Abstract:
A lubricating oil supply control device for delivering lubricating oil to the transmission of a vehicle is provided which overcomes disadvantages of the prior art by providing a simple and reliable configuration which does not require the addition of new sensors to an existing device. The lubricating oil supply control device includes, in part, an engine controller and a transmission controller, a lubricating oil supplying oil passage, a bypass oil passage, a relief valve or a control valve, a restrictor, and a lubricating oil supply controlling controller.

Description:
TECHNICAL FIELD 
     The present invention relates to a device for controlling supply of lubricating oil to a transmission of a vehicle. 
     BACKGROUND ART 
     It is necessary to supply lubricating oil to gears and friction engagement elements (speed change clutch) and the like which configure the transmission of the vehicle to perform reduction of mechanical friction, cooling, corrosion prevention and the like. 
     Patent literature 1 described later discloses an invention that supplies a lubricating oil amount, which is required in accordance with an operating state of a planetary gear transmission, to the transmission. 
     Specifically, the patent literature 1 has achieved its object by the following means. 
     a) A speed change stage, a throttle opening and the like are detected by individual sensors, the detection signals by the individual sensors are input to an electronic control device (controller), the lubricating oil amount required for the transmission is calculated by the controller, and an electric signal indicating the required lubricating oil amount is output. 
     b) A first regulator adjusts the pressure of the pressure oil, which is discharged from the hydraulic pump, to a line pressure and outputs to a line pressure oil passage. 
     c) An electric signal corresponding to the required lubricating oil amount output from the controller is input to a solenoid valve, and a lubrication signal pressure is output from the solenoid valve to a lubrication signal pressure oil passage. 
     d) A second control valve is connected to the line pressure oil passage and the lubrication signal pressure oil passage, and the second control valve operates a spool in accordance with the lubrication signal pressure which is supplied from the lubrication signal pressure oil passage, with the line pressure, which is supplied from the line pressure oil passage, determined as a base pressure, and outputs a lubrication pressure to the upstream side of an orifice. 
     e) The required lubricating oil amount corresponding to the lubrication pressure is supplied to the transmission via the orifice. The pressure on the upstream side of the orifice is input as a feedback pressure to the second control valve. 
     Patent Literature 1: Japanese Patent Application Laid-Open No. 10-141480 
     BRIEF SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     According to the invention described in the patent literature 1, it is necessary to dispose various types of sensors for detecting a speed change stage, a throttle opening and the like to calculate the required lubricating oil amount as described in the above item a). Therefore, it is necessary to add a new sensor to the existing device. It is also necessary to convert the sensor-detected signal to an engineering unit necessary for arithmetic processing by performing signal processing by the controller. The controller needs to perform processing to calculate the lubricating oil amount for the transmission in accordance with the detection values of the individual sensors. Therefore, the processing performed by the controller becomes complex. As a result, the cost for configuring the device of a control system increases. 
     As described in the above items b), c), d) and e), it is necessary to convert finally the discharge pressure of the hydraulic pump to a desired lubrication pressure by the hydraulic circuit. Therefore, the regulator is essential as a control valve, and lots of hydraulic pipes are required to transfer hydraulic pressure signals among the valves. Therefore, when a device of a hydraulic system is configured, the structure of the valve body and the arrangement of the hydraulic pipes become complex, and the cost increases. 
     The present invention has been made under the circumstances described above and remedies the problems by eliminating the necessity of addition of a new sensor at the time of configuring a lubricating oil supply control device for a transmission and simplifying arithmetic processing which is performed by a controller, thereby simplifying the device of the control system and educing cost. 
     And, the present invention simplifies the structure of the device of the hydraulic system by simplifying the configuration of the valve body and the arrangement of the hydraulic pipes at the time of configuring the lubricating oil supply control device of the transmission, thereby enabling to configure it at a low cost. 
     Means for Solving the Problems 
     A first embodiment of the present invention is a lubricating oil supply control device for a transmission of a vehicle that is driven by an output of an engine transmitted to the transmission, comprising: 
     an engine controller for controlling the engine; 
     a transmission controller for controlling the transmission; 
     a lubricating oil supplying oil passage for guiding lubricating oil, which is discharged from a hydraulic pump, to the transmission; 
     a bypass oil passage for guiding the lubricating oil, which is in the lubricating oil supplying oil passage, to a tank; 
     a relief valve for discharging the lubricating oil, which is in the lubricating oil supplying oil passage, to the tank through the bypass oil passage, and the relief valve being operated in accordance with a control electric signal; 
     a restrictor that is disposed in a part of an outlet or an inlet of the relief valve; and 
     a lubricating oil supply controlling controller to which control information of the engine controller and/or control information of the transmission controller is input and that generates and outputs the control electric signal for operating the relief valve in accordance with the control information. 
     A second embodiment of the present invention is a lubricating oil supply control device for a transmission of a vehicle that is driven by an output of an engine transmitted to the transmission, comprising: 
     an engine controller for controlling the engine; 
     a transmission controller for controlling the transmission; 
     a lubricating oil supplying oil passage for guiding lubricating oil, which is discharged from a hydraulic pump, to the transmission; 
     a bypass oil passage for guiding the lubricating oil, which is in the lubricating oil supplying oil passage, to a tank; 
     a control valve for adjusting an amount of the lubricating oil that is guided to the transmission through the lubricating oil supplying oil passage and an amount of the lubricating oil that is guided from the lubricating oil supplying oil passage to the tank through the bypass oil passage, and the control valve being operated in accordance with a control electric signal; and 
     a lubricating oil supply controlling controller to which control information of the engine controller and/or control information of the transmission controller is input, and that generates and outputs the control electric signal for operating the control valve in accordance with the control information. 
     A third embodiment of the present invention is a lubricating oil supply control device for a transmission of a vehicle that is driven by an output of an engine transmitted to the transmission, comprising: 
     a lubricating oil supplying oil passage for guiding lubricating oil, which is discharged from a hydraulic pump, to the transmission; 
     a bypass oil passage for guiding the lubricating oil, which is in the lubricating oil supplying oil passage, to a tank; 
     a relief valve for discharging the lubricating oil, which is in the lubricating oil supplying oil passage, to the tank through the bypass oil passage, and the relief valve being operated in accordance with a control electric signal; 
     a restrictor that is disposed in a part of an outlet or an inlet of the relief valve; and a lubricating oil supply controlling controller for outputting the control electric signal for operating the relief valve. 
     A fourth embodiment of the present invention is a lubricating oil supply control device for a transmission of a vehicle that is driven by an output of an engine transmitted to the transmission, comprising: 
     a lubricating oil supplying oil passage for guiding lubricating oil, which is discharged from a hydraulic pump, to the transmission; 
     a bypass oil passage that guides the lubricating oil, which is in the lubricating oil supplying oil passage, to a tank; 
     a control valve for adjusting an amount of the lubricating oil that is guided to the transmission through the lubricating oil supplying oil passage and an amount of the lubricating oil that is guided from the lubricating oil supplying oil passage to the tank through the bypass oil passage, and the control valve being operated in accordance with a control electric signal; and 
     a lubricating oil supply controlling controller for outputting the control electric signal for operating the control valve. 
     As shown in  FIG. 1  and  FIG. 2 , the lubricating oil supply control device for the transmission  3  according to the first invention comprises an engine controller  30  for controlling an engine  1 ; a transmission controller  40  for controlling the transmission  3 ; a lubricating oil supplying oil passage  17  for guiding lubricating oil, which is discharged from a lubricating hydraulic pump  9 , to the transmission  3 ; bypass oil passages  21 ,  23  for guiding the lubricating oil, which is in the lubricating oil supplying oil passage  17 , to a lubricating oil tank  8 ; a relief valve  22  for discharging the lubricating oil, which is in the lubricating oil supplying oil passage  17 , to the lubricating oil tank  8  through the bypass oil passages  21 ,  23  and operating in accordance with a control electric signal i; a restrictor  28  which is disposed in a part of an outlet of the relief valve  22 ; and a lubricating oil supply controlling controller  50  to which control information of the engine controller  30  and (or) control information of the transmission controller  40  are input and which generates and outputs the control electric signal i for operating the relief valve  22  in accordance with the control information. 
     When the control electric signal i for operating the relief valve  22  is output from the lubricating oil supply controlling controller  50  (judged YES in either step  102  or  103  in  FIG. 3 ; step  104 ), the relief valve  22  operates to open. 
     Therefore, the lubricating oil which is guided to the lubricating oil supplying oil passage  17  is partly flown through the relief valve  22  via the bypass oil passage  21 . The lubricating oil which has flown through the relief valve  22  is discharged to the lubricating oil tank  8  via the bypass oil passage  23  and the restrictor  28 . 
     The rest of the lubricating oil which is guided to the lubricating oil supplying oil passage  17  is supplied to the transmission  3 . 
     According to the present invention, when the engine  1  has a low load or the transmission  3  has a low load (judged YES in step  102  or judged YES in step  103 ), the control electric signal i is output from the lubricating oil supply controlling controller  50  (step  104 ), and the lubricating oil which is to be supplied to the transmission  3  is partly discharged to the lubricating oil tank  8 . Thus, a mechanical friction of the transmission  3  is decreased and its cooling is performed to protect the component parts of the transmission  3 , while the lubricating oil is prevented from being supplied excessively to decrease a power loss of the transmission  3 , thereby enabling to improve the fuel consumption of the engine  1  and to attain energy saving. 
     And, according to the present invention, the control information of the engine controller  30  and the control information of the transmission controller  40  are input to the lubricating oil supply controlling controller  50 , and the control electric signal i is output in accordance with the control information to operate the relief valve  22 , thereby controlling the supply of the lubricating oil. Therefore, the control system can be configured easily at a low cost by using the existing control information which is used by the existing engine controller  30  and transmission controller  40 . In other words, it is not necessary to add a new sensor in order to obtain the control information. It is not necessary to process the detection signals of the sensors by the controller and to convert into an engineering unit required for arithmetic processing. And, it is not necessary to calculate newly the load of the engine and the load of the transmission by the controller in accordance with the detections values of the various types of sensors. Therefore, the processing performed by the controller can be simplified as exemplified in  FIG. 3 . 
     According to the invention, the hydraulic circuit is configured such that the relief valve  22  is operated to discharge the lubricating oil, which is in the lubricating oil supplying oil passage  17 , to the lubricating oil tank  8  through the bypass oil passage  21 , the relief valve  22 , and the bypass oil passage  23 . Therefore, it is sufficient by adding a valve body and piping to the existing lubricating oil supplying oil passage  17  of the hydraulic circuit to discharge the lubricating oil, which is in the lubricating oil supplying oil passage  17 . Thus, to configure the device of the hydraulic system, the valve body structure and the arrangement of the hydraulic pipes can be made simple, and the cost can be reduced. 
     According to the second invention, instead of the relief valve  22  and the restrictor  28  of the first invention, a control valve  60  having the same functions is used. In other words, as shown in  FIG. 6 , the control valve  60  adjusts an amount of the lubricating oil which is guided to the transmission  3  through the lubricating oil supplying oil passage  17  and an amount of the lubricating oil which is guided from the lubricating oil supplying oil passage  17  to the lubricating oil tank  8  through the bypass oil passage  23  in accordance with the control electric signal i which is output from the lubricating oil supply controlling controller  50 . 
     According to the first invention and the second invention, the control information of the engine controller  30  and the transmission controller  40  is input to the lubricating oil supply controlling controller  50  to control the supply of the lubricating oil, but the lubricating oil supply controlling controller  50  may control the supply of the lubricating oil in accordance with information other than the control information of the engine controller  30  and the transmission controller  40  (the third invention, and the fourth invention). 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the lubricating oil supply control device for the transmission of the vehicle according to the invention will be described below with reference to the drawings. It is assumed in the embodiments that the vehicle is a wheel loader. 
     First Embodiment 
       FIG. 1  is a diagram showing a structure of a power transmission path of a wheel loader  100 .  FIG. 2  is a diagram showing a structure of a lubricating oil supply circuit of the wheel loader  100 . 
     The lubricating oil supply control device for a transmission  3  of this embodiment is generally comprised of the engine controller  30  for controlling the engine  1 , the transmission controller  40  for controlling the transmission  3 , the lubricating oil supplying oil passage  17  for guiding the lubricating oil, which is discharged from the lubricating oil pump  9 , to the transmission  3 , the bypass oil passages  21 ,  23  for guiding the lubricating oil, which is in the lubricating oil supplying oil passage  17 , to the lubricating oil tank  8 , the relief valve  22  for discharging the lubricating oil, which is in the lubricating oil supplying oil passage  17 , to the lubricating oil tank  8  through the bypass oil passages  21 ,  23  and operating in accordance with the control electric signal i, the restrictor  28  which is disposed in the part of the outlet of the relief valve  22 , and the lubricating oil supply controlling controller  50  to which control information of the engine controller  30  and control information of the transmission controller  40  are input and which generates and outputs the control electric signal i for operating the relief valve  22  in accordance with the control information. 
     Additionally, an output shaft of the engine  1  of the wheel loader  100  is coupled with a PTO shaft  7 . The PTO shaft  7  is coupled with the torque converter  2 . Output of the engine  1  is transmitted to driving wheels  5  via the PTO shaft  7 , the torque converter  2 , the transmission  3 , and a differential gear  4 . 
     A gas pedal  6  is disposed in the operator&#39;s cabin of the wheel loader  100 . An operation amount (depressing amount) is detected by a stroke sensor  6   a  which is disposed for the gas pedal  6 , and a signal indicating the operation amount is input to the engine controller  30 . 
     The engine controller  30  controls the engine  1  in accordance with the input signal from the stroke sensor  6   a  so that the number of revolutions of the engine  1  becomes a target number of revolutions corresponding to the operation amount of the gas pedal  6 . 
     The engine  1  is a diesel engine, and its output is controlled by adjusting an injection quantity injected into a cylinder. This adjustment is made by changing a stroke of a plunger of the fuel injection pump of the engine  1  by a control rack of an electric governor. 
     The engine controller  30  receives input of actual engine revolutions, control rack position and the like and outputs a control electric signal to the electric governor so that a difference between a target number of revolution and the actual number of revolution is eliminated, thereby controlling a control rack position of the electric governor. 
     The control electric signal which is output from the engine controller  30  is output as control information indicating a load (fuel injection quantity) of the engine  1 , as described later, to the lubricating oil supply controlling controller  50  through an electrical signal line  31 . 
     The transmission  3  is configured of, for example, a planetary gear transmission. The planetary gear transmission is comprised of plural sets of hydraulic clutches and plural sets of planetary gear mechanisms and changes a speed by changing a flow of power for transmitting the plural sets of planetary gear mechanisms in accordance with the selection of the hydraulic clutches. The plural sets of hydraulic clutches comprise a forward hydraulic clutch, a reverse hydraulic clutch, and a speed stage hydraulic clutch, namely, a first speed hydraulic clutch, a second speed hydraulic clutch, a third speed hydraulic clutch and a fourth speed (maximum speed stage) hydraulic clutch. While the forward hydraulic clutch or the reverse hydraulic clutch is selected, any of the speed stage hydraulic clutches is selected, depending on the vehicle speed or the like, to change the speed. 
     The transmission  3  is provided with a proportional electromagnetic control valve for each of the hydraulic clutches. According to the control electric signal (control information) applied to the proportional electromagnetic control valve, the pressure oil is supplied to the corresponding hydraulic clutch, and the hydraulic clutch is engaged. 
     The transmission controller  40 , by receiving inputs of an operation position of the running operation lever, a vehicle speed and the like, selects either the forward hydraulic clutch or the reverse hydraulic clutch and any of the speed stage clutches, and outputs the control electric signal for engaging the selected hydraulic clutch to the proportional electromagnetic control valve of the corresponding hydraulic clutch. 
     The control electric signal which is output from the transmission controller  40  is output, as control information indicating a load (speed stage) of the transmission  3 , to the lubricating oil supply controlling controller  50  through an electrical signal line  41  as described later. 
     The transmission  3  comprises a speed change mechanism section having a planetary gear mechanism (mating mechanism) and a clutch portion having a clutch (friction engagement element). 
     It is necessary to supply the lubricating oil to the speed change mechanism section of the transmission  3  and the clutch portion to perform reduction of mechanical friction, cooling, corrosion prevention and the like. 
     The lubricating oil tank  8  which configures a part of the casing of the transmission  3  is disposed below the transmission  3 . 
     The drive shaft of the lubricating oil pump  9  is coupled to the PTO shaft  7 . 
     The output of the engine  1  is transmitted to the lubricating oil pump  9  through the PTO shaft  7  to drive the lubricating oil pump  9 . 
     A suction port  9   a  of the lubricating oil pump  9  is communicated with the lubricating oil tank  8  through a sucking oil passage  10 . The sucking oil passage  10  is provided with a strainer  12 . 
     A discharge port  9   b  of the lubricating oil pump  9  is communicated with an inlet port of a main relief valve  13  through a pump outlet oil passage  11 . The outlet port of the main relief valve  13  is communicated with an inlet of the torque converter  2  through an oil passage  14 . 
     An oil passage  15  is communicated with the oil passage  14 . The oil passage  15  is provided with a restrictor  15   a  and communicated with the PTO shaft  7 . 
     The outlet of the torque converter  2  is communicated with the inlet of an oil cooler  16 . 
     The lubricating oil which flows through the oil cooler  16  is cooled by a flow of air formed by an unshown cooling fan. 
     The outlet of the oil cooler  16  is communicated with the lubricating oil supplying oil passage  17 . The lubricating oil supplying oil passage  17  is communicated with the transmission  3  and supplies the lubricating oil to the speed change mechanism section of the transmission  3 , the clutch portion and the like. The pressure oil discharged from the lubricating oil pump  9  is also used as an original pressure of the pressure oil which is supplied to the hydraulic clutch. 
     The lubricating oil supplying oil passage  17  is communicated with the bypass oil passage  21 . 
     The bypass oil passage  21  is communicated with an inlet port  22   a  of the relief valve  22 . An outlet port (tank port)  22   b  of the relief valve  22  is communicated with the bypass oil passage  23 . The bypass oil passage  23  is provided with the restrictor  28 . The downstream side of the restrictor  28  is communicated with the lubricating oil tank  8 . 
     One end of a spring  22   c  which determines a prescribed relief pressure is contacted to one end of a spool or a ball of the relief valve  22 . A pressure receiving surface of the other end (the opposite side of the spring  22   c ) of the spool or the ball of the relief valve  22  is communicated with the inlet port  22   a  through a pilot oil passage  24 . 
     Similarly, the other end (the opposite side of the spring  22   c ) of the spool or the ball of the relief valve  22  is provided with a pilot port  22   d  to which a pilot pressure Pc is applied. 
     The pump outlet oil passage  11  is branched to a pilot oil passage  25 . 
     The pilot oil passage  25  is communicated with an inlet port  26   c  of an electromagnetic control valve  26 . 
     An outlet port  26   d  of the electromagnetic control valve  26  is communicated with the pilot port  22   d  of the relief valve  22  through a pilot oil passage  27 . 
     A tank port  26   f  of the electromagnetic control valve  26  is communicated with the lubricating oil tank  8  through an oil passage  29 . 
     An electromagnetic solenoid  26   e  of the electromagnetic control valve  26  is electrically connected to the lubricating oil supply controlling controller  50  through an electrical signal line  51 . 
     The lubricating oil supply controlling controller  50  is electrically connected to the engine controller  30  through the electrical signal line  31 . 
     The lubricating oil supply controlling controller  50  is electrically connected to the transmission controller  40  through the electrical signal line  41 . 
     In  FIG. 2 , the lubricating oil supply controlling controller  50  is shown as a separate body of the engine controller  30  and the transmission controller  40 , but the lubricating oil supply controlling controller  50  may be configured as one body with the engine controller  30 . The lubricating oil supply controlling controller  50  may also be configured into one body with the transmission controller  40 . 
     The electromagnetic control valve  26  is a two position valve having two valve positions  26 A,  26 B. One end of a spring  26   g  is contacted to the spool of the electromagnetic control valve  26  on the side opposite to the electromagnetic solenoid  26   e.    
     The electromagnetic control valve  26  is switched between the valve positions  26 A and  26 B depending on the control electric signal i applied to the electromagnetic solenoid  26   e.    
     In a case where the control electric signal i is not applied to the electromagnetic solenoid  26   e , the spool of the electromagnetic control valve  26  is switched to the lubricating oil supply position  26 A by a spring force of the spring  26   g . And, the outlet port  26   d  and the tank port  26   f  of the electromagnetic control valve  26  are mutually communicated. 
     Where the control electric signal i is applied to the electromagnetic solenoid  26   e , a pushing force is generated by the electromagnetic solenoid  26   e . The pushing force is more powerful than the spring force of the spring  26   g  and switches the spool of the electromagnetic control valve  26  to the lubricating oil discharge position  26 B. Then, the inlet port  26   c  and the outlet port  26   d  of the electromagnetic control valve  26  are mutually communicated. 
       FIG. 3  is a flow chart showing a processing procedure performed by the lubricating oil supply controlling controller  50 . A program corresponding to the flow chart has been installed in the lubricating oil supply controlling controller  50 . 
     Control information of the engine controller  30  is sent to the lubricating oil supply controlling controller  50  through the electrical signal line  31 . And, control information of the transmission controller  40  is sent to the lubricating oil supply controlling controller  50  through the electrical signal line  41 . A data frame signal in accordance with a prescribed protocol is sent between the individual controllers. In the engine controller  30 , the control information which is in the engine controller  30  is written in the data frame signal, and it is sent to the electrical signal line  31 . In the transmission controller  40 , the control information which is in the transmission controller  40  is written in the data frame signal, and it is sent to the electrical signal line  41 . 
     In the lubricating oil supply controlling controller  50 , the control information of the engine controller  30  and the control information of the transmission controller  40  are read from the input data frame signal (step  101 ). 
     Then, according to the control information of the engine controller  30  and the control information of the transmission controller  40 , it is judged whether or not a load of the engine  1  and a load of the transmission  3  are low (steps  102 ,  103 ). If the load of the engine  1  or the load of the transmission  3  is low (judged YES in step  102  or judged YES in step  103 ), it is judged that the lubricating oil which is supplied to the transmission  3  is excessive and must be reduced. In other words, if the load is light, the lubricating oil is sufficient in a small amount to protect the component parts of the transmission  3  by decreasing the mechanical friction and cooling by the lubricating oil. If the oil is supplied in an amount more than necessary, it becomes resistant when the planetary gear and the like revolve, a power loss is caused, and the fuel consumption of the engine  1  becomes poor. Therefore, when it is judged that the load is light and the lubricating oil to be supplied to the transmission  3  must be decreased, the control electric signal i for decreasing the lubricating oil to be supplied to the transmission  3  is output in order to decrease the lubricating oil which is supplied to the transmission  3  (step  104 ). After the process in step  104 , the process returns to step  101 . 
     Specifically, it is judged whether or not a load a (fuel injection quantity) of the engine  1  is a prescribed threshold value ac or less, namely it is judged whether or not the engine  1  is operating under a low load. Here, the threshold value ac can be set to 70% of the maximum torque (step  102 ). 
     It is also judged whether or not a speed stage β which is selected by the transmission  3  is a light-load speed stage βc, namely it is judged whether or not the transmission  3  is operating under a low load. Here, the light-load speed stage βc is set to, for example, “forward 4th-speed” which is the forward maximum speed stage. The case where the “forward 4th-speed” is selected is a case where the forward hydraulic clutch and the four speed hydraulic clutch are mutually engaged (step  103 ). 
     If it is judged NO in steps  102  and  103 , it is judged that the lubricating oil to be supplied to the transmission  3  must be increased. In other words, where the load is high, the oil is required in a large amount to protect the component parts of the transmission  3  by reducing the mechanical friction and cooling by the lubricating oil. Therefore, where the load is high and it is judged that the lubricating oil to be supplied to the transmission  3  must be increased, the process returns to step  101  with the control electric signal i for decreasing the lubricating oil to be supplied to the transmission  3  remaining off so that the lubricating oil to be supplied to the transmission  3  is not decreased. 
     An operation of this embodiment will be described additionally referring to the hydraulic circuit of  FIG. 2 . 
     Where the output of the control electric signal i from the lubricating oil supply controlling controller  50  is off (judged NO in steps  102  and  103 ), the control electric signal i is not added to the electromagnetic solenoid  26   e  of the electromagnetic control valve  26 , and the electromagnetic control valve  26  is switched to the lubricating oil supply position  26 A by the spring force of the spring  26   g.    
     The lubricating oil which is in the lubricating oil tank  8  is sucked from the suction port  9   a  of the lubricating oil pump  9  through a sucking oil passage  10  and discharged from the discharge port  9   b  of the lubricating oil pump  9  to the pump outlet oil passage  11 . The lubricating oil which is pump outlet pressure oil is supplied to the torque converter  2  via the pump outlet oil passage  11 , the main relief valve  13  and the oil passage  14 . The lubricating oil which is supplied to the torque converter  2  is used as operating oil for transmitting the driving force of the torque converter  2 . 
     The lubricating oil guided to the oil passage  14  is supplied to the PTO shaft  7  via the oil passage  15  and the restrictor  15   a  disposed in the oil passage  15 . Thus, the component parts of the PTO shaft  7  are lubricated. The lubricating oil which has lubricated the PTO shaft  7  is discharged to the lubricating oil tank  8 . 
     The lubricating oil which has flown through the torque converter  2  is guided to the lubricating oil supplying oil passage  17  via the oil cooler  16 . 
     The lubricating oil which is guided to the lubricating oil supplying oil passage  17  is supplied to the transmission  3 . Thus, the transmission  3  is lubricated. The lubricating oil which has lubricated the transmission  3  is discharged to the lubricating oil tank  8 . 
     The lubricating oil which is guided to the pump outlet oil passage  11  is supplied as the pilot pressure oil (pilot pressure Pc) to the inlet port  26   c  of the electromagnetic control valve  26  through the pilot oil passage  25 . 
     Here, the pilot pressure oil which is supplied to the inlet port  26   c  is cut off by the inlet port  26   c  of the electromagnetic control valve  26  because the electromagnetic control valve  26  has been switched to the lubricating oil supply position  26 A. The pilot port  22   d  of the relief valve  22  is communicated with the lubricating oil tank  8  via the pilot oil passage  27 , the outlet port  26   d  and the tank port  26   f  of the electromagnetic control valve  26 , and the oil passage  29 . 
     Therefore, the pressure acting on the pilot port  22   d  of the relief valve  22  becomes a tank pressure, and the relief valve  22  does not reach a predetermined relief pressure and is closed by the spring force of the spring  22   c.    
     Therefore, the lubricating oil, which is guided to the lubricating oil supplying oil passage  17 , is not discharged to the lubricating oil tank  8  via the bypass oil passage  21 , the relief valve  22  and the bypass oil passage  23 , but its all amount is supplied to the transmission  3 . 
     Meanwhile, in a case where the control electric signal i is being output from the lubricating oil supply controlling controller  50  (judged YES in step  102  or  103 , step  104 ), a pushing force is generated by the electromagnetic solenoid  26   e  of the electromagnetic control valve  26 , and the pushing force becomes more powerful than the spring force of the spring  26   g , and the electromagnetic control valve  26  is switched to the lubricating oil discharge position  26 B. 
     Thus, the inlet port  26   c  and the outlet port  26   d  of the electromagnetic control valve  26  are mutually communicated, the pilot pressure oil (pilot pressure Pc) which is supplied to the inlet port  26   c  is applied to the pilot port  22   d  of the relief valve  22  through the outlet port  26   d  of the electromagnetic control valve  26  and the pilot oil passage  27 . 
     The pilot pressure Pc acting on the pilot port  22   d  of the relief valve  22  is equivalent to or higher than the predetermined relief pressure of the relief valve  22 , a force corresponding to the pilot pressure Pc becomes more powerful than the spring force of the spring  22   c , and the relief valve  22  is opened. 
     Therefore, the lubricating oil which is guided to the lubricating oil supplying oil passage  17  is partly flown through the relief valve  22  via the bypass oil passage  21 . The lubricating oil which has passed through the relief valve  22  is discharged to the lubricating oil tank  8  through the bypass oil passage  23  and the restrictor  28 . 
     And, the rest of the lubricating oil which has been guided to the lubricating oil supplying oil passage  17  is supplied to the transmission  3 . 
     A ratio of a discharge flow rate of the lubricating oil which is discharged to the lubricating oil tank  8  from the lubricating oil supplying oil passage  17  through the relief valve  22  and a supply flow rate of the lubricating oil which is supplied from the lubricating oil supplying oil passage  17  to the transmission  3  can be adjusted depending on the setting of a size of the opening area of the restrictor  28  which is disposed in the outlet side of the relief valve  22 . 
     The discharge flow rate of the lubricating oil, which is discharged from the lubricating oil supplying oil passage  17  to the lubricating oil tank  8  through the relief valve  22 , becomes higher as the opening area of the restrictor  28  becomes larger, and the supply flow rate of the lubricating oil which is supplied from the lubricating oil supplying oil passage  17  to the transmission  3  decreases. 
     If clogging or the like occurs within the transmission  3 , the pressure of the lubricating oil within the bypass oil passage  21  increases. Therefore, a pressure which acts on the pressure receiving surface of the relief valve  22 , which is the opposite side to the spring  22   c , through the bypass oil passage  21  and the pilot oil passage  24  increases to become higher than the predetermined relief pressure, and the relief valve  22  is opened. Therefore, if the clogging or the like occurs within the transmission  3 , the lubricating oil, which is guided to the lubricating oil supplying oil passage  17 , is partly discharged to the lubricating oil tank  8  through the bypass oil passage  21 , the relief valve  22 , the bypass oil passage  23  and the restrictor  28  even if the output of the control electric signal i from the lubricating oil supply controlling controller  50  is off (judged NO in steps  102  and  103 ). 
     According to this embodiment described above, if the load of the engine  1  is low or the load of the transmission  3  is low (judged YES in step  102  or judged YES in step  103 ), the control electric signal i is output from the lubricating oil supply controlling controller  50  (step  104 ), and the lubricating oil which should be supplied to the transmission  3  is partly discharged to the lubricating oil tank  8 , so that the mechanical friction of the transmission  3  is decreased and cooling is performed to protect the component parts of the transmission  3 , and the excessive supply of the lubricating oil is prevented to decrease a power loss of the transmission  3 , thereby capable of improving the fuel consumption of the engine  1  and attaining energy saving. 
     And, according to this embodiment, the supply of the lubricating oil is controlled so that control information of the engine controller  30  and control information of the transmission controller  40  are input to the lubricating oil supply controlling controller  50 , and the control electric signal i is generated and output in accordance with the control information to operate the relief valve  22 . Therefore, the control system can be configured easily at a low cost by using conventional control information, which is used for the conventional engine controller  30  and transmission controller  40 , for the vehicle control system. In other words, it is not necessary to add a new sensor in order to obtain the control information. And, it is not necessary to perform signal processing of the detected signal from the sensor by the controller to convert it to an engineering unit required for arithmetic processing. And, it is not necessary to newly calculate a load of the engine and a load of the transmission by the controller in accordance with the detection values by the various types of sensors. Therefore, the processing performed by the controller can be simplified as exemplified in  FIG. 3 . 
     According to this embodiment, the hydraulic circuit is configured so that the relief valve  22  is operated to discharge the lubricating oil, which is in the lubricating oil supplying oil passage  17 , to the lubricating oil tank  8  through the bypass oil passage  21 , the relief valve  22  and the bypass oil passage  23 . Therefore, it is sufficient by adding a valve body and piping for discharging the lubricating oil which is in the lubricating oil supplying oil passage  17  to the existing lubricating oil supplying oil passage  17  of the hydraulic circuit, so that the structure of valve bodies and the arrangement of hydraulic pipings can be made simple and the cost can be reduced when the hydraulic device is configured. 
     The above-described first embodiment can be modified in various ways. 
     Although, in the first embodiment, the control information of the engine controller  30  and the control information of the transmission controller  40  are input to the lubricating oil supply controlling controller  50 , either the control information of the engine controller  30  or the control information of the transmission controller  40  may be input. In this case, either processing in step  102  or step  103  is omitted in the processing shown in  FIG. 3 . 
     In the first embodiment, both the control information of the engine controller  30  and the control information of the transmission controller  40  are input to the lubricating oil supply controlling controller  50 . And if it is established whether the load of the engine  1  is low or the load of the transmission  3  is low as shown in  FIG. 3  (judged YES in step  102  or judged YES in step  103 ), the control electric signal i for operating the relief valve  22  is output (step  104 ). 
     As shown in  FIG. 4 , however, it is also possible to output the control electric signal i for operating the relief valve  22  (step  104 ) on condition that the load of the engine  1  is low and the load of the transmission  3  is low (judged YES in step  102  and judged YES in step  103 ). 
     And, in the first embodiment, the control electric signal which is output from the engine controller  30  to an electric governor of the engine  1  is input as control information to the lubricating oil supply controlling controller  50 . It is just an example, and the detection value of the stroke sensor  6   a  which is input to the engine controller  30 , namely an operation amount of the gas pedal  6 , may be input as control information indicating the load of the engine  1  to the lubricating oil supply controlling controller  50 . Where the operation amount of the gas pedal  6  is not higher than a prescribed operation amount, it may be judged by the lubricating oil supply controlling controller  50  that the load of the engine  1  is small. 
     In the first embodiment, the restrictor  28  is disposed in the bypass oil passage  23  on the outlet side of the relief valve  22  to discharge the lubricating oil having a flow rate corresponding to the opening area of the restrictor  28  to the lubricating oil tank  8 . But, the restrictor  28  may be disposed in the bypass oil passage  21  on the inlet side of the relief valve  22  instead of its disposition in the bypass oil passage  23 . And, the restrictor  28  may be disposed in each of the bypass oil passage  23  on the outlet side of the relief valve  22  and the bypass oil passage  21  on the inlet side of the relief valve  22 . 
     Second Embodiment 
     In the first embodiment, the pilot pressure oil (pilot pressure Pc) which is output from the electromagnetic control valve  26  is caused to act on the pilot port  22   d  of the relief valve  22 , such that the relief valve  22  operates to open. By configuring in this way, the electromagnetic solenoid (the electromagnetic solenoid  26   e  of the electromagnetic control valve  26 ) to which the control electric signal i is input can be made compact. 
     As shown in  FIG. 5A , however, it may be configured to make the control electric signal i output from the lubricating oil supply controlling controller  50  directly act on the relief valve  22  through the electrical signal line  51 . 
     In other words,  FIG. 5A  is a diagram of a hydraulic circuit corresponding to  FIG. 2 . It should be noted that component elements not shown in  FIG. 5A  are same as those of  FIG. 2  unless otherwise specified. In  FIG. 5A , however, the disposition of the electromagnetic control valve  26 , the pilot oil passages  25 ,  27  and the discharge oil passage  29  which are disposed in the hydraulic circuit of  FIG. 2  are omitted. And, the relief valve  22  is provided with an electromagnetic solenoid  22   e  instead of the pilot port  22   d  show in  FIG. 2 . 
     Where the control electric signal i is not output from the lubricating oil supply controlling controller  50 , the electromagnetic solenoid  22   e  of the relief valve  22  is not energized, and the relief valve  22  is closed by the spring force of the spring  22   c.    
     Therefore, the lubricating oil, which is guided to the lubricating oil supplying oil passage  17 , is not discharged to the lubricating oil tank  8  through the bypass oil passage  21 , the relief valve  22  and the bypass oil passage  23 , but its all amount is supplied to the transmission  3 . 
     Meanwhile, where the control electric signal i is being output from the lubricating oil supply controlling controller  50 , a pushing force is generated by the electromagnetic solenoid  22   e  of the relief valve  22 , and the pushing force becomes more powerful than the spring force of the spring  22   c , and the relief valve  22  is opened. 
     Therefore, the lubricating oil which is guided to the lubricating oil supplying oil passage  17  is partly discharged to the lubricating oil tank  8  through the bypass oil passage  21 , the relief valve  22 , the bypass oil passage  23  and the restrictor  28 . And, the rest of the lubricating oil which is guided to the lubricating oil supplying oil passage  17  is supplied to the transmission  3 . 
     Third Embodiment 
     In the above-described embodiment, the relief valve  22  is used as the control valve to discharge the lubricating oil to the lubricating oil tank  8  through the bypass circuits  21 ,  23 . But, a control valve other than the relief valve  22  can also be used to discharge the lubricating oil. Specifically, any type of control valve may be used if it adjusts an amount of the lubricating oil which is guided to the transmission  3  through the lubricating oil supplying oil passage  17  and an amount of the lubricating oil which is guided from the lubricating oil supplying oil passage  17  to the lubricating oil tank  8  through the bypass oil passage  23 . 
       FIG. 6  is a diagram of the hydraulic circuit of this embodiment and corresponds to  FIG. 2 . It should be noted that component elements not shown in  FIG. 6  are same as those of  FIG. 2  unless otherwise specified. 
     As shown in  FIG. 6 , the control valve  60  configured as a two position valve is disposed instead of the relief valve  22  of  FIG. 2 . 
     The outlet of the oil cooler  16  is communicated with the lubricating oil supplying oil passage  17 . 
     The lubricating oil supplying oil passage  17  is communicated with an inlet port  60   c  of the control valve  60 . An outlet port  60   d  of the control valve  60  is communicated with the transmission  3  and supplies the lubricating oil to the speed change mechanism section of the transmission  3 , the clutch portion and the like. 
     A tank port  60   f  of the control valve  60  is communicated with the bypass oil passage  23 . The bypass oil passage  23  is communicated with the lubricating oil tank  8 . 
     The control valve  60  is a two position valve having two valve positions  60 A (lubricating oil supply position) and  60 B (lubricating oil discharge position). The control valve  60  is switched between the valve positions  60 A and  60 B in accordance with the pilot pressure Pc which is applied to a pilot port  60   e . The pilot port  60   e  is communicated with the outlet port  26   d  of the electromagnetic control valve  26  through the pilot oil passage  27 . 
     One end of a spring  60   g  is contacted on the spool of the control valve  60  on the side opposite to the pilot port  60   e . The pressure receiving surface of the spool of the control valve  60  on the pilot port  60   e  side (the opposite side of the spring  60   g ) is communicated with the inlet port  60   c  through the pilot oil passage  24 . 
     When the control valve  60  is switched to the lubricating oil supply position  60 A, the inlet port  60   c  is communicated with the outlet port  60   d  via a restrictor  61 . 
     When the control valve  60  is switched to the lubricating oil discharge position  60 B, the inlet port  60   c  is communicated with the outlet port  60   d  via a restrictor  62 , and the inlet port  60   c  is communicated with the tank port  60   f  via a restrictor  63 . 
     A ratio of a discharge flow rate of the lubricating oil which is discharged from the lubricating oil supplying oil passage  17  to the lubricating oil tank  8  through the control valve  60  and a supply flow rate of the lubricating oil which is supplied from the lubricating oil supplying oil passage  17  to the transmission  3  can be adjusted by adjusting a ratio of the opening area of the restrictor  63  and the opening area of the restrictor  62  which are disposed in the control valve  60 . 
     The discharge flow rate of the lubricating oil which is discharged from the lubricating oil supplying oil passage  17  to the lubricating oil tank  8  through the control valve  60  becomes higher while the supply flow rate of the lubricating oil which is supplied from the lubricating oil supplying oil passage  17  to the transmission  3  decreases as the opening area of the restrictor  63  is made larger in comparison with the opening area of the restrictor  62 . 
     Then, an operation to be performed by the hydraulic circuit of  FIG. 6  will be described assuming that the processing shown in  FIG. 3  or  FIG. 4  has been performed by the lubricating oil supply controlling controller  50 . 
     Where the output of the control electric signal i from the lubricating oil supply controlling controller  50  is off, the control electric signal i is not added to the electromagnetic solenoid  26   e  of the electromagnetic control valve  26 , and the electromagnetic control valve  26  is switched to the lubricating oil supply position  26 A by the spring force of the spring  26   g.    
     The lubricating oil which has flown through the torque converter  2  is guided to the lubricating oil supplying oil passage  17  via the oil cooler  16 . 
     The lubricating oil which is guided to the lubricating oil supplying oil passage  17  is supplied to the inlet port  60   c  of the control valve  60 . 
     The lubricating oil which is guided to the pump outlet oil passage  11  is supplied as the pilot pressure oil (pilot pressure Pc) to the inlet port  26   c  of the electromagnetic control valve  26  through the pilot oil passage  25 . 
     Here, the pilot pressure oil which is supplied to the inlet port  26   c  is cut off at the inlet port  26   c  of the electromagnetic control valve  26  because the electromagnetic control valve  26  has been switched to the lubricating oil supply position  26 A. The pilot port  60   e  of the control valve  60  is communicated with the lubricating oil tank  8  via the pilot oil passage  27 , the outlet port  26   d  and the tank port  26   f  of the electromagnetic control valve  26 , and the oil passage  29 . 
     Therefore, the pressure acting on the pilot port  60   e  of the control valve  60  becomes a tank pressure, and the control valve  60  is positioned at the lubricating oil supply position  60 A by the spring force of the spring  60   g.    
     Therefore, the lubricating oil, which is guided to the lubricating oil supplying oil passage  17 , is supplied in full amount to the transmission  3  through the restrictor  60   d  of the control valve  60 . 
     Therefore, the lubricating oil, which is guided to the lubricating oil supplying oil passage  17 , is not discharged to the lubricating oil tank  8  through the bypass oil passage  23  but its all amount is supplied to the transmission  3 . 
     On the other hand, where the control electric signal i is output from the lubricating oil supply controlling controller  50 , a pushing force is generated by the electromagnetic solenoid  26   e , and the pushing force becomes more powerful than the spring force of the spring  26   g , and the electromagnetic control valve  26  is switched to the lubricating oil discharge position  26 B. 
     Thus, the inlet port  26   c  and the outlet port  26   d  of the electromagnetic control valve  26  are mutually communicated, the pilot pressure oil (pilot pressure Pc) which is supplied to the inlet port  26   c  is applied to the pilot port  60   e  of the control valve  60  through the outlet port  26   d  of the electromagnetic control valve  26  and the pilot oil passage  27 . 
     A force corresponding to the pilot pressure Pc, which acts on the pilot port  60   e  of the control valve  60 , becomes more powerful than the spring force of the spring  60   g , and the control valve  60  is positioned at the lubricating oil discharge position  60 B. 
     Therefore, the lubricating oil, which is guided to the lubricating oil supplying oil passage  17 , is partly discharged to the lubricating oil tank  8  through the restrictor  63  of the control valve  60  and the bypass oil passage  23 . And, the rest of the lubricating oil, which has been guided to the lubricating oil supplying oil passage  17 , is supplied to the transmission  3  via the restrictor  62  of the control valve  60 . 
     If clogging or the like occurs within the transmission  3 , the pressure of the inlet port  60   c  of the control valve  60  increases. Therefore, through the pilot oil passage  24 , the pressure which acts on the pressure receiving surface of the control valve  60  on the opposite side of the spring  60   g  increases, and the control valve  60  is switched to the lubricating oil supply position  60 B. Therefore, if clogging or the like occurs within the transmission  3 , even when the output of the control electric signal i from the lubricating oil supply controlling controller  50  is off, the lubricating oil, which has been guided to the lubricating oil supplying oil passage  17 , is partly discharged to the lubricating oil tank  8  through the control valve  60  and the bypass oil passage  23 . 
     Fourth Embodiment 
     In the above-described third embodiment, the pilot pressure oil (pilot pressure Pc) which is output from the electromagnetic control valve  26  is caused to act on the pilot port  60   e  of the control valve  60  to make the control valve  60  perform a switching operation. By configuring in this way, the electromagnetic solenoid (electromagnetic solenoid  26   e  of the electromagnetic control valve  26 ) to which the control electric signal i is applied can be made compact. 
     As show in  FIG. 5B , however, it may be configured such that the control electric signal i, which is output from the lubricating oil supply controlling controller  50 , is directly acted on the electromagnetic solenoid  60   h  of the control valve  60  through the electrical signal line  51  in the same manner as in  FIG. 5A . 
     Fifth Embodiment 
     In the above-described third embodiment and fourth embodiment, the position of the control valve  60  is switched in binary depending on the judged result whether the load is small or not, but the position of the control valve  60  may be changed continuously depending on the magnitude of the load. 
     Specifically, it may be controlled by the lubricating oil supply controlling controller  50 , such that the control electric signal i for changing the control valve  60  to a position corresponding to the magnitude of the load is generated and output in accordance with control information on the magnitude of the load of the engine  1  or the load of the transmission  3 , the control valve  60  is gradually moved from the lubricating oil discharge position B side to the lubricating oil supply position A side as the load becomes larger, and the control valve  60  is gradually moved from the lubricating oil supply position A side to the lubricating oil discharge position B side as the load becomes smaller. 
     The above-described individual embodiments were described assuming that the control information of the engine controller  30  and the transmission controller  40  was input to the lubricating oil supply controlling controller  50 , and the supply of the lubricating oil was controlled. But, it is also possible to control the supply of the lubricating oil by the lubricating oil supply controlling controller  50  in accordance with information other than the control information of the engine controller  30  and the transmission controller  40 . For example, it may be conducted by inputting an existing sensor-detected signal to the lubricating oil supply controlling controller  50 , performing arithmetic processing in accordance with the sensor-detected value, and generating and outputting the control electric signal i. 
     In the above-described embodiments, it was assumed that the vehicle was a wheel loader, the engine was a diesel engine, and the transmission was a planetary gear transmission. But, the present invention can be applied regardless of a vehicle type, an engine type, and a transmission structure. In other words, the present invention can be applied to not only construction machines but also vehicles other than the construction machines. The invention may be applied to a vehicle having a gasoline engine and a vehicle having a parallel-shaft gear transmission not using a hydraulic clutch. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a structure diagram of a vehicle of an embodiment. 
       FIG. 2  is a hydraulic circuit diagram of the first embodiment. 
       FIG. 3  is a flow chart showing a processing procedure performed by the controller of an embodiment. 
       FIG. 4  is a flow chart showing another processing procedure different from  FIG. 3 . 
       FIG. 5A  and  FIG. 5B  are hydraulic circuit diagrams of the second embodiment and the fourth embodiment. 
       FIG. 6  is a hydraulic circuit diagram of the third embodiment.