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The roar developments of the modern industry not only give people many material benefits but also bring a series of social difficulties, such as environmental pollution and energy crisis that are taken into great consideration by all over the world people. Automobiles consume about half of the petrol of the world and at the same time they have been polluting our atmosphere seriously. At present, for auto engineers, the most important job is to design and develop more clean substitute fuel engines. We will solve the problems of environmental pollution and energy crisis strategically by using these engines.
The computer Simulation has developed gradually along with the development of the computer .The rapid progress of the computer software and hardware not only provide the computer simulation research powerful technological support ,but also accelerated the development of the computer simulation further . As a result, a good many models come into being .Among them, the Quasi-dimensional model becomes popular because its practicability and low cost.
In this paper, the emphasis is laid on the spark-ignited engine. A computer model for in-cylinder working process of spark-ignited engine is developed via using quasi-dimensional model. The model consists of a thermodynamic model, a heat transfer sub model ,a chemical equilibrium model and a two-zone combustion model. The model is anticipated to accurately predict performance of a LPG engine. Based on the model ,a relevant program is written by VB. In order to test the program, we did some experiments on a 4105LPG engine of Chaoyang Diesel Factory. The calculated results is relatively consistent with the experimental results. In the paper ,the changing pressure of 4105LPG engine during the cylinder-closed phase(with the exception of exchanging gas phase) under different rotate speed and different spark-ignited advanced angle conditions is calculated. The total produce of NO emission is also did. In addition, influence of different parameters to the performance of the engine analyzed, and the reason is pointed .In final, the characteristic of 4105LPG engine and that of original engine is compared. Based on the comparison, the feasibility of a diesel engine retrofitted to LPG engine is studied. The study results show that it is feasible to retrofit a diesel engine retrofitted to LPG engine.
In the design of a car the comfort of occupants is clearly of prime importance, and the basic functional of its suspension system is therefore to provide a flexible support for the vehicle which allows the occupants to ride conformability, isolated from road surface imperfections An additional and no less important requirement of the suspension system is that it should stabilize the vehicle under all conditions of driver handling, namely cornering, braking and accelerating. These two basic requirements in respect of vehicle ride and handling generally tend to conflict in practice, since very flexible or soft springing is indicated on the one hand and relatively hard springing on the other.
A significant step toward reducing this conflict was the proper application of independent front wheel suspension which followed chiefly from the research work done in the early 1930s by NMaurice Olley, an ex-Roils-Royce engineer then working for the Cadillac Motor Car Company in America. With an independent front wheel suspension system the steered wheels are located by entirely separate linkages rather than being of independent front suspension (IFS) has long been established practice for all conventional motor cars for the following reasons.
The more precisely controlled location of the front wheels afforded by using an independent linkage system in conjunction with a rigid vehicle structure permits them to have a greater range of Suspension movement. This in turn allows the use of much softer springs, which reduce the magnitude of impact loads transmitted by the front suspension to the car structure. Further-more, the springs themselves are generally no longer required to play any part in locating the wheels, so that leaf springs can be discarded in favor of other types of springs possessing very little internal friction and thereby prevent harshness of ride.
Better road holding
To some extent the springs can be made softer with an IFS system without reducing the roll resistance at the front end of the car, which otherwise could lead to over steer on corners as a result of the rear suspension then offering too much resistance to roll. With beam axle suspension the lateral Separation of its pair of semi-elliptic leaf springs is restricted to about one-half the wheel track dimension so as to leave sufficient clearance for the wheels to be steered. This narrow spring base compares unfavorably with that of an independent system where it is always equal to the wheel track irrespective of the lateral separation of the springs.
More accurate steering
An independent linkage is better able to ensure that each front wheel follows its prescribed geometrical path relative to the car structure and hence those parts of the steering linkage carried thereon. This can be difficult to achieve with a beam axle which is located solely by semi-elliptic leaf springs. For example, early attempts to increase their flexibility usually required the addition of an axle control linkage to prevent the axle from winding up on its springs and causing instability during braking.
Reducing steering joggles I
As compared with a beam axle system, an independent linkage can be arranged to reduce by about one-half the amount either front wheel tilts inwards when passing over an obstacle. This serves to lessen the gyroscopic forces acting on the road wheels, because in tilting inwards they also attempt to steer themselves inwards and this produces an unwanted reaction or joggle at the steering wheel. Furthermore, both wheels of a beam axle system are tilted in unison when either of them passes over an obstacle, a state of affairs that at worst can lead to a wobble or shimmy of the steered wheels.
Increased passenger space.
Last, but by no means least, the introduction of IFS made a direct contribution to improved passenger accommodation by having the power unit mounted further forward in the tar, an arrangement which removed the need to provide front end clearance for the moving center portion of the axle beam. It thus became practicable to reposition the rear seats from above the rear axle to a lower level within the wheelbase. Similarly, the rear-mounted fuel tank could then be moved forward, thereby increasing the capacity of the luggage boot. The linkages used in modern IFS systems generally fall into two basic categories: the unequal transverse links, or wishbone system; and the transverse link and strut, or MacPherson system.
Unequal transverse links IFS
This system, pioneered by General Motors of American the mid 1930s, is sometimes referred to as a wishbone system, because in plan view the front suspension links of their Buick models were originally of this form. With this type of IFS, each wheel: is guided over obstacles by a short upper and a long l!0wer link, the inner ends of these links being pivoted from the car structure and their outer ends now ball jointed to a stub axle carrier or yoke.
As viewed from the front, the relative lengths and angles of these links are chosen so as to offer the following basic compromise:
Independent rear suspension (IRS)
Whereas a few car manufacturers continue to mount the rear wheals on a sprung live axle, many others have long since adopted various forms of independent rear suspension (usually abbreviated to IRS). It first became widely used by German and Middle European manufacturers during the 1930s, notably in the designs of Drs Ferdinand Porsche and Hans Ledwinka, but this development did not really gain popularity elsewhere until some thirty years later.
The chief benefits to be expected from using a modern IRS system are generally concerned with the inter-related qualities, of ride, handling and, in the case of rear-wheel-drive cars reaction. Ride comfort in particular should benefit from the reduction by about one-half in the unsprung mass of the suspension mechanism, resulting from the final drive assembly being mounted on the vehicle structure. Also an increase in useful space within the body rear portion is implicit with IRS, since the propeller shaft and final drive assembly do not rise and fall in sympathy with the suspension movements of the rear, wheels.
The improvement in traction to be expected with independently sprung and driven rear wheels deserves a few words of explanation. Mention was made in Section 19.4 of the antics performed by the live axle of a Hotchkiss drive system during acceleration and braking. Taking matters a little further, we find that during acceleration the axle casing rocks on its springs not only in opposition to crown wheel torque, but also to a lesser extent (as related to the final drive gear ratio) in sympathy with pinion torque. In other words, the tendency during acceleration is to press one rear wheel harder against the ground and to lift the other one off it. This effect, combined with the one mentioned previously, can cause the axle and wheels to writhe about a conical path and generate an unstable handling condition known as axle tramp. Although this state of affairs may to some extent be alleviated by additional means of axle control, as earlier described, such misbehavior is absent from IRS systems. The reason for this is, of course, that the final drive is divorced from the road wheel mountings and is attached to the vehicle structure; the drive to the wheels being transmitted through universally jointed drive shafts.
Comparing different types of IRS
Although we are required only to identify the various systems by their basic geometric layout, a few brief notes on their general characteristics may prove useful to explain their current popularity or otherwise. The systems may conveniently be classified into four types as in the following sections.
Swing axle: pure and diagonal
A pure swing axle system was once widely favored by Continental manufacturers, especially for rear-engined cars where its use proved mechanically expedient. Although body roll tends to be less with this type of IRS, hard cornering can produce outward lean of the outer wheel and a smaller inward lean of the inner wheel, the result being that the rear end of the car is lifted. The sudden onset of this jacking effect can lead to an unstable over steering condition. For normal ride motions of the car there is pronounced tilting of the wheels, with accompanying changes in wheel track as they rise and fall. These undesirable effects can, to some extent, be reduced by using a diagonal swing axle. This system involves less tilting of the wheels and also causes them to steer inwards or toe-in slightly as they rise and fall, which counteracts the over steering tendency.
Trailing arm: pure and semi
The trailing arm system has long been favored for the relatively lightly laden rear wheels of front-wheel-drive cars. In its pure form the arms pivot about an axis that lies parallel with the ground and normal to the centerline of the car. Although the wheels can rise and fall vertically during normal rifle motions of the car, they are necessarily tilted to the same angle as the body with cornering roll, which tends to be greater with this type of IRS. This leaning away from the curve the wheels has the disadvantage of reducing their cornering power. In the case of rear-wheel-driven cars, a departure is usually made from the pure system to one where the pivot axis of each arm is moderately angled in plan view and known as the semi-trailing arm.The purpose of this modified geometry is to maintain more nearly upright during cornering and also to cause them to steer inwards or toe-in slightly as they rise and fall, thereby contributing to a stable under steering condition.
Unequal transverse links
This system of IRS is comparatively little used, because of its potentially greater intrusion into valuable rear body space. On the credit side, a better compromise with respect to suspension geometry can fairly readily be obtained, a particular advantage being that the heavily loaded outer wheel can be maintained more nearly upright in the presence of body roll during cornering. By allowing each drive shaft to perform a dual role and serve also as the upper link, as so ably demonstrated by the Jaguar Company, the unequal transverse links system of IRS may be simplified, its unsprung mass lessened and its vertical space requirements reduced.
Also sometimes referred to as a Chapman strut, so named after the, Lotus car designer who first applied the MacPherson transverse link and strut principle to rear wheel suspension (, this type of IRS hassince become widely used for the non-driven rear wheels of front-wheel-drive cars. For the lateral and longitudinal location of the non-steered rear wheels, the transverse link may pivot about an axis parallel to the centerline of the car. The link may comprise either a substantial wishbone arm, a track control arm that is located fore-and-aft by a trailing link, or a similarly located parallelogram linkage that better maintains wheel alignment with optimum compliance as developed by Mazda. Alternatively, the transverse link may be skewed in the manner of a diagonal swing axle, again with the purpose of correcting for any over steering tendency that may be present, because the geometry of the transverse link and strut is not quite as good as the unequal transverse links system of IRS.
TYPES OF SUSPENSION SPRING Basic requirements
When the road wheels rise and fall over surface irregularities, the springs momentarily act as energy storage devices and thereby greatly reduce the magnitude of loading transmitted by the suspension system to the vehicle structure. Springs that utilize the elastic properties of metal rubber and air are variously employed in motor vehicle suspension systems, the actual choice made being determined largely by versatility, in application and best economy of material in terms of energy storage per unit volume.
At one time, the conventional multileaf spring was built up from a large number of narrow, thin leaves, which in rubbing against each other with flexing of the spring exerted an appreciable friction damping effect, on suspension movements of the wheels. For private cars at least, it is no longer considered desirable that the suspension springs should also act as friction shock dampers, so that leaf springs are now designed with fewer leaves of relatively greater width and thickness.
Furthermore, the leaves are separated at their ends by anti-friction thrust pads such as recessed plastics buttons (Figtire.22.11).A series of retaining clips positioned along the length of the spring has the twofold purpose of preventing the leaves from separating during rebound travel of the spring and ensuring that the sideways loads imposed on tile spring are not borne solely by the uppermost or master leaf.
Another established feature of multileaf spring construction is that of providing nip between the leaves by forming the leaves below the master leaf with successively reducing radii of curvature . This gives a beneficial stress; reduction for the master leaf, because when the leaves are clamped together it is subject to a bending preload opposite in direction to that caused by the vehicle load.
In more recent years advances made in spring manufacturing technology have resulted in the limited use of single-leaf springs. This type of construction is similar in principle to the previously mentioned simple plate spring, but it avoids the excessive width disadvantage by having its single leaf varying in both width and thickness. Advantages generally claimed for this simplified form of Construction are the useful reduction in unsprung weight and the elimination of interleaf friction, both of which contribute to improved ride comfort of the vehicle.
This type of spring represents a compromise between the conventional multileaf and single-leaf springs, and it can be described in effect as a stacked single-leaf spring. It comprises several full-length leaves of constant width but of tapering thickness towards their ends. At their thick middle portion the leaves are separated by interleaf liners and contact one another only towards their ends. Since the tapered-leaf spring offers advantages similar to those of the single-leaf spring, but: with a much greater load-carrying capacity, it has been used to advantage in some commercial vehicles where it gives better cushioning for both cargo and driver.
Whichever type of leaf spring is used, its mounting must locate it positively with respect to both the axle and the vehicle structure, as follows.
The center portion of the spring is attached to a seating or saddle formed towards either end 6f the axle. For installation purposes, the leaves are generally held together by a center bolt the head :of which further serves as a dowel for locating the spring relative to its seating: To avoid the stress-raising effect of a hole through the leaves, the usual center bolt may be dispensed with in some heavy-duty applications arid replaced by dimples or cups pressed into successive leaves, with a corresponding depression being provided n the axle seating. Final attachment of the spring to the axle is effected through the medium of either U-bolts or normal bolts and nuts, together with a clamping plate if required. For the driven rear axles of cars it has long been established practice for the spring-to-axle clamping arrangements to be rubber lined. This not only reduces the transmission of road nose through the spring mounting, but also minimizes stress concentration on the leaves where they emerge from the clamp.
The flexing of a semi-elliptic leaf spring is such that its curvature, and hence its effective length, change constantly with suspension movements of the axle. To locate the axle positively, and at the same time accommodate these lengthwise movements of the spring, the latter is provided with fixed and free end pivots. The fixed end of the master leaf, usually the front end, is provided with a rolled eye embracing a suitable pivot connection on the vehicle structure.
For cars the pivot, or spring pin, clamps the inner sleeve of a rubber bushing pressed into the spring eye, while for commercial vehicles lubricated metal bushings are generally required. The free end of the master leaf is provided with either a similar rolled eye or a plain end. In the former case, the roiled eye and its bushing connect by means of a shackle pin t6 a shackle link, which in turn is hinged from :the vehicle structure .
For commercial vehicles this usually requires a separate shackle bracket fixed to the chassis frame The shackle link bushings are complementary to those used at the fixed pivot of the spring. A plain end mounting for the master leaf is used in conjunction with a slipper-type bracket, an firrangement now conined to commercial vehicles. Flexing of the spring thus produces metal-to-metal sliding Contact of its plain end against the curved underside Of the slipper bracket.
Helical compression or coil springs are-probably now the most widely used type of suspension spring for motor cars. in comparison with a leaf spring, the coil spring can store more than twice the amount of energy per unit volume of material, and it possesses minimal internal friction.However, the vertical space requirements of a coil spring are greater and its inherently low resistance to buckling is such,’ttihi it can function as a spring medium only when used in conjunction with a separate wheel