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However, if the two wheels are steered through the same angle then they must slip sideways somewhat during cornering, which greatly increases the resistance to motion in tight turns. This is very obvious when a parallel-steered cart is being moved by hand.

Analyzing the Vehicle Dynamics – Lassonde Motorsports

To solve this, the two wheels must be steered through different angles, as in Figure 1. The origin of this notion may be due to Erasmus Darwin himself in , or to Richard Edgeworth, who produced the earliest known drawing of such a system. The simplest way to achieve the desired geometry is to angle the steering arms inwards in the straight-ahead position, and to link them by a tie rod also known as a track rod , as was done by Langensperger.

However, there are certainly other methods, as demonstrated by French engineer Amedee Bollee in , Figure 1.


In Benz obtained a German patent for the same system, Figure 1. This shows tiller control of the steering, the common method of the time. In Benz introduced the steering wheel, a much superior system to the tiller, for cars. This was rapidly adopted by all manufacturers. For comparison, it is interesting to note that dinghies use tillers, where it is suitable, being convenient and economic, but ships use a large wheel, and aircraft use a joystick for pitch and roll, although sometimes they have a partial wheel on top of a joystick with only fore—aft stick movement.

With the limited technology of the period, simple wrought-iron beam springs were the practical method, and these were made in several layers to obtain the required combination of compliance with strength. These multiple-leaf springs became known simply as leaf springs. To increase the compliance, a pair of leaf springs were mounted back-to-back. They were curved, and so then known, imprecisely, as elliptical springs, or elliptics for short. Single ones were called Figure 1. Introduction and History 3 In the very earliest days of motoring, these were carried over from the stage coaches as the one practical form of suspension, as may be seen in Figure 1.

The leaf spring was developed in numerous variations over the next 50 years, for example as in Figure 1. With improvingquality of steels in the early twentieth century, despite the increasing average Figure 1. The steering wheel is C and the foot brake D. The complete vehicle of Figure 1.

Avery real advantage of the leaf spring in the early days was that the spring provides lateral and longitudinal location of the axle in addition to the springing compliance action. However, as engine power and speeds increased, the poor location geometry of the leaf spring became an increasing problem, particularly at the front, where the steering system caused many problems in bump and roll. Figures 1. Greatly improved production machinery by the s made possible the mass production of good quality coil springs, which progressively replaced the leaf spring for passenger cars.


However, leaf-spring use on passenger cars continued through into the s, and even then it functioned competitively, at the rear at least, Figure 1. The leaf spring isstill widely used forheavilyloaded axles on trucks and military vehicles, and has some advantages for use in remote areas where only basic maintenance is possible, so leaf-spring geometry problems are still of real practical interest. Introduction and History 5 In bump, the axle arc of movement is centred at the front of the spring, but the steering arm arc is centred at Figure 1.

The axle clamps on top of the springs Maserati. The large bump steer angle change also contributed to the shimmy problems by causing gyroscopic precession moments on the wheels. Truck and van steering with a leaf spring generally has the steering box ahead of the axle, to give the maximum payload space, as seen in Figure 1. In bump, the arc of motion of the steering arm and the axle on the spring are in much better agreement than with the rear box arrangement of Figure 1.

Also, the springs are likely to be much stiffer, with reduced range of suspension movement, generally reducing the geometric problems. Road testers at the time found this system in no way inferior to more modern designs. Steering geometry was a major problem because of the variability of rigid axle movements.

Introduction and History 7 There have been many applications with transverse leaf springs. In some cases, these were axles or wheel uprights located by separate links, to overcome the geometry problems, with the leaf spring providing only limited location service, or only the springing action. Some transverse leaf examples are given in Figures 1. The steering geometry problems are different in detail, but may be less overall because a stiffer suspension is more acceptable.

Introduction and History 9 Despite considerable thought and experimentation by suspension design engineers, no way had been found to make a steering system that worked accurately. In other words, there were major problems with bump steer, roll steer and spring wind-up, particularly during braking. Any one of these problems might be solved, but not all at once. With increasing engine power and vehicle speeds, this was becoming increasingly dangerous, and hard front springs were required to ameliorate the problem, limiting the axle movement, but this caused very poor ride comfort.

The answer was to use independent front suspension, for which a consistently accurate steering system could be made, allowing much softer springs and greater comfort.

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Sloan took action, as he describes in his autobiography Sloan, Around , Sloan considered the problem of ride quality as one of the most pressing and most complex in automotive engineering, and the problem was getting worse as car speeds increased. In the s, tyres became even softer, which introduced increased problems of handling stability and axle vibrations. On a trip to Europe, Sloan met French engineer Andre Dubonnet who had patented a successful independent suspension, and had him visit the US to make contact with GM engineers.

Also, by Rolls-Royce already had an independent front suspension, which was on cars imported to the USA. Maurice Olley, who had previously worked for Rolls-Royce, was employed by GM, and worked on the introduction of independent suspensions there. In they built the K-squared rig i. This brought home the realisation that a much superior ride could be achieved by the use of softer front springs, but soft springs Figure 1.

The parallel pair of springs at the top or bottom acted as equal-length wishbones, with length equal to three-quarters of the cantilever length. The driveshaft length can be chosen to match this length, to minimisethe plungerequirementatthe splines. The engineers were pleased with the ride and handling, but shimmy steering vibration was a persistent problem requiring intensive development work. In Chevrolet and Pontiac had cars available with Dubonnet suspension, whilst Cadillac, Buick and Oldsmobile offered double-wishbone front suspension, and the rigid front axlewas effectivelyhistory, forpassenger cars at least.

A serious concern forproduction was the ability of the machine tool industry to produce enough suitable centreless grinders to make all the coil springs that would be required. With some practical experience, it became apparent that with development the wishbone suspension was easier and cheaper to manufacture, and also more reliable, and was universally adopted.

As covered in detail in Chapter 6, the track-rod length and angle can be adjusted to give good steering characteristics, controlling bump steer and roll steer.

The dampers were the lever- operated double-piston type, incorporated into the upper wishbone arms. Such a system would still be usable today.

Suspension Geometry and Computation

The wheels are on leading or trailing arms, with the spring contained in a tube on the Figure 1. Introduction and History 11 The type shown has a single tie rod with a steering box, as was usual then, but the system is equally adaptable to a steering rack. The Ackermann effect is achieved here by angling the steering arms backwards and inwards in Figure 1. The steering action is entirely on the sprung mass, so there is no question of bump or roll steer due to the steering, and there are no related issues over the length of the steering members.

Analyzing the Vehicle Dynamics

Bump steer effects depend only on the angle of the pivot axis of the arms, in this case simply transverse, with zero bump steer and zero bump camber. Other versions had this axis at various angles. The leading link type at the front of a vehicle gives considerable anti-dive in braking, but is harsh over sharp bumps. The trailing-arm version is better over sharp bumps but has strong pro-dive in braking.

Another early form of independent suspension was that due to Brouhliet in France, who used sliding splines, with ball bearings for low friction, for the suspension action, Figure 1. Section 1. Subsequent to the leaf spring, torsion bar suspensions were quite common. However, the modern independent suspension is almost invariably based on the coil spring, with location by two wishbones A-arms or by a strut with one wishbone at the bottom.

With the spring and damper unit enclosed, it was very Figure 1. Introduction and History 13 When introduced, this was regarded by the manufacturer as the best suspension design regardless of cost. On the Gordon-Armstrong this could be supplemented with, or replaced by, coils springs used in compression with draw bars, with double action on the spring.

Again, this was a very compact system.

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  • The steering can be laid out to give zero bump steer, as in the Aston Martin version of Figure 1. A transverse single swing-arm type of front suspension can be used, as in Figure 1. There is a large bump camber effect with this design, such as to effectively eliminate roll camber completely. Steering is by Figure 1. Unusually, the track- rod connections are on the rear of the rack, which affects only the plan view angle of the track rods, and hence the Ackermann factor.

    The Glas Isar had double wishbones, as seen in Figure 1. The steering system ishighup, andasymmetrical. Analysis of bump steerrequires afull three-dimensional solution, but with the asymmetrical steering on this design there could be problems unless the track-rod connections to the steering box arm are aligned with the upper wishbone axes.

    Some early double-wishbone systems were very short, particularly on racing cars, as in Figure 1.