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.

Description:
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 23a which are engaged with the outer teeth 22a 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 22a and, the inner teeth 23a are designed in a trochoid curve or a cycloid curve shape. 
     The oil pump 20 includes a suction opening 21a connected to the oil pan 40 through a suction conduit 43, a discharge opening 21b connected to the discharge conduit 41, a main suction port 21c constantly connected to the suction opening 21a, a sub-suction port 21d selectively connected to or disconnected from the main suction port 21c by the control valve 30 and a discharge port 21e constantly connected to the discharge opening 21b. The ports 21c, 21d and 21e are separated and disconnected from each other by a plurality of pump chambers R disposed between each pair of outer teeth 22a and each corresponding pair of inner teeth 23a. 
     As shown in FIGS. 2 and 3, the control valve 30 includes a valve housing 31 having a cylinder 31a, a control port 31b, a sub-port 31c and a main port 31d. The control valve 30 also includes a valve spool 32 slidably disposed in the cylinder 31a. Oil pressure generated by the oil pump 20 is applied at the upper-end of valve spool 32 through the control port 31b, so as to control connections between the ports 31b, 31c and 31d. 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 31a, against the biasing force of spring 33, in proportion to the amount of oil pressure applied through the control port 31b. 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 31a. 
     The control port 31b is constantly connected to the discharge port 21e, the sub-port 31c is constantly connected to the sub-suction port 21d and the main port 31d is constantly connected to the main suction port 21c of the oil pump 20. 
     Since chamber 31a 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 31b 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 31b from the sub-port 31c (first condition). 
     When the oil pressure applied to the control port 31b 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 31c from the main port 31d (second condition). 
     When the oil pressure applied to the control port 31b 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 31b and the sub-port 31c, but still disconnects both of said ports from the main port 31d (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 &#34;a&#34; or &#34;A&#34;, the second condition of the control valve 30 corresponds to point &#34;b&#34; or &#34;B&#34; and the third condition of the control valve 30 corresponds to the condition shown as point &#34;c&#34;. 
     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 N1, as shown on FIG. 7 (e.g. 1500 rpm), when the actuator 51 is not operated, the sub-port 31c is disconnected from the control port 31b but is connected to the main port 31d. Therefore, a large amount of operation oil is sucked by the oil pump 20 through both the main suction port 21c and the sub suction port 21d of the oil pump 20. This is represented in FIG. 7 as a bold line &#34;O˜a&#34;, 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 N1 and N2 (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 31c to the control port 31b and to the main port 31d, respectively, are controlled by the crank shaft 10 rotation speed. 
     Therefore, a portion of the operational oil which flows into the discharge opening 21b from the discharge port 21e is made to flow into the sub suction port 21d through the control valve 30, and the operational oil is also sucked from the main suction port 21c into the sub suction port 21d. Consequently, the quantity of the sucked operational oil by the sub suction port 21d 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 21c. This is shown on FIG. 7 as bold line &#34;a˜b&#34;, 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 N2 and N3 (e.g. 5000 rpm) when the actuator 51 is not operated, the sub-port 31c is disconnected from the main port 31d and the size of passage formed between the valve spool 32 and the valve housing 31 which connects the sub-port 31c to the control port 31b 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 21b from the discharge port 21e flows into the sub suction port 21d through the control valve 30. Consequently, only the main suction port 21c sucks the operational oil. This is shown on FIG. 7 as a bold line &#34;b˜c&#34;, 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 rotation speed higher than N3, at such higher speed the control port 31b is fully connected to the sub-port 31c and the size of passage B formed with the valve spool 32 and the valve housing 31 which connect the main port 31d to the control port 31b and the sub-port 31c 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 21b from the discharge port 21e flows into both the sub suction port 21d and the main suction port 21c through the control valve 30. Consequently, the sub suction port 21d does not entirely suck the operational oil and the quantity of the sucked operational oil by the main suction port 21c 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 &#34;c&#34;, 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 N1a, 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 N2a 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 21c, 21d 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 N1 when the actuator is not operated and the relief valve starts to relieve the oil pressure at the crank shaft 10 rotation speed N1a 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 82a is disposed at an upper end of the valve spool 82 so as to receive the oil pressure which is forced from the control port 81b to the main port 81c at a third control mode (described later). The valve spool 82 has a slope 82b (tapered surface) which is sloped from an outer circumferential portion of the rand portion 82a towards the axis of the valve spool 82. The slope 82b is disposed at a lower portion of the rand portion 82a as shown in FIG. 9. Furthermore, the valve spool 82 has a stepped portion 82c disposed between the outer circumferential portion of the rand portion 82a and the upper end portion of the slope 82b. 
     The control valve 80 has a first control mode (see FIG. 11) at which the sub-port 81c, as determined by the amount of oil pressure applied to the control port 81b, is only connected to the main port 81d. In the second control mode of the control valve 80 (see FIG. 12) the sub-port 81c is also connected to the main port 81d through the variable restriction portion A. This second control mode provides for the flow of the operational oil into the sub-port 81c from both the main port 81d and the control port 81b. In the third control mode of the control valve 80 (see FIG. 13), the sub-port 81c is connected to the control port 81b and is also connected to the main port 81d through the variable restriction portion B so as to provide for the flow of the operational oil from the control port 81b into both the sub-port 81c and the main port 81d. In the fourth control mode of the control valve 80 (see FIG. 14), the sub-port 81c is only connected to the control port 81b. In the fifth control mode of the control valve 80 (see FIG. 15), the sub-port 81c is connected to the control port 81b and the main port 81d so as to provide for the flow of the operational oil from the control port 81b into both the sub-port 81c and the main port 81d. 
     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 &#34;O˜a&#34;, the second control mode is illustrated as a diagram &#34;a˜b&#34;, the third control mode is illustrated as a diagram &#34;b˜c&#34;, the fourth control mode is illustrated as a diagram &#34;c˜d&#34; and the fifth control mode is shown as a bold line on the right side of &#34;d&#34;. 
     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 N1, the sub-port 81c is disconnected from the control port 81b and is connected to the main port 81d. Therefore, a relatively large amount of operational oil is sucked by the oil pump 20 through both the main suction port 21c and the sub suction port 21d of the oil pump 20. This is shown as a line &#34;O˜a&#34; 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 NI and N2, the sub-port 81c is connected to the main port 81d (whereby a relatively small quantity of the operational oil flows into the sub-port 81c from the main port 81d 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 81c from the control port 81b 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 81c from the main port 81d and the control port 81b. 
     Therefore, a portion of the operational oil which flows into the discharge opening 21b from the discharge port 21e flows into the sub suction port 21d through the control valve 80 and the operational oil is also sucked from the main suction port 21c into the sub suction port 21d. Consequently, the quantity of the operational oil sucked by the sub suction port 21d is restricted in proportion to the quantity of the operational oil flowed into the sub-port 81c from the control port 81b through the variable restriction portion A, and a sufficient quantity of operational oil is sucked by the main suction port 21c. 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 &#34;a˜b&#34; 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 21d. 
     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 N2 and N3, the sub-port 81c is connected to the control port 81b (whereby a relatively small quantity of the operational oil flows into the sub-port 81c from the control port 81b due to the restriction imposed by the restriction portion A), and the quantity of the operational oil flowing into the main port 81d from the control port 81b 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 81c and the main port 81d from the control port 81b. 
     Therefore, a portion of the operational oil which flows into the discharge opening 21b from the discharge port 21e flows into the sub suction port 21d and the main suction port 21c through the control valve 80. Consequently, the sub suction port 21d sucks a relatively small quantity of operational oil and the quantity of the sucked operational oil by the main suction port 21c is restricted in proportion to the quantity of the operational oil flowed into the main port 81d from the control port 81b through the variable restriction portion B. This operation of the oil pump apparatus is shown as a line &#34;b˜c&#34; 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 21d and the main suction port 21c. 
     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 N3 and N4, the sub-port 81c is connected to the control port 81b and disconnected from the main port 81d. When the valve spool 82 is in this position, the operational oil flows into the sub-port 81c from the control port 81b, but said oil cannot flow into the main port 81d from the control port 81b. 
     Therefore, a portion of the operational oil flowing into the discharge opening 21b from the discharge port 21e flows into the sub suction port 21d through the control valve 80 and none of said oil flows into the main suction port 21c. Consequently, the main suction port 21c sufficiently sucks the operational oil and the sub suction port 21d scarcely sucks the operational oil. This is shown on FIG. 10 as line &#34;c˜d&#34; 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 21d. 
     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 N4, the control port 81b is fully connected to the sub-port 81c and the quantity of the operational oil flowed into the main port 81d from the control port 81b 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 81c and the main port 81d from the control port 81b. 
     Therefore, a portion of the operational oil which flows into the discharge opening 21b from the discharge port 21e flows into the sub suction port 21d and the main suction port 21c through the control valve 80. Consequently, the sub suction port 21d scarcely sucks the operational oil and the quantity of the sucked operational oil by the main suction port 21c is restricted in proportion to the quantity of the operational oil flowed into the main port 81d from the control port 81b through the variable restriction portion A. This is shown on FIG. 10 as line to the right side of point &#34;d&#34;. 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 21d and the main suction port 21c. 
     In accordance with the above embodiment of the present invention, since the oil pressure generated at a lower portion of the slope 82b (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 82a does not include a slope 82b, 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 82d 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 82c extending in the radial direction of the valve spool 82 is formed between the outer circumferential portion of the rand portion 82a and the upper end portion of the slope 82b, a size L of the rand portion 82a (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 82b, in order to maintain stable efficiency of the oil pump apparatus. Further, a size D of the stepped portion 82c 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 131a, a first control port 131b, a sub-port 131c, a main port 131d and a second control port 131e. The control valve 130 includes a valve spool 132 slidably disposed in the cylinder 13 la and to which an oil pressure generated by the oil pump 20 is applied through the second control port 131e (shown in FIG. 17) so as to control a connection between the ports 131b, 131c, 131d and 131e. 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. 
     The control ports 131b, 131e are constantly connected to the discharge port 21e, the sub-port 131c is constantly connected to the subsuction port 21d, and the main port 131d is constantly connected to the main suction port 21c 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 131c is only connected to the main port 131d. 
     In the second control mode (see FIG. 18), the sub-port 131c is connected to the main port 131d through a semi-restricted position of the variable restriction portion B, and the sub-port 131c is also connected to the first control port 131b through a relatively highly restricted position of the variable restriction portion A, so that the operational oil flows into the sub-port 131c from both the main port 131d and the first control port 131b . In the third control mode (see FIG. 19), the sub-port 131c is connected to the first control port 131b and the sub-port 131c is connected to the main port 131d through the variable restriction portion B so that the operational oil flows from the first control port 131b into both the sub-port 131c and the main port 131d. In the fourth control mode (see FIG. 20), the sub-port 131c is only connected to the first control port 131b. Finally, in the fifth control mode (see FIG. 21), the sub-port 131c is connected to the first control port 131b, and the second control port 131e is connected to the main port 131d. In this fifth control mode the operational oil from the first control port 131b into the sub-port 131c, and the operational oil also flows from the second control port 131e into the main port 131d. 
     A characteristic diagram showing the quantity of the operational oil discharged from the oil pump 20 with respect to this third embodiment of the 10. 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.