Hydraulic circuit

Abstract

To provide a hydraulic circuit capable of suppressing clogging of a filter for preventing intrusion of foreign matters from a hydraulic actuator to a control valve, in the hydraulic circuit in which an oil bidirectionally flows between the control valve and the hydraulic actuator.SOLUTION: A hydraulic circuit 1 includes: a secondary hydraulic passage 71 which communicates a control valve 13 with a secondary drive oil chamber 132 and in which an oil bidirectionally flows; a filter 73 interposed in a secondary hydraulic passage 71 for capturing foreign matters in the oil discharged to the control valve 13 from the secondary drive oil chamber 132; a second oil passage 72 for communicating a downstream side of the filter 73 of the secondary hydraulic passage 71 with an oil pan 11; and a selector valve 75 for opening the secondary hydraulic passage 71 and closing the second oil passage 72 when an oil pump 10 is driven, and closing the secondary hydraulic passage 71 and opening the second oil passage 72 when the oil pump 10 is stopped.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a hydraulic circuit. [Background technology]

[0002] An automatic transmission for a vehicle (for example, a stepped automatic transmission (Step AT) or a continuously variable transmission (CVT)) is equipped with an oil pump that is driven by engine power and discharges high-pressure oil, and the high-pressure oil discharged from the oil pump is adjusted by a control valve (valve body) and supplied to various components to achieve various functions such as gear shifting and forward / reverse switching.

[0003] Here, because the control valve is vulnerable to foreign matter (contamination) getting caught in it, an oil strainer, which is a filtering device that captures and removes foreign matter in the oil, is usually provided upstream of the oil pump. That is, the oil pump draws in oil stored in the oil pan, raises the pressure, and supplies it to the control valve through the oil strainer, which captures foreign matter in the oil to prevent foreign matter from entering the control valve.

[0004] For example, Patent Document 1 discloses a hydraulic oil filtration device for a continuously variable transmission that has a secondary pressure regulating valve that regulates the pressure of hydraulic oil discharged from an oil pump driven by an engine and supplies it to an oil chamber of a secondary cylinder that changes the pulley groove width of a secondary pulley, a clutch pressure regulating valve that is provided in a clutch pressure path that connects a drain port of the secondary pressure regulating valve with a forward clutch and a reverse brake and that regulates clutch pressure using the drain pressure of the secondary pressure regulating valve as a source pressure, and a filter provided upstream of the clutch pressure path, and that filters the hydraulic oil supplied via the clutch pressure path using the filter.

[0005] According to this hydraulic oil filter device for a continuously variable transmission, the hydraulic oil discharged from the drain port of the secondary pressure regulating valve is cleaned of foreign matter (contamination) and then supplied to each of the valves, oil chambers, bearings and sliding parts that make up the hydraulic circuit of the continuously variable transmission, thereby making it possible to maintain the control performance of the continuously variable transmission, prevent a decrease in function, and maintain and improve the reliability and durability of each sliding part. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2001-221324 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, there are cases where bidirectional oil (hydraulic oil) flows exist in one oil passage. More specifically, for example, in an oil passage that communicates a hydraulic actuator (such as a hydraulic cylinder of a continuously variable transmission pulley) with a switching valve that is provided in a control valve and switches between supplying and discharging oil to the hydraulic actuator, the flow of oil reverses (reverses) when the oil is being supplied and when it is being discharged.

[0008] In an oil passage in which oil flows in both directions between such a control valve (switching valve) and hydraulic actuator, if an attempt is made to interpose a filter between the hydraulic actuator and the control valve to capture foreign matter in the oil to prevent foreign matter (contamination) from entering the control valve from the hydraulic actuator, it is expected that the filter will trap the foreign matter and become clogged, causing a decrease in hydraulic function, such as increased pressure loss in the hydraulic circuit and reduced responsiveness.

[0009] The present invention has been made to solve the above problems, and has an object to provide a hydraulic circuit in which oil flows in both directions between a control valve and a hydraulic actuator, capable of suppressing clogging of a filter that prevents foreign matter (contamination) from entering the control valve from the hydraulic actuator. [Means for solving the problem]

[0010] A hydraulic circuit according to one aspect of the present invention is characterized in that it includes an oil pump that sucks in, pressurizes, and discharges oil stored in an oil pan through an oil strainer that captures foreign matter in the oil; a control valve that adjusts the oil pressure of a hydraulic actuator using the oil discharged from the oil pump; a first oil passage that connects the control valve to the hydraulic actuator and through which oil supplied from the control valve to the hydraulic actuator and oil discharged from the hydraulic actuator to the control valve flow in both directions; a filter that is interposed in the first oil passage and captures foreign matter in the oil discharged from the hydraulic actuator to the control valve; a second oil passage that connects between the filter of the first oil passage and the hydraulic actuator and the oil pan; and a changeover valve that opens the first oil passage and closes the second oil passage when the oil pump is driven, and closes the first oil passage and opens the second oil passage when the oil pump is stopped.

[0011] According to a hydraulic circuit according to one aspect of the present invention, a filter is provided in a first oil passage that communicates between a control valve and a hydraulic actuator and through which oil flows in both directions, and the first oil passage is opened when the oil pump is driven. Therefore, foreign matter in the oil from the hydraulic actuator is captured by the filter so as not to enter the control valve. Then, when the oil pump is stopped, the first oil passage is closed and a second oil passage that communicates between the filter of the first oil passage and the hydraulic actuator and the oil pan is opened. Therefore, the foreign matter captured by the filter is discharged through the second oil passage. Also, when the next oil pump starts to be driven, the discharged foreign matter is sucked (sucked) into the oil strainer by the suction negative pressure of the oil pump, and can be filtered out (collected collectively) by the oil strainer. Effect of the Invention

[0012] According to the present invention, in a hydraulic circuit in which oil flows in both directions between a control valve and a hydraulic actuator, it is possible to suppress clogging of a filter that prevents foreign matter (contamination) from entering the control valve from the hydraulic actuator. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram showing a configuration of a hydraulic circuit according to the embodiment. [Diagram 2] 1 is a diagram showing a configuration of a continuously variable transmission to which a hydraulic circuit according to an embodiment is applied; [Diagram 3] FIG. 4 is a diagram for explaining the operation of the hydraulic circuit according to the embodiment (a diagram showing the state of the hydraulic circuit (spool, etc.) when the oil pump is driven). [Figure 4] FIG. 4 is a diagram for explaining the operation of the hydraulic circuit according to the embodiment (a diagram showing the state of the hydraulic circuit (spool, etc.) when the oil pump is stopped). [Diagram 5]FIG. 4 is a diagram for explaining the operation of the hydraulic circuit according to the embodiment (a diagram showing the state of the hydraulic circuit (spool, etc.) when the oil pump starts to be driven). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals will be used for the same or corresponding parts. In each drawing, the same reference numerals will be used for the same elements, and duplicated explanations will be omitted.

[0015] First, the configuration of a hydraulic circuit 1 according to an embodiment will be described with reference to Fig. 1 and Fig. 2. Note that, here, the present invention will be described as being applied to a secondary pulley 131 of a continuously variable transmission (CVT) 110. Fig. 1 is a diagram showing the configuration of the hydraulic circuit 1. Fig. 2 is a diagram showing the configuration of the continuously variable transmission 110 to which the hydraulic circuit 1 is applied.

[0016] The continuously variable transmission 110 is connected to a crankshaft of an engine 160 via, for example, a torque converter (not shown), and converts and outputs driving force from the engine 160. The continuously variable transmission 110 has a primary shaft (input shaft) 120 connected to an output shaft of the torque converter, and a secondary shaft (output shaft) 130 disposed in parallel to the primary shaft 120.

[0017] A primary pulley 121 is provided on the primary shaft 120. The primary pulley 121 has a fixed sheave 121a joined to the primary shaft 120 and a movable sheave 121b opposed to the fixed sheave 121a and attached to be slidable in the axial direction of the primary shaft 120 and non-rotatable relative thereto, and is configured to be able to change the cone surface spacing between the sheaves 121a and 121b, i.e., the pulley groove width. On the other hand, a secondary pulley 131 is provided on the secondary shaft 130. The secondary pulley 131 has a fixed sheave 131a joined to the secondary shaft 130 and a movable sheave 131b opposed to the fixed sheave 131a and attached to be slidable in the axial direction of the secondary shaft 130 and non-rotatable relative thereto, and is configured to be able to change the pulley groove width.

[0018] A chain 140 for transmitting a driving force is stretched between the primary pulley 121 and the secondary pulley 131. The gear ratio is continuously changed by changing the groove width of the primary pulley 121 and the secondary pulley 131 to change the ratio (pulley ratio) of the winding diameter of the chain 140 to each of the pulleys 121, 131. If the winding diameter of the chain 140 around the primary pulley 121 is Rp and the winding diameter of the chain 140 around the secondary pulley 131 is Rs, the gear ratio i is expressed as i=Rs / Rp. Moreover, the gear shift speed is expressed as di / dt.

[0019] Here, a primary driving oil chamber (hydraulic cylinder chamber) 122 is formed in the primary pulley 121 (movable sheave 121b). Meanwhile, a secondary driving oil chamber (hydraulic cylinder chamber) 132 is formed in the secondary pulley 131 (movable sheave 131b). The groove widths of the primary pulley 121 and the secondary pulley 131 are set and changed by adjusting the primary hydraulic pressure introduced into the primary driving oil chamber 122 and the secondary hydraulic pressure introduced into the secondary driving oil chamber 132. The secondary driving oil chamber (hydraulic cylinder chamber) 132 corresponds to a hydraulic actuator recited in the claims.

[0020] The hydraulic pressure for shifting the continuously variable transmission 110, that is, the above-mentioned primary hydraulic pressure and secondary hydraulic pressure, are controlled by a control valve (valve body) 13. The control valve 13 adjusts the hydraulic pressure discharged from the oil pump 10 by opening and closing an oil passage formed therein using a plurality of spool valves and a solenoid valve (electromagnetic valve) for moving the spool valve, and supplies the oil pressure to the primary driving oil chamber 122 and the secondary driving oil chamber 132 of the continuously variable transmission 110. That is, the control valve 13 adjusts (adjusts) the hydraulic pressure of a hydraulic actuator (in this embodiment, the secondary driving oil chamber (hydraulic cylinder chamber) 132) by using the oil (hydraulic pressure) discharged from the oil pump 10. Note that FIG. 1 shows only some circuits of the control valve 13 (a line pressure adjustment circuit and a shift pressure (secondary pressure) adjustment circuit).

[0021] The oil pump 10 is driven by, for example, the engine 160, sucks in oil stored in an oil pan 11 through an oil strainer 12 and an intake oil passage 80, pressurizes the oil, and discharges it. A line pressure oil passage 70 is connected to the discharge port of the oil pump 10, and the oil discharged from the oil pump 10 is pressure-fed (supplied) to the control valve 13 through the line pressure oil passage 70. Note that, for example, a trochoid pump or a vane pump is suitably used as the oil pump 10.

[0022] Oil strainer 12 is disposed upstream of oil pump 10 and traps foreign matter (contamination) in the oil stored in oil pan 11 so that the foreign matter does not enter control valve 13. Oil strainer 12 is disposed below continuously variable transmission 110 so as to be immersed in the oil stored in oil pan 11.

[0023] Here, the oil strainer 12 is configured to have, for example, a housing (strainer body) composed of an upper body and a lower body formed by dividing them into upper and lower halves, and a screen provided near the mating surface between the lower body and the upper body to separate the inside of the housing into upper and lower halves. The screen is a filter material that captures foreign matter in the oil, and for example, a filter made of nonwoven fabric, metal, glass fiber, sponge, etc. is used.

[0024] A line pressure control valve 30 is provided in the line pressure oil passage 70 to adjust the oil pressure (discharge pressure) of the oil discharged from the oil pump 10 to the oil pressure (line pressure) required by the continuously variable transmission 110.

[0025] The line pressure control valve 30 is connected to a first control pressure oil passage 91, which communicates with the line pressure linear solenoid 20 described later, a line pressure oil passage 70, and a drain oil passage 93 for discharging oil. The line pressure control valve 30 accommodates a spool 31 therein so as to be slidable in the axial direction. A spring 32 is disposed at the end of the spool 31, and the amount of oil discharged from the line pressure oil passage 70 to the drain oil passage 93 is adjusted by driving the spool 31 in the axial direction according to the balance between the pressing force (line pressure control pressure x pressure receiving area) due to the line pressure control pressure generated by the line pressure linear solenoid 20 and the spring force (biasing force) of the spring 32, thereby adjusting the line pressure.

[0026] That is, when the spring force (biasing force) of the spring 32 is larger than the pushing force due to the line pressure control pressure, the line pressure control valve 30 communicates the line pressure oil passage 70 with the drain oil passage 93 and adjusts the line pressure by discharging the oil in the line pressure oil passage 70 through the drain oil passage 93. On the other hand, when the spring force (biasing force) of the spring 32 is smaller than the pushing force due to the line pressure control pressure, the line pressure control valve 30 cuts off communication between the line pressure oil passage 70 and the drain oil passage 93 and stops discharging oil from the line pressure oil passage 70.

[0027] The line pressure linear solenoid 20 has a linear solenoid that displaces a valve in the axial direction according to a current value applied from a transmission control unit (hereinafter referred to as "TCU") 150 based on the line pressure required for the continuously variable transmission 110, and adjusts the balance between the supply pressure and the drain from the line pressure oil passage 70 according to the current applied to the linear solenoid, thereby adjusting the line pressure control pressure. The adjusted line pressure control pressure is supplied to the line pressure control valve 30 through a first control pressure oil passage 91, thereby driving and controlling the line pressure control valve 30 as described above. Here, as the current value applied to the line pressure linear solenoid 20 increases, the line pressure control pressure increases linearly, and accordingly, the actual line pressure also increases linearly.

[0028] The upshift solenoid 51 adjusts the pilot pressure generated from the line pressure in accordance with the duty ratio applied by the TCU 150 to generate an upshift control pressure. The generated upshift control pressure is supplied to the upshift valve 63 via an upshift control pressure oil passage 94. Note that, as the upshift solenoid 51, for example, a duty solenoid whose opening is adjusted in accordance with the duty ratio is preferably used. The upshift solenoid 51 is controlled by the TCU 150.

[0029] The upshift valve 63 is connected to the line pressure oil passage 70, the upshift control pressure oil passage 94, and the secondary pressure oil passage 71. The upshift valve 63 accommodates a spool 64 therein so as to be slidable in the axial direction. A spring 65 is disposed at the end of the spool 64, and the spool 64 is driven in the axial direction according to the balance between the pressing force (upshift control pressure × pressure receiving area) due to the upshift control pressure generated by the upshift solenoid 51 and the spring force (biasing force) of the spring 65. During an upshift, the line pressure is adjusted according to the upshift control pressure to generate an upshift oil pressure. The generated upshift oil pressure is supplied to the secondary pulley 131 (secondary driving oil chamber 132) via the secondary pressure oil passage 71. As a result, the gear ratio is upshifted.

[0030] Meanwhile, the downshift solenoid 52 adjusts the pilot pressure created from the line pressure in accordance with the duty ratio applied by the TCU 150 to generate a downshift control pressure. The generated downshift control pressure is supplied to the downshift valve 66 via a downshift control pressure oil passage 95. Note that, as the downshift solenoid 52, for example, a duty solenoid whose opening is adjusted in accordance with the duty ratio is preferably used. The downshift solenoid 52 is controlled by the TCU 150.

[0031] The downshift valve 66 is connected to the secondary pressure oil passage 71, the downshift control pressure oil passage 95, and the drain oil passage 96. During a downshift, the downshift valve 66 drains oil from the secondary pulley 131 (secondary drive oil chamber 132) via the drain oil passage 96 in accordance with the downshift control pressure. As a result, the gear ratio is downshifted.

[0032] A protection valve (relief valve) 69 is interposed in a secondary pressure oil passage 71 (more specifically, downstream of the junction where the oil from the upshift valve 63 and the oil from the downshift valve 66 join) that supplies or discharges hydraulic pressure to or from the driving oil chamber 132 of the secondary pulley 131 that constitutes the continuously variable transmission 110. The protection valve 69 is configured to include, for example, a spring and a valve, and in order to protect the primary pulley 121 (primary driving oil chamber 122), when the hydraulic pressure in the secondary pressure oil passage 71 reaches or exceeds a predetermined pressure, it discharges oil to lower the hydraulic pressure.

[0033] As described above, the secondary pressure oil passage 71 (corresponding to the first oil passage described in the claims) connects the control valve 13 and the secondary drive oil chamber (hydraulic cylinder chamber) 132, and oil supplied from the control valve 13 to the secondary drive oil chamber 132 and oil discharged from the secondary drive oil chamber 132 to the control valve 13 flow in both directions.

[0034] A filter (in-circuit filter) 73 that captures foreign matter in the oil discharged from the secondary driving oil chamber 132 to the control valve 13 is disposed in the secondary pressure oil passage 71 .

[0035] Here, the hydraulic circuit 1 has the function of suppressing clogging of the filter 73, which prevents foreign matter (contamination) from entering the control valve 13 from the secondary drive oil chamber 132 in the secondary pressure oil passage 71, where oil flows in both directions between the control valve 13 and the secondary drive oil chamber 132.

[0036] Therefore, a second oil passage (contamination discharge passage) 72 is connected to the secondary pressure oil passage 71, which connects the downstream side of the filter 73, i.e., the area between the filter 73 of the secondary pressure oil passage 71 and the secondary driving oil chamber 132, to the oil pan 11.

[0037] That is, the second oil passage (contamination discharge passage) 72 has one end (one end) connected to the secondary pressure oil passage 71 downstream of the filter 73, and the other end (the other end) positioned in the vicinity of the oil strainer 12 arranged in the oil pan 11 (the range where the suction negative pressure of the oil pump 10 acts).

[0038] In addition, the second oil passage 72 is preferably disposed so as to become lower (to descend) from one end to the other end so that foreign matter (contamination) captured by the filter 73 sinks (makes it easier to sink) under its own weight when the oil pump 10 is stopped. In other words, it is preferable that the other end is disposed at a lower position than the one end.

[0039] Each of the secondary pressure oil passage 71 and the second oil passage 72 is configured to be able to be opened and closed (connected, cut off) by a changeover valve 75. When the oil pump 10 is driven, the changeover valve 75 opens (connected) the secondary pressure oil passage 71 and closes (cuts off) the second oil passage 72, and when the oil pump 10 is stopped, the changeover valve 75 closes (cuts off) the secondary pressure oil passage 71 and opens (connects) the second oil passage 72.

[0040] More specifically, the switching valve 75 is connected to the suction oil passage 80, the secondary pressure oil passage 71, and the second oil passage 72. The switching valve 75 accommodates a spool 75a therein so as to be slidable in the axial direction. The spool 75a is configured such that one end (end face) is connected to the suction port (suction oil passage 80) of the oil pump 10, and the suction negative pressure caused by the drive of the oil pump 10 acts on the one end (end face), and the other end (end face) is connected to the secondary pressure oil passage 71, and the hydraulic pressure of the secondary pressure oil passage 71 adjusted by the control valve 13 acts on the other end (end face). In addition, a coil spring 75b (corresponding to the biasing means described in the claims) is disposed at one end of the spool 75a, which applies a biasing force to the one end in a direction to close the secondary pressure oil passage 71 and open the second oil passage 72.

[0041] When the oil pump is driven, "the pushing force due to the suction negative pressure applied to one end face of spool 75a and the hydraulic pressure applied to the other end face>the biasing force of coil spring 75b", so secondary pressure oil passage 71 is opened and second oil passage 72 is closed. On the other hand, when the oil pump is stopped, "the pushing force due to the suction negative pressure applied to one end face of spool 75a and the hydraulic pressure applied to the other end face (=zero)<the biasing force of coil spring 75b", so secondary pressure oil passage 71 is closed and second oil passage 72 is opened.

[0042] In addition, it is preferable to tune (adjust) the timing at which the spool 75a (second oil passage 72) closes so that when the oil pump 10 starts to operate, suction negative pressure is generated, foreign matter is sucked in, and the spool 75a (second oil passage 72) is gradually closed (however, without interfering with the gear shifting operation).

[0043] Next, the operation of the hydraulic circuit 1 will be described with reference to Figures 3 to 5. Figures 3 to 5 are diagrams for explaining the operation of the hydraulic circuit 1. More specifically, Figure 3 is a diagram showing the state of the spool 75a and the like constituting the hydraulic circuit 1 when the oil pump is driven, Figure 4 is a diagram showing the state of the spool 75a and the like constituting the hydraulic circuit 1 when the oil pump is stopped, and Figure 5 is a diagram showing the state of the spool 75a and the like constituting the hydraulic circuit 1 when the oil pump starts to be driven.

[0044] First, as shown in FIG. 3, when the oil pump is driven (when the engine is running), the "pressure due to the suction negative pressure applied to one end face of spool 75a and the oil pressure applied to the other end face > the biasing force of coil spring 75b," so that secondary pressure oil passage 71 is opened and second oil passage 72 is closed.

[0045] Therefore, oil flows in both directions through secondary pressure oil passage 71 in response to gear changes in continuously variable transmission 110. That is, during an upshift, oil flows (is supplied) from control valve 13 to secondary drive oil chamber 132, and during a downshift, oil flows (is discharged) from secondary drive oil chamber 132 to control valve 13. Furthermore, foreign matter (contamination) in the oil from secondary drive oil chamber 132 is captured by filter 73 to prevent it from entering control valve 13.

[0046] 4, when the oil pump is stopped, the "pressing force (=zero) due to the suction negative pressure applied to one end face of spool 75a and the oil pressure applied to the other end face of spool 75a < the biasing force of coil spring 75b", and secondary pressure oil passage 71 is closed and second oil passage 72 is opened. Therefore, foreign matter captured by filter 73 sinks due to its own weight and is discharged through second oil passage 72.

[0047] 5, when the oil pump starts to be driven next time (when the engine is started (cranked)), the discharged foreign matter is sucked (into) the oil strainer 12 by the suction negative pressure of the oil pump 10, and is filtered out (collected all at once) by the oil strainer 12. As described above, the timing at which the spool 75a (second oil passage 72) closes is tuned (adjusted) so that the spool 75a (second oil passage 72) is gradually closed (however, without interfering with the gear shifting operation) as the oil pump 10 starts to be driven, generating suction negative pressure, and the foreign matter is sucked in. Then, the state of FIG. 3 described above is restored.

[0048] As described above in detail, according to this embodiment, the filter 73 is interposed in the secondary pressure oil passage 71, which communicates the control valve 13 and the secondary driving oil chamber (hydraulic cylinder chamber) 132 and through which oil flows in both directions, to capture foreign matter in the oil discharged from the secondary driving oil chamber 132 to the control valve 13. When the oil pump 10 is driven, the secondary pressure oil passage 71 is opened. Therefore, foreign matter (contamination) in the oil from the secondary driving oil chamber 132 is captured by the filter 73 so as not to enter the control valve 13. Then, when the oil pump 10 is stopped, the secondary pressure oil passage 71 is closed and the second oil passage (contamination discharge passage) 72 is opened. Therefore, the foreign matter captured by the filter 73 is discharged through the second oil passage 72. Furthermore, when the oil pump 10 starts to be driven next time (when the engine is started), the discharged foreign matter is sucked (intaken) into the oil strainer 12 by the suction negative pressure of the oil pump 10, and can be filtered out (captured collectively) by the oil strainer 12. In other words, the foreign matter captured by the filter 73 and discharged through the second oil passage 72 can be captured collectively by the oil strainer 12 every time the oil pump 10 starts to be driven.

[0049] As a result, in the hydraulic circuit 1 (secondary pressure oil passage 71) in which oil flows in both directions between the control valve 13 and the secondary drive oil chamber 132, it is possible to suppress clogging of the filter 73, which prevents foreign matter (contamination) from entering the control valve 13 from the secondary drive oil chamber 132 (and thus prevent a decrease in hydraulic function).

[0050] According to this embodiment, the switching valve 75 is configured to include a spool 75a having one end connected to the suction port of the oil pump 10, on which the suction negative pressure caused by the drive of the oil pump 10 acts and the other end connected to the secondary pressure oil passage 71, on which the oil pressure of the secondary pressure oil passage 71, which is boosted by the oil pump 10 and adjusted by the control valve 13, acts, and a coil spring 75b that applies a biasing force to one end of the spool 75a in a direction to close the secondary pressure oil passage 71 and open the second oil passage 72. Therefore, when the oil pump is driven, "the pushing force due to the suction negative pressure applied to one end face of the spool 75a and the oil pressure applied to the other end face>the biasing force of the coil spring 75b", and the secondary pressure oil passage 71 is opened and the second oil passage 72 is closed. On the other hand, when the oil pump is stopped, "the pushing force (=zero) due to the suction negative pressure applied to one end face of spool 75a and the oil pressure applied to the other end face < the biasing force of spring 75b", and the secondary pressure oil passage 71 is closed and the second oil passage 72 is opened. Therefore, the secondary pressure oil passage 71 and the second oil passage 72 can be appropriately switched between opening and closing (communication and cut-off) depending on whether the oil pump 10 is driven or stopped.

[0051] According to this embodiment, the second oil passage 72 is disposed so as to become lower (slope downward) from one end to the other end so that foreign matter (contamination) trapped in the filter 73 sinks under its own weight when the oil pump 10 is stopped. This makes it easier to discharge the foreign matter trapped in the filter 73.

[0052] Furthermore, according to this embodiment, one end of the second oil passage 72 is connected to the secondary pressure oil passage 71 downstream of the filter 73, and the other end is disposed in the vicinity of the oil strainer 12 (in a range where the suction negative pressure of the oil pump 10 acts). Therefore, foreign matter discharged through the second oil passage 72 can be effectively sucked in by the suction negative pressure of the oil pump 10 and captured by the oil strainer 12.

[0053] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, the present invention is applied to the secondary pressure oil passage 71 that supplies or discharges oil to the secondary pulley 131 (secondary driving oil chamber 132) of the continuously variable transmission 110, but the present invention may also be applied to the hydraulic circuit of the primary pulley 121.

[0054] The hydraulic circuit 1 according to the above embodiment is merely an example, and may be applied to other hydraulic circuits in which oil flows in both directions. For example, the hydraulic circuit may be applied to a hydraulic circuit that is connected to a hydraulic clutch, a torque converter, or the like, and in which oil flows in both directions.

[0055] In the above embodiment, the second oil passage 72 is arranged so that it becomes lower (decreases) from one end to the other end, but the second oil passage 72 may be arranged horizontally (laterally) as long as the foreign matter discharged through the second oil passage 72 can be sucked in by the suction negative pressure of the oil pump 10 (through the oil strainer 12).

[0056] In the above embodiment, the present invention has been described as being applied to a continuously variable transmission (CVT) 110, but the present invention can also be applied to a stepped automatic transmission (Step AT) or DCT. Also, in the above embodiment, the present invention has been applied to a chain-type continuously variable transmission 110, but instead of a chain-type continuously variable transmission, the present invention can also be applied to, for example, a belt-type continuously variable transmission or a toroidal-type continuously variable transmission.

[0057] In the above embodiment, a one-port type oil pump 10 having a single discharge port has been described as an example. However, instead of the one-port type oil pump 10, for example, a two-port type oil pump having two discharge ports may be used.

[0058] In the above embodiment, duty solenoids are used as the upshift solenoid 51 and the downshift solenoid 52. However, instead of the duty solenoids, for example, linear solenoids or the like may be used. [Explanation of symbols]

[0059] 1 Hydraulic circuit 10. Oil pump 11 Oil pan 12 Oil strainer 13 Control valve (valve body) 20 Line pressure linear solenoid 30 Line pressure control valve 51 Upshift solenoid 52 Downshift solenoid 63 Upshift valve 66 Downshift valve 69 Protection valve 70 Line pressure oil passage 71 Secondary pressure oil passage (first oil passage) 72 2nd oil path (contamination discharge path) 73 Filters 75 Switching valve 75a spool 75b coil spring 80 Suction oil path 91 First control pressure oil passage 93 Drain oil passage 94 Upshift control pressure oil passage 95 Downshift control pressure oil passage 96 Drain oil passage 110 Continuously variable transmission 121 Primary pulley 131 Secondary pulley 132 Secondary drive oil chamber (hydraulic actuator) 150 TCU 160 Engine

Claims

1. an oil pump that draws in, pressurizes, and discharges oil stored in an oil pan through an oil strainer that captures foreign matter in the oil; a control valve that adjusts the hydraulic pressure of a hydraulic actuator by using the oil discharged from the oil pump; a first oil passage that communicates the control valve with the hydraulic actuator and through which oil supplied from the control valve to the hydraulic actuator and oil discharged from the hydraulic actuator to the control valve flow in both directions; a filter that is disposed in the first oil passage and that captures foreign matter in the oil discharged from the hydraulic actuator to the control valve; a second oil passage that communicates between the first oil passage, a portion between the filter and the hydraulic actuator, and the oil pan; a switching valve that opens the first oil passage and closes the second oil passage when the oil pump is driven, and closes the first oil passage and opens the second oil passage when the oil pump is stopped.

2. The switching valve is a spool having one end connected to a suction port of the oil pump, to which a suction negative pressure caused by driving the oil pump acts, and having the other end connected to the first oil passage, to which the oil pressure of the first oil passage adjusted by the control valve acts; a biasing means for applying a biasing force to one end of the spool in a direction to close the first oil passage and open the second oil passage; 2. The hydraulic circuit according to claim 1, further comprising:

3. 3. The hydraulic circuit according to claim 2, wherein one end of the second oil passage is connected to the first oil passage downstream of the filter, and the other end is disposed in the vicinity of the oil strainer disposed in the oil pan.

4. 4. The hydraulic circuit according to claim 3, wherein the second oil passage is disposed so as to become lower from the one end to the other end so that foreign matter trapped in the filter sinks under its own weight when the oil pump is stopped.

5. 5. The hydraulic circuit according to claim 4, wherein the hydraulic actuator is a hydraulic cylinder for a pulley that constitutes a continuously variable transmission.

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