A device for steering the front wheel of a motor vehicle

Abstract: The steering device comprises a first hub (9) to support the wheel (1), an internal second hub (10) rotatably and coaxially supporting the first, a steering pivot (6) accommodated internally of the second hub (10), on which the wheel can be swung from side to side, and an axle pivot (8), disposed perpendicular to the steering pivot and suspended from the frame (3) on quadrilateral linkages (7), which is able to rise and fall while remaining fixed in relation to the wheel; the inner hub (10) is integral with a lever (13) that projects clear of the first hub (9) and is hinged by way of its projecting end to a control rod (16), the rod in turn connecting by way of a mechanical linkage (17, 18) with the handlebars of the machine.

Description: The invention relates to a device for steering the front wheel of a motor vehicle. Italian Patent n° 1 171 971, property of the same applicant, discloses a steering device of the type question, which is designed to overcome certain drawbacks typical of the front suspension forks of motor cycles. The problems encountered with these front forks, which consist generally in a pair of telescopic damper struts located one on either side of the front wheel and carrying the relative pivot, derive from the difference in reaction of the two dampers and their inability to absorb shock from minor surface irregularities while compensating smoothly at the same time for major irregularities. The device in question was also designed to address new problems stemming from previous devices, which had succeeded in overcoming the drawbacks typical of front forks but required a non-symmetrical wheel and did not permit of designing an efficient and easily handled motor cycle. The patent device referred to above consisted in a first hub carrying the front wheel, a second hub mounted coaxial with, internally of and rotatable in relation to the first, a steering pivot located internally of the second hub, perpendicular and rotatable with respect thereto about its own axis, and an axle pivot disposed at right angles to and rigidly associated with the steering pivot. The axle pivot, disallowed rotation about its own axis, was permanently associated with the frame of the motor cycle by way of a parallelogram linkage. A lever associated with the second hub emerged from the first hub and was hinged by its projecting end to control means operated from the handlebars. The inventor of the device envisaged the use of hydraulic control means, for example a fluid power cylinder installed between the lever of the second hub and the parallelogram linkage, which would be operated by the handlebars. Whilst such a system might appear contemporary, given its similarity to servo linkages adopted in the great majority of motor vehicles to give easier handling, the drawbacks betrayed are nonetheless unacceptable for a machine intended for road use, and more especially for use in competition. A first drawback is that of an insufficient level of safety, given that the cylinder can only operate if connected to a pressurized hydraulic circuit. This can be achieved either by using the engine of the vehicle to pressurize a hydraulic circuit into which the cylinder is connected, or by connecting the cylinder into an independent hydraulic circuit pressurized by a gas accumulator. In either case, there are drawbacks: in the first instance, the front wheel can be steered only when the engine of the motor vehicle is running, whereas the second option involves an additional and not infrequent routine servicing operation. In effect, the gas in a container of the type in question must be charged at high pressure (a significant number of atmospheres) in order to function effectively, but this same high pressure, besides increasing the likelihood of leaks, cannot be topped up utilizing normal low cost compressors. Accordingly, whilst a pressurized gas supply guarantees safe operation even with the engine off, the guarantee is limited in terms of duration, and if the acceptability of such a solution is doubtful enough in the case of a competition machine, it must be totally excluded in a standard production machine for obvious reasons. Yet another drawback connected with the hydraulic control is that of its own inertia; notwithstanding the high pressure to which the fluid operating the hydraulic cylinder is subject, movement of the handlebars is not transmitted instantaneously to the front wheel. Such inertia is hazardous in a road machine, especially when effecting sharp and sudden manoeuvres, but altogether intolerable in a competition machine where swift handling response is a fundamental requirement. British Patent No. GB-A-1 274 441 (DIFAZIO) discloses a steering device of the same type question, having an inner and outer hubs, the outer hub being connected to rotate with the rim of the wheel, while the inner hub is non-rotary, a spindle passing through the inner hub and having a pivotal steering connection to the inner hub and within said hub a pivotal steering axis, a pair of pivoted arms for connecting a respective end of the spindle tot a position on the frame of the motor vehicle lying at the same level above the ground as the spindle, a forked structure bridging the wheel and connected at each of its lower ends tot adjacent point on the inner hub, a pair of spaced apart parallel and horizontal links each pivotally, connected at one end to a point of the forked structure, and pivotally connected at the other end to a crosspiece adapted to be secured to a steering column of the motor vehicle, the arrangement being such that the links lie parallel with the arms and act both as radius arms for suspension purposes and also as steering rods for controlling the steering movements of the wheel about its pivotal steering axis. The principal drawback of this system is that when the handlebars is rotated, the movement of the suspension generates an extra-rotation of the front wheel about the steering axis. The principal advantage is that the system is fully mechanic, and all the problems of the hydraulic system are avoided. Accordingly, the object of the present invention is to provide a steering device for motor vehicles, possessing the necessary precision and swiftness of response typical of a normal front fork, together with the positive features characteristic of the patent systems outlined above. The stated object is realized in a steering device as characterized in the appended claims. The invention will now be described in detail, by way of example, with the aid of the accompanying drawings, in which: fig. 1 is a schematic representation of the front wheel of a motor vehicle incorporating the device according to the invention, viewed in cross section with certain parts cut away to reveal others; fig 2 is a schematic side elevation of the front part of a motor vehicle fitted with the device according the invention; fig 3 is a further schematic of the front part of a vehicle, viewed in perspective from the opposite direction to that of fig 2 and with certain parts omitted better to reveal others. With reference to the accompanying drawings, the steering device according to the present invention essentially comprises a pair of coaxial hubs 9 and 10, and two rigidly associated pivots, a steering pivot 6 and an axle pivot 8. A first outer hub 9, serving to support the disc 1a of a wheel 1, is supported in turn by the internal second hub 10 and freely rotatable in relation thereto about a longitudinal axis. The steering pivot 6 is accommodated internally of the second hub 10, perpendicularly disposed as shown in fig 1, and in such a way that the hub 10 can be rotated transversely about the axis 6a of the pivot 6, which is also the steering axis of the vehicle; fig 2 illustrates the operative position of this same axis 6a, angled away from the vertical toward the vehicle. The axle pivot 8 is disposed at right angles to the steering pivot 6 and projects from the hub 10 on either side through respective slots 11, which are formed in the hub 10 itself and of dimensions such as to ensure that no contact will occur with the axle pivot 8 when the hub 10 is rotated about the steering axis 6a. The axle pivot 8 is connected to the chassis or frame 3 of the vehicle by way of an articulated quadrilateral linkage 7 consisting in two arms 2 and 4 and a connecting rod 5. The two arms 2 and 4 are pivotably anchored to the frame 3 at one end, and at their remaining ends to each end of the connecting rod 5. The point of articulation between the arm denoted 2 and the rod 5 is provided by the axle pivot 8, as discernible from figs 1 and 2. More exactly, the one arm 2 and the axle pivot 8 are coupled in such a way as to enable their mutual rotatation, whereas the connecting rod 5 is keyed to the pivot 8 (see fig 1), for example by way of splines. Thus, the axle pivot 8 possesses freedom of movement in relation to the frame 3 through one direction only, i.e. a circumferential arc disposed concentrically in relation to the axis 2a about which the arm denoted 2 is rotatable in relation to the frame 3. Accordingly, the axle pivot 8 is fixed for steering purposes, and rotation of the wheel 1 about the steering axis 6a is produced by rotation of the hub 10, as will become clear in due course. In a device thus embodied, it becomes possible for the arm denoted 2, which replaces the fork of a conventional steering device, to be embodied either as a single strut supporting a cantilevered axle pivot 8, or as a yoke with two members (see fig 3). In the example of fig 1, the axle pivot 8 will be seen to comprise an intermediate section 14 with which two coaxial pins 66 are associated, one on either side of the longitudinal axis 8a of the axle pivot 8; in practice, these two pins 66 combine to create the steering pivot 6. For a more precise and swifter response at the pivot 6, the pins 66 can be supported internally of the inner hub 10 by means of respective bearings 66a accommodated in seatings afforded by the hub itself and secured against the intermediate section 14 from the opposite sides by respective caps 15 (see fig 1). With the axle pivot 8 and steering pivot 6 arranged in this manner, the pins 66 can be disposed such that their axes coincide with the steering axis 6a, perpendicular to but not intersecting the axis 8a of the axle pivot 8. In particular, the axle pivot axis 8a is located forward of the steering axis 6a in such a way that the wheel 1 remains in a state of constant instability, as regards its alignment balance, with the vehicle in motion; this, the normal setting adopted for a conventional front fork, permits of steering the wheel 1 swiftly and with a minimum of effort. 13 denotes a lever associated with the inner hub 10 and projecting from the outer hub 9, of which the projecting end articulates with a control rod 16; the control rod 16 in its turn is connected by way of a linkage mechanism 18 to the steering control of the vehicle, generally a pair of handle bars 23. In the embodiment shown in fig 3, the mechanism 18 consists in a rocker lever, pivoted centrally to the frame 3 and connected by way of a transmission rod 22 to a point on the handlebars 23 offset from their axis of rotation. The lever 18 is connected by its opposite ends to the control rod 16 and the transmission rod 22, and embodied as an essentially upright barrel 18a carried by the frame 3, capable of rotating about its own axis and incorporating two arms 18c and 17 located one at each end, with which the two respective rods 16 and 22 articulate. The distances between the various pivot axes of the mechanical linkage connecting the wheel hub 10 to the handlebars 23 are calculated such, that with the handlebars 23 stationary at any angle and the fork 2 in motion, there is no relative movement between hub 10 and steering pivot 6. With a device embodied according to the invention, rotation of the handlebars 23 in either direction, however slight, will be transmitted instantly and directly to the hub 10 by way of the control rod 16 and the lever 13, these two being articulated at a point offset from the steering axis 6a, and the hub is duly rotated through a corresponding angle about the steering axis 6a. To exploit the various structural elements of the device thus described to best advantage, the arm denoted 4 and the control rod 16 are positioned on opposite sides of the wheel 1, as discernible from figs 2 and 3. According to a further expedient of the invention aimed at enhancing the performance of the device, the fork 2 is associated rigidly with a top and a bottom bracket denoted 24 and 25 respectively. The top bracket 24 articulates with one end of a short connecting rod 19, of which the remaining end articulates in turn with one end of a rocker 20 pivoted at mid length to the frame 3. The bottom bracket 25 is embodied, advantageously from the weight standpoint, in two straight lengths joined together and hinged to one end of a damper 21 of which the remaining end is hinged to the remaining end of the rocker 20 (see fig 2). To ensure an efficient balancing of the forces in play, and in the event that the wheel is supported by a fork 2 as in fig 3 rather than the single strut, a pair of brackets 24 and 25 might be fitted to each member of the fork 2, associated with a single damper 21 positioned between the two members. The distances between the various articulations of the arrangement thus described are such that the damper 21 will react swiftly when any irregularity in the road or track surface is encountered by the wheel 1, and such also, that stresses not directly affecting the wheel 1, e.g. braking stresses, will be absorbed almost entirely by the frame 3 of the machine before reaching the damper 21. Accordingly, optimum response is obtained from the machine when braking on rough surfaces; indeed without such a response the effect of braking stress and irregular surfaces would be to compress the damper 21 and produce an incorrect reaction. The foregoing description implies no limitation in terms of embodiment; for example, rotation of the linkage mechanism 18 might be transmitted from the handlebars 23 through a cardan shaft or indeed any other mechanical transmission substantially devoid of inertia.

Claims: A device for steering the front wheel of a motor vehicle comprising : a first hub (9) disposed with its axis horizontal and supporting a disc (1a) of the wheel (1); a second hub (10) coaxial with, accommodated internally of and associated rotatable in relation to the first hub (9); a steering pivot (6), accommodated internally of and associated rotatably with the second hub (10), of which the axis (6a) diverges from a vertical axis which is perpendicular to a ground surface; an axle pivot (8), rigidly associated with and occupying a plane perpendicular to the steering pivot (6), and projecting from the second hub (10) through slots (11) of which the dimensions are such as to ensure that the second hub (10) does not enter into contact with the axle pivot (8) when rotated about the steering pivot (6); at least one quadrilateral linkage, comprising two arms (2, 4) pivotably anchored to the chassis or frame (3) of the motor vehicle, and an interconnecting rod (5), of which the rod (5) and one arm (2) are associated rigidly and rotatably with the axle pivot (8), respectively, at a point externally of the second hub (10); transmission means comprising a lever (13) rigidly associated with the second hub (10) and projecting clear of the first hub (9), a control rod (16) pivotably connected by one end to the projecting end of the lever (13), and a linkage (17, 18), by way of which the second hub (10) is connected mechanically to the handlebars of the motor vehicle; characterized in that the remaining end of the control rod (16) is pivotably connected to a lever arm (17) pivotably anchored to the chassis or frame (3) of the motor vehicle and rotated left or right about its relative fulcrum (17f) by means of a linkage (18) connected mechanically and directly to the handlebars of the motor vehicle, said lever arm (17) is embodied as the first arm of a rocker lever (18) pivoted intermediately to the chassis or frame (3) of the motor vehicle, of which the remaining arm (18c) is pivotably connected to one end of a transmission rod (22) articulated at the opposite end with the handlebars (23) at a point offset from their centre of rotation, in such a way that the dimensions and pivot axes of the handlebars (23), the transmission rod (22), the lever (18), the control rod (16) and the hub lever (13) combine to disallow rotational movement of the second hub (10) about the axis of the steering pivot (6) deriving from movement of the front wheel (1) in relation to the chassis or frame (3). A steering device as in claim 1, characterized in that the axle pivot (8) is axially offset from the steering pivot (6), positioned forward of the steering axis (6a) in relation to the direction of forward motion of the motor vehicle. A steering device as in claim 1, preferably in conjunction with a further linkage whereby the quadrilateral arm (2) connected to the second hub (10) articulates uppermost with one end of a connecting rod (19) articulated at its remaining end with a rocker (20), pivotably anchored at mid point to the chassis or frame (3) of the vehicle and articulated by the remaining end with one end of a telescopic damper strut (21) of which the remaining end is articulated with the quadrilateral arm (2) at a height lower than the point of articulation between the arm (2) and the connecting rod (19), characterized in that the distances separating the various points of articulation between the quadrilateral arm (2), connecting rod (19), rocker (20) and damper (21) are such as to ensure that forces not directly associated with the front wheel (1) are absorbed by the chassis or frame (3).

Inventors: MORRI GIUSEPPE, MORRI, GIUSEPPE
Applicants: BIMOTA SPA, BIMOTA S.P.A.
Application year: 1990
Main classification: B62K21
IPC codes: B62K21