This invention relates to shock absorbers for motor vehicles as well as motor vehicles utilising such shock absorbers.
Shock absorbers are used in motor vehicles to absorb or dampen road induced vibrations caused by uneven road surfaces, or compendiously to "absorb shock", thus providing comfort and safety to driver and passenger or rider in the case of a motorcycle or motor scooter. Shock absorbers also bear vehicle loads.
A typical shock absorber comprises a hydraulic cylinder operatively disposed with respect to a helical compression spring pre-compressed to a predetermined load value and disposed over the hydraulic cylinder. The spring may be disposed over the hydraulic cylinder between the lower spring seat and upper spring seat of the shock absorber. Sometimes the hydraulic cylinder itself is referred to as the "shock absorber" since it is the cylinder and fluid contained within it that absorbs energy arising from the vibration of the vehicle.
The spring is compressed to a predetermined load value having regard to parameters such as the vehicle weight and load acting on the vehicle as well as the desired shock absorption capacity of the shock absorber. During motion of the vehicle, the spring is subjected to frequent compression and expansion due to road induced vibrations. This creates shear stresses in the spring, leads to spring fatigue and may cause premature spring failure thereby reducing the life of the shock absorber. Spring failure during motion of the vehicle may also lead to serious accidents.
The capacity of the shock absorbers to absorb or dampen road induced vibrations and bear vehicle load depends on various factors including the spring characteristics such as spring mean coil diameter, wire diameter, number of coils, spring length and damping characteristics. This is necessary for rider comfort. Reduction in length of a spring leads to a reduction in the number of turns for a given spring wire diameter and mean coil diameter and given spring stroke and, consequently, harder suspension and reduced rider comfort. The overall length of the shock absorber depends on the pre-compressed length of the spring. Minor

length adjustment of the spring, may be possible by adjusting the position of the lower spring seat. However, in the usual case where the shock absorber is located dose to the motorcycle body the chain case on one side and muffler or silencer on the other side of the vehicle are generally required to have depressions to provide sufficient clearance for proper location of the lower spring seat of the shock absorbers. Fabrication of such depressions creates additional manufacturing costs as additional manufacturing is required. Further, the consequential limitation in the orientation of the silencer, increased irritating noise due to motorcycle chain wearing against the depression in the chain case and reduced aesthetics of the vehicle are problems with such arrangements.
An alternative to such arrangements is mounting of a shock absorber away from the vehicle body. Such an arrangement requires additional reinforcement which adds to the cost of a vehicle.
The applicant has previously developed a shock absorber which has improved reliability and life. This shock absorber allows increased ride comfort; optimally with an arrangement which may be conveniently mounted on the motorcycle without cost inducing additional fabrication operations. These advantages are achieved by use of a spring combination having first and second spring elements having capacity to store energy from vehicle vibrations, said first and second spring elements being operatively disposed to share the load due to road induced vibrations and resultant shear stresses resulting from compression and expansion of the spring elements during motion of the vehicle, are well below permissible limits. This shock absorber is described in the Applicant's co-pending International Application N0.PCT/INO6/OO2OI the contents of which are hereby incorporated by reference.
The shock absorber may comprise a spacer element provided between the springs for preventing friction and wear through relative motion of the inner and outer springs. This spacer element may be located in one of the spring seats, for example the upper spring seat. The spacer element may take the form of a protective sheath isolating spring elements and/or spring elements and a damping element such as an inner hydraulic cylinder or damping tube. The Applicant has found that, in certain

applications, the spring element(s) may buckle or twist and the spacer element may become trapped between coils of the inner spring and / or an inner hydraulic cylinder or damper tube over which the inner spring is disposed. This may be contingent on buckling of one or both of the spring elements and may result in damage to the spacer element and subsequent wear caused damage to the shock absorber, particularly those wear susceptible components such as the damper tube and the inner and outer springs.
The potential for damage or interference between a spring and another spring and/or the damping element is exacerbated due to the fact that the spacing of the coils of the spring at the buckling location are spaced apart and therefore are more likely to interference with the other spring and/or the damping element.
(t is the object of the present invention to provide a shock absorber having spring elements which is less susceptible to wear.
With this object in view, the present invention provides a shock absorber for a motor vehicle comprising a damping element; and at least one spring element for co¬operating with the damping element to absorb shock and comprising a plurality of coils wherein spacing of the coils of the first portion of the spring element is less than spacing of the coils in a second portion of coils of the spring element.
The spacing referred to above may be the spacing between coils and/or the pitch of coils in a shock absorber or spring element for the shock absorber, the terms spacing and pitch being used in the ordinary spring design sense. However, it may also relate to the spacing between coils or the pitch of coils during practical use of the shock absorber, that is, when buckling or twisting forces act on the spring element(s). The spacing and pitch of the coils may thus vary along the length of the spring element reaching a minimum at a point most subject to buckling and twisting forces when the shock absorber is in use. No spacing between the coils may be provided for adjacent coils of the first portion of coils.

Configuration of adjacent coils in at least the first portion of coils of the spring element may be further selected to minimise wear in the shock absorber and/or interference between the spring element and other elements of the shock absorber. The configuration of adjacent coils in at least the first portion of coils may be selected with reference to at least one further spring design parameter selected from the group consisting of spring element material, coil diameter, spring element length to coil diameter ratio and spring stiffness or other spring design parameters.
The first portion of coils may correspond to a portion of the spring element which is more susceptible to buckling and/or wear damage particularly in those cases where the springs stiffness is relatively low. Such event is most likely to occur in a mid span of the spring element so the first portion of coils may correspond with the mid span of the spring element. The spacing of coils in this mid span portion may then be reduced to avoid portion of the spacer becoming entrapped between these coils. The spacing may be reduced to the extent that the coils are closed or "dead". Adjacent coils in the first portion of coils may be in solid contact though a spacing remains between adjacent coils in the second portion of coils. The pitch of the coils may also, or alternatively, be altered in the mid span portion to similar effect. In this manner, the shock absorber retains its capacity to absorb load and shear stresses while being less susceptible to damage through buckling and twisting.
A spacer element may be included in the shock absorber to separate spring element(s) from the damping element, such as a hydraulic cylinder or damper tube, forming part of the shock absorber. The spacer element may prevent contact between coil(s) of the first portion of the spring element and the damping element. Where adjacent coils of the first portion of coils are in solid contact, the probability of entrapment of spacer element between these coils is lessened considerably.
Such a shock absorber may comprise a single spring element or a spring combination as adopted in the Applicant's preferred dual spring shock absorber. In this form, the shock absorber comprises first and second spring elements. The second spring element may be disposed externally over the first spring element which may be defined as an inner spring element. The inner spring element may

include the first portion of coils, advantageously in the mid span, having lesser spacing than a second portion of coils of the inner spring element.
The coil diameters for the first and second spring elements may be different, coils in the second spring element having greater diameter than coils in the first spring element. The spring elements may be disposed to share shear and compressive stresses resulting from road induced vibration during motion of a vehicle comprising the above shock absorber.
The spring elements may be compressible coil springs such as helical spring coils. Other forms of spring elements could be adopted, spring elements for use in the shock absorber forming a further aspect of the present invention.
In this manner, there is less susceptibility of a spring element to buckling and the shock absorber is more flexible in the face of constraints on its design. In addition, even if the spring was to buckle, the fact that the coils are more closely grouped together minimizes the likely interference between the spring and the hydraulic cylinder or spacer (the closely packed coils forming a guide "sleeve" that minimizes the interference). For example, in a smaller scooter, certain customers may wish for a softer suspension than for larger vehicles. "Softness" may be gauged by reference to a comfort setting or spring stiffness measured in weight/displacement (e.g kg/mm) terms. A lesser spring stiffness corresponds with a softer suspension. However, below certain spring stiffness, the spring may have a length to coil diameter ratio at which buckling of a spring element may occur. Under such circumstances, the design of the spring element to prevent buckling or Intrusion - for example - by inclusion of dead coils in a mid span portion where such buckling is most likely to occur will avoid this problem while providing the desired soft suspension.
The shock absorber of the present invention may be applied to a variety of two and three wheel vehicles.

The shock absorber of the invention may be more fully understood from the following description of preferred embodiments thereof described with reference to the accompanying drawings in which:
Figure 1 is a side cross-sectional view of a shock absorber in compressed condition in accordance with one embodiment of the present invention;
Figure 2 is a side cross-sectional view of a shock absorber in retracted position in accordance with the first embodiment of the present invention;
Figure 3 is a view of the shock absorber of Figures 1 and 2 showing coils of the inner spring element in compressed condition;
Figure 4 is a view of the shock absorber of Figures 1 and 2 showing colls of the inner spring element in retracted condition;
Figure 5 is a rear perspective view of a motor scooter employing a shock absorber as shown in Figures 1 to 4;
Figure 6 is a side sectional view of an inner spring of the Applicant's prior shock absorber in a free condition;
Figure 7 is a side sectional view of an inner spring of the Applicant's prior shock absorber shown in Figures 1 to 4 in compressed condition; and
Figure 8 is a side sectional detail view of an inner spring of the shock absorber of the embodiment shown in Figures 1 to 4.
Referring now to Figures 1 to 4, there is shown the location and design of a shock absorber 1 utilised as part of the rear wheel suspension of a scooter 100 as shown in Figure 5. The shock absorber 1 for rear wheel 102 comprises a damper body 2 comprising a damping element in the form of a hydraulic cylinder 4 which absorbs vibrations caused by driving motorcycle 100 along an uneven road. Hydraulic cylinder 4 includes a piston 8 and piston rod 9 which moves through the cylinder 4 in accordance with the motion of scooter 100 along the road. The compressed condition of shock absorber 1 is shown in Figure 1 and the free condition of shock absorber 1 is shown in Figure 2. Piston rod 9 is locked into position by lock nut 14. The hydraulic fluid is an oil of desired density and viscosity for the suspension application and the working portion 4a of the cylinder 4 is sealed by oil seal washer 10. The shock absorber 1 also includes a spring combination

comprising a pair or combination of spring elements in the form of springs 11 and 12. Springs 11 and 12 are helical compression springs pre-stressed to a predetermined load value having regard to parameters such as vehicle weight and load on the vehicle and desired shock absorption capacity of the shock absorber 1. Springs 11 and 12 may have different colour schemes allowing for easy discrimination and creation of brand awareness for the spring combination.
Spring 12 is an inner spring disposed over hydraulic cylinder 4 and more detail of the inner spring 12, particularly the configuration of its constituent coils is shown in Figures 3 and 4. Spring 11 is an outer spring disposed externally over hydraulic cylinder 4 and inner spring 12. Springs 11 and 12 are operatively disposed relative to each other and bind, during use, to share shear and compressive stresses acting on scooter 100 during its travel along the road.
A spacer element or protective sheath 13 may be provided between the springs 11 and 12. The spacer element prevents contact and wear by rubbing action of springs 11 and 12 against each other. The spacer element is therefore ideally made of a low friction polymer such as nylon or polypropylene. A spacer element or protective sheath 13a is also provided between the hydraulic cylinder 4 and the inner spring 12 to prevent contact and wear by rubbing action of spring against the hydraulic cylinder 4.
Other constructional details of the shock absorber 1 are described in the Applicant's co-pending International Application No. PCT/IN06/00201, the contents of which, are hereby incorporated by reference.
However, the coils 120 of inner spring 12 are designed in a different manner to the prior shock absorber to address the problems of buckling and wear, particularly where a soft suspension is desired for a smaller scooter 100 where there may be a number of constraints on the design of the shock absorber. The problem may be illustrated with reference to Figures 6 and 7 which show the inner spring element 112 of the Applicant's prior shock absorber. The coils of the spring element 112 are illustrated to form three portions. Buckling is most likely to occur in the mid-

span 115 of the first or inner spring element 112 where a soft suspension is desired, It can be seen that there is a spacing "i" between adjacent coils of the mid-span 115 of the inner spring element 112. If buckling occurs, spacing "i" is sufficient to enable portions of a protective sheath to interfere with the spring. Entrapment of a portion of the protective sheath may then occur between the coils and hydraulic cylinder 4 as shown in Figures 1 to 4 above, the hydraulic cylinder 4 or damper tube element being common to the Applicant's prior shock absorber as well as the shock absorber 1 of the illustrated embodiment. Wear due to this and other causes, such as rubbing of inner spring 112 against hydraulic cylinder 4, may then result as may failure of the shock absorber. It may be noted with regard to Figures 6 and 7 that the dimension "m" of the spacing of coils in the coil end portions 117 and 118 is less than the spacing "i". Buckling in these coil end portions 117 and 118 is less likely than in the mid-span coil portion 115.
Referring now to Figure 8, there is shown detail of the inner spring element 12 for a shock absorber 1 forming one embodiment of the present invention. In this case, it will be seen that the first or mid-span coil portion 31 comprises a number of adjacent coils 31a, the spacing "z" between the coils 31a being reduced to substantially less than the dimension of spacing "i" and "m" of coils shown in Figures 6 and 7. These coils 31a are closed or dead at the centre, increasing resistance to buckling even where the length to coil diameter of the inner spring element 12 is increased to provide a softer suspension. The coils 31a may be in solid contact. The spring stiffness may be less than 1.5 kg/mm. The dimension of spacing "z" between adjacent coils 31a is selected to minimise the possibility of buckling and destructive wear.
It may also be noted that the dimension of spacing "y" between coils 35a in the second or coil end portions 35 is significantly greater than the spacing "z" such that the spring element 12 retains a higher degree of resilience in the coil end portions. The shock absorber continues to work effectively, notwithstanding the closed coils 31a in its mid-span 31.

Modifications and variations to the shock absorber of the present invention may be apparent to the skilled reader of this disclosure. Such modifications and variations are deemed w/ithin the scope of the present invention.

WE CLAIM:
A shock absorber for a motor vehicle comprising a damping element; and at least one spring element for co-operating with the damping element to absorb shock and comprising a plurality of coils wherein the spacing of the coils of a first portion of said spring element is less than spacing of the coils in a second portion of coils of said spring element.
The shock absorber of claim 1 wherein spacing of the coils is measured as spacing, including no spacing, between coils; and/or coil pitch.
The shock absorber of claim 1 or 2 wherein configuration of adjacent coils in at least said first portion of coils of said spring element is selected to minimise wear in the shock absorber.
The shock absorber of claim 3 wherein configuration of adjacent coils in at said at least first portion of coils is selected with reference to at least one further spring design parameter selected from the group consisting of spring element material, coil diameter, spring element length to coil diameter ratio and spring stiffness.
The shock absorber of any one of claims 1 to 4 wherein the first portion of coils corresponds to a portion of said spring element which is more susceptible to buckling and/or wear damage.
The shock absorber of claim 5 where the first portion of coils corresponds to a mid span of said spring element.
The shock absorber of any one of the preceding claims wherein a spacer element prevents contact between the first portion of said spring element and the damping element.

The shock absorber of any one of the preceding claims wherein the first portion of the spring element comprises adjacent coils in solid contact.
The shock absorber of any one of the preceding claims wherein said shock absorber comprises first and second spring elements and the second spring element is disposed externally over the first spring element.
The shock absorber of claim 9 wherein diameter of coils in the second spring element is greater than diameter of coils in the first spring element.
The shock absorber of claim 9 or 10 wherein the two spring elements are disposed to share shear load and compressive stresses.
The shock absorber of any one of the preceding claims wherein the two spring elements are compressible coil springs.
The shock absorber of any one of the preceding claims wherein the two spring elements are in the form of spiral wound springs, such spiral windings being in opposite directions to each other.
The shock absorber of any one of the preceding claims wherein each of the two spring elements has a different visual colour scheme.
The shock absorber as claimed in any one of the preceding claims applied to a two wheel vehicle.
The shock absorber as claimed in any one of the preceding claims applied to a three wheel vehicle.
A spring element for a shock absorber as claimed In any one of the preceding claims and having a plurality of coils wherein spacing of the coils of a first portion of the spring element is less than spacing of the coils in a second portion of the spring element.

A motor vehicle including a shock absorber as claimed in any one of claims 1 to 16.