Lubrication pressure controller

A lubrication pressure controller comprises a lubrication pressure regulating valve 41, which is provided in a lubrication oil passage 36 directing hydraulic oil to lubricated parts, and a cooler pressure regulating valve 42, which is provided in a discharge oil passage 51b of the lubrication pressure regulating valve 41. The lubrication pressure regulating valve 41 adjusts the pressure in the lubrication oil passage 36, and the cooler pressure regulating valve 42 adjusts the pressure supplied to an oil cooler 55. The hydraulic oil discharged from the cooler pressure regulating valve 42 is returned through a recirculation line 52 to a suction oil passage 31 of a pump. In this construction, an adequate supply of lubrication oil is maintained even if one of the valves experiences locking of a valve spool on an open side. Moreover, by providing signal pressure generating means 60, which applies a signal pressure to these two valves in correspondence with a driving condition, the lubrication pressure controller can be set to acquire a desired balance in the lubrication, cooling and recirculation for the hydraulic oil in response to a driving condition.

FIELD OF THE INVENTION
 The present invention relates generally to a hydraulic controller which
 controls the pressure of hydraulic oil, and particularly to a hydraulic
 controller which has a cooling circuit that cools part of the hydraulic
 oil through an oil cooler.
 BACKGROUND OF THE INVENTION
 Vehicles such as automobiles are equipped with a hydraulic controller which
 controls actuators for the transmission, the clutch, etc. and also
 provides pressure necessary for the lubrication of these parts. Many of
 such hydraulic controllers include an air- or water-cooled oil cooler,
 which cools the hydraulic oil whose temperature increases while it is used
 for the control and lubrication of the transmission, the clutch, etc.
 In such a hydraulic controller, the following method is used commonly. A
 pressure regulating valve is provided in the circuit of the hydraulic oil
 to adjust the pressure of the hydraulic oil, and the oil discharged from
 this pressure regulating valve is returned through an oil cooler to a tank
 (or a drain pan). In addition to this method, there is another method in
 which the discharge port of the above mentioned pressure regulating valve
 is constructed in two ports, one for a line which passes through the oil
 cooler and the other for a line used for recirculation. In this
 construction, when the amount of the oil discharged from the pressure
 regulating valve increases, the oil is directly returned through the
 recirculation line to the suction port of the pump.
 FIG. 6 is a circuit diagram of a conventional lubrication pressure
 controller which includes a recirculation line. In this device, the
 hydraulic oil in a tank T is sucked by a pump P through a suction strainer
 and a suction oil passage 31. After the pressure of the oil is adjusted by
 two regulator valves 33 and 34 to a predetermined hydraulic pressure (line
 pressure), the oil is then supplied through a line 35 to a speed change
 control valve. Excess oil in the pressure adjustment performed by the
 regulator valves 33 is dumped to a lubrication oil passage 36 (36a and
 36b), and the oil in this oil passage is supplied as lubrication oil to
 the components of the transmission which need lubrication (e.g., to the
 starting clutch, the planetary gears, the bearing parts of the shafts,
 etc.). The lubrication oil after being supplied to the speed change
 mechanism and the other components which require lubrication returns to
 the tank T through oil passages, for example, passages constituted by the
 inner walls of the transmission (not shown).
 In the lubrication oil passage 36 (between 36a and 36b), which leads the
 hydraulic oil to the parts which require lubrication, a lubrication valve
 71 is provided to adjust the pressure of the oil used for the lubrication.
 This valve comprises a spool 71a which is biased leftward by a spring 71b.
 The hydraulic oil moves this spool 71a rightward in correspondence with
 the magnitude of the pressure supplied into the oil chamber 71c and
 performs a pressure adjustment which achieves a predetermined lubrication
 pressure Pb needed for supplying the oil to the parts of the transmission
 which require lubrication.
 For example, when the supply pressure (i.e., the discharge pressure of the
 regulator valves 33 and 34) in the lubrication oil passage 36a is smaller
 than the predetermined lubrication pressure Pb, the spool 71a is shifted
 leftward by the spring 71b, so the hydraulic oil flowing in the
 lubrication oil passage 36a is partly supplied through a line 80 to the
 parts requiring lubrication but not through the other lines except the
 line 36b. On the other hand, if the supply pressure in the lubrication oil
 passage 36a becomes greater than the predetermined lubrication pressure
 Pb, the spool 71a is shifted rightward by the hydraulic pressure supplied
 into the oil chamber 71c, the pressure overpowering the resistance of the
 spring 71b. In this condition, the line 81a which passes through an oil
 cooler 85 to the tank T is open together with the line 80, so part of the
 hydraulic oil is cooled and returned to the tank T. If the supply pressure
 increases further, then the spool 71a is shifted further rightward (this
 condition is shown in FIG. 6). In this condition, another line 82 is open
 together with these lines 80 and 81a. This line 82, which is called
 "recirculation line", returns directly to the suction oil passage 31 of
 the pump P without passing through the oil cooler 85 and the tank T.
 In vehicular transmissions, it is general that the pump P is directly
 connected to the output shaft of the engine, so the rotational speed of
 the pump P is proportional to that of the engine. Thus, there is a
 tendency that the greater the rotational speed of the engine, the higher
 the pressure of the hydraulic oil which is discharged from the regulator
 valves 33 and 34 and supplied into the lubrication oil passage 36a. This
 means that the operation of the valves described above is performed in
 correspondence with the rotational speed of the engine and that when the
 rotational speed of the engine is relatively high, the oil is flown
 through the recirculation line 82 directly to the suction oil passage 31
 of the pump P in addition to the line 81 (81a and 81b) passing through the
 oil cooler 85.
 In addition to this method, which controls the supply of the hydraulic oil
 to the oil cooler in correspondence with the pressure in the lubrication
 oil passage by means of the stroke of a valve spool as described above,
 there is another method in which the oil passage leading to the parts
 requiring lubrication and the oil passage leading to the oil cooler are
 switched by a (three-way) electromagnetic valve. This method is disclosed,
 for example, in Japanese Laid-Open Patent Publication No. H4(1992)-316766.
 Yet another method, which controls the flow of the hydraulic oil to the
 oil cooler, is disclosed in Japanese Laid-Open Utility-Model Publication
 No. H1(1989)-135254. In this method, an electromagnetic valve is provided
 in the oil passage leading to the oil cooler, and the flow of the
 hydraulic oil is changed by the on-off control of the valve.
 However, in the previously mentioned prior-art lubrication pressure
 controller (e.g., one shown in FIG. 6), if the lubrication valve 71 is
 disturbed by an external factor, for example, if the pressure in the
 lubrication oil passage 36a is disturbed by a drastic change in the amount
 discharged from the pump or in the control back pressure of the regulator
 valve 33, and thereby the spool of the lubrication valve experiences an
 overstroke rightward, then the hydraulic oil flows excessively into the
 recirculation line 82 and causes a shortage in the amount of the hydraulic
 oil which is supplied to the lubrication oil passage 36b and to the oil
 cooler. Furthermore, if the spool is locked in such an overstroke
 condition, then there is a possibility that the recirculation line 82 will
 experience a negative pressure by the suction pressure of the pump P and
 will draw the hydraulic oil into the lubrication oil passage 36a. There is
 a concern that if this condition occurs, then the shortage of the
 hydraulic oil which should be supplied to the parts requiring lubrication
 would continue and result in a lubrication failure.
 In the method which switches the oil passage leading to the parts requiring
 lubrication and the oil passage leading to the oil cooler by a (three-way)
 electromagnetic valve as disclosed, for example, in Japanese Laid-Open
 Patent Publication No. H4(1992)-316766, by construction, this switching
 involves all the hydraulic oil. Thus, the system requires a large
 electromagnetic valve capable of handling a relatively large flow, and
 this requirement makes it difficult that this method is to be applied to
 the condition which requires both the lubrication and the cooling of the
 transmission.
 In the method which is disclosed in Japanese Laid-Open Utility-Model
 Publication No. H1(1989)-135254, the electromagnetic valve that is
 provided in the oil passage leading to the oil cooler is used for the
 on-off control of the valve to change the flow of the hydraulic oil. This
 control can adjust the flow to the oil cooler only to two levels.
 Therefore, to balance the flow for the oil cooler with the flow for the
 recirculation line, another additional valve is necessary.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to enable control of lubrication
 oil supply even under the above mentioned spool lock condition.
 It is another object of the present invention to prevent locking of one
 valve spool on an open side (i.e., an open stick condition) from causing a
 lubrication failure.
 It is yet another object of the present invention to supply hydraulic oil
 appropriately to oil passages for lubrication, cooling and recirculation,
 respectively in correspondence with an operational condition.
 In order to achieve these objectives, the present invention provides a
 lubrication pressure controller which comprises a tank, a pump, a
 lubrication oil passage, a lubrication pressure regulating valve, a first
 discharge oil passage (e.g., the line 51 of the embodiment described in
 the following section), an oil cooler, a cooler pressure regulating valve
 and a second discharge oil passage (e.g., the line 52 of the embodiment
 described in the following section). The tank stores hydraulic oil, which
 is sucked by the pump. The hydraulic oil discharged from the pump is led
 by the lubrication oil passage to parts which need lubrication, and in the
 lubrication oil passage, the lubrication pressure regulating valve adjusts
 the pressure of the hydraulic oil. The first discharge oil passage returns
 the hydraulic oil which is discharged in the pressure adjustment performed
 by the lubrication pressure regulating valve to the tank, and the oil
 cooler is provided at one point en route in the first discharge oil
 passage. The cooler pressure regulating valve is provided between the
 lubrication pressure regulating valve and the oil cooler and adjusts the
 pressure of the hydraulic oil being supplied to the oil cooler. The second
 discharge oil passage returns the hydraulic oil discharged in the pressure
 adjustment performed by the cooler pressure regulating valve into a
 suction oil passage (e.g., the line 31 of the embodiment described in the
 following section) located between the tank and the pump.
 In this construction, the lubrication pressure controller includes the
 lubrication pressure regulating valve, which adjusts the pressure of the
 oil supplied to the lubricated parts, and the cooler pressure regulating
 valve, which is positioned in the discharge oil passage of the lubrication
 pressure regulating valve and which adjusts the pressure of the oil
 supplied to the oil cooler, and the discharge oil passage of the cooler
 pressure regulating valve comprises a recirculation line. Thus, even if
 one of the regulating valves is stuck in its open condition, the other
 valve is still capable of adjusting the pressure of the line. Therefore,
 this lubrication pressure controller has a good lubrication performance.
 A second embodiment of lubrication pressure controller according to the
 present invention comprises a tank, which stores hydraulic oil, a pump,
 which sucks and discharges the hydraulic oil, a lubrication oil passage,
 which leads the hydraulic oil discharged from the pump to lubricated
 parts, a lubrication pressure regulating valve, which adjusts the pressure
 of the hydraulic oil in the lubrication oil passage, a first discharge oil
 passage (e.g., the line 51 of the embodiment described in the following
 section), which returns the hydraulic oil discharged in the pressure
 adjustment performed by the lubrication pressure regulating valve to the
 tank, an oil cooler, which is provided at one point en route in the first
 discharge oil passage and which cools the hydraulic oil, and signal
 pressure generating means, which applies a signal pressure to the
 lubrication pressure regulating valve in correspondence with a driving
 condition. In this controller, the pressure in the lubrication oil passage
 is adjusted by the signal pressure in correspondence with a driving
 condition.
 In this construction, the lubrication pressure controller is capable of
 changing the pressure of the oil supplied to the lubricated parts, which
 pressure is adjusted by the lubrication pressure regulating valve, in
 correspondence with a driving condition. Thus, the hydraulic oil can be
 allocated both for the lubrication and for the cooling as desired in
 correspondence with, for example, the rotational speed of the engine, the
 speed change ratio, the temperature of the oil, etc. Therefore, the
 distribution of the hydraulic oil is adjustable with an appropriate
 balance between the flows for the lubrication and for the cooling without
 sacrificing any of the flows.
 A third embodiment of lubrication pressure controller according to the
 present invention comprises a tank, which stores hydraulic oil, a pump,
 which sucks the hydraulic oil from the tank and discharges it, a
 lubrication oil passage, which leads the hydraulic oil discharged from the
 pump to lubricated parts, a return oil passage (e.g., the line 51 of the
 embodiment described in the following section), which returns portion of
 the hydraulic oil to the tank, an oil cooler, which is provided at one
 point en route in the return oil passage and cools the hydraulic oil, a
 cooler pressure regulating valve, which is provided in the return oil
 passage on the upstream side of the oil cooler and which adjusts the
 pressure of the hydraulic oil being supplied to the oil cooler, a second
 discharge oil passage (e.g., the line 31 of the embodiment described in
 the following section), which returns the hydraulic oil discharged in the
 pressure adjustment performed by the cooler pressure regulating valve into
 a suction oil passage located between the tank and the pump, and signal
 pressure generating means, which applies a signal pressure to the cooler
 pressure regulating valve in correspondence with a driving condition. In
 this controller, the pressure of the oil supplied to the oil cooler in the
 return discharge oil passage is adjusted by the signal pressure, which
 corresponds to a driving condition.
 In this construction, the lubrication pressure controller is capable of
 changing the pressure of the oil supplied to the oil cooler, which
 pressure is adjusted by the cooler pressure regulating valve, in
 correspondence with a driving condition. Thus, the hydraulic oil can be
 allocated both to the oil cooler and to a recirculation line as desired in
 correspondence with, for example, the temperature of the oil, the oil
 level, the rotational speed of the engine, etc. Therefore, the balance of
 the flows of the hydraulic oil to the oil cooler and to the recirculation
 line is adjustable appropriately.
 Further scope of applicability of the present invention will become
 apparent from the detailed description given hereinafter. However, it
 should be understood that the detailed description and specific examples,
 while indicating preferred embodiments of the invention, are given by way
 of illustration only, since various changes and modifications within the
 spirit and scope of the invention will become apparent to those skilled in
 the art from this detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIGS. 1 and 2 show the construction of a continuously variable transmission
 CVT, which is equipped with a hydraulic controller according to the
 present invention. This continuously variable transmission CVT is a
 belt-type continuously variable transmission which uses a metal V-belt,
 and it comprises a metal V-belt mechanism 10, which is disposed between
 the input shaft 1 and the countershaft 2 of the transmission, a planetary
 gear type forward-reverse selector mechanism 20, which is disposed between
 the input shaft 1 and the drive pulley 11 of the metal V-belt mechanism
 10, and a starting clutch 5, which is disposed between the countershaft 2
 and the output member (including a differential mechanism 8). This
 continuously variable transmission CVT is used on a vehicle, so the input
 shaft 1 is connected through a coupling mechanism CP with the output shaft
 of the engine ENG, and the power transmitted to the differential mechanism
 8 is used for driving the right and left wheels of the vehicle.
 The metal V-belt mechanism 10 comprises the drive pulley 11, which is
 disposed over the input shaft 1, a driven pulley 16, which is disposed on
 the countershaft 2, and the metal V-belt 15, which is disposed around
 these pulleys 11 and 16.
 The drive pulley 11 comprises a stationary pulley half 12, which is
 disposed rotatably over the input shaft 1, and a movable pulley half 13,
 which is movable with respect to the stationary pulley half 12 in the
 axial direction of the pulley 11. On the outside of the movable pulley
 half 13, a drive-side cylinder chamber 14 is defined by a cylinder wall
 12a which is fixed to the stationary pulley half 12. The pressure supplied
 into the cylinder chamber 14 generates a thrust which shifts the movable
 pulley half 13 in the axial direction of the drive pulley.
 The driven pulley 16 comprises a stationary pulley half 17, which is fixed
 on the countershaft 2, and a movable pulley half 18, which is movable with
 respect to the stationary pulley half 17 in the axial direction of the
 pulley. On the outside of the movable pulley half 18, a driven-side
 cylinder chamber 19 is defined by a cylinder wall 17a which is fixed to
 the stationary pulley half 17. The pressure supplied into the cylinder
 chamber 19 generates a thrust which shifts the movable pulley half 18 in
 the axial direction of the driven pulley.
 The hydraulic pressure which is supplied into these cylinder chambers 14
 and 19 is controlled to generate appropriate lateral thrusts in these two
 pulleys, which thrusts change the widths of the V grooves of the drive and
 driven pulleys 11 and 16 without any slip of the belt 15 and thereby
 change the pitch radii of the respective pulleys for the V belt 15 to vary
 the speed change ratio of the transmission continuously.
 The planetary gear type forward-reverse selector mechanism 20 comprises a
 double-pinion planetary gear train. This planetary gear train comprises a
 sun gear 21, which is connected to the input shaft 1, a carrier 22, which
 is connected to the stationary pulley half 12 of the drive pulley 11, and
 a ring gear 23, which can be held against rotation by a reverse brake 27.
 The planetary gear train also comprises a forward clutch 25, which can
 connect the sun gear 21 and the ring gear 23. When this forward clutch 25
 is engaged, all the gears 21, 22 and 23 rotate together with the input
 shaft 1 as a one body, and the drive pulley 11 is driven in the same
 direction as the input shaft 1 (i.e., the forward direction of the
 vehicle). On the other hand, if the reverse brake 27 is engaged, the ring
 gear 23 is held stationary, so the carrier 22 rotates in the direction
 opposite to that of the sun gear 21, and the drive pulley 11 is driven in
 the direction opposite to that of the input shaft 1 (i.e., the reverse
 direction).
 The starting clutch 5 is a clutch which controls the power transmission
 between the countershaft 2 and the output members of the transmission.
 When the starting clutch 5 is engaged, it is possible to transmit the
 power therebetween. The pressure supplied to the starting clutch 5 (clutch
 control pressure) is controlled to adjust the hydraulic engaging force of
 the clutch so that the torque transmission capacity (torque capacity)
 between the input side and the output side of the clutch is controllable.
 Therefore, when the starting clutch 5 is engaged, the output of the
 engine, after going through the speed change by the metal V-belt mechanism
 10, is transmitted through gears 6a, 6b, 7a and 7b to the differential
 mechanism 8 and then divided and transmitted by the differential mechanism
 8 to the right and left wheels (not shown). When the starting clutch 5 is
 released, this power transmission is not carried out, and the transmission
 is in the neutral condition.
 The hydraulic controller comprises a speed change controller, a lubrication
 pressure controller and an oil cooler. The speed change controller
 controls the actuation of hydraulic actuators such as the forward clutch
 25, the reverse brake 27 and the starting clutch 5 of the planetary gear
 type forward-reverse selector mechanism 20 and the drive and driven
 pulleys 11 and 16 of the continuously variable transmission CVT. The
 lubrication pressure controller supplies lubrication oil to the parts
 which need lubrication in the mechanisms of the transmission, and the oil
 cooler cools the oil whose temperature has risen after actuating the
 actuators and being used as lubricant.
 FIG. 3 shows the whole construction of the hydraulic controller. The
 hydraulic oil supplied from the tank T by the pump P acquires a constant
 pressure by the regulator valves 33 and 34, which are included in the
 speed change controller 30, and this pressure is used through speed
 control valves, each of which is controllable to actuate a respective
 hydraulic actuator, such hydraulic actuators being the starting clutch 5,
 the forward clutch 25, the reverse brake 27 and the cylinder chambers 14
 and 19 of the drive and driven pulleys. Excess oil in the pressure control
 carried out at the regulator valves is supplied through lubrication oil
 passages to lubricated parts 38 such as actuation devices and bearing
 portions. The lubrication pressure controller 40 is positioned in the
 lubrication oil passages, and it performs pressure control to adjust the
 pressure of the oil being supplied to the lubricated parts and to return
 portion of the oil supplied into the lubrication oil passages to the oil
 cooler 55 or directly to an oil passage which leads to the suction of the
 pump without passing the oil through the oil cooler, etc. In addition, the
 speed change controller 30 includes signal pressure generating means 60,
 which generates a signal pressure in correspondence with the driving
 condition of the transmission. The signal pressure is generated in
 correspondence with, for example, the rotational speed of the engine, the
 speed change ratio, the temperature of the hydraulic oil, etc. and is
 applied to the lubrication pressure controller 40.
 FIG. 4 shows the lubrication pressure controller according to the present
 invention. The hydraulic oil in the tank T is sucked by the pump P through
 a suction strainer provided in the tank and through the suction oil
 passage 31, and the pressure of the oil is adjusted to a predetermined
 working pressure (referred to as "line pressure") by the two regulator
 valves 33 and 34. Then, this oil is supplied through a line 35 to the
 speed change control valves of the transmission. Excess oil in the
 pressure control performed at the regulator valves is dumped into the
 lubrication oil passage 36 (36a and 36b) and is led as lubrication oil to
 the parts of the transmission which need lubrication (e.g., the starting
 clutch 5, the planetary gear 20, and the bearing portions of the shafts).
 The oil supplied to the speed change controller and the lubricated parts
 in this way returns to the tank T through passages constituted by, for
 example, the inner walls of the transmission (not shown in the drawing).
 Each "X" mark in the drawings represents a connection to drainage.
 A lubrication pressure regulating valve 41 is provided to the lubrication
 oil passage 36 (between 36a and 36b), which lead the hydraulic oil to the
 lubricated parts, to adjust the pressure of the oil for the lubrication.
 The lubrication pressure regulating valve 41 includes a spool 41a, which
 is biased leftward by a spring 41b. The pressure applied into the oil
 chamber 41c of this valve pushes the spool rightward with the displacement
 which is proportional to the magnitude of the pressure. When the pressure
 in the oil chamber 41c becomes equal to or greater than the lubrication
 pressure Pb, this valve discharges the hydraulic oil into a line 51b to
 reduce the pressure in the line 36. In this way, the balance between the
 force generated in the spring 41b and the pressure applied into the oil
 chamber 41c adjusts the opening of the valve to the line 51b so that the
 pressure applied for the lubrication is adjusted to the predetermined
 lubrication pressure Pb in this pressure adjustment operation.
 To the lubrication pressure regulating valve 41, a line 51a with an orifice
 is provided to discharge a certain amount of oil into the line 51b even
 when the pressure in the lubrication oil passage 36a is smaller than the
 lubrication pressure Pb, in which condition, this valve is closed. In
 addition, the signal pressure generating means 60, whose signal pressure
 is supplied to the lubrication pressure regulating valve 41 through a line
 61, sets the lubrication pressure Pb to a desired pressure in
 correspondence with a driving condition.
 The hydraulic oil discharged from the lubrication pressure regulating valve
 41 returns to the tank T through the line 51 which includes the oil cooler
 55 on the way, and a cooler pressure regulating valve 42 is provided
 between the lubrication pressure regulating valve 41 and the oil cooler
 55.
 The cooler pressure regulating valve 42 is an inline type regulating valve,
 and it includes a spool 42a, which is biased leftward by a spring 42b. The
 pressure applied into the oil chamber 42c of this valve acts against the
 force of the spring 42b and shifts the spool 42a rightward. When the
 pressure in the oil chamber 42c increases to a certain point, the
 hydraulic oil is released into a line 52 to balance the force of the
 spring with the force generated from the pressure so that the supply
 pressure to the oil cooler 55 is adjusted to and maintained at a
 predetermined cooler supply pressure Pc. In addition, the signal pressure
 generating means 60, whose signal pressure is supplied to the cooler
 pressure regulating valve 42 through a line 62, sets the cooler supply
 pressure Pc to a desired pressure in correspondence with a driving
 condition.
 The hydraulic oil discharged from the cooler pressure regulating valve 42
 is recirculated through the recirculation line 52, which leads to the
 suction oil passage 31 of the pump P, without passing through the oil
 cooler and the tank T.
 In this embodiment, the signal pressure generating means 60 is constructed,
 for example, as shown in FIG. 5 with two electromagnetic valves, which are
 used in the speed change controller 30. As shown in the drawing, these
 electromagnetic valves receive the line pressure (or a pressure which is
 lower than the line pressure, produced by an additional reducing valve)
 through a line 37, respectively, and they generate the signal pressure
 into the lines 61 and 62 in response to an electrical control signal which
 is received depending upon the driving condition of the transmission.
 One of the valves 65 is a normally open type solenoid valve, and to control
 the supply of the signal pressure into the line 61, the opening and
 shutting of this valve is controlled by an electrical control signal. The
 other valve 66 is a linear solenoid valve, and the pressure supplied into
 the line 62 is controlled in correspondence with the magnitude of the
 electrical current which is applied to the linear solenoid 66a of this
 valve. The mention of these types here is not intended to specify these
 electromagnetic valves, and any type of valves can be used here as long as
 the signal pressure is produced appropriately.
 In this construction of the lubrication pressure controller, the hydraulic
 oil discharged from the regulator valves 33 and 34 into the line 36a is
 adjusted by the lubrication pressure regulating valve 41 to achieve the
 predetermined lubrication pressure Pb, which oil is then supplied through
 the line 36b to the lubricated parts 38. The hydraulic oil dumped by the
 lubrication pressure regulating valve 41 into the line 51b is supplied to
 the cooler pressure regulating valve 42, which adjusts the pressure
 applied to the oil cooler to the predetermined cooler supply pressure Pc.
 The oil at this cooler supply pressure Pc passes through the line 51c and
 is cooled by the oil cooler 55, and it then returns through a filter 86 to
 the tank T. The oil dumped from the cooler pressure regulating valve 42 in
 the pressure adjustment returns through the recirculation line 52 into the
 suction oil passage 31 without passing through the oil cooler 55 and the
 tank T.
 In this construction of the lubrication controller, the cooler pressure
 regulating valve 42 is positioned in the discharge oil passage 51b of the
 lubrication pressure regulating valve 41, and the oil discharged is
 returned through the recirculation line 52 to the suction oil passage 31
 of the pump. Therefore, a priority can be set for the hydraulic oil
 supplied through the line 36 in the following order:
 lubrication&gt;cooling&gt;recirculation. Furthermore, the ratio of the amount of
 the oil going through these three routes can be set to a desired ratio.
 Moreover, if the cooler pressure regulating valve 42 is locked in its open
 condition (open stick), in which the line 51b and the recirculation line
 52 are open, as the lubrication pressure regulating valve 41 maintains the
 pressure adjustment function for the lubrication oil passage 36b, the
 hydraulic oil will not be drawn into the recirculation line 52 in an
 amount to cause a shortage of lubrication oil. In a similar way, if the
 lubrication pressure regulating valve 41 is locked in an open stick
 condition for some reason, as the cooler pressure regulating valve 42
 maintains the pressure adjustment function, the lubrication oil is kept in
 a sufficient amount to maintain a good lubrication performance.
 The lubrication pressure controller is constructed such that a certain flow
 of the hydraulic oil is maintained to the lubrication pressure regulating
 valve 41 even when the pressure supplied to the lubrication oil passage 36
 is smaller than the predetermined lubrication pressure Pb and even when
 this valve is closed. Therefore, a flow to the oil cooler 55 is
 maintained, for example, even when the vehicle is kept in idling condition
 for a long time, so any increase in the temperature of the hydraulic oil
 is prevented.
 The lubrication pressure controller includes an on-off solenoid valve 65
 (signal pressure generating means 60), which applies the signal pressure
 to the lubrication pressure regulating valve 41 in correspondence with a
 driving condition. Therefore, the actuation of the solenoid valve 65 is
 controlled in correspondence with a driving condition (e.g., the
 rotational speed of the engine, the speed change ratio, the temperature of
 the hydraulic oil, the oil level in the tank T, etc.) to adjust the
 balance between the amount of the oil for the lubrication and the amount
 cooled by the oil cooler 55 as desired.
 Therefore, even when the rotational speed of the engine is relatively low,
 for example, because the vehicle is cruising at a low rotational speed,
 and thereby the pressure applied to the lubrication oil passage 36a is
 also low, the above mentioned predetermined lubrication pressure Pb is
 lowered by turning off the signal pressure or by lowering the signal
 pressure. In this way, the flow discharged into the line 51b is increased
 to maintain the flow of the oil to the oil cooler 55, thereby preventing
 the oil from overheating. Also, if a high oil level in the tank T (oil
 pan) is preferred while the lubrication does not require much pressure
 (e.g., the vehicle is in deceleration at a low temperature), then the oil
 level in the tank T is increased by increasing the flow of the oil to the
 oil cooler 55 in the same way as the above, to prevent inclusion of the
 air into the suction oil passage 31 of the pump.
 As mentioned above, the lubrication pressure controller includes the linear
 solenoid valve 66 (signal pressure generating means 60), which applies the
 signal pressure to the cooler pressure regulating valve 42 in
 correspondence with a driving condition. Therefore, the balance between
 the flow of the oil being cooled by the oil cooler and the flow returning
 directly to the suction oil passage 31 of the pump P is adjustable as
 desired in correspondence with a driving condition (e.g., the temperature
 of the hydraulic oil, the oil level in the tank T, the rotational speed of
 the engine, etc.).
 As such, when the temperature of the hydraulic oil is relatively low, i.e.,
 there is no need for the oil to be cooled by the oil cooler 55, and the
 oil has a high viscosity (and a high resistance to pass through the
 suction strainer), the cooler supply pressure Pc is lowered by lowering
 the signal pressure to increase the flow into the recirculation line 52,
 thereby supplementing the oil being sucked into the pump and preventing an
 occurrence of shortage of oil for the pump. On the other hand, when the
 temperature of the oil is high, or a high oil level in the tank is
 preferred, the cooler supply pressure Pc is increased by raising the
 signal pressure to reduce the amount of the oil being discharged into the
 recirculation line 52, thereby promoting the cooling performed by the oil
 cooler 55 and increasing the amount of the oil being returned to the tank.
 In this way, the flow of the oil is adjustable finely in correspondence
 with the driving condition.
 The invention being thus described, it will be obvious that the same may be
 varied in many ways. Such variations are not to be regarded as a departure
 from the spirit and scope of the invention, and all such modifications as
 would be obvious to one skilled in the art are intended to be included
 within the scope of the following claims.
 RELATED APPLICATIONS
 This application claims the priority of Japanese Patent Application
 No.10-231549 filed on Aug. 18, 1998, which is incorporated herein by
 reference.