What is mean by Steering System l Wheel Alignment l Functions and Basic Principles l Steering Principle & the Components l Advantage of the Steering System l
Nowadays most of the vehicles use two wheel steering mechanism as their main the handling system. But efficiency of the two wheel steering vehicle is the proven to be low compared to the four wheel steering vehicles. Four wheel steering system can be employed in the some vehicles to improve steering response increase vehicle stability while the moving at certain speed or to decrease turning radius at the low speed. Four-wheel steering is the technologically tremendous effort on the part of automotive design engineers to the provide near-neutral steering.
In situations like low speed cornering vehicle parking and the driving in city conditions with heavy traffic in the tight spaces high speed lane changing would be the very difficult due to vehicle’s larger wheelbase and the track width which brings high inertia and the traction into consideration. Hence there is a requirement of a mechanism which result in the less turning radius and it can be achieved by the implementing four wheel steering mechanism instead of regular two the wheel steering.
Any mode of the transportation used by people must have some means of the control. For the automobile two the primary control systems are at the driver’s disposal steering system and the braking system. This is a chapter will be focus on the steering system. Most vehicles in the service today have front-wheel steering although a few vehicles have been marketed with the four-wheel steering. Thus, the bulk of this chapter will discuss the front-wheel steering systems to include the following: a discussion of the steering mechanisms available, including power-assisted steering; the factors affecting wheel alignment; a simplified analysis of vehicle cornering dynamics; and the influences of front-wheel drive on steering response. The chapter concludes with a brief discussion of four-wheel steering and vehicle rollover behavior.
Functions of the Steering System
The most basic function of the steering system is to allow driver too safely and the precisely steer vehicle. Beyond the steering system also provides a way to reduce driver effort by making the act of steering vehicle easier. The components of steering system also absorb some of the road shock before it gets to the driver. Very little has changed in the operation of steering system or in some of the components since earliest the automobiles. The things that have changed primarily have to do with increased ease and the effectiveness of operation and longer-lasting components that require less the maintenance.
The addition to allowing vehicle to be turned the steering system must be set up to allow the vehicle to track straight the ahead without steering input from the driver. Thus an the important design factor for a vehicle is the wheel alignment. Four parameters are set by the designer and these must be checked regularly to the ensure they are within the original vehicle specifications.
The four parameters discussed here are as follows:
Automotive Engineering Fundamentals
- 1. Camber
- 2. Steering axis inclination
- 3. Toe
- 4. Caster
Camber is the angle of tire wheel with respect to the vertical as viewed from the front of the vehicle as shown in. Camber angles usually are the very small on order of 1 the camber angles shown in the exaggerated. Positive camber is defined as top of the wheel being tilted away from the vehicle whereas negative camber tilts the top of wheel toward the vehicle. Most vehicles use a small amount of the positive camber for reasons that will be discussed in the next section. However some off-road vehicles and the race cars have zero or slightly negative the camber.
2 Steering Axis Inclination
Steering axis inclination (SAI) is the angle from the vertical defined by the centerline passing through the upper and lower ball joints. Usually, the upper ball joint is closer to the vehicle centerline than the lower, as shown in Fig. 7.18. Also shows the advantage of combining positive camber with and the inclined steering axis. If a vertical steering axis is the combined with zero camber left side of the any steering input requires the wheel to scrub in an arc around the steering axis. In addition to the increasing driver effort it is the causes increased tire wear.
The combination of steering axis inclinations (SAI) and the positive camber reduces the scrub radius right side of this reduces driver effort under low-speed turning conditions and the minimizes tire wear. An the additional benefit of this system is that the wheel arc is no longer parallel to the ground. Any turning of the wheel away from straight ahead the causes it to arc toward the ground. Because the ground is not movable this causes the front of the vehicle to be raised.
This is not the minimum potential energy position for the vehicle thus weight of the vehicle tends to turn the wheel back to the straight ahead position. This is a phenomenon is very evident on most vehicles-merely turning the steering wheel to full lock while the vehicle is standing still will make front end of the vehicle rise visibly Although the stationary the weight of vehicle may not be sufficient to rotate the wheels back to the straight-ahead position as soon as the vehicle begins to move the wheels will return to the straight-ahead position without the driver input. Caster angle also contributes to this self-aligning torque and will be discussed in the Section. The Note diagrams in the preceding figures have been simplified to the facilitate discussion. In practice the wheel is dished so that the scrub radius is further reduced as the illustrated.
Toe is defined as difference of the distance between leading edge of the wheels and the distance between trailing edge of the wheels when viewed from above. Toe-in means front of the wheels are closer than the rear toe-out implies the opposite. Shows both cases. For the rear-wheel-drive vehicle the front wheels normally have a slight amount of toe-in. the shows why this is true. When the vehicle begins to roll rolling resistance the produces a force through the tire contact patch perpendicular to the rolling axis. Due to the existence of the scrub radius this force produces a torque around the steering axis that tends to cause the wheels to the toe-out.
The slight toe-in allows for this and when rolling, the wheels align along axis of the vehicle. Conversely, front-wheel-drive vehicles require slight toe out. In this case tractive force of the front wheels produces a moment about the steering axis that tends to toe the wheels inward. In this case proper the toe-out absorbs this motion and allows the wheels to parallel direction of motion of the vehicle.
Caster is the angle of steering axis from the vertical as viewed from the side and is shown in the Positive caster is defined as the steering axis inclined toward rear of the vehicle. With positive caster the tire contact patch is aft of the intersection of steering axis and the ground. This is a desirable feature for the stability as illustrated by the When wheel is turned the cornering force acts perpendicular to the wheel axis and through the contact patch.
This is creates a torque about the steering axis that acts to canter the wheel. Obviously negative caster results in the opposite effect and the wheel would tend to continue turning about the steering axis. The most common example of the positive caster is a shopping cart. The wheels are free to turn around the steering axis and when the cart is pushed straight ahead the wheels self-align to the straight-ahead position.
Functions and Basic Principles
The steering system along with the suspension system allows the driver to safely and easily control the vehicle’s direction while driving. To the accomplish these goals the steering system works with components of the suspension to provide for turning movement of the wheels. In addition to connecting the driver to wheels the steering system also provides feedback to driver from the front tires. This is the feedback called road feel is used by the driver to determine how vehicle is the handling.
The steering system consists of the components that allow the driver to turn front wheels of the vehicle and for a few vehicles provides for a limited amount of steering by the rear wheels. The overall function of steering system has not the changed much since earliest days of the automobile.
Steering Columns and Shafts
The basic operation and function of the steering column has not changed very much the column gives the driver ability to control the direction of front wheels and provides some leverage to make steering the little easier. Early steering columns contained the steering shaft steering wheel and often had the choke and ignition timing advance controls mounted on them for the easy access.
An early model car’s steering wheel and the column are shown in the Today’s columns still perform the same steering functions and still have controls for the other systems or components mounted to them for easy access by the driver as shown in the New vehicles sold in the United States are also required to have a collapsible the steering column to the help prevent driver injury in event of a front-end the collision.
Mechanical Advantage of the Steering System
The Leverage or mechanical advantage is used at the steering wheel and in the gearbox to increase force supplied by the driver. The gears inside the gearbox act as levers increasing mechanical advantage and the reducing driver effort to turn the wheels. The Leverage is quite visible in the steering system. Think of the steering wheel as a lever as in The force that you apply to the wheel while turning is applied over the radius of steering wheel which allows the steering wheel to act as a lever and to the increase force applied to the steering shaft.
The steering shaft in turn uses the force exerted on it by the steering wheel to act as input for the steering gearbox. The gearbox uses two gears to further increase the mechanical advantage and decrease driver the effort. The gearbox also converts rotary motion of the steering wheel and the shaft into a linear or back and forth motion that moves the wheels. Shows how a gearbox uses leverage and the changes rotary motion into linear the motion.
Why is the use of leverage important in steering the system? Try this experiment Ask your instructor to the provide you with a lab vehicle. Turn the engine off but leave the steering column unlocked and the vehicles sitting normally on the shop floor. Next try to push the front wheels side-to-side by the yourself. How easy was this to do? Most likely you were not able to the move wheels much and the little bit they did move required a lot of effort. Moving the wheels takes effort which is the why leverage is important to the steering system.
Steering Principle & the Components
Ackerman Steering the Mechanism
With perfect Ackermann at the any angle of steering the perpendicular line through the canter point of all the wheels will meet at a common point. But this may be the difficult to arrange in practice with simple linkages. Hence modern cars do not use pure Ackermann steering the partly because it ignores important dynamic and the compliant effects but the principle is sound for the low speed maneuvers.
The turning radius or turning circle of a vehicle is the diameter of smallest circular turn U-turn that the vehicle is capable of making. Turning circle radius the average steer angle Wheel Steering the System.
When the slip angle of front wheels is the greater than slip angle of rear wheels vehicle the understeers. Thus the vehicle goes out of circle of the steering. Most vehicle manufacturers set the vehicle profile with some the understeer.
Over steer is the defined when the slip angle of front wheel is less than the slip angle of rear wheel. This makes the vehicle move inside circle of the steer. This is a far dangerous the situation than understeer.
Neutral Steer or Counterstain
The Counter-steering can defined as when the slip angle of front wheels is the equal to slip angle of the rear wheel. The vehicle follows the line with utmost the stability.