Patent Publication Number: US-9890837-B1

Title: Tensioner

Description:
FIELD OF THE INVENTION 
     The invention relates to a tensioner, and more particularly, to a tensioner having a pivot shaft having two facing frustoconical portions disposed on a common axis, each of the first pivot arm and second pivot engaged with a respective facing frustoconical portion. 
     BACKGROUND OF THE INVENTION 
     Most engines used for automobiles and the like include a number of belt driven accessory systems which are necessary for the proper operation of the vehicle. The accessory systems may include an alternator, air conditioner compressor and a power steering pump. 
     The accessory systems are generally mounted on a front surface of the engine. Each accessory has a pulley mounted on a shaft for receiving power from some form of belt drive. In early systems, each accessory was driven by a separate belt that ran between the accessory and the crankshaft. Due to improvements in belt technology, single serpentine belts are now generally used in most applications. A single serpentine belt routed among the various accessory components drives the accessories. The engine crankshaft drives the serpentine belt. 
     Since the serpentine belt must be routed to all accessories, it has generally become longer than its predecessors. To operate properly, the belt is installed with a pre-determined tension. As it operates, it stretches slightly over its length. This results in a decrease in belt tension, which may cause the belt to slip. Consequently, a belt tensioner is used to maintain the proper belt tension as the belt stretches during use. 
     A current trend of automobile manufacturers is to replace the traditional starting motor and generator with a single reversible starter-generator, which is connected to the crankshaft by means of a drive belt. During the start step, the starter-generator functions as a motor and drives the crankshaft of the internal-combustion engine; when the vehicle is in motion, instead, the starter-generator is driven by the internal-combustion engine and generates electric current for recharging the battery and running the auxiliary systems. 
     In the case where a starter-generator is used, the belt spans will have differing tensions according to the mode of operation. The span that is tight during the starting phase, in which the starter-generator is the driving member and the internal-combustion engine is the driven member, becomes slack in the stage of normal running, in which the internal-combustion engine is the driving member and the starter-generator is the driven member. 
     To overcome this problem bi-directional belt tensioners or two-arm belt tensioners, i.e., which comprise two arms provided with pulleys, each acting on a respective span of the belt are known. The two arms can be mounted on the same pivot point in order to pivot about a common axis. The arms are loaded in the direction of one another by a spring so that the respective pulleys will co-operate with respective spans of the belt, thereby ensuring their proper tension. 
     Representative of the art is US 2002/0039944 which discloses an improved belt tensioner for a belt drive system having a belt tensioner, a crankshaft pulley, an accessory pulley, and a motor/generator pulley. The belt drive system further includes a power transmission belt trained about the crankshaft pulley, the accessory pulley, and the motor/generator pulley. The belt tensioner is of the type including an attachment point adapted to be affixed to a stationary point relative to a cylinder block of an engine, a first belt tensioner pulley, a biasing member, and a connective portion adapted to communicate a force from the biasing member to the power transmission belt via the first belt tensioner pulley. It is improved by the belt tensioner including a second tensioner pulley, and the connective portion being adapted to communicate the force from the biasing member to the first tensioner pulley and to the second tensioner pulley and thereby mutually asymmetrically biasing the first tensioner pulley and the second tensioner pulley toward movement tending to increase tension upon the power transmission belt. 
     What is needed is a tensioner having a pivot shaft having two facing frustoconical portions disposed on a common axis, each of the first pivot arm and second pivot engaged with a respective facing frustoconical portion. The present invention meets this need. 
     SUMMARY OF THE INVENTION 
     The primary aspect of the invention is to provide a tensioner having a pivot shaft having two facing frustoconical portions disposed on a common axis, each of the first pivot arm and second pivot engaged with a respective facing frustoconical portion. 
     Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
     The invention comprises a tensioner comprising a first pivot arm having a first pulley journalled thereto, a second pivot arm having a second pulley journalled thereto, a frustoconical base having a base vertex, a frustoconical pivot shaft having a pivot shaft vertex, the base vertex is oriented opposite the pivot shaft vertex on a common axis, the first pivot arm disposed for pivoting movement about the frustoconical pivot shaft, the second pivot arm disposed for pivoting movement about the frustoconical base, a first bushing damping movement of the first pivot arm on the frustoconical pivot shaft, a second bushing damping movement of the second pivot arm on the frustoconical base, and a spring in compression urging engagement of the first pivot arm with the frustoconical pivot shaft and the second pivot arm with the frustoconical base. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention. 
         FIG. 1  is a perspective view. 
         FIG. 2  is an exploded view. 
         FIG. 3  is a cross-section view. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a perspective view. Tensioner  1000  comprises a first pivot arm  100  and a second pivot arm  200 . Pulley  101  is journalled to pivot arm  100 . Pulley  201  is journalled to pivot arm  200 . Pivot arm  100  and pivot arm  200  independently pivot about a common axis A-A. In operation the pivot arms are biased toward each other in a scissor like manner by a torsion spring. 
       FIG. 2  is an exploded view. Fastener  800  extends through pivot shaft  400  and base  700  to attach the tensioner to a mounting surface. Bushing  500  is disposed between pivot shaft  400  and pivot arm  100 . Bushing  600  is disposed between base  700  and pivot arm  200 . Pivot arm  100  and pivot arm  200  pivot about pivot shaft  400  which is aligned with axis A-A. Spring  300  torsionally bias pivot arm  100  and pivot arm  200  such that a load is imposed upon a belt (B) engaged with each pulley  101  and  201 . 
     Bushing  500  and bushing  600  are each frustoconical in shape. A frustoconical portion  401  of pivot arm  400  cooperatively engages bushing  500 . Base  700  has a frustoconical shape which cooperatively engages bushing  600 . Portion  401  describes a vertex angle α. Base  700  describes a vertex angle β. Vertex angle α and vertex angle β may be adjusted by a user. They may be equivalent or not depending upon design requirements. They are each typically in the range of about 30 degrees to about 120 degrees. The numbers are offered as examples and are not intended to limit the scope of the invention. 
     The vertex of bushing  500  points opposite the vertex of bushing  600 . The vertex  402  of portion  401  points opposite the vertex  702  of base  700 . This orientation captures pivot arm  100  and pivot arm  200  between portion  401  and base  700 . 
     Fastener  102  retains pulley  101  on pivot arm  100 . Fastener  202  retains pulley  201  on pivot arm  200 . Dust shield  103  prevents debris from contaminating pulley bearing  104 . Dust shield  203  prevents debris from contaminating pulley bearing  204 . 
       FIG. 3  is a cross-section view. Pivot shaft  400  cooperatively engages base  700 . Base vertex  702  points opposite pivot shaft vertex  402 . 
     Pivot arm  100  and pivot arm  200  are pinched between pivot shaft frustoconical portion  401  and frustoconical base  700 . Torsion spring  300  exerts an axial spring force on the first pivot arm and the second pivot arm, thereby urging pivot arm  100  into pivot shaft portion  401  and pivot arm  200  into base  700 . 
     Bushing  500  and bushing  600  each act to damp movements of the respective pivot arm  100  and  200 . The frictional force is created by the axial force exerted by spring  300  on each pivot arm. Spring  300  is in axial compression between pivot arm  100  and pivot arm  200 . The frictional force is a function of the spring force developed by the axial compression of the spring. 
     Surface  701  of base  700  engages a mounting surface, such as an engine (not shown). Fastener  800  fixes the tensioner to the mounting surface. 
     In operation pivot arm  100  moves independently of pivot arm  200 . A small gap “G” between the pivot arms allows independent movement of the pivot arms. Portion  401  and base  700  combined may also comprise a pivot shaft with facing frustoconical sections on a common axis A-A, between which pivot arms  100 ,  200  are captured. The facing frustoconical shapes of portion  401  and base  700  allow ease of orientation such that the independent pivot arm motion is possible in a compact tensioner package. The frustoconical shape of the pivot shaft and base each provide an automatic means of alignment of the pivot arms during operation. The alignment is maintained as the bushings wear. 
     A tensioner comprising a first pivot arm having a first pulley journalled thereto, a second pivot arm having a second pulley journalled thereto, a frustoconical base having a base vertex, a frustoconical pivot shaft having a pivot shaft vertex, the base vertex is oriented opposite the pivot shaft vertex on a common axis, the first pivot arm disposed for pivoting movement about the frustoconical pivot shaft, the second pivot arm disposed for pivoting movement about the frustoconical base, a first bushing damping movement of the first pivot arm on the frustoconical pivot shaft, a second bushing damping movement of the second pivot arm on the frustoconical base, and a spring in compression urging engagement of the first pivot arm with the frustoconical pivot shaft and the second pivot arm with the frustoconical base. 
     A tensioner comprising a first pivot arm having a first pulley journalled thereto, a second pivot arm having a second pulley journalled thereto, the first pivot arm and second pivot arm captured between opposing frustoconical surfaces, and a torsional spring in compression between the first pivot arm the second pivot arm. 
     A tensioner comprising a first pivot arm having a first pulley journalled thereto, a second pivot arm having a second pulley journalled thereto, a pivot shaft having two facing frustoconical portions disposed on a common axis, each of the first pivot arm and second pivot arm engage with a respective facing frustoconical portion, and a torsion spring in axial compression between the first pivot arm and the second pivot arm, the torsion spring urging the first pivot arm and the second pivot arm toward each other. 
     Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts and method without departing from the spirit and scope of the invention described herein.