CA2271402A1 - Rear suspension system for a land vehicle - Google Patents

Abstract

A suspension assembly for mounting an endless track to a chassis of a snowmobile, the suspension assembly having a pair of pivoting arms centrally mounted to the slide members, or rails, and a weight transfer dynamic compensator capable of compensating for the weight transfer of the snowmobile when the track is pulling on the chassis. The weight transfer dynamic compensator prevents the chassis from rotating excessively with respect to the slide rails during rapid acceleration. Such a rotation of the chassis is detrimental to rider comfort and stability.
The suspension assembly is coupled such the rails remain somewhat parallel to the chassis when encountering a bump at either the front of the rails or at the rear of the rails, also enhancing rider comfort and stability. The suspension assembly is coupled by virtue of a limited-translation slide bar at the rear of the suspension assembly and a tension-only member, or pulling belt, located at the front of the suspension assembly. The suspension assembly having the weight transfer dynamic compensator improves the cornering of the snowmobile by ensuring that there is ample weight on the front skis, especially when accelerating out of a turn.

Description

Rear Suspension System for a Land Vehicle FIELD OF THE INVENTION
This invention relates to a single generally centrally mounted structure in a rear suspension system for a land vehicle, and more particularly to a weight transfer system for providing an adjustment between alternative riding conditions.
DISCUSSION OF RELATED ART
Rear suspension systems in land vehicles conventionally comprise apparatus which are mounted to the chassis of the vehicle in a plurality of locations. Typically, the rear suspension systems are heavy due to the number of components in the system, and the impact of the energy absorbed during the ride of the vehicle is absorbed by the driver.
Several rear suspension systems for snowmobile vehicles have been patented.
For example, U.S. Patent No. 4,826,260 to Plourde discloses a suspension system for an endless track vehicle, such as a snowmobile. The suspension system comprises a shock absorber unit being pivotally connected to a forwardly located crank arm, a strap and a retainer rod. The retainer rod extends across and is fixed to a front portion of a pair of lateral slides.
The strap limits the downward movement of the front portion of the lateral slides by means of coil springs and a shock absorber unit. Furthermore, the shock absorber unit exerts a downward force on both the front and rear portions of the slides.
Another example of a rear suspension system for a snowmobile vehicle is U. S.
Patent No.
4,407,386 to Yasui et al. This patent discloses a suspension unit comprising a first shock absorber in a front portion of the rear suspension system, and a second shock absorber in a rear portion of the rear suspension system. The first shock absorber is connected to a proximal end of a guiderail by means of a cross tube, which is pivotally supported to the vehicle by means of bolts. The second shock absorber is connected to a distal end of the guide rail by means of bellcranks and arms. The bellcranks are pivotally supported on an axle which is journaled in the body of the snowmobile vehicle. Furthermore, the rear portion of the rear suspension system comprises a strap for limiting the maximum vertical travel of the guiderails with respect to the body of the vehicle at such time as the vehicle is vertically lifted off the ground. Accordingly, S this patent limits the vertical lift of the guiderails by means of a two sets of shock absorber units, inc combination with springs, a strap, bellcranks and arms.
Other examples of patented rear suspension systems for land vehicles and snowmobiles include: U.S. Patent No. 5,033,572 to Zulawski, U.S. Patent No. 4,787,470 to Badsey, U.S.
Patent No. 4,546,842 to Yasui, U.S. Patent No. 3,913,692 to Lohr et al, Japanese document 62-214065, and Japanese document 3-157283.
While each of the above described and cited rear suspension systems for land vehicles function adequately, they each have certain drawbacks. The major drawback is that the rear suspension systems are mounted to the underside of the chassis at both a front and rear portions thereof. The dual attachment of the prior art suspension systems in some circumstances add increased weight to the vehicle, reduce travel of the suspension, and increase the drag on a returning section of an endless track thereby decreasing the maximum speed achievable.
Therefore, what is desirable in a rear suspension system for a land vehicle is a generally centrally mounted rear suspension system capable of providing improved acceleration and cornering, an increase in the maximum speed achievable, a reduction in the weight of the vehicle by reducing the number of components in the suspension system, and an improved shock system for decreasing the workload of the components of the suspension system.
BACKGROUND OF THE INVENTION
A rear suspension system on a snowmobile serves essentially two purposes: (i) to improve control of the snowmobile by keeping the slide rails in engagement with the ground and (ii) to isolate the driver from the terrain over which the snowmobile is traversing.

One of the primary factors determining the performance of a suspension system is the ratio of the suspended mass to the unsuspended mass. The suspended mass is defined as the mass of the vehicle supported above the springs of the suspension. The unsuspended mass is defined as the mass of the vehicle that is not supported by the springs (i.e.
the mass "below" the springs). It should be noted that these definitions are idealized in that some suspension systems contain members that are, strictly speaking, neither supported above nor below the springs. In calculating the suspended and unsuspended masses, therefore, the suspension engineer will often have to consider certain members as being partially suspended and apportion percentages of the mass of these members to the unsuspended and suspended mass totals.
As illustrated in the idealized example in Figure 26, the suspended mass is the mass above the spring whereas the mass of the wheel and axle below the spring constitutes the unsuspended mass. For optimal control, the ratio of the suspended mass to the unsuspended mass should be as large as possible. For instance, referring again to the example illustrated in Figure 26, if the wheel and axle are light compared to the supported mass of the vehicle and assuming the spring supporting the mass of the vehicle is stiff enough to support the mass of the vehicle, the wheel will closely follow the terrain because the relatively large spring force divided by the relatively small mass of the wheel and axle produces a large acceleration that quickly returns the wheel and axle toward the undeformed equilibrium position.
Furthermore, the frequency, f, of a suspension system is governed by the spring rate, K, and the suspended mass, M, according to the following relation:
f. K
M
Evidently, as the suspended mass increases, the frequency of vibration of the suspension system decreases. As the frequency diminishes, the comfort generally increases. Vehicles with large suspended masses (e.g. trains) are often considered comfortable because they vibrate at a low frequency.
Another factor that improves the ride comfort of a snowmobile is the use of a pair of substantially long, flat rails. These rails are analogous to the wheels on a car. The larger the diameter of the wheels, the more comfortable the ride is. When traversing rough terrain, a larger wheel is less likely to enter into a crevice than a smaller wheel, thus providing a greater degree of comfort. The rails of a snowmobile are effectively like a wheel of 40-foot diameter, thus providing a tremendous insulation from small crevices in the terrain.
All snowmobile rear suspension systems have a front arm (or at least an equivalent thereof) linking the rails to the chassis. As illustrated in Figure 27, the track tension exerts a forward force on the rails. This forward force on the rails is transmitted to the chassis via the front arm and is the force that is responsible for accelerating the snowmobile. The front arm also plays a critical role in keeping the track in tension. With a track perimeter of 3000 mm and an allowable stretch of 15 mm, it is important to keep the track relatively taut around the perimeter defined by the rails and idler wheels. If the track goes slack and track tension is lost, the track "ratchets". This ratcheting phenomenon is highly undesirable because the snowmobile loses traction. Thus, in designing a snowmobile rear suspension, it is important to design the kinematics such that the track remains relatively taut at all degrees of compression. In other words, when the suspension is fully compressed, there must still be sufficient track tension to prevent ratcheting. This requires a careful kinematic analysis to determine the optimal length, position and angle of the front arm (with respect to the rails).
Beside the position, location and angle of the front arm, the position of the idler wheels and the curvature of the rails have important effects on the maintenance of proper track tension.
Thus, in designing a rear suspension system, the front arm, idler wheels and curvature of the rails are parameters that can be varied in order to arrive at a kinematically optimal configuration for preventing ratcheting of the track.
In addition to the problem of ratcheting, the suspension engineer must maximize the travel of the suspension. In so doing, the components of the suspension must be free from interference so that the suspension can collapse to a compressed configuration. For instance, it is common practice to use rotational springs because they are stiff and compact and because they are not as susceptible to becoming jammed up with ice. In operation, it is not uncommon for a suspension to accumulate between 10 and 20 pounds of ice in the mechanism which can reduce the travel of the suspension and hamper the operation of coil springs.
For that reason, coil springs are often protected with a rubber shroud that prevents ice from forming between the coils.
The geometry, spring rate and damping coefficient of the shocks determine the response of the suspension system. A suspension has a "rising rate" if it becomes stiffer as it is compressed. A suspension has a "falling rate" if it becomes softer as it is compressed. In many suspension systems, the rate changes because the angle of the shocks changes with respect to the applied loads. This means that it is possible to have a configuration where during compression of the suspension the response changes from a falling rate to a rising rate or vice versa.
In addition to the front arm, practically all suspension systems have a rear arm (or the equivalent thereof). The rear arm actuates the spring and dampers and also links the chassis to the rails so as to regulate the motion of the chassis with respect to the rails. The rear arm, unlike the front arm, however, cannot be of a fixed length. This would result in a parallelogram geometry which would reduce the motion of the suspension to a single degree of freedom. A
parallelogram geometry would poorly handle bumps in the terrain. Thus, the rear arm should be variable in length to provide the suspension with two degrees of freedom. The two degrees of freedom can be thought of as a vertical displacement of the rails with respect to the chassis and a rotation of the rails (again with respect to the chassis).
In designing a suspension for optimal dynamic response, there are essentially two general load cases that need to be considered: (i) bumps and (ii) internal forces due to weight transfer caused by track tension. It should be noted that inertial forces due to the acceleration of the vehicle are rather negligible.
In the first general load case, bumps can be categorized into three types, depending on the point of application of the load: (a) front of the rails, causing the rails to pivot upwardly at the front; (b) rear of the rails, causing the rear of the rails to pivot upwardly with respect to the chassis; and (c) center of the rails, causing the rails to rise in a substantially parallel manner with respect to the chassis. The desired response for a suspension system is to have the rails rise in -S-a substantially parallel manner. Recent innovations in suspension technology have introduced mechanisms that cause the rails to rise in a substantially parallel manner for load cases (a) and (b).
In the second general load case, internal forces due to track tension cause the rear of the chassis to fall toward the rails and the front of the chassis to rise, as shown in Figures 28 and 29.
Consequently, the weight on the front skis is diminished so much so that the skis may even tend to lift off the ground as illustrated in Figure 30. Clearly, when accelerating out of a turn (i.e.
when the track is pulling forcefully), the reduction in traction on the front skis hinders steering and thus limits the performance of the snowmobile. Thus, to improve steering, it is necessary to limit the movement of the chassis with respect to the rails such that the chassis remains mainly parallel to the rails at all times. Furthermore, in terms of ride comfort, any tilting, or pitching, of the chassis is much more unbalancing for the driver than a mainly vertical disturbance.
Attempting to maintain the chassis parallel to the rails can be accomplished by coupling the front and rear of the suspension system so that a displacement of the front of the rails causes the rear of the rails to displace as well. Similarly, a displacement of the rear of the rails causes the front of the rails to displace. Thus, coupling of the suspension ensures that the rails remain mainly parallel to the chassis both when encountering a variety of bumps and when the track is pulling. Coupling of the front and rear of the suspension normally means that over an initial range of motion the suspension operates as if it has two degrees of freedom (i.e. in an uncoupled manner) and then, at a certain point, the suspension becomes coupled and loses one degree of freedom.
SUMMARY OF THE INVENTION
It is therefore the general object of the present invention to provide a single generally centrally mounted structure in a rear suspension unit of a land vehicle, such as snowmobiles and other recreational vehicles.
Another object of the invention is to provide a rear suspension system for a land vehicle which can provide for an adjustment between alternative riding conditions during weight transfer of the vehicle, especially during acceleration and cornering.
Additionally, it is a further object of the invention is to reduce the weight of the rear suspension system by reducing the number of components therein.
Furthermore, it is a further object of the invention is to transfer the energy impact on the land vehicle toward the center of gravity of the land vehicle, thereby reducing the kick back effect, and transfernng the energy impact away from the driver of the vehicle.
In accordance with the invention, these and other objectives are achieved by providing a suspension system for the rear portion of a land vehicle comprising a single mounting structure in a central portion of the suspension system, and further providing a weight dynamic compensator for allowing adjustment between alternative riding conditions.
As embodied and broadly described herein, the invention seeks to provide a suspension assembly for mounting an endless track to a chassis of a snowmobile, said suspension assembly comprising:
(a) two substantially parallel and spaced-apart elongated slide members connected together by at least one transversely mounted bridge member;
(b) two substantially parallel and elongated pivoting arms, each having a first end portion pivotally connected to said slide members and a second end portion adapted for connection to the chassis;
(c) a rocker arm assembly pivotally connected to said pivoting arms, said rocker arm assembly having:
- a first end portion pivotally connected to a substantially rigid link, said link being pivotally connected to the chassis;
- a second end portion connected to a tension-only member, said tension-only member being connected to said slide members;
(d) a resilient member connected at a first end portion to the chassis and at a second end portion to the slide members; and (e) a slide bar having a first end portion connected to the chassis and a second end portion slidingly engaged to a holder, said holder being pivotally mounted to a rear portion of said slide members whereby said slide bar is capable of limited translation relative to said holder thereby limiting the displacement of said slide members relative to the chassis.
This suspension assembly compensates for dynamic weight transfer which occurs when the track pulls downwardly on the rear portion of the chassis. The dynamic weight transfer compensation enables the snowmobile to maintain traction on its front skis which is very important for enhancing the ability to turn and accelerate simultaneously.
Other objects and features of the present invention will become apparent by reference to the following description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other obj ects, features and advantages of the invention, as well as the invention itself, will become better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
Figure 1 is a side view of a snowmobile, including the rear suspension system according to the present invention;
Figure 2 is a perspective view of the rear suspension system;
Figure 3 is a side view of a snowmobile vehicle, including a rear suspension system and a longitudinal slide bar, according to the present invention;
Figure 3A is a side view of a snowmobile vehicle, including a rear suspension system and a cable, according to the present invention;
Figure 4 is a side view of a snow mobile, displaying the displacement of the pivoting _g_ arms, according to the present invention.
Figure 5 is a side view of a second embodiment of the travel means;
S Figure 6a is a side view of the bracket;
Figure 6b is a front elevational view of a support holding the bracket;
Figure 7a is a side elevational view of the secondary pivoting arm;
Figure 7b is a front elevational view of a support and the secondary pivoting arm attachment;
Figure 8a is a front elevational view of the pulling belt;
Figure 8b is a right side view of the pulling belt;
Figure 9 is a side view of the slide bar;
Figure 10 is a side elevational view of the rear suspension system in accordance with the present invention showing possible adjustments to the bracket;
Figure 11 is a side elevational view partially showing the Weight Transfer Dynamic Compensator (WTDC);
Figure 12 is a side elevational view of the slide bar; and Figure 13 is a side view of a snowmobile showing different comfort zones, according to the present invention.
Figure 14 is a side elevational view of the most preferred embodiment of the rear suspension system, shown mounted to a typical snowmobile;
Figure 15 is a side elevational view of the most preferred embodiment of the rear suspension system, shown mounted to a cut-away of a typical snowmobile;
Figure 16 is a rear isometric view of the most preferred embodiment of the rear suspension system;
Figure 17 is a side elevational view of the rear suspension system of Figure 16;
Figure 18 is a side elevational view of the rear suspension system of Figure 16, shown in its uncompressed configuration;
Figure 19 is a side elevational view of the rear suspension system of Figure 16, shown in its partially compressed configuration;
Figure 20 is a side elevational view of the rear suspension system of Figure 16, showing how the rear suspension system compensates for the effects of weight transfer;
Figure 21 is a first variant of the rear suspension system of Figure 16 wherein the WTDC
comprises a unitary L-shaped rocker arm;
Figure 22 is a second variant of the rear suspension system of Figure 16 wherein the WTDC comprises a pulley arrangement;
Figure 23 is a third variant of the rear suspension system of Figure 16 wherein the WTDC
comprises a reversed pulley arrangement from that shown in Figure 23;
Figure 24 is a fourth variant of the rear suspension system of Figure 16 wherein the WTDC comprises a straight rocker arm;

Figure 25 is a fifth variant of the rear suspension system of Figure 16 wherein the WTDC
comprises an L-shaped rocker arm having a curved outer surface to which is affixed a pulling belt;
Figure 26 is a simple, idealized illustration of the role of suspended mass and unsuspended mass in the evaluation of the control of a suspension system;
Figure 27 is a force vector diagram illustrating the how the force generated by the track tension is transmitted to the chassis to propel the snowmobile;
Figure 28 is a diagram illustrating a suspension at rest;
Figure 29 is a diagram illustrating the response of a suspension to weight transfer;
Figure 30 is an illustration of the weight transfer problem;
Figure 31 is an illustration of the effect of a bump on the front of the rails;
Figure 32 is an illustration of the effect of a bump near the center of the rails; and Figure 33 is an illustration of the effect of a bump on the rear of the rails.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Although the disclosed invention may have broad applicability, it relates primarily to a rear suspension system for a land vehicle, and more specifically to a land vehicle with a track, such as a snowmobile. The following description will indicate certain items as occurring in pairs when only one of the pairs is shown in the accompanying drawings. It is to be understood that the portion of each pair which is not shown is identical to the illustrated part and performs the same function as the illustrated item. Accordingly, it should be noted that like reference numerals are used throughout the attached drawings to designate the same or similar elements or components.
Refernng now to the drawings, Fig. 1 illustrates a novel rear suspension system 20 for a snowmobile vehicle 10. The vehicle 10 has a front portion 2, with a forwardly mounted engine therein (not shown), forwardly mounted travel means 8, and a rear portion 30, comprising a seat area 12, steering means 14, a chassis 16, rearwardly mounted travel means 18 (also known as slide members), and a rear suspension system 20 (see Figure 3). The center of gravity 22 of the vehicle is in the front portion 2 of the vehicle 10 at 22 as indicated.
The rear suspension system 20 of the vehicle is located adjacent the rear portion of the land vehicle 10, on an underside of the chassis 16 and is attached to the chassis 16 by means of two horizontal bars. A first horizontal bar 40 is attached to an underside of the chassis directly below the seat area, and a second horizontal bar 50 is attached to an underside of the chassis directly below the steering means 14.
In the following description, the terms 'proximal' and 'distal' are with reference to the front portion 2 of the vehicle. The rear suspension system 20, as shown in Fig. 2, comprises rearwardly mounted travel means 18 having proximal and distal portions. The suspension system further comprises a pair of inclined primary pivoting arms 60, having proximal ends 62 and 20 distal ends 64. The proximal ends to the primary pivoting arms 62 are attached to the second horizontal bar 50, and the distal portion of the primary pivoting arms 64 are connected to a third horizontal bar 70 at distal portion of the rearwardly mounted travel means 18 . Accordingly, the primary pivoting arms are mounted between the second horizontal bar and the third horizontal bar such that the primary pivoting arms are inclined at an acute angle with respect to the rearwardly mounted travel means, when the vehicle is in a rest position.
The rear suspension system 20 further comprises a primary suspension means 80, having a proximal end 82 and a distal end 84. The proximal end of the primary suspension means 82 is attached to the first horizontal bar 40 at a rear portion of the underside of the chassis 16, and a distal end of the primary suspension means 84 is attached to the third horizontal bar 70 at a distal portion of the rearwardly mounted travel means 18. In a preferred embodiment, the primary suspension means, which is mounted between the first and third horizontal bars, is inclined at an acute angle with respect to the rearwardly mounted travel means when the vehicle is in a rest position. The third horizontal bar 70 also holds together the rearwardly mounted travel means. In sum the third horizontal bar 70 acts as a support for the primary pivoting arms 60 and the primary suspension means 80, thereby enabling the primary suspension system to control the displacement of the rearwardly mounted travel means 18.
Furthermore, due to the structure and support of the suspension system 20 with respect to the vehicle, the stress and pressure of the primary suspension means 80 is transferred to the chassis 16 at two relatively near points. Accordingly, in a preferred embodiment, the chassis comprises a reinforcing plate 400 to reinforce the chassis, as shown in Fig. 1.
As further illustrated in Figs. 1 and 2, the distal ends of the primary pivoting arms 64 are attached to the third horizontal bar 70 by an attachment means 66. The distal ends of the primary pivoting arms 64 have an aperture therein of approximately 0.750 inches for receiving the attachment means 66. Preferably, the attachment means 66 is a bolt for securing the primary pivoting arm 60 to the third horizontal bar 70. Each proximal end of the primary pivoting arms 62 has an aperture of approximately 1.250 inches for receiving the second horizontal bar 50 at an underside of the chassis, and for securing the primary pivoting arm thereto. Preferably, the primary pivoting arms may be comprised of a metallic material, such as aluminum. However, instead of aluminum, the primary pivoting arms may be made from another metallic material having suitable or similar quality. The configuration of the primary pivoting arms 60 allows the rearwardly mounted travel means 18 to remain generally horizontal when the rearwardly mounted travel means rises over a bump. The configuration of the primary pivoting arms also allows the rear suspension to rock backwards during inertial weight transfer caused by hard accelerations.
The distal end of the primary suspension means 80 is attached to the third horizontal bar at 70, as shown in FIG. 2. More specifically, the distal ends of the primary suspension means 84 are attached to a bracket 86 which is further secured to the third horizontal bar 70. The bracket 86 has an aperture therein, for receiving the third horizontal bar and securing the primary suspension means 80 thereto. In addition, the proximal end of the primary suspension means have an aperture having a diameter of approximately 0.875 inches for securing the primary suspension means 80 to the first horizontal bar 40. Both the proximal ends 82 and distal ends 84 of the primary suspension means are attached to the first and third horizontal bars, 40 and 70 respectively, at an interior portion of the suspension system. Preferably, the primary suspension means 80 are shock absorbers designed to withstand the weight and suspension of the vehicle.
Fig. 6a clearly illustrates a side view of the bracket 86 comprising a plurality of angularly spaced-apart apertures 220, 222 and 224, arranged circumferentially around the third horizontal bar's aperture. The apertures are adapted to receive securing means, such as nuts and bolts, for locking the bracket 86 into a specific position. The bracket 86 can further be rotated about the axis of the third horizontal bar 70, thereby altering the angle of inclination of the primary suspension means and securing the primary suspension means into a specified inclination.
As illustrated in Figs. 2 and 6a, the distal end of the bracket 86 is adjacent to a distal portion of the travel means 18, which further comprise a plurality of apertures 220, 222 and 224.
Rotation of the bracket 86 further requires adjustment and securing of the travel means 18 and the corresponding apertures 220, 222 and 224. The primary suspension means 80 may be angularly positioned by attaching the distal end 84 of the primary suspension means to one of the apertures 220, 222 and 224. By positioning the primary suspension means 80, the falling rate of the primary suspension means is altered, as shown in Fig. 10.
In a further embodiment, the rear suspension system 20 comprises a Weight Transfer Dynamic Compensator (WTDC) for maintaining the front end of the vehicle in close proximity to the ground surface, thereby providing an improved traction for the entire vehicle. The features of the WTDC are clearly illustrated in Fig. 2. The WTDC in combination with the primary pivoting arms 60 and the primary suspension means 80 provides improved acceleration of the vehicle while increasing travel of the rear suspension system 20. More specifically, the WTDC
comprises a rod 110, a secondary pivoting arm 120, and a pair of pulling belts 130, for providing further adjustment of the primary suspension means 80 between alternative riding conditions.
The rod 110 comprises a first end 112 and a second end 114 . The first end of the rod 112 is attached to the first horizontal bar 40. The first end of the rod 114 further comprises an aperture therein for receiving the first horizontal bar therein. The second end of the rod 114 is attached to the secondary pivoting arm 120 by means of a bolt. The secondary pivoting arm 120 further comprises a first end 124 which is attached to a fourth horizontal bar 75. The proximal end of the secondary oscillating arm 124 comprises an aperture therein for receiving the fourth S horizontal bar 75 and is secured thereto at a central area of the fourth horizontal bar 75. Finally, the WTDC comprises a pair of pulling belts 130, one on each lateral side of the suspension system. The pulling belts comprises lower ends 132 and upper ends 134. The lower ends of the pulling belts 132 are attached to the rearwardly mounted travel means 18 at a front portion thereof by means of a fifth horizontal bar 78, as shown in FIG. 2, and the upper ends of the pulling belts 134 are attached to the fourth horizontal bar 75 by an attachment means. The upper ends of the pulling belts are attached to the fourth horizontal bar at an interior portion thereof and adjacent the primary pivoting arms 60. The pulling belts function to connect the suspension system 20 with the front portion of the rear travel means, and insures that the front portion of the rear travel means remains in close proximity to the suspension system 20.
Accordingly, the pulling belts of the WTDC system pulls down a front portion of the chassis while maintaining the rearwardly mounted travel means 18 to remain in contact with the ground whenever there is a rearward transfer of weight, notably during rapid forward acceleration.
Alternatively, the suspension comprises a single pulling belt 130 and an auxiliary limiting strap which would prevent components of the suspension from colliding with the endless track in the unlikely event that the pulling belt 130 were to break. The combination of the generally centrally mounted suspension system and the WTDC allows for improved traction of the vehicle.
Fig. 11 further illustrates the WTDC in combination with the generally centrally mounted suspension system. More specifically, Fig. 11 is illustrative of the primary elements of the WTDC secured in two different positions for different riding conditions. The solid lines represent the positioning of the rod and the secondary pivoting arm in a standard position for comfortable recreational touring while the shadow lines represent the position of the rod and the secondary pivoting arm in a more aggressive, racing position wherein the suspension compensates for greater weight transfer by allowing greater travel in the mechanism.
The rear suspension system 20 further comprises a secondary suspension means 140, have an aperture having a diame having a proximal end 142 and a distal end 144 as illustrated in Fig. 1. The proximal end of the secondary suspension means 142 is attached to a fifth horizontal bar 78, and the distal end of the secondary suspension means 144 having an aperture therein for receiving a sixth horizontal bar 90 and being attached thereto. The secondary suspension means 140 of the rear suspension system 20 may be a shock absorber. The secondary suspension means 140 work to absorb shocks during movement or vertical weight transfer of the vehicle.
In an alternative embodiment, the suspension system comprises a longitudinal slide bar 150 located at a rear portion of said vehicle, with the secondary suspension means 140 at a proximal portion of the vehicle being removed as illustrated in Fig. 3. The longitudinal slide bar 150 further comprises a proximal end 152 and a distal end 154. The proximal end of the slide bar 152 has an aperture therein, having a diameter of approximately 0.875 inches for receiving the first horizontal bar 40 and securing the slide bar 150 thereto. The distal end of the slide bar 154 has an elongated aperture therein, having a width of approximately 1.375 inches and a radius of curvature of approximately 1.000 inches, for receiving an eighth horizontal slide bar 94 adjacent a set of rear wheels of said vehicle at 300 in Fig. 5. In a preferred embodiment, the slide bar has a length of 24.50 inches, a width at a midsection of 1.50 inches, and a depth of 0.375 inches. As shown in Figs. 3 and 5, when the rear suspension system 20 comprises the slide bar 150, the rearwardly mounted travel means 18, such as a pair of longitudinal slides 160, comprise a plurality of apertures at 300 for attaching the slide bar 150 to the rearwardly mounted travel means 18. Figs. 12 and 13 further illustrate the attachment of the slide bar 150 to the travel means. The aperture at the distal end of the slide bar may be secured without a gap (i.e. for a tight fit) between the aperture at the distal end of the slide bar 154 and the attachment to the longitudinal slide 160 at 300, as shown in Fig. 12. In this arrangement, the slide bar cannot translate longitudinally. Such a configuration provides for a stiffer riding of the slide bar and the vehicle, as shown in zone 1 of Fig. 13. Alternatively, the aperture at the distal end of the slide bar 150 may be secured with a gap (i.e. in a sliding fit) of 0.250 inches between the aperture at the distal end of the slide bar 154 and the attachment to the slide at 300, as shown in Fig. 12. In this arrangement, the slide bar can translate longitudinally within the elongated aperture. Such a configuration provides for a softer riding of the slide bar and the vehicle, as shown in zone 2 of Fig. 12. The longitudinal slide bar 150 functions in a tension mode only, and extends from the eighth horizontal bar 94 to the first horizontal bar 40. The eighth horizontal bar 94 comprises eccentric bolts for rotating the eighth horizontal bar and thus adjusting the stiffness of the suspension system 20. The slide bar 150 is held in tension, and maintains a constant distance from the rear wheels 6 to the first horizontal bar 40, thereby transferring the force of an impact on the suspension system to the primary suspension means 80. In a preferred embodiment, the longitudinal slide bar 150 may be comprised of a thermoplastic type material.
However, instead of a thermoplastic material, the slide bar 150 may be made from another material having suitable or similar quality and strength, provided that the material of the slide bar 150 enables it to accommodate the force of the suspension system in a tension mode.
In an alternative embodiment, the slide bar 150 may be replaced by a cable 150a or a strap (as illustrated in Fig. 3A) comprised of a material having suitable or similar strength as that provided by the slide bar 150.
The forwardly and rearwardly mounted travel means are shown in the attached drawings as a pair of longitudinal slides 160. In a preferred embodiment, the longitudinal slides 160 comprise a stopper 162 at a proximal end of the slide. The stopper 162 is preferably comprised of a rubber material and is located on a top surface of the slide adj acent the proximal end, so as to prevent the proximal portion of the slide from damaging the chassis and the suspension system during full extension of the primary pivoting arms 60 and the primary suspension means 80. In addition, the primary pivoting arms 60 comprise a stopper 68 at a midsection and on a top surface of the primary pivoting arms. The stopper 68 is preferably comprised of a rubber material, so as to prevent the primary pivoting arms from damaging the chassis and the suspension system during full extension of the primary pivoting arms and the suspension system 20. Accordingly, stopper 162 and stopper 68 may be made from another material having suitable or similar quality and strength to a rubber type material.
FIGS. 1, 2, and 3 illustrate in detail a preferred embodiment wherein the forwardly and rearwardly mounted travel means 18 are in the form of longitudinal slides 160 of a snowmobile.
The travel means further comprise a flexible endless track 164, for supporting the chassis, and a plurality of wheels displaced along the length of the travel means for enabling the endless track to move. The longitudinal slides 160 are placed on an inside surface of the endless track and support the rear suspension system 20. In a preferred embodiment, the longitudinal slides may be comprised of a metallic type material, such as aluminum. However, instead of aluminum, the longitudinal slides 160 may be made from another metallic material having suitable or similar quality and strength. The longitudinal slides 160 preferably comprises a thickness of approximately 0.375 inches. An underside portion of the longitudinal slide, which is in direct contact with the endless track 164 of the suspension system, preferably has a width of approximately 1.000 inches and a depth of approximately 0.187 inches. The underside portion of the slide is also comprised of a metallic material, and preferably of an aluminum type material.
However, instead of aluminum, the underside portion of the slide 160 may be comprised from another material having a suitable or similar quality and strength. The slide further comprises a plurality of apertures disposed throughout the length of the slide for receiving a plurality of horizontal bars for attaching the longitudinal slides 160 to rear suspension system 20 of the vehicle 10.
As shown in FIG. 4, the centrally mounted primary pivoting arms 60 of the rear suspension system provides for improved maneuverability of the rear suspension when compared to the prior art. In a preferred embodiment, the primary pivoting arms 60 are comprised of a metallic type material, and preferably of an aluminum material. However, instead of aluminum, the primary pivoting arms 60 may be made from another material having suitable or similar quality. The arrangement of the primary pivoting arms permit the rearwardly mounted travel means to rise vertically and generally horizontally when bumps are encountered. The primary pivoting arms 60 have a length of approximately 27.00 inches, a maximum width of 3.50 inches, and a depth of 0.25 inches. At a proximal end of the pivoting arms 62, there is an aperture having a radius of 1.250 inches for receiving a second horizontal bar 50 and securing the primary pivoting arm 60 to the chassis of the vehicle. A distal end of the primary pivoting arm 64 comprises an aperture having a diameter of approximately 1.50 inches for receiving the third horizontal bar 70 and securing the distal end of the primary oscillating arms 64 thereto.
FIG. 4 shows the primary pivoting arms 60 in several different positions for a given snowmobile vehicle, wherein each position depicted is dependent upon the weight being applied to the suspension system 20. When the suspension system is at rest, the vertical distance between a top surface of the rear bumper 4 of the vehicle and the distal end of the primary pivoting arms 64 is 19.892 inches. However, when the suspension system is active and at its maximum flexibility, the primary pivoting arms are in a relatively horizontal position allowing for a vertical clearance of at least 11.500 inches from the ground to the top surface of the rear bumper 4 of the vehicle. As is further illustrated in shadow lines in Fig. 4, track tension creates a compression of the rearward portion of the suspension system. The pulling belts are able to pull down a front portion of the chassis so that the rearwardly mounted travel means remain generally horizontal and remain in contact with the ground thereby maintaining good traction.
For purposes of completeness, the following is a chart of the angle of displacement of the primary pivoting arms 60, and the vertical distance from the distal end of the primary pivoting arms 60 to a top horizontal surface of the rear bumper 4 of the particular land vehicle given in this example:
An~le of Displacement (degrees Clearance (inches) 18.92 8.392 26.52 12.219 34.43 16.784 When the suspension system 20 is in full extension, the minimum angle of displacement from the distal end of the primary pivoting arm is 18.92 degrees, and when the suspension system is at rest, the maximum angle of displacement from the distal end of the primary pivoting arm is 34.43 degrees.
The above description is of a generally centrally mounted rear suspension system for a land vehicle, such as a snowmobile. In an alternative embodiment, the suspension system may be in the form of a kit separate from the vehicle as a whole. The kit may be assembled and attached to a conventional snowmobile and used to modify an already existing suspension system.

In the most preferred embodiment, a suspension assembly, designated comprehensively by the numeral 20, is able to mount an endless track 164 to a chassis 16 of a snowmobile 10 as best illustrated in Figures 14 and 15. While the suspension assembly 20 is, in the most preferred embodiment, attached to a snowmobile, such a suspension assembly could also be adapted for mounting to other types of tracked vehicles.
As shown in Figures 16-19, in the most preferred embodiment, the suspension assembly 20 comprises two substantially parallel and spaced-apart elongated slide members 18. The slide members 18 are connected together by at least one transversely mounted bridge member 70, 78.
The slide members 18 guide the endless track 164 and are commonly referred to in the art as "slide rails". The slide members 18 are typically made of a light, rigid metal such as aluminum.
The undersides of the slide members 18 are normally covered with a wear-resistant polymer.
The slide members 18 often have a front portion that is curved upwards to facilitate the traversing of rough terrain.
In the most preferred embodiment, the suspension assembly 20 further comprises two substantially parallel and elongated pivoting arms 60, each having a first end portion 64 pivotally connected to said slide members 18 and a second end portion 62 adapted for connection to the chassis 16. The pivoting arms 60 are shaped so as to resist bending and to minimize the interference with other components of the suspension assembly 20 when the suspension assembly 20 is compressed. In the most preferred embodiment, the pivoting arms 60 are made of a light, rigid material such as aluminum.
In the most preferred embodiment, the suspension assembly 20 further comprises a rocker arm assembly 120, 137 pivotally connected to said pivoting arms 60. The rocker arm assembly 120, 137 has a first end portion 11 S pivotally connected to a substantially rigid link 110. The rocker arm assembly also has a second end portion 135 connected to a tension-only member 130, said tension-only member being connected to said slide members 18. The tension-only member 130 is a linking member capable of withstanding only a tension load (i.e. it cannot support a compressive load). Some examples of tension-only members are ropes, cords, belts and straps.

In the most preferred embodiment, the suspension assembly 20 further comprises a resilient member 80 (also referred to as the primary suspension means). The resilient member 80 is connected at a first end portion 82 to the chassis 16 and at a second end portion 84 to the slide members 18. When compressed, the resilient member 80 urges the slide members 18 away from the chassis 16. When the suspension is in static equilibrium, the resilient force produced by the resilient member 80 that urges the slide members 18 away from the chassis 16 is counterbalanced by the weight of the chassis and vehicle supported above it.
When the suspension encounters bumps in the terrain, the resilient member 80 absorbs and dissipates most of the impact energy.
In the most preferred embodiment, the suspension assembly 20 further comprises a slide bar 150. The slide bar 150 has a first end portion 152 connected to the chassis 16 and a second end portion 154 slidingly engaged to a holder 170. The holder 170 is pivotally mounted (at pivot 174) to a rear portion 19 of said slide members 18. The slide bar 150 is capable of limited 1 S translation relative to said holder 170 by virtue of the washer 159 and nut 1 SS on the threaded end 157 of the slide bar 150. The slide bar 150 is thus restricted to move within the internal gap of the holder 170. Thus, the slide bar 1 SO limits the displacement of the slide members 18 relative to the chassis 16.
Preferably, the resilient member 80 includes at least one spring 81. The most common and logical arrangement is to provide the suspension assembly 20 with two identical, symmetrically-disposed springs 81 in order to give the suspension assembly a balanced and stable response to impacts. More preferably, the resilient member 80 further includes a damper 83. The damper 83 is advantageously arranged in tandem with each spring 81 as illustrated in Figure 17. The two symmetrical spring-damper units absorb and dissipate the kinetic energy imparted to the slide members 18 when the snowmobile 10 encounters a bump. The quick and controlled absorption and dissipation of the impact energy by the spring-damper combination maximizes comfort and handling. By varying the spring rate, damping ratio, and geometry of the shocks, the dynamic response of the suspension can be tailored from a hard, "sport"
suspension to a softer, "touring" suspension. A suspension can have a "rising rate" (the stiffness of the springs increases as they are compressed) or a "falling rate"
(the stiffness of the springs is decreased as they are compressed) or a combination thereof (i.e.
the response of the suspension varies as a function of the position and angle of the shocks).
Preferably, the tension-only member 130 is a pulling belt. The pulling belt is capable of limiting the upward motion of the rocker arm assembly 120, 137 away from the slide members 18. The pulling belt thus restrains the front portion 15 of the chassis 16 during rapid accelerations when the front portion of the chassis has a tendency to rise.
Preferably, the rocker arm assembly 120, 137 is integral with a tube 75a. The tube 75a may be permanently fixed to the rocker arm assembly by welding, soldering or bonding (depending on the materials used). In the most preferred embodiment, the tube 75a is welded to the rocker arm assembly. Rotatable within the tube 75a is a shaft 75, shown in Figure 16. The shaft 75 is mounted transversely between the pivoting arms 60 by a threaded fastener on either end. The shaft 75 ensures that any tensile force generated by the pulling belt 130 is distributed equally on both pivoting arms 60. Most preferably, the pulling belt is located midway between the pivoting arms to ensure an equal distribution of forces. However, the pulling belt need not be located midway in order for the suspension to function properly. The shaft 75 may also serve as a cross-brace between the pivoting arms 60 to ensure that both pivoting arms move in unison.
Preferably, the rocker arm assembly 120, 137 further comprises two rocker arms 120 and 137 mounted to the tube 75a in a transversely spaced-apart relation as shown in Figure 16. The rocker arms are angled with respect to one another (as seen in the plane defined normal to the axis of the tube 75a, i.e. in the plane shown in Figures 17-19). The rocker arms 120 and 137 are welded to the tube 75a. As will be shown below, other rocker arm configurations are also possible as indeed are other methods of rigid attachment.
In a second variant, instead of two distinct rocker arms, the rocker arm assembly comprises a unitary, generally L-shaped rocker arm 137 as shown in Figure 21.
This arrangement is similar to the previous variant except that the arms of the rocker are not transversely spaced-apart. The second variant functions almost identically to the first variant shown in Figures 16-19. The generally L-shaped rocker arm 137 is pivotally mounted to the tube 75a and pivotally connected to the rigid link 110 at pivotal end 115. The generally L-shaped rocker arm is also connected to the pulling belt 130. If the pulling belt 130 is again located midway between the pivoting arms 60, then the rigid link 110 will be also located midway between the pivoting arms. To locate the rigid link midway between the pivoting arms, the middle idler wheel on the first transverse member 40 would need to be displaced to allow the rigid link to attach to the first transverse member 40. Alternatively, the rigid link could have a forked end so that the rigid link attaches to the first transverse member 40 at two attachment points on either side of the middle idler wheel.
In a third variant, the rocker arm assembly comprises a pulley 139 around which the pulling belt 130 is partially wrapped as shown in Figure 22. The pulley 139 is connected to a rocker arm 120. When the pivoting arms 60 move upwards, the pulley 139 rotates making the pulling belt taut. When the pulling belt is taut, the tensile force of the pulling belt 130 limits the upward movement of the front portion 15 of the chassis 16.
A fourth variant is illustrated in Figure 23 in which the rocker arm assembly comprises a pulley 139 around which the pulling belt 130 is partially wrapped. In the variant of Figure 23, the pulling belt is partially wrapped around the rear-facing side of the pulley 139 as opposed to the front-facing side of the pulley as was the case in Figure 22. In Figure 23, the rocker arm 120 is oriented toward the front portion 15 of the chassis 16 whereas, in Figure 22, the rocker arm 120 is oriented toward the slide members 18.
A fifth variant is illustrated in Figure 24 in which the rocker arm assembly comprises a generally linear rocker arm 120. In Figure 24, the rocker arm 120 is pivotally connected to the tube 75a around shaft 75. The pulling belt 130 is connected to one end of the rocker arm 120.
The rigid link 110 is connected to the rocker arm 120 at the pivotal end 115.
A sixth variant is illustrated in Figure 25 in which the rocker arm assembly comprises a generally L-shaped pulley-like member 137 capable of exerting a tensile force on said pulling belt 130. The generally L-shaped pulley-like member 137 is pivotally mounted to the shaft 75 and connected to the rigid link 110 at pivotal end 115. The pulling belt 130 is mounted to the front-facing surface of the L-shaped pulley-like member 137. When the L-shaped pulley-like member 137 rotates, the pulling belt becomes taut thereby exerting a restraining force on the pivoting arms 60 which tends to limit the upward movement of the front portion 15 of the chassis 16.
For any of the foregoing variants, the suspension assembly 20 may further comprise a second tension-only member 131 connected at one end to said rocker arm assembly 120,137 and connected at a second end to said slide members 18 via a transverse member 78.
The second tension-only member functions in precisely the same manner as the first tension-only member (i.e. the pulling belt 130). The second tension-only member 131 is simply a backup member that limits the upward movement of the front 15 of the chassis 16 in case the pulling belt 130 breaks.
The second tension-only member 131 is preferably a limiting strap made of a tough, light material such as nylon or reinforced rubber.
1 S In any of the foregoing variants, the resilient member 80 and the rigid link 110 may be connected to a first transverse member 40, the transverse member 40 being connected to the chassis 16. The first transverse member 40 is preferably made of steel, aluminum or an alloy and is rigid enough not to deflect or deform substantially under the loads imposed upon it by the chassis 16, the resilient member 80, the slide bar 150 and the rigid link 110.
Similarly, in any of the foregoing variants, the second end portion 62 of the pivoting arms 60 may be connected to a second transverse member 50, the second transverse member being connected to the chassis 16 at the front portion 15. The transverse member 50 is preferably a hollow shaft made of steel or aluminum and which is disposed with two flanges welded thereto.
The flanges are provided with holes for fastening to the pivoting arms 60. The transverse member should be rigid enough to withstand all loads imposed on it by the chassis and pivoting arms without substantial deformation.
In operation, the suspension assembly 20 functions firstly to absorb and dissipate impact energy transmitted to the suspension assembly while traversing rough terrain and, secondly, to compensate for the weight transfer induced when the engine is pulling on the track.

In the latter case, when the snowmobile 10 undergoes rapid acceleration, the engine pulls on the track, thereby putting a portion of the track into tension. This tensile force creates internal reactions which cause the rear of the chassis to dip and the front 15 of the chassis to rise. Thus, when viewed from the left side as in Figures 17-25, the chassis tends to rotate in a clockwise direction. When the front of the chassis rises and the acute angle between the pivoting arms 60 and the slide members 18 increases, the second transverse member (shaft 50) rises with respect to the first transverse member (shaft 40). Since both members 50 and 40 are fixed to the chassis, the distance between them necessarily remains the same. However, since the shaft 75 is rigidly attached to the pivoting arms 60, the distance between the shaft 75 and the first transverse member 40 diminishes. As the shaft 75 nears the first transverse member 40, the rigid link 110 exerts a force on the rocker arm 120 at the pivotal end 115 causing the rocker arm 120 and hence the tube 75a to pivot about the shaft 75 in a clockwise orientation (again as viewed from the left side). The clockwise rotation of the tube 75a about the shaft 75 also causes the rocker arm 137 to rotate about the shaft 75. The rotation of the rocker arm 137 causes the second end portion 135 to rise with respect to the slide members 18. As the second end portion 135 rises, the pulling belt 130 becomes taut, as shown in Figure 20, thereby precluding any further upward movement of the front portion 15 of the chassis 16. Thus, during rapid accelerations, when the front portion 15 of the chassis 16 tends to rise due to track tension, the suspension assembly counteracts the weight transfer by restraining the front portion 15 of the chassis 16 from further elevation.
When traversing bumpy terrain, the suspension assembly 20 absorbs impacts and ensures that the rails (i.e. slide members) remain essentially parallel to the chassis. In the foregoing analysis of the suspension's weight transfer dynamic compensation, the slide members were treated as if they remained on the ground at all times and the chassis moved with respect to the slide members. When considering the suspension's response to a bump, the point of view is reversed: the chassis can be treated as being somewhat fixed while the rails move.
A bump acting at the rear of the slide members produces essentially the same relative response as the weight transfer dynamic compensation described above. In other words, the rear of the slide members moving toward the rear portion of the chassis is essentially equivalent to the rear of the chassis dipping toward the rear of the slide members. The suspension, being coupled, will react by lifting the front of the slide members so that the slide members rise in a substantially parallel manner. When the bump acts on the rear of the slide member 18, the slide members rotate counterclockwise as shown in Figure 33.
This rear bump compresses the resilient members 80 and causes the slide bar 150 to translate within the holder 170 such that the nut 155 moves toward the surface 176. Due to the counterclockwise rotation of the slide members 18, the acute angle between the pivoting arms 60 and the slide members 18 increases until the pulling belt 130 becomes taut.
The slide members 18 are thus limited from further counterclockwise rotation. The front and rear of the suspension are coupled and any further compression in the form of a counterclockwise rotation of the suspension necessarily compresses the resilient members 80. The slide members 18 remain substantially parallel to the chassis once the suspension is coupled.
1 S Another way to visualize the effect of a rear bump is to imagine a bump propagating under the slide members moving from the front of the slide members toward the rear. When the bump is exactly midway along the slide members, as shown in Figure 32, the suspension is in its "ideal posture" because the slide members are instantaneously parallel to the chassis and to the ground. Then, when the bump moves toward the rear, the front of the slide members drop.
This dropping of the front of the slide members amounts to a counterclockwise rotation which causes the angle between the pivoting arms 60 and the slide members to increase until the pulling belt 130 become taut enough to preclude any further counterclockwise rotation of the slide members. The suspension is thus coupled.
A bump acting at the front of the slide members causes the slide members to rotate clockwise as shown in Figure 31. As the rear portion 19 of the slide members drops, the distance between the pivot 174 (of the holder 170) and the first transverse member 40 diminishes until the washer 159 and nut 155 abut the holder 170. In other words, the slide bar slides in the cavity 172 of the holder 170 until the washer 159 and the nut 155 collide with the inner surface of the holder. At that point, as shown in Figure 31, the suspension becomes coupled.
The slide members 18 are no longer able to freely rotate clockwise. Any further attempt to rotate the slide members clockwise is resisted by the resilient members 80. With the slide bar 150 abutting the holder 170, the suspension is coupled and the rear of the slide members will then rise with the front of the slide members. Thus, the slide members remain substantially parallel to the chassis when encountering a bump on the front of the slide members.
In summation, the rocker arm assembly 120, 137, pulling belt 130 and rigid link 110 function collectively as a Weight Transfer Dynamic Compensator ("WTDC"). The WTDC is essentially a mechanical chain linking the slide members 18 to the chassis 16.
The six variants described above illustrate that there are numerous ways to implement a WTDC.
In all of the variants, there is a tension-only member that is activated by a pivotal or rotational movement governed by the pivoting arms.
The WTDC compensates dynamically for the weight transfer of the snowmobile that arises when the engine is pulling on the track. A snowmobile with a WTDC is not only more comfortable to ride during rapid acceleration but it maintains better ground contact. When the weight on the front skis is diminished (as a direct result of weight transfer), the steering capacity is commensurately reduced. Thus, the WTDC ensures that even though the snowmobile is undergoing rapid accelerations, there is still enough weight on the front skis to permit proper steering of the snowmobile. This enhances cornering performance since the snowmobile rider is able to steer and accelerate concurrently.
Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims and the scope should not be limited to the dimensions indicated hereinabove.

Claims (35)

1. A suspension assembly for mounting an endless track to a chassis of a snowmobile, said suspension assembly comprising:
(a) two substantially parallel and spaced-apart elongated slide members connected together by at least one transversely mounted bridge member;
(b) two substantially parallel and elongated pivoting arms, each having a first end portion pivotally connected to said slide members and a second end portion adapted for connection to the chassis;
(c) a rocker arm assembly pivotally connected to said pivoting arms, said rocker arm assembly having:
- a first end portion pivotally connected to a substantially rigid link, said link being pivotally connected to the chassis;
- a second end portion connected to a tension-only member, said tension-only member being connected to said slide members;
(d) a resilient member connected at a first end portion to the chassis and at a second end portion to the slide members; and (e) a slide bar having a first end portion connected to the chassis and a second end portion slidingly engaged to a holder, said holder being pivotally mounted to a rear portion of said slide members whereby said slide bar is capable of limited translation relative to said holder thereby limiting the displacement of said slide members relative to the chassis.

2. A suspension assembly as defined in claim 1 wherein said resilient member includes at least one spring.

3. A suspension assembly as defined in claim 2 wherein said resilient member further includes a damper.

4. A suspension assembly as defined in claim 3 wherein said tension-only member is a pulling belt.

5. A suspension assembly as defined in claim 4 wherein said rocker arm assembly comprises a shaft mounted transversely between said pivoting arms.

6. A suspension assembly as defined in claim 5 wherein said rocker arm assembly further comprises two rocker arms mounted to said shaft in a transversely spaced-apart relation.

7. A suspension assembly as defined in claim 6 wherein said rocker arms are angled with respect to one another in the plane normal to the axis of said shaft.

8. A suspension assembly as defined in claim 5 wherein said rocker arm assembly further comprises a unitary, generally L-shaped rocker arm.

9. A suspension assembly as defined in claim 5 wherein said rocker arm assembly further comprises a pulley capable of exerting a tensile force on said pulling belt.

10. A suspension assembly as defined in claim 5 wherein said rocker arm assembly further comprises a generally linear rocker arm.

11. A suspension assembly as defined in claim 5 wherein said rocker arm assembly further comprises a generally L-shaped pulley-like member capable of exerting a tensile force on said pulling belt.

12. A suspension assembly as defined in claim 7 further comprising a second tension-only member connected at one end to said rocker arm assembly and connected at a second end to said slide members, said second tension-only member capable of limiting the displacement of the pivoting arms with respect to the slide members.

13. A suspension assembly as defined in claim 12 wherein said second tension-only member is a limiting strap.

14. A suspension assembly as defined in claim 13 wherein said resilient member and said rigid link are connected to a first transverse member, said first transverse member being connected to the chassis.

15. A suspension assembly as defined in claim 14 wherein said second end portion of said pivoting arms is connected to a second transverse member, said second transverse member being connected to the chassis.

16. A suspension assembly as defined in claim 8 further comprising a second tension-only member connected at one end to said rocker arm assembly and connected at a second end to said slide members, said second tension-only member capable of limiting the displacement of the pivoting arms with respect to the slide members.

17. A suspension assembly as defined in claim 16 wherein said second tension-only member is a limiting strap.

18. A suspension assembly as defined in claim 17 wherein said resilient member and said rigid link are connected to a first transverse member, said first transverse member being connected to the chassis.

19. A suspension assembly as defined in claim 18 wherein said second end portion of said pivoting arms is connected to a second transverse member, said second transverse member being connected to the chassis.

20. A suspension assembly as defined in claim 19 further comprising a second tension-only member connected at one end to said rocker arm assembly and connected at a second end to said slide members, said limiting strap capable of limiting the displacement of the pivoting arms with respect to the slide members.

21. A suspension assembly as defined in claim 20 wherein said second tension-only member is a limiting strap.

22. A suspension assembly as defined in claim 21 wherein said resilient member and said rigid link are connected to a first transverse member, said first transverse member being connected to the chassis.

23. A suspension assembly as defined in claim 22 wherein said second end portion of said pivoting arms is connected to a second transverse member, said second transverse member being connected to the chassis.

24. A suspension assembly as defined in claim 10 further comprising a second tension-only member connected at one end to said rocker arm assembly and connected at a second end to said slide members, said second tension-only member capable of limiting the displacement of the pivoting arms with respect to the slide members.

25. A suspension assembly as defined in claim 24 wherein said second tension-only member is a limiting strap.

26. A suspension assembly as defined in claim 25 wherein said resilient member and said rigid link are connected to a first transverse member, said first transverse member being connected to the chassis.

27. A suspension assembly as defined in claim 26 wherein said second end portion of said pivoting arms is connected to a second transverse member, said second transverse member being connected to the chassis.

28. A suspension assembly as defined in claim 11 further comprising a second tension-only member connected at one end to said rocker arm assembly and connected at a second end to said slide members, said second tension-only member capable of limiting the displacement of the pivoting arms with respect to the slide members.

29. A suspension assembly as defined in claim 28 wherein said second tension-only member is a limiting strap.

30. A suspension assembly as defined in claim 29 wherein said resilient member and said rigid link are connected to a first transverse member, said first transverse member being connected to the chassis.

31. A suspension assembly as defined in claim 30 wherein said second end portion of said pivoting arms is connected to a second transverse member, said second transverse member being connected to the chassis.

32. A snowmobile comprising:
- a chassis;
- an engine mounted on said chassis;
- an engine cowling enveloping said engine and supporting a windshield;
- a seat mounted on said chassis;
- a steering member mounted on said chassis and connected to a pair of steerable front skis;
-a front suspension mounted on said chassis and connected to said front skis;
- a ground-engaging track connected to said engine via a drive sprocket;
- a suspension assembly as defined in any one of the preceding claims for mounting said track to said chassis.

33. A suspension assembly for mounting an endless track to a chassis of a snowmobile, said suspension assembly comprising:
(a) two substantially parallel and spaced-apart elongated slide members connected together by at least one transversely mounted bridge member;
(b) a substantially parallel and elongated pivoting arm having a first end portion pivotally connected to one of said bridge members and a second end portion adapted for connection to the chassis;
(c) a rocker arm assembly pivotally connected to said pivoting arm, said rocker arm assembly having:

- a first end portion pivotally connected to a substantially rigid link, said link being pivotally connected to the chassis;
- a second end portion connected to a tension-only member, said tension-only member being connected to said slide members;
(d) a resilient member connected at a first end portion to the chassis and at a second end portion to the slide members; and (e) a slide bar having a first end portion connected to the chassis and a second end portion slidingly engaged to a holder, said holder being pivotally mounted to a rear portion of said slide members whereby said slide bar is capable of limited translation relative to said holder thereby limiting the displacement of said slide members relative to the chassis.

34. A suspension assembly for mounting an endless track to a chassis of a snowmobile, said suspension assembly comprising:
(a) two substantially parallel and spaced-apart elongated slide members connected together by at least one transversely mounted bridge member;
(b) two substantially parallel and elongated pivoting arms, each having a first end portion pivotally connected to said slide members and a second end portion adapted for connection to the chassis;
(c) a rocker arm assembly pivotally connected to said pivoting arms, said rocker arm assembly having:
- a first end portion pivotally connected to a substantially rigid link, said link being pivotally connected to the chassis;
- a second end portion connected to a tension-only member, said tension-only member being connected to said slide members; and (d) a resilient member connected at a first end portion to the chassis and at a second end portion to the slide members.

35. A suspension assembly for mounting an endless track to a chassis of a snowmobile, said suspension assembly comprising:
(a) a pair of rail-like slide members;
(b) a pair of pivoting anus pivotally connecting said slide members to said chassis;

(c) a rocker arm assembly pivotally connected to said pivoting arms, said rocker arm assembly being pivotally connected at a first end to a substantially rigid link, said link being pivotally connected to the chassis; said rocker arm assembly being connected at its opposite end to a tension-only member, said tension-only member being connected to said slide members;
(d) means for resiliently connecting said chassis to said slide members; and (e) a displacement-limiting means having a first end portion connected to the chassis and a second end portion connected to a rear portion of said slide members for limiting the displacement of said slide members relative to the chassis.