Patent Application
20050181901
This invention relates generally to internal combustion engines for motor vehicles, and relates more particularly to a belt tensioner for accessory drives of an internal combustion engine.
Conventional motor vehicles are provided with belts for rotatably connecting various components. In one example, various motor vehicle accessories are powered by a continuous drive belt which is driven by an engine crankshaft through a crankshaft pulley. In another example, a drive belt is used to synchronize engine drive and rotatably connect an engine crankshaft and cam shaft sprockets. Proper vehicle operation requires the maintenance of adequate tension in such drive belts and drive belts.
Tensioners are used to maintain proper tensioning of the drive and drive belts. Conventional tensioners include two types—manual and automatic. Manual accessory belt tensioners require user action to maintain proper tension throughout the life of a belt. Automatic accessory belt tensioners typically are biased into engagement with the belt for maintaining the belt under tension. A typical automatic belt tensioner includes a tension arm pivotally mounted on a hub. A tension pulley is rotatably attached to a free end of the tension arm. A compression coil spring biases the pulley into engagement with the belt to thereby reduce the vibration of the belt by tensioning.
One aspect of the present invention is a belt tensioner comprising first and second pulleys, a main arm and a sub-arm. The first pulley is displacable relative to an engine, and the second pulley is displacable relative to the first pulley. The main arm is connected to the first pulley, and a first spring is connected to the main arm and resists displacement of the first pulley when the engine is started. The sub-arm is connected to the second pulley, and a second spring is connected between the main arm and the sub-arm and maintains the second pulley generally equidistant from the first pulley while the engine is running.
In an alternative embodiment, the belt tensioner comprises a main sliding block connected to the first pulley, and at least one first spring connected to the main sliding block and resisting displacement of the first pulley when the engine is started. A sub-sliding block is connected to the second pulley, and at least one second spring is connected between the main sliding block and the sub-sliding block and maintains the second pulley generally equidistant from the first pulley while the engine is running.
Accordingly, it is an object of the present invention to provide a device of the type described above that provides both running tension and starting tension for an accessory belt of a motor vehicle.
Another object of the present invention is to provide a device of the type described above that provides damping against any residual oscillation of the pulleys.
These and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.
A pulley 36 is rotatably mounted on the distal end of the sub-arm 32 in a manner similar to the mounting of the pulley 30 on the main arm 28. A relatively small displacement spring, preferably such as a coil spring 38, is connected between the sub-arm 32 and the main arm 28. One or more forced contact embossments 40 may be applied on both sides of the sub-arm 32. On one side of the sub-arm 32, the embossments 40 ride against the main arm 28. On the opposite side of the sub-arm 32, the embossments 40 ride against a cover (not shown). The belt tensioner 10 is preferably attached to the engine 12 by a bolt (not shown) extending through a hole 42 in the sub-arm 32, through similar holes in the main arm 28 and in the clock spring unit 26, and into a block of the engine 12. Various covers may also be provided for the tensioner 10.
While the engine 12 is operating normally or at rest, the spring 38 biases the sub-arm 32 toward the main arm 28, and thereby maintains running tension in the drive belt 18.
While the engine 12 is operating normally or at rest, the springs 126 and 138 bias the sub-sliding block 132 toward the main sliding block 128, to the position shown in the figures, to thereby maintain running tension in the drive belt. Engagement of the alternator/starter develops tension in the drive belt, and at least initially this force tends to shorten that length of drive belt and exert a downward force on the lower pulley 130 of the main sliding block 128. Downward movement of the lower pulley 130 pulls the sub-sliding block 132 downwardly through the springs 138, and is resisted by the main sliding block springs 126. Any residual oscillation of the pulleys 130 and 132 may be damped by forced contact between linear bearings 144 and 146 and their respective sliding guide.
While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the description of the appended claims.
