Friction gear transmission systems or components – Spring urges contacting gears into engagement
Reexamination Certificate
2001-07-12
2002-11-19
Joyce, William C (Department: 3682)
Friction gear transmission systems or components
Spring urges contacting gears into engagement
C476S067000, C180S221000
Reexamination Certificate
active
06482121
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drive apparatus for clamping a tire or an output disc of a bicycle equipped with an electric assist or of various small motor vehicles such as a welfare-specific vehicle at an outer periphery of the tire (or output disc) from both sides of the tire (or output disc) in an axial direction of thereof to drive the tire (or output disc) with a friction force.
2. Description of the Related Art
A drive apparatus employed as electric assist in a bicycle or the like often possesses a mechanism for reducing a rotation speed of a high speed motor with a gear train (or gear units) or a friction-driven planetary roller speed-reduction device to directly drive an axle of wheels or indirectly drive the axle via chains or belts.
Such drive apparatus reduces the rotation speed of the motor (several-thousand revolutions per minute) to or less than twentieth to ninetieth (two-hundred revolutions per minute at maximum) so as to obtain a large torque and drive the wheel axle. In order to achieve a large speed reduction ratio, the speed reduction device has to have a large dimension. Further, the drive apparatus should be rigid to bear great forces imposed on various parts thereof upon speed reduction. This often results in not only an increased weight of the drive apparatus but also additional reinforcement required to a bicycle body for supporting the large forces.
Since the bicycle requires drive power sufficient for its weight increased due to the motor, the speed-reduction device, the battery and the body reinforcement parts, the total weight of the bicycle is further increased. As a result, a common bicycle equipped with an electrically assisting device (drive apparatus) is almost twice as heavy as an ordinary bicycle without the electrically assisting device, and its cost is greatly raised.
In order to avoid such great increase in the weight and cost, portions to be driven should be limited to those having a large diameter such as the tire, rim or nearby spokes. By doing so, a speed-reduction device of large reduction ratio is not needed, the bicycle only requires a small reduction ratio to drive itself, and forces acting on various parts are reduced so that no reinforcement is required to the body. Accordingly, the drive apparatus including the drive mechanism can be designed to be compact and light-weight. A low cost drive apparatus that can be attached to the common existing bicycle is therefore obtainable.
To such an end, some bicycles are provided with a drive apparatus of which driving roller is forced against an outer diameter surface of a tire and rotated so as to drive the wheel with a friction force generated between the driving roller and the tire outer diameter surface.
If the drive apparatus drives the wheel with the friction force of the driving roller in contact with the outer diameter surface of the tire, it is necessary to apply a large presser force having a certain margin in order to prevent a slip from occurring between the drive surface of the driving roller and the outer diameter surface of the tire in spite of weather conditions such as rain that makes the road and tire slippery, adhesion of ground, sand and mud, and mechanical factors such as tire air pressure drop, tire wear, axle eccentricity, vehicle body deformation and wheel deformation. Since a large contact area should be insured to maintain a contact force between the driving roller and the tire, and the biting of the driving roller into the tire should be reduced, the driving roller has to have a relatively large diameter.
However, when the bicycle sticks in the mud, for example, a large amount of mud adhering to the tire outer diameter surface is not easy to spin off during the riding. Thus, a slip occurs between the tire and the driving roller and the tire is locally worn. This can disable further movement of the bicycle.
In order to compensate for the drop in the driving force due to the adhesion of the mud, the driving roller should be pressed against the tire with a still greater force. However, it results in the reduced life of the tire because application of the large force and deformation are repeated.
It is necessary to employ a driving roller of larger diameter and enlarge a contact area between the tire and the driving roller in order to reduce the deformation caused by the large presser force. This inevitably makes the rotation speed of the driving roller slower. In other words, the rotation speed of the motor is greatly reduced and the driving roller is driven by such a motor.
Gears or belts are often utilized to reduce the motor rotation speed considerably. However, if a smaller gear or pulley has a very small diameter, duration drops and therefore extremely small diameter cannot be adopted. Accordingly, a large gear or pulley has to have a large diameter if a reduction ratio is large. This makes it difficult to attach the drive apparatus to the bicycle since a limited space is only available. Consequently, a large reduction ratio cannot be expected, and a low speed motor has to be selected.
In general, a motor can be made compact if it is designed to rotate faster and to demonstrate the same output. Thus, use of a low speed motor is disadvantageous because the size, weight and cost of the motor increase.
The above described drive apparatus that drives the outer diameter surface of the tire therefore has a large size, and is particularly difficult to mount on a bicycle since the installation space for the drive apparatus is limited.
If the tire is held between the two drive rollers that are rotated in opposite directions to drive lateral surfaces of the tire with friction forces, the number of points of drive becomes two so that the drive force is dispersed. Since the lateral surfaces of the tire are less affected by the mud as compared with the outer diameter surface, the drive roller can have a smaller diameter and the drive motor of higher rotation speed can be employed as compared with an arrangement that drives the tire at the outer diameter surface. This is advantageous in terms of size reduction of the drive apparatus.
A common approach to rotate the two driving rollers in opposite directions relative to each other is as follows: two spur gears having the same number of teeth are coaxially provided on the two driving rollers respectively such that they mesh with each other, and one of the gears is driven by a motor. Therefore, each of these spur gears has a pitch circle diameter which has the same value as a distance between axes of the two driving rollers. Thus, the spur gear has a larger diameter than the driving roller and a casing for housing these gears becomes large.
If the two spur gears have a smaller diameter and two intermediate (or loading) gears are located between the spur gears, the size of the casing may be reduced. However, a cost will be raised since bearings for supporting two shafts of the intermediate gears are additionally provided. Further, a larger load is exerted on the teeth as the gear diameter is reduced. Gears used in an inexpensive mechanism such as the electric drive apparatus attached to the bicycle are generally made from plastic. Therefore, the smaller gears may jeopardize strength reliability; use of the small gears is not practical. In sum, a compact gear casing cannot be realized so that the drive apparatus cannot be mounted on the bicycle, and drive power loss is increased due to the increased load acting on the tooth surfaces and the increased points of gear engagement from one to three, and noises are also increased for the same reason.
Further, the drive mechanism employing the plastic gears cannot have sufficient accuracy in the gears and the teeth greatly deform elastically so that increased noises and torque irregularity upon gear meshing are unavoidable.
Moreover, when the bicycle equipped with the electrical drive apparatus runs by its inertia without being assisted by the associated motor, the motor becomes a brake to hinder the bicycle's coasting as
Hideo Okoshi
Joyce William C
Young & Thompson
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