Abstract:
A device which drives accessories such as an alternator or a cooling water pump utilizing output of an automobile engine, includes an input shaft rotating at speed corresponding to an output shaft of the engine, and a nonstage transmission installed between the shaft and a pulley connected to the accessories. The nonstage transmission is provided with a planetary cone rotating in revolution around the input shaft and also in self-rotation, and a shifting ring engaged in frictional engagement with the conical surface of the planetary cone and movable along the axial direction of the pulley, thereby the transmission ratio corresponding to displacement of the gear shifting ring is obtained. Variation of the position of the shifting ring is performed by action of a hydraulic piston/cylinder assembly working at hydraulic pressure corresponding to the rotational speed of the pulley.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a device for driving various accessories such as an alternator, a cooling water pump or the like, utilizing power of an engine of an automobile or the like. 
     2. Description of the Prior Art 
     In an engine of an automobile or the like, accessories such as an alternator, a cooling water pump, an air-conditioning compressor, an oil pump for hydraulic servo steering or the like are belt-driven by a crank pulley installed at an end of a crank shaft. Since the accessory drive is accompanied with large power loss during the high speed running of the engine, in order to avoid it, various methods have been proposed that gear shifting of a crank pulley is performed with respect to the engine rotational speed and the running speed of the accessory is limited. 
     For example, Japanese patent application laid-open No. 200838/1983 discloses technology that a reduction drive system comprising a planetary reduction gear and a one-directional clutch, and a direct-coupled drive system comprising a lock-up clutch composed of a hydraulic piston are constituted between a crank shaft and a crank pulley of an engine, thereby the rotational speed of the crank pulley is selectively changed at two stages with respect to the engine rotational speed. In the prior art, however, since rapid speed variation is produced at the speed changing state, variation of the driving force of a accessory applies the variation shock to the vehicle driving force of the engine, thereby the running stability of the vehicle is deteriorated and resulting in unpleasantness to the driver. Moreover, there are problems in durability of the planetary reduction gear and noise is liable to occur. Consequently, this method is not practicable. 
     On the other hand, for example, Japanese utility model application laid-open No. 86434/1983 discloses technology utilizing a variable pitch pulley to vary effective pitch diameter, wherein a driving pulley of variable pitch is installed on a crank shaft, and a driven pulley also with variable pitch follows the driving pulley and integrally connects an accessory drive pulley. A movable sheave of the driven pulley is controlled by a hydraulic cylinder so as to control the accessory drive speed. 
     In this example of the prior art, the high hydraulic source is required to control the movable sheave of the drive pulley, and structure of the hydraulic actuator is considerably complicated. Further a comparatively wide installation space projecting in the crank axial direction of the engine is required. Consequently, this method is not suitable for a front wheel drive car with the engine laterally installed which is commonly used, because there is insufficient installation space. 
     SUMMARY OF THE INVENTION 
     In order to eliminate above-mentioned disadvantages in the prior art, an object of the invention is to provide an accessory drive device of an engine, wherein shock or noise does not occur during the gear shifting, the installation space is sufficient to enable the replacement for a usual crank pulley, and the rotational speed of the accessory drive pulley can be automatically varied with respect to the engine rotational speed so that it becomes approximately constant while the engine is running at intermediate or high speed. 
     An accessory drive device of an engine according to the invention includes a nonstage transmission with differential planetary mechanism of a frictional transmission system installed between a crank shaft and a crank pulley, a skimming action hydraulic pressure generating mechanism employing a Pitot tube for transmission of operation power for the nonstage transmission utilizing a frictional transmission oil infused within the nonstage transmission, and a hydraulic cylinder driven by the hydraulic pressure. 
     According to constitution of the invention, a transmission and a transmission actuator can be constituted integrally in compact structure within an inner circumferential space of a usual crank pulley, frictional driving system enables running at low noise, and the mechanism of the transmission actuator of hydraulic action by skillfully utilizing the skimming action of a Pitot tube can be manufactured simply at low cost. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of an accessory drive device of an engine according to the invention, partly cut away to reveal the inside thereof; 
     FIG. 2 is a sectional view taken along line II--II of FIG. 1; 
     FIG. 3 shows a planetary cone and a member contacting thereto in the drive device shown in FIG. 1 illustrating contacting point and relative dimension; and 
     FIG. 4 is a graph illustrating rotational speed of an accessory drive pulley versus rotational speed of an engine. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the invention will now be described referring to the accompanying drawings. 
     In FIG. 1, reference numeral 1 designates an input shaft directly coupled to an output shaft such as a crank shaft of an engine, numeral 2 an input transmission member supported by the input shaft, and numeral 3 a cam device for generating pressure interposed between the input shaft 1 and the input transmission member 2. Numeral 4 designates a plurality of cone friction wheels or planetary cones, each composed of a frictional transmission surface 4a on a conical surface, a frictional transmission surface 4b on a bottom surface of each cone, and a frictional transmission surface 4c on a circumferential surface of each shaft leading to the bottom surface of cone. Numeral 5 designates a shifting ring which is engaged in frictional engagement with the frictional transmission surface 4a of the planetary cone 4 and moved in the axial direction so as to vary the frictional transmission radius of the planetary cone 4, and numeral 6 an orbit ring which is engaged in frictional engagement with the frictional transmission surface 4c of the planetary cone 4 and, in its non-rotation state, guides rotation of the planetary cone 4 about the input shaft 1, i.e., the revolution. The frictional transmission surface 4b of the planetary cone 4 is engaged in frictional engagement with outer circumferential edge of the input transmission member 2. The cam force of the cam device 3 acting to move the input transmission member 2 in the axial direction acts as the pressure in the normal direction of the frictional transmission surfaces 4a, 4b, 4c of the planetary cone 4, and its acting direction and amount are set so as to provide balance with the reaction applied to the gear shifting ring 5, the input transmission member 2 and the orbit ring 6, respectively. Numeral 7 designates an accessory drive pulley, numeral 7a a plurality of key grooves on inner circumferential surface of the pulley 7 in the axial direction, and numeral 8 a roller key which transmits the rotational force of the gear shifting ring 5 to the pulley 7 and suppresses the movement in the axial direction and is engaged with the grooves 7a. Numerals 9, 10 designate side plates to support the pulley 7 at both ends. Neral 11 designates a stationary plate which fixedly supports the orbit ring 6 and is securely supported by a mounting part 11a to the stationary member of the engine. 
     A transmission actuator to move the shifting ring 5 in the axial direction comprises a hydraulic piston/cylinder assembly 12 constituted to push the shifting ring 5 in the axial direction. The piston/cylinder assembly 12 is provided with a cylinder 12a integral with the side plate 9, a ring-like piston 12b, a plurality of rods 12c fixed to the piston 12b and abutting on the gear shifting ring 5, and a flow path 12d to guide the acting hydraulic pressure. Numeral 13 designates a Pitot tube which communicates with the flow path 12d at one end and has the other end opened forward in the rotational direction of the side plate 9 as shown in FIG. 2. Numeral 14 designates a return spring. 
     In the device constituted as above described, the closed space surrounded by the pulley 7, the side plates 9, 10 and the input shaft 1 is filled with a frictional transmission oil 15 as medium for the frictional transmission. 
     Operation of the embodiment in the above constitution will be described. The driving force of the input shaft 1 is transmitted through the cam device 3 to the input transmission member 2, thereby the planetary cone 4 rotates on its own axial center, and at the same time performs the revolution around the axial center of the input shaft 1 along the frictional transmission surface 4c with the orbit ring 6 being the stationary element. The shifting ring 5 engaged in frictional engagement with the frictional transmission surface 4a of the planetary cone 4 is rotated around the axial center of the input shaft 1 at the speed determined on the basis of the differential action between the self-rotation and the revolution of the planetary cone 4 and the transmission radius ratio, and drives the pulley 7 through the roller key 8. The rotational speed ratio between the input shaft 1 and the shifting ring 5 can be arbitrarily set by moving the shifting ring 5 in the axial direction so that the effective radius ratio of the frictional transmission between the input shaft 1 and the shifting ring 5 becomes a prescribed value. 
     FIG. 3 illustrates the effective radius a-f of each element of the transmission system in the drive device shown in FIG. 1. Assuming that rotational speed of the input shaft 1 be N 1  and rotational speed of the gear shifting ring 5 be N 2 , it follows that ##EQU1## If the value of a is varied, N 2  /N 1 , i.e., ratio of the rotational speed of the pulley 7 to that of the input shaft 1, can be arbitrarily varied. 
     Effective radius a-f is as follows: 
     a: effective radius of the frictional transmission surface 4a of the planetary cone 4 to the shifting ring 5. 
     b: effective radius of the frictional transmission surface 4b of the planetary cone 4 to the input transmission member 2. 
     c: inner radius of the shifting ring 5. 
     d: effective radius of the input transmission member 2. 
     e: effective radius of the frictional transmission surface 4c of the planetary cone 4 to the orbit ring 6. 
     f: effective radius of the orbit ring 6. 
     The position of the shifting ring 5 in the axial direction is controlled by the hydraulic cylinder 12 as hereinafter described. Since the Pitot tube 13 rotates integrally with the side plate 9, the frictional transmission oil 15 is received at the opening of the Pitot tube 13 and thereby pump action is effected to introduce the hydraulic pressure through the flow path 12d to the hydraulic cylinder 12. The hydraulic pressure generated then has an amount proportional to square of the relative rotational speed between the Pitot tube 13 and the frictional transmission oil 15. On the other hand, since the rotational speed of the Pitot tube 13 is equal to that of the pulley 7, output of the hydraulic cylinder 12 varies depending on the rotational speed of the pulley 7. For example, when the input of the hydraulic cylinder 12 increases, the shifting ring 5 is pushed towards the cone vertex of the planetary cone 4. As a result, speed of the pulley 7 is reduced and the hydraulic pressure from the Pitot tube 13 is reduced and output of the hydraulic cylinder is decreased by receiving a negative feedback. In the reverse operation, a positive feedback is added. Accordingly, since the output of the hydraulic cylinder 12 continuously controls the axial position of the shifting ring 5 in equilibrium to the reaction of the return spring 14, the rotational speed of the pulley 7 can be made approximately constant regardless of variation in the rotational speed of the input shaft 1. In FIG. 4 illustrating an example of the rotational speed control characteristics, the abscissa represents the engine rotational speed and the ordinate represents the accessory drive pulley rotational speed in the accessory drive device of the invention. In the region shown by line OA of FIG. 4, the rotational speed of the engine, i.e., the input shaft 1 is low and also the rotational speed of the pulley 7 is low and the output of the hydraulic cylinder 12 is low, thereby when the shifting ring 5 is pushed away from the cone vertex of the planetary cone 4 by the load of the return spring 14, the pulley 7 has the same rotational speed as that of the engine. In the region shown by line AA&#39; of FIG. 4, output of the hydraulic cylinder 12 is in equilibrium to the reaction of the return spring 14, and even if the engine rotational speed rises the rotational speed of the pulley 7 is controlled to remain approximately constant. In addition, the pulley 7 may be constituted by another transmission output member such as a sprocket or a gear. 
     Accordingly to the invention as above described, since the nonstage transmission of the differential planetary mechanism of the frictional transmission type and the transmission actuator comprising the hydraulic cylinder acting by the skimming action, hydraulic pressure of the Pitot tube acting in the frictional transmission oil infused within the transmission are constituted integrally in a compact structure within the inner circumferential space of a usual crank pulley, the installation space is sufficiently wide to enable the replacement for the usual crank pulley, the frictional transmission is not accompanied with noise during running, the mechanism of the transmission actuator is simple and made at low cost, and the rotational speed of the accessory drive pulley can be controlled to remain approximately constant from an intermediate range of the engine rotational speed, thereby providing energy saving operation of the accessories and improving the fuel cost of engine and the power performance.