1. Field of the Invention
The invention pertains to the field of tensioners. More particularly, the invention pertains to a self-energizing brake for a tensioner.
2. Description of Related Art
Chain drive applications require a tensioning device to maintain tension to control the motion of the chain. Blade spring tensioners are often used to tension a chain drive, and conventional blade spring tensioners apply similar damping forces in both directions of travel. Increased damping is desired when the chain tensioner is being compressed by the chain drive, and then when the tensioner is extending to take up slack in the system.
U.S. Pat. No. 5,935,032 discloses a wheeled tensioner for belts. As the tension from the belt presses on the wheeled tensioning pulley, a first pivot arm having an end with an arcuate surface, compresses a spring that moves a second pivot arm having an end with a movable shoe, and creates friction between the shoe convex arcuate friction surface and the arcuate surface of the first pivot arm.
U.S. Pat. No. 6,699,148 discloses a self adjusting contact mechanism for a belt that includes a contact shoe with a low friction surface with a belt, and a mechanism for biasing the low friction surface of the shoe against the belt with a controlled force profile. The shoe is mounted to a lever arm through a first pivot joint. The first pivot joint maintains the shoe in alignment with and in parallel with the belt. The second pivot connects a lever onto a belt drive system.
Japanese Publication No. 06193693 discloses a blade tensioner in which at the proximal end is a rocker fulcrum and a wedge type interspace formed in an interval between a cam surface and a cylindrical bore. A friction member and a spring member are built in each wedge type interspace. When the tension in the chain increases the friction member is thrust into a narrow part of the interspace and any rocking motion of the chain guide is prevented.
Japanese Publication No. 2001-355688 discloses a first embodiment in which a friction material is inset into the distal end of the blade shoe and contacts the sliding surface of the bracket, increasing dampening. In another embodiment, a friction surface is inset into the sliding surface of the bracket. In an alternative embodiment, the friction surface is inset into the curled ends between the end of the blade shoe and the blade spring.
Japanese Publication No. 08-336809 discloses an energized brake that stops rotation of a chainsaw blade when the motor is turned off. The brake device includes a brake band surrounding a brake drum with an end of the brake band operable by a hand guard, so that when activated, the brake drum is clamped by the brake band, stopping the chain. At the same time, a wire energizes a coil spring contacting a brake shoe, so that when a switch is turned off, the wire energizes the coil spring and thus the brake shoe, causing the shoe to engage the brake drum. When the switch is turned on, the brake shoe resists the coil spring and the shoe does not engage to brake drum.
Therefore, there is a need in the art for a self-energizing brake that increases damping of the blade tensioner during compression of the blade shoe rather than during extension of the blade shoe.