CONTINUOUSLY VARIABLE TRANSMISSION WITH CONTROL VALVE

Abstract: A control valve (70) has ports (71b, 71c, 71d) and a spool (72) which has lands (91, 92) and an annular groove between the lands (91, 92). The land has a plurality of retracted peripheral portions (93, 94) at a circumferential edge portion (91a, 92a) adjacent to the annular groove (90) so as to gradually increase the opening area of one of the ports. Each retracted peripheral portion (93, 94) is formed by an oblique plane.

Description: The present invention relates to a continuously variable transmission system (CVT). From EP-A 117 264 a continuously variable transmission system according to the pre-characterising clause of claim 1 is known. The transmission ratio control valve operates to upshift and downshift the transmission. The line pressure control valve controls the line pressure in accordance with the transmission ratio of the engine speed. The line pressure is controlled such as to prevent the belt from slipping on pulleys in order to transmit the output of the engine. In the known system, upshifting and downshifting of the transmission may result in a shock or an overshoot which is unpleasant. Moreover, when decreasing the shifting speed it takes a long time for arriving at a desired transmission ratio. From DE-A-2 223 419 a control valve is known. However, the document is silent with respect to up and downshifting of a transmission. The object of the present invention is to provide a continuously variable transmission in which the time-response during up and downshifting of the transmission is improved. According to the present invention, there is provided a continuously variable transmission system as defined in claim 1. The other objects and features of this invention will be apparently understood from the following description with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a schematic illustration of a continuously variable belt-drive transmission; Fig. 2 is a schematic diagram of a transmission ratio control valve; Fig. 3a is a side view of a spool mounted in the transmission ratio control valve of the invention; Fig. 3b is a part of a sectional view of the spool; Fig. 3c is a graph showing an opening area characteristic of a port regulated by the spool; Fig. 4a is a side view showing a part of a second embodiment of the spool of the present invention; Fig. 4b is a graph showing an opening area characteristic of Fig. 4a; Fig. 5a is a part of a sectional view showing a part of a third embodiment of the spool; Fig. 5b is a graph showing an opening area characteristic of Fig. 5a; Fig. 6a is a part of a sectional view showing a fourth embodiment of the spool; Fig. 6b is a perspective view showing a part of the spool of Fig. 6b; and Fig. 6c is a graph showing an opening area characteristic of Fig. 6a. Referring to Fig. 1, a motor vehicle is provided with an engine 1 and an electromagnetic powder clutch 2 for transmitting the power of the engine to a continuously variable belt-drive transmission 4 through a selector mechanism 3. The belt-drive transmission 4 has a main shaft 5 and an output shaft 6 provided in parallel with the main shaft 5. A drive pulley (primary pulley) 7 and a driven pulley (secondary pulley) 8 are mounted on shafts 5 and 6 respectively. A fixed conical disc 7b of the drive pulley 7 is integral with the main shaft 5 and an axially movable conical disc 7a is axially slidably mounted on the main shaft 5. The movable conical disc 7a also slides in a cylinder 9a formed on the main shaft 5 to provide a servo device. A fixed conical disc 8b of the driven pulley 8 is formed on the output shaft 6 opposite to a movable conical disc 8a. The conical disc 8a has a cylindrical portion which is slidably engaged in a cylinder 6a of the output shaft 6 to form a servo device. A drive belt 11 engages with the drive pulley 7 and the driven pulley 8. Secured to the output shaft 6 is a drive gear 12 which engages with an intermediate reduction gear 13 on an intermediate shaft 14. An intermediate gear 15 on the shaft 14 engages with a final gear 16. The rotation of the final gear 16 is transmitted to axles 18 of vehicle driving wheels 19 through a differential 17. A chamber 9 is formed between the axially movable disc 7a and the cylinder 9a of the drive pulley 7. The chamber 9 is supplied with pressurized oil by an oil pump 21 from an oil reservoir 26 passing through a passage 22, a line pressure control valve 40, a transmission ratio control valve 70, and a passage 53. A chamber 10 formed between the movable disc 8a and the cylinder 6a of driven pulley 8 is supplied with pressurized oil through a passage 52 from the line pressure control valve 40. The passage 52 also communicates with the transmission ratio control valve 70. The movable conical disc 7a of the drive pulley 7 is so designed that the pressure receiving area thereof is larger than that of the movable conical disc 8a of the driven pulley 8. Oil flows back to the oil reservoir 26 through drain passages 25 and 55 which are in communication with the valves 40 and 70, respectively. The drive pulley 7 has an annular groove 7c and a rotation speed sensor 28 in the form of a pitot tube is provided for detecting the pressure of the oil in the groove 7c that is the speed of the main shaft 5 which varies dependent on the engine speed. The pitot pressure produced by the rotation speed sensor 28 is applied to one end of both of valves 40 and 70 through a passage 57. As shown in Fig. 2, the transmission ratio control valve 70 comprises a valve body 71, a spool 72, an operating plunger 73, and a spring 74 provided between the spool 72 and the plunger 73. A chamber 71a communicates with a passage 57 to be applied with the pitot pressure. The control valve 70 further comprises an annular groove 71e for a port 71b communicating with the passage 53, an annular groove 71f for a port 71c communicating with the passage 52, and an annular groove 71g for a port 71d communicating with a drain passage 55. An annular groove 90 is formed on the spool 72 so as to communicate the ports 71b and 71c or 71b and 71d for supplying or discharging line pressure to or from the chamber 9 in dependence on the position of the spool 72. A regulator plunger 75 is slidably provided in an axial cavity 72c in the spool 72. A regulator spring 77 is provided between the operating plunger 73 and a retainer 76 securely mounted on a projecting end of the regulator plunger 75. A spring 78 is provided between a flange of the plunger 75 and a retainer 72b of the spool 72. The force of the regulator spring 77 is determined by the projecting extent of the plunger 75 from the spool 72, and the position of the plunger 75 is dependent on the line pressure at the port 71c which is supplied to the inside of the spool 72 through a small aperture 79. The plunger 73 is slidably mounted in the valve body 71 and has an axial cavity 73a. A rod 81 is axially slidably mounted in the valve body 71, and a flange 81b of the rod 81 is slidably engaged with the wall of the cavity 73a. A small spring 82 is provided between the flange 81b and the plunger 73, and the flange 81b engages with a stopper 83 secured to the plunger 73. The cavity 73a is applied with the pitot pressure through a port 84 and a passage 86 having an orifice 85 and communicated with the chamber 71a. A spring 87 is provided between an end of the spool 72 and the valve body 71 to adjust the load on the spring 82. One end of the rod 81 engages with a cam 80 which is operatively connected to an accelerator pedal of the vehicle so as to be rotated in dependence on the depression of the pedal. When the spool 72 is moved by the pitot pressure to communicate the port 71b with the port 71c, the line pressure is applied to the chamber 9 of the drive pulley 7 to upshift the transmission. On the oher hand, when the port 71b communicates with the port 71d, the chamber 9 is drained to downshift the transmission. The transmission ratio is determined by the balance between the pitot pressure and the forces of the springs 74, 77. At a stop of the vehicle, the line pressure is at the highest value, and the plunger 75 is located at a right end position, and the force of the spring 77 becomes zero. When the transmission starts to upshift, the line pressure begins to decrease, thereby increasing the force of the spring 77. As the engine speed rises, the transmission is upshifted. Referring to Figs. 3a and 3b, the spool 72 has a land 91 for the supply port 71c and a land 92 for the drain port 71d. An annular groove 90 is formed between the lands 91 and 92. A circumferential edge portion 91a of land 91 adjacent the groove 90 is obliquely cut away at four positions at an angular interval of 90° to form four oblique planes 93. Thus, partially retracted peripheral portions are formed on the edge 91a. The land 92 also has four oblique planes 94 formed on a circumferential edge portion 92a corresponding to the oblique portions 93. As shown in Fig. 3b, an oblique angle ϑ1 of the oblique plane 93 is set to be smaller than an oblique angle ϑ2 of the oblique plane 94 (ϑ1 < ϑ2). Accordingly, as shown in Fig. 3c, the characteristics of a changing rate of opening area ℓ1 and ℓ2 are very small or shallow in an initial period, while oblique planes 93 and 94 face to the ports 71c and 71d,and rapidly increase at and after an opening point P where the groove 90 opens to port 71c or 71d. Describing the operation, in the transmission ratio control valve 70, the force of the spring 74 or springs 74 and 77 by the compression of the cam 80 corresponding to the throttle valve opening degree acts on the spool 72 at an end portion thereof. Further, the spool 72 is applied with the pitot pressure responsive to the engine speed in the port 71a. When the pitot pressure and the spring force are balanced, the spool 72 is balanced in a neutral position to close ports 71c and 71d by the lands 91 and 92, respectively. When the force of the springs reduces or the pitot pressure is increased, the spool 72 is shifted to the left. The land 91 is moved to open the port 71c by oblique planes 93. The oil is supplied to the chamber 9 through the passage 53 to start upshifting of the transmission. Although the line pressure is high, the changing rate of the opening area for the port 71c is small as shown by the ℓ1 of Fig. 3c. Since the flow rate of the oil is restricted, the transmission is slowly upshifted at a low transmission ratio changing speed without shock or overshoot. After that, the groove 90 opens to the port 71c for supplying a large amount of oil to the chamber 9, so that the transmission ratio changing speed increases, thereby quickly upshifting transmission to a desired transmission ratio. When the force of the springs increases or the pitot pressure decreases, the spool 72 is shifted to the right. The oblique planes 94 face to the port 71d so that the chamber 9 of the drive pulley 7 is drained to start downshifting the transmission. In this state, the pressure level in the chamber 9 is lower than a predetermined value of the line pressure, having a characteristic as shown by the line ℓ2 of Fig. 3c. Thus, the drain oil is restricted, thereby slowly downshifting the transmission. When the groove 90 opens to the port 71d, the transmission is prefectly downshifted to a desired transmission ratio. Figs. 4a and 4b show another embodiment of the spool 72 of the present invention. The land 92 for the drain port 71d has two oblique planes 94 which are formed on diametrically opposite positions of the edge 92a and has two diametrically opposite indented oblique planes 94a. The oblique plane 94a is indented in a sectional view along an axial line as shown in Fig. 4a. As shown by line ℓ3 in Fig. 4b, the characteristic for the changing rate of the opening area for the port 71d is larger at the initial period compared with line ℓ2 of Fig. 3c. Accordingly, a large amount of oil is drained at the start of the downshift, thereby dissolving a delay of timing at the downshift and effectively preventing spaces on the oblique planes 94, 94a from clogging with any dust. Referring to Figs. 5a and 5b showing a further embodiment of the present invention, all of the oblique planes consist of indented oblique planes 94a. A characteristic thereof is shown by a line ℓ4 in Fig. 5b. Thus, the transmission ratio changing speed at the start of the downshift further increases a little compared with the previous embodiment. Figs. 6a to 6c show a fourth embodiment. In this embodiment, each retracted peripheral portion is formed by cutting away the indented portion to form a deeply retracted recess having a bottom 96a which has a level close to the groove 90. On the edge 91a, two retracted portions 96 are provided. On the edge 92a, four retracted portions 97 are formed. As shown in Fig. 6c, characteristics of the retracted portions 96 and 97 are shown by a line ℓ5 and a line ℓ6, respectively. In this embodiment, the transmission ratio changing speed further increases, and the entering of any dust in the spaces is completely prevented. From the foregoing, it will be understood that the present invention provides a transmission ratio control valve having a spool of simplified structure with a small size. Further, the spool has retracted peripheral portions partly formed on the circumferential edge portions, so that manufacturing process by cutting can easily be performed with accuracy. It is possible to extremely reduce the changing rate of the port opening area, thereby the characteristic thereof can easily be adjusted. Accordingly, the transmission during upshifting and downshifting is properly controlled.

Claims: A continuously variable transmission system (CVT) of the V-pulley belt-type comprising a control valve (70) for controlling a transmission ratio of said CVT, a body (71) of said valve having at least two inside annular grooves (71e, 71f), a first and a second port (71b, 71c) communicating with the respective grooves, and a spool (72) having two lands (91, 92) and an annular groove (90) provided therebetween, wherein each land comprises at least one retracted peripheral portion (93, 94) at a circumferential edge portion adjacent to said annular groove so as to gradually increase the opening area at the respective port during movement of the spool by a defined characteristics of changing rate, characterized in that each land is provided with a plurality of retracted peripheral portions which are formed such that the characteristics of changing rate at said first port (71b) differs from that of said second port (71c). The system according to claim 1, wherein the retracted peripheral portions are formed by oblique planes (93, 94, 94a). The system according to claim 1 or 2, wherein the oblique planes (93, 94) are inclined under different angles (ϑ1, ϑ2). The system according to any of claims 1 to 3, wherein the retracted peripheral portions are formed by portions (94a) indented to the axis of the spool (72). The system according to any of claims 1 to 4, wherein the retracted peripheral portions are formed by concave recesses having a bottom (96a) with a level close to the annular groove (90). The system according to any of claims 1 to 5, wherein the retracted peripheral portions (96, 97) are different in number in the respective two lands (91, 92) adjacent to the annular groove (90).

Inventors: IIJIMA, YOICHI, SAKAI, YASUHITO
Applicants: FUJI JUKOGYO KABUSHIKI KAISHA, VAN DOORNE'S TRANSMISSIE B.V.
Application year: 1988
Main classification: F16H59
IPC codes: B60W10, F16H61