Motorcycle

The invention relates to a motorcycle comprising a frame, in which at least an engine is mounted; a front fork pivoted to the frame, in which at least a front wheel is mounted; a rear fork pivoted to the frame, in which at least a rear wheel to be driven by the engine is mounted; as well as a spring system connected to the rear fork and to the frame, wherein the spring system is arranged for exerting forces on the frame in a forward direction substantially parallel to the direction of movement of the motorcycle.

FIELD OF THE INVENTION

The invention relates to a motorcycle comprising a frame, in which at least an engine is mounted; a front fork pivoted to the frame, in which at least a front wheel is mounted; a rear fork pivoted to the frame, in which at least a rear wheel to be driven by the engine is mounted; as well as a spring system connected to the rear fork and to the frame, which comprises at least one shock absorber which is horizontally oriented in the motorcycle and which is positioned under the engine, said shock absorber being connected to the frame on the one hand and to the rear fork on the other hand.

BACKGROUND OF THE INVENTION

Such a motorcycle is known, for example from U.S. Pat. No. 6,446,996 B1. Known motorcycles of the type referred to in the introduction comprise a spring system which, upon inward springing of the rear wheel, for example on an uneven surface with bumps and hollows, such as a motocross circuit, transmits forces to the frame, the rider and the front wheel in such a manner as to have an adverse effect on the driving characteristics of the motorcycle (the stability, the balance and the roadability).

Inward springing of the rear wheel causes the frame to spring upwards (“kicking”) and the front wheel to spring downwards in reaction thereto, resulting in a jolting behaviour of the motorcycle. As a result, the rear wheel as well as the front wheel constantly lose contact with the surface, which has an adverse effect on the traction or propulsion in the case of the rear wheel and on the steering behaviour in the case of the front wheel. Thus, also the engine efficiency decreases accordingly.

OBJECT OF THE INVENTION

The object of the invention is to obviate the above drawbacks and to provide a motorcycle as referred to in the introduction that has improved driving characteristics.

SUMMARY OF THE INVENTION

According to the invention, the motorcycle is to that end characterized in that the spring system is arranged for exerting forces on the frame in a forward direction substantially parallel to the direction of movement of the motorcycle.

As a result, the extent to which jolting upward and downward springing of the frame and the front wheel takes place is significantly reduced, and the traction of the rear wheel and the steering behaviour of the front wheel are advantageously affected. All this results in a motorcycle exhibiting significantly improved driving characteristics (stability, balance and roadability), which offers major advantages in particular in the case of motocross races.

The aim is to convert all the upward forces that cause the rear wheel of the motorcycle to spring upwards (“kicking”) under the influence of the unevennesses in the terrain into forward forces by means of the spring system according to the invention, so that the motorcycle as a whole will exhibit an improved stability, balance and traction (on the rear wheel) and, as a result, will be safer.

Especially in the case of motocross races, it will be possible to realize faster lap times when using such a spring system.

In a special embodiment of the motorcycle according to the invention, the spring system comprises at least one shock absorber that is horizontally oriented in the motorcycle, which shock absorber is connected to the frame on the one hand and to the rear fork on the other hand.

Since the shock absorber is positioned under the engine in a very functional embodiment, a more compact motorcycle having a lower centre of gravity is obtained, which motorcycle, in addition to being lighter, is also more easily maneuverable and more stable.

In one embodiment, the forces can act in the direction of movement of the motorcycle in that the spring system comprises a lever, which lever is connected to the rear fork at a first pivoting point and to the shock absorber at a second pivoting point.

Furthermore, the spring system may comprise an auxiliary arm that is pivoted to the frame with a first end, which auxiliary arm is connected to a third pivoting point of the lever with the other end.

In a specific embodiment, the first end of the auxiliary arm is located in the immediate vicinity of the hinge point of the rear fork and the frame. As a result of this construction, the rear fork extends at a small angle with respect to the horizontal, thus preventing unexpected extension of the spring system by the drive chain (upon acceleration).

In a first suitable embodiment of this spring system, the first pivoting point is located between the second and the third pivoting point, whilst in another functional embodiment the third pivoting point is located between the first and the second pivoting point.

In a specific embodiment, said first end and said other end of the auxiliary arm as well as the hinge point of the rear fork and the first pivoting point of the lever furthermore form the corner points of a trapezium, which, in addition to a simplification of the construction, also enables an improved control of the interaction of forces that occurs in the motorcycle.

The shock absorber and/or the auxiliary arm may be oriented substantially parallel to the rear fork in a position of rest.

A further advantage of the construction of the spring system according to the invention is achieved in that the air inlet passage from the air filter to the engine is of rectilinear construction. As a result of the horizontal orientation of the spring system in the motorcycle, additional mounting space is obtained, which space can be utilized for creating a rectilinear air inlet passage. Thus, not only the construction of the motorcycle but also the air inlet passage to the engine is improved, resulting in an improved efficiency thereof. As a result of the improved fuel-air mixture, the engine delivers more power and a larger torque, which leads to a reduced fuel consumption, therefore.

Reference is furthermore made to U.S. Pat. No. 6,581,711, which likewise discloses a motorcycle as referred to in the introduction. In said US Patent, use is made of a specific spring/shock absorbing mechanism, in which a shock absorber and an arm extending parallel thereto are jointly pin-pivoted to the rear fork.

In this specific construction, however, the parallel arm will exert a force on the frame larger than the force of the shock breaker, which force acts in a direction opposed to the direction of movement of the motorcycle. Said force engages below the centre of gravity of the motorcycle, resulting in strong diving of the front of the motorcycle, comparable to the situation when a vertically disposed shock absorber is used. Furthermore, the assembly of the shock absorber and the parallel arm is mounted below the hinge point of the rear fork to the engine block, as a result of which the rear fork, too, is mounted higher in the frame.

The angle at which the rear fork extends with respect to the horizontal as a result thereof is larger than usual, which adversely affects the traction of the motorcycle. The forces exerted by the drive chain upon acceleration of the motorcycle will attempt to extend the spring of the shock absorber unit, as it were.

In motocross races it is furthermore desirable for the motorcycles to have a large ground clearance of at least 35 cm. Since the shock absorber unit and the parallel arm are mounted under the rear fork of the motorcycle, the engine block, too, will be mounted higher in the frame. Apart from the fact that this also leads to a larger angle between the rear fork and the horizontal, the centre of gravity of the motorcycle will be positioned higher as well. This has a negative effect on the stability and the roadability of the motorcycle during motocross races.

For a better understanding of the invention, like parts will be indicated by the same numerals in the description of the figures below.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1shows a motorcycle according to the prior art. The motorcycle1consist of a frame10including a front tube10a, in which a front fork11is rotatably mounted. The front fork11can be rotated by means of handlebars (not shown). A front wheel12is mounted in the front fork11. The motorcycle1according to the prior art furthermore comprises a rear fork13, in which a rear wheel14is mounted. The rear fork13is pivoted to the frame10via point of attachment13a.

The frame10accommodates an engine assembly built up of an engine16with a cylinder17as well as a carburetor15, which carburetor is connected to an air filter18bby means of an air inlet passage18a. The air filter18bis positioned under the seat10b.

The motorcycle according to the prior art furthermore includes a spring system19consisting of a shock absorber19, which is connected to the frame10on the one hand and to the rear fork13on the other hand at points of attachment19aand19b, respectively.

During movement of the motorcycle1over the surface20, the rear wheel14springs inward, which inward springing movement is transmitted to the frame10via the rear fork13and the vertically disposed shock absorber19. Said inward springing of the rear wheel, for example on an uneven surface20comprising bumps and hollows, such as a motocross circuit, results in upward springing (“kicking”) of the frame10, and thus in a jolting behaviour of the motorcycle1. The inward springing movement of the rear wheel14is indicated by the arrow A, whilst the upward “kicking” movement of the frame10/the motorcycle1is indicated by the arrow B.

This interaction of forces furthermore causes the front wheel12to spring downward, as is indicated by the arrow C. The jolting behavior of the motorcycle1according to the prior art results in the rear wheel14and the front wheel constantly losing contact with the surface20. This leads to a less efficient traction or propulsion of the rear wheel14and to less favorable steering characteristics of the front wheel12. In addition to that, it leads to a reduced efficiency of the engine12.

FIG. 2shows an embodiment of a motorcycle according to the invention that does not have the drawbacks of the prior art motorcycle1as described above. The motorcycle2according to the invention likewise comprises a spring system19, the shock absorber19of which is horizontally mounted in the frame10. Analogously toFIG. 1, the shock absorber19is connected to the frame10at point of attachment19aand to the rear fork13at point of attachment19b.

More in particular, the spring system of the motorcycle2according to the invention includes an additional lever21that is connected to the rear fork13at a first pivoting point21a. The lever21is connected to the shock absorber19via a second pivoting point21b(point of attachment19b) The lever21further comprises a third pivoting point21c, which functions as the point of attachment22bfor an auxiliary arm22, which is connected to the frame10with its other end22a.

The spring system according to the invention functions as follows. Upward springing of the rear wheel14/the rear fork13(arrow A) results in an upward movement of the first pivoting point21aof the lever21about the hinge point13aof the rear fork13. Likewise, the third pivoting point21cof the lever21will move upwards and impart a pivoting movement about the first pivoting point21ato the lever21via the auxiliary arm22, which pivoting movement takes place in clockwise direction.

Accordingly, the second pivoting point21bconnected to the shock absorber19will undergo a movement in the forward direction of the motorcycle2. Said forward movement of the pivoting point21bresults in a force (indicated by the arrow0) being exerted in forward direction on the frame10, and thus on the motorcycle2, by the shock absorber19.

As a result of this construction of the spring system according to the invention, inward springing of the rear wheel14(arrow A) does not cause the frame10to spring upwards (“kicking”), as is the case with prior art motorcycles, but the spring system according to the invention prevents the front wheel12springing inwards and outwards in a jolting manner.

This has an advantageous effect on the traction of the rear wheel14as well as on the steering behaviour of the front wheel12. The action of the forces being exerted in forward direction (parallel to the direction of movement) on the frame10/the motorcycle2according to the invention by the spring system19,21,22results in a motorcycle exhibiting improved driving characteristics as regards stability, balance and roadability. In combination with the improved steering characteristics of the front wheel12, these improved characteristics can be used to advantage during motocross races.

Another embodiment is shown inFIG. 3. In the embodiment of inFIG. 3, the third pivoting point21cis located between the first pivoting point21aand the second pivoting point21b, whereas in the embodiment ofFIG. 2the first pivoting point21aof the lever21is located between the second pivoting point21band the third pivoting point21c. AsFIG. 3clearly shows, the auxiliary arm22is mounted under the rear fork13, in contrast to the embodiment that is shown inFIG. 2.

This provides a more compact construction of the spring system according to the invention. In addition to that, the centre of gravity will be located further down, resulting in an improved roadability of the motocross bike.

In this second embodiment, too, upward springing movement of the rear wheel14(and the rear fork13) results in upward movement of the first pivoting point21aabout the hinge point13of the rear fork13and pivoting movement of the lever21in clockwise direction. Said pivoting movement about the first pivoting point21aresults in a movement of the second pivoting point21bin forward direction. The shock absorber19will transmit this movement in the form of forces as indicated by the arrow D.

It will be understood that the two embodiments as shown inFIGS. 2 and 3provide a motocross bike according to the invention that exhibits strongly improved driving characteristics, which give the motorcycle an advantage over prior art motorcycles during motocross races. Since the rear wheel14retains a better hold on the surface20, in particular on unevennesses such as the bumps and hollows or ruts of a motocross circuit, the motorcycle2or3(FIGS. 2 and 3) exhibits an improved traction, which has a very positive effect on the movement and/or the acceleration of the motorcycle.

Especially when deep ruts are present in the surface20, the motorcycle according to the invention exhibits an improved stability as a result of the action of the forces being exerted in forward direction on the frame10of the motorcycle by the spring system. Furthermore, the rear wheel will spring upward less strongly (“kicking”) while braking in bends, so that also the front wheel12will spring upwards and downwards less. As a result, the front wheel12will have more traction on the surface20as well, resulting in strongly improved steering characteristics, in particular while cornering.

The strongly improved balance of the motorcycle according to the invention increases the safety level for the rider, resulted in significantly faster lap times (up to two seconds per lap) during motocross races.

A further aspect of the motorcycle according to the invention is furthermore shown inFIGS. 2 and 3(in combination withFIG. 1). The vertical position of the shock absorber19in the frame10of a motorcycle according to the prior art (seeFIG. 1) makes it necessary to use a complex, bent construction of the air inlet passage18aaround the shock absorber19for supplying air through the filter18bvia the air inlet passage18ain the direction of the carburetor15and the cylinder17of the engine16. This complex, bent construction of the air inlet passage18interferes with an adequate, efficient supply of air to the engine16and thus results in a reduced efficiency level.

The spring system according to the invention makes it possible to use a rectilinear air inlet passage18a, as is clearly shown inFIGS. 2 and 3(in comparison withFIG. 1). The rectilinear construction of the air inlet passage18afrom the air are filter18bto the carburetor15and the cylinder17results in a strongly improved air supply to the engine, which is thus supplied with an improved combustion mixture (fuel-air mixture).

Not only is the fuel consumption significantly reduced as a result of that, but the engine16will have more power and be capable of transmitting a larger torque to the rear wheel14. As a result of the strongly improved engine efficiency that is achieved in this way, a more powerful motorcycle having an improved traction and acceleration, in particular during motocross races, is realized.