BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The invention relates to a lubricating device.

2. Description of Related Art

[0002] Japanese Patent Application Publication No. 2010-71420 (JP-A-2010-71420), for example, discloses a lubricating device using micro-bubbles as a lubricating device applied to a power transmission device for a vehicle or the like. In this lubricating device, micro-bubbles are generated by intermixing air into lubricating oil using a spiral flow type micro-bubble generating device, and the lubricating oil intermixed with the micro-bubbles is supplied to a multiplate wet clutch in order to lubricate the multiplate wet clutch. As a result, drag torque generated by the multiplate wet clutch is reduced.

[0003] However, there is room for further improvement in the lubricating device using micro-bubbles described in JP-A-2010-71420 with respect to configurations for generating the micro-bubbles and supplying the micro-bubbles to the multiplate wet clutch, for example.

SUMMARY OF THE INVENTION

[0004] The invention provides a lubricating device that can perform lubrication using micro-bubbles appropriately.

[0005] A lubricating device according to an aspect of the invention includes: a discharge port that is provided in a control valve for controlling a liquid medium supplied to a power transmission device transmitting power from a drive source to a drive wheel of a vehicle, and that generates micro-bubbles in the liquid medium by reducing a pressure of the liquid medium when the liquid medium is discharged from the control valve; and a micro-bubble-medium mixture supply passage that connects the discharge port to a frictional engagement element of the power transmission device.

[0006] The lubricating device described above may further include a discharge device that is provided in the micro-bubble-medium mixture supply passage in order to discharge the liquid medium from the interior of the micro-bubble-medium mixture supply passage to the outside when an internal pressure of the micro-bubble-medium mixture supply passage reaches or exceeds a preset predetermined pressure.

[0007] The lubricating device described above may further include a switching device that prohibits supply of the liquid medium intermixed with the micro-bubbles to the frictional engagement element in accordance with a condition of the vehicle.

[0008] Further, in the lubricating device described above, the switching device may prohibit supply of the liquid medium intermixed with the micro-bubbles to the frictional engagement element during an engagement operation of the frictional engagement element.

[0009] Further, in the lubricating device described above, the switching device may prohibit supply of the liquid medium intermixed with the micro-bubbles to the frictional ⁽ engagement element when a rotation speed of the frictional engagement element reaches or exceeds a preset predetermined speed.

[0010] Further, in the lubricating device described above, the switching device may operate in accordance with a differential pressure between a primary pressure and a secondary pressure of a belt type continuously variable transmission (CVT) that performs a shift operation in accordance with the pressure of the liquid medium.

[0011] The lubricating device described above may further include a switch supply passage capable of supplying the liquid medium to the frictional engagement element without passing through the discharge port, and the switching device may prohibit supply of the liquid medium intermixed with the micro-bubbles to the frictional engagement element by switching a passage through which the liquid medium is supplied to the frictional engagement element from the micro-bubble-medium mixture supply passage to the switch supply passage.

[0012] With the lubricating device according to the invention, lubrication using micro-bubbles can be performed appropriately. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic diagram of a vehicle installed with a lubricating device according to a first embodiment;

FIG. 2 is a schematic diagram of the lubricating device according to the first embodiment;

FIG. 3 is a schematic diagram of a lubricating device according to a second embodiment;

FIG. 4 is a schematic diagram of a lubricating device according to a third embodiment;

FIG. 5 is a schematic diagram of a lubricating device according to a fourth embodiment;

FIG. 6 is a schematic sectional view of a lubricating device according to a fifth embodiment;

FIG. 7 is a flowchart illustrating an example of switching control performed in the lubricating device according to the fifth embodiment;

FIG. 8 is a schematic diagram of a lubricating device according to a sixth embodiment;

FIG. 9 is a diagram showing an example of a relationship between a clutch rotation speed and a drag torque;

FIG. 10 is a flowchart illustrating an example of switching control performed in the lubricating device according to the sixth embodiment;

FIG. 11 is a schematic diagram of a lubricating device according to a seventh embodiment; and

FIG 12 is a diagram showing an example of the relationship between the clutch rotation speed and the drag torque. DETAILED DESCRIPTION OF EMBODIMENTS

[0014] Embodiments of the invention will be described in detail below on the basis of the drawings. Note that the invention is not limited by these embodiments. Further, constitutional elements of the following embodiments include simplified elements, substantially identical elements, and elements that could be substituted by a person skilled in the art.

[0015] [First Embodiment]

FIG. 1 is a schematic diagram of a vehicle installed with a lubricating device according to a first embodiment, and FIG. 2 is a schematic diagram of the lubricating device according to the first embodiment.

[0016] As shown in FIG. 1, for example, a lubricating device 1 according to this embodiment is incorporated into an oil pressure control circuit of an oil pressure control device 6, which controls a pressure of oil supplied as a liquid medium to a power transmission device 5 of a vehicle 2, in order to lubricate predetermined sites of the power transmission device 5.

[0017] The vehicle 2 to which the lubricating device 1 is applied includes an engine 3 serving as a drive source, drive wheels 4, the power transmission device 5, the oil pressure control device 6, and an engine control unit (ECU) 7 serving as a control device.

[0018] The engine 3 is a drive source (a prime mover) that causes the vehicle 2 to travel by consuming fuel in order to generate power that is applied to the drive wheels 4 of the vehicle 2. As the fuel burns, the engine 3 generates mechanical power (engine torque) in a crankshaft 8 serving as an engine output shaft and outputs this mechanical power from the crankshaft 8 toward the drive wheels 4.

[0019] The power transmission device 5 transmits the power from the engine 3 to the drive wheels 4. The power transmission device 5 is provided on a power transmission path extending from the engine 3 to the drive wheels 4, and is operated by a pressure (oil pressure) of the oil serving as the liquid medium.

[0020] More specifically, the power transmission device 5 is configured to include a torque converter 9, a forward-reverse switching mechanism 10, a transmission 11, a reduction mechanism 12, a differential gear 13, and so on. In the power transmission device 5, the crankshaft 8 of the engine 3 and an input shaft 14 of the transmission 11 are connected via the torque converter 9, the forward-reverse switching mechanism 10, and so on, while an output shaft 15 of the transmission 11 is connected to the drive wheels 4 via the reduction mechanism 12, the differential gear 13, a drive shaft 16, and so on.

[0021] The torque converter 9 transmits power transmitted to a front cover, which is joined to the crankshaft 8 to be capable of rotating integrally therewith, to the forward-reverse switching mechanism 10 either after performing torque amplification via a fluid transmission mechanism constituted by a pump and a turbine or at an unvaried torque via a lockup clutch. The lockup clutch of the torque converter 9 is switched between a disengaged condition (lockup OFF) and an engaged condition (lockup ON) in accordance with the pressure of oil supplied from the oil pressure control device 6, to be described below.

[0022] The forward-reverse switching mechanism 10 is capable of shifting the power (rotation output) from the engine 3 and switching a rotation direction thereof. The forward-reverse switching mechanism 10 is configured to include a planetary gear mechanism 17, a forward-reverse switching clutch (a forward clutch) 18 and a forward-reverse switching brake (a reverse brake) 19 serving as frictional engagement elements, and so on. The planetary gear mechanism 17 is a differential mechanism configured to include a sun gear, a ring gear, a carrier, and so on as a plurality of rotary elements capable of mutually differential rotation. The forward-reverse switching clutch 18 and the forward-reverse switching brake 19 are engagement elements used to switch an operating condition of the planetary gear mechanism 17, and may be constituted by fractional engagement mechanisms such as multiplate clutches or the like, for example. Here, hydraulic multiplate wet clutches are used.

[0023] The forward-reverse switching clutch 18 and forward-reverse switching brake 19 of the forward-reverse switching mechanism 10 are operated to switch the operating condition by the pressure of oil supplied from the oil pressure control device 6, to be described below. When the forward-reverse switching clutch 18 is engaged (ON) and the forward-reverse switching brake 19 is disengaged (OFF), the forward-reverse switching mechanism 10 transmits the power from the engine 3 to the input shaft 14 in a normal rotation direction (a rotation direction of the input shaft 14 when the vehicle 2 travels forward). When the forward-reverse switching clutch 18 is disengaged and the forward-reverse switching brake 19 is engaged, the forward-reverse switching mechanism 10 transmits the power from the engine 3 to the input shaft 14 in a reverse rotation direction (a rotation direction of the input shaft 14 when the vehicle 2 travels in reverse). When the forward-reverse switching mechanism 10 is in a neutral condition, both the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 are disengaged.

[0024] The transmission 11 is provided on the power transmission path from the engine 3 to the drive wheels 4 between the forward -reverse switching mechanism 10 and the drive wheels 4 in order to shift and then output the power from the engine 3. The transmission 11 is operated by the pressure of oil supplied from the oil pressure control device 6, to be described below.

[0025] The transmission 11 shifts the rotary power (rotation output) from the engine 3, which is transmitted to (input into) the input shaft 14, at a predetermined speed ratio, transmits the shifted power to the output shaft 15 serving as a transmission output shaft, and then outputs the shifted power from the output shaft 15 toward the drive wheels 4. Here, the transmission 11 is a belt type CVT, for example, which is configured to include a primary pulley 20 coupled to the input shaft (primary shaft) 14, a secondary pulley 21 coupled to the output shaft (secondary shaft) 15, a belt 22 wound between the primary pulley 20 and the secondary pulley 21, and so on. The transmission 11 performs a shift operation in accordance with a pressure (primary pressure, secondary pressure) of oil supplied to a primary sheave oil pressure chamber 23 of the primary pulley 20 and a secondary sheave oil pressure chamber 24 of the secondary pulley 21 from the oil pressure control device 6, to be described below. More specifically, a pressure (a belt sandwiching pressure) at which the secondary pulley 21 and so on sandwiches the belt 22 is adjusted while continuously modifying the speed ratio, which is a ratio between an input rotation speed (primary rotation speed) corresponding to an input rotation speed of the primary pulley 20 and an output shaft rotation speed (secondary rotation speed) corresponding to an output rotation speed of the secondary pulley 21, and power is transmitted at a corresponding torque capacity.

[0026] The reduction mechanism 12 reduces the rotation speed of the power transmitted from the transmission 11 and transmits the reduced-speed power to the differential gear 13. The differential gear 13 transmits the power from the reduction mechanism 12 to each drive wheel 4 via the respective drive shafts 16. The differential gear 13 absorbs a rotation speed difference between the drive wheel 4 located on a center side of a turn generated when the vehicle 2 turns, or in other words an inside drive wheel 4, and an outside drive wheel 4.

[0027] The power transmission device 5 configured as described above is capable of transmitting the power generated by the engine 3 to the drive wheels 4 via the torque converter 9, the forward-reverse switching mechanism 10, the transmission 11, the reduction mechanism 12, the differential gear 13, and so on. As a result, a driving force [N] is generated on a ground contact surface contacting the surface of the drive wheels 4, and the vehicle 2 can use this driving force to travel.

[0028] The oil pressure control device 6 operates the power transmission device 5, including engagement elements such as the lockup clutch of the torque converter 9 and the forward-reverse switching clutch 18 and forward-reverse switching brake 19 of the forward-reverse switching mechanism 10, using the oil pressure of oil serving as a fluid. The oil pressure control device 6 is configured to include various oil pressure control circuits controlled by the ECU 7, for example. The oil pressure control device 6 includes a plurality of oil passages, an oil reservoir, an oil pump, a plurality of solenoid valves, and so on, and controls a flow rate or the oil pressure of the oil supplied to the respective parts of the power transmission device 5 in response to signals from the ECU 7, to be described below. The oil pressure control device 6 also functions as a lubricating oil supply device for lubricating predetermined sites of the power transmission device 5, as will be described below.

[0029] The ECU 7 controls driving of respective parts of the vehicle 2. The ECU 7 is an electronic circuit having as a main body a conventional microcomputer including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an interface. Various sensors and detection devices, for example, provided in respective parts of the vehicle 2 are electrically connected to the ECU 7. A fuel injection device, an ignition device, a throttle device, the oil pressure control device 6, and so on, provided in the engine 3, are electrically connected to the ECU 7. Electric signals corresponding to detection results obtained from the various sensors are input into the ECU 7, and the ECU 7 controls driving of the respective parts by outputting drive signals thereto in accordance with the input detection results. For example, the ECU 7 adjusts an intake air amount taken into the engine 3 by adjusting a throttle opening on the basis of an accelerator depression amount, a vehicle speed, and so on. Further, the ECU 7 controls a fuel injection amount in accordance with variation in the intake air amount, and controls an output of the engine 3 by adjusting an amount of air-fuel mixture charged into a combustion chamber. Furthermore, the ECU 7 performs shift control on the transmission 11 by adjusting the speed ratio, typically the input rotation speed, of the transmission 11 on the basis of the accelerator depression amount, the vehicle speed, and so on.

[0030] As shown in FIG. 2, the lubricating device 1 incorporated into an oil pressure control circuit of the oil pressure control device 6 according to this embodiment includes a drain 33 serving as a discharge port that generates micro-bubbles in the oil serving as the liquid medium, and a supply oil passage 34 serving as a micro-bubble-medium mixture supply passage that connects the drain 33 to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 serving as the frictional engagement elements of the power transmission device 5. With this configuration, the lubricating device 1 is capable of performing lubrication using micro-bubbles appropriately.

[0031] The oil pressure control device 6 into which the lubricating device 1 is incorporated is configured to include an oil pan 25, an oil pump 26, various control valves such as a primary regulator valve 27, a secondary regulator valve 28, a line pressure control valve 29, and a sheave pressure control valve 30, and various oil passages for connecting the various control valves to respective parts of the power transmission device 5, such as the primary sheave oil pressure chamber 23, the secondary sheave oil pressure chamber 24, and respective clutch oil pressure chambers 31, 32 for operating the lockup clutch, forward-reverse switching clutch 18, and forward-reverse switching brake 19 of the torque converter 9, such that oil can flow therebetween.

[0032] The oil pan 25 is storage means for storing the oil serving as the liquid medium. The oil pump 26 is driven in synchronization with rotation of the crankshaft 8 (see FIG. 1) of the engine 3 to suction the oil stored in the oil pan 25, pressurize the oil, and discharge the pressurized oil. Here, the oil pump 26 is assumed to use the engine 3 as a drive source, but is not limited thereto, and may use an electric motor or the like as a drive source.

[0033] The primary regulator valve 27 and secondary regulator valve 28 regulate a first line pressure. For example, the primary regulator valve 27 and secondary regulator valve 28 regulate the first line pressure to a pressure of a predetermined magnitude in accordance with a solenoid pressure input from a solenoid valve, not shown in the drawing. The first line pressure is a source pressure of the oil in all of the oil pressure control circuits of the oil pressure control device 6 that controls the oil supplied to the power transmission device 5. The primary regulator valve 27 includes a spool valve element and a plurality of ports (an input port, an output port, a drain port, and so on; likewise hereafter), wherein a discharge port of the oil pump 26 is connected to the input port, and an input port of the secondary regulator valve 28, lubricating holes provided in respective parts, and so on are connected to the output port, for example. Further, for example, the lockup clutch of the torque converter 9 is connected to the output port of the primary regulator valve 27 via a lockup control valve, not shown in the drawing, or the like for controlling a lockup pressure. The secondary regulator valve 28 includes a spool valve element and a plurality of ports, wherein the output port of the primary regulator valve 27 is connected to an input port and a suction port of the oil pump 26 is connected to an output port, for example.

[0034] The line pressure control valve 29 regulates a second line pressure to a fixed pressure having at least a predetermined value, for example. The second line pressure is a source pressure of oil that is introduced into a clutch control valve, not shown in the drawing, or the like for controlling a clutch pressure introduced into the respective clutch oil pressure chambers 31, 32. The line pressure control valve 29 includes a, spool valve element and a plurality of ports, wherein the discharge port of the oil pump 26 is connected to an input port and the respective clutch oil pressure chambers 31, 32, and so on are connected to an output port via the clutch control valve, not shown in the drawing, and so on, for example.

[0035] The sheave pressure control valve 30 controls a sheave pressure. The sheave pressure is the pressure (primary pressure, secondary pressure) of the oil supplied to the primary sheave oil pressure chamber 23 or the secondary sheave oil pressure chamber 24. The sheave pressure control valve 30 includes a spool valve element and a plurality of ports, wherein the discharge port of the oil pump 26 is connected to an input port and the primary sheave oil pressure chamber 23, the secondary sheave oil pressure chamber 24, and so on are connected to an output port via a control valve, not shown in the drawing, and so on, for example.

[0036] The oil pressure control device 6 configured as -described above supplies oil at respective predetermined pressures as working oil to the respective clutch oil pressure chambers 31, 32 via the line pressure control valve 29, the clutch pressure control valve, not shown in the drawing, and so on, to the primary sheave oil pressure chamber 23 and secondary sheave oil pressure chamber 24 via the sheave pressure control valve 30 and so on, and to the lockup clutch of the torque converter 9 via the primary regulator valve 27, the lockup control valve, not shown in the drawing, and so on.

[0037] The drain 33 of the lubricating device 1 according to this embodiment is provided in the oil pressure control device 6 in a control valve that controls the oil supplied to the power transmission device 5, typically a control valve in which the oil pressure of the introduced oil tends to be relatively high and which is capable of securing a sufficient pressure reduction amount for generating micro-bubbles. Here, for example, the drain 33 is provided in the sheave pressure control valve 30. The drain 33 generates micro-bubbles in the oil by causing the pressure of the oil to decrease when the oil is discharged from the sheave pressure control valve 30.

[0038] Here, the micro-bubbles are typically small air bubbles having a diameter of no more than several tens of μπι, and are so small that visible recognition thereof is difficult. The micro-bubbles are not easily incorporated or absorbed into each other, and tend to float in a liquid for a long time. Eventually, the micro-bubbles melt into the oil serving as the liquid so as to disappear. Note that the micro-bubbles may be so-called nano-bubbles, which are extremely small air bubbles having a diameter of no more than 1 μπι, for example.

[0039] The supply oil passage 34 of the lubricating device 1 connects the drain (drain port) 33 of the sheave pressure control valve 30 to lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19. The supply oil passage 34 supplies oil intermixed with micro-bubbles, which is generated during discharge from the drain 33, to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19.

[0040] In the lubricating device 1 configured as described above, oil is discharged from the drain 33 of the sheave pressure control valve 30, and micro-bubbles are generated in the oil by a rapid pressure reduction occurring in the oil at this time. The lubricating device 1 supplies the oil intermixed with the micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the supply oil passage 34. Hence, the lubricating device 1 can lubricate and cool the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 appropriately using the oil intermixed with the micro-bubbles, and therefore drag torque generated by the forward-reverse switching clutch 18 and forward-reverse switching brake 19 can be reduced, leading to a reduction in power loss and an improvement in fuel efficiency, for example.

[0041] Further, the lubricating device 1 is configured to supply oil intermixed with micro-bubbles generated using a pre-existing control valve such as the sheave pressure control valve 30, for example, to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the supply oil passage 34, thereby eliminating the need to provide a separate micro-bubble generating device in order to generate the micro-bubbles, and therefore an increase in the number of constitutional components can be suppressed. As a result, the lubricating device 1 can perform lubrication using micro-bubbles within a limited space and at a low cost.

[0042] Furthermore, since the lubricating device 1 is configured to supply oil intermixed with micro-bubbles generated using a pre-existing control valve such as the sheave pressure control valve 30 to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the supply oil passage 34, a pump, a pressure regulation unit, a compressor, and so on for generating the micro-bubbles are not required, and therefore an increase in energy loss occurring during micro-bubble generation can be suppressed. Likewise in this respect, a reduction in power loss and an improvement in fuel efficiency can be achieved.

[0043] Moreover, the lubricating device 1 can supply the oil intermixed with the micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the supply oil passage 34 without passing the oil intermixed with the micro-bubbles through the oil pump 26, a filter, not shown in the drawings, and so on. Hence, a reduction in the amount of bubbles mixed into the oil before the oil is supplied to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 can be suppressed such that the micro-bubbles are supplied to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 in a sufficient amount. Furthermore, the lubricating device 1 can prevent air entrapment or the like in the oil pump 26, and therefore an increase in a pump load, a reduction in pump efficiency, and so on can be suppressed. Likewise in this respect, a reduction in power loss and an improvement in fuel efficiency can be achieved.

[0044] The lubricating device 1 according to the embodiment described above includes the drain 33, which is provided in the sheave pressure control valve 30 that controls the oil supplied to the power transmission device 5 for transmitting power from the engine 3 to the drive wheels 4 of the vehicle 2 and generates micro-bubbles in the oil by reducing the pressure of the oil when the oil is discharged from the sheave pressure control valve 30, and the supply oil passage 34 that connects the drain 33 to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 of the power transmission device 5.

[0045] Hence, the lubricating device 1 generates micro-bubbles in the oil by rapidly reducing the pressure of the oil when the oil is discharged from the drain 33 of the sheave pressure control valve 30, and supplies the oil intermixed with the micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 serving as frictional engagement elements through the supply oil passage 34. Accordingly, the lubricating device 1 is capable of performing lubrication using micro-bubbles appropriately and with a simplified configuration, for example.

[0046] Note that according to the above description, the supply oil passage 34 connects the drain 33 of the sheave pressure control valve 30 to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, but is not limited thereto. The discharge port to which the supply oil passage 34 is connected may be any discharge port in which micro-bubbles are generated by a pressure reduction occurring as the oil is discharged from a control valve, and as long as micro-bubbles are generated when the oil is discharged, a drain of the line pressure control valve 29 or the like, for example, may be used instead. Further, the frictional engagement element connected to the supply oil passage 34 is not limited to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 of the forward-reverse switching mechanism 10, and any other frictional engagement element included in the power transmission device 5 may be used instead.

[0047] [Second Embodiment]

FIG 3 is a schematic diagram of a lubricating device according to a second embodiment. The lubricating device according to the second embodiment differs from that of the first embodiment in being provided with a discharge device. Wherever possible, duplicate description of configurations, actions, and effects that are shared with the above embodiment has been omitted (due to similarities to the embodiment to be described below).

[0048] As shown in FIG 3, a lubricating device 201 according to this embodiment includes the drain 33, the supply oil passage 34, and a check valve 235 serving as the discharge device.

[0049] The check valve 235 is provided in the supply oil passage 34. More specifically, the check valve 235 is provided in the supply oil passage 34 between the drain (drain port) 33 of the sheave pressure control valve 30 and the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19.

[0050] When an internal pressure of the supply oil passage 34 reaches or exceeds a preset predetermined pressure, the check valve 235 discharges oil from the interior of the supply oil passage 34 to the exterior. When the internal pressure of the supply oil passage 34 reaches or exceeds a preset predetermined valve opening pressure, the check valve 235 opens so as to discharge the oil to the exterior of the system.

[0051] With the lubricating device 201 according to the embodiment described above, micro-bubbles are generated in the oil by rapidly reducing the pressure of the oil when the oil is discharged from the drain 33 of the sheave pressure control valve 30, and the oil intermixed with the micro-bubbles is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 serving as frictional engagement elements through the supply oil passage 34. Accordingly, the lubricating device 201 is capable of performing lubrication using micro-bubbles appropriately and with a simplified configuration, for example.

[0052] Further, the lubricating device 201 includes the check valve 235 that is provided in the supply oil passage 34 and discharges the oil from the interior of the supply oil passage 34 to the exterior when the internal pressure of the supply oil passage 34 reaches or exceeds the preset predetermined pressure. Hence, the lubricating device 201 discharges the oil from the check valve 235 when the supply oil passage 34 reaches or exceeds the predetermined pressure, and therefore a circuit oil pressure in the supply oil passage 34 and so on can be prevented from rising excessively. As a result, the lubricating device 201 can suppress a reduction in the responsiveness of the sheave pressure control performed by the sheave pressure control valve 30, for example, thereby suppressing a reduction in shift responsiveness. In other words, a reduction in the controllability of the power transmission device 5 can be suppressed.

[0053] [Third Embodiment]

FIG. 4 is a schematic diagram of a lubricating device according to a third embodiment. The lubricating device according to the third embodiment differs from those of the first and second embodiments in being provided with a switching device.

[0054] As shown in FIG 4, a lubricating device 301 according to this embodiment includes the drain 33, the supply oil passage 34, the check valve 235, a switch oil passage 336 serving as a switch supply passage, and a manual valve 337 serving as the switching device.

[0055] Using the switch oil passage 336, oil can be supplied to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 without passing through the drain 33 that generates micro-bubbles. The switch oil passage 336 is formed separately as a different oil passage to the supply oil passage 34. The switch oil passage 336 is connected to the output port of the secondary regulator valve 28, and converges with a branch oil passage extending from the output port of the line pressure control valve 29.

[0056] The supply oil passage 34 and the switch oil passage 336 are connected to the manual valve 337. In accordance with a condition, one of the supply oil passage 34 and the switch oil passage 336 is connected to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 while the other is connected to a drain.

[0057] When oil intermixed with micro-bubbles is to be supplied to the forward-reverse switching clutch 18 and forward-reverse switching brake 19, the manual valve 337 connects the supply oil passage 34 to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 and connects the switch oil passage 336 to the drain. Thus, the lubricating device 301 can supply oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 through the supply oil passage 34.

[0058] When oil not intermixed with micro-bubbles is to be supplied to the forward -reverse switching clutch 18 and forward-reverse switching brake 19, the manual valve 337 connects the switch oil passage 336 to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 and connects the supply oil passage 34 to the drain. Thus, the lubricating device 301 can prohibit the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 such that oil not intermixed with micro-bubbles is supplied to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 through the switch oil passage 336.

[0059] The manual valve 337 prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 in accordance with a condition of the vehicle 2. As described above, the manual valve 337 prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 by switching the passage through which oil is supplied to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 from the supply oil passage 34 to the switch oil passage 336.

[0060] The manual valve 337 switches between the supply oil passage 34 and the switch oil passage 336 in accordance with the engagement condition of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, which serves as the condition of the vehicle 2. Here, the manual valve 337 prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 during an engagement operation on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19. When a driver performs a shift range operation via a shift lever, the manual valve 337 according to this embodiment switches the passage in mechanical conjunction with the shift range operation.

[0061] The manual valve 337 sets the supply oil passage 34 to be connected to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 when a drive range (D range) for performing forward travel is selected as the shift range. Hence, when the drive range is selected as the shift range, the lubricating device 301 supplies oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the supply oil passage 34. As a result, the lubricating device 301 can reduce the drag torque generated in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19.

[0062] When the driver performs a shift range operation via the shift lever from a condition in which the drive range is selected to a condition in which the another range (a parking range, a reverse range, a neutral range, or the like, for example) is selected as the shift range, on the other hand, the manual valve 337 switches the passage through which oil is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 from the supply oil passage 34 to the switch oil passage 336 in conjunction with the shift range operation. As a result, the lubricating device 301 can prohibit the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 at least during an engagement operation on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, or in other words while clutch engagement control is underway on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, such that oil not intermixed with micro-bubbles is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the switch oil passage 336.

[0063] With the lubricating device 301 according to the embodiment described above, micro-bubbles are generated in the oil by rapidly reducing the pressure of the oil when the oil is discharged from the drain 33 of the sheave pressure control valve 30, and the oil intermixed with the micro-bubbles is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 serving as frictional engagement elements through the supply oil passage 34. Accordingly, the lubricating device 301 is capable of performing lubrication using micro-bubbles appropriately and with a simplified configuration, for example.

[0064] Further, the lubricating device 301 includes the manual valve 337 that prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 in accordance with the condition of the vehicle 2, and therefore a lubrication condition of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 can be switched by the manual valve 337 appropriately in accordance with the condition of the vehicle 2.

[0065] In other words, in the lubricating device 301, the manual valve 337 prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 during an engagement operation on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, and therefore variation in surface properties such as a frictional characteristic (a μ characteristic) of a frictional engagement surface and an oil film property caused by the micro-bubbles during clutch engagement control of the forward-reverse switching clutch 18 and the forward -reverse switching brake 19 can be suppressed. As a result, the lubricating device 301 can suppress the occurrence of so-called shuddering and slipping in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 while clutch engagement control is underway on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19.

[0066] Further, the lubricating device 301 realizes a configuration for prohibiting the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 using the pre-existing manual valve 337, for example, and therefore the lubrication condition of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 can be switched in accordance with the shift range operation reliably and at low cost. In other words, the lubricating device 301 can supply oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 once a changeover to the drive range is complete, and reliably prevent oil intermixed with micro-bubbles from being supplied during an engagement operation on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19.

[0067] [Fourth Embodiment]

FIG. 5 is a schematic diagram of a lubricating device according to a fourth embodiment. The lubricating device according to the fourth embodiment differs from that of the third embodiment in the configuration of the switching device.

[0068] As shown in FIG 5, a lubricating device 401 according to this embodiment includes the drain 33, the supply oil passage 34, the check valve 235, the switch oil passage 336 serving as the switch supply passage, and a shift valve 437 serving as the switching device.

[0069] The supply oil passage 34 and the switch oil passage 336 are connected to the shift valve 437. In accordance with a condition, one of the supply oil passage 34 and the switch oil passage 336 is connected to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 while the other is connected to a drain. The shift valve 437 prohibits the supply of oil intermixed with micro-bubbles to the forward- reverse switching clutch 18 and the forward-reverse switching brake 19 in accordance with a condition of the vehicle 2.

[0070] The shift valve 437 switches between the supply oil passage 34 and the switch oil passage 336 in accordance with the engagement condition of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, which serves as the condition of the vehicle 2. The shift valve 437 prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 during an engagement operation on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19. The shift valve 437 according to this embodiment switches the passage in conjunction with the supply and discharge of oil to and from the clutch oil pressure chambers 31, 32, or in other words in conjunction with an engagement/disengagement operation performed on the forward-reverse switching brake 19. For example, the shift valve 437 switches the passage in accordance with a magnitude relationship between an oil pressure that varies in conjunction with the supply and discharge of oil to and from the clutch oil pressure chambers 31, 32 and a biasing force generated by a spring.

[0071] When the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 are fully engaged or fully disengaged, the shift valve 437 sets the supply oil passage 34 to be connected to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19. Hence, when the forward-reverse switching brake 19 is fully engaged or fully disengaged, the lubricating device 401 can supply oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the supply oil passage 34. As a result, the lubricating device 401 can reduce the drag torque generated in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19.

[0072] When, on the other hand, an engagement operation is underway in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, typically when the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 are semi-engaged, the shift valve 437 switches the passage through which oil is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 from the supply oil passage 34 to the switch oil passage 336. As a result, the lubricating device 401 can prohibit the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 during an engagement operation on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, or in other words while clutch engagement control of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 is underway, such that oil not intermixed with micro-bubbles is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the switch oil passage 336.

[0073] With the lubricating device 401 according to the embodiment described above, micro-bubbles are generated in the oil by rapidly reducing the pressure of the oil when the oil is discharged from the drain 33 of the sheave pressure control valve 30, and the oil intermixed with the micro-bubbles is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 serving as frictional engagement elements through the supply oil passage 34. Accordingly, the lubricating device 401 is capable of performing lubrication using micro-bubbles appropriately and with a simplified configuration, for example.

[0074] Further, the lubricating device 401 includes the shift valve 437 that prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 in accordance with the condition of the vehicle 2, and therefore the lubrication condition of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 can be switched by the shift valve 437 appropriately in accordance with the condition of the vehicle 2.

[0075] In other words, in the lubricating device 401, the shift valve 437 prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 during an engagement operation on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, and therefore variation in the frictional characteristic (μ characteristic) of the frictional engagement surface caused by the micro-bubbles during clutch engagement control of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 can be suppressed. As a result, the lubricating device 401 can suppress the occurrence of so-called shuddering and slipping in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 while clutch engagement control of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 is underway.

[0076] Further, the lubricating device 401 realizes a configuration for prohibiting the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 using the pre-existing shift valve 437, for example, and therefore the lubrication condition of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 can be switched at low cost. Furthermore, the lubricating device 401 is capable of preventing oil intermixed with micro-bubbles from being supplied during an engagement operation on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, and supplying oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 even when a range other than the drive range is selected. As a result, the drag torque generated in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 can be reduced.

[0077] [Fifth Embodiment]

FIG. 6 is a schematic diagram of a lubricating device according to a fifth embodiment, and FIG. 7 is a flowchart illustrating an example of switching control performed in the lubricating device according to the fifth embodiment. The lubricating device according to the fifth embodiment differs from those of the third and fourth embodiments in the configuration of the switching device.

[0078] As shown in FIG. 6, a lubricating device 501 according to this embodiment includes the drain 33, the supply oil passage 34, the check valve 235, the switch oil passage 336 serving as the switch supply passage, and a solenoid valve 537 serving as the switching device.

[0079] The supply oil passage 34 and the switch oil passage 336 are connected to the solenoid valve 537. In accordance with a condition, one of the supply oil passage 34 and the switch oil passage 336 is connected to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 while the other is connected to a drain. The solenoid valve 537 prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 in accordance with a condition of the vehicle 2.

[0080] The solenoid valve 537 switches between the supply oil passage 34 and the switch oil passage 336 in accordance with the engagement condition of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, which serves as the condition of the vehicle 2. The solenoid valve 537 prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and forward-reverse switching brake 19 during an engagement operation on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19. The solenoid valve 537 according to this embodiment is a solenoid valve driven in response to a control signal from the ECU 7 serving as the control device. The ECU 7 switches the passage by outputting a control signal to the solenoid valve 537 in accordance with the engagement condition of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19.

[0081] When the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 are fully engaged or fully disengaged, the ECU 7 sets the solenoid valve 537 in an inoperative condition (a non-energized condition). In this case, the solenoid valve 537 sets the supply oil passage 34 to be connected to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19. Hence, when the forward-reverse switching brake 19 is fully engaged or fully disengaged, the lubricating device 501 can supply oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the supply oil passage 34. As a result, the lubricating device 501 can reduce the drag torque generated in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19.

[0082] When, on the other hand, an engagement operation is underway in the forward-reverse switching clutch 18 and the forward -reverse switching brake 19, typically when the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 are semi-engaged, the ECU 7 sets the solenoid valve 537 in an operative condition (an energized condition). In this case, the solenoid valve 537 switches the passage through which oil is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 from the supply oil passage 34 to the switch oil passage 336. As a result, the lubricating device 501 can prohibit the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 during an engagement operation on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, or in other words while clutch engagement control of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 is underway, so that oil not intermixed with micro-bubbles can be supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the switch oil passage 336.

[0083] Next, an example of control of the lubricating device 501 will be described with reference to the flowchart shown in FIG. 7. Note that this control routine is executed repeatedly at control period intervals of several ms to several tens of ms.

[0084] First, the ECU 7 measures various signals (ST1) and determines on the basis of the signal measurement results whether or not a clutch engagement control signal relating to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 is present (ST2).

[0085] After determining that a clutch engagement control signal is not present (ST2: No), or in other words that clutch engagement control is not underway and therefore that the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 are either fully engaged or fully disengaged, the ECU 7 sets the solenoid valve 537 in an inoperative condition (a non-energized condition) (ST3) such that the supply oil passage 34 is connected to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 by the solenoid valve 537. The ECU 7 then terminates the current control period and advances to the next control period.

[0086] After determining that a clutch engagement control signal is present (ST2: Yes), or in other words that clutch engagement control is underway and therefore that the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 are semi-engaged, the ECU 7 sets the solenoid valve 537 in an operative condition (an energized condition) (ST4) such that the switch oil passage 336 is connected to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 by the solenoid valve 537. The ECU 7 then terminates the current control period and advances to the next control period.

[0087] With the lubricating device 501 according to the embodiment described above, micro-bubbles are generated in the oil by rapidly reducing the pressure of the oil when the oil is discharged from the drain 33 of the sheave pressure control valve 30, and the oil intermixed with the micro-bubbles is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 serving as frictional engagement elements through the supply oil passage 34. Accordingly, the lubricating device 501 is capable of performing lubrication using micro-bubbles appropriately and with a simplified configuration, for example.

[0088] Further, the lubricating device 501 includes the solenoid valve 537 that prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 in accordance with the condition of the vehicle 2, and therefore the lubrication condition of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 can be switched by the solenoid valve 537 appropriately in accordance with the condition of the vehicle 2.

[0089] In other words, in the lubricating device 501, the solenoid valve 537 prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 during an engagement operation on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, and therefore variation in the frictional characteristic (μ characteristic) of the frictional engagement surface caused by the micro-bubbles during clutch engagement control of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 can be suppressed. As a result, the lubricating device 501 can suppress the occurrence of so-called shuddering and slipping in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 while clutch engagement control of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 is underway.

[0090] Furthermore, the lubricating device 501 is capable of preventing oil intermixed with micro-bubbles from being supplied during an engagement operation on the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, and supplying oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 even when a range other than the drive range (the parking range, reverse range, neutral range, or the like, for example) is selected. As a result, the drag torque generated in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 can be reduced. Moreover, the lubricating device 501 realizes a configuration for prohibiting the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 using the newly provided solenoid valve 537, for example, and therefore freedom can be secured in a disposal location of the solenoid valve 537.

[0091] [Sixth Embodiment]

FIG. 8 is a schematic diagram of a lubricating device according to a sixth embodiment, FIG. 9 is a diagram showing an example of a relationship between a clutch rotation speed and the drag torque, and FIG. 10 is a flowchart illustrating an example of switching control performed in the lubricating device according to the sixth embodiment. The lubricating device according to the sixth embodiment differs from that of the fifth embodiment in the control content of the switching control.

[0092] As shown in FIG. 8, a lubricating device 601 according to this embodiment includes the drain 33, the supply oil passage 34, the check valve 235, the switch oil passage 336, the solenoid valve 537, and a clutch rotation speed sensor 638.

[0093] The clutch rotation speed sensor 638 detects respective rotation speeds of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 as clutch rotation speeds, and outputs detection results to the ECU 7.

[0094] The solenoid valve 537 according to this embodiment switches between the supply oil passage 34 and the switch oil passage 336 in accordance with a rotation condition of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 serving as the frictional engagement elements, i.e. the condition of the vehicle 2. When the clutch rotation speeds (rotation speeds) of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 reach or exceed a preset predetermined rotation speed (speed), the solenoid valve 537 prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and forward-reverse switching brake 19. The ECU 7 switches the passage by outputting a control signal to the solenoid valve 537 in accordance with the clutch rotation speed of the forward-reverse switching clutch 18 or the clutch rotation speed of the forward-reverse switching brake 19, detected by the clutch rotation speed sensor 638.

[0095] Here, FIG. 9 shows the clutch rotation speed on the abscissa and the drag torque generated by the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 on the ordinate. In the drawing, a solid line LI shows an example of the relationship between the clutch rotation speed and the drag torque when oil not intermixed with micro-bubbles is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19, and a dotted line L2 shows an example of the relationship between the clutch rotation speed and the drag torque when oil intermixed with micro-bubbles is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19.

[0096] As is evident from FIG. 9, in a case where the clutch rotation speed is relatively low, the drag torque generated by the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 tends to be relatively lower when oil intermixed with micro-bubbles is supplied than when oil not intermixed with micro-bubbles is supplied. However, when an engine rotation speed gradually increases, leading to a gradual increase in the clutch rotation speed, the micro-bubbles intermixed into the oil tend to cause an increase in an apparent viscosity of the oil. Hence, after the clutch rotation speed reaches a high rotation region at or above a predetermined rotation speed, the drag torque generated by the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 tends to be relatively lower when oil not intermixed with micro-bubbles is supplied than when oil intermixed with micro-bubbles is supplied. [0097] Here, the ECU 7 sets, in advance, a predetermined rotation speed at which the magnitude relationship between the clutch rotation speed and the drag torque in a case where oil not intermixed with micro-bubbles is supplied and a case where oil intermixed with micro-bubbles is supplied reverses as an upper limit rotation speed N at which a drag torque reduction effect is obtained from the micro-bubbles. The ECU 7 then obtains respective clutch rotation speeds Nc of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 from the clutch rotation speed sensor 638, compares the clutch rotation speeds Nc with the upper limit rotation speed N, and controls driving of the solenoid valve 537 in accordance with the comparison result.

[0098] After determining that the clutch rotation speed Nc detected by the clutch rotation speed sensor 638 is lower than the upper limit rotation speed N, the ECU 7 sets the solenoid valve 537 in an inoperative condition (a non-energized condition). Hence, when the clutch rotation speed Nc is lower than the upper limit rotation speed N, the lubricating device 601 can supply oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the supply oil passage 34. As a result, the lubricating device 601 can reduce the drag torque generated by the forward-reverse switching clutch 18 and the forward -reverse switching brake 19.

[0099] After determining that the clutch rotation speed Nc detected by the clutch rotation speed sensor 638 equals or exceeds the upper limit rotation speed N, on the other hand, the ECU 7 sets the solenoid valve 537 in an operative condition (an energized condition). Hence, when the clutch rotation speed Nc equals or exceeds the upper limit rotation speed N, or in other words when the clutch rotation speed Nc is in the high rotation region where the drag torque reduction effect generated by the micro-bubbles weakens, the lubricating device 601 can prohibit the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 and supply oil not intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the switch oil passage 336. As a result, the lubricating device 601 can reduce the drag torque generated by the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 further, even in the high rotation region of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19.

[0100] Next, an example of control of the lubricating device 601 will be described with reference to the flowchart shown in FIG. 10. Note that this control routine is executed repeatedly at control period intervals of several ras to several tens of ms.

[0101] First, the ECU 7 measures the clutch rotation speeds Nc of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 on the basis of the detection results obtained by the clutch rotation speed sensor 638 (ST21) and determines whether or not the clutch rotation speeds Nc are lower than the preset upper limit rotation speed N (ST22).

[0102] After determining that the clutch rotation speeds Nc are lower than the upper limit rotation speed N (ST22: Yes), the ECU 7 measures various signals (ST23) and determines on the basis of the signal measurement results whether or not a clutch engagement control signal relating to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 is present (ST24).

[0103] After determining that a clutch engagement control signal is not present (ST24: No), the ECU 7 sets the solenoid valve 537 in an inoperative condition (a non-energized condition) (ST25) such that the supply oil passage 34 is connected to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 by the solenoid valve 537. The ECU 7 then terminates the current control period and advances to the next control period.

[0104] After determining in ST22 that the clutch rotation speeds Nc equal or exceed the upper limit rotation speed N (ST22: No) and determining in ST24 that a clutch engagement control signal is present (ST24: Yes), the ECU 7 sets the solenoid valve 537 in an operative condition (an energized condition) (ST26) such that the switch oil passage 336 is connected to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 by the solenoid valve 537. The ECU 7 then terminates the current control period and advances to the next control period.

[0105] With the lubricating device 601 according to the embodiment described above, micro-bubbles are generated in the oil by rapidly reducing the pressure of the oil when the oil is discharged from the drain 33 of the sheave pressure control valve 30, and the oil intermixed with the micro-bubbles is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 serving as frictional engagement elements through the supply oil passage 34. Accordingly, the lubricating device 601 is capable of performing lubrication using micro-bubbles appropriately and with a simplified configuration, for example.

[0106] Further, the lubricating device 601 includes the solenoid valve 537 that prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 in accordance with the condition of the vehicle 2, and therefore the lubrication condition of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 can be switched by the solenoid valve 537 appropriately in accordance with the condition of the vehicle 2.

[0107] In other words, in the lubricating device 601, the solenoid valve 537 prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 when the rotation speeds (the clutch rotation speeds Nc) of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 equal or exceed the preset predetermined speed (the upper limit rotation speed N), and therefore power loss can be reduced even in the high rotation region of the forward-reverse switching clutch 18 and the forward -reverse switching brake 19. As a result, an improvement in fuel efficiency can be achieved over a wider operating region, for example.

[0108] [Seventh Embodiment]

FIG. 11 is a schematic diagram of a lubricating device according to a seventh embodiment, and FIG. 12 is a diagram showing an example of the relationship between the clutch rotation speed and the drag torque. The lubricating device according to the seventh embodiment differs from that of the sixth embodiment in the configuration of the switching device.

[0109] As shown in FIG. 11, a lubricating device 701 according to this embodiment includes a drain 733 serving as the discharge port that generates micro-bubbles in the oil, the supply oil passage 34, the check valve 235, the switch oil passage 336, and an oil pressure switch valve 737 serving as the switching device.

[0110] Here, an oil pressure control device 706 into which the lubricating device 701 according to this embodiment is incorporated includes, in addition to the oil pan 25, the oil pump 26, the primary regulator valve 27, the secondary regulator valve 28, the line pressure control valve 29, the sheave pressure control valve 30, and so on, a line pressure control valve 739 serving as a control valve.

[0111] The sheave pressure control valve 30 according to this embodiment controls the primary pressure of the oil supplied to the primary sheave oil pressure chamber 23, i.e. the sheave pressure. The sheave pressure control valve 30 includes a spool valve element and a plurality of ports, wherein the discharge port of the oil pump 26 is connected to an input port and the primary sheave oil pressure chamber 23 and so on are connected to an output port via a control valve, not shown in the drawing, for example.

[0112] The line pressure control valve 739 regulates a third line pressure to a fixed pressure having at least a predetermined value, for example. The third line pressure is a source pressure of oil that is introduced into a sheave control valve, not shown in the drawing, or the like for controlling the secondary pressure introduced into the secondary oil pressure chamber 24. The line pressure control valve 739 includes a spool valve element and a plurality of ports, wherein the discharge port of the oil pump 26 is connected to an input port and the secondary sheave oil pressure chamber 24 and so on are connected to an output port via the sheave control valve, not shown in the drawing, for example.

[0113] The drain 733 of the lubricating device 701 according to this embodiment is provided in the line pressure control valve 739. The drain 733 generates micro-bubbles in the oil by reducing the pressure of the oil when the oil is discharged from the line pressure control valve 739. The supply oil passage 34 of the lubricating device 701 connects the drain (drain port) 733 of the line pressure control valve 739 to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 of the power transmission device 5. The supply oil passage 34 supplies oil intermixed with micro-bubbles generated when the oil is discharged from the drain 733 to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 serving as the frictional engagement elements.

[0114] The oil pressure switch valve 737 according to this embodiment switches between the supply oil passage 34 and the switch oil passage 336 in accordance with the rotation condition of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 serving as the frictional engagement elements, i.e. the condition of the vehicle 2. When the clutch rotation speeds (rotation speeds) of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 reach or exceed a preset predetermined rotation speed (speed), the oil pressure switch valve 737 prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and forward-reverse switching brake 19.

[0115] Here, the oil pressure switch valve 737 operates in accordance with a differential pressure between the primary pressure (the pressure in the primary sheave oil pressure chamber 23) and the secondary pressure (the pressure in the secondary sheave oil pressure chamber 24) of the transmission 11 serving as the belt type CVT that performs shift operations in accordance with the pressure of the oil. The oil pressure switch valve 737 switches the passage in accordance with the differential pressure between the primary pressure and the secondary pressure. The oil pressure switch valve 737 switches the passage in accordance with a magnitude relationship between the primary pressure and the secondary pressure when the primary pressure and the secondary pressure are introduced.

[0116] In the power transmission device 5 according to this embodiment, as shown in FIG. 12, a performance of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 is set such that a peak of the drag torque generated by the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 is positioned within a clutch rotation speed region T used during high-speed cruising.

[0117] When the magnitude relationship between the primary pressure and the secondary pressure is such that the speed ratio of the transmission 11 shifts to a speed increasing side no greater than 1, typically when a relationship of primary pressure Ppri > secondary pressure Psec is established, a biasing force of a spring or the like is set such that the oil pressure switch valve 737 connects the supply oil passage 34 to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19. Hence, when the speed ratio of the transmission 11 is on the speed increasing side no greater than 1, for example when the clutch rotation speed Nc is lower than the preset predetermined rotation speed during high-speed cruising, the lubricating device 701 can supply oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the supply oil passage 34. As a result, the lubricating device 701 can reduce the drag torque generated by the forward-reverse switching clutch 18 and the forward -reverse switching brake 19.

[0118] When the magnitude relationship between the primary pressure and the secondary pressure is such that the speed ratio of the transmission 11 shifts to a speed reducing side greater than 1, typically when a relationship of primary pressure Ppri < secondary pressure Psec is established, the oil pressure switch valve 737 connects the switch oil passage 336 to the lubricating holes in the forward-reverse switching clutch 18 and the forward-reverse switching brake 19. Hence, when the speed ratio of the transmission 11 is on the speed reducing side greater than 1, for example when the clutch rotation speed Nc equals or exceeds the preset predetermined rotation speed, the lubricating device 701 can prohibit the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 so that oil not intermixed with micro-bubbles can be supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 through the switch oil passage 336. As a result, the lubricating device 701 can reduce the drag torque generated by the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 further, even in the high rotation region of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19.

[0119] With the lubricating device 701 according to the embodiment described above, micro-bubbles are generated in the oil by rapidly reducing the pressure of the oil when the oil is discharged from the drain 733 of the line pressure control valve 739, and the oil intermixed with the micro-bubbles is supplied to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 serving as frictional engagement elements through the supply oil passage 34. Accordingly, the lubricating device 701 is capable of performing lubrication using micro-bubbles appropriately and with a simplified configuration, for example.

[0120] Further, the lubricating device 701 includes the oil pressure switch valve 737 that prohibits the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-Teverse switching brake 19 in accordance with the condition of the vehicle 2, and therefore the lubrication condition of the forward-reverse switching clutch 18 and the forward -reverse switching brake 19 can be switched by the oil pressure switch valve 737 appropriately in accordance with the condition of the vehicle 2.

[0121] In other words, in the lubricating device 701, the oil pressure switch valve 737 operates in accordance with the differential pressure between the primary pressure and the secondary pressure of the transmission 11 that performs shift operations in accordance with the pressure of the oil so as to prohibit the supply of oil intermixed with micro-bubbles to the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 when the rotation speeds (the clutch rotation speeds Nc) of the forward-reverse switching clutch 18 and the forward- reverse switching brake 19 equal or exceed the preset predetermined speed (the upper limit rotation speed N). Therefore, the lubricating device 701 can be made capable of reducing power loss even in the high rotation region of the forward-reverse switching clutch 18 and the forward-reverse switching brake 19 while suppressing the cost and size thereof, and as a result, an improvement in fuel efficiency can be achieved over a wide operating region, for example.

[0122] The drive source described above is not limited to an engine. Further, the transmission described above may be a manual transmission (MT), a stepped automatic transmission (AT), a toroidal continuously variable transmission (CVT), a multimode manual transmission (MMT), a sequential manual transmission (SMT), a dual clutch transmission (DCT), and so on, for example. In the above description, oil (lubricating oil) is used as the liquid medium, but the liquid medium is not limited thereto.

[0123] While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various example combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.