Patent Abstract:
An oil pump apparatus which includes an oil pump for being driven by a driving source and for being connected to a plurality of components to which an oil is supplied from the oil pump and a control valve preventing the oil which is unnecessary to the components from flowing into the components, wherein at least one of the components is an actuator operated by an oil pressure generated by the oil pump and wherein the control valve permits the oil of which the quantity is smaller than that of the oil which is consumed by the actuator to flow into the components when the actuator is not operated and the control valve permits the oil of which the quantity is larger than that of the oil which is consumed by the actuator to flow into the components when the actuator is operated.

Full Description:
This application is a Divisional of nonprovisional application Ser. No. 09/066,565 filed Apr. 27, 1998, which issued as U.S. Pat. No. 6,004,111. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an oil pump apparatus including an oil pump and a control valve for controlling the flow of oil back to a suction port of the oil pump. 
     2. Description of the Prior Art 
     A conventional oil pump apparatus installed on a vehicle engine is disclosed in Japanese Utility Model laid open No. 61 (1986)-23485. The oil pump apparatus disclosed in this publication includes an oil pump and a control valve through which flows a portion of oil (a portion of the oil exceeding the quantity of the oil consumed at a component to which the oil is supplied) pumped out from the oil pump back to a suction port of the oil pump, an oil pan, an oil reservoir, an oil tank and so on, in order to reduce a load applied to the oil pump at a medium and high rotation speed ranges of the oil pump. 
     In accordance with the above device, when a plurality of components, at least one of which is an actuator operated by the oil pressure generated by the oil pump (e.g., an actuator applied to a variable valve timing mechanism or a variable valve lift mechanism of the engine) are connected to the oil pump, only the excess oil exceeding the quantity of the oil consumed at all components (including an operating actuator) is returned to the suction port of the oil pump even though the actuator is not operated. Therefore, a large amount of the oil which is unnecessary to the components is supplied to the components when the actuator is not operated. 
     SUMMARY OF THE INVENTION 
     The present invention provides an oil pump apparatus which prevents excess oil which is unnecessary to the components from flowing into the components. The present invention also provides an oil pump apparatus which is small in size and light in weight. The present invention can be basically described as an oil pump apparatus comprising an oil pump for being driven by a driving source and for being connected to a plurality of components to which an oil is supplied from the oil pump and a control valve for preventing the oil which is unnecessary to the components from flowing into the components, wherein at least one of the components is an actuator operated by oil pressure generated by the oil pump. In this invention the control valve permits an amount of oil, of which the quantity is smaller than that of the oil which is consumed by the actuator, to flow into the components when the actuator is not operated. When the actuator is operated, the control valve permits an amount of oil, of which the quantity is larger than that of the oil which is consumed by the actuator to flow into the components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the oil pump apparatus according to the present invention will be more clearly appreciated from the following description in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a view illustrating the oil pump apparatus of the invention; 
     FIG. 2 is an enlarged cross-sectional view illustrating the control valve shown in FIG. 1; 
     FIG. 3 is an enlarged detailed cross-sectional view illustrating the control valve of the present invention; 
     FIG. 4 is an enlarged detailed cross-sectional view illustrating the first condition of the control valve shown in FIG. 2; 
     FIG. 5 is an enlarged detailed cross-sectional view illustrating the second condition of the control valve shown in FIG. 2; 
     FIG. 6 is an enlarged detailed cross-sectional view illustrating the third condition of the control valve shown in FIG. 2; 
     FIG. 7 is a characteristic diagram illustrating the relation between the crank shaft rotational speed and the quantity of the oil pumped out from the pump apparatus of the present invention; 
     FIG. 8 is a characteristic diagram illustrating the relation between the crank shaft rotational speed and the quantity of the oil pumped out from the pump apparatus of a modification of the first embodiment of the present invention; 
     FIG. 9 is an enlarged detail cross-sectional view of the control valve of the second embodiment of the present invention; 
     FIG. 10 is a characteristic diagram illustrating the relation between the crank shaft rotational speed and the quantity of the oil pumped out from the pump apparatus of the second embodiment of the present invention; 
     FIG. 11 is a schematic cross-sectional view illustrating the operation of the first control mode of the control valve shown in FIG. 9; 
     FIG. 12 is a schematic cross-sectional view illustrating the operation of the second control made of the control valve shown in FIG. 9; 
     FIG. 13 is a schematic cross-sectional view illustrating the operation of the third control mode of the control valve shown in FIG. 9; 
     FIG. 14 is a schematic cross-sectional view illustrating the operation of the fourth control mode of the control valve shown in FIG. 9; 
     FIG. 15 is a schematic cross-sectional view illustrating the operation of the fifth control mode of the control valve shown in FIG. 9; 
     FIG. 16 is an enlarged detailed cross-sectional view illustrating the control valve which does not include a slope on the valve spool corresponding to FIG. 3; 
     FIG. 17 is a schematic cross-sectional view illustrating the operation of the first control mode of the control valve of the oil pump apparatus of the third embodiment of the present invention; 
     FIG. 18 is a schematic cross-sectional view illustrating the operation of the second control mode of the control valve of the oil pump apparatus of the third embodiment of the present invention; 
     FIG. 19 is a schematic cross-sectional view illustrating the operation of the third control mode of the control valve of the oil pump apparatus of the third embodiment of the present invention; 
     FIG. 20 is a schematic cross-sectional view illustrating the operation of the fourth control mode of the control valve of the third embodiment of the present invention; and 
     FIG. 21 is a schematic cross-sectional view illustrating the operation of the fifth control mode of the control valve of the third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIG. 1, an oil pump apparatus comprises an oil pump  20  (which is a partially cut-away view) which is driven by a crank shaft  10  of a vehicle engine (not shown in Figures), and a control valve  30  which returns a portion of the operational oil pumped out from the oil pump  20  to a suction opening of the oil pump  20 . 
     The oil pump  20  pumps the operational oil to a plurality of components through a discharge conduit  41 . These components comprise an actuator  51  of a variable valve timing mechanism of the vehicle engine which is operated by the oil pressure, a lubrication portion  52  of the vehicle engine (e.g. a bearing) and a portion  53  of the vehicle engine to be cooled (e.g. cylinders and pistons). A drain conduit  42  connects the components  51 ,  52  and  53  to an oil pan  40  of the vehicle engine. 
     The crank shaft  10  rotates the oil pump  20  in the counter-clockwise direction. The oil pump  20  includes a pump housing  21 , an inner rotor  22  rotatably installed in the pump housing  21  so as to be rotated by the crank shaft  10  and an outer rotor  23  eccentrically disposed in the pump housing  21  relative to the inner rotor  22 . The outer rotor  23  includes inner teeth  23   a  which are engaged with the outer teeth  22   a  of the inner rotor  22  so as to be rotated by the inner rotor  22  in the same direction as the rotation of the inner rotor  22 . The outer teeth  22   a  and, the inner teeth  23   a  are designed in a trochoid curve or a cycloid curve shape. 
     The oil pump  20  includes a suction opening  21   a  connected to the oil pan  40  through a suction conduit  43 , a discharge opening  21   b  connected to the discharge conduit  41 , a main suction port  21   c  constantly connected to the suction opening  21   a,  a sub-suction port  21   d  selectively connected to or disconnected from the main suction port  21   c  by the control valve  30  and a discharge port  21   e  constantly connected to the discharge opening  21   b.  The ports  21   c,    21   d  and  21   e  are separated and disconnected from each other by a plurality of pump chambers R disposed between each pair of outer teeth  22   a  and each corresponding pair of inner teeth  23   a.    
     As shown in FIGS. 2 and 3, the control valve  30  includes a valve housing  31  having a cylinder  31   a,  a control port  31   b,  a sub-port  31   c  and a main port  31   d.  The control valve  30  also includes a valve spool  32  slidably disposed in the cylinder  31   a.  Oil pressure generated by the oil pump  20  is applied at the upper-end of valve spool  32  against the end portion  32   b  through the control port  31   b,  so as to control connections between the ports  31   b,    31   c  and  31   d.  The control valve  30  further includes a spring  33  biasing the valve spool  32  in the upper direction shown in FIG.  2 . The valve spool  32  is pushed downward within cylinder  31   a,  against the biasing force of spring  33 , in proportion to the amount of oil pressure applied through the control port  31   b.  The valve spool  32  includes variable restriction portions A and B (shown in FIG.  3 ), which variably restrict the flow of oil through their respective restrictive portions, the degree of restriction determined by the position of the valve spool  32  within the cylinder  31   a.    
     The control port  31   b  is constantly connected to the discharge port  21   e,  the sub-port  31   c  is constantly connected to the sub-suction port  21   d  and the main port  31   d  is constantly connected to the main suction port  21   c  of the oil pump  20 . Since chamber  31   a  in which the spring  33  is installed is constantly connected to the oil pan  40 , no oil pressure is generated which would force the valve spool  32  in the upward direction. 
     In accordance with this embodiment of the present invention, when the oil pressure applied to the control port  31   b  from the oil pump  20  ascends to a first predetermined value, the valve spool  32  is moved in the downward direction against the biasing force of the spring  33  so as to locate at a position (shown in FIG. 4) at which the valve spool  32  still disconnects the control port  31   b  from the sub-port  31   c  (first condition). 
     When the oil pressure applied to the control port  31   b  from the oil pump  20  ascends to a second predetermined value (which is larger than the first predetermined value), the valve spool  32  is moved against the biasing force of the spring  33  so as to locate at a position (shown in FIG. 5) at which the valve spool  32  still disconnects the sub-port  31   c  from the main port  31   d  (second condition). 
     When the oil pressure applied to the control port  31   b  from the oil pump  20  ascends to a third predetermined value (which is larger than the second predetermined value), the valve spool  32  is moved against the biasing force of the spring  33  so as to locate at a position (shown in FIG. 6) at which the valve spool  32  connects the control port  31   b  and the sub-port  31   c,  but still disconnects both of said ports from the main port  3   d  (third condition). 
     A characteristic diagram of this embodiment of the present invention showing the quantity of the operational oil discharged from the oil pump  20  is shown in FIG.  7 . As shown on FIG. 7, the first condition of the control valve  30  corresponds to point “a” or “A”, the second condition of the control valve  30  corresponds to point “b” or “B” and the third condition of the control valve  30  corresponds to the condition shown as point “c”. 
     FIG. 7 also illustrates, by a bold dash-single dot-dash line, the amount of oil discharged from a conventional oil pump apparatus (such oil pump apparatus includes an oil pump and a control valve through which flows a portion of the oil pumped out from the oil pump back to a suction port of the oil pump, an oil pan, an oil reservoir, an oil tank and so on in order to reduce the load applied to the oil pump at a medium and high rotation speed range of the oil pump  20 .). 
     In accordance with the above-described embodiment of the present invention, since the valve spool  32  of the control valve  30  is not moved in the downward direction from the position shown in FIG. 4 at a low crank shaft  10  rotation speed between 0 and N 1 , as shown on FIG. 7 (e.g. 1500 rpm), when the actuator  51  is not operated, the sub-port  31   c  is disconnected from the control port  31   b  but is connected to the main port  31   d.  Therefore, a large amount of operation oil is sucked by the oil pump  20  through both the main suction port  21   c  and the sub suction port  21   d  of the oil pump  20 . This is represented in FIG. 7 as a bold line “O˜a”, which shows the quantity of the operational oil discharged from the oil pump  20  at such low rotation speed. The operational oil is discharged from the oil pump  20  to the components  51 ,  52  and  53  through the discharge conduit  41 . 
     Since the valve spool  32  of the control valve  30  is moved between the first and second positions which are shown in FIGS. 4 and 5, respectively, and is not moved further in the downward direction from the position shown in FIG. 5 at a crank shaft  10  rotation speed of between N 1  and N 2  (e.g. 3000 rpm) when the actuator  51  is not operated, the size of the passages A and B formed between the valve spool  32  and the valve housing  31  which connect the sub-port  31   c  to the control port  31   b  and to the main port  31   d,  respectively, are controlled by the crank shaft  10  rotation speed. 
     Therefore, a portion of the operational oil which flows into the discharge opening  21   b  from the discharge port  21   e  is made to flow into the sub suction port  21   d  through the control valve  30 , and the operational oil is also sucked from the main suction port  21   c  into the sub suction port  21   d.  Consequently, the quantity of the sucked operational oil by the sub suction port  21   d  is restricted in inverse proportion to the oil pressure generated by the oil pump  20 , and a sufficient quantity of operational oil is sucked by the main suction port  21   c.  This is shown on FIG. 7 as bold line “a˜b”, showing the quantity of operational oil discharged from oil pump  20 . The operational oil is discharged from the oil pump  20  to the components  51 ,  52  and  53  through the discharge conduit  41 . 
     Since the valve spool  32  of the control valve  30  is moved between the positions of the second and third conditions, which are shown in FIGS. 5 and 6, respectively, and is not moved in the downward direction from the position shown in FIG. 6 at a crank shaft  10  rotation speed between N 2  and N 3  (e.g. 5000 rpm) when the actuator  51  is not operated, the sub-port  31   c  is disconnected from the main port  31   d  and the size of passage formed between the valve spool  32  and the valve housing  31  which connects the sub-port  31   c  to the control port  31   b  is controlled such that the size of said passage is in proportion to the crank shaft  10  rotation speed. 
     Therefore, a portion of the operational oil which flows into the discharge opening  21   b  from the discharge port  21   e  flows into the sub suction port  21   d  through the control valve  30 . Consequently, only the main suction port  21   c  sucks the operational oil. This is shown on FIG. 7 as a bold line “b˜c”, which shows the quantity of the operational oil discharged from the oil pump  20 . The operational oil is discharged from the oil pump  20  to the components  51 ,  52  and  53  through the discharge conduit  41 . 
     Since the valve spool  32  of the control valve  30  is moved in the downward direction from the position shown in FIG. 6 at a high crank shaft  10  rotation speed higher than N 3 , at such higher speed the control port  31   b  is fully connected to the sub-port  31   c  and the size of passage B formed with the valve spool  32  and the valve housing  31  which connect the main port  31   d  to the control port  31   b  and the sub-port  31   c  is controlled such that the size of said passage is in proportion to the crank shaft  10  rotation speed. 
     Therefore, a portion of the operational oil which is flows into the discharge opening  21   b  from the discharge port  21   e  flows into both the sub suction port  21   d  and the main suction port  21   c  through the control valve  30 . Consequently, the sub suction port  21   d  does not entirely suck the operational oil and the quantity of the sucked operational oil by the main suction port  21   c  is restricted in proportion to the oil pressure generated by the oil pump  20 . This is shown on FIG. 7 as a bold line on the right side of point “c”, which shows the quantity of operational oil discharged from oil pump  20 . The operational oil is discharged from the oil pump  20  to the components  51 ,  52  and  53  through the discharge conduit  41 . 
     When the actuator  51  is operated, the oil pressure generated by the oil pump  20  is reduced because a portion of the operational oil discharged from the oil pump  20  is consumed by the actuator  51 . Therefore, the crank shaft  10  rotation speed at which the valve spool  32  is moved to the position shown in FIG. 4 ascends to N 1   a,  as shown in FIG.  7 . Furthermore, the crank shaft  10  rotation speed at which the valve spool  32  is moved to the position shown in FIG. 5 ascends to N 2   a  as shown in FIG.  7 . This is shown on FIG. 7 as a bold line between a-A, and a bold dash-two dot-dash line between A-B, showing the quantity of the operational oil discharged from the oil pump  20  during this stage while the actuator is in operation. Consequently, a quantity of the operational oil larger than that consumed by the actuator  51  (see the characteristic diagram illustrated by a dashed line in FIG. 7) is discharged from the oil pump  20  to the components  51 ,  52  and  53  through the discharge conduit  41 . 
     In accordance with the present invention, the oil pump apparatus may comprise an oil pump including the suction ports  21   c,    21   d  constantly connected to each other (a conventional trochoid pump) and a relief valve disposed at the discharge portion of the oil pump, which can be represented by the characteristic diagram shown in FIG. 8, instead of the control valve  30 . 
     In FIG. 8, the relief valve starts to relieve the oil pressure at the crank shaft  10  rotation speed N 1  when the actuator is not operated and the relief valve starts to relieve the oil pressure at the crank shaft  10  rotation speed N 1   a  when the actuator is operated. Therefore, a quantity of the operational oil smaller than that consumed by the actuator (see a characteristic diagram illustrated by a broken line in FIG. 8) is discharged from the oil pump to the components when the actuator is not operated and the quantity of the operational oil exceeding that consumed by the actuator is discharged from the oil pump to the components when the actuator is operated. 
     In accordance with the present invention, the oil pump  20  may include a plurality of (more than two) suction ports. In this case, the number of the ports and the number of valve portions of the control valve each have to be increased so as to correspond to the number of the suction ports of the oil pump  20 . 
     In accordance with the present invention, the oil pump apparatus can be applied to any industrial oil farming equipment, and is not restricted to use only with motor vehicle engines. Further, the type of the oil pump and the driving mechanism of the oil pump can be adequately altered to correspond to a wide variety of uses. 
     A second embodiment of the control valve of the oil pump apparatus of the present invention will be described hereinafter. As shown in FIG. 9, a rand portion  82   a  is disposed at an upper end of the valve spool  82  so as to receive against the end portion  82   e  the oil pressure which is forced from the control port  81   b  to the main port  81   c  at a third control mode (described later). The valve spool  82  has a slope  82   b  (tapered surface) which is sloped from an outer circumferential portion of the rand portion  82   a  towards the axis of the valve spool  82 . The slope  82   b  is disposed at a lower portion of the rand portion  82   a  as shown in FIG.  9 . Furthermore, the valve spool  82  has a stepped portion  82   c  disposed between the outer circumferential portion of the rand portion  82   a  and the upper end portion of the slope  82   b.    
     The control valve  80  has a first control mode (see FIG. 11) at which the sub-port  81   c,  as determined by the amount of oil pressure applied to the control port  81   b,  is only connected to the main port  81   d.  In the second control mode of the control valve  80  (see FIG. 12) the sub-port  81   c  is also connected to the main port  81   d  through the variable restriction portion A. This second control mode provides for the flow of the operational oil into the sub-port  81   c  from both the main port  81   d  and the control port  81   b.  In the third control mode of the control valve  80  (see FIG.  13 ), the sub-port  81   c  is connected to the control port  81   b  and is also connected to the main port  81   d  through the variable restriction portion B so as to provide for the flow of the operational oil from the control port  81   b  into both the sub-port  81   c  and the main port  81   d.  In the fourth control mode of the control valve  80  (see FIG.  14 ), the sub-port  81   c  is only connected to the control port  81   b.  In the fifth control mode of the control valve  80  (see FIG.  15 ), the sub-port  81   c  is connected to the control port  81   b  and the main port  81   d  so as to provide for the flow of the operational oil from the control port  81   b  into both the sub-port  81   c  and the main port  81   d.    
     The operation of the control valve  80  of the second embodiment of the present invention may be represented by a characteristic diagram of the quantity of the operational oil discharged from the oil pump  20 , as shown in FIG.  10 . The first control mode is illustrated as a diagram “O˜a”, the second control mode is illustrated as a diagram “a˜b”, the third control mode is illustrated as a diagram “b˜c”, the fourth control mode is illustrated as a diagram “c˜d” and the fifth control mode is shown as a bold line on the right side of “d”. 
     In accordance with the above embodiment of the present invention, since the valve spool  82  of the control valve  80  is located at a position schematically shown in FIG. 11 at a rotation speed range of the crank shaft  10  between 0 and N 1 , the sub-port  81   c  is disconnected from the control port  81   b  and is connected to the main port  81   d.  Therefore, a relatively large amount of operational oil is sucked by the oil pump  20  through both the main suction port  21   c  and the sub suction port  21   d  of the oil pump  20 . This is shown as a line “O˜a” in FIG. 10, which shows the amount of operational oil discharged by the oil pump  20 . The operational oil is discharged from the oil pump  20  to the components  51 ,  52  and  53  through the discharge conduit  41 . 
     Since the valve spool  82  of the control valve  80  is located at a position schematically shown in FIG. 12 at a crank shaft  10  rotation speed between N 1  and N 2 , the sub-port  81   c  is connected to the main port  81   d  (whereby a relatively small quantity of the operational oil flows into the sub-port  81   c  from the main port  81   d  due to the flow restriction imposed by the variable restriction portion B) and the quantity of the operational oil which flows into the sub-port  81   c  from the control port  81   b  is controlled by the variable restriction portion A in inverse proportion to the crank shaft  10  rotation speed (restriction portion A is pushed open in proportion to the amount of oil pressure). When the valve spool  82  is in this position, the operational oil flows into the sub-port  81   c  from the main port  81   d  and the control port  81   b.    
     Therefore, a portion of the operational oil which flows into the discharge opening  21   b  from the discharge port  21   e  flows into the sub suction port  21   d  through the control valve  80  and the operational oil is also sucked from the main suction port  21   c  into the sub suction port  21   d.  Consequently, the quantity of the operational oil sucked by the sub suction port  21   d  is restricted in proportion to the quantity of the operational oil flowed into the sub-port  81   c  from the control port  81   b  through the variable restriction portion A, and a sufficient quantity of operational oil is sucked by the main suction port  21   c.  This may be represented by a characteristic diagram of the quantity of the operational oil discharged from the oil pump  20 , which is shown as a line “a˜b” in FIG.  10 . Thus, the load applied to the oil pump  20  is reduced by the restriction of the quantity of the operational oil which is sucked by the sub suction port  21   d.    
     Since the valve spool  82  of the control valve  80  is located at a position schematically shown in FIG. 13 at a crank shaft  10  rotation speed between N 2  and N 3 , the sub-port  81   c  is connected to the control port  81   b  (whereby a relatively small quantity of the operational oil flows into the sub-port  81   c  from the control port  81   b  due to the restriction imposed by the restriction portion A), and the quantity of the operational oil flowing into the main port  81   d  from the control port  81   b  is controlled by the restriction portion B due to the amount of restriction imposed by restriction proportion B which varies in proportion to the crank shaft  10  rotation speed. Thus, the operational oil flows into the sub-port  81   c  and the main port  81   d  from the control port  81   b.    
     Therefore, a portion of the operational oil which flows into the discharge opening  21   b  from the discharge port  21   e  flows into the sub suction port  21   d  and the main suction port  21   c  through the control valve  80 . Consequently, the sub suction port  21   d  sucks a relatively small quantity of operational oil and the quantity of the sucked operational oil by the main suction port  21   c  is restricted in proportion to the quantity of the operational oil flowed into the main port  81   d  from the control port  81   b  through the variable restriction portion B. This operation of the oil pump apparatus is shown as a line “b˜c” in FIG. 10, which shows the quantity of oil discharged by the oil pump  20 . Therefore the load applied to the oil pump  20  is reduced by the restriction of the quantity of the operational oil which is sucked by the sub suction port  21   d  and the main suction port  21   c.    
     In this second embodiment of the present invention, when the valve spool  82  of the control valve  80  is located at a position schematically shown in FIG. 14, which occurs at a crank shaft  10  rotation speed between N 3  and N 4 , the sub-port  81   c  is connected to the control port  81   b  and disconnected from the main port  81   d.  When the valve spool  82  is in this position, the operational oil flows into the sub-port  81   c  from the control port  81   b,  but said oil cannot flow into the main port  81   d  from the control port  81   b.    
     Therefore, a portion of the operational oil flowing into the discharge opening  21   b  from the discharge port  21   e  flows into the sub suction port  21   d  through the control valve  80  and none of said oil flows into the main suction port  21   c.  Consequently, the main suction port  21   c  sufficiently sucks the operational oil and the sub suction port  21   d  scarcely sucks the operational oil. This is shown on FIG. 10 as line “c˜d” in FIG. 10, which represents the quantity of oil discharged from oil pump  20 . Therefore the load applied to the oil pump  20  is reduced by the restriction of the quantity of the operational oil which is sucked by the sub suction port  21   d.    
     When the valve spool  82  of the control valve  80  is located at a position schematically shown in FIG. 15, which occurs at a crank shaft  10  rotation speed higher than N 4 , the control port  81   b  is fully connected to the sub-port  81   c  and the quantity of the operational oil flowed into the main port  81   d  from the control port  81   b  is controlled by the variable restriction portion A, such that the amount of restriction imposed by restriction portion B is in inverse proportion to the crank shaft  10  rotation speed. In this position, the operational oil flows into both the sub-port  81   c  and the main port  81   d  from the control port  81   b.    
     Therefore, a portion of the operational oil which flows into the discharge opening  21   b  from the discharge port  21   e  flows into the sub suction port  21   d  and the main suction port  21   c  through the control valve  80 . Consequently, the sub suction port  21   d  scarcely sucks the operational oil and the quantity of the sucked operational oil by the main suction port  21   c  is restricted in proportion to the quantity of the operational oil flowed into the main port  81   d  from the control port  81   b  through the variable restriction portion A. This is shown on FIG. 10 as line to the right side of point “d”. Therefore the load applied to the oil pump  20  is reduced by the reduction of the quantity of the operational oil which is sucked by the sub suction port  21   d  and the main suction port  21   c.    
     In accordance with the above embodiment of the present invention, since the oil pressure generated at a lower portion of the slope  82   b  (shown in FIG. 9) is smaller than that generated at the variable restriction portion B, a the amount of force applied to the valve spool  82  by the oil pressure in the same direction as the force applied by the spring  83  to the valve spool  82  is reduced. Therefore, the increasing characteristic of the quantity of the operational oil discharged by the oil pump  20  at the third control mode is close to the decreasing characteristic (the hysterisis is small), so that the efficiency of the oil pump apparatus is relatively stable. 
     When the rand portion  82   a  does not include a slope  82   b,  as shown in FIG. 16, a comparatively high amount of oil pressure generated at the variable restriction portion B is applied to the underside surface  82   d  so as to strongly bias the valve spool  82  in the same direction as the spring  83  forces the valve spool  82 . Therefore, the oil pressure which acts to force the valve spool  82  in a downward direction, when measured at the time when the restriction portion B becomes closed, becomes higher so that the characteristic diagram of the quantity of the operational oil discharged by the oil pump  20  at the third control mode is illustrated as a two dotted line in FIG. 10, which shows a higher hysteresis. 
     In accordance with the second embodiment of the present invention, because the stepped portion  82   c  extending in the radial direction of the valve spool  82  is formed between the outer circumferential portion of the rand portion  82   a  and the upper end portion of the slope  82   b,  a size L of the rand portion  82   a  (shown in FIG. 9) in the axial direction of the valve spool  82  can be prevented from being varied by any manufacturing variation of the slope  82   b,  in order to maintain stable efficiency of the oil pump apparatus. Further, a size D of the stepped portion  82   c  should be preferably small in order to reduce the hysteresis with respect to the quantity of the operational oil discharged by the oil pump  20 . 
     The control valve of the oil pump apparatus of the third embodiment of the present invention (shown in FIGS. 17 to  21 ) will be described hereinafter. The control valve  130  includes a valve housing having a cylinder  131   a,  a first control port  131   b,  a sub-port  131   c,  a main port  131   d  and a second control port  131   e.  The control valve  130  includes a valve spool  132  slidably disposed in the cylinder  131   a  and to which an oil pressure generated by the oil pump  20  is applied through the second control port  131   e  (shown in FIG. 17) so as to control a connection between the ports  131   b,    131   c,    131   d  and  131   e.  The control valve  130  further includes a spring  133  biasing the valve spool  132  in the left direction, as shown in FIG.  17 . The valve spool  132  includes variable restriction portions A and B between the valve spool  132  and the valve housing  131  and an and portion  132   c  against which the oil pressure is applied. 
     The control ports  131   b,    131   e  are constantly connected to the discharge port  21   e,  the sub-port  131   c  is constantly connected to the subsuction port  21   d,  and the main port  131   d  is constantly connected to the main suction port  21   c  of the oil pump  20 . 
     In this embodiment, the control valve  130  has a first control mode (see FIG. 17) at which the sub-port  131   c  is only connected to the main port  131   d.  In the second control mode (see FIG.  18 ), the sub-port  131   c  is connected to the main port  131   d  through a semi-restricted position of the variable restriction portion B, and the sub-port  131   c  is also connected to the first control port  131   b  through a relatively highly restricted position of the variable restriction portion A, so that the operational oil flows into the sub-port  131   c  from both the main port  131   d  and the first control port  131   b.  In the third control mode (see FIG.  19 ), the sub-port  131   c  is connected to the first control port  131   b  and the sub-port  131   c  is connected to the main port  131   d  through the variable restriction portion B so that the operational oil flows from the first control port  131   b  into both the sub-port  131   c  and the main port  131   d.  In the fourth control mode (see FIG.  20 ), the sub-port  131   c  is only connected to the first control port  131   b.  Finally, in the fifth control mode (see FIG.  21 ), the sub-port  131   c  is connected to the first control port  131   b,  and the second control port  131   e  is connected to the main port  131   d.  In this fifth control mode the operational oil from the first control port  131   b  into the sub-port  131   c,  and the operational oil also flows from the second control port  131   e  into the main port  131   d.    
     A characteristic diagram showing the quantity of the operational oil discharged from the oil pump  20  with respect to this third embodiment of the present invention is shown in FIG.  10 . Because the operation of the control valve  130  is substantially equivalent to that of the control valve  80 , further description of said operation is omitted herein. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details can be made therein without departing from the spirit and scope of the invention.

Technology Classification (CPC): 5