Car suspensions

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Information about Car suspensions

Published on November 25, 2008

Author: sanyam89


Suspension : Suspension TEAM MEMBERS:- Ashutosh kr.,Sanyam Sharma,Prateek Nagalia,Ankit Tyagi INTRODUCTION : INTRODUCTION Factors affecting design : Factors affecting design Functional constraints Performance targets Rules/laws Cost Weight Packaging space Robustness and reliability Manufacturing, assembly and maintenance costs Vehicle motion : Vehicle motion Sprung mass has 6 degrees of freedom Three translations –lateral, longitudinal and vertical Three rotations –pitch, roll and yaw Definitions for wheel orientation : Definitions for wheel orientation Camber angle ◦Angle between the wheel plane and vertical ◦Positive leaning away from vehicle, negative leaning inwards Front Suspension Types : Front Suspension Types Front suspension - independent systems : Front suspension - independent systems Trailing-arm suspension : Trailing-arm suspension The trailing arm system is literally that - a shaped suspension arm is joined at the front to the chassis, allowing the rear to swing up and down. Pairs of these become twin-trailing-arm systems and work on exactly the same principle as the double wishbones in the systems described above. The difference is that instead of the arms sticking out from the side of the chassis, they travel back parallel to it. This is an older system not used so much any more because of the space it takes up, but it doesn't suffer from the side-to-side scrubbing problem of double wishbone systems. McPherson Strut : McPherson Strut This is also a type of double-A arm suspension although the lower arm in these systems can sometimes be replaced with a single solid arm .This transfers the load-bearing capability of the suspension almost entirely to the upper arm and the spring mounts.The lower arm in this instance becomes a control arm. This particular type of system isn't so popular in cars as it takes up a lot room. Double wishbone : Double wishbone This is a type of double-A or double wishbone suspension. The wheel spindles are supported by an upper and lower 'A' shaped arm. In this type, the lower arm carries most of the load. If you look head on at this type of system, what you'll find is that it's a very parallelogram system that allows the spindles to travel vertically up and down. When they do this, they also have a slight side-to-side motion caused by the arc that the wishbones describe around their pivot points. This side-to-side motion is known as scrub. Unless the links are infinitely long the scrub motion is always present. There are two other types of motion of the wheel relative to the body when the suspension articulates. The first and most important is a toe angle (steer angle). The second and least important, but the one which produces most pub talk is the camber angle, or lean angle. Steer and camber are the ones which wear tyres. Multi-link suspension : Multi-link suspension This is the latest incarnation of the double wishbone system described above. It's currently being used in the Audi A8 and A4 amongst other cars. The basic principle of it is the same, but instead of solid upper and lower wishbones, each 'arm' of the wishbone is a separate item. These are joined at the top and bottom of the spindle thus forming the wishbone shape. The super-weird thing about this is that as the spindle turns for steering, it alters the geometry of the suspension by torque in all four suspension arms. They have complex pivot systems designed to allow this to happen.Car manufacturers claim that this system gives even better road-holding properties, because all the various joints make the suspension almost infinitely adjustable. There are a lot of variations on this theme appearing at the moment, with huge differences in the numbers and complexities of joints, numbers of arms, positioning of the parts etc. but they are all fundamentally the same. Note that in this system the spring (red) is separate from the shock absorber (yellow). Front suspension – semi independent -Transverse leaf-spring : Front suspension – semi independent -Transverse leaf-spring This system is a bit odd in that it combines independent double wishbone suspension with a leaf spring like you'd normally find on the rear suspension. Famously used on the Corvette, it involves one leaf spring mounted across the vehicle, connected at each end to the lower wishbone. The centre of the spring is connected to the front sub frame in the middle of the car. There are still two shock absorbers, mounted one to each side on the lower wishbones. The centre of the spring is connected to the front subframe in the middle of the car Rear Suspension Types : Rear Suspension Types Solid-axle, leaf-spring : Solid-axle, leaf-spring This system was favoured by the Americans for years because it was dead simple and cheap to build. The ride quality is decidedly questionable though. The drive axle is clamped to the leaf springs and the shock absorbers normally bolt directly to the axle. The ends of the leaf springs are attached directly to the chassis, as are the tops of the shock absorbers. The main drawback with this arrangement is the lack of lateral location for the axle, meaning it has a lot of side-to-side slop in it. Solid-axle, coil-spring : Solid-axle, coil-spring The basic idea is the same, but the leaf springs have been removed in favour of either 'coil-over-oil' spring and shock combos, or as shown here, separate coil springs and shock absorbers. Because the leaf springs have been removed, the axle now needs to have lateral support from a pair control arms. The front ends of these are attached to the chassis, the rear ends to the axle. The variation shown here is more compact than the coil-over-oil type, and it means you can have smaller or shorter springs. This in turn allows the system to fit in a smaller area under the car. Beam Axle : Beam Axle This system is used in front wheel drive cars, where the rear axle isn't driven. The beam runs across under the car with the wheels attached to either end of it. Spring / shock units or struts are bolted to either end and seat up into suspension wells in the car body or chassis. The beam has two integral trailing arms built in instead of the separate control arms required by the solid-axle coil-spring system. Variations on this system can have either separate springs and shocks, or the combined 'coil-over-oil' variety as shown here. Advanced suspensions : Advanced suspensions Hydrolastic Suspension Quadraphonic Suspension Hydropneumatic Suspension Hydrolastic Suspension : Hydrolastic Suspension The principle is simple. The front and rear suspension units have Hydrolastic displacers, one per side. These are interconnected by a small bore pipe. Each displacer incorporates a rubber spring (as in the Moulton rubber suspension system), and damping of the system is achieved by rubber valves. These units are inteconnected by pipes,rubber acts as a spring & fluid acts as a damping medium.The rubber springs are only slightly brought into play and the car is effectively kept level and freed from any tendency to pitch. That's clever enough, but the fact that it can do this without hindering the full range of motion of either suspension unit is even more clever, because it has the effect of producing a soft ride. Hydropneumatic Suspension : Hydropneumatic Suspension Ultra-smooth suspension is provided by the fluid's interaction with a pressurised gas, and in this respect, its very similar to the hydragas system described above. The system is powered by a large hydraulic pump, typically belt-driven by the engine like an alternator or an air conditioner. the pump provides fluid to an accumulator at pressure, where it is stored ready to be delivered to servo a system. This system uses a belt fom the engine to pressurise the fluid. This is effectively a balloon which allows pressurised fluid to compress the gas, and then as pressure drops the gas pushes the fluid back to keep the system's pressure up. Quadraphonic Suspension : Quadraphonic Suspension The new technology enabled the car in their demonstration stayed almost still even though it was cornering, entering a bump or even sudden braking. The car’s body stayed perfectly still and steady. Bose does this by using technology of electro-magnetic motors.They work on the principle that they telescope up or down to prevent the car from rolling. This is done very fast and is controlled by an algorithm. To explain the working, assume the car’s right wheel is entering a dip.As soon as the wheel is lowered, an accelerometer sends data to the central control.The algorithm is then executed and the motor lowers right wheel into the dip so that the car stays level. Various suspensions : Various suspensions THANK YOU…… : THANK YOU……

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