Hydraulic circuit for belt-type continuously variable transmission

Abstract: Disclosed is an oil-hydraulic circuit of a belt-type continuous variable speed-change transmission, in which at the time when a failure occurs in a solenoid valve 81 or 82, the line pressure of a necessary minimum level is ensured through increasing the oil-hydraulic operating fluid supplied to a secondary pulley 41. On the other hand, the discharge side of a regulator valve 63 and a primary pulley 31 are maintained in a state of mutual communication to thereby make the speed-change ratio equal to or smaller than 1. Also, when the oil pressure supplied to the secondary pulley 41 has increased up to a prescribed, or higher than prescribed, level, this oil pressure that is supplied thereto is reduced by means of a second outlet valve 90. As a result of this, in the oil-hydraulic circuit, even when a failure occurs in the control circuit, the safety of driving of the vehicle is reliably ensured with a simple construction of the oil-hydraulic circuit. This enables the simplification of the oil-hydraulic circuit and the reduction in the cost.

Description: BACKGROUND OF THE INVENTION: FIELD OF THE INVENTION The present invention relates to an oil-hydraulic circuit of a belt-type continuous variable speed-change transmission. DESCRIPTION OF THE RELATED ART A belt-type continuous variable speed-change transmission generally is so arranged as to stretch a belt over both a primary pulley connected to the input shaft and a secondary pulley connected to the outlet shaft. By increasing and decreasing oil pressure of the respective cylinders of those pulleys and by causing a relative change in the respective groove widths of such pulleys, the transmission causes a change in the speed. As a conventional control apparatus for use on this belt-type continuous variable speed-change transmission, there is, for example, the one that is disclosed in Japanese Patent No. 2848177. However, in this conventional control apparatus for use on the belt-type continuous variable speed-change transmission, to provide for a simple case where the first or the second control valve is not functioning properly, the third control valve and the speed-change-limiting valve must be additionally provided. Therefore, there exists the problem that the cost of the product inconveniently rises due to an increase in the number of parts. From US-A-5 334 102, or DE-A-19721027, there is already known an oil-hydraulic circuit of a belt-type continuous variable speed-change transmission according to the preamble of claim 1. The present invention as defined by the features of claim 1 has been made in order to improve the above-described known circuit concretely. Further embodiments of the invention are illustrated in the sub-claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view illustrating an oil-hydraulic circuit of a belt-type continuous variable speed-change transmission according to an embodiment of the present invention; Fig. 2 is a schematic construction view illustrating a drive apparatus of the vehicle to which the belt-type continuous variable speed-change transmission of this embodiment is applied; and Fig. 3 is a schematic construction view illustrating the belt-type continuous variable speed-change transmission of this embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will hereafter be explained in detail with reference to the drawings. Fig. 1 illustrates the oil-hydraulic circuit of a belt-type continuous variable speed-change transmission according to an embodiment of the present invention; Fig. 2 illustrates a schematic construction of a drive apparatus of the vehicle to which the belt-type continuous variable speed-change transmission of this embodiment is applied; and Fig. 3 illustrates a schematic construction of the belt-type continuous variable speed-change transmission of this embodiment. In the drive apparatus to which the belt-type continuous variable speed change transmission of this embodiment is applied, as illustrated in Fig. 2, it is arranged that the torque outlet from an engine (internal combustion engine) 11 be transmitted to the belt-type continuous variable speed change transmission 14 via a torque converter 12 and a normal-/reverse-rotation switching mechanism 13, and it is arranged that the torque be transmitted from this belt-type continuous variable speed-change transmission 14 to right and left drive wheels 16 via a front differential 15. The normal-/reverse-rotation switching mechanism 13 is intended for the purpose of switching from forward to backward movement or vice versa and has a reverse brake 21 and a forward clutch 22. As illustrated in Fig. 3, the belt-type continuous variable speed-change transmission 14 comprises a primary pulley 31 connected to the outlet end of the engine 11, a secondary pulley 41 connected to the drive-shaft side of the vehicle, and a belt 51 stretched over both pulleys 31 and 41. The rotating force input from the normal-/reverse-rotation switching mechanism 13 to the primary shaft 32 is transmitted from the primary pulley 31 to the secondary pulley 41 via the belt 51 and is then transmitted to a secondary shaft 42. Namely, the primary pulley 31 has a stationary sheave 33 and a movable sheave 34. A primary cylinder 31a is formed on a rear-surface side of the movable sheave 34. Accordingly, by the supplying or draining of an oil-hydraulic operating fluid of the primary cylinder 31a, it is possible to move the movable sheave 34 with respect to the stationary sheave 33 and thereby make variable the groove width of the pulley. On the other hand, similarly, the secondary pulley 41 has a stationary sheave 43 and a movable sheave 44. A secondary cylinder 41a is formed on the rear side of the movable sheave 44. Accordingly, by the supplying or draining of the oil-hydraulic operating fluid of the secondary cylinder 41a, it is possible to move the movable sheave 44 with respect to the stationary sheave 43 and thereby make variable the groove width of the pulley. In this case, the piston of the secondary cylinder 41a has its pressure-receiving area set to be at around 1/2 of that of the piston of the primary cylinder 31a. The secondary cylinder 41a has applied thereto a secondary oil pressure Ps (line pressure PL) that has been adjusted by a regulator valve 63 serving as a pressure regulator valve that is the pressure-regulating element, while the primary cylinder 31a has applied thereto a primary oil pressure Pp that has been obtained by adjusting the line pressure PL by a speed-change-ratio controlling valve 64 that is the speed-change-ratio controlling element. It is to be noted that a reference numeral 61 denotes an oil pan; and a reference numeral 62 denotes an oil pump for supplying the oil within the oil pan 61 to the regulator-valve 63 side. The secondary oil pressure Ps (line pressure PL) and the primary oil pressure Pp are each controlled according to an instruction signal from an electronic control unit (ECU) 65. Namely, the ECU 65 is arranged to have input thereto detection signals from an engine revolution speed sensor (a crank angle sensor or a cam angle sensor) 71, a throttle opening sensor 72, a primary rotational-speed sensor 73 for sensing the rotational speed of the primary pulley 31, a secondary rotational-speed sensor 73 for sensing the rotational speed of the secondary pulley 41, a line-pressure sensor 75 for sensing the line pressure, a vehicle-speed sensor 76, a shift position sensor 77 for sensing the position of the shift lever, a primary-pressure sensor 78 for sensing the primary pressure, etc. It is arranged that the ECU 65 control the regulator valve 63 and the speed-change-ratio controlling valve 64 in the system of supplying the oil-hydraulic fluid to the respective pulleys 31 and 41 according to these detection signals. It is to be noted that, in place of the throttle-opening sensor 72, there may be used a sensor for sensing a parameter value indicating the load on the engine. Here, the oil-hydraulic circuit of the belt-type speed-change transmission according to this embodiment will be explained. As illustrated in Fig. 1, the regulator valve 63 has spools 63a and 63b, between which there is disposed a spring 63c serving as a first urging-force-generating element. The speed-change-ratio-controlling valve 64 has spools 64a and 64b. Between one end of the spool 64a and an end surface of the housing is disposed a spring 64c serving as a second urging-force-generating element while between the spools 64a and 64b is disposed a spring 64d. An oil-hydraulic operating fluid introduction port 63d of the regulator valve 63 is connected to a discharge port of an oil-hydraulic pump 62 while a discharge port 63e is connected to the secondary cylinder 41a and simultaneously is connected to an oil-hydraulic operating fluid introduction port 64e of the speed-change-ratio-controlling valve 64. Also, a discharge port 64f of the speed-change-ratio-controlling valve 64 is connected to the primary cylinder 31a. Solenoid valves 81 and 82 that are first and second control elements, respectively, and that are used as first and second electromagnetic valves, respectively, control the regulator valve 63 and the speed-change-ratio-controlling valve 64. Namely, the solenoid valve 81 supplies a control pressure Pva to one side of the regulator valve 63 through a first operating-oil passage 83. Also, the solenoid valve 82 supplies a control pressure Pvb to one side of the speed-change-ratio-controlling valve 64 through a second operating-oil passage 84. It is to be noted that these solenoid valves 81 and 82 are each of a normal-close-type valve. And it is arranged that each of such solenoid valves be duty controlled through the operation of the ECU 65 (operation-controlling element) and be operated according to an amount of electricity supplied from the ECU 65. Further, it is arranged that as the amounts of electricity supplied to the solenoid valves 81 and 82 become smaller, i.e. as the action of the solenoid valves 81 and 82 becomes smaller, the control pressure Pva and the control pressure Pvb discharged from the solenoid valves 81 and 82 also become lower. On the other hand, when it has been detected by the ECU 65 ( failure-detecting element) that the ECU 65 itself, solenoid valves 81 and 82, various sensors, etc. are improperly functioning, the ECU 65 stops supplying electricity to the solenoid valves 81 and 82. As a result of this, the solenoid valves 81 and 82 decrease in operation, with the result that the respective control pressures Pva and Pvb of the solenoid valves 81 and 82 also decrease. As a result, the regulator valve 63 and the speed-change-ratio-controlling valve 64 are respectively moved by the spring pressure of the spring 63c and reducing pressure Pred, and by the spring pressure of the spring 64c and reducing pressure Pred. As a result, the oil-hydraulic operating fluid supplied to the secondary cylinder 41a is increased. On the other hand, the state of communication between the oil-hydraulic operating fluid introduction port 64e and the discharge port 64f of the speed-change-ratio-controlling valve 64 is maintained as is. Further, on a branch passage 86 that branches from a midway position of a line pressure passage 85 that connect the discharge port 63e of the regulator valve 63 with the secondary cylinder 41a and that connects to the oil-hydraulic operating fluid introduction port 64e of the speed-change-ratio-controlling valve 64 there is disposed a first outlet valve 87. Also, on an operating-oil passage 88 that connect the discharge port 64f of the speed-change-ratio-controlling valve 64 with the primary pulley 31 there is disposed a outlet valve 90 serving as oil-pressure-reducing means through a communication passage 89. The first outlet valve 87 has a spool 87a and a spring 87b for urging the spool 87a in the direction so that it prevents the oil from being drained from the first outlet valve 87. The second outlet valve 90 also has a spool 90a and a spring 90b for urging the spool 90a in the direction so that it prevents oil from being drained from the valve 90. The set outlet pressure of the first outlet valve 87 is set to be at a level higher than that of the second outlet valve 90. Accordingly, even when the solenoid valves 81, 82, ECU 65, etc. are in order, in the case where the regulator valve 63 becomes inoperable due to a valve stick, etc. and there arises in the line-pressure passage 85 a line pressure P equal to or higher than the set value (the set outlet pressure of the first outlet valve 87), it becomes possible to decrease the line pressure PL through operation of the first outlet valve 87. On the other hand, even when a solenoid valve 81, 82 , or ECU 65, etc. gets out of order and the line pressure PL goes up, since the state of communication between the oil-hydraulic operating fluid introduction port 64e and the discharge port 64f of the speed-change-ratio-controlling valve 64 is maintained as is, the line pressure PL is decreased by the second outlet valve 90. An unnecessary rise in the level of the line pressure PL is thereby prevented. Here, as a result of the disposition of the second outlet valve 90 on the operating-oil passage 88 between the speed-change-ratio controlling valve 64 and the primary cylinder 31a, even at the time of normal travel, no oil pressure equal to or higher than the set outlet pressure of the second outlet valve 90 acts upon the primary cylinder 31a. In the continuous variable speed-change transmission in which it is possible for the same oil pressure to be supplied to the primary cylinder 31a and secondary cylinder 41a, the case where the highest line pressure acts upon the primary cylinder 31a for some reason or other is to be considered, although such a case should never be allowed to occur. Further, in a type of continuous variable speed-change transmission wherein the piston pressure-receiving area of the primary pulley 31 is made larger than that of the secondary pulley 41, a force greater than that acting upon the secondary pulley 41 acts upon the primary pulley 31. Therefore, it is necessary to increase the strength of the primary pulley side. However, such parts design where prevention of malfunctioning is also taken into consideration leads to an increase in the cost, and therefore such designing is not appropriate. However, in the construction of this embodiment, owing to the second outlet valve 90 provided between the speed-change-ratio-controlling valve 64 and the primary cylinder 31a, the increase in the line pressure PL is prevented. Therefore, it is possible to design the primary pulley 31 side to be at a strength value conforming to the set outlet pressure of the second outlet valve 90. This eliminates the necessity of making a "high-spec" design for which a great increase in the line pressure PL is prepared, thereby enabling a reduction in the cost. Also, an outlet passage 91 of the second outlet valve 90 is connected to a lubrication passage (not illustrated) of the continuous variable speed-change transmission. Accordingly, because at the time when a failure occurs in the ECU 65, etc. the line pressure PL is conjectured to become the highest possible, the oil-hydraulic operating fluid outlet from the regulator valve 63 is decreased to become somewhat deficient in lubrication. However, since the operating oil outlet from the second outlet valve 90 is supplementarily supplied to the lubrication passage through the outlet passage 91, it is possible to prevent the seizure of the portions such as the normal-/reverse-rotation switching mechanism 13 which should be lubricated. Additionally, in Fig. 1, the line pressure PL that has been adjusted by the regulator valve 63 is led to the introduction port 92a of a reducing valve 92. The reducing pressure Pred that has been obtained by decreasing the line pressure PL with the reducing valve 92 is supplied to the regulator valve 63, speed-change-ratio-controlling valve 64, and outlet valves 87, 90 through the discharge port 92b. And it is thereby arranged that the prescribed control pressure acts upon each of those valves. Especially, the reducing pressure Pred supplied to the regulator valve 63 acts upon the regulator valve 63 so as to urge this valve 63 in the direction (the leftward direction in Fig. 1) causing an increase in the secondary pressure Ps (line pressure PL) supplied to the secondary cylinder 41a, as the spring 63c does. Also, the reducing pressure Pred supplied to the speed-change-ratio-controlling valve 64 acts upon the speed-change-ratio-controlling valve 64 so as to urge this valve 64 in the direction (the rightward direction in Fig. 1) causing an increase in the primary pressure Pp supplied to the primary cylinder 31a, i.e. the direction causing an increase in the amount of the line pressure PL regulated by the regulator valve 63 and supplied to the primary cylinder 31a, as the spring 64c does. Also, the reducing pressure Pred serves as the base pressure for each of the solenoid valves 81 and 82. The operation of the belt-type continuous variable speed-change transmission of this embodiment will now be explained. The solenoid valves 81 and 82 are duty controlled according to the instruction from the ECU 65 based on the operational condition of the vehicle, and outlet the control pressures Pva and Pvb. The regulator valve 63 adjusts the discharge pressure of the oil-hydraulic pump 62 to the secondary oil pressure Ps (line pressure PL), adjusting for the control valve Pva, the spring pressure of the spring 63c, the reducing pressure Pred from the reducing valve 92, etc., and outlets the resulting pressure to the line-pressure passage 85. When the control pressure Pva from the solenoid valve 81 is high, the spool 63a is urged to the right in the illustration against the spring pressure of the spring 63c and the reducing pressure Pred. As a result, the state of communication between the oil-hydraulic operating fluid introduction port 63d and the discharge port 63e is contracted, with the result that the secondary pressure Ps (line pressure PL), which is the oil pressure supplied to the secondary cylinder 41a, is reduced. On the other hand, when the control pressure Pva is low, the spool 63a is urged to the left in the illustration by the spring pressure of the spring 63c and the reducing pressure Pred. As a result, the state of communication between the oil-hydraulic operating fluid introduction port 63d and the discharge port 63e is expanded, with the result that the secondary pressure Ps (line pressure PL), which is the oil pressure supplied to the secondary cylinder 41a, is increased. On the other hand, the speed-change-ratio-controlling valve 64 adjusts the line pressure PL to a prescribed primary oil pressure Pp adjusting for the control pressure Pvb, the spring pressures of the springs 64c and 64d, the reducing pressure Pred from the reducing valve 92, etc., and discharges the resulting pressure to the operating-oil passage 88. When the control pressure Pvb from the solenoid valve 82 is high, the spool 64a is urged to the left in the illustration against the spring pressure of the spring 64c and the reducing pressure Pred. As a result, the communication between the oil-hydraulic operating fluid introduction port 64e and the discharge port 64f of the speed-change-ratio-controlling valve 64 is cut off while, at the same time, the discharge port 64f and the outlet port 64g are communicated with each other. The operating oil of the primary cylinder 31a is outlet. Conversely, when the control pressure Pvb of the solenoid valve 82 becomes low, the spool 64a of the speed-change-ratio-controlling valve 64 is urged to the right in the illustration by the spring pressure of the spring 64c and the reducing pressure Pred. As a result, the outlet port 64g is cut off while, at the same time, the oil-hydraulic operating fluid introduction port 64e and the discharge port 64f are communicated with each other. And, as the control pressure Pvb is lower, the state of communication between the port 64e and the port 64f is more expanded. As a result, the amount of the line pressure PL, that has been regulated by the regulator valve 63, and that is supplied to the primary cylinder 31a, is increased, with the result that the primary oil pressure Pp becomes high. This primary pressure Pp is supplied to the primary cylinder 31a. Also, even when the solenoid valves 81, 82, ECU 65, various sensors, etc. are normally in order, it is possible that valve sticking, etc. occurs in the regulator valve 63 due to the dust, etc. that has entered the oil and thus a line pressure PL that is higher than the set value, occurs. However, this line pressure PL is reduced through the operation of the first outlet valve 87 disposed on the branch passage 86. Due to the line pressure PL that has become high, the spool 87a is moved to the right in the illustration against the spring pressure of the spring 87b. Then, the branch passage 86 and the outlet port 87c of the first outlet valve 87 become communicated with each other . As a result, the line pressure PL that has become abnormally high is drained through this outlet port 87c, with the result that an abnormal rise in the line pressure PL is prevented. Now, assume that, during the travel of the vehicle, the solenoid valve 81 has malfunctioned, e.g. has undergone breakage of its wire. Then, the ECU 65 detects the wire breakage of the solenoid valve 81 and stops controlling all solenoid valves. Since each of the both solenoid valves 81 and 82 is of a normal-close-type, when control is stopped the respective control pressures Pva and Pvb become zero. Therefore, in the regulator valve 63, the spool 63a is moved to the left in the illustration due to the spring pressure of the spring 63c, whereby adjustment of the pressure is made so that the secondary oil pressure Ps (line pressure PL) increases to the maximum. On the other hand, in the speed-change-ratio-controlling valve 64, the spool 64a is moved to the right in the illustration due to the spring pressure of the spring 64c and the reducing pressure Pred. As a result, the oil-hydraulic operating fluid introduction port 64e and the discharge port 64f are brought to the state of mutual communication, whereby the line pressure PL, which had been regulated by the regulator valve 63, continues to be supplied to the primary cylinder 31a. The maximum line pressure, which had been regulated by the regulator valve 63, is caused to act upon the primary cylinder 31a directly. However, because the second outlet valve 90 is disposed in the communication passage 89 branching from the midway of the operating-oil passage 88, the maximum line pressure supplied to the primary cylinder 31a acts upon the port 90c of the second outlet valve 90. As a result, the spool 90a is pushed to the right in the illustration against the spring 90b. Then, the port 90c and the port 90d become communicated with each other. But, because the port 90d is the outlet port connected to the portions where lubrication is necessary, the maximum line pressure is reduced down to a prescribed pressure by the second outlet valve 90. This pressure-reduced operating oil is then supplied to the primary cylinder 31a. It is to be noted that that prescribed pressure is set as the minimum necessary pressure at which no slip occurs of the belt 51. Accordingly, the line pressure PL is ensured to be at least a minimum necessary level capable of preventing the slip of the belt. As a result, it is possible to decrease the loss of drive power to the oil pump and, even at the time of a failure, to reduce the consumption of the fuel. On the other hand, in the regulator valve 63, the line pressure PL is reliably adjusted so that this pressure PL may have the highest level, as a result of the stoppage of control by the solenoid valve 81. However, because the line pressure PL is reduced down to the prescribed pressure by the second outlet valve 90 through the speed-change-ratio-controlling valve 64 with which the branch passage 86 (oil-hydraulic operating fluid introduction port 64e) and the operating-oil passage 88 (discharge port 64f) are kept in the state of mutual communication, the line pressure PL that has been reduced down to that prescribed pressure is supplied to the secondary cylinder 41a as well. Also, in this way, it results that the line pressure, the same in level, is supplied to the primary cylinder 31a and to the secondary cylinder 41a. However, because the piston pressure-receiving area of the primary cylinder 31a is set at a value approximately twice as great as that of the secondary cylinder 41a, the groove width of the primary pulley 31 is narrower and that of the secondary pulley 41 is wider. Accordingly, the change-of-speed ratio is adjusted to the over-drive (OD) side. For this reason, for example, even when a failure occurs during high-speed driving, because the change-of-speed ratio is OD, it is possible to prevent the over-fast revolution of the engine. Further, in the construction of this embodiment, by stopping control by the solenoid valves 81, 82 when a failure has occurred, the control logic executed for fail-safe operation is simplified. On the other hand, because, at the same time, the maximum line pressure adjusted by the regulator valve 63 is also reduced by the second outlet valve 90, and for that reason the design specifications of the primary pulley 31 side can be at values ordinarily used heretofor. It is thereby advantageously possible to suppress the cost. Also, when a failure is detected, the oil-hydraulic operating fluid supplied to the secondary cylinder 41a is increased due to the spring pressure of the spring 63c and the reducing pressure Pred in the regulator valve 63. And, on the other hand, there continues to be supplied to the primary cylinder 31a the line pressure PL due to the oil-hydraulic operating fluid introduction port 64e and discharge port 64f of the speed-change-ratio-controlling valve 64 being communicated with each other due to the spring pressure of the spring 64c and reducing pressure Pred in the speed-change-ratio-controlling valve 64. Since, in this way, the oil-hydraulic circuit is constructed without separately providing any special control valves for fail-safe operations, the oil-hydraulic circuit can be simplified and therefore reduced in cost. Further, at the time when a failure occurs in the solenoid valve 81, the regulator valve 63 operates so that the line pressure PL may be made the highest. As a result the amount of the oil discharged from the regulator valve 63 decreases to become insufficient for lubrication. However, because the operating oil drained from the second outlet valve 90 is supplemented to the lubrication passage through the outlet passage 91, it is possible thereby to prevent the seizure of the portions where lubrication is necessary. Additionally, in the foregoing description, an explanation has been given of an example wherein the fail-safe operation element for maximizing the line pressure and simultaneously causing the line pressure PL to continue to be supplied to the primary cylinder 31a at the time of a failure of the solenoid valve 81 is made up of the springs 63c, 64c and the reducing pressure Pred. However, this fail-safe operation element may be made up only of either the springs 63c, 64c or the reducing pressure Pred, or be made up of other elements. Further, in the foregoing description, an explanation has been given of a case where a failure has occurred in the solenoid valve 81 during the driving of the vehicle. However, in any case where a failure has occurred in the solenoid valve 82 or a case where a failure has occurred in the ECU 65, various sensors, etc., the control by the solenoid valves 81, 82 is stopped to make zero each of the control pressures Pva, Pvb. Therefore, the operation becomes the same as that stated above. As has been explained in detail in the above-described embodiment, according to the oil-hydraulic circuit of the belt-type continuous variable speed-change transmission of the present invention, when a failure is detected, the slip of the belt can be prevented by increasing the oil-hydraulic operating fluid supplied to the secondary cylinder. Also, the operating oil, the pressure of which has been regulated by the pressure-regulating element, is maintained while it is supplied to the primary cylinder. By maintaining this supply, the same high oil pressure is supplied to the secondary pulley and the primary pulley. However, the secondary pulley is constructed to have a piston pressure-receiving area equal to or smaller than that of the primary pulley and, therefore, the change-of-speed ratio is made to be a value equal to or smaller than 1. For this reason, even when a failure occurs during high-speed driving, the engine is prevented from making over-fast revolution to thereby prevent the breakage of the engine. 31a primary cylinder 41a secondary cylinder 63 regulator valve 64 speed-change-ratio controlling valve 81,82 solenoid valve 87 first outlet valve 90 second outlet valve

Claims: An oil-hydraulic circuit of a belt-type continuous variable speed-change transmission, the belt-type continuous variable speed-change transmission including: a primary pulley (31) connected to the input shaft side; a secondary pulley (41) connected to the outlet shaft side; a belt (51) stretched over both pulleys and enabling the transmission of power between the both pulleys; an oil-hydraulic secondary cylinder (41a) that makes variable the groove width of the secondary pulley; and an oil-hydraulic primary cylinder (31a) that makes variable the groove width of the primary pulley and that is formed so that a pressure-receiving area thereof is larger than that of the secondary cylinder; whereby, by performing the supply and outlet of an oil-hydraulic operating fluid with respect to each of the cylinders, the groove width of either the primary pulley or secondary pulley is changed relative to the groove width of the other thereof to thereby cause a change in the speed, the oil-hydraulic circuit comprising: a pressure-regulating element (63) that regulates the oil-hydraulic operating fluid supplied to the secondary cylinder; a first control element (81) that controls the pressure-regulating element; a speed-change-ratio-controlling element (64) that, by performing the supply or outlet of the operating oil pressure-regulated by the pressure-regulating element with respect to the primary cylinder, controls the change-of speed ratio of the belt-type continuous variable speed-change transmission; a second control element (82) that controls the speed change ratio controlling element; an operation-controlling element (65) that operationally controls the first control element and the second control element according to the state of operation of the vehicle; a failure-detecting element (65) that detects a failure of the first control element, second control element, or operation-controlling element; and a fail-safe operation element that, when the failure-detecting element has detected a failure, causes an increase in the oil-hydraulic operating fluid supplied to the secondary cylinder and simultaneously causes the operating oil pressure-regulated by the pressure-regulating element to continue to be supplied to the primary cylinder, characterized in that an oil-pressure-reducing means (90) is disposed in the oil passage between the pressure-regulating element (63) and the primary cylinder, the oil-pressure-reducing means (90) reducing the oil pressure within the oil passage when the oil pressure has become equal to or higher than a prescribed value, wherein said oil-pressure-reducing means includes a first outlet valve (87) disposed in said oil passage between said pressure-regulating element (63) and said speed-change-ratio-controlling element (64) and the set outlet pressure of the first outlet valve (87) is set to be at a level higher than that of said oil-pressure-reducing means (90). An oil-hydraulic circuit of a belt-type continuous variable speed-change transmission as set forth in claim 1, wherein the oil-pressure-reducing means (90) is disposed between the speed-change-ratio-controlling element and the primary cylinder. An oil-hydraulic circuit of a belt-type continuous variable speed-change transmission as set forth in claim 1, wherein the outlet passage of the oil-pressure-reducing means (90) is connected to a lubrication passage. An oil-hydraulic circuit of a belt-type continuous variable speed-change transmission as set forth in claim 1, wherein the pressure-regulating element (63) is constructed so that, when there is less action of the first control element (81), the oil-hydraulic operating fluid supplied to the secondary cylinder is increased; the speed-change-ratio-controlling element (64) is constructed so that, when there is less action of the second control element (82), the amount of the oil-hydraulic operating fluid pressure-regulated by the pressure-regulating element (63) and supplied to the primary cylinder is increased; and when the failure-detecting element (65) has detected a failure, the fail-safe operation element causes a reduction in the action of the first control element (81) and that of the second control element (82). An oil-hydraulic circuit of a belt-type continuous variable speed-change transmission as set forth in claim 4, wherein the first control element (81) is constructed of a first electromagnetic valve that discharge a control pressure according to the electricity supplied from the operation-controlling element (65) ; the second control element (82) is constructed of a second electromagnetic valve that discharges the control pressure according to the electricity supplied from the operation-controlling element (65) ; the pressure-regulating element (63) is constructed of a pressure-regulating valve; the speed-change-ratio-controlling element (64) is constructed of a speed-change-ratio-controlling valve, whereby, the control pressure discharged from the first electromagnetic valve is led to one side of the pressure-regulating valve (63) through a first operating-oil passage (83), with the result that the pressure-regulating valve is controlled according to the control pressure from the first electromagnetic valve while the control pressure discharged from the second electromagnetic valve is led to one side of the speed-change-ratio-controlling valve (64) through a second operating-oil passage (84), with the result that the speed-change-ratio-controlling valve is controlled according to the control pressure from the second electromagnetic valve; and the fail-safe operation element includes a first urging-force generating element (63 c) that is disposed on the other side of the pressure-regulating valve and that generates an urging force resisting the control pressure of the first electromagnetic valve lessens the oil-hydraulic operating fluid supplied by the pressure-regulating valve to the secondary cylinder increases; and a second urging-force generating element (64 c) that is disposed on the other side of the speed-change-ratio-controlling valve and that generates an urging force resisting the control pressure of the second electromagnetic valve by which as the control pressure from the second electromagnetic valve lessens, the amount of the operating oil pressure-regulated by the pressure-regulating valve and supplied to the primary cylinder increases.

Inventors: MIZUI HIROYUKI, MIZUI, HIROYUKI, Mizui, Hiroyuki, c/o Mitsubishi Jidosha Kogyo K.K.
Applicants: MITSUBISHI MOTORS CORP, MITSUBISHI JIDOSHA KOGYO KABUSHIKI KAISHA
Application year: 2000
Main classification: F16H61
IPC codes: F16H61, F16H9