Motor vehicles – Special wheel base – Having only two wheels
Patent
1994-05-24
1999-06-01
Swann, J J
Motor vehicles
Special wheel base
Having only two wheels
280277, 280285, B62K 1100, B62M 700
Patent
active
059080787
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a suspension/transmission mechanism for motorcycles and the like, comprising at least one swinging arm which pivots at one end on one or both sides of at Least one of the wheels and at the other end on the frame of the vehicle, and comprising a power or drive shaft output pinion and a driven pinion or crown gear on the shaft of the drive wheel joined together by at least one chain or the like.
BACKGROUND OF THE INVENTION
In vehicles which use a suspension/transmission mechanism of the type described, the combined action of the force of the chain and the contact force due to traction can produce reaction forces on the swinging arm which are the cause of considerable instabilities in the vehicle.
The basic design of the chain transmission geometry of conventional motorcycles is suitable for avoiding the lifting or sinking of the rear end during acceleration or deceleration while the traction wheel is fully gripping the ground.
Nevertheless, when the traction wheel loses or recovers its grip with the ground an abrupt change in the equilibrium of forces is produced giving rise to considerable reaction forces on the swinging arm which cause instabilities in the motorcycle such as the phenomena known as "pitching" and "high sider".
Independently of the type of motorcycle suspension/transmission system, the resultant force on the drive wheel at the point of contact with the ground, due to acceleration and in the absence of slipping (the forces due to weight being eliminated), is in a direction known as "antisquat" which is defined by the wheelbase of the motorcycle and the height of the center of gravity.
The effect of any force applied to a wheel which can rotate freely is transferred to the support (in this case the swinging arm) via the pivot while the wheel accelerates.
If the traction wheel suddenly loses its grip with the ground, the contact force disappears and the wheel accelerates. Then only the force of the chain is transferred to the swinging arm via the wheel pivot.
This gives rise to a considerable opening moment of the swinging arm relative to the frame, an effect which is converted into a lifting of the rear end of the vehicle if it is in the vertical position, or an escape of the wheel if the motorcycle is in an inclined position.
If, after hard acceleration, the drive wheel completely and suddenly recovers its grip with the ground, without the force of the chain acting, the contact force reappears due to the rapid deceleration of the wheel.
Then only the contact force is transferred to the swinging arm via the wheel pivot. This force gives rise to a considerable closing moment of the swinging arm relative to the frame which is converted into a dropping of the rear end of the vehicle.
Assuming that the force of the chain is approximately constant while the vehicle accelerates, after the first wheel slip a complex phenomenon of self-sustaining oscillations of the system of forces appears, leading to an oscillation of the contact force intensity relative to its initial value.
This oscillation provokes an opening and closing phenomenon of the swinging arm which gives rise to the continuous instability of the vehicle while accelerating at the limit of its grip.
In fact, as the wheel begins to slip (increasing its angular velocity to a value above that corresponding to the velocity of the vehicle) the couple of the force of the chain becomes greater than that of the contact force of the wheel. Due to the first of the phenomena described above, this produces a tendency for the swinging arm to open which causes an increase in the contact force.
The increase in the contact force causes the drive wheel to decelerate (returning to the wheel velocity which corresponds to the velocity of the vehicle), giving rise to a couple of the contact force on the swinging arm which is greater than that of the force of the chain. Due to the second of the phenomena described above, this produces a tendency for the swinging arm to close, which causes the wheel to lose its grip with the g
REFERENCES:
patent: 5014808 (1991-05-01), Savard et al.
patent: 5050699 (1991-09-01), Savard
patent: 5060749 (1991-10-01), Horiike et al.
patent: 5323869 (1994-06-01), Kurayoshi et al.
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