Independent Wheel Vehicle Suspension
Published on Jan 10, 2016
The suspension system connecting a vehicle body to wheels and its tyre allows the wheel to move in an essentially vertical direction in response to good surface irregularities, a spring element temporarily stores and releases energy thus insulating the vehicle body form acceleration peaks. A shock absorber ‘damper’ insures that oscillation induced by road unevenness or aerodynamic forces which would impair ride comfort and road holding die away quickly.
Conventional system provides greater simplicity. They contain systems like rigid axle suspension. They are most widely used in heavy carriers. Suspension is directly using leaf spring hence they have less complexity. In this system both wheels of the vehicle are suspended in combination as directly axle is suspended. Simplicity is the only advantage, they do not provide effective suspension.
With development of technology a new concept called independent wheel suspension has emerged. In this system both the wheels are suspended independently as every wheel has it’s independent suspension system. This provides suspension for actual road conditions. This system is very complex but have advantages like low weight, plenty of scope for achieving favorable elasto-kinematics effects, no coupling of masses, no suspension parts that run right across the vehicle. Hence now a days in most of the passenger cars this system is used and preferred over conventional system, providing the real smooth drive.
The Wheel Carrier
Every wheel is attached to the suspension by a wheel bearing normally of the rolling element (ball or roller) type. The part of the suspension on which this bearing is mounted is called the wheel carrier. In the independent suspension, the swing- axle type, the swing axle itself represents the wheel carrier, which is immediately connected to the vehicle body by a single joint.
The suspension of Fig. is, on the other hand, a kinematic mechanism—a four—joint system, consisting of the wheel carrier as its ‘coupler’ and two links which guide the wheel carrier in non-linear motion. The rigid axle of Fig is simply a wheel carrier with two wheels.
The Kinematic Chain
Except for the case where a wheel suspension system is based on an immediate connection of the wheel carrier and the vehicle body by a joint suspension forms a kinematic chain, consisting of one or several wheel carriers, links and on “fixed part” Fig shows schematically such a kinematic chain, where the most important types of joints links are utilized.The only wheel carrier K is the coupler of the spatial suspension mechanism, and the vehicle body S is the fixed part.
Independent Suspension Layouts
The simple way to give a wheel carrier one degree of freedom with respect to the vehicle body is to connect the two by joint. However, the only joint with one degree of freedom is the tuning joint, trailing arm suspension, semi-trailing arm suspension (b) or swing axle suspension (c).
A tuning and sliding joints provide two degrees of freedom and is therefore not on its own sufficient to form an independent suspension. The surplus degree of freedom can be cancelled by a rod link, and the layout hence becomes an example of rare but still encountered vertical telescopic suspension for front wheels.
If the wheel carrier and the vehicle body are immediately connected by a ball joint which introduces three degree of freedom, the suspension needs two additional rod links to reduce the overall degree of freedom to F=1. The “double-wishbone” version, has quit often been employed, while there has been only one instance of the semi-trailing link version.
The suspension layout shown in Fig clearly represents a transition stage from a direct to an indirect connection of wheel carrier and vehicle body. As all points of the wheel carrier travel on surface of spheres centered on the ball joints at the vehicle body these suspension can be described as “spherical” mechanisms.
Damper Strut Front Suspension
In a damper- strut suspension, the spring usually acts on the transverse link and loads the wheel carrier via its supporting ball-joint in Fig. The supporting ball-joint should be as near to the wheel center plane as possible to minimize the moment generated by the wheel load, and hence the transverse force at the piston rod. This optimum positioning follows almost automatically if the scrub radius is desired to be very small or even negative the “King pin axis” is the line between the supporting ball-joint and the struts upper mounting.
This system is very complex but have advantages like,
2.Plenty of scope for achieving favourable elasto-kinematics effects.
3.No coupling of masses.
4.No suspension parts that run right across the vehicle.
Hence now a days in most of the passenger cars, this system is used and preferred over conventional system, providing the real smooth drive.
“Road Vehicle Suspensions” -Wolfgang Matschinsky
“Race Car Vehicle Dynamics”-
William F. Milliken ,
Douglas L. Milliken
“Theory Of Machines”-
R. S. Khurmi,
J. K. Gupta
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