1. Field of the Invention
This invention relates to an automatic pedal for a bicycle, especially a pedal for a touring bicycle, allowing the footwear of the cyclist to form a nonpositive connection to the pedal.
2. Description of the Related Art
The automatic pedal conventionally comprises a pedal body that is rotationally mounted on the pedal shaft with the capacity to be joined to the crank of the chain transmission. The concept of “automatic” is linked to the fact that the footwear bears a retaining block or plate that is fixed underneath the sole of the footwear of the cyclist and is designed to initiate hands-free fixing by quite simply drawing this retaining plate against the catch means provided on the pedal. The pedal is, moreover, provided with a support surface above the pedal shaft against which the retaining plate comes to rest.
The catch means provided on the pedal body generally comprises a front fixed catch element of the retaining plate and a rear movable catch element mounted to pivot on the pedal body around an axis of rotation parallel to the pedal shaft between a retaining position of said plate engaged between the front and rear catch elements, and a position of release of the plate by the pivoting of said rear catch element against the action of an elastic return means, of which one end is connected to the rear catch element and the other end is connected to said pedal body.
Such a quick-connect automatic pedal with a retaining plate is standard and is described in document EP 0 146 454, for example.
The plate is automatically engaged with the pedal by inserting the front end of the retaining plate into the front catch element on the pedal and by a pivoting motion of the plate downward; this makes the rear catch element pivot to the outside against the action of the elastic return means in order to allow insertion of the free end of the latter into the rear catch element. Then, the rear catch element automatically returns to its initial position by the action of the elastic return means.
Disengagement of the retaining plate, i.e., its release from the pedal, is done by a rotary motion of the plate around a vertical axis near the front end of the plate; this causes pivoting of the rear catch element that thus disengages. The interaction between these elements is described in detail in the aforementioned document. Moreover, this release of the retaining plate can also be controlled independently of the will of the cyclist during a fall, when the foot of the cyclist accomplishes the required movement; the pedal in this case plays a role of safety and protection.
There are a large number of automatic pedals that differ from one another essentially by the implementation of the automatic retaining means used to connect the block to the pedal body. They all share in common that they comprise an elastic return means of the movable rear catch element that prestresses this element toward the retaining position of the plate on the pedal body.
One of the ends of this elastic return means is thus connected to the rear catch element, while the other end is connected to the pedal body. In general, the elastic return means is thus composed of a metallic helical spring that can work by compression, as in the aforementioned document EP 0 146 454, or by torsion, as in publication FR 2 620 410.
These metallic helical springs are subject to a certain number of deficiencies because they are limited in overall dimensions, are characterized by major variations of stiffness, and accordingly require rather broad production tolerances or even additional devices for controlling the spring tension. They are by nature sensitive to corrosion and fatigue.
The use of elastomer springs to eliminate these deficiencies is also known, but these springs entail other problems due to the fact that they are easily affected by temperature and their creep can diminish their performance level and thus limit the possibilities of their use.