Spring devices – Vehicle – Leaf
Reexamination Certificate
1998-08-13
2002-03-26
Schwartz, Christopher P. (Department: 3613)
Spring devices
Vehicle
Leaf
Reexamination Certificate
active
06361026
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a suspension system for a vehicle, in which a leaf spring is provided to suspend the main body or chassis of the vehicle from a Wheel-bearing axle of the vehicle.
Leaf springs are commonly used in vehicle suspension systems and act to deflect under load changes so as to isolate the main body from vibrations and irregularities occasioned in the course of the vehicle's travel over a surface. The leaf spring, in an unladen, or partly laden state, assumes a curved shape, the curvature of which increases or decreases under load changes, with concurrent changes in the length of the spring end points.
BACKGROUND AND PRIOR ART
It is normal practice to provide positive location at one end, usually the front end, of the spring, for example by means of a spring eye and a bush. This arrangement affords a substantially longitudinally fixed disposition for the vehicle's axle in relation to the main body. The other end, usually the rear end, of the spring is mounted in such a way as to accommodate changes in length of the spring and the shape of the spring at various load conditions is used dynamically to influence the steering and handling of the vehicle.
As an alternative to the use of rubber or polymer mountings, commonly known methods of mounting the relatively unfixed, for example, rear end of the spring, so as to accommodate length changes are a) by the provision of a shackle, or b) by the provision of a cam slider bracket.
In a known suspension system to be described hereinbelow the vehicle main body is suspended from a vehicle axle through a leaf spring having, at its front end, in the intended direction of normal travel of the vehicle, a spring eye and bush which affords a substantially longitudinally fixed disposition of the axle relative to the body. At its rear end, a pivotal shackle for accommodating changes of length of the spring as its curvature changes under varying load conditions, is used. In this known arrangement, forces produced by the angle of the shackle can affect the spring deflection rate in a non-uniform manner at various loads.
In another known suspension system also to be described hereinbelow the arrangement is similar to that described above but the shackle is replaced by a cam slider bracket in which an upper element has a lower surface of non-uniform curvature which bears upon an upper surface of the spring leaf in frictional contact therewith. As the spring leaf angle changes, in the locality of the cam slider bracket, the upper surface of the spring leaf bears upon differing zones of the lower curved surface of the upper element of the bracket, which alters the effective length of the spring leaf. This also changes the spring leaf deflection rate in a non-uniform manner at various loads and the friction between the lower curved surface of the upper element and the spring leaf has an adverse effect on the quality of the ride experienced on the main body of the vehicle. Further, measures to reduce or eliminate wear of the upper element be can made at additional expense in bracket design and manufacture. Even further, the effective length change of the spring leaf can also change the stress distribution along the spring leaf, thus deleteriously affecting its fatigue life. The shape of the lower curved surface of the upper element, and the ineffective length of the spring leaf beyond that element, use up considerable longitudinal installation space which reduces the effective length of the spring leaf available when the longitudinal installation space is limited, which is normally the situation. A modification of this known system includes a cam slider bracket also but at the front end of the spring leaf and a separate radius leaf affording positive longitudinal location for the axle.
In a further known suspension system disclosed in British Patent No. 937027 (Nilsson), the rate of a leaf spring is changed by using a torsion spring to connect at least one of the ends of the leaf spring pivotally to the vehicle frame or chassis, the torsion spring comprising a core element of polygonal cross-section surrounded by a sleeve element of corresponding cross-section Roller-shaped members of rubber or the like are provided between the core and sleeve elements and are deformed upon relative rotational movement therebetween. The leaf spring end is connected rigidly to one of the core and sleeve elements, so that it is tangential to a cylinder surface co-axial to the axis of the torsion spring. Thus, the torsion spring creates a torsional force (torque) as the core and sleeve elements rotate relatively to each other due to the leaf spring and change angle. This resultant torque acts on the leaf spring and, as a consequence, increases the spring rate to stiffen the leaf spring.
Nilsson states that the leaf spring could be preloaded to change the range of deflection of the spring and, also, that the length of the leaf spring could be selected to give the correct geometry capable of avoiding any horizontal deflection. This is a very inefficient way of using a spring rate modifier arrangement. If the spring length is not capable of avoiding a horizontal deflection, then Nilsson suggests that a shackle should be introduced into the system. Thus, the Nilsson suspension system uses torsion springs solely to increase the rates of the leaf springs by stiffening the springs at higher loads and is not capable of reducing the rates of the leaf springs by softening the springs at lower loads.
SUMMARY OF THE INVENTION
The invention aims to provide an improved suspension system with mounting for the spring which better accommodates changes in spring length. The inventive system combines the advantage of a low friction of the shackle arrangement but with the simplicity of a smaller number of components and with the ability to vary the deflection rate of the spring under different load conditions, whilst also increasing the load-carrying capacity of the spring at higher loads. All this being achieved with a saving of cost and weight.
The invention also aims to provide a further improved suspension system wherein the spring rate can be altered to create a notional horizontal deflection which is resisted to generate a corresponding horizontal linear force, as opposed to a torsional force (torque), which can act upon the spring to either reduce or increase its rate (softer or stiffer), as required. This softening or stiffening of the spring can take place at different parts of the total defection of the spring within the same suspension system.
Accordingly, one aspect of the invention provides a suspension system for a vehicle, comprising a leaf spring adapted to suspend a main body or chassis of a vehicle from a wheel-bearing axle thereof a rigid arm having one end thereof connected rigidly to the leaf spring at or adjacent an end thereof, and an axis to which the other end of the radial arm is connected pivotally, which is located at a position substantially offset from the neutral axis of the leaf spring and which extends generally normal to the regular working plane of the leaf spring, wherein the position of the offset pivotal axis with respect to the neutral axis of the leaf spring is adapted to vary the rate of the leaf spring, to soften or stiffen the suspension system.
Preferably, the other end of the arm is pivoted substantially freely to the offset pivotal axis. That is to say, the arm is pivotable substantially freely about that axis. Such pivotal axis may be provided by a bush, as will be described hereinbelow, in which case, any resistance to pivotal movement of the arm about the axis would be negligible so that, within the working range of the suspension system, including softening and stiffening of the spring, the other end of the arm would still be pivoted to the axis in a substantially free manner with negligible torsional resistance if any.
Thus, the rate of the leaf spring can be varied or altered by selecting an arm length to create a notional horizontal deflection and by resisting that deflection, create
Bartz C. T.
Detroit Steel Products Co. Inc.
Fildes & Outland, P.C.
Schwartz Christopher P.
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