Continuously variable transmission

Abstract: In the V belt type continuously variable transmission, after the output power from the prim mover has been transmitted to the input pulley shaft, two paths is operable to transmit the output power from the input pulley shaft to the output pulley shaft, two paths which are a main power transmitting path through a V belt engaged between the input pulley and the output pulley and a sub power transmitting path through the 2-way differential clutch. The drive ratio of the sub power transmitting path is set in a slightly smaller value than the maximum drive ratio of the main power transmitting path. When the movable input half pulley of the input pulley has been moved near the position of the maximum drive ratio in the main power transmitting path, the rotational speed of the output gear in the 2-way differential clutch become slower than that of the input gear, and as a result a rotational force is given to the output gear so that the output pulley shaft is rotated through the sub power transmitting path in addition to the main power transmitting path so that it becomes possible to increase driving power and accelerating force and also to decrease load to be added to the V belt.

Description: The present invention relates to a V-shaped belt (hereinafter referred to as V belt) type continuously variable transmission. In general, a V belt type continuously variable transmission contains an input pulley composed of a pair of half pulleys mounted on an input pulley shaft to move axially toward and away from each other, an output pulley composed of a pair of half pulleys mounted on an output pulley shaft to move axially toward and away from each other, and a V belt which frictionally engages the pulleys to transmit the rotation from the input pulley shaft to the output pulley shaft to vary the rotational speed continuously. The means to transmit the rotation between both pulley shafts depends upon the V belt member only in the V belt type continuously variable transmission which is actually used at present. In such a construction, there are several defects as follows; First the allowable transmission capacity is limited by the V belt strength so that the improvement of the transmission capacity and the compaction of the construction are obstructed. Secondly when the V belt stuck into the groove between half pulleys of the output pulley shaft because the vehicle stopped suddenly and its wheels and the output pulley shaft connected to them are brought to stop, power transmitting becomes impossible. Or the drive ratio is made to the higher position so that the restart becomes difficult or the acceleration is not accomplished satisfactorily due to weak drive power. If the movable input half pulley is forced to be moved by large power to change the drive ratio in the state of V belt stuck, the pulley or V belt is damaged. When the V belt is cut away, it goes without saying that the vehicle becomes impossible to operate. To overcome those defects, countermeasures have been proposed in which a sub power transmitting path is provided in addition to the power transmitting path with the V belt so that either one of them selectively transmits its output power through a hydraulic clutch or the like to the wheels in compliance with the drive ratio. A transmission of the generic type is disclosed in EP-A-0004487. The above proposed construction, however, still has the following problems. First switching the paths is accompanied by shock. Secondly two clutches are required at least to switch respective output from each power transmitting path so that the construction becomes large size with great weight and high production cost, and controlling of the system tends to be complicated. Thirdly condition of sliding malfunction or sticking of V belt is apt to be irregular so that appreciating the condition is difficult and effective recovery action is not performed. Furthermore, in a V belt type continuously variable transmission of this kind, as shown in FIG.16, one input half pulley B of a pair of input half pulleys B, C mounted on a input pulley shaft A is made to move axially along the input pulley shaft and the position of the input half pulley B is controlled by a half pulley position control D operated through an actuator not shown. The half pulley position control D contains an outer slider E to be rotatably operated by the actuator and an inner slider F to be engaged through screw with the outer slider E which supports the rear end of the input movable half pulley B. Consequently, when the outer slider E moves toward and away along the input pulley shaft through the actuator, the input movable half pulley B is moved to be controlled in its position. In such conventional V belt type continuously variable transmission, however, the axial load due to the V belt H during operation is directly added to the power transmitting members of the actuator such as a bearing G, an outer slider E, so that those members, for instance the bearing G, are damaged or great operating power is necessary for the actuator. According to the present invention there is provided a V-belt type continuously variable transmission, comprising: main power transmission path means having a V-belt frictionally engaged between an inlet pulley, composed of a pair of relatively axially movable half pulleys provided on an input pulley shaft, and an output pulley, composed of a pair of relatively axially movable half pulleys provided on an output pulley shaft, the V-belt being arranged to transmit rotation of the input pulley shaft to the output pulley shaft through a main power transmission path, and the rotational speed of the output pulley shaft relative to the input pulley shaft (18) being continuously variable by adjusting the relative positions of the half pulleys of each pair of half pulleys; and sub power transmission path means for the transmission of rotation of the input pulley shaft to the output pulley shaft through a sub power transmission path separate from the main power transmission path; characterised in that a two-way differential clutch is provided in the sub power transmission path and is arranged to transmit power through the sub power transmission path when the drive ratio of the main power transmission path is high, to cause the output pulley shaft to be driven through both the main and sub power transmission paths. In the hereinafter-described embodiment of the present invention, the ability of the output pulley shaft to be driven through both the main and sub power transmission paths provides for an increase in driving power and accelerating force, as well as a decrease in the loading applied to the V-belt. By co-operatively transmitting power to the output pulley shaft through both paths at the range near the maximum drive ratio, sufficient driving power and accelerating force can be delivered during low speed operation when large torque is required. A provision of the hereinafter-described embodiment of the present invention with a two-way differential clutch provides for a simple transmission construction and a weight saving, due to the decrease in the number of clutches required relative to prior art transmissions. In the hereinafter-described preferred embodiment of transmission, a half pulley position control is provided, operable by an actuator, to control the position of the movable input half pulley. The half pulley control includes a spring biasing the movable input pulley in a direction opposite to the axial force applied to it by the V-belt. This allows for the net axial force to be reduced, improving the life of the actuator, decreasing the actuator driving torque and allowing for smooth shifting of the drive ratio. An embodiment of the transmission in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG.1 is a diagrammatic illustration of an embodiment of a V belt type continuously variable transmission in accordance with the present invention. FIG.2 is an enlarged side elevation view, partly in half cross section, of a movable half pulley position control of the input pulley shown in FIG.1 FIG.3 is a sectional view taken along line III-III in FIG.2. FIG.4 is a side sectional view of a 2-way differential clutch shown in FIG.1. FIG.5 is a sectional view taken along line V-V in FIG.4. FIG.6 is an enlarged sectional view of the relevant parts shown in FIG.5. FIG.7 is an enlarged sectional view similar to that of FIG.6 in the different operational condition. FIG.8 is a flow chart of controlling by the drive ratio control. FIG.9 to FIG.14 are characteristic diagrams in respective results of controlled position of the movable input half pulley in several shift conditions in relation to load parameters on the main and sub power transmitting paths. FIG.15 is a characteristic diagram in the relation between axial forces of the movable input half pulley vs. drive ratios of the V belt type continuously variable transmission shown in FIG.2 and 3 compared to those of the prior art. FIG.16 is a side elevation view, partly in half cross section, of relevant parts of a conventional V belt type continuously variable transmission. Referring to FIG.1, there is shown a V belt type continuously variable transmission in which the output shaft 10 of a prime mover E,such as an internal combustion engine, is coaxially connected to a main drive shaft 14 through a clutch 12. The end of the main drive shaft 14 is also coaxially connected to a input pulley shaft 18 through a bearing 16. Parallel to the main drive shaft 14 and the input pulley shaft 18 there is arranged a shaft 22 of a synchro-coupling 20 for switching forward and backward movement, and a counter driven gear 24 secured to the shaft 22 engages a main drive gear 26 secured to the main drive shaft 14. Moreover the shaft 22 of the synchro-coupling 20 is slidably provided with a forward counter gear 28 and a backward counter gear 30 for the rotation of the shaft 22 to be transmitted while switching to forward or backward movement. The forward counter gear 28 engages No.1 pulley shaft gear 32 secured to the end of the input pulley shaft 18, while the backward counter gear 30 engages an idler gear 36 which engages No.2 pulley shaft gear 34 secured to the midway of the input pulley shaft 18. The rest part of the input pulley shaft 18 is provided with a stationary input half pulley 38 secured thereto, a movable input half pulley 40 slidably inserted thereon, and a half pulley position control 42 to control the position of the movable input half pulley 40 in the axial direction. Parallel to the input pulley shaft 18 there is arranged a output pulley shaft 44, which is provided with a stationary output half pulley 46 secured thereto and a movable output half pulley 48 mounted thereon to move in the axial direction. The stationally input half pulley 38 and movable input half pulley 40 have respective opposite conical surfaces to form a V-shaped groove 50 therebetween to thereby constitute a input pulley 52. Also the stationally output half pulley 46 and movable output half pulley 48 have respective opposite conical surfaces to form a V-shaped groove 56 therebetween to thereby constitute a output pulley 58. The input pulley 52 and output pulley 58 are frictionally engaged through respective V-shaped grooves 50 and 56 by a V belt 60, which causes continuously to vary the drive ratio of the rotations between the input pulley shaft 18 and output pulley shaft 44 when the half pulley position control 42 governs the position of the movable input half pulley 40 to vary the width of the V-shaped groove 50. Referring now to FIG.2 and 3 there is shown the construction of the half pulley position control 42. In FIG.2, the end of input pulley shaft 18 is provided with a bearing 62, which supports an inner slider 66 integrally having cylindrical portion 66a with male screw. The inner slider 66 is fixed with pins 70 to a case 68, partly shown in FIG.2, covering the front area of the movable input half pulley 40, the case 68 which is mounted on a stationary part not shown. The cylindrical portion 66a with male screw extends axially along the input pulley shaft 18 with appropriate clearance to engage cylindrical portion 72a with female screw of the outer slider 72 which is rotated clockwise or counterclockwise by an actuator not shown. The front side portion of the movable input half pulley 40 is integrally formed with a cylindrical portion 40a, which is connected to the cylindrical portion 72a with female screw of the outer slider 72 through a bearing 74 relatively to rotate and axially to move together. The input pulley shaft 18 is provided with an annular roller holder 76 with a C ring 78 within the cylindrical portion 40a of the movable input half pulley 40. On the radially outer end of the roller holder 76 there is formed a lug 76a, which projects into a groove between a pair of projected stripes 80, 80 (refer to FIG.3) axially formed on the inner surface of the cylindrical portion 40a. Moreover the lug 76a is provided with a roller bearing 82 being in slidable contact with opposite inner surfaces of the stripes 80, 80 to make up a guide for the movable input half pulley 40 in the axial direction. Within the cylindrical portion 40a of the movable input half pulley 40 there is inserted a compression coil spring 84 between the inner surface of a conical portion 40b and the roller holder 76 so that the movable input half pulley 40 is forced to the stationary 38 by the compression coil spring 84. In the half pulley position control 42 described above the movable input half pulley 40 guided through the projected stripes 80, 80 and the lug 76a of the roller holder 76 axially moves toward the stationary input half pulley 38 to reduce the width of the V-shaped groove 50 as the outer slider 72 is rotated in one direction by the actuator, or the movable input half pulley 40 moves away from the stationary input half pulley 38 to spread the width of the V-shaped groove 50 as the slider 72 is rotated in the other direction. Moreover the movable input half pulley 40 is capable of rotating together with the input pulley shaft 18 because of engagement of the projected stripes 80, 80 and the lug 76a. In addition, the movable input half pulley 40 is always loaded in the axial forward direction or the direction in which V-shaped groove 50 is widened while the V belt 60 transmits the rotation to the output pulley 58, and as the result the loading force acts on the supporting portion of the outer slider 72 at the front end of the cylindrical portion 40a. In the half pulley position control 42, however, such loading force is canceled by the force of the compression coil spring 84 so that the loads to the outer slider 72 and also to the bearing 74 are reduced. Besides, the vibration of the movable input half pulley 40 mounted on the rotating shaft 18 is absorbed by the compression coil spring 84 so that noise during the operation is reduced. Referring to FIG.15, there is shown a characteristic diagram in the relation between axial forces (kg) of the movable input half pulley 40 vs. drive ratios of the V belt type continuously variable transmission compared to those of the prior art. In the drawing the curve A shows the characteristic of this embodiment and the curve B shows that of the prior art. In this case the change of the load by the compression coil spring 84 is shown with the curve C in the drawing. It will be appreciated that the significant effect of axial force reduction is obtained in this embodiment comparing to the prior art. Referring to FIG.1 again, there is shown a countershaft 86 disposed between the input pulley shaft 18 and the output pulley shaft 44, the countershaft 86 which is provided with a 2-way differential clutch 88. Referring now more particularly to FIG.4 to 7 in detail, the countershaft 86 has several stepped forms on the peripheral surface. On a stepped part of the countershaft 86 there is slidably mounted an input gear 90 through spline 90a. Teeth 90b are formed on the peripheral of the input gear 90 and engages a No.1 pulley shaft gear 32 of the input pulley shaft 18. Another stepped part of the peripheral of the countershaft 86 is provided with a polygonal cam 92 parallel to the input gear 90. An output gear 94 is inserted on the peripheral of the polygonal cam 92 with clearance 93. Teeth 94a are formed on the peripheral of the output gear 94 and engages a driven gear 96 of the output pulley shaft 44. Referring to FIG.6 of enlarged sectional view of the relevant parts, a pair of rollers 102, 102′ are disposed on the surrounding surface 98, 98′, 100, 100′ of double-wedge-shaped clearance 93 (hereinafter referred to as double-wedge-shaped surface) which is formed between the inner cylindrical surface 98 of the output gear 94 and the polygonal cam-shaped surface of the countershaft 86. A pair of the rollers 102, 102′ are respectively accommodated in a pocket 104a of a retainer 104, and a spring 106 is disposed between the rollers 102, 102′ and urges respective rollers 102, 102′ toward the opposite walls of the pocket 104a. It will be noted that the rollers 102, 102′ in the neutral condition shown in FIG.6 do not contact to any of the wedge-shaped surfaces 100, 100′. Referring to FIG.4, a sub gear 108 is inserted between the input gear 90 and the output gear 94. Teeth 108a are formed on the peripheral of the sub gear 108 and engages the No.1 pulley shaft gear 32 similarly to the input gear 90. Within the inner peripheral of the sub gear 108 the retainer 104 is slidably inserted on the peripheral of the countershaft 86. The retainer 104 and the sub gear 108 are forced to contact to each other by a disc spring 110 between an end surface of the sub gear 108 and a side surface of the input gear 90. A recess 112 is formed in a part of the inner peripheral of the retainer 104 while a stopper 86a is projected on a peripheral of the countershaft 86 in the position facing the recess 112. The countershaft 86 is supported by bearings 116 to 118. In the 2-way differential clutch 88 described above, the rotation of the input pulley shaft 18 is transmitted to the input gear 90 and the sub gear 108 respectively engaging No.1 pulley shaft gear 32. The number of teeth 90b of the input gear 90 is set to be smaller than that of teeth 108a of the sub gear 108, the numbers of tooth 90b are 53 while those of tooth 108a are 54 for instance, so that the rotation of the sub gear 108 delays as compared with that of the input gear 90. Consequently, as seen in FIG.7, the retainer 104 pressed to contact with the sub gear 108 has a differential speed against the rotation of the countershaft 86 so that it relatively rotates in the right direction until the left side surface of the recess 112 contacts with the stopper 86a. Then the right side roller 102' of a pair of rollers 102, 102' accommodated in the pocket 104a of the retainer 104 is urged to contact with the wedge-shaped surface 100', 98' by the force of the spring 106. In such condition, when the rotational speed of the output gear 94 is faster than that of the input gear 90, the roller 102′ slips and does not stick to the wedge-shaped surface 100′, 98′. It will be appreciated that the roller 102 does not stick to the wedge-shaped surface 100, 98 since it does not contact with the surface. On the contrary, when the rotational speed of the output gear 94 is slower than that of the input gear 90, the rotational speed of the polygonal cam 92 becomes faster than that of the output gear 94, and then the roller 102′ sticks to the wedge-shaped surface 100′, 98′ to thereby cause to transmit the rotation of the countershaft 86 to the output gear 94. In this case, after the stopper 86a has contacted with the wall surface of the recess 112, the retainer 104 slips relatively to the sub gear 108 and as a result the sub gear 108 does not be damaged. Such wedge effect of the rollers 102, 102′ due to the differential speed of the sub gear 102 is regardless of the rotational direction of the input gear 90. Referring to FIG.1 again, a differential pinion 120 is secured to the output pulley shaft 44 to engage an idler gear 122, which in turn engages a differential gear 126 of a differential gear case 124. A computer 128 composed of microprocessors is input with signals from an input pulley rotational speed sensor 130 detecting the rotational speed of the input pulley 52, an output pulley rotational speed sensor 132 detecting the rotational speed of the output pulley 58, an half pulley position sensor 34 detecting the position of the movable input half pulley 40 of the input pulley 52, and a shift position sensor, not shown, of the selector 136. The computer 128, depending upon those signals, controls an actuator of the outer slider 72, the actuator which moves the input pulley 52 to control it toward a position appropriate to engine operational conditions. In the V belt type continuously variable transmission of this invention, after the output power from the prime mover E has been transmitted to the input pulley shaft 18 through the clutch 10 and the synchro-coupling 20, two paths is operable to transmit the output power from the input pulley shaft 18 to the output pulley shaft 58. That is, two paths are a main power transmitting path through a V belt engaged between the input pulley 52 and the output pulley 58 and a sub power transmitting path through the 2-way differential clutch 88. The drive ratio of the sub power transmitting path is set in a slightly smaller value than the maximum drive ratio of the main power transmitting path. Consequently, when the movable input half pulley 40 of the output pulley 50 has been moved near the position of the maximum drive ratio in the main power transmitting path, the rotational speed of the output gear 94 in the 2-way differential clutch 88 become slower than that of the input gear 90, and as a result a rotational force is given to the output gear 94 so that the output pulley shaft 44 is rotated through the sub power transmitting path in addition to the main power transmitting path. Similarly according to such construction, when the selector is manipulated such as D-N-R or R-N-D, the 2-way differential clutch 88 is capable of smoothly switching the transmitting rotational direction by idling and power transmitting. Referring to FIG.8, there is shown a flow chart of controlling the position of the input pulley 52 through the actuator by the computer 128, wherein; ia: drive ratio through the main power transmitting path VSPD: rotational speed of the output pulley shaft 58 TVO: throttle valve open position of the carburetor FLG RNG: condition flag due to range, vehicle speed FLG R: flag of R or not FLG RS: selective flag during R I₁ : Lowmax I₁₅: vehicle speed reference (I₁₅ > I₁₈) I₁₆: target ratio correction I₁₈: vehicle speed reference Firstly, evaluate shift position in Step a. When shift position is D, N, then go to Step b, and when R, go to Step c. Evaluate condition flag FLG RNG due to range and vehicle speed in Step b. When flag is Ø, go to Step d. When flag is 1, then go to Step e. And when flag is 2, then go to Step f. Evaluate FLG R = Ø in Step d. When YES, go to Step e, and when NO, go to Step f. Evaluate VSDP ≦ I₁₅ in Step f. When YES, go to Step g, where put FLG RNG ← 2, and go to Step h, where put ia ← I₁+ I₁₆. When NO, go to Step i, where put FLG RNG ← Ø, FLG R ← 1, and FLG RS ← Ø. Then go to Step j, where get ia which is determined from VSPD and TVO according to normal control. Evaluate VSPD ≦ I₁₈ in Step e. When YES, go to Step k, where put FLG R ← 1 and go to Step g. When NO, go to Step 1, where put FLG RNG ← 1 and go to Step h. And put FLG RNG ← Ø and FLG R ← Ø in Step c. Then go to Step m, where evaluate VSPD > I₁₅. When YES, go to Step n, where put FLG RS ← Ø. Then go to Step o, where put ia ← I₁. When NO, go to Step p, where put FLG RS ← 1 and go to Step h. Referring to FIG.9 to FIG.14, there are shown respective results of controlled position of the movable input half pulley in several shift conditions in relation to load parameters on the main and sub power transmitting paths. The V belt type continuously variable transmission according to the present invention is sufficiently operative in the following particular cases during the operation. That is, for instance, if the V belt 60 is cut away, the output power is capable of being transmitted to the output pulley shaft 44 through the 2-way differential clutch 88 in the sub power transmitting path. Similarly, if V belt 60 is stuck into the output pulley 58 due to sudden stop of the vehicle, the stick of V belt 60 can be recovered and smooth restart of the engine is accomplished because even if the drive ratio is in high speed side when the restarting, it can be varied to the low speed side or the maximum drive ratio, and simultaneously the rotation is transmitted to the output pulley shaft 44 through the 2-way differential clutch 88 in the sub power transmitting path.

Claims: A V-belt type continuously variable transmission, comprising: main power transmission path means (52, 60, 58) having a V-belt (60) frictionally engaged between an inlet pulley (52), composed of a pair of relatively axially movable half pulleys (38, 40) provided on an input pulley shaft (18), and an output pulley (58), composed of a pair of relatively axially movable half pulleys (46, 48) provided on an output pulley shaft (44), the V-belt (60) being arranged to transmit rotation of the input pulley shaft to the output pulley shaft through a main power transmission path, and the rotational speed of the output pulley shaft (44) relative to the input pulley shaft (18) being continuously variable by adjusting the relative positions of the half pulleys of each pair of half pulleys; and sub power transmission path means (32, 88, 96) for the transmission of rotation of the input pulley shaft (18) to the output pulley shaft (44) through a sub power transmission path separate from the main power transmission path; characterised in that a two-way differential clutch (88) is provided in the sub power transmission path and is arranged to transmit power through the sub power transmission path when the drive ratio of the main power transmission path is high, to cause the output pulley shaft (44) to be driven through both the main and sub power transmission paths. A transmission as claimed in claim 1, wherein the two-way differential clutch (88) is mounted on a countershaft (86) provided between the input pulley shaft (18) and the output pulley shaft (44). A transmission as claimed in claim 1 or claim 2, wherein the drive ratio of the sub power transmission path has a value near to a maximum value of the drive ratio of the main power transmission path. A transmission as claimed in claim 3, wherein the drive ratio value of the sub power transmission path is slightly smaller than the maximum value of the drive ratio of the main power transmission path. A transmission as claimed in any of the preceding claims, further comprising a sensor (130, 132) detecting the drive ratio of the main power transmission path, a sensor (134) detecting the relative axial positions of the input half pulleys (38, 40), a sensor detecting the shift position of a gear selector (136), an actuator (72) moving the movable input half pulley (40) and a control unit (128) operating the actuator (72) in accordance with signals received from said sensors. A transmission as claimed in any of claims 1-4, further comprising half pulley position control (42), operable by an actuator to control the position of the movable input half pulley (40), the half pulley position control (42) including a spring (84) biasing said movable input half pulley (40) in a direction opposite to an axial force applied to it by the V-belt (60).

Inventors: MORISHITA AKIYOSHI, TAKAYAMA MITSUNAO, YAMAUCHI KOZO, YASUE TSUTOMU, MORISHITA, AKIYOSHI AICHI KIKAI KOGYO K.K., TAKAYAMA, MITSUNAO AICHI KIKAI KOGYO K.K., YAMAUCHI, KOZO AICHI KIKAI KOGYO K.K., YASUE, TSUTOMU AICHI KIKAI KOGYO K.K.
Applicants: AICHI MACHINE IND, AICHI KIKAI KOGYO KABUSHIKI KAISHA
Application year: 1989
Main classification: F16H37
IPC codes: F16H61, F16H59, F16H63, F16H37, F16H9