WO2006095032A1

WO2006095032A1 - Suspension system for motorcycle front forks

Info

Publication number: WO2006095032A1
Application number: PCT/ES2005/000674
Authority: WO
Inventors: Juan Lorenzo Real Rebollo
Original assignee: Juan Lorenzo Real Rebollo
Priority date: 2005-03-04
Filing date: 2005-12-12
Publication date: 2006-09-14
Also published as: ES2259912B1; ES2259912A1

Abstract

The invention relates to a suspension system for motorcycle front forks. Motorcycle front suspensions comprise a fork with two telescopic arms forming a suspension system which must absorb irregularities in the terrain and provide sufficient stability such that the driver can retain control of the motorcycle in different driving conditions. According to the invention, significant progressivity is achieved over approximately the first half of the total course of the fork, through the incorporation, in series, of a gas spring (1, 1', 1 ) and a spiral spring (12) with greater than normal stiffness in each of the telescopic arms. The gas spring (1) includes an upper cover (3) for sealing a case (2), comprising an axial valve (6) with an inner piston (7) bearing a rod (8) that is topped with an element for spreading/centring (9) the spiral spring (12). The upper chamber (15) of the piston (7) comprises a determined volume of oil (16), the remainder consisting of pressurised gas.

Description

SUSPENSION SYSTEM FOR FRONT FORKS OF

MOTORCYCLES OBJECT OF THE INVENTION

The present invention, as expressed in the description of this specification, refers to a suspension system for motorcycle front forks, with which a progressive behavior of the elastic function is achieved, that is, of the spring that is within the telescopic fork. The front suspension system of a motorcycle is generally formed by a telescopic fork that has two built-in functions:

- Elastic function performed by a coil spring that can be of constant stiffness or variable stiffness. - Hydraulic damping function, performed by two methods basically: cartridge and conventional.

The springs of constant stiffness are characterized, among other aspects, by having the same spiral diameter and the same step (distance between turns measured longitudinally), achieving a linear behavior in the force-deformation graph, as we will see later in relation to the figures. Variable stiffness springs have a variable pitch, achieving a variable behavior in the force-deformation graph, as we will see later. The progressivity of the variable stiffness spring is limited and usually has only two slopes.

In motorcycle front suspensions, the most common concept found is that of a telescopic fork that includes two parallel arms joined together by two pieces called disposed seatposts, one of them at the upper end of both arms, and the second to a variable distance down, to make a set sufficiently rigid. The suspension must fulfill a function of absorbing the irregularities of the terrain, giving the vehicle, in this case the motorcycle, sufficient stability so that the driver can have control of the same before the various driving conditions.

BACKGROUND OF THE INVENTION

The motorcycle must have a stable behavior when passing through wavy or bumpy roads. This is particularly important in field bikes such as: Trial, Enduro, Rally, etc. To achieve a stable behavior, the coil spring is designed following parameters such as the weight of the motorcycle, geometry, specialty for which it is designed, etc.

As the spring is an element that stores a considerable amount of energy during operation, parasitic movements, rebounds, vibrations, overshoots, etc. occur, and to mitigate this undesirable effect, it is necessary to incorporate a hydraulic shock absorber.

This system is incorporated in the fork itself, and the damping liquid is generally a special oil that is forced to pass through calibrated holes, and the damping force increases with the speed of passage of said oil through the holes. The good adjustment of the two functions, elastic and cushioning, is essential for the stable behavior of the motorcycle.

DESCRIPTION OF THE INVENTION

In ₁ general lines, the suspension system for motorcycle front forks, object of the present invention, must meet the following characteristics:

Be as progressive as possible in approximately 50% of the total race. Adjustable easily.

Compatible with the original motorcycle fork (not to compromise the rigidity structural structure defined by the

maker) .

Modular and simple to manufacture. - Effective before the physical principle with which progressivity is achieved.

Progressivity is achieved with the compression of a gas. Since the total stroke of the telescopic fork is limited, you have to make the best use of it. This means that it is not possible to do the elastic function only with a gas, because the force that would be obtained at the end of the stroke (for example at 150 mm in the case of a fork of about 150-180 mm of stroke) would be insufficient to the dynamics and stability of the motorcycle.

Therefore, the concept of a system formed by two elastic elements arranged in series is developed:

The first element defined by a compressed gas, and a second element materialized by a helical spring, of simple rigidity and clearly increased with respect to the original spring. The gas spring grants progressive behavior in the first half of the fork's compression stroke.

The set of both elements arranged in series, can be mounted on each of the arms of the original fork of the motorcycle, replacing the internal elements thereof with the respective assemblies object of the invention.

The gas spring includes an upper sealing plug of a tube or sleeve inside which a sliding piston runs. In the upper chamber there is a gas under pressure and a certain amount of oil to optimize the sliding. In the plug there is a mounting hole for the gas filling valve. The piston has a rod topped at the bottom a spacer-centering of the coil spring which constitutes the second elastic damper arranged in series.

To facilitate the understanding of the features of the invention and forming an integral part of this specification, some sheets of drawings are attached in whose figures, for illustrative and non-limiting purposes, the following has been represented:

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1.- It is a scheme of the variable stiffness of a spring of a conventional suspension, of variable step in two stages.

Figure 2. - It is a scheme of the deformation experienced only by a coil spring; only by the gas, - and the deformation experienced by the set of both elements arranged in series, the latter graph corresponding to the suspension system object of the invention.

Figure 3. - It is a graph showing the behavior of the conventional suspension of the motorcycle and that obtained with the suspension system object of the invention more flexible and progressive initially and more rigid afterwards.

Figure 4.- It is a comparative scheme according to the characteristic curves of the suspension, where the gas flexibility curve is sensitive to the volume of the chamber, starting with the curves of the same point.

Figure 5.- It is another scheme that shows the sensitivity of the suspension system to the initial setting pressure, that is, each curve has a starting point dependent on the initial pressure.

Figure 6.- It is a partial sectioned longitudinal elevation view of the suspension system for motorcycle front forks, according to the invention, to be mounted on each fork arm. Figure 7a.- It is a schematic view in sectioned longitudinal elevation of the original suspension system, with a telescopic arm in a distended position.

Figure 7b.- It is a view similar to Figure 1, in compressed position.

Figure 7c- It is a view similar to Figure 7a with the same coil spring subjected to an initial claim.

Figure 8 .- It is a view similar to Figure 6, showing the assembly inside the tube corresponding to one of the fork arms.

Figure 9 .- It is a view similar to Figure 6, according to a different embodiment.

Figure 10.- It is a view similar to Figure 9, according to a third embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the numbering adopted in the figures, we can see how in Figure 1 a conventional way of achieving a progressive spring is shown, making it variable pitch. It is highly desirable that for the spring response to be proportional to the request to which it is submitted, it should be as progressive as possible. It is achieved that in a first stage, generally around 80-100 mm, a soft first part of the spring (with a smaller passage between turns) becomes deformed until it becomes a block, then a more rigid part (with greater passage between you turn).

In the graph of this figure 1 a more elastic first part is seen and from a point the shape of the curve changes to become more rigid. This makes for small bumps or disturbances, the fork movement is smoother. However, this design has the limitation of not being adjustable, and the need to change the spring if the elastic characteristic is to be changed. Any change in stiffness goes through a spring change. - S -

In the graph of figure 2, the curve passing through the points materialized by small circumferences, represents the deformation only of the gas contained in a cylinder, thus achieving a remarkable force with little relative stroke. The curve passing through the points indicated as rhombuses, shows the deformation achieved only with the spring: nothing progressive at the beginning. Finally, the curve that joins the points marked with squares corresponds to the resulting deformation using the set of the two springs in series, according to the invention: progressive at the beginning, deforming with a lot of force absorption with the available stroke (around 200 mm in this case).

The mathematical model with which this optimal result is achieved, includes the simulation of real gas behavior, based on the Van der Waals state equation. It is possible to simulate the behavior, quite similar qualitatively with reality (passing through the circles). The rigidity of the new spring is approximately double or more than in the original fork of the motorcycle.

In the graph shown in Figure 3, the actual result obtained with the mathematical model is indicated, and based on real data of a real model as a prototype has been manufactured and put into operation for more than 1,200 km for all types of Terrains and situations. The virtually linear through-the-curve curve corresponds to the original motorcycle spring. The passing curve through the points in the form of squares, is the behavior of the suspension successfully installed on the real motorcycle, according to the invention. You can see how the recommended objective is achieved: more flexible and progressive up to a stroke of about 130 mm to evolve even more rigid from the original spring, from this point (crossing curves). As for the regulation capacity, the suspension system that is recommended meets the objective of simple regulation because the gas flexibility curve is sensitive to: - Chamber volume. - Initial pressure.

In the graph corresponding to figure 4, the volume sensitivity of the chamber is simulated and in the graph of figure 5 the sensitivity to the initial set pressure is simulated.

It is observed that in the first case, that is, in the scheme of figure 4, all the curves start from the same point (same initial pressure), and in the second case (in the scheme of figure 5) each curve has a point Starting dependent on initial pressure. This has also been tested with the real prototype built.

In said figure 4, as shown in the lower right three cases are indicated by changing the volume of the chamber (20 was ^3, 25 cm ³ 30 cm ³ respectively). Figure 5 also shows three cases with different pressures in the chamber, corresponding respectively to pressures of 1.8 bars, 1.6 bars and 1.4 bars respectively.

Figure 6 shows the structure of a prototype built in accordance with the invention, which is attachable to the fork tube itself (mountable in each of its arms). It includes the gas spring referenced in general with the number 1 and constituted by a jacket 2 closed by an upper plug 3 and which in turn will be covered by the original plug 4 of the fork, provided with an axial bore 5 for fixing the valve 6 (see figure 9). Inside the jacket 2 runs the piston 7 which is connected internally with the rod 8 in turn finished in a lower guide piece 9 in the tube of the respective arm of the fork. In figures 7 and 8 This tube is referenced with the number 10. The reference 11 designates the sliding band of the guide piece 9, the latter having a support projection for the helical spring 12 that materializes the second damping element, arranged in series the gas spring 1.

On the other hand, the piston 7 has another guide band 13 and an oil seal 14 to compress the pressurized gas that is in the upper chamber 15, which is partially occupied by oil 16. This oil seal 14 has the mission to ensure that during the compression operation of the elastic element, the oil found by gravity in the lower part of the gas chamber does not escape from its housing. The oil 16 is deposited inside the gas chamber 15, before pressurizing it.

The upper cap 3 of the jacket 2 of the gas spring 1 has an O-ring 17 of the chamber 15.

The coil spring 12 is an element calculated and designed so that, together with the rod 8 of the piston 7 and the gas spring 1 itself, they can withstand the efforts generated by the natural movement of the telescopic suspension fork when it is in operation, that is to say , absorbing the irregularities of the terrain through which the vehicle in which the system is installed passes.

With special reference now to Figure 9, we see a simple embodiment variant, also in accordance with the invention, but where the compression of the gas is achieved by mounting a piston 7 'which has the oil seal 14 and one or two anti-friction bands 13 incorporated. (in this case two).

What is achieved with this design is to make it easier. It has the limitation that the design of the piston 7 'is delicate because it has to adapt to the inner diameter of the tube 10 of the original fork of the motorcycle, in each of his arms. It has the advantage that simply by drilling the original upper cap 4, the valve 6 is screwed and is now available to pressurize with a suitable pump. The spring 12 rests on the guide piece 9 by means of a washer 18.

In figure 10, a gas cylinder has been referenced with 1 '' which represents a more evolved embodiment even than the embodiment shown in figure 6 of the gas spring 1, with the same operating principle. In this case, the upper cap is referenced with the number 3 'because unlike the one referenced with 3 in Figure 6, it integrates the original cap 4 of the motorcycle and the previous cap, (it is passed from two pieces to one).

Also included is a polyamide closure 19 which has the mission of voiding the chamber that is left by the necessary axial bore of the upper cap 3 'for the assembly of the valve 6. The reason for eliminating this small chamber is due to the gas behavior itself under pressure, because it is interesting that in the last millimeters of the compression stroke, the diameter of the chamber 15 corresponds to that of the piston 7 that compresses (according to the mathematical model).

Claims

1.- SUSPENSION SYSTEM FOR FRONT FORKS

MOTORCYCLES, with two telescopic arms with elastic function by means of a helical spring, and damping with a hydraulic system, characterized in that the elastic function is achieved with two elements arranged in series inside said telescopic arms a helical metal spring (12 ) of rigidity higher than usual, and a gas spring (1, I ¹ , 1 '') that gives progressive behavior during the first half of the fork's compression stroke.

2. SUSPENSION SYSTEM FOR FRONT FORK MOTORCYCLES, according to claim 1, characterized in that the set of both elements (1, 1 ', I' ¹ , 12) arranged in series, can be mounted on the tube (10) that materializes the corresponding arm of the original fork of the motorcycle, replacing the original internal elements of the motorcycle.

3.- SUSPENSION SYSTEM FOR FRONT MOTORCYCLE FORKS, according to claim 1, characterized in that the gas spring (1) includes an upper sealing plug (3) of a jacket (2) with an axial valve (6) and a piston sliding interior (7) and whose rod (8) is finished internally in a spacer-centering (9) of the coil spring (12) and as a guide piece (9) in the tube

(10) of the fork through an anti-friction band

(11), the upper chamber (15) of the piston (7) having a certain volume of oil (16) and the rest a gas under pressure.

4.- SUSPENSION SYSTEM FOR FRONT FORKS

OF MOTORCYCLES, according to claim 1, characterized in that the gas spring (I ¹ ) is determined by the tube (10) of the fork arm itself as a piston sleeve (7 ¹ ), with the upper cap (4) of each arm of the same, a threaded hole for insertion of the filling valve (6), incorporating the piston (7 ¹ ) an oil seal (14) and at least one anti-friction band

(13), and the upper chamber of the piston (V) being filled with a partial volume of oil (16) and the remaining gas under pressure.

5. SUSPENSION SYSTEM FOR FRONT MOTORCYCLE FORKS, according to claim 3, characterized in that the upper sealing plug (3 ') has a threaded portion for anchoring in the initial threaded section of the original tube (10) of the corresponding fork arm , an axial mounting hole of the gas filling valve (6), and a polyamide closure (19) that cancels the mounting hole of said valve (6).