driver with feedback on what the car is doing. The output of these sensors would be used to control a motorized steering system. This would free up space in the engine compartment by eliminating the steering shaft. It would also reduce vibration inside the car. General Motors has introduced a concept car, the Hy-wire, which features this type of driving system. One of the most exciting things about the drive-by-wire system in the GM Hy-wire is that you can fine-tune vehicle handling without changing anything in the car's mechanical components -- all it takes to adjust the steering is some new computer software. In future drive-by-wire vehicles, you will most likely be able to configure the controls exactly to your liking by pressing a few buttons, just like you might adjust the seat position in a car today. It would also be possible in this sort of system to store distinct control preferences for each driver in the family. In the past fifty years, car steering systems haven't changed much. But in the next decade, we'll see advances in car steering that will result in more efficient cars and a 8

9 more comfortable ride. STEERING GEOMETRY Definition: The group of design variables outside the steering mechanism that affect steering behavior, including camber, caster, linkage arrangement, ride steer, scrub radius, toe-in, and trail. Wheel Balancing Wheel balancing, also known as tire balancing, is the process of equalizing the weight of the combined tire and wheel assembly so that it spins smoothly at high speed. Balancing involves putting the wheel/tire assembly on a balancer, which centers the wheel and spins it to determine where the weights should go. But Why? The need to balance your wheels is just part of the general maintenance every car requires. As tyres wear, the distribution of weight around their circumference becomes uneven. Eventually, even if the wheel was perfectly balanced to start with, this change in weight will cause the wheel to become unbalanced. But your tyres don t look too bad? An imbalance of as little as 30 grams can cause a noticeable vibration at 100 kph. Mechanics generally recommend balancing all four wheels every 20,000 kilometers as a matter of course. New Tyres Need Balancing Too Whenever you buy a new tyre the tyre technician should balance it as part of the fitting process. A new tyre may look perfectly round and evenly balanced, but there are small variations in weight around its circumference that must be corrected for. And the tyre isn t the only factor that must be taken into consideration your wheel rim, too, will contribute its own set of imbalances. Other Causes of Imbalance Hitting a pothole or a curb with your tyre or rim can throw out a previously balanced wheel. Wheel impacts and the normal stresses of driving may cause a wheel balancing weight to become dislodged. If this happens you are likely to experience the immediate onset 9

10 of vibration. The Wheel Balancing Process When you take your car for a wheel balancing, the mechanic will remove the wheels and place them one by one on a machine which spins them and measures the amount and location of the imbalance. A small weight will then be attached to the rim of the wheel to even out the weight distribution and bring the wheel back into balance. The end result of wheel balancing will be a smoother, less tiring ride, a safer car, lower fuel bills and tyres that last longer. It s worth doing. An Environmental Note Wheel balancing weights which fall from cars and trucks are one of the largest remaining sources of unregulated lead pollution. As lead is a soft metal, they break down in the environment and the lead dust finds its way into the atmosphere, soil and waterways. A simple way to eliminate this source of toxic metal pollution is to use alternative metals such as zinc or steel to fabricate wheel balancing weights. Lead balancing weights have been outlawed in Europe since Centre Point Steering Relative steered-wheel positioning to the swivel axis so that coincidence is obtained between the intersection point of the swivel axis with both the road and wheel plane. Steerability: The ability of vehicle to steer is called steerability 10

Wheel Alignment Defined

Wheel Alignment Defined While it's often referred to simply as an "alignment" or "wheel alignment," it's really complex suspension angles that are being measured and a variety of suspension components