SUSPENSION SYSTEM FOR THE DRIVE WHEEL OF A MOTOR-POWERED VEHICLE

Abstract: A suspension system for the drive wheel (17) of a motorcycle driven by a chain (25) cooperating with sprockets (23, 24) on the engine and wheel shafts. The suspension system comprises a linkage arrangement associated with the swing arm (22), with inboard linkage parts (27, 28, 32, 33) positioned in the region between the wheel and the motor, with the swing arm (23) substantially in a plane containing the axes of the engine sprocket (23) and the wheel sprocket (24), and with an obliquely inclined link (34d) interconnecting the swing arm (22) and the inboard linkage parts (27, 28, 32, 33).

Description: SUSPENSION SYSTEM FOR THE DRIVE WHEEL OF A MOTOR-POWERED VEHICLE BACKGROUND AND STATEMENT OF OBJECTS: This invention relates to a drive wheel suspension system for motor-driven vehicles of the kind in which a drive wheel is driven by a chain cooperating with sprockets provided on the motor or engine shaft and on the wheel shaft. Motorcycles are typical of such.motor-driven vehicles and the invention is described as applied to a motorcycle. In a typical motorcycle, it has been common practice to employ a swing arm for mounting the drive wheel, the swing arm having a pivot usually located in the region between the engine sprocket and the periphery of the driven wheel. With this configuration, the motion of the swing arm, which accompanies deflection of the wheel, results in change in the length of the path to be followed by the drive chain interconnecting the engine and wheel sprockets; and a chain slack take-up device is commonly employed in order to maintain proper driving engagement of the chain with the sprockets. In addition, with this prior arrangement, certain undesirable forces are present in the motorcycle, especially during acceleration and braking. One such undesirable force is commonly referred to as "squat", i e., a force tending to cause the rider's seat to deflect downwardly during acceleration. It has also been known (see for example U.S.A. patent *4,058,181) to provide a parallelogram type of swing arm suspension arrangement for mounting the drive wheel, this arrangement, in effect, comprising multiple swing arms located above and below the axes of the driving sprockets, the multiple swing arms being interconnected and arranged to provide for pivotal motion of the drive wheel about the axis of the engine sprocket, thereby eliminating the change in the length of the chain path. Although this makes possible elimination of the chain slack take up device, the prior art arrangement has a number of disadvantages, notably the fact that the multiple swing arm elements used for the parallelogram arrangement of said prior patent extensively increase the mass of the parts which must move with the wheel. Moreover, with the multiple swing arms located above and below the axes of the sprockets, certain undesirable forces during acceleration and braking are still present in the overall structure of the motorcycle, and, in fact, are even exaggerated. In prior U.S.A. patent No. 4,408,674, issued October 11, 1983, there is disclosed a suspension arrangement having a parallelogram linkage adapted to be associated with the inner or pivoted end of the swing arm preferably in a region between the periphery of the wheel and the axis of the engine sprocket, and arranged to provide an effective swing arm axis which is coincident with the axis of the engine sprocket. By locating the linkage parts in the region between the periphery of the wheel and the axis of the engine sprocket, the weight of the parts involved is concentrated relatively close to the effective axis of swing motion. This greatly reduces the overall weight of the parts and also reduces the inertia of the parts moving with the wheel and, consequently, improves the responsiveness of the wheel under various operating conditions including, for example, travel over rough terrain such as is commonly encountered in motocross racing. Such an arrangement also provides for use of a swing arm structure lying substantially in a plane containing the axes of the driving and driven sprockets, and this reduces certain of the undesirable forces which tend to occur especially during acceleration. The present invention contemplates use of an arrangement generally conforming with that of the prior patent 4,408,674 above referred to, but further provides certain suspension linkage elements positioned in a novel manner with respect to other linkage elements, thereby providing for further reduction of the forces which tend to induce "squats when acceleration occurs. BRIEF DESCRIPTION OF THE DRAWINGS: How the foregoing and other objects and advantages are attained will be clear from the following description referring to the accompanying drawings, which illustrate a structural embodiment, and also include several diagrammatic views showing alternative positions of the parts. Figure 1 is a partial side elevational view of a motorcycle equipped with the drive wheel suspension of the present invention, this view showing the drive wheel in partially deflected position; Figure 2 is a perspective view of some of the linkage parts associated with the swing arm, these parts being arranged in the manner provided by the present ininvention; and Figures 3, 4 and 5 are diagrammatic views illustrating the action of the suspension parts when arranged as disclosed in Figures 1 and 2. DETAILED DESCRIPTION OF THE DRAWINGS: The motorcycle illustrated in the drawings is typical of motorcycles employed for motocross racing; and while the invention is applicable to vehicles of a variety of types, the arrangement of the invention is particularly desirable for motorcycles, and especially for motorcycles used for motocross racing. The invention is, therefore, illustrated and described in relation to such specific use. The motorcycle includes main frame components some of which are indicated at 9, 10, 11 and 12. The framing provides for support of an engine as indicated at 33, a rider's seat 14 and a fuel tank 15. Other parts of the motorcycle include the following parts. The front wheel (not shown) is located to the left of the figure and the rear wheel is shown at 17, these wheels being mounted on the frame structure, only portions of which are shown. In the embodiment illustrated, the suspension system for the rear or driving wheel 17 includes a swing arm 22 of a type commonly employed on motorcycles and comprising a forked structure embracing the rear wheel 17, as will be understood from Figure 2. Commonly, the swing arm has heretofore been pivotally mounted at some point on the frame structure, usually to the rear of the engine; but in the arrangement illustrated, the swing arm is mounted in the manner fully described hereinafter. The drive system for the rear wheel 17 includes a sprocket 23 mounted on the engine shaft and a sprocket 24 mounted on the wheel 17, with a drive chain 25 engaging the engine and wheel sprockets, as clearly appears in the drawings. For the purpose of eliminating change in the length of the path of the drive chain 25, it is desirable that the motion of the swing arm 22 occur about an axis close to or coincident with the center 26 of the engine sprocket 23. However, the direct pivotal mounting of the swing arm 22 on the shaft or axis 26 is not practical because of interference with other parts and the undesired complexity of having the swing arm connected with the engine drive shaft, thereby interfering'with separate mounting and removal of the engine and of other parts. With the foregoing in mind, the arrangement of the invention utilizes a suspension system which achieves the objective of providing for pivotal motion of the swing arm 22 about or substantially about the axis of the engine or drive sprocket shaft 26; but this is accomplished without the complexity of direct pivotal mounting of the swing arm on the axis 26. Thus, a suspension linkage system is provided having an effective pivotal axis for the swing arm which is either coincident with or close to the axis of the sprocket 23, which latter is also customarily coincident with the engine shaft. In such embodiments, the commonly used chain slack take-up device may be eliminated. However, the linkage arrangement herein disclosed achieves reduction in undesirable forces, even where the swing arm motion is not precisely coincident with the axis of the driving sprocket, as brought out more fully hereinafter. As shown in Figures 1 and 2, the structure provided includes a pair of levers 27 and 28 which are pivotally mounted on axes 29 and 30, carried by mounting brackets secured to the motorcycle framing, one offset above and the other offset below the sprocket shaft 26. These two levers lie in vertical planes laterally offset from each other and extend in a direction toward the drive wheel 17. The free ends of these levers are interconnected by a linkage system including a shaft 31, having at one end, an upwardly extended link arm 32, and at the other end, a downwardly extended link arm 33. The arms 32 and 33 and the shaft 31 thus form a generally upright link interconnecting the levers 27 and 28. The swing arm 22 is mounted on the shaft 31; and the lower pivoted arm 28 has an extension 28a with which a link 34a is pivoted, the link 34a being extended upwardly for pivotal attachment to the swing arm 22 at the pivot point 35a. The swing arm link 34a is positioned at an oblique angle to the swing arm for reasons more fully brought out hereinafter. It is also contemplated that a shock absorber mechanism, preferably including both a spring and hydraulic damper, be arranged to react on the linkage, such as above described, rather than at an outboard point on the swing arm itself. Thus, the mechanism for yieldably resisting upward deflection of the drive wheel includes a shock absorber mechanism comprising a spring and hydraulic damper unit generally indicated at 36, this unit or assembly being compressible between end abutment elements reacting between the arm extension 28a and the arm 39 of a bellcrank pivoted on the frame of the motorcycle at 40 and having another arm 41 pivotally connected by means of link 42 with the pivot axis interconnecting the linkage parts 27 and 32. As is pointed out in prior U.S.A. patent 4,408,674 above referred to, the arrangement of the linkage for the swing arm and for the shock resisting mechanism not only minimizes the inertia effects of these parts in relation to the motion or deflection of the driving wheel, but still further, the disposition of these various parts is important from the standpoint of concentrating those parts close to the center of gravity of the motorcycle as a whole. Moreover, the geometry of the parts as described has special advantages in minimizing tendency for the deflection resisting forces to induce or contribute to undesirable motions of the motorcycle about its overall center of gravity. In addition, the disclosed arrangement is characterized by the fact that the driving wheel is, in effect, more isolated from the remainder of the motorcycle, particularly with regard to the motions of the drive wheel and the dynamic and inertia forces involved in such motions and also in the action of the shock absorber or other motion-resisting mechanism. Still further, the linkage parts involved in the arrangement disclosed may be accommodated in a smaller lateral or transverse space than is the case with certain other suspension mechanisms of the prior art. Because of this, notwithstanding the fact that the linkage provides a parallelogram effect causing the motion of the drive wheel to occur about the axis of the driving sprocket, the relatively small overall lateral dimension of the parts provides ground clearance at the two sides of the motorcycle even when making sharp turns, which ground clearance is greater than in many prior suspension arrangements. Because of this increased lateral ground clearance, various parts, especially the suspension parts, may be mounted in lower positions, with consequent lowering of the overall center of gravity of the motorcycle; and this is of advantage for reasons well understood in this art. In the arrangement disclosed, the tendency for the rear end of the motorcycle frame to deflect downwardly ("squat) in acceleration, is greatly reduced as compared with prior art suspensions, and this reduction is effected with the primary levers of the linkage either parallel, as illustrated in the drawings or in similar arrangements where the primary levers have somewhat diverging or converging relationships. Although certain forces, such as "squat" forces occurring during acceleration, may vary somewhat depending upon the specific lever and pivot arrangement employed, nevertheless, forces of this type are greatly reduced, compared with various prior art suspension mechanisms. The improvement with respect to reduction of squat" is further enhanced by the arrangement of the swing arm link of the present invention as illustrated in Figures 1 to 5. The general arrangement of these figures conforms with the embodiment of the prior U.S.A. patent 4,408,674 above referred to, but the present invention provides further improvement as described herebelow. Thus, the swing arm link 34a is obliquely inclined, having a pivotal connection 35a with the swing arm 22 and extending downwardly at an inwardly inclined angle with its lower end pivoted to a portion of the suspension linkage. As shown in the drawings, the swing arm link 34a is pivotally connected at its lower end with the outward extension 28a of the lower arm or lever 28 of the inboard portion of the linkage, and it will be seen that the swing arm link 34a is extended from the swing arm in a direction forming an oblique angle µ (see Figure 1) with respect to the generally upright link 32 - 33 of the inboard linkage parts. Specifically, the swing arm link 34a is extended in a direction forming an acute angle with respect to the generally upright link 32 - 33 of the inboard suspension coupling mechanism. Figures 3, 4 and 5 diagramatically illustrate the geometric interrelationship of the major components of the system structurally shown in Figures 1 and 2, Figure 3 showing the parts in the mid or partially deflected position of the suspension. Figure 4 shows the relationship of the parts at the maximum upwardly deflected position; and Figure 5 shows the relationship of the parts at the lowermost wheel position. From Figures 3, 4 and 5 it will be observed that the angle of the swing arm link 34a with respect to the swing arm 22 changes¯with deflection, the angle on the inboard side being the smallest in the maximum upward deflected position shown in Figure 4. In consequence of the action of the parts when positioned as disclosed, there is a very considerable reduction in the tendency toward "squat", i.e. in the tendency for the rear end of the cycle to deflect downwardly in consequency of acceleration of the cycle. This is desirable for most motorcycles and is especially important in motorcycles used for motocross racing because of the extensive and repeated acceleration used in such racing. The arrangement of the present invention thus not only achieves the advantages of the arrangement of prior U.S.A. patent 4,408,674 above identified but still further reduces undesirable tendancies to "squat", and this is accomplished where the principal levers 27 and 28 are mounted one above and one below the drive sprocket, or where the levers are mounted both above or below the drive sprocket and still further where the levers are somewhat divergent or convergent. The angle e of the link 34a relative to the general plane of the linkage parts 32 - 33 should be at least 100 in the middle setting of its pivotal range and may be up to about 75 . Values of ¯ lying between about 150 and about 50e for the middle setting of its pivotal range are effective in many cases. The angle of # illustrated in Figure 1 is around 15 and in Figures 3, 4 and 5 it is 160 in the middle setting of its pivotal range (Figure 3), 14 e in the Figure 4 setting and 18b in the Figure 5 setting.

Claims: CLAIMS 1. A motor-powered vehicle having a frame (9, 10, 11, 12), a drive wheel (17), a motor (13), and wheel drive mechanism including a motor sprocket (23), a wheel sprocket (24), a drive chain (25) connecting the sprockets, a drive wheel suspension system comprising first (27) and second (28) levers pivotally mounted on first (29) and second (30) axes spaced one above the other in a generally upright plane in the region of the axis (26) of the motor sprocket (23) and extended from said plane toward the drive wheel (17), coupling means (32, 33) interconnecting said levers (27, 28) and providing for concurrent pivotal motion of said levers on said first and second axes (29, 30), the coupling means including at least one generally upright link (32, 33), a swing arm (22) for the drive wheel (17) extended forwardly of the wheel sprocket (24) and pivotally connected with said upright link (32, 33) on a swing arm mounting axis (31) lying substantially in a plane containing the axes of the motor and wheel sprockets (23, 24), a linkage (28a, 34a) connected with at least one of said levers (28) and including a swing arm link (34a) having a pivotal connection (35a) with the swing arm (22) intermediate the axis of the drive wheel (17) and said swing arm mounting axis (31), the linkage (28a, 34a) which is connected with one of said levers including an element (28a) extended to a region between the drive wheel sprocket (23) and said generally upright link (32, 33) of the lever coupling means, the swing arm link (34a) being pivotally connected with said element (28a) of said linkage, and means (36) connected with the drive wheel suspension system for resisting drive wheel deflection, characterised in that a swing arm link (34a) is employed which is extended from the swing arm (22) in a direction forming an oblique angle (0) with said generally upright link (32, 33) of the lever coupling means. 2. A vehicle as defined in claim 1, characterised in that the swing arm link (34a) is extended from the swing arm (22) in a direction forming an acute angle (#) with said generally upright link (32, 33) of the coupling means interconnecting said levers (27, 28). 3. A vehicle as defined in claim 1 or claim 2, characterised in that said linkage connected with one of said levers (28) comprises an extension (28a) of said lever extended beyond said lever coupling means (32, 33) in a direction toward the drive wheel (17), the swing arm link (34a) being pivotally connected with said extension (28a). 4. A vehicle as defined in claim 3, characterised in that said extension (28a) extends from the lower lever (28) to a position below the swing arm (22), the swing arm link (34a) being pivotally connected with said lever extension (28a) below the level of the swing arm (22). 5. A vehicle as defined in any preceding claim, characterised in that the oblique angle ( i ) formed between the swing arm link (34a) and the generally upright link (32, 33) is at least 100 in the middle setting of its pivotal range. 6. A vehicle as defined in claim 5, characterised in that the oblique angle (#) formed between the swing arm link (34a) and the generally upright link (32, 33) is not more than 750 in the middle setting of its pivotal range. 7. A vehicle as defined in any of claims 1 to 4, characterised in that the oblique angle ((9) formed between the swing arm link (34a) and the generally upright link (32, 33) lies between 15 and 500 in the middle setting of its pivotal range. 8. A vehicle as claimed in any preceding claim in the form of a motorcycle.

Inventors: BOYESEN, EYVIND
Applicants: PERFORMANCE INDUSTRIES, INC.
Application year: 1985
Main classification: B62K25
IPC codes: B62K25, F02B61