A CONTINUOUSLY VARIABLE SPEED-SHIFTING DEVICE

Abstract: In a speed-shifting device (24) of a variable speed pulley (3, 8) type, a transmission raito is changed by an inversely synchronized operation between each movable sideplate (6, 11) of the driving (3) and driven (8) pulleys. The tension to a belt (13) is given by a bias mechanism (25) biasing its slack part (13A). In addition, the bias mechanism (25) can be arranged to be movable for decreasing the tension of the belt member (13) to serve as a clutch mechanism interrupting the power transmission between both pulleys (3, 8).

Description: 2. Technical Field to which the invention belongs This invention relates to an important of a speed-­ shifting device including variable speed pulleys to change a transmission ratio of a pair of transmission shafts by varying the effective radius of the pulleys to a belt member. 3. Related Background Art In agricultural implements and the like conventionally used were many belt transmission type speed-­ shifting device utilizing a belt drive for transmitting the power of an engine to a driven wheel or an operating device changing speed. As a belt transmission type speed-­ shifting device utilizing belt drive, a variable speed type one is well known, for example, comprising a pair of transmission shafts placed parallelly, variable speed pulleys composed of fixed sideplates solidly rotatably and axially non-slidably mounted to each transmission shaft and movable sideplates solidly rotatably and axially slidably mounted on each transmission shaft forming a V-­ shaped groove with the fired sideplates facing thereto, and a belt member trained to the V-shaped grooves between both sideplates, wherein a transmission ratio between both transmission shafts is adjusted by changing an effective radius of the pulleys with a belt member with moving axially the movable sideplates of each variable pulley to and from the fixed sideplates. In such a speed-shifting device of variable speed pulley type, generally, a variable speed pulley on one of the transmission shafts is a driving pulley axially moved by a driving mechanism utilizing, for example, hydraulic equipment or a cam mechanism to change an effective radius of the driving pulley, and a variable speed pulley on the other transmission shaft is a driven pulley, the effective radius thereof being adjusted in dependence on a movement of the bolt member by a change of the effective radius of the driving pulley under a bias of a spring urging the movable sideplate to the fixed sideplate. However, there occurs various problems as described below resulting from the high bias to the movable sideplate in the driven pulley. Namely: (1) Since a tension of the belt member trained to both pulleys is substantially given by the spring adapted to urge the movable sideplate of the driven pulley to the fixed sideplate, it is required to increase the bias of the movable sideplate by increasing the force of the spring in order to ensure the power delivery between both transmission shafts. Though, since a cost of the high force spring is high, there is the problem of an increase of the total cost. In addition to the problem, when assembling a speed-shifting device, setting the spring thereinto is not promptly done. (2) Also, since the speed shifting process is such that when the effective radius of said driving pulley is changed by a movement of the movable sideplate the belt member moves in accordance therewith resulting that the change of the effective radius between the driven pulley is varied and the transmission ratio between both transmission shafts varies thereafter, a certain period of time is required for shifting the speed. Particularly, when the transmission ratio is shifted from low speed mode to high speed mode, high handling force is required to move the movable sideplate of the driven pulley from the fixed sideplate against the bias of the spring. In the result, it is hard to shift the transmission ratio between both transmissions shafts quickly and smoothly with slight handling force. (3) Moreover, as shown in Fig.9, when the driving mode changes from the unload mode in which a driving power is not transmitted between both transmissions shafts(a) and (b) into the load mode in which a certain driving power is transmitted, a patch line of the belt member(c) located at the position shown as a full line in this figure in the unload mode of the driven pulley(d) moves to the middle position thereof shown as a virtual line by an inner thrust of the belt member(c). Neverthelss, in the driven pulley(e) its movable sideplate(el) is urged by the spring. Therefore, its pitch line moves to outside radially attended with an elongation of whole belt member(c) and decrease of the effective radius by the inner thrust of the belt member(c) in said driving pulley(d) , resulting in a certain decrease of rotational speed at the output transmission shaft(b). In order to solve abovementioned problem totally, the objects of this invention is to reduce the force of the spring for giving a tension to the belt member, to smooth the speed shifting operation with slight handling force, and to prevent decrease of rotational speed of the driven shaft by the elongation of the belt member during the shifting process of the driving mode from unload to load, by providing a means for moving synchronously the movable sideplates of both pulleys and by giving the tension of the belt member by other means except the bias of the movable sideplate to the fixed sideplate of the driven pulley. 4. Summary of the Invention In order to attain these objects, the speed-shifting device of this invention is provided with a mechanism for moving axially the movable sideplates of both pulleys inversely to and from the fixed sideplates facing thereto, and a means for giving the tension to the belt member trained to both pulleys by biasing a slack part thereof. Concretely, as abovementioned, this invention is based on the speed-shifting device comprising a pair of transmission shafts placed parallelly, a driving pulley and a driven pulley each of which is composed of fixed sideplates solidly rotatably and axially non-slidably mounted on each of said transmission shafts and movable sideplate axially slidably and solidly rotatably mounted on each of tranmission shafts forming V-shaped grooves with the fixed sideplates, and a belt member trained between both said pulleys engaging both the V-shaped grooves thereof, arranged so that a transmission ratio between both transmission shafts can be changed by varying an effective radius of the engagement of each pulley with the belt member by moving each movable sideplate axially to and from a fixed sideplate facing thereto. In the speed-shifting device, a speed-shifting mechanism is provided to change the transmission ratio between both transmission shafts by operating each movable sideplate of both pulleys so as to move the movable sideplate from the fixed sideplate on one transmission shaft when the movable sideplate on another transmission shaft is moved to the fixed sideplate. Also, a bias mechanism is provided between both pulleys, adapted for biasing a slack part of the belt member to increase a tension thereof. As a preferable concrete example, abovementioned speed-shifting mechanism comprises a cam mechanism adapted to move axially the movable sideplate of the driving pulley to and from the fixed sideplate, a cam mechanism adapted to move axially the movable sideplate of the driven pulley to and from the fixed sideplate, and connecting mechanism including wires, linkages or the like for connecting both cam mechanisms, arranged so that when the movable sideplate of one pulley moves axially to the fixed sideplate the movable sideplate of the other pulley simultaneously moves axially from the fixed sideplate. Also, in this case, each cam mechanism is composed of a driving cam and a driven cam contacted therewith, and more preferably a cam roller is replaced for one of the driving cam or the driven cam in order to reduce the handling force by the decrease of the frictional resistance while shifting the speed. On the other hand, concretely, abovementioned bias mechanism comprises a tension roller put contactably on a slack part of the belt member and a spring adapted for biasing said tension roller to the belt member, wherein the outer or inner circumferential surface in a slack part of the belt member may be selected to be urged. The bias mechanism is preferably put in nearly middle position of the place between both pulleys where the movement of the belt member is the least in a moving range thereof depending on the shift of a transmission ratio between both transmission shafts, so that an appropriate tension to the belt member is always given during shifting speed. Also, the bias mechanism may be put at the position offsetted to the one side between both transmision shafts. For example, the bias mechanism is put at the position offsetted to the transmission shaft which is applied to the driving pulley in order to increase the tension given to the belt member in the low speed mode and to decrease at the high speed mode. On the contrary, the bias mechanism is put in the position offsetted to the transmission shaft which is applied to the driven trolley in order to increase the tension given to the belt member in the high speed mode and to decrease in the low speed mode. When the condition using the speed-shifting device or the transmission ratio of high frequency is changed, the bias mechanism is arranged for adjusting quickly in accordance with the change of the condition or the like by moving the bias mechanism to the optimum position for the change. Further, abovementioned bias mechanism is arranged to be movable to reduce the tension of the belt member and served as a clutch mechanism for interrupting the power transmission between both transmission shafts with the tension reduction of the belt member in order to interrupt the power transmission between both transmission shafts in any transmission ratio and to re-transmit the power with the exact transmission ratio when interrupted. As a concrete arrangement, for example, the bias mechanism is provided with a turn arm and a tension roller mounted at the end thereof contactably to the slack part of the belt member and arranged movably by turning the turn arm. 5. Brief Description of the Drawings The drawings show the embodiments of this invention, wherein Fig. 1 is an elevation partly in section of a speed-­ shifting device in the high speed mode. Fig.2 is an elavation partly in section of the speed-shifting device in the low speed mode. Fig.3 is a cross-sectional view from III - III line in Fig.1. Fig.4 is a schematic sectional view showing a movement of a pitch line of the belt member while the driving mode changes from unload to load. Fig.5 is a schematic sectional view showing several examples of the urging position of the bias mechanism. Fig.6 is a schematic sectional view showing the embodiment having a bias mechanism mounted inside of the pitch line. Fig.7 is a schematic sectional view showing the embodiment where a bias mechanism is also served as a clutch mechanism. Fig.8 is an elevation partly in section showing another embodiment of a speed-shifting device. Fig.9 is a schematic sectional view showing the movement of a pitch line in a conventional device. 6. Description of Special Embodiment Embodiments as the best mode for carrying out this invention are described below, with reference to the drawings. Fig.1 and Fig.2 show whole arrangements of a pulley type speed-shifting device (A) for the embodiments of this invention, wherein 1 is an input shaft as a transmission shaft and 2 is an output shaft as the other transmission shaft as well. These input and output shafts 1 and 2 are placed parallelly. A driving pulley 3 is mounted on said input shaft 1. This driving pulley 3 is composed of a flange shaped fixed sideplate 5 solidly rotatably and axially non-slidably mounted on the input shaft 1 with a screw 4 and a flange shaped movable sideplate 6 axially slidably and solidly rotatably mounted with a spline on the input shaft 1 at a boss part 6a so as to face to said fixed sideplate 5. A V-shaped belt groove 7 is formed between both sideplates 5 and 6. On the other part, a driven pulley 8 is mounted on the output shaft 2. This driven pulley 8 is arranged to be same as the driving pulley 3, being composed of a flange shaped fixed sideplate 10 solidly rotatably and axially non-slidably mounted on the output shaft 2 with a screw 9 and a flange shaped movable sideplate 11 axially slidably and solidly rotatably mounted with a spline on the output shaft 2 at a boss part 11a so as to face to the fixed sideplate 10 in inverse direction with the movable sideplate 6 to the fixed sideplate 5 at the driving pulley 3 on the input shaft 1. A V-shaped groove 12 is also formed between both these sideplates 10 and 11. A V-belt 13 as a belt member is trained between both pulleys 7 and 8 engaging the two V-shaped grooves 7 and 12 thereof. An effective radius of the engagement of each pulley 3 and 8 with the V-belt 13 is adjusted by moving axially each movable sideplate 6 and 11 of both pulleys 3 and 8 to and from the fixed sideplates 5 and 10. When the movable sideplate 6 of the driving pulley 3 is moved to the fixed sideplate 5 and the movable sideplate 11 of the driven pulley 8 is moved from the fixed sideplate 10, the effective radius of the driving pulley 3 is increased and the effective radius of the driven pulley 8 is decreased. As a result, the transmission ratio of the input shaft 1 to output shaft 2 is increased. On the contrary, when the movable sideplate 6 of the driving pulley 3 is moved from the fixed sideplate 5 and the movable sideplate 11 of the driven pulley 8 is moved to the fixed sideplate 10, the effective radius of the driving pulley 3 is decreased and the effective radius of the driven pulley 8 is increased. As a result, the transmission ratio of the input shaft 1 to output shaft 2 is decreased. On the input shaft 1 and the output shaft 2 Cam mechanisms 14 and 15, are also mounted coaxially to both pulleys 3 and 8, adapted to move axially each movable sideplate 6 and 11 to and from each fixed sideplate 5 and 10. Since each cam mechanism 14 and 15 is samely arranged, only arrangement with the cam mechanism 14 of the input shaft 1 is explained below, and an explanation about the cam mechanism 15 is omitted with the same reference numerals. Namely, the cam mechanism 14 comprises a cylindrical driven cam 17 solidly rotatably and axially non-slidably mounted on an outer race of a ball bearing 16 whose inner race is mounted on a boss part 6a of the movable sideplate 6. On the input shaft 1, having an opposite arrangement to the fixed sideplate 5 with the movable sideplate 6, a cylindrical sleeve 18 is mounted solidly rotatably and axially non-slidably with a screw 19. A cylindrical driving cam 20 is mounted rotatably and axially non-slidably on an outer race of a ball bearing 21 whose inner race is mounted on said sleeve 18. Abovementioned driving and driven cams 20 and 17 are provided with cam parts 21a and 17a projecting to each other. These cam parts 20a and 17a are formed nearly same as devided by oblique sections when a cylinder is cut diagonally. At the ends of each cam part 20a and 17a inclined cam faces 20b and 17b are formed contacting in cam engagement with each other, and is arranged so that with turn of the driving cam 20 around the input shaft 1 the driven cam 17 is moved with the movable sideplate 6 of the driving pulley 3 to the fixed sideplate 5 axially to the input shaft 1 increasing the effective radius of the driving pulley 3 with the V-belt. In each cam mechanism 14 and 15 both driving cams 20 and 20 are connected with a shift lever 23 by a connecting mechanism 22 including linkages, wires or the like to rotate them in accordance with the shifting lever 23. Namely, a speed-shifting mechanism 24 is so arranged as to vary the transmission ratio between the shifts 1 and 2 by operating each movable sideplate 6 and 11 of both pulleys 3 and 8 in the manner when the movable sideplates 6 (or 11) is moved to the confronting fixed sideplate 5 (or 10), the other movable sideplate 11 (or 6) is moved from the fixed sideplate 10 (or 5). Moreover, between both pulleys 3 and 8 provided is a bias mechanism 25 addapted to bias a slack part 13a of the V-belt 13 (the part moving from driving pulley to the driven pulley) from its outside for increasing the tension of the V-belt 13. This bias mechanism 25, as shown in Fig. 3, comprises a cylindrical tension roller 26 placed contactably on the V-belt at the outer circumferential surface (back side) in the slack part 13a. a supporting shaft 27 placed parallelly with the shafts 1 and 2 axially rotatably supporting the tension roller 26, a pair of rods 28 and 28 (only one of them is shown) solidly mounted to both ends of the supporting shaft 27 movably supporting the tension roller 26 to a direction crossing at nearly right angle to the face through the shafts 1 and 2 to a retaining member 30, and springs 29 mounted on each rod 28 being compressed between the spring holders 28a and said retaining member 30 biasing the roller 26 and the supporting shaft 27 to the direction in which the tension of the V-belt 13 is increased. Namely, the bias mechanism 25 is arranged so that the tension is given to the V-belt 13 by urging the tension roller 26 to the outer circumferential surface of the V-belt 13 with the force of each spring 29. Abovementioned tension roller 26 is formed axially long enough to keep contact with the outer circumferential surface of the V-belt 13 which fluctuates parallelly with shafts 1 and 2. An operation of abovementioned speed-shifting device is explained below. The movable sideplates 6 and 11 of both pulleys 3 and 8 and the sleeves 18 and 18 are rotated solidly with both shafts 1 and 2. Each driven cam 17 on the boss parts 6a and 11a of the movable sideplates 6 and 11 and the driving cams 20 on the sleeves 18 is suspended without rotating with the both shafts 1 and 2. For example, when the transmission ratio of the input shaft 1 to the output shaft 2 is increased to change into the high speed mode from this state, the position of the shifting lever 23 in the speed-shifting mechanism 24 is shifted to the high speed position. Following this shifting operation with the shifting lever 23, as shown in Fig.1 and Fig.3, the driving cam 20 of the cam mechanism 14 on the input shaft 1 is turned around the input shaft 1 in one direction (for example, clockwise). When by this turn of the driving cam 20 the driven cam 17, contacting at the ends of the inclined cam faces 20b and 17b of each cam part 20a and 17a is formed to move from the driving cam 20 (to the left direction in the figure) on the input shaft 1, the movable sideplate 6 of the driving pulley 3 connected solidly movably with this driven cam 17 via the ball bearing 16 is moved in the same direction to approach the fixed sideplate 5. In result, a space at the belt groove 7 of the driving pulley 3 is decreased, resulting in the increase of effective radius thereof with the V-belt 13. Also, inversely synchronized with the movement of the driving pulley 3, the driving cam 20 in the cam mechanism 15 on the output shaft 2 is turned arround the output shaft 2 in one direction (for example, clockwise) by the shifting operation with the shifting lever 23. When by this turn of the driving cam 20 the driven cam 17 is released from the bias and urged by the tension of the V-­ belt to move on the output shaft 2 in the direction to approach the driving cam 20 (to the left direction in the figure), the movable sideplate 11 of the driven pulley 8 is moved in the same direction to remove from the fixed sideplate in accordance with the movement of the driven cam 17, resulting that the effective radius of the driving pulley 3 with the V-belt 13 is decreased. As a whole, the effective radius of the driving pulley 3 with the V-belt 13 is shifted to be larger than that of the driven pulley 8, and rotation of the input shaft 1 is transmitted to the output shaft 2 with increased speed. On the other hand, when the transmission ratio between shafts 1 and 2 is to be lowered to change into the low speed mode, the position of abovementioned shifting lever 23 is shifted to the low speed position. Following the shifting operation with the shifting lever 23, as shown in Fig.2, the driven cam 20 in the cam mechanism 14 on the input shaft 1 is turned arround the input shaft 1 in the other direction (counterclockwise) . When by this turn of the driving cam 20 the driven cam 17 is released from the bias and urged by the tension of the V-belt 13 to move the driven cam 17 on the input shaft 1 in the direction to approach the driving cam 20 (to the right in the figure), the movable sideplate 6 of the driving pulley 3 is moved to the fixed sideplate 5 in the same direction, resulting in the decrease of the effective radius thereof with the V-belt 13 . Also, on the output shaft 2, the driving cam 20 in the cam mechanism 15 is turned around the output shaft 2 in the other direction (counterclockwise). When by this turn of the driving cam 20 the driven cam 17 is urged to remove on the output shaft 2 from the driving cam 20 (to the right direction in the figure), the movable sideplate 11 of the driven pulley 8 is moved in the same direction to approach the fixed sideplate 10, resulting in the increase of the effective radius of the driven pulley 8 with the V-belt 13. As a whole, the effective radius of the driving pulley 3 is shifted to be smaller than that of the driven pulley 8 and rotation of the input shaft 1 is transmitted to the output shaft 2 with decreased speed. Abovementioned outer circumferential surface of the slack part 13a of the V-belt 13 is biased to inside by the tension roller 26 of the bias mechanism 25 put between both pulleys 3 and 8. A predetermined tension is given to the V-belt 13 with the bias of the roller 26. In this case, therefore, since the V-belt 13 is given the tension by urging on the outer circumferential surface of the slack part 13a of the V-belt 13 with the roller 26 of the bias mechanism 25, the force of each spring 29 for giving the tension to the V-belt 13 can be reduced, the cost can be lowered, and it can be easy to set up the springs 29 and total assembly workability can be improved. Furthermore, since the movable sideplates 6 and 11 of both pulleys are mechanically driven to move axially by the speed-shifting mechanism 24, such a high handling force as in the conventional device for moving the movable sideplate 11 against the bias of the spring is not needed when shifting speed. In addition, the action of shifting speed becomes quick because of the syncronous movement of the movable sideplates 6 and 11 of both pulleys 3 and 8, therefore the speed shifting operation between shafts 1 and 2 can be done smoothly with little handling force. For example, in our test result, to transmit the power of 7 HP between both shafts, about 100Kg/f of the bias force (axial force) is required by springs in the case of conventional device, but it only requires about 10 Kg/f in the case of this invention. The force of the spring can be reduced to be about one-tenth as in the formar. Moreover, while the movement from the unload mode in which the power is not transmitted between both shafts 1 and 2 to the load mode in which the power is really transmitted, as shown in Fig.4, at the driving pulley 3 in the conventional device, the pitch line of the V-belt 13 is moved radially inside by the inner thrust of the V-­ belt, arising an elongation of the V-belt 13. However, in this invention, the elongation of the V-belt is prevented by the bias mechanism 25, for the tension to the V-belt 13 is given by the bias mechanism 25. Therefore, since the pitch line in the driven pulley 8 is not moved radially outside as observed in conventional device, decrease of the rotational speed of the output shaft 2 can be suppressed effectively. Furthermore, the position of the bias mechanism 25 placed between both pulleys 3 and 8 can be selected, for example, among three of the first position (P1) to the third position (P3), as shown in Fig.5. The first one (P1) is located in nearly middle position of the space between both pulleys 3 and 8 where the movement of the V-belt 13 is the least in a moving range in dependence with shifting of the tranmission ratio of the input shaft 1 to the output shafts 2. The second position (P2) and the third position (P3) are at each position offsetted to the input shaft 1 or to the output shaft 2 from said first position (P1). When the bias mechanism 25 is placed at the first position (P1), the tension of the V-belt 13 can be always kept nearly constant. In the case placed at the second position (P2), the force for biasing the tension roller 26 to the V-belt 13 is raised to increase the tension of the V-belt when the transmission ratio is shifted into the high mode (a location of the V-belt at that time is shown in full lines), and the bias force to the V- belt is lowered to decrease the tension of the V-belt 13 at the low mode. On the other hand, in the case placed at the third position (P3), a reverse characteristics of a tension variation occurs when placed at the second position (P2). Therefore, when the condition for using the speed-shifting device (A) or the transmission ratio of high frequency is changed, the tension of the V-belt 13 can be quickly adjusted with that by moving the position of the bias mechanism 25 to the optimum one in dependence with its change. Other embodiments in this invention are shown in Fig.6 -Fig.8. In the Fig.6 to Fig.8, detailed explanations about the same portions as equivalent arrangement of abovementioned embodiment are omitted with the same referential numerals. In the embodiment as shown in Fig.6, a bias mechanism 25′ for giving the tension to the V-belt 13 is placed inside of the pitch line. The same effects as in the abovementioned embodiment are obtained with this embodiment. In other embodiment, also as shown in Fig.7, in the arrangement corresponding to the abovementioned embodiment, a bias mechanism 25″ is movably arranged to lower the tension of the V-belt 13 by including a retaining member 30′ for retaining the tension roller 26 to the end of a turn arm 31. As a result, the bias mechanism 25″ is also served as a clutch mechanism to stop the power transmission between both shafts 1 and 2 in correspondence with a lowering of the tension of the V-­ belt 13. In the case of this embodiment, the power transmission between both shafts 1 and 2 can be interrupted by turning of the turn arm 31, in addition to the same working effect as obtained in the abovemintioned embodiment. Further, since interrupted and permit of the power transmission can be done independently on the transmission ratio of the input shaft 1 to the output shaft 2, the interrupt of the power transmission can be done immediately whenever required and the transmission ratio when the interrupt of the power transmission is released can be kept equal to the previous one before interrupted. In consequence, there is an advantage that the previous transmission ratio can be obtained quickly after the clutch mechanism stopped working, which can not be obtained in a clutch mechanism arranged so that the power transmission is interrupted by moving the movable sideplate of the pulley to the remote position from the fixed sideplate. Furthermore, Fig.8 shows an embodiment wherein the arrangement of the cam mechanisms 14 and 15 is altered. Namely, in this embodiment, in each driving cam 20′ of both cam mechanisms 14′ and 15′, one roller follower 20′a which rotates keeping contact with the inclined cam face 17b at the end of the cylindrical cam part 17a in the driven cam 17 is mounted at a predetermined peripheral position replacing the cam part 20a in the abovementioned example. In this arrangement, while changing speed by shifting operation with the shifting lever 23, when the driving cam 20′ is turned, the roller follower 20′a is urged to the cam face 17b, rotating along the inclined cam face 17b formed at the end of the cylindrical cam part 17a in the driven cam 17. As a result, a frictional resistance between the driving cam 20′ and the driven cam 17′ is extremely reduced, so there is an advantage that the handling force for shifting speed can be quite reduced. In addition, in this case, the roller follower 20′a can be replaced by any cam follower, roller bearing, or the like. Also, the roller follower 20′a may be provided in the driven cam 17 instead of the driving cam 20′. Though, in each abovementioned embodiment, the movable sideplates 6 and 11 of pulleys 3 and 8 on shafts 1 and 2 are moved axially by the cam mechanism 14 and 15 composed of the driving cams 20 and the driven cam 17, the movable sideplates 6 and 11 can be moved by other mechanisms, for example, composed of a screw members axially moved by a relative turns of the input shaft 1 and output shaft 2. 7. Industrial Applicability According to a speed-shifting device in this invention, a bias force of a spring for giving a tension to the belt member can be reduced by giving the tension with a bias mechanism put between both pulleys, obtaining a lowering of the costs and improvement of assembling work. Also, shifting speed can be done smoothly with the slight handling force by opening and closing of both grooves in pulleys inversely synchronized with each other. Moreover, there is a superb effect for practical use that decrease of rotational speed of output shaft is prevented by suppressing an elongation of the belt member with a bias mechanism in the primary stage of the load mode. Furthermore, when abovementioned bias mechanism is arranged to be movable to decrease the tension of the belt member and served as a clutch mechanism interrupting the power transmission between both transmission shafts by the decrease of the tension of the belt member, the transmission of the rotation of both transmission shafts can be interrupted and recovering can be done with the exact transmission ratio when interrupted in any transmission ratio.

Claims: 1. In a speed-shifting device having a pair of transmission shafts placed parallelly, a driving pulley and a driven pulley each of which is composed of fixed sideplates solidly rotatably and axially non-slidably mounted to each of said transmission shafts and movable sideplates axially slidably and solidly rotatably mounted on each of transmission shafts forming V-shaped groove with said fixed sideplates, and a belt member trained between said driving pulley and said driven pulley engaging both said V-shaped grooves thereof, arranged so that a transmission ratio between both transmission shafts can be changed by varying an effective radius of the engagement of each said pulley with said belt member by moving each said movable sideplate axially to and from said fixed sideplate facing thereto, the improvement comprising : a speed-shifting mechanism adapted for changing a transmission ratio between both said transmission shafts by operating said each movable sideplate of said driving pulley and said driven pulley so as to move said movable sideplate from said fixed sideplate on one transmission shaft when said movable sideplate on another transmission shaft is moved to said fixed sideplate; and a bias mechanism placed between said driving pulley and said driven pulley, adapted for biasing a slack part of said belt member to increase the tension thereof. 2. The speed-shifting device of Claim 1 wherein the speed-shifting mechanism comprises the first cam mechanism adapted to move axially and movable sideplate of said driving pulley to and from said fixed sideplate, the second cam mechanism adapted to move axially said movable sideplate of said driven pulley to and from said fixed sideplate, and a connecting mechanism connected said first cam mechanism with said second cam mechanism, adapted for synchronizing inversely both said cam mechanisms so that when said movable sideplate of one pulley moves axially to said fixed sideplate the movable sideplate of the other pulley simultaneoiusly moves axially from said fixed sideplate. 3. The speed-shifting device of Claim 2 wherein said connecting mechanism includes wires adapted for connecting said first cam mechanism with said second cam mechanism. 4. The speed-shifting device of Claim 2 wherein said connecting mechanism includes linkages adapted for connecting said first cam mechansim with said second cam mechanism. 5. The speed-shifting device of Claim 2 wherein said cam mechanisms are composed of a driving cam and a driven cam contacted therewith. 6. The speed-shifting device of Claim 2 wherein said cam mechanisms are composed of a cam and a roller follower contacted therewith. 7. The speed-shifting device of Claim 1 wherein said bias mechanism is provided with a tension roller adapted for placement contactably on a slack part of said belt member, and a spring adapted for biasing said tension roller to said belt member. 8. The speed-shifting device of Claim 1 wherein said bias mechanism is adapted for urging the outer circumferential face in the slack part of said belt member. 9. The speed-shifting device of Claim 1 wherein said bias mechanism is adapted for urging the inner circumferential face in the slack part of said belt member. 10. The speed-shifting device of Claim 1 wherein siad bias mechanism is placed in nearly middle position of the place between both said driving pulley and said driven pulley where the movement of said belt member is the least of a moving range thereof depending on the shift of the transmission ratio between both said transmission shafts. 11. The speed-shifting device of Claim 1 wherein said bias mechanism is placed at the position offsetted to one side between both said transmission shafts. 12. The speed-shifting device of Claim 1 wherein said bias mechanism is arranged to bo movable to reduce the tension of said belt member and serves as a clutch mechanism for interrupting the power transmission between both said transmission shafts with the tension reduction of said belt member. 13. The speed-shifting device of Claim 12 wherein said bias mechanism is provided with a turn arm and a tension roller mounted at the end thereof contactably to the slack part of said belt member, arranged to be movable by turning of said turn arm.

Inventors: KUCHISUBO, KATSUSHIRO C/O BANDO CHEMICAL, MIYATA, HIROFUMI C/O BANDO CHEMICAL, SAKAMOTO, CHIKARA C/O BANDO CHEMICAL
Applicants: BANDO CHEMICAL INDUSTRIES, LIMITED
Application year: 1988
Main classification: F16H9
IPC codes: F16H9, F16H61