GB2199793A - An automative vehicle equipped with at least four road wheels and having a short turning radius - Google Patents

Abstract

An automotive vehicle having a short turning radius and equipped with a conventional frame (2) is provided with two front steerable road wheels (3) and two rear drive wheels as well as an additional steerable wheel (6) which is orientable by means of a hydraulically actuated steering mechanism (13). The additional steerable wheel can be turned through a substantial turning angle on each side of a longitudinal median position and is also mounted as to be capable of vertical displacement with respect of the vehicle frame. During periods of specialized-duty service during which the vehicle travels at low speed, the additional steerable wheel is placed in the bottom position in contact with the ground whilst the two front steerable road wheels are lifted above the ground by means of a lifting device for compressing the suspension provided for the front road wheels, with the result that the vehicle then runs on three wheels and affords high manoeuvrability. Outside periods of specialized-duty service, the additional wheel is placed in the top raised position above the ground and the vehicle can then travel at a relatively high speed on its tour road wheels while affording good stability and road-holding characteristics. <IMAGE>

Description

AN AUTOMOTIVE VEHICLE EQUIPPED WITH AT LAST FOUR ROAD WHEELS AND HAVING A SHORT TURNING RADIUS The present invention relates to an automotive vehicle having a chassis or frame normally equipped with at least four road wheels, namely two front steerable wheels and two rear drive wheels, the two front steerable wheels being connected to the frame by means of a coupling device providing resilient suspension.

Four-wheeled vehicles having two steerable road wheels usually exhibit good road-holding performances and are capable of running at relatively high speeds. On the other hand, they have a relatively large minimum turning radius and therefore poor maneuverability. It is in fact well-known that the turning angle of the wheels of a conventional axle with two steerable road wheels is limited by the mechanical components (axles, steering-gear pitman arms (drop arms), tie-rods, and so on).

In the case of an axle having two steerable road wheels, it is known that the turning angle can be appreciably increased bv making solely use o hydraulic control devices. However, in this case, highway code regulations limit the maximum speed of the vehicle to a very low value (25 km/h in France). In consecuence, this solution is usually reserved for highly specialized wheeled ecuipment such as "self propelled" vehicles designed for åispl cement of heavy undivided loads. In vehicles of this type, the chassis or frame is commonly equipped with eight to ten axles on which all the road wheels (with the possible exception of the central axle) are steerable wheels with suitable angular variations.

Another well-established fact is that threewheeled vehicles having two drive wheels and a single steerable wheel have a minimum turning radius of very small value and therefore afford good maneuverability.

The turning angle of the single steerable road wheel is in fact no longer /limited by mechanical components in this case but solely by the road adherence of the steerable wheel. However, it is also well known that three-wheeled vehicles always have a low maximum speed (usually between 35 and 40 km/h) by reason of their low road-holding capability when turning corners or negotiating curves (with the attendant danger of overturning).

In the case of certain special vehicles such as, for example, those designed for maintenance or cleaning of public thoroughfares, a desirable property of such vehicles is high maneuverability and therefore a very short minimum turning radius. This property ensures that the vehicle is capable, for example, of avoiding and passing around obstacles while remaining as close as possible to these latter or of turning-back to travel in the opposite direction within a very small space during different stages of work.It is also desirable to ensure that, outside periods of specializedduty service and whenever they are required, for example, to travel from a garage or parking location to their work location which may involve a considerable distance, these vehicles are capable of running at a rate corresponding to normal traffic flow (in particular at speeds of at least 40 km/h) while travelling on major roads and urban motorways and at the same time remaining in compliance with highway code regulations governing road vehicles.

In special vehicles of the type referred-to in the foregoing, this second requirement can be satisfied by making use of a chassis or frame equipped with four wheels, two of which are steerable wheels. The advantage offered by this solution is that four-wheeled vehicle frames equipped with an engine and driver's cabin which are ready to receive operating equipment according to the user's choice are commercially available at advantageous prices as far as they are manufactured on a relatively large scale.

It is merely necessary in such cases for a manufacturer of special vehicles to adapt the operating equipment desired by users. On the other hand, this solution does not make it possible to satisfy the first requirement of high maneuverability by reason of the fact that, as stated earlier, conventional four-wheeled frames having two steerable road wheels have a minimum turning radius of relatively substantial length.

On the other hand, the solution which is adopted in special vehicles of the type mentioned above and which consists of a vehicle frame equipped with three road wheels including a single steerable wheel makes it possible to satisfy the requirement of high maneuverability but fails to satisfy the second requirement (the possibility of high speed of travel outside periods of specialized-duty service). Furthermore, special three wheeled vehicles usually call for a vehicle frame which is specially designed for the work equipment to be mounted thereon. Since these vehicles are usually manufactured on a small scale, they are consequently relatively costly.

The object of the present invention is therefore to provide an automotive vehicle, in particular a special vehicle such as those designed for maintenance or cleaning of public thoroughfares, said vehicle being capable of satisfying the two requirements mentioned in the foregoing (high maneuverability during periods of specialized-duty service and the possibility of travelling at high speed outside such periods) while making use of a conventional chassis or frame having four road wheels including two steerable wheels.

To this end, the distinctive feature of the vehicle in accordance with the present invention lies in the fact that provision is also made for at least one additional steerable wheel which is mounted at the frort porticn of the frame so as to be capable of vertical displaceent with respect to the frame between top and bottom positions in which the additional steerable wheel is located respectively above the ground and in contact with the ground, said additional steerable wheel being also pivotally mounted with respect to the frame about an axis which is substantially vertical, at least in the bottom position of said additional steerable wheel. The vehicle further comprises a steering mechanism coupled with the additional steerable eel for causing said wheel to pivot about said axis, a first lifting device coupled with the additional steerable wheel for displacing said wheel between its top and bottom positions, and a second lifting device mounted between the chassis or frame and the device for coupling the two front wheels for displacing said two front keels between a first position in which they are in contact with the ground and the resilient suspension associated therewith is free to operate when the additional steerable wheel is in the top position and a second position in which said two front wheels are located above the ground and said resilient suspension is compressed when the additional steerable wheel is in the bottom position.

The arrangement outlined in the foregoing is such that, outside specialized-duty periods, the additional steerable wheel is raised to the top position and the vehicle accordingly behaves as a four-wheeled vehicle which is capable of travelling at high speeds with good road-holding characteristics. During periods of specialized-duty service, the additional steerable wheel is lowered into contact with the ground and the two wheels located nearest said additional steerable wheel are lifted, with the result that the vehicle accordingly behaves as a three-wheeled vehicle and consequently affords high maneuverability.

Other features and advantages of the present invention will become more readily apparent from the following description of different embodiments, reference being made to the accompanying drawings, wherein - Fig. 1 is a view in side elevation showing the front portion of a vehicle equipped with an additional steerable wheel in accordance with a first embodiment of the present invention - Fig. 2 is a top view showing the front portion of the chassis or frame of the vehicle of Fig. 1; - Fig. 3 is a view which is similar to Fig. 1 and shows the additional steerable wheel in another position ; - Fig. 4 is a front view of the frame of the vehicle of Fig. 3 ; - Fig. 5 is a sectional view taken along line V-V of Fig. 3 ;; - Figs. 6 and 7 are views which are similar to Figs. 1 and 2 but show another embodiment of the additional steerable wheel and of the associated lifting device - Fig. 8 is a view to a larger scale showing the additional steerable wheel of the vehicle of Figs. 6 and 7, and - Figs. 9 and 10 are views which are similar to Figs. 1 and 2 but show another arrangement of the additional steerable wheel and of the associated lifting device The automotive vehicle shown in Figs. 1 to 4 comprises a driver's cabin 1 mounted on a conventional chassis or frse 2 nor"a iy equipped wit four road te= namely two steerable front wheels 3 carried by a front axle 4 and two rear drive-wheels (not shown in Figs. 1 to 4).The engine of the vehicle, the transmission which conveys driving power to the rear wheels and the steering-gear components which serve to turn the front wheels 3 have not been illustrated in Figs. 1 to 4 since these elements are wholly conventional and wellknown.

In accordance with customary practice, the vehicle frame 2 is made up of two side members 2a suitably braced by a number of horizontal cross-members such as the front tubular cross-member 2b. The front axle 4 is suspended from the frame 2 by means of a resilient-suspension coupling device which is illustrated diagrammatically at 5 in Fig. 4 and can consist, for example, of a leaf-spring suspension.

The vehicle of the present invention further comprises an additional steerable wheel 6 which is located in the longitudinal mid-plane 7 of the vehicle and is rotatably mounted at the lower end of a support leg 8. At its upper end, the support leg 8 is rigidly fixed to a pivot-Maft9 which is rotatably mounted in a bearing 10 and the axis of which is located in the longitudinal mid-plane 7. The bearing 10 is rigidly fixed to a cylindrical sleeve 11 which is rotatably mounted on the front tubular cross-member 2b. A control arm 12 (shown in Figs. 1 and 3) is rigidly fixed at one end to the sleeve 11 and is connected at the other end to an actuating device 13.As shown in Figs. 1 to 3, the actuating device 13 can consist of a double-acting pneumatic jack, the piston-rod of which is connected to the control arm 12 and the cylinder of which is connected to a cross-member 14 rigidly fixed to the side members 2a of the vehicle frame 2. Thus, by retracting the piston-rod of the hydraulic jack 13 into the cylinder thereof, the assembly consisting of the elements 6, 8-11 undergoes a pivotal displacement in the anticlockwise direction about the cross-member 2b and the wheel 6 is then brought into contact with the ground as shown in Fig. 3.

Conversely, by extending the piston-rod out of the cylinder of the jack 13, the assembly consisting of elements 6, 8-11 undergoes a pivotal displacement in the clockwise direction about the cross-member 2b and the wheel 6 is then raised above the ground as shown in Fig.l.

As will readily be apparent, the pneumatic jack 13 can be replaced by a hydraulic jack or any other suitable actuating device such as, for example, a rack and pinion or screw and nut system with either electrical or manual control.

As shown in Fig. 4, a lifting device 15 serves to lift the two normal steerable road wheels 3 of the vehicle when the additional steerable wheel 6 is in contact with the ground. By way of example, this lifting device can be constituted by two single-acting hydraulic jacks 15, the piston-rods of which are attached to the front axle 4 and the cylinders of which are attached to the vehicle frame 2 or to the vehicle body. Thus, when the piston-rods of the two jacks 15 are retracted, the leaf springs 5 of the suspension are compressed and the two road wheels 3 are lifted above the ground. Conversely, when the pressure within the two jacks 15 is relieved, the two road wheels 3 are restored to contact with the ground under the action of their own weight as well as that of the axle 4 and under the action of the leaf springs 5.

The steering mechanism associated with the additional steerable wheel 6 will now be described. As shown in Fig. 5, this steering mechanism can advantageously comprise in a manner known per se 9 pinion 16 rigidly fixed or keyed on the pivot-shaft 9 of the additional steerable wheel 6 , a toothed rack 17 engaged with the pinion 16 and at least one hydraulic jack (one double-acting jack or two single-acting jacks mounted in opposition), the piston of which is connected to the toothed rack 17. As shown in Fig. 5, a piston 18 is fixed at each end of the toothed rack 17 and slidably mounted within a cylinder 19 formed in a single piece with the bearing 10 of the pivot-pin 9 so that the cylinder 19 and the bearing 10 thus form a single casing 20.A fluid under pressure such as oil, for example, can be admitted at either end of the cylinder 19 respectively through the ports 21 and 22. An oil pump (not shown) driven by the engine of the vehicle supplies with oil either the port 21 or the port 22, depending on the desired direction of turning of the steerale wheel 6, through a rotary distributor which is connected mechanically to the vehicle steering gear (but which is not shown in the drawings). By means of the steering mechanism described in the foregoing, the additional steerable wheel 6 can be pivotally displaced about the axis of its pivot-shaft 9 through an angle at least equal to 750 on each side of the central longitudinal axis of the vehicle.

As can be seen more particularly in Fig. 2, the support leg 8 provided for the additional wheel 6 can consist of a fork, for example. This fork can be wholly rigid or else provided with a resilient suspension system. By way of example, the fork 8 can have an upper portion 8a which is rigidly fixed to the pivot aft 9 and two lower arms Rb pivotally coupled to the upper portion 8a by means of a horizontal shaft 23.

Resilient coupling members (not shown) such as compression springs, for example, are interposed between the upper portion 8a and the arms 8b of the fork 8.

One or a number of known work equipment units of the type employed for cleaning public thoroughfares, for example, can be installed on the vehicle frame 2 behind the driver's cabin 1.

When the vehicle described in the foregoing is being used outside specialized-duty periods for such purposes as displacements between a garage location and the work location, for example, the additional steerable wheel 6 is placed in the position shown in Fig. 1 and the fluid pressure in the jacks 15 is relieved so that the leaf springs 5 of the suspension may thus operate normally. Under these conditions, the vehicle behaves as a conventional four-wheeled vehicle and is capable of travelling at relatively high speeds if so desired and if such speeds are permitted by traffic conditions while at the same time maintaining good stability and satisfactory road-holding performance.

During specialized-duty periods, the additional steerable wheel 6 is lowered into contact with the ground (as shown in Fig. 3) by actuating the jack 13, and the jacks 15 are actuated so as to compress the leaf springs 5 of the suspension and to lift the two front road wheels 3 (as shown in Figs. 3 and 4). Under these conditions, the vehicle behaves as a three-wheeled vehicle with two rear drive-wheels and a single steerable front wheel and is endowed with the high maneuverability of such a vehicle.

In the embodiment shown in Figs. 6 to 8, the elements which are identical or perform the same functions as those of Figs. 1 to 5 are designated by the same reference numerals and will therefore not be described again'in detail. The embodiment shown in Figs. 6 to 8 differs essentially from that of Figs. 1 to 4 by the fact that the cylindrical sleeve 11 is rigidly fixed to the front cross-member 2b, in such a manner that the axis of the bearing 10 always remains substantially vertical.In this case, the actuating device 13 for lowering and lifting the additional steerable wheel 6 can consist for example of a rotary, hydraulic or pneumatic jack, the cylinder of which is rigidly fixed to one of the two arms 8b and the central shaft of which is rigidly fixed to the upper portion 8a of the support leg 8 of the additional wheel 6 and forms the pivot axis 23 of the two portions 8a and 8b of said support leg. In this case, in order to permit displacement of the two arms 8b and the additional wheel 6 from the top position shown in Fig. 6 to the bottom position shown in Fig. 8 and conversely, it may prove necessary to lift the vehicle momentarily when the axis of rotation of the wheel 6 oversteps the vertical plane containing the pivot axis 23.

of the support leg 8. To this end, it is possible to make use of the jacks 15 which, in this case, no longer consist of single-acting jacks but consist of doubleacting jacks. Thus, by admitting a fluid under pressure into the cylinders of the two jacks 15 above their pistons, it is possible to lift the vehicle by applying a bearing force on the ground through the two road wheels 3, the axle 4 and the piston-rods of the two jacks 15.Once the axis of rotation of the additional wheel 6 has passed beyond the vertical plane which contains the axis of articulation 23 and when the two arms Sb and the wheel 6 occupy the position shown in Fig. 8, the fluid under pressure can be admitted into the cylinders of the two jacks 15 at the piston-rod end in order to lower the vehicle and when the wheel 6 is in contact with the ground in order to lift the two road wheels 3 by compressing the leaf springs 5 of the suspension. With tha additional wheel 6 in the position shown in Fig. 8, a resilient coupling is provided between the two arms Sb and the upper portion 8a of the support leg 8.By way of example, this resilient coupling can be constituted by two stops 24 of elastomeric material such as rubber which are located on each side of the upper portion 8a of the support leg 8.and by two bearing surfaces 25 which are provided respectively on the two arms 8b and which are in contact respectively with the two resilient stops 24 (a single stop 24 and a single bearing surface 25 are visible in Fig. 8).

In the embodiment shown in Figs. 9 and 10, the elements which are identical or perform the same functions as those of the preceding figures are designated by the same reference numerals and will therefore not be described again in detail. The embodiment of Figs. 9 and 10 differs from the two previous embodiments by the fact that the additional steerable wheel 6 is located behind the two steerable front road wheels 3 while nevertheless remaining in the front portion of the vehicle frame 2. In this case, the single casing 20 formed by the bearing 10 and the cylinder 19 of the steering mechanism of the wheel 6 is rigidly fixed to a horizontal cross-member 2c which is in turn secured to the two side members 2a of the vehicle frame 2 behind the front axle 4. The actuating device 13 for lifting and lowering the additional steerable wheel 6 can be constituted by a rotary, hydraulic or pneumatic jack which is similar to the jack shown in Figs. 6 and 7 or else, as shown in Figs. 9 and 10, by two double-acting hydraulic or pneumatic jacks 13, the cylinder of which are connected to the upper portion 8a of the support leg 8 and the pistonrods of which are connected respectively to the two arms 8b of said support leg.

lt should in any case be clearly understood that the embodiments of the present invention have been described in the foregoing solely by way of example without any limitation being implied and that any number of modifications may readily be made by those versed in the art without thereby departing from the scope of the appended claims.

Thus it follows that, instead of carrying out lifting and lowering of the additional steerable wheel 6 by pivotal displacement about the cross-member 2b or 2d of the vehicle frame 2 or by pivotal displacement about the axis of articulation 23 of the support leg 8, lifting and lowering of the additional wheel 6 can be performed by vertical translational displacement of the pivot-pin 9 as performed, for example, by means of a hydraulic jack located in coaxial relation to the bearing 10. It is also clear that the additional wheel 6 can be replaced by two twin wheels if so desired.

Furthermore, in view of the fact that the additional steerable wheel or wheels are placed in contact with the ground and utilized only during periods of specialized-duty service which always take place at low speeds, it is also clearly apparent that, without contravening highway code regulations, the vehicle in accordance with the present invention may be provided with two additional steerable wheels placed on each side of the vehicle either at the front end or at the rear end whilst a hydraulically actuated steering mechanism similar two that described earlier may be associated with each additional wheel. However, a solution of this nature is less economical than the embodiments described earlier.

Claims (8)

CLAIMS:

1. An automotive vehicle having a chassis normally equipped with at least four road wheels consisting of two front steerable wheels and two rear drive wheels, the two front steerable road wheels being connected to the chassis by means of a resilient-suspension coupling device, characterized in that said vehicle further compromises at least one additional steerable wheel which is mounted at the front portion of the chassis so as to be capable of vertical displacement with respect to the chassis between top and bottom positions in which the additional steerable wheel is located respectively above the ground and in contact with the ground, said additional steerable wheel being also pivotally mounted with respect to the chassis about an axis which is substantially vertical at least in the bottom position of said additional steerable wheel, a steering mechanism coupled with the additional steerable wheel for causing said wheel to pivot about said axis, a first lifting device coupled with the additional steerable wheel for displacing said wheel between its top and bottom positions, and a second lifting device mounted between the chassis and the device for coupling the two front road wheels for displacing said two front road wheels between a first position in which they are in contact with the ground and the resilient suspension associated therewith is free to operate when the additional steerable wheel is in the top position and a second position in which said two front road wheels are located above the ground and said resilient suspension is compressed when the additional steerable wheel is in the bottom poSition.

2. A vehicle in accordance with claim 1, characterized in that the additional steerable wheel is located in the longitudinal median plane of the vehicle.

3. A vehicle in accordance with claim 1 or 2, characterized in that the additional steerable wheel is rotatab-ly mounted at the lower end of a support leg whose upper end is rigidly fixed to a pivot shaft rotatably mounted in a bearing whose axis is located in a longitudinal vertical plane, and the steering mechanism comprises in known manner a pinion attached to the pivot-shaft, a toothed rack engaged with said pinion and at least one hydraulic jack, the piston of said jack being connected to the toothed rack and the cylinder of said jack being formed in one piece with the pivot-pin bearing within a single casing.

4. A vehicle in accordance with claim 3, characterized in that said casing is rigidly fixed to a cylindrical sleeve rotatably mounted on a tubular horizontal cross-member of the chassis and that the first lifting device comprises a control arm rigidly fixed to said sleeve and an actuating device mounted between the chassis and said control arm.

5. A vehicle in accordance with claim 3, characterized in that said casing is rigidly fixed to a horizontal cross-member of the chassis, said support leg has two portions consisting respectively of an upper portion and a lower portion pivotally connected to each other by means of a horizontal shaft, and the first lifting device comprises an actuating device mounted between the two portions of the support leg so as to cause pivotal displacement of the lower portion with respect to the upper portion.

6. A vehicle in accordance with claim 4 or claim 5, characterized in that the actuating device is a double-acting hydraulic or pneumatic jack.

7. A vehicle in accordance with claim 6 in dependence on claim 5, characterized in that one of the two portions of the support leg is provided with at least one stop of elastomeric material whilst the other portion of said support leg has a bearing surface which is in contact with said stop in the bottom position of the additional steerable wheel.

8. An automotive vehicle equipped with at least one additional steerable wheel, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.