Field of the invention

The present invention relates to a ski suspension for snowmobiles or other ski-mounted vehicles with at least one rotatable steering spindle, said ski suspen¬ sion comprising a shock absorber which is associated with spring means and which consists of a piston-cylin¬ der mechanism whose one end is hingedly connected with a ski at a first, fixed hinge point and whose opposite end is hingedly connected with a pivotable link at a second, movable hinge point, said link being hingedly connected with the ski at a third, fixed hinge point as well as with the steering spindle, optionally by means of a fastener associated therewith, at a fourth, movable hinge point, the link, when pivoting downwardly about said third hinge point under a downwardly directed load on the vehicle, causing a shortening of the piston-cy¬ linder mechanism and a compression of the spring means. Background of the invention

In some known ski suspensions, the requisite spring means consists of a curved leaf spring which has its two opposing ends connected with the ski and with which the steering spindle, or a fastener mounted thereon, is con- nected at a point located approximately in the middle of said curve on the upper side thereof. Such leaf springs are, however, ill-suited for cross-country driving. Al¬ though the resilience and the steering quality obtainable with these springs are quite acceptable for driving at medium speeds on flat ground, that is not the case in rough and difficult terrain of the type prevalent, for in¬ stance, when the vehicle is used for forestry work, and, consequently, also slow driving becomes jerky. Neither are these springs suited for racing at high speeds, despite the fact that this usually takes place on reasonably flat ground, because of the poor steering quality caused by the comparative flexibility of the springs. The poor perfor-

mance of leaf springs is partly due to the fact that there is no possibility of a variable adjustment of the spring resistance.

In recent years, suspensions of the type (McPherson) occurring on wheel-mounted vehicles, especially cars, have been designed, above all for racing snowmobiles, with the intention of eliminating the inconveniences associated with ski suspensions of leaf spring type. These new sus¬ pensions comprise a rather complicated system of link arms which are hingedly mounted at a number of different points on the chassis, as well as on the ski. Such spring ar¬ rangements give satisfactory resilience and steering qua¬ lity, in particular at high speeds, but they have the dis¬ advantage that the link arms are situated in an exposed position in the space between the ski and the chassis, for which reason they are easily damaged by, for example, stones and stumps when driving on rough forest ground. Therefore, snowmobiles with such McPherson suspensions can, in actual practice, not be used in, for example, forestry work. Another serious disadvantage of the

McPherson suspension is that it can only be mounted on a newly-made chassis especially adapted therefor, and not on a conventional chassis with simple steering spindles for the skis. In other words, it is impossible to replace the existing ski suspensions of leaf spring type, which are used on conventional snowmobiles equipped with steering spindles, by the more sophisticated McPherson suspensions.

Furthermore, US Patent Specification 3,854,541 dis¬ closes a ski suspension of the type mentioned by way of introduction, which per se solves the problem of mounting in that the suspension in its entirety can be mounted at one single point on the steering spindle, there being no other connections with the chassis. In this suspension, however, the only shock absorber, as well as the spring associated therewith, is positioned in the area in front of the steering spindle. More precisely, the shock absor¬ ber extends between a first, fixed hinge point situated at

the front end of the ski, and a second, movable hinge point situated in the area in front of the steering spindle. This position of the shock absorber and the spring entails that the ski, when moving downwardly in re- silient fashion, is given a tendency to move forwards in relation to the chassis. In other words, the forwardly di¬ rected movement of the ski is an absolute requirement for the downwardly directed resilient movement. If this for¬ wardly directed movement of the ski is prevented or coun- teracted, e.g. in consequence of the ski being on an up¬ ward slope or, as is often the case in actual practice, in consequence of the snowmobile being driven on ground com¬ prising not only snow but also, for instance, gravel, pieces of wood, or the like having considerable frictional resistance, also the resilient movement will be positively counteracted and, possibly, even prevented. Summary of the invention

The present invention aims at eliminating the incon¬ veniences associated with the ski suspension known from US 3,854,541 and providing a suspension which, irrespective of the ground in question, affords satisfactory resilience and steering quality. According to the invention, this is achieved in that the suspension comprises, in addition to the above shock absorber, a second shock absorber posi- tioned in front of the steering spindle and connecting a front portion of the ski with said steering spindle, op¬ tionally by means of a fastener associated therewith, while the first shock absorber and the spring means asso¬ ciated therewith are positioned behind the steering spindle.

Since the first shock absorber, which is connected with the steering spindle by means of the lever action type link, is positioned behind said steering spindle, a movement which is rearwardly directed in relation to the chassis will be applied to the ski when the latter is moving downwards in resilient fashion, said rearward movement not being affected by bumps in the ground in-

creasing the fractional resistance. Furthermore, the se¬ cond shock absorber positioned in front of the steering spindle and cooperating with the first, rear shock ab¬ sorber efficiently counteracts any fluttering tendency of the ski and ensures that the front portion of the ski does not dip obliquely downwards and forwards when hang¬ ing in the air.

In actual practice, the spring means may advanta¬ geously consist of a helical compression spring applied on the outside of the piston-cylinder mechanism serving as second shock absorber, more precisely between a first abutment means on the cylinder of said mechanism, and a second abutment means on the piston rod of said mechanism. It should here be pointed out that it is also conceivable to incorporate the spring function in the shock absorbing cylinder itself, e.g. in the form of a pneumatic spring inside said cylinder. Brief description of the drawings In the drawings, FIG. 1 is a side view of the ski suspension according to the invention, Fig. 2 is a similar side view on a reduced scale, show¬ ing the suspension mounted on the chassis of a snowmobile, and Fig. 3 is another side view showing the ski associated with the supsension in a position suitable for reversing the snowmobile. Detailed description of a preferred embodiment

In the drawings, 1 generally designates the chassis of a snowmobile which, in conventional manner, comprises a steering spindle 2 for a ski 3. Usually, the snowmobile has, at its front end, two parallel spaced-apart skis, but some snowmobiles, namely the ones having double driving belts, may have only one ski at the front end of the chas- sis. The ski 3 may be of conventional type and consist of a compression-moulded, curved metal sheet having a broad point 4 inclined forwardly and upwardly.

The ski suspension 5 in Fig. 1 comprises a rear, first shock absorber 7 and a front, second shock absorber 6, the latter being mounted between a front mounting 6' on the ski 3 and a member 8 in the form of a sheet metal arm nonrotatably connected with the steering spindle 2. The first shock absorber 7, which like the shock absorber 6 consists of a piston-cylinder mechanism comprising a cy¬ linder 9 and a piston rod 10, is, at its rear end, hinged¬ ly connected with the ski 3 at a first, fixed hinge point 11 and, at its opposite front end, hingedly connected with a pivotable link 12 at a second, movable hinge point 13. The link 12 is hingedly connected with the ski at a third, fixed hinge point 14 and hingedly connected with the steering spindle, in this case by means of the fastener 8, at a fourth, movable hinge point 15. On its upper side, the link 12 has two separate mounting plates, a pin which forms the hinge point 15 extending therebetween. In ana¬ logous manner, two separate mounting plates are arranged on the underside of said link, a pin which forms the hinge point 13 extending therebetween. Also the hinge point 14 consists of a pivot pin extending between two mounting plates fixedly arranged on the ski 3.

As mentioned by way of introduction, the first shock absorber 7 has a spring function and comprises in the em- bodiment shown a helical compression spring 16 arranged on the outside of the cylinder 9, more precisely between a first abutment member 17 on the cylinder, and a second abutment member 18 on the piston rod 10 of said mechanism. The abutment member 18, which suitably consists of a col- lar with about the same diameter as the helical compres¬ sion spring, is suitably fixedly mounted on the piston rod, whereas the abutment member 17, which also suitably consists of a collar with the same diameter as the helical compression spring, is movable and adjustable to different positions along the cylinder 9, such that the degree of compression of the spring 16 is variably adjustable, the adjustability being achieved by means of a threaded joint

between the abutment collar 17 and the cylinder 9. Thus, an external thread 19 is arranged on the outside of the cylinder and cooperates with an analogous, internal thread on the annular abutment collar 17. Most suitably, the spring 16 is progressive so as to provide increasing spring resistance when the degree of compression is in¬ creased. This is apparent from Fig. 1 which illustrates how the two opposing ends of the spring are more tightly wound than the midportion. An abutment means 20 is mounted on the ski 3 and com¬ prises a body 21 which is made of rubber or similar, elas¬ tic material and against which the link 12 may be applied in a lower end position.

In operation, the link 12 will pivot about the two hinge points 14 and 15 when relative movements occur be¬ tween the ski and the chassis, e.g. when driving on rough ground. Thus, when the chassis tends to move downwards towards the ski, the link will pivot clockwise about the hinge point 14 and, via the mounting plates for the hinge point 13, which serve as lever, will cause the piston rod 10 to move into the cylinder 9. This movement is counter- acted by the helical spring 16 causing a cushioning there¬ of. At the same time, the conventional shock-absorbing function of the cylinder 9 cushions the movements of the piston rod in both directions. Since the difference in level between the hinge points 13 and 14 is less than the distance between the hinge points 14 and 15, rather large movements between the chassis and the ski can be taken up by means of comparatively small movements of the piston rod in relation to the cylinder, and this fact, combined with the progressiveness of the helical compression spring, provides for an efficient resilience within a wide range of movements all the way from exceedingly small re¬ lative movements which are smoothly taken up by the coil- ings in the jmiddle of the spring, to very large movements which are taken up by a complete compression of the spring. Since the hinge points 14, 15 can be arranged on

strong and stable mounting plates, it is, in actual prac¬ tice, possible to obtain a practially nonrotatable connec¬ tion between the steering spindle and the ski, such that an excellent steering quality of the ski is obtained, also when there are intense pivoting movements vertically re¬ lative to the chassis.

Fig. 1 illustrates how the front shock absorber 6 has been provided with a spring in the form of a progressive helical compression spring 22 which, however, can be dis- pensed with, as is shown in Figs. 2 and 3.

As is also plain from Figs. 2 and 3, a blocking mem¬ ber 23 may be connected with the front shock absorber 6 and be movable between an inactive position shown in Fig. 2 and an active position shown in Fig. 3, in which it prevents the piston rod 24 forming part of the shock absorber and occupying a certain projecting position from being pushed into the associated cylinder 25. Thus, the ski 3 can be locked in the rearwardly and upwardly in¬ clined position shown in Fig. 3, such that the back por- tion of the ski does not dig into the snow when the ve¬ hicle is reversed. In actual practice, the blocking ele¬ ment 23 may consist of a cross-sectionally U-shaped arm which is hingedly connected with the mounting 6' and which, if the snowmobile gets stuck, can be moved to the active position shown in Fig. 3 after the driver manually has moved the ski to the rearwardly and upwardly inclined position.