Continuously variable transmission

Abstract: A second pulley ratio is set at a value higher than a first pulley ratio for a gear-neutral state. In a region below the second pulley ratio, a movable sheave of a primary pulley is moved to an O/D side. The amount of the movement is detected by a sensor shoe (detecting means) which is associated with the movable sheave. A ratio sensing valve (inhibition means) associated with the sensor shoe, in turn, clogs a port, halting a hydraulic pressure supplied by a primary regulator valve. As a result, no hydraulic pressure is supplied to the second hydraulic chamber by way of a down-shift relief valve, a manual valve or a low-high control valve, inhibiting a down shift.

Description: The invention relates to a continuously variable transmission using a belt-type continuously variable transmission apparatus which has primary and secondary pulleys comprising two sheaves respectively and a belt wound around the primary and secondary pulleys, more specifically to a start control adopted in a continuously variable transmission which is suitable for motor vehicle use and realized by combining a belt-type continuously variable transmission apparatus with a planetary gear. In recent years, continuously variable transmissions of a vehicle realized by combining a belt-type continuously variable transmission apparatus with a planetary gear have been proposed to further improve fuel efficiency and driving performance of the vehicle. Such a continuously variable transmission is disclosed for instance, in U.S. Patent No. 4,644,820. Such a belt-type continuously variable transmission apparatus employed in a continuously variable transmission has primary and secondary pulleys respectively comprising two sheaves, that is, a fixed sheave and a movable sheave and a belt wound around the primary and secondary pulleys. A pulley ratio can be changed by changing a narrowing pressure of the belt determined by the movable sheave. More specifically, the pulley ratio is decreased when the narrowing pressure on the primary side is raised, while the pulley ratio is decreased when the narrowing pressure on the secondary side is raised. The rotations of a sun gear and a carrier of a planetary gear can be adjusted properly in accordance with the value of the pulley ratio. In this way, the rotation of the ring gear and an output shaft as an integral body can be set in the normal direction, stopped or set in the reverse direction in order to establish a forward drive state, a neutral state or a backward drive state respectively. When a vehicle starts to move forward, a select lever is put in a drive (D) range, the power is turned on and the rotational speed of an input shaft is increased. Then, the narrowing pressure on the secondary side is raised in order to increase the pulley ratio. In this way, an up shift operation is carried out. When the vehicle is to move in a backward direction, the select lever is put in a reverse (R) range, on the other hand, the power is turned on and the rotational speed of the input shaft is increased. Then, the narrowing pressure on the secondary side is raised in order to carry out an up shift operation while decreasing the pulley ratio. Thus, the vehicle transits from a neutral state to a forward or backward drive state. According to the continuously variable transmission described above, however, when the vehicle starts to move from a neutral state, whether it moves forward or backward is completely dependent upon whether the pulley ratio is increased or decreased, that is, whether the narrowing pressure on the primary or secondary side is raised. As a result, if control is carried out by mistake to decrease the pulley ratio due to computer malfunction or the like when the vehicle is supposed to move forward, it actually moves backward against the driver's will. On the other hand, if control is carried out by mistake to increase the pulley ratio when the vehicle is supposed to move backward, it actually moves forward. US-A-3 552 232 axial force applying means discloses a continuously variable transmission (CVT) with a control means for controlling the axial force applied to the pulleys and with an axial force reversing means. It is an object of the invention to provide a continuously variable transmission that ensures a selected forward or backward drive of a vehicle with a high degree or reliability when the vehicle starts to move from a neutral state. This object is achieved with the features of the claims. According to the invention, the axial force reserving means reserves a relation in magnitude between axial forces applied to the first and second pulleys in accordance with a change in torque transmission direction between the first and second pulleys. Then, the inhibition means inhibits reversal of the relation in magnitude between the axial forces applied to the first and second pulleys carried out by the axial force reversing means when a pulley ratio detected by the pulley-ratio detecting means is in a predetermined pulley-ratio range including a pulley ratio implementing the neutral state. As a result, since the relation in magnitude between the axial forces is changed so that the axial force on the driving side is greater than the axial force on the driven side in accordance with a change in torque transmission direction in an area outside the predetermined pulley-ratio range, it is possible to implement all kinds of shift such as the power-on up and down shifts and the power-off up and down shifts. In the predetermined pulley-ratio range, however, only certain shifts can be implemented because the reversal of the relation in magnitude between the axial forces is regulated. In addition, the predetermined pulley-ratio range is set in the vicinity of a pulley ratio implementing the neutral state and a pulley-ratio range implementing the forward drive state as well as a pulley-ratio range implementing the backward drive state. Furthermore, the inhibition means inhibits the reversal of the relation in magnitude between the axial forces so as to inhibit a power-off down shift. The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein: Fig. 1 is a skeleton diagram showing a power transmitting apparatus of a continuously variable transmission provided by an embodiment of the invention; Fig. 2 is a speed diagram of the power transmitting apparatus as shown in Fig. 1; Fig. 3 is a diagram showing a relation between the output torque and the pulley ratio of a belt-type continuously variable transmission apparatus (CVT) employed in the power transmitting apparatus as shown in Fig. 1; Fig. 4 is a diagram showing a relation between the output rotational speed and the pulley ratio of the CVT employed in the power transmitting apparatus as shown in Fig. 1; Fig. 5 is a table showing engagement of a low clutch and a high clutch in a plurality of ranges; Fig. 6 is a diagram showing cross sections of double-chamber-type hydraulic servos which apply axial forces to a primary pulley and to a secondary pulley respectively; Fig. 7 is a diagram showing a hydraulic circuit of a hydraulic control mechanism; Fig. 8 is a diagram showing the structure of a low-high control valve and an interlock rod; and Fig. 9 is a diagram showing a narrowing pressure of a belt generated by a movable sheave. The invention will become apparent from the following detailed description of some preferred embodiments with reference to accompanying diagrams showing the embodiments. First of all, a power transmitting mechanism of the continuously variable transmission provided by the invention is explained by referring to Fig. 1. As shown in the figure, an automatic continuously variable transmission 1, which is referred to hereafter simply as a continuously variable transmission, comprises a first shaft 3 linked to an engine crank shaft 2, a second shaft 5 and third right and left drive shafts 6a and 6b linked to the vehicle front wheels. The first shaft 3 supports a primary (first) pulley 7 while the second shaft 5 supports a secondary (second) pulley 9. A belt 10 is wound around this primary pulley 7 and secondary pulley 9 to constitute a belt-type continuously variable transmission apparatus 11. Furthermore, the first shaft 3 is linked to the engine crank shaft 2 by way of a damper 12. An input-side member 13 of a low clutch C L is fixed on the first shaft 3 while an output-side member 15 thereof is rotatably supported by the first shaft 3. A primary-side sprocket 16 forming a power transmitting means is linked integrally to the output-side member 15. In addition, a fixed sheave 7a of the primary pulley 7 is fixed to the first shaft 3 and an oil pump 17 is attached to the end of the first shaft 3. A movable sheave 7b of the primary pulley 7 is supported by the fixed sheave 7a movably in the shaft direction. The secondary pulley 9 is rotatably supported by the second shaft 5. The secondary pulley 9 comprises a fixed sheave 9a, a movable sheave 9b supported by the fixed sheave 9a movably in the shaft direction and a secondary shaft 9c integrally linked to the fixed sheave 9a. In addition, a high clutch C H is provided between the second shaft 5 and the secondary shaft 9c. A planetary gear 19 is provided on the second shaft 5 and a secondary-side sprocket 20 is rotatably supported by the planetary gear 19. An output gear 21 is fixed on one end of the second shaft 5 to form an output shaft. The planetary gear 19 comprises a sun gear 19s, a ring gear 19r, a pinion 19p engaged with both the sun and ring gears 19s and 19r and is a single pinion planetary gear having a carrier 19c for rotatably supporting the pinion 19p. The sun gear 19s is linked to the secondary shaft 9c, serving as a second rotary element while the ring gear 19r is linked to the second shaft 5, serving as a third rotary element. On the other hand, the carrier 19c is linked to the secondary-side sprocket 20, serving as a first rotary element. A wound component 22 such as a silent chain, a roller chain or a timing belt is wound around the primary-side and secondary-side sprockets 16 and 20. In addition, the gear 21 fixed on the second shaft 5 is engaged with a large gear 23a of a speed reducing gear unit 23 and a small gear 23b of the speed reducing gear unit 23 is engaged with a ring gear 24 of a differential apparatus 25. The differential apparatus 25 produces a differential rotation to each of the left and right drive shafts 6a and 6b constituting the third shaft 6. Next, operations based on the power transmitting mechanism of the continuously variable transmission 1 are explained by referring to Figs. 1, 2, 3, 4 and 5. The rotation of the engine crank shaft 2 is transmitted to the first shaft 3 by way of the damper 12. In the low (L) mode in which the low clutch C L is engaged while the high clutch C H is disengaged, the rotation of the first shaft 3 is transmitted to the primary pulley 7 and is also transmitted to the carrier 19c of the planetary gear 19 by way of a power transmitting apparatus 26 comprising the primary-side sprocket 16, the wound component 22 and the secondary-side sprocket 20. On the other hand, while the rotational speed of the primary pulley 7 is being continuously varied by properly adjusting the pulley ratio of the primary pulley 7 to the secondary pulley 9 by means of an axial force applying means such as a hydraulic servo to be described later, the variable speed rotation of the primary pulley 7 is transmitted to the secondary pulley 9. The variable speed rotation of the secondary pulley 9 is further transmitted to the sun gear 19s of the planetary gear 19. In the planetary gear 19, as shown in the speed diagram of Fig. 2, the carrier 19c to which a constant speed rotation is transmitted by way of the power transmitting apparatus 26 becomes a reactive element, transmitting the continuously variable speed rotation from the belt-type continuous variable transmission apparatus (CVT) 11 to the sun gear 19s. The rotations of the carrier. 19c and the sun gear 19s are combined before being transmitted to the second shaft 5 by way of the ring gear 19r. Since the ring gear 19r, a rotary element other than the reactive support element, is linked to the second shaft 5, the planetary gear 19 creates a torque environment and, at the same time, the sun gear 19s and the carrier 19c rotate in the same direction. As a result, the second shaft 5 rotates in the forward (Low) and reverse (Rev) directions, crossing the zero rotational speed. That is to say, in the torque environment, in the state of a normal direction (forward direction) rotation of the second shaft 5, the belt-type continuously variable transmission apparatus (CVT) 11 transmits a torque from the secondary pulley 9 to the primary pulley 7 but, in the state of a reverse direction (backward direction) rotation of the second shaft 5, a torque is transmitted from the primary pulley 7 to the secondary pulley 9. In the high (H) mode in which the low clutch C L is disengaged while the high clutch C H is engaged, the transmission of power to the planetary gear 19 by way of the power transmitting apparatus 26 is cut off. In this mode, the engagement of the high clutch C H puts the planetary gear 19 in an integrally rotating state. As a result, the rotation of the first shaft 3 is transmitted to the second shaft 5 by way of the belt-type continuously variable transmission apparatus (CVT) 11 and the high clutch C H . That is to say, the CVT 11 transmits power from the primary pulley 7 to the secondary pulley 9. By the same token, the rotation of the second shaft 5 is transmitted to the differential apparatus 25 by way of the output gear 21 and the speed reducing gear unit 23 as well as to the right and left front wheels by way of the right and left drive shafts 6a and 6b respectively. As shown in the speed diagram of Fig. 2, the output torque diagram of Fig. 3, the diagram of the output rotational speed of Fig. 4, and the clutch engagement table of Fig. 5, in the low mode, that is, when the CVT 11 is at the limit (the O/D end) of the O/D (overdrive) direction (the position of a line (a) shown in Fig. 2), based on the fact that the sun gear 19s is rotating at a maximum speed, the rotation of the ring gear 19r is reversed into a reverse (REV) rotation relative to the rotation of the carrier 19c which is rotating at a constant speed and the reverse (REV) rotation is transmitted to the second shaft 5. As the CVT 11 makes a shift in the U/D (underdrive) direction, the rotational speed in the reverse direction decreases, arriving at a neutral position (an NEU position) at which the rotational speed of the second shaft 5 is reduced to zero at a predetermined pulley ratio determined by the gear ratios of the planetary gear 19 and the power transmitting apparatus 26. In addition, as the CVT 11 makes a shift to the U/D (underdrive) direction, the rotation of the ring gear 19r is switched to the normal direction and the rotation in the normal direction, that is, in the forward drive direction is transmitted to the second shaft 5. At that time, the torque produced by the second shaft 5 increases to an infinite value in a region in close proximity to the neutral (NEU) position as is obvious from Fig. 3. When the CVT 11 is at the limit (the U/D end) of the U/D (underdrive) direction, the high clutch C H is engaged and an operation to switch to the high mode is carried out. In the high mode, the output rotation of the CVT 11 is transmitted to the second shaft 5 as it is. As a result, the speed line is parallel to the horizontal axis as shown by a line (b) in the speed diagram of Fig. 2. As the CVT 11 makes a shift in the overdrive direction (the O/D direction), the rotation of the second shaft 5 also varies in the O/D (overdrive) direction, reducing the transmitted torque by an amount corresponding to the increase in rotational speed. It should be noted that, λ shown in Fig. 2 is a ratio of the sun gear tooth count Zs to the ring gear tooth count Zr (that is, Zs/Zr). Next, a hydraulic control mechanism of the continuously variable transmission provided by an embodiment of the invention is explained. As shown in Fig. 6, the movable sheave 7b of the primary pulley 7 is supported movably in the shaft direction by a boss 7c of the fixed sheave 7a of the primary pulley 7 by way of a ball spline 30. By the same token, the movable sheave 9b of the secondary pulley 9 is supported movably in the shaft direction by a boss 9c of the fixed sheave 9a of the secondary pulley 9 by way of a ball spline 31. On the back surface of the movable sheave 7b, a primary-side hydraulic servo 32 serving as axial force applying means for applying an axial force to the primary pulley 7 is provided. Similarly, on the back surface of the movable sheave 9b, a secondary-side hydraulic servo 33 serving as an axial force applying means for applying an axial force to the secondary pulley 9 is provided. The primary-side hydraulic servo 32 comprises a partition member 35 fixed to the fixed sheave 7a, a cylinder member 37, a drum member 40 fixed to the back surface of the movable sheave 7b and a second piston member 42. Likewise, the secondary-side hydraulic servo 33 comprises a partition member 36 fixed to the fixed sheave 9a, a cylinder member 39, a drum member 41 fixed to the back surface of the movable sheave 9b and a second piston member 43. The partition member 35 is fitted to the drum member 40 in a hydraulic-sealed state and also fitted to the second piston member 42, the cylinder member 37 and the partition member 35 forming a double piston structure comprising a first hydraulic chamber 45 and a second hydraulic chamber 47. By the same token, the partition member 36 is fitted to the drum member 41 in a hydraulically sealed state and also fitted to the second piston member 43, the cylinder member 39 and the partition member 36 forming a double piston structure comprising a first hydraulic chamber 46 and a second hydraulic chamber 49. In addition, in the first hydraulic chamber 45 of the primary-side hydraulic servo 32, the back surface of the movable sheave 7b forms a piston surface on the primary side. Similarly, in the first hydraulic chamber 46 of the secondary-side hydraulic servo 33, the back surface of the movable sheave 9b forms a piston surface on the secondary side. An effective pressure receiving area on the piston surface on the primary side is equal to an effective pressure receiving area on the secondary side. In addition, hydraulic paths 50 and 52 connected to the first and second hydraulic chambers 45 and 47 are formed on the boss 7c of the fixed sheave 7a on the primary side. By the same token, hydraulic paths 51 and 53 connected to the first and second hydraulic chambers 46 and 49 are formed on the boss 9c of the fixed sheave 9a on the secondary side. In addition, a spring 55 for pre-loading use is provided in a contracted state in the first hydraulic chamber 45 of the primary-side hydraulic servo 32. In addition, as shown in Fig. 7, a hydraulic control mechanism (means) 54 employed in the present embodiment comprises a primary regulator valve 56, a ratio control valve (axial force reversing means) 57, a down-shift relief valve (axial force reversing means) 58, a manual valve 59, a low-high control valve (or a low-high switching valve) 60 serving as a low-high switching means, a low clutch relief valve 61 and a clutch modulation valve 62. For details of the low-high control valve 60, refer to Fig. 8. Furthermore, the hydraulic control mechanism (means) 54 also includes a ratio sensing valve (inhibition means) 63, a sensor shoe (a movable member) 65 used as a position-detecting member (pulley-ratio detecting means) and an interlock rod (lock means) 66. The sensor shoe 65 is supported slidably by a guide member 67 installed in parallel to the axis of the primary pulley 7. Two linkage portions 65b and 65c protrude from the sensor shoe 65. The linkage portion 65b is engaged with the movable sheave 7b of the primary pulley 7 while the linkage portion 65c is engaged with the ratio sensing valve 63 described above, with this arrangement, therefore, when the movable sheave 7b moves along the shaft in the O/D or U/D direction, the distance by which the movable sheave 7b moves is transmitted to the ratio sensing valve 63 as it is by way of the sensor shoe 65. Furthermore, a dent 65a is formed on the sensor shoe 65. A base end 66a, one end of the interlock rod 66, is engaged with and disengaged from the dent 65a. The interlock rod 66 is installed so as to pass through a valve body. The other end 66b of the interlock rod 66 is engaged with and disengaged from dents 60a and 60b of the low-high control valve 60. Fig. 7 shows the interlock rod 66 which is split into the base end 66a and the other end 66b. It should be noted, however, that in actuality, the interlock rod 66 is a single rod. In addition, when the base end 66a of the interlock rod 66 is engaged with the dent 65a of the sensor shoe 65, the other end 66b is engaged with neither the dent 60a nor the dent 60b of the low-high control valve 60. Instead, the other end 66b is brought into contact with the surface of the low-high control valve 60. When the base end 66a of the interlock rod 66 is disengaged from the dent 65a of the sensor shoe 65 and brought into contact with a protrusion on the surface of the sensor shoe 65, on the contrary, the other end 66b is engaged with either the dent 60a or the dent 60b of the low-high control valve 60. Next, the operation of the hydraulic control mechanism 54 with the structure described above is explained by referring to Fig. 7. Operations in the following modes and ranges will be explained in the order they are listed as follows: (1) D range L mode (Low mode of drive range) (2) D range H mode (High mode of drive range) (3) R range (Reverse range) (4) N and P ranges (Neutral and parking ranges) A first pulley ratio A shown in Fig. 4 is a pulley ratio in a neutral state and a second pulley ratio B is greater than the first pulley ratio A. A vertical line passing through the second pulley ratio B is the border between a region with high pulley ratios on the left side of the figure and a region with low pulley ratios on the right side of the figure. The low and high modes of the drive ranges (1) and (2) are set by changing control in the regions on the left and right sides of the second pulley ratio B. By changing the control in this way, as will be described later, a down shift is inhibited in the low mode of the drive range and in the reverse range in the region below the second pulley ratio B. Also in the region below the second pulley ratio B, a jump from the high mode of the drive range to the low mode of the drive range and to the reverse range is inhibited. First of all, in any one of the modes and the ranges (1) to (4) described above, a hydraulic pressure from the oil pump 17 is appropriately regulated by the primary regulator valve 56 and output from an output port (v) thereof as shown in Fig. 7. At the same time, the regulated hydraulic pressure is also supplied to the first hydraulic chambers 45 and 46 of the hydraulic servos 32 and 33 respectively. Control is executed so as to produce that hydraulic pressures in both the first hydraulic chambers 45 and 46 equal to each other. The regulated hydraulic pressure is also supplied to the clutch modulation valve 62. Then, a hydraulic pressure output by the clutch modulation valve 62 is selectively supplied to the low clutch C L or the high clutch C H except during the N and P ranges (4). Operations in the modes and ranges (1) to (4) are described one mode/range after another by referring to Figs. 4 and 7 as well as a narrowing force balance table shown in Fig. 9. (1) L mode in drive (D) range Equal hydraulic pressures are supplied to the first hydraulic chambers 45 and 46 respectively. The low clutch C L is engaged and, in an up shift, a hydraulic pressure is further supplied to the second hydraulic chamber 49. In addition, in a down shift, a hydraulic pressure is supplied to the second hydraulic chamber 47 but, in the region below the second pulley ratio B, the supply of the hydraulic pressure is halted, inhibiting the down shift. That is to say, in the up shift, the manual valve 59 is operated at a D range position, opening hydraulic paths between a port (a) and a port (b), a port (c) and a port (d) as well as a port (e) and a port (f) thereof. In addition, the low-high control valve 60 is set at an L mode position, opening hydraulic paths between a port (h) and a port (i), a port (j) as well as a port (k) and a port (l) and a port (m) thereof. At the same, a switching operation is carried out to open a hydraulic path between a port (g) and a drain port Ex of the low-high control valve 60 and sustain the hydraulic path in this state. As a result, the hydraulic pressure from the clutch modulation valve 62 is supplied to the low clutch C L by way of the ports (a) and (b) of the manual valve 59, the ports (h) and (i) of the low-high control valve 60 and ports (n) and (0) of the low clutch relief valve 61, putting the low clutch C L in an engaged state. In addition, the hydraulic pressure from the output port (v) of the primary regulator valve 56 is gradually increased by the ratio control valve 57 to a value corresponding to a target pulley ratio. The gradually increasing hydraulic pressure is then supplied to the second hydraulic chamber 49 through ports (p) and (q) of the ratio control valve 57, the ports (c) and (d) of the manual valve 59 and the ports (j) and (k) of the low-high control valve 60. It should be noted that, in this state, a hydraulic path between the port (g) of the low-high control valve 60 and the drain port Ex is opened as described above, hence putting the hydraulic chamber of the high clutch C H in a released state. In addition, the second hydraulic chamber 47 of the primary-side hydraulic servo 32 has a hydraulic path opened to a drain port Ex of the down-shift relief valve 58 by way of the ports (m) and (l) of the low-high control valve 60, the ports (f) and (e) of the manual valve 59 and a port (s) of the down-shift relief valve 58. As a result, the low clutch C L is engaged and, at the same time, in the CVT 11, an axial force generated by the secondary-side hydraulic servo 33 in which hydraulic pressures are applied to both the first and second hydraulic chambers 46 and 49 exceeds an axial force generated by the primary-side hydraulic servo 32 in which a hydraulic pressure is applied only to the first hydraulic chamber 45. The axial force generated by the secondary-side hydraulic servo 33 is further increased gradually to raise the pulley ratio. At that time, the movable sheave 7b of the primary pulley 7 is moved to the U/D side. In this state, an engine torque transmitted from the first shaft 3 to the carrier 19c of the planetary gear 19 by way of the low clutch C L and the power transmitting apparatus 26 is output to the second shaft 5 by way of the ring gear 19r while the engine torque is being controlled in the CVT 11 by a predetermined pulley ratio through the sun gear 19s. When an up shift is continued, the pulley ratio is gradually increased. Before the pulley ratio reaches the second pulley ratio B shown in Fig. 4, however, the operation of the low-high control valve 60 driven by on/off operations of a solenoid valve which is not shown in the figure is inhibited. That is to say, in an up shift, the movable sheave 7b of the primary pulley 7 is moved to the U/D (underdrive) side and the sensor shoe 65 associated with the movable sheave 7b is moved in the downward direction in the figure. Before the pulley ratio reaches the second pulley ratio B, however, the base end 66a of the interlock rod 66 is brought into contact with the surface of the sensor shoe 65 without being engaged with the dent 65a. As a result, the other end 66b of the interlock rod 66 on the opposite side to the base end 66a is engaged with the dent 60a of the low-high control valve 60, mechanically locking the low-high control valve 60 in a state sustaining the low mode. In this state, operations are inhibited. As the up shift brings the pulley ratio to the second pulley ratio B, the base end 66a of the interlock rod 66 is engaged with the dent 65a of the sensor shoe 65. The other end 66b on the opposite side is moved to the right in the figure, freeing the engagement thereof with the dent 60a of the low-high control valve 60. As a result, at a pulley ratio above the second pulley ratio B, the operation of the low-high control valve 60 is enabled. It should be noted that, also in the high mode of the drive range, at a pulley ratio below the second pulley ratio B, the low-high control valve 60 is locked mechanically as will be described later. A down shift in the low mode of the drive range in the region below the second pulley ratio B is inhibited but enabled in the region above the second pulley ratio B. To put it in detail, in the former region, the ratio sensing valve 63 which moves in an associated manner with the movable sheave 7b of the primary pulley 7 by way of the sensor shoe 65 is in a state shown in the figure. In this state, the hydraulic pressure from the port (v) of the primary regulator valve 56 is halted by the ratio sensing valve 63, making it impossible to supply a hydraulic pressure necessary for a down shift to the second hydraulic chamber 47. It should be noted that, also in this state, a hydraulic path between the port (q) of the ratio control valve 57 and the drain port Ex thereof is opened, allowing the hydraulic pressure of the second hydraulic chamber 49 to be drained to the port Ex by way of the ports (k) and (j) of the low-high control valve 60, the ports (d) and (c) of the manual valve 59 and the port (q) of the ratio control valve 57. As a result, a down shift till Pri = Sec shown in Fig. 9 is possible. In the region above the second pulley ratio B, on the other hand, a down shift is possible by virtue of, among other components, the ratio sensing valve 63. That is to say, in the region above the second pulley ratio B, the movable pulley 7b of the primary pulley 7 is moved to the U/D side, driving the ratio sensing valve 63 in the downward direction of the figure by way of the sensor shoe 65. As a result, since the hydraulic path between ports (t) and (u) of the ratio sensing valve 63 is opened, the hydraulic pressure from the primary regulator valve 56 is led to the down-shift relief valve 58 by way of a check valve 69. The hydraulic pressure moves the down-shift relief valve 58 in the upward direction of. the figure, opening a hydraulic path between the port (r) and the port (s) thereof. In this state, it becomes possible to supply a hydraulic pressure to the second hydraulic chamber 47 by way of the ports (e) and (f) of the manual valve 59 and the ports (l) and (m) of the low-high control valve 60. In other words, a down shift can be carried out. It should be noted that, by properly setting the second pulley ratio B, in a region where a down shift is required, it is possible to make a down shift work effectively. For example, if the second pulley ratio B is set at a location in close proximity to the first pulley ratio A which corresponds to the neutral state, with a change gear ratio of the continuously variable transmission as a whole set at about the same value as the first gear ratio (the first speed) of an ordinary automatic transmission (A/T), the pulley ratio is fixed at the second pulley ratio B, allowing an effective engine brake to function. (2) H mode of drive range Equal hydraulic pressures are supplied to the first hydraulic chambers 45 and 46 respectively. The high clutch C H is engaged and, in an up shift, a hydraulic pressure is further supplied to the second hydraulic chamber 49. In addition, in a down shift, a hydraulic pressure is supplied to the second hydraulic chamber 47. In the region below the second pulley ratio B, the operation of the low-high control valve 60 is mechanically inhibited. That is to say, in the high mode of the drive range, the manual valve 59 is placed at the D range position as shown in Fig. 7 as is the case with the low mode explained previously. However, the low-high control valve 60 is switched to the H mode position, opening hydraulic paths between the ports (h) and (g), the ports (j) and (m) and the ports (l) and (k) as well as a hydraulic path between the port (i) and the drain port Ex. In this state, the hydraulic pressure from the output port (v) of the primary regulator valve 56 is supplied to the hydraulic servo of the high clutch C H by way of the ports (a) and (b) of the manual valve 59 and the ports (h) and (g) of the low-high control valve 60, putting the high clutch C H in an engaged state. In addition, the hydraulic pressure from the output port (v) of the primary regulator valve 56 is also supplied to the second hydraulic chamber 47 of the primary-side hydraulic servo 32 by way of the ports (p) and (q) of the ratio control valve 57, the ports (c) and (d) of the manual valve 59 and the ports (j) and (m) of the low-high control valve 60. It should be noted that, in this state, a hydraulic path between the port (i) of the low-high control valve 60 and the drain port Ex thereof is opened, hence putting the hydraulic servo of the low clutch C L in a released state. In addition, the second hydraulic chamber 49 of the secondary-side hydraulic servo 33 has a hydraulic path opened to a drain port Ex of the down-shift relief valve 58 by way of the ports (k) and (l) of the low-high control valve 60, the ports (f) and (e) of the manual valve 59 and the port (s) of the down-shift relief valve 58. As a result, the high clutch C H is engaged and, at the same time, in the CVT 11, an axial force generated by the primary-side hydraulic servo 32 in which hydraulic pressures are applied to both the first and second hydraulic chambers 45 and 47 exceeds an axial force generated by the secondary-side hydraulic servo 33 in which a hydraulic pressure is applied only to the first hydraulic chamber 46, putting the CVT 11 in an axial forcestate for torque transmission from the primary pulley 7 to the secondary pulley 9. In this state, by properly regulating the ratio control valve 57, the hydraulic pressure in the second hydraulic chamber 47 of the primary-side hydraulic servo 32 can be regulated. As a result, the axial force produced by the primary-side hydraulic servo 32 is also regulated to give an appropriate pulley ratio (that is, an appropriate torque ratio). In this state, a torque transmitted from the engine to the first shaft 3 is properly changed by the CVT 11 in which transmission from the primary pulley 7 to the secondary pulley 9 is under way and further output to the second shaft 5 by way of the high clutch C H . In the high mode of the drive range described above, as the pulley ratio goes below the second pulley ratio B, the operation of the low-high control valve 60 is mechanically inhibited. This is because, at a pulley ratio equal to or greater than the second pulley ratio B, the movable sheave 7b of the primary pulley 7 is placed on the U/D side shown in the figure and the base end 66a of the interlock rod 66 is engaged with the dent 65a of the sensor shoe 65 while, on the other hand, the other end 66b thereof on the opposite side is out of the dent 60b of the low-high control valve 60 and moves to the right in the figure, enabling the operation of the low-high control valve 60. At a pulley ratio equal to or smaller than the second pulley ratio B, on the contrary, the movable sheave 7b of the primary pulley 7 is placed on the O/D side shown in the figure and the base end 66a of the interlock rod 66 is brought into contact with the surface of the sensor shoe 65 while, on the other hand, the other end 66b thereof on the opposite side is engaged with the dent 60b of the low-high control valve 60. As a result, the low-high control valve 60 is mechanically locked in a state in which the high mode is sustained, inhibiting the operation thereof. That is to say, at a pulley ratio equal to or smaller than the second pulley ratio B, the operation of the low-high control valve 60 is mechanically inhibited, be it in the low mode of the drive range or the high mode of the drive range, sustaining the low or high mode as it is. As a result, at a high rotational speed of the second shaft 5, even if a signal is by any chance output to the solenoid valve to carry out a switching operation from the high mode of the drive range to the low mode of the drive range in the event of an electrical failure, the low-high control valve 60 will not operate, which effectively prevents over revolution of the engine and a backward drive. In addition, in the high mode of the drive range, even at a pulley ratio equal to or smaller than the second pulley ratio B, a down shift is never inhibited unlike the low mode of the drive range. That is to say, in the high mode of the drive range, in the region below the second pulley ratio B, the hydraulic pressure from the output port (v) of the primary regulator valve 56 is halted by the ratio sensing valve 63 which is put in a state shown in Fig. 7. Thus, the hydraulic pressure is never supplied to the second hydraulic chamber 49 by way of the down-shift relief valve 58, the manual valve 59 and the low-high control valve 60. In place of the hydraulic pressure from the output port (v) of the primary regulator valve 56, however, a hydraulic pressure from the high clutch C H is supplied to the second hydraulic chamber 49 by way of the check valve 69, the ports (r) and (s) of the down-shift relief valve 58, the ports (e) and (f) of the manual valve 59 and the ports (l) and (k) of the low-high control valve 60. As a result, in the high mode of the drive range, a down shift is possible over the entire range of the pulley ratio. (3) Reverse (R) range In the reverse range, a predetermined hydraulic pressure is supplied to the first and second hydraulic chambers 45 and 47 of the primary-side hydraulic servo 32, the first hydraulic chamber 46 of the secondary-side hydraulic servo 33 and the hydraulic servo of the low clutch C L as shown in Fig. 7. That is to say, in the reverse range, the manual valve 59 is placed at an R range position and the low-high control valve 60 is at an L mode position as shown in the figure. In this state, hydraulic paths between the ports (a) and (b), the ports (c) and (f) as well as the ports (e) and (d) of the manual valve 59 are opened. In addition, much like the low mode described earlier, hydraulic paths between the ports (h) and (i), the ports (j) and (k), the ports (l) and (m) as well as the port (g) and the drain port Ex of the low-high control valve 60 are opened. As a result, the hydraulic pressure from the output port (v) of the primary regulator valve 56 is supplied to the hydraulic servo of the low clutch C L by way of the ports (a) and (b) of the manual valve 59 and the ports (h) and (i) of the low-high control valve 60. The hydraulic pressure from the output port (v) of the primary regulator valve 56 is also supplied to the second hydraulic chamber 47 of the primary-side hydraulic servo 32 by way of the ports (p) and (q) of the ratio control valve 57, the ports (c) and (f) of the manual valve 59 and the ports (l) and (m) of the low-high control valve 60. In addition, a hydraulic path between the port (s) and the drain port Ex of the down-shift relief valve 58 is opened. As a result, the low clutch C L is engaged and, at the same time, in the CVT 11, an axial force generated by the primary-side hydraulic servo 32 in which hydraulic pressures are applied to both the first and second hydraulic chambers 45 and 47 exceeds an axial force generated by the secondary-side hydraulic servo 33 in which a hydraulic pressure is applied only to the first hydraulic chamber 46, putting the CVT 11 in an axial force state for torque transmission from the primary pulley 7 to the secondary pulley 9. In this state, by properly regulating the ratio control valve 57, the hydraulic pressure in the second hydraulic chamber 47 of the primary-side hydraulic servo 32 is regulated. As a result, the axial force produced by the primary-side hydraulic servo 32 is also regulated to give an appropriate pulley ratio. In this state, the pulley ratio of the CVT 11 has a predetermined O/D value and an engine torque from the first shaft 3 is transmitted to the carrier 19c of the planetary gear 19 by way of the low clutch C L and the power transmitting apparatus 26. At the same time, an engine torque is also transmitted to the sun gear 19s by way of the CVT 11 in which torque transmission from the primary pulley 7 to the secondary pulley 9 is under way. Both the torques are combined in the planetary gear 19 and output to the second shaft 5 as a rotation in the reverse direction by way of the ring gear 19r. Also in the reverse range, the supply of a hydraulic pressure to the down-shift relief valve 58 is inhibited by the sensor shoe 65 and the ratio sensing valve 63 as in the case of a pulley ratio equal to or smaller than the second pulley ratio B in the low mode of the drive range. As a result, a down shift is also inhibited as well. It should be noted that, in the reverse range, basically, the engine brake is not required in particular. Thus, no problem arises whatsoever even if the down shift is inhibited. (4) Neutral (N) and parking (P) ranges When the manual valve 59 is placed at a P range or N range position, both the low (first) and high clutches C L and C H are disengaged and a predetermined hydraulic pressure is supplied to the first hydraulic chambers 45 and 46 of the primary-side and secondary-side hydraulic servos 32 and 33 respectively. This is because, in these ranges, hydraulic paths between the ports (c) and (d), the ports (e) and (f) as well as the port (b) and the drain port Ex of the manual valve 59 are opened. In addition, the low-high control valve 60 is sustained in the low mode of the drive range described earlier. On the top of that, a hydraulic path between the port (q) and the drain port Ex of the ratio control valve 57 is opened and the ratio sensing valve 63 is held at a position shown in Fig. 7. As a result, a hydraulic pressure from the output port (v) of the primary regulator valve 56 is supplied only to the first hydraulic chamber 45 of the primary-side hydraulic servo 32 and the first hydraulic chamber 46 of the secondary-side hydraulic servo 33 and is not applied to either of the valves. Thus, equal hydraulic pressures are supplied only to the first hydraulic chambers 45 and 46 of the primary-side and secondary-side hydraulic servos 32 and 33 respectively, resulting in about equal axial forces working on both the primary (first) and secondary pulleys 7 and 9. It should be noted that, at the D, N and R positions and in the low and high modes, a predetermined hydraulic pressure from the primary regulator valve 56 is supplied to the first hydraulic chambers 45 and 46 of the primary-side and secondary-side hydraulic servos 32 and 33 respectively, securing a predetermined axial force corresponding to a transmitted torque so as to prevent the belt from slipping. In addition, a regulated hydraulic pressure from the ratio control valve 57 is supplied to either the second hydraulic chamber 47 of the primary-side hydraulic servo 32 or the second hydraulic chamber 49 of the secondary-side hydraulic servo 33 in order to adjust the ratio of the axial force of the primary pulley 7 to the axial force of the secondary pulley 9 in a transmission operation so as to produce a predetermined pulley ratio. In the embodiment described above, the second pulley ratio B is used as a threshold pulley ratio for inhibiting a down shift in the low mode of the drive range as well as a threshold pulley ratio for mechanically inhibiting the operation of the low-high control valve 60 in the low and high modes of the drive range. It should be noted, however, that the threshold pulley ratios can also be set at values different from each other. For example, the threshold pulley ratio for inhibiting a down shift in the low mode of the drive range can be set at a value closer to the first pulley ratio A while the threshold pulley ratio for mechanically inhibiting the operation of the low-high control valve 60 in the low and high modes of the drive range can be set at a value farther from the first pulley ratio A. At any rate, it is desirable to set the threshold pulley ratio for inhibiting a down shift in the low mode of the drive range and the threshold pulley ratio for mechanically inhibiting the operation of the low-high control valve 60 in the low (L) and high modes of the drive range at values determined by actual running conditions of the vehicle. According to the continuously variable transmission, when the vehicle starts to move, an up shift is carried out by sustaining the relation in magnitude between the axial forces applied to the first and second pulleys to give a high pulley ratio if the forward drive state is selected or by sustaining the relation in magnitude between the axial forces to give a low pulley ratio if the backward drive state is selected. As a result, it is possible to achieve a running state according to the will of the driver with a high degree of reliability. In addition, according to the continuously variable transmission, the hydraulic servos of the first and second pulleys each have first and second hydraulic chambers and hydraulic pressures are supplied to both the first hydraulic chambers all the time while a hydraulic pressure is supplied selectively to only one of the second hydraulic chambers in order to reverse the relation in magnitude between the axial forces. Since the inhibition means inhibits an operation to selectively supply the hydraulic pressure to one of the second hydraulic chambers in order to reverse the relation in magnitude between the axial forces in a predetermined pulley-ratio range, the control is simple and can be carried out with a high degree of reliability. According to the continuously variable transmission, since the hydraulic pressures supplied to the second hydraulic chambers of both the hydraulic servos are controlled by the down-shift valve serving as an axial force reversing means and the ratio control valve respectively, and the control valve serving as inhibition means is provided on the upstream side of the down-shift valve, the reversal of the relation in magnitude between the axial forces can be ragulated without regard to the operation of the down-shift valve, allowing control to be carried out with an even higher degree of reliability. According to the continuously variable transmission, when an operation to switch from a low mode to a high mode and vice versa can be carried out, both the low and high modes can be set at the same pulley ratio. With the high mode selected, the hydraulic pressure supplied to the second clutch is also supplied to the down-shift valve without passing through the control valve which serves as inhibition means. As a result, the relation in magnitude between the axial forces can be reversed in the entire pulley-ratio range, allowing the engine brake to be operated effectively. In addition, according to the continuously variable transmission, the pulley ratio is detected by the position detecting member which is used for monitoring the position of the movable sheave of one of the first and second pulleys and the position detecting means and the inhibition means are coupled to each other. As a result, control can be carried out with a high degree of reliability even in the event of an electrical failure. Furthermore, according to the continuously variable transmission, since the predetermined pulley-ratio range is set in the vicinity of a pulley ratio implementing the neutral state and a pulley-ratio range implementing the forward drive state as well as a pulley-ratio range implementing the backward drive state, the vehicle can be started to move from the neutral state with a high degree of reliability. In other regions, the relation in magnitude between the axial forces can be reversed, making a power-off down shift possible and allowing the engine brake to be operated effectively. In addition, in the predetermined pulley-ratio range, even though the engine brake can not be operated effectively, in the vicinity of a pulley ratio implementing the neutral state and a pulley-ratio range implementing the forward drive state, the speed of the vehicle is low. As a result, the engine brake is not required in particular. On the top of that, in the pulley-ratio range implementing the backward drive state, a shift is not necessary from the beginning. So no problem arises whatsoever even if the relation in magnitude between the axial forces is regulated.

Claims: A continuously variable transmission comprising: an input shaft (3) associated with an engine output shaft (2); an output shaft (5) associated with vehicle wheels; a belt-type continuously variable transmission apparatus (11) comprising a first pulley (7) associated with said input shaft (3), a second pulley (9) provided on the side of said output shaft (5), a belt (10) wound around said first and second pulleys (7,9) and axial force applying means (32,33) for applying axial forces to said first and second pulleys (7,9) in order to change a pulley ratio; a planetary gear (19) comprising a first rotary element (19c) associated with said input shaft (3), a second rotary element (19s) associated with said second pulley (9) and a third rotary element (19r) associated with said output shaft (4); pulley-ratio detecting means (65) detecting the pulley ratio of said belt-type continuously variable transmission apparatus (11); and control means (54) controlling said axial forces applied to said first and second pulleys (7,9) by said axial force applying means (32,33) so that said axial forces applied to said first and second pulleys (7,9) are different from each other by an amount corresponding to a target pulley ratio, wherein a direction in which torque is transmitted between said first and second pulleys (7,9) via said planetary gear (19) is changed and a forward drive state, a neutral state and a backward drive state of a vehicle can be set in accordance with a change in said pulley ratio, and said control means (54) comprises axial force reversing means (57,58) reversing a relation in magnitude between said axial forces applied to said first and second pulleys (7,9) in accordance with a change in the direction in which torque is transmitted between said first and second pulleys (7,9); characterised in that said control means (54) comprises inhibition means (63) inhibiting reversal of said relation in magnitude between said axial forces applied to said first and second pulleys (7,9) performed by said axial force reversing means when a pulley ratio detected by said pulley-ratio detecting means (65) is within a predetermined pulley-ratio range including a pulley ratio for achieving said neutral state, wherein said axial force reversing means (57,58) comprises a ratio control valve (57) controlling one of hydraulic pressures supplied to said axial force applying means (32,33) and a down-shift valve (58) controlling the other of said hydraulic pressures supplied to said axial force applying means (32,33) and wherein said inhibition means (63) has a control valve (63), which is provided on the upstream side of said down-shift valve (58), to prevent a hydraulic pressure from being supplied to said down-shift valve (58). A continuously variable transmission according to Claim 1, wherein said axial force applying means (32,33) comprises a first hydraulic servo (32) for applying an axial force to said first pulley (7) and a second hydraulic servo (33) for applying an axial force to said second pulley (9). A continuously variable transmission according to claim 2, wherein said control means (54) supplies equal hydraulic pressures to first hydraulic chambers (45,46) of said first and second hydraulic servos (32,33) and said ratio control valve (57) is provided for controlling one of hydraulic pressures supplied to second hydraulic chambers (47,49) of said first and second hydraulic servos (32,33) and said down-shift valve (58) is provided for controlling the other of said hydraulic pressures supplied to said second hydraulic chambers (47,49) of said first and second hydraulic servos (32,33). A continuously variable transmission according to Claim 3, wherein said control means (54) selectively supplies a hydraulic pressure to either of said second hydraulic chambers (47,49) of said first or second hydraulic servo (32,33) by means of said axial force reversing means (57,58); and said control means (54) prevents the hydraulic pressure from being supplied to either of said second hydraulic chambers (47,49) by said axial force reversing means (57,58) by means of said inhibition means (63) when a pulley ratio detected by said pulley-ratio detecting means is within said predetermined pulley-ratio range A continuously variable transmission according to Claim 1, 2, 3 or 4 further comprising: a first clutch (C L ) for selectively engaging said input shaft (3) with said first rotary element (19c); a second clutch (C H ) for selectively engaging any two of said three rotary elements (19c,19s,19r) of said planetary gear (19) with each other; mode switching means (60) for switching operation between a low mode in which a large torque is generated by engaging said first clutch (C L ) and disengaging said second clutch (C H ) and a high mode in which a small torque is generated by engaging said second clutch (C H ) and disengaging said first clutch (C L ); and an auxiliary hydraulic path for supplying a hydraulic pressure of said second clutch (C H ) to said down-shift valve (58) without using said control valve (63) when said high mode is selected by said mode switching means (60). A continuously variable transmission according to any one of Claims 2 to 5, wherein said first pulley (7) has a first movable sheave (7b) driven with a hydraulic pressure supplied to said first hydraulic servo (32); said second pulley (9) has a second movable sheave (9b) driven with a hydraulic pressure supplied to said second hydraulic servo (33); said pulley-ratio detecting means (65) has a position detecting member (65b,65c) which accompanies one of said first and second movable sheaves (7b,9b) to detect the position of said one of said first and second movable sheaves (7b,9b); and said inhibition means (63) is coupled to said position detecting member (65c). A transmission according to any one of Claims 1 to 6, wherein said predetermined pulley-ratio range is set in the vicinity of a pulley ratio for achieving said neutral state and a pulley-ratio range for achieving said forward drive state as well as a pulley-ratio range for achieving a backward drive state. A transmission according to any one of Claims 1 to 7, wherein said inhibition means (63) inhibits reversal of said relation in magnitude between the axial forces applied to said first and second pulleys (7,9) performed by said axial force reversing means (57,58) to prevent a power-off down-shift when a pulley ratio detected by said pulley-ratio detecting means (65) is within said predetermined pulley-ratio range. A transmission according to any one of Claims 1 to 8, wherein said first, second and third rotary elements (19c,19s,19r) of said planetary gear (19) are a carrier, a sun gear and a ring gear respectively.

Inventors: HATTORI MASASHI, INUZUKA TAKESHI, TSUKAMOTO KAZUMASA, HATTORI, MASASHI, INUZUKA, TAKESHI, TSUKAMOTO, KAZUMASA, Hattori, Masashi, Aisin AW Co., Ltd.,, Inuzuka, Takeshi, Aisin AW Co., Ltd.,, Tsukamoto, Kazumasa, Aisin AW Co., Ltd.,
Applicants: AISIN AW CO, AISIN AW CO., LTD.
Application year: 1996
Main classification: F16H37
IPC codes: F16H61, F16H37