A WHEEL TILTING SYSTEM FOR VEHICLES WITH THREE OR MORE WHEELS

DESCRIPTION

The present invention relates to a wheel tilting system for vehicles with three or more wheels, wherein at least two wheels are coupled on the same axle and capable of tilting to enable the vehicle to lean in relation to the ground when it goes through a bend.

The types of vehicle considered herein that are already known in the sector include three-wheel motorcycles, for instance (in which the pair of wheels on the same axle are generally at the front), and quad or ATV (ali-terrain vehicles), i.e. four-wheel vehicles used not only as a means of transport and for recreational activities, but also and increasingly often as a working vehicle, for carrying or towing loads. Among these categories of vehicles with two or more wheels, there are also known types of vehicle fitted with wheels paired on the same axle that are capable of tilting towards the inside of the bend as the vehicle travels along the road. This characteristic is achieved by more or less sophisticated wheel tilting mechanisms and affords the vehicle a much better performance, especially when taking a bend at high speeds, when the attitude of the vehicle is strongly influenced by the distribution of the combined load of the vehicle and driver, and particularly by the position of the centre of gravity of said load, and by the gyroscopic effect produced as a result of the angle of roll of the vehicle. Systems for mechanically controlling the attitude of a vehicle, and particularly the tilting of pairs of wheels on the same axle, are already known in the sector. Such mechanical systems involve the use of linkage for connecting the hubs of the two paired wheels so as to enable them to lean into a bend. The wheel on the inside of the bend rises in relation to the vehicle and the wheel on the outside of the bend drops, effectively enabling the vehicle to tilt, or roll, in relation to the ground. These mechanical wheel tilting systems suffer from numerous drawbacks, however. When in transit on uneven terrain (where the term uneven terrain may also be used to mean the sort of roughness typical of public roads), a change in the position of the wheel on one side of the vehicle may induce corresponding

undamped movements of the wheel on the other side of the vehicle, irreparably interfering with the stability and drivability of the vehicle, due to a loss of steering control around the bend and of wheel grip on the road surface. Wheel tilting systems of purely mechanical type are consequently unable to absorb any movements of one of the two wheels due to bumps in the road.

To overcome this drawback, a hydraulic tilting system has been developed, wherein the mechanical linkage is replaced by a hydraulic circuit and a calibrated braking effect on the oil passing from one cylinder to the other is used to dampen the tilting movements, as described in WO 02/44008. Although it has proved extremely effective, this known system nonetheless has certain aspects that could be improved.

In particular, this solution of known type involves the use of a hydraulic cylinder located in line with each of the wheels located side by side on the same axle, said hydraulic cylinders being connected together by a circuit, i.e. a pipe, that also acts as a hydraulic brake depending on its flow cross-section. In fact, the viscosity of the oil generates friction forces that brake the flow of oil in transit through the pipe in a manner proportional to the flow cross-section.

With reference to figure 1 , which illustrates this known system, numerals 101a and 101b are used to indicate the two hydraulic tilting cylinders, and 102 is the shock absorber cylinder, 103 the hydraulic pipe, and 103a and 103b the two lengths of pipe that join the hydraulic cylinders to the shock absorber cylinder, while 104 is the valve for connecting the shock absorber cylinder 102 to the pipe 103. With this configuration of the known system, however, blocking the tilting of the wheels by preventing the passage of the oil in the connection pipe between the hydraulic cylinders, by means of a valve for instance, also has the effect of blocking the damping effect achieved thanks to the presence of the shock absorber cylinder, which consequently serves a dual purpose. This is a drawback that restricts the potential use of vehicles fitted with this type of wheel tilting system because, once the tilting mechanism has been blocked, the vehicle effectively becomes impossible to drive because it has no shock absorber system. Blocking the tilting of the wheels may consequently be useful only for the stable parking the vehicle.

Three- and four-wheel vehicles are being increasingly used as working vehicles too, however. In this situation, and especially in the case of the four-wheel vehicles commonly called quads, it would often be extremely useful to have a system that enables the vehicle to be used both as a traditional quad with non- tilting wheels, especially when driving at low speeds or in conditions of poor road grip, and as a vehicle with tilting wheels in other conditions of use, and especially at moderate and high speeds.

The main technical aim of the present invention is thus to provide a hydraulic system for tilting the wheels of vehicles with three- or more wheels that enables the drawbacks intrinsic in the solutions of known type to be overcome.

As part of this technical aim, one object of the present invention is to provide a hydraulic vehicle suspension system that enables the vehicle to be used in several ways, i.e. both as a tilting vehicle and as a non-tilting vehicle. Another object of the present invention is to provide a hydraulic vehicle suspension system in which the wheels have a shock absorber system that is independent of their tilting system, so that blocking the wheels' ability to tilt does not interfere with the functionality of the shock absorber system. Another object of the present invention is to provide a hydraulic vehicle suspension system that enables an independent control of the hydraulic braking effect on the wheel tilting system with respect to the hydraulic braking effect on the shock absorber system.

This technical aim, and these and other objects that will emerge more clearly below, are achieved by a wheel tilting system comprising at least one hydraulic cylinder connected to the hub of each of two wheels paired on the same axle, said hydraulic cylinders being placed in communication with one another by a pipe that consequently defines with said cylinders a hydraulic circuit suitable for achieving the effect of tilting the vehicle, and the system is characterised in that it also comprises at least one shock absorber cylinder located in line with each of said hydraulic cylinders. Further characteristics and advantages of the present invention will emerge more clearly from the following detailed description, given as a non-limiting example and illustrated in the attached figures, wherein:

figure 1 shows a hydraulic tilting system of the known type; figure 2 schematically shows the attitude of a vehicle with tilting wheels on a straight road and on a bend; figure 3 shows a general view of the vehicle tilting system according to the present invention; figure 4 shows a schematic perspective view of the system according to the present invention; figure 5 schematically shows a partial cross-sectional view of the system according to the present invention. According to a preferred embodiment of the present invention, illustrated as a non- limiting example in the above-mentioned figures from 2 to 4, the tilting system according to the present invention comprises a pair of hydraulic cylinders 1a, 1b located each in line with one of the two tilting wheels installed on the same axle. Each of said hydraulic cylinders 1a, 1b takes effect between the hub of one of the two tilting wheels and the chassis of the vehicle to which it is hinged.

The chamber of each hydraulic cylinder is then connected, in an area proximal to the upper end of the chamber, to a pipe 3 that places the chambers of the two cylinders 1a and 1b in communication with one another. Basically, the system comprising the two cylinders 1a and 1b connected together by the pipe 3 forms a closed circuit and when one cylinder is compressed the oil contained in the circuit is forced by this cylinder through the pipe 3 towards the other cylinder. This system of communicating hydraulic cylinders thus ensures the proper transmission of the movements between the two wheels and consequently ensures a correct tilting of one wheel of a function of the tilting of the other, thus obtaining the desired leaning effect.

The pipe 3 is suitably sized in terms of its flow cross-section so as to adjust the braking effect on the tilting action due to the force needed to make the viscous fluid circulate in a pipe of limited cross-section. Figure 4, for instance, indicates a throttled portion of the pipe 3 with the reference number 5. Such a reduction in the diameter of a pipe that already has a limited cross-section contributes significantly to increasing the braking effect on the tilting action. The higher the resistance that the oil encounters as it flows through the pipe 3 the greater the braking effect on

the tilting of the wheels, and the greater the resistance of the system to the tilting of the vehicle.

There is a tilt blocking device 4 on the pipe 3. Said tilt blocking device 4 may consist, for instance, in the situation described herein, of a valve capable of blocking the flow of oil in the pipe 3. When the valve 4 is closed, the two cylinders 1a and 1b are no longer in communication and there is consequently no longer any transmission of the tilting motion from one wheel to the opposite wheel on the same axle. Again with reference, for instance, to figure 4, there is a pair of shock absorber cylinders 2a, 2b installed along said pipe 3, and preferably in a position immediately adjacent to each of the cylinders 1a and 1b.

Between the hydraulic cylinders 1a, 1b and the shock absorber cylinders 2a, 2b, there may also be valves 6a, 6b each suitable for interrupting the flow of oil from the hydraulic cylinders 1a, 1b to the corresponding shock absorber cylinders 2a, 2b.

Moreover, according to the embodiment of the present in their invention described herein as an example, each shock absorber cylinder 2a, 2b can be connected to the pipe 3 by a pair of pipes that contribute to defining the hydraulic braking of the shock absorber system. In particular, taking the shock absorber cylinder 2a as an example, this will be connected to the pipe 3 by means of a first pipe indicated in figure 5 by the reference number 7°, through which the oil emerges from the cylinder 2a during the cylinder extension or return phase, and by means of a second pipe 8°, through which the oil flows into the cylinder 2a during the cylinder compression or delivery phase.

Suitable check valves, indicated generically as 9a, 10a, are naturally provided on the delivery and return pipes in order to separate the oil flows. As shown in figure 5, which provides a partial cross-sectional view of the system according to the present invention, the hydraulic cylinders 1a and 1b are advantageously cylinders in which the piston acts as a separating septum between the chamber containing oil and the chamber containing gas.

In particular, in the hydraulic cylinder shown in figure 5, the oil fills the cylinder chamber that acquires a smaller volume when there is a piston movement associated with the stem being inserted in the cylinder, so that a substantially upward movement of the wheels pushes the piston inside the cylinder and the piston in turn pushes the oil contained in the cylinder, forcing it to flow through the pipe 3 into the chamber in the other hydraulic cylinder, where it causes the expansion of the chamber and a thrust on the piston in the direction corresponding to the emergence of the stem from the cylinder, with a consequent downward thrust on the opposite wheel. The gas fills the portion of the hydraulic cylinder that increases in volume when the piston moves in the direction corresponding to the insertion of the stem in the cylinder (see figure 5 again).

The presence of the gas in the cylinder helps to stabilise the tilting of the vehicle. Gas is likewise contained in the shock absorber cylinders 2a, 2b. In this case, the gas serves to provide a shock absorbing effect for the vehicle.

The functionality of the tilting of the wheels according to the present invention is thus as described below.

The hydraulic circuit comprising the two hydraulic cylinders 1a, 1b and the pipe 3 that places said hydraulic cylinders in communication with one another enables a co-ordinated movement, and consequent tilting, of the interconnected tilting wheels.

When the vehicle enters a bend and the attitude of the vehicle has to be such as to enable it to tilt, communication between the two cylinders 1a and 1b is enabled by means of the passage of oil in the pipe 3. The tilting of the vehicle to one side, e.g. to the right, induces an axial compressive action on the stem of the hydraulic cylinder serving the right-hand wheel. This compression of the stem causes an inward displacement of the piston connected to said stem inside the cylinder, which drives the oil through the pipe 3 and into the other hydraulic cylinder associated with the opposite wheel, inducing a thrust on the stem of the second hydraulic cylinder. This has the effect of coordinating the tilting of opposite wheels on the same axle. With reference, for instance, to figure 5, a suitable valve 4 can be provided along the pipe 3. The valve 4 divides the pipe 3 into two sections 3a

and 3b. Given the above-described functionality of the system, closing the valve 4 enables the wheel tilting system associated with the hydraulic system of the cylinders 1a and 1b to be blocked. In fact, closing the valve 4 prevents any passage of the oil in the pipe 3, thereby blocking any movement of the hydraulic cylinders 1a and 1b.

By means of the return and delivery pipes 7a, 8a and 7b, 8b, the two shock absorber cylinders 2a and 2b are in communication with the hydraulic circuit coinciding with the first section of the pipe 3. In particular, each shock absorber cylinder 2a, 2b is installed on the stretch of pipe 3a, 3b between the hydraulic cylinder 1a, 1b and the for tilt blocking valve 4.

Positioning the shock absorber cylinder 2a on the pipe 3a, between the hydraulic cylinder 1a and the valve 4, makes the shock absorbing action exerted by the shock absorber cylinder 2a independent of the wheel tilting system. In other words, closing the valve 4 to prevent any tilting of the vehicle's wheels does not prevent the operation of the shock absorber cylinders, and consequently does not interfere with their shock absorbing action.

Valves 6a, 6b for disabling the shock absorber cylinders 2a, 2b from the hydraulic circuit may also be provided, if appropriate. This enables the vehicle's user to choose how to establish the system's operation in three different ways:

A. all the valves, 4, 6a, 6b are open: the vehicle can be used with the wheel tilting system and the shock absorber system both operational. The vehicle thus has a suspended attitude designed to optimise its grip on the road when travelling through a bend at moderate and high speeds, an attitude particularly suitable for normal road holding conditions;

B. the valves 6a and 6b are open, while the valve 4 is closed: the vehicle thus has a normal attitude, the hydraulic circuit - and the shock absorber cylinders 2a, 2b in particular, serve their shock absorbing purpose, while the valve 4 prevents any tilting of the vehicle. The vehicle thus has the attitude of a conventional vehicle with non-tilting wheels. This attitude may be preferable to the former when the vehicle is used for operations that include carrying or towing heavy loads, or when the road surface does not afford a good grip. In such cases, when the vehicle will

naturally have to travel more slowly, it is preferable to give priority to the vehicle's stability, preventing any tilting and driving the vehicle like a conventional vehicle fitted with a hydraulic shock absorber system;

C. all the valves 6a, 6b and 4 are closed: both the tilting system and the shock absorber system are disabled. The vehicle cannot be driven safely in this configuration because there would be no system to absorb the roughness of the terrain, but such a vehicle attitude may nonetheless be useful, for instance, when parking the vehicle. It is thus demonstrated that the wheel tilting system for a vehicle with three or more wheels according to the present invention achieves the previously-stated technical aim and objects.

In particular, it has been illustrated that the wheel tilting system according to the present invention enables the tilting system to be separated from the shock absorber system. Moreover, the wheel tilting system according to the present invention enables the user to choose whether to disable the wheel tilting system without disabling the shock absorber system, and thereby choose whether to use the vehicle with a tilting attitude or a traditional non-tilting attitude. This choice is particularly useful and appreciable in the case of four-wheel vehicles. Another advantage achievable with the wheel tilting system according to the present invention consists in a more rapid and efficient shock absorbing response thanks to the fact that the shock absorber cylinders are located in the vicinity of the hydraulic cylinders, thereby reducing the length of the stretch of pipe between the hydraulic cylinder and the shock absorber cylinder. A shorter length of pipe coincides with a smaller volume of oil that has to be displaced and a consequently reduced inertia and faster response times.

Last but not least, another advantage achieved by the tilting system according to the present invention lies in that the configuration of the pipes in the hydraulic circuit can be chosen at will to define the hydraulic braking effect according to need. In particular, the pipe 3 connecting the two hydraulic cylinders is responsible for the tilting effect because it places the two tilting wheels in communication with one another. The diameter of the throttled portion of pipe 5

can be suitably sized to obtain the required braking effect on the oil flowing through the pipe. Since the shock absorber cylinders 2a, 2b are located upstream from the respective stretches of pipe 3a, 3b in the system according to the present invention, the hydraulic braking action associated with the size of the throttled portion of pipe 5 does not influence the response of the braking system on the shock absorber, so the two (tilting and shock absorbing) systems are, to all intents and purposes, systems that can be configured at will and independently. Numerous changes may be made by an person skilled in the art without departing from the scope of the concept of the present invention protected by the patent. The scope of protection outlined in the claims shall consequently be limited neither by the illustrations nor by the preferred embodiment described as an example herein; the claims shall rather be intended to include all patentable innovative characteristics deducible from the present invention, including all the characteristics that would be considered as equivalent by a person skilled in the art.