Patent Publication Number: US-10788038-B2

Title: Control device for internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2018-166590 filed on Sep. 6, 2018, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a control device for an internal combustion engine that is lubricated or cooled by oil, and to an internal combustion engine control device that is preferable for applications in which a very short drive is repeated in a cold area, for example. 
     Description of the Related Art 
     In general, oil viscosity is high under conditions where oil temperature is low, such as during warm-up of the internal combustion engine, and therefore the flow rate of oil supplied from the oil pump to the internal combustion engine is likely to be insufficient, which may cause the performance of the internal combustion engine to go down. 
     Japanese Laid-Open Patent Publication No. 2018-003795 (hereinafter referred to as JPA 2018-003795) proposes a technique in which the flow rate of oil is increased when the oil temperature is lower than a given temperature. In this technique, the amount of discharge of a variable displacement oil pump is switched from low discharge to high discharge when the oil temperature is lower than the given temperature. This technique suggests that it is then possible to suppress lack of the oil flow rate under conditions where oil temperature is low (see JPA 2018-003795 [0009], [0042]). 
     SUMMARY OF THE INVENTION 
     However, indiscriminately increasing the amount of discharge of an oil pump when the oil temperature is lower than a given temperature causes the problem below. 
     When an internal combustion engine is started at a low oil temperature, e.g., below the freezing point (0° C.), the air-fuel ratio (air/fuel) is controlled on the rich side just after the startup. At this time, if the amount of discharge of oil is increased, the friction of the internal combustion engine increases. When the friction of the internal combustion engine increases, the fuel is set further on the increasing side in order to increase engine torque. 
     When the fuel is set further on the increasing side, much fuel adheres in the combustion chamber of the internal combustion engine, and the adhered fuel dilutes the oil. Thus, so-called oil dilution (the phenomenon in which fuel and water mix into the oil and dilute the oil) occurs and may impair the function of the oil and worsen fuel consumption and emission. 
     Especially, when a very short drive is repeated in a cold area at the freezing point or lower temperatures, for example, the fuel does not volatilize from the oil sufficiently and the amount of dilution of the oil by fuel further increases. 
     The present invention has been devised taking such a problem into consideration, and an object of the present invention is to provide an internal combustion engine control device that is capable of controlling the dilution of oil by fuel and water drops, i.e., controlling the amount of so-called oil dilution. 
     According to an aspect of the present invention, a control device for an internal combustion engine that is lubricated or cooled by oil, includes: 
     a variable displacement oil pump configured to vary an amount of discharge of the oil; 
     an air-fuel ratio sensing unit configured to sense an air-fuel ratio of the internal combustion engine; and 
     a control unit configured to control the amount of discharge of the variable displacement oil pump, 
     wherein the control unit is configured to control the amount of discharge of the variable displacement oil pump, based on the air-fuel ratio sensed by the air-fuel ratio sensing unit. 
     According to the present invention, it is possible to control dilution of the oil by fuel, i.e., to control the amount of so-called oil dilution, by controlling the amount of discharge of the variable displacement oil pump, based on the air-fuel ratio. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing the configuration of an internal combustion engine system to which an internal combustion engine control device according to an embodiment is applied; 
         FIG. 2A  is a diagram illustrating a normal mode map as an oil-pressure control map,  FIG. 2B  is a diagram illustrating a high-pressure mode map as an oil-pressure control map; 
         FIG. 3  is a flowchart used to explain operation of the internal combustion engine control device shown in  FIG. 1 ; 
         FIG. 4  is a timing chart used to explain the operation of the internal combustion engine control device shown in  FIG. 1 ; and 
         FIG. 5  is a diagram showing characteristics that is used to explain how the oil temperature rises with operating time after startup of the internal combustion engine in a conventional technique, a comparative example, and an embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The control device for an internal combustion engine according to the present invention will now be described in detail in conjunction with preferred embodiments while referring to the accompanying drawings. 
     Embodiment 
     [Configuration] 
       FIG. 1  is a schematic diagram showing the configuration of an internal combustion engine system  10  to which an internal combustion engine control device  12  of one embodiment is applied. 
     The internal combustion engine system  10  basically includes an internal combustion engine  20 , an oil supply system  22  for supplying oil to the internal combustion engine  20  in a circulating manner, a cooling water supply system  24  for supplying cooling water, e.g., antifreeze like coolant, to the internal combustion engine  20  in a circulating manner, and an ECU (Electronic Control Unit, controlling means)  26  for controlling these elements. The ECU  26  includes a CPU and a storage device  27 , such as ROM, RAM, where the CPU executes programs stored in the storage device  27  to function as various functions means (function sections). 
     The internal combustion engine  20  can be a port fuel injection engine or a direct injection engine. 
     The oil supply system  22  includes an oil pan  28  in which oil accumulates, a variable displacement oil pump  30  that draws the oil from the oil pan  28  through an oil path  31  and delivers it through an oil path  32 , and an oil gallery  36  that distributes the oil supplied from the oil path  32  to different parts in the internal combustion engine  20  through an oil path  33 . The oil that has lubricated or cooled various parts in the internal combustion engine  20  is returned to the oil pan  28  through a plurality of passageways (referred to as oil paths)  34  and pooled therein. 
     An oil pressure Poil of the oil gallery  36  is sensed by an oil pressure sensor  38  and fed to the ECU  26  as a signal. 
     An oil temperature Toil in the oil pan  28  is sensed by an oil temperature sensor  40  and fed to the ECU  26  as a signal. 
     The variable displacement oil pump  30  is a known pump that is capable of varying the amount of oil discharge at two levels of high discharge amount (high oil pressure) and low discharge amount (low oil pressure) in accordance with a drive signal Dp from the ECU  26  (for example, FIG. 4 of JPA 2018-003795). 
     The variable displacement oil pump  30  includes a solenoid  29  that is ON/OFF controlled by the drive signal Dp, a pilot valve (not shown) having an oil path controlled according to ON/OFF of the solenoid  29 , and a vane pump including a hydraulic chamber in which oil pressure is controlled by the stroke of the pilot valve and having an axis rotated by the crankshaft (shown by the broken line arrow directed from the internal combustion engine  20  to the variable displacement oil pump  30 ). 
     A drive signal Dpon for turning on the solenoid  29  (a state in which current flows to the solenoid  29 ) sets a low discharge amount (low oil pressure) control state, and a drive signal Dpoff for turning off the solenoid  29  (a state in which current does not flow to the solenoid  29 ) sets a high discharge amount (high oil pressure) control state. 
     The variable displacement oil pump  30  can be a variable displacement oil pump that can vary the amount of discharge linearly and continuously, or a motor-driven pump. 
     On the other hand, the cooling water supply system  24  includes a radiator  50  for effecting heat exchange of the cooling water as antifreeze, a water path (circulation path)  41  for supplying the cooling water cooled at the radiator  50  to the internal combustion engine  20 , a water pump  52  for drawing through a plurality of water paths (water jacket, water gallery)  42  the cooling water that has captured heat from different parts of the internal combustion engine  20  and become hot, and a water path (circulation path)  43  for supplying the hot cooling water to the radiator  50 . 
     A temperature Tw of the cooling water in the radiator  50  (engine water temperature) is sensed by a water temperature sensor  54  and fed to the ECU  26  as a signal. 
     The water pump  52  is usually driven by the internal combustion engine  20  (shown by the broken line arrow directed from the internal combustion engine  20  to the water pump  52 ), but can be an electric pump. 
     The exhaust pipe of the internal combustion engine  20  has an air-fuel ratio sensor  56  attached thereto and the air-fuel ratio sensor  56  checks the concentration of oxygen in the exhaust gas and feeds the air-fuel ratio A to the ECU  26  as a signal. 
     The internal combustion engine control device  12  of this embodiment is composed of the variable displacement oil pump  30 , the air-fuel ratio sensor  56 , the water temperature sensor  54 , and the ECU  26 . 
     The storage device  27  of the ECU  26  has stored therein a normal oil-pressure control map Mn shown in  FIG. 2A  (also called a normal mode map or base map) and a temperature-increase oil-pressure control map Mh shown in  FIG. 2B  (also called a high-pressure mode map or temperature-increase mode map). 
     In the maps, the horizontal axis shows the engine rotational speed and the vertical axis shows the engine load factor, where the engine load factor becomes larger as the engine load becomes larger. 
     As shown in  FIG. 2A , the normal mode map Mn is a map that includes: a “low oil-pressure control region” (drive signal Dp=Dpon) where the amount of oil discharge (which is proportional to the oil pressure) is generally kept in a low oil-pressure state when the engine rotational speed (horizontal axis) is intermediate or lower and the engine load factor (vertical axis) is low; and a “high oil-pressure control region” where the amount of oil discharge is generally kept in a high oil-pressure control state when the engine rotational speed and engine load factor are high. 
     As shown in  FIG. 2B , the temperature-increase mode map Mh is a map that includes a “high oil-pressure control region” (drive signal Dp=Dpoff) where the amount of oil discharge is generally kept in a high oil-pressure state regardless of the values of the engine rotational speed and engine load factor. 
     In the normal mode map Mn of  FIG. 2A , a “high oil-pressure control region” is set at idle rotational speeds regardless of the engine load factor, for the purpose of reducing power consumption. At this time, power consumption is reduced because the drive signal Dp for the solenoid  29  is set as drive signal Dpoff. 
     Also, in the temperature-increase mode map Mh of  FIG. 2B , a “low oil-pressure control region” is set when the engine load factor is zero or very low (low load) and the engine rotational speed is intermediate because the necessity of operating the variable displacement oil pump  30  in the “high oil-pressure control region” is low and for the purpose of reducing vibration noise entering the vehicle interior. 
     [Operations] 
     Next, operations of the internal combustion engine system  10  to which the internal combustion engine control device  12  basically structured as described above is applied will be explained in detail referring to the flowchart of  FIG. 3 . The process of the flowchart is executed by the ECU  26  unless otherwise stated. Mention is made of it only where necessary, in order to avoid complexity. 
     Step S 1  monitors whether the internal combustion engine  20  starts; for example, starting of the internal combustion engine  20  is sensed through a starter motor according to a shift of a non-illustrated power switch (ignition switch) from off position to start position (step S 1 : YES). 
     In this case, as shown at step S 2 , the normal mode map Mn is selected as the oil-pressure control map during stoppage before the startup of the internal combustion engine  20 . At the startup, the variable displacement oil pump  30  is controlled using the normal mode map Mn. That is, at the startup, the variable displacement oil pump  30  is generally operated in the “low oil-pressure control region”. 
     Next, at step S 3 , in order to catch timing of starting the switch from the normal mode map Mn to the temperature-increase mode map Mh, the ECU  26  captures and senses the air-fuel ratio λ, engine water temperature Tw, and oil temperature Toil from the air-fuel ratio sensor  56 , water temperature sensor  54 , and oil temperature sensor  40 , respectively. 
     Next, step S 4  determines whether the air-fuel ratio A is on the lean side where it is larger than a given air-fuel ratio λth. 
     The air-fuel ratio λ is set as λ=1 at the theoretical air-fuel ratio, i.e., stoichiometric. On the rich side where the fuel ratio is larger than at the theoretical air-fuel ratio λ=1, the air-fuel ratio λ is smaller than 1 as λ&lt;1. On the lean side where the air ratio is larger, the air-fuel ratio λ takes a value of 1 or larger as λ≥1. The given air-fuel ratio λth is set as λth=1 at the stoichiometric state, for example, but it may be set on somewhat richer side (λth&lt;1). 
     Thus, when step S 4  determines that the air-fuel ratio λ is still not on the lean side, i.e., when the internal combustion engine  20  is still being controlled on the rich side of the air-fuel ratio λ (λ&lt;λth) (step S 4 : NO), the variable displacement oil pump  30  is driven generally in the “low oil-pressure control region” in the normal mode map Mn of step S 2 . 
     While the internal combustion engine  20  is controlled by repeating step S 2 →S 3 →S 4 : NO→S 2  after the startup at step S 1 , then the internal combustion engine  20  is just after the startup and the air-fuel ratio λ is controlled on the rich side. At this time, if the oil-pressure control map is immediately switched from the normal mode map Mn to the temperature-increase mode map Mh, then the increased amount of oil discharge increases the friction of the internal combustion engine  20  and the air-fuel ratio λ is then set further on the rich side, which may further accelerate oil dilution. 
     However, according to this embodiment, at startup, when the air-fuel ratio λ is on the rich side (step S 4 : NO (λ&lt;λth)), the variable displacement oil pump  30  is controlled in the “low oil-pressure control region” in the normal mode map Mn (step S 2 ) so that oil dilution is suppressed. 
     While the process of step S 2 →S 3 →S 4 : NO→S 2  is repeated after the startup at step S 1 , if the determination at step S 4  becomes affirmative (step S 4 : YES), that is, when the air-fuel ratio λ has become equal to or larger than the given air-fuel ratio λth, then step S 5  next determines whether the engine water temperature Tw exceeds a given engine water temperature Twth. 
     If the engine water temperature Tw is over the given engine water temperature Twth (step S 5 : NO, Tw&gt;Twth), the internal combustion engine  20  has been warmed up and the oil temperature Toil of the oil, which has a low specific heat, has also increased, and therefore the problem of oil dilution does not occur. Hence, the control of the variable displacement oil pump  30  using the normal mode map Mn at step S 2  is continued. 
     On the other hand, if the air-fuel ratio λ is larger than the given air-fuel ratio λth (step S 4 : YES) and also the engine water temperature Tw is equal to or less than the given engine water temperature Twth, then the oil temperature Toil is considered to be less than a given oil temperature Toilth at which oil dilution may occur. Then, at step S 6 , the oil-pressure control map is switched from the normal mode map Mn to the temperature-increase mode map Mh and the drive signal Dp is switched from Dpon to Dpoff so that the variable displacement oil pump  30  is controlled generally in the “high oil-pressure control region” ( FIG. 2B ). 
     In this case, the amount of discharge from the variable displacement oil pump  30  increases and an increased amount of oil is delivered from the oil gallery  36  to different parts of the internal combustion engine  20 . As the amount of oil discharged increases, the oil receives an increased amount of heat from the internal combustion engine  20  and the oil temperature Toil can be raised rapidly. 
     Next, at step S 7 , in order to catch the timing of returning from the temperature-increase mode map Mh to the normal mode map Mn when the oil temperature Toil has increased and the possibility of oil dilution disappeared, the ECU  26  captures and senses the air-fuel ratio λ, engine water temperature Tw, and oil temperature Toil from the air-fuel ratio sensor  56 , water temperature sensor  54 , and oil temperature sensor  40 . 
     Next, at step S 8 , it is determined whether the oil temperature Toil has risen to the given oil temperature Toilth that is a high temperature at which oil dilution does not have to be considered (such a temperature that fuel and water mixed in the oil volatilize and vaporize). 
     The determination of step S 8 : No→S 6 →S 7 →S 8  are repeated, and when step S 8  determines that the oil temperature Toil has become equal to or higher than the given oil temperature Toilth (step S 8 : YES), then step S 9  switches the oil-pressure control map from the temperature-increase mode map Mh to the normal mode map Mn. The drive signal Dp is thus switched from Dpoff to Dpon and the variable displacement oil pump  30  is stably controlled in the “low oil-pressure control region” when the engine rotational speed is low to intermediate and the engine load factor is relatively low, and in the “high oil-pressure control region” when the engine rotational speed is intermediate to high and the engine load factor is relatively high. 
     [Explanation with Timing Chart] 
     An example of the operation described with the flowchart of  FIG. 3  will now be explained referring to the timing chart of  FIG. 4 . 
     At time t 0 , the internal combustion engine  20  starts and the engine torque rises. It is assumed that at the time t 0  the engine water temperature Tw is much lower than the given engine water temperature Twth, e.g., at a temperature below the freezing point. When the stoppage period is long, the engine water temperature Tw and oil temperature Toil decrease to outside air temperature. 
     At time t 0 , the normal mode map Mn is set as the oil-pressure control map (corresponding to step S 2 ). 
     At the startup at time t 0 , the air-fuel ratio λ is on a very rich side (λ&lt;λth). 
     After time t 0 , the air-fuel ratio λ is set on the lean side and exceeds the given air-fuel ratio λth at time t 1  (corresponding to step S 4 : YES), and if the engine water temperature Tw is equal to or less than the given engine water temperature Twth (corresponding to step S 5 : YES), then the oil-pressure control map is switched from the normal mode map Mn to the temperature-increase mode map Mh (corresponding to step S 6 ) and the variable displacement oil pump  30  is switched generally from the low oil-pressure control (low discharge) to the high oil-pressure control (high discharge). 
     After that, time passes and the oil temperature Toil rises past the given oil temperature Toilth at time t 2  (corresponding to step S 8 : YES) and then the oil-pressure control map is switched from the temperature-increase mode map Mh to the normal mode map Mn (corresponding to step S 9 ). 
     [Comparison Between Conventional Technique, Comparative Example, and Embodiment] 
     Now, the relation between the operating time of the internal combustion engine  20  after startup and the rise of the oil temperature Toil will be explained referring to  FIG. 5  about a conventional technique, comparative example, and embodiment. 
     In  FIG. 5 , the characteristic shown by one-dot chain line shows an oil-temperature variation characteristic Coilc of a conventional technique where the variable displacement oil pump  30  is controlled with the normal mode map Mn, the characteristic shown by broken line shows an oil-temperature variation characteristic Coilb of a comparative example where the variable displacement oil pump  30  is controlled with the temperature-increase mode map Mh from time to, i.e., from startup, and the characteristic shown by solid line shows an oil-temperature variation characteristic Coila of the embodiment where the air-fuel ratio λ is considered and the variable displacement oil pump  30  is controlled with the normal mode map Mn from time t 0  to time t 1  and the variable displacement oil pump  30  is controlled with the temperature-increase mode map Mh after time t 1 . 
     The stoppage temperature of the oil temperature [° C.] at the startup time t 0  of the operating time 0 [sec] is below the freezing point and the map is switched to the temperature-increase mode map Mh at time t 1  at which the temperature is still below the freezing point. At the same operating time after time t 1 , the oil temperature Toil of the oil-temperature variation characteristic Coila of the embodiment is higher by about 10 [° C.] than the oil temperature Toil of the oil-temperature variation characteristic Coilc of the conventional technique, which shows that the oil temperature Toil can be raised by switching to the temperature-increase mode map Mh. 
     It is also seen that, at the same operating time after time t 1 , when the oil temperature Toil is at or above the freezing point (Toil≥0 [° C.]), there is almost no difference between the oil-temperature variation characteristic Coilb of the comparative example (where the temperature-increase mode map Mh is adopted from time t 0 ) and the oil-temperature variation characteristic Coila of the embodiment (where the normal mode map is adopted from time t 0  to time t 1  and the temperature-increase mode map Mh is adopted from time t 1 ). 
     Thus, according to the oil-temperature variation characteristic Coila of the embodiment, it is seen that temperature increase of the oil at and after time t 1  is ensured while reducing oil dilution (from time t 0  to time t 1 ). 
     [Modification] 
     When an abnormality of the oil supply system  22  takes place, e.g., when the oil temperature Toil sensed by the oil temperature sensor  40  is abnormally high, or when an abnormality of the cooling water supply system  24  takes place, e.g., when the engine water temperature Tw sensed by the water temperature sensor  54  is abnormally high, the drive signal Dpoff is supplied to the solenoid  29  so as to provide control to increase the amount of oil discharge from the variable displacement oil pump  30 . Controlling in this way can prevent degradation of the performance of the internal combustion engine  20 . 
     [Invention Grasped from Embodiment] 
     The invention that can be grasped from the above-described embodiment and modification will be recited below. The constituent elements are labeled using the reference numerals used in the embodiment in order to facilitate understanding but the constituent elements are not limited to those shown by the reference numerals. 
     The control device for the internal combustion engine according to the present invention is the control device  12  for the internal combustion engine that is lubricated or cooled by oil, including: 
     the variable displacement oil pump  30  configured to vary an amount of discharge of the oil; 
     the air-fuel ratio sensing unit  56  configured to sense the air-fuel ratio λ of the internal combustion engine  20 ; and 
     the control unit  26  configured to control the amount of discharge of the variable displacement oil pump  30 , 
     wherein the control unit  26  is configured to control the amount of discharge of the variable displacement oil pump  30 , based on the air-fuel ratio λ sensed by the air-fuel ratio sensing unit  56 . 
     Thus, it is possible to control dilution of the oil by fuel, i.e., to control the amount of so-called oil dilution, by controlling the amount of discharge of the variable displacement oil pump  30 , based on the air-fuel ratio λ. 
     In this case, the control device may further include the temperature sensing unit  54  configured to sense the temperature Tw of the internal combustion engine  20 , 
     and the control unit  26  may be configured to control the amount of discharge of the variable displacement oil pump  30 , based on the air-fuel ratio λ sensed by the air-fuel ratio sensing unit  56  and the temperature Tw of the internal combustion engine  20  sensed by the temperature sensing unit  54 . 
     Thus, by controlling the amount of discharge of the variable displacement oil pump  30 , based on the temperature Tw of the internal combustion engine  20  in addition to the air-fuel ratio λ, it is possible to more reliably control the dilution of the oil by fuel. 
     In this case, the control unit  26  may be configured to provide control so as to increase the amount of discharge of the variable displacement oil pump  30  when the air-fuel ratio λ is equal to or greater than the given air-fuel ratio λth and the temperature Tw of the internal combustion engine  20  is equal to or lower than the given temperature Twth. 
     If the air-fuel ratio λ is equal to or greater than the given air-fuel ratio λth, the dilution of the oil by fuel is accelerated. However, the amount of discharge of the variable displacement oil pump  30  is increased if the temperature Tw of the internal combustion engine  20  is equal to or lower than the given temperature Twth, and then the oil receives an increased amount of heat from the internal combustion engine  20 . As a result, the temperature of the oil is increased to cause the fuel in the oil to volatilize (transpire) and dilution of the oil is avoided. 
     The storage device  27  may have stored therein the normal oil-pressure control map Mn adopted to control the amount of discharge of the variable displacement oil pump  30  and the temperature-increase oil-pressure control map Mh adopted to provide control so as to increase the amount of discharge of the variable displacement oil pump  30  more than when the normal oil-pressure control map Mn is adopted, 
     and the control unit  26  may be configured to provide control so as to switch from the normal oil-pressure control map Mn to the temperature-increase oil-pressure control map Mh when the air-fuel ratio λ is equal to or greater than the given air-fuel ratio λth and the temperature Tw of the internal combustion engine  20  is equal to or lower than the given temperature Twth. 
     When the air-fuel ratio λ is equal to or greater than the given air-fuel ratio λth, dilution of the oil by fuel is accelerated. However, the map is switched to the temperature-increase oil-pressure control map Mh so as to provide control to increase the amount of discharge of the variable displacement oil pump  30  when the temperature Tw of the internal combustion engine  20  is at or lower than the given temperature Twth, and then the oil receives an increased amount of heat from the internal combustion engine  20 . As a result, the temperature of the oil is increased to cause the fuel in the oil to volatilize (transpire) and thus dilution of the oil is avoided. 
     The temperature sensing unit may be the cooling water temperature sensor  54  configured to sense a temperature of cooling water for cooling the internal combustion engine  20 . 
     The temperature of the internal combustion engine  20  is proportional to the temperature Tw of the cooling water for cooling the internal combustion engine  20 . Therefore, the temperature Tw of the cooling water, which is easy to sense, can be sensed as the temperature of the internal combustion engine  20 . 
     Preferably, the control device may further include the oil temperature sensing unit  40  configured to sense the temperature Toil of the oil, 
     and the control unit  26  may be configured to stop the control of increasing the amount of discharge of the variable displacement oil pump  30  when the temperature Toil of the oil becomes a temperature equal to or higher than the given temperature Toilth. 
     Oil dilution does not take place when the temperature Toil of the oil is equal to or higher than the given temperature (a temperature at which fuel in the oil transpires) Toilth. It is therefore preferable to stop the control of increasing the amount of discharge of the variable displacement oil pump  30  so that the friction of the internal combustion engine  20  is reduced. 
     The control device may further include the oil temperature sensing unit  40  configured to sense the temperature Toil of the oil, 
     and the control unit  26  may be configured to provide control to switch from the temperature-increase oil-pressure control map Mh to the normal oil-pressure control map Mn when the temperature Toil of the oil becomes a temperature equal to or higher than the given temperature Toilth. 
     Oil dilution does not take place when the temperature Toil of the oil is equal to or higher than the given temperature (a temperature at which fuel in the oil transpires) Toilth. It is therefore preferable to provide control to switch from the temperature-increase oil-pressure control map Mh to the normal oil-pressure control map Mn so that the friction of the internal combustion engine  20  is reduced. 
     Preferably, the control unit  26  provides control to increase the amount of discharge of the variable displacement oil pump  30  when an abnormality of the system  22  for supplying the oil or the system  24  for supplying the cooling water is sensed. 
     It is possible to prevent degradation of the performance of the internal combustion engine  20  by providing control to increase the amount of discharge of the variable displacement oil pump  30  when an abnormality of the system  22  for supplying the oil or the system  24  for supplying the cooling water is sensed. 
     Also, preferably, the control unit  26  is configured to control the variable displacement oil pump  30  using the temperature-increase oil-pressure control map Mh when an abnormality of the system  22  for supplying the oil or the system  24  for supplying the cooling water is sensed. 
     When an abnormality of the system  22  for supplying the oil or the system  24  for supplying the cooling water is sensed while control is being provided using the normal oil-pressure control map Mn, the map is then switched to the temperature-increase oil-pressure control map Mh. It is thus possible to prevent degradation of the performance of the internal combustion engine  20  by providing control so as to increase the amount of discharge of the variable displacement oil pump  30  using the temperature-increase oil-pressure control map Mh. 
     The present invention is not limited to the embodiments described above and it is of course possible to employ various configurations based on the description of the invention.