Abstract:
A hydraulic control system for an internal combustion engine is provided which comprises a first hydraulic operating mechanism and a second hydraulic operating mechanism, the first hydraulic operating mechanism and the second hydraulic operating mechanism being operated independently by oil pressure of a common oil press source, and a circulation line that supplies pressure oil discharged from the first hydraulic operating mechanism to the second hydraulic operating mechanism.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a hydraulic control system for an internal combustion engine, which has two hydraulic operating mechanisms operated independently by oil pressure of a common oil pressure source. The present invention further relates to a hydraulic control system for an internal combustion engine, which has two variable valve timing control mechanisms capable of varying lift characteristics of at least one of an intake valve and an exhaust valve. 
     In the field of internal combustion engines, it is a common practice to actuate various kinds of hydraulic operating mechanisms by using an oil pump for circulation of lubrication oil as an oil pressure source. Examples of such hydraulic operating mechanism are a variable valve timing control mechanism for varying the opening and closing timings and the lift of the intake and exhaust valves in accordance with the operating condition of the engine and a variable compression ratio control mechanism for varying the piston stroke of each cylinder and thereby varying the compression ratio in accordance with the operation condition of the engine. 
     An example of a hydraulic variable valve timing control mechanism is disclosed in Japanese Patent Provisional Publication No. 5-248217. This variable valve timing control mechanism is capable of varying the opening and closing timings of the intake and exhaust valves in two steps by switching from one of a low-speed rocker arm and a high-speed rocker arm to another. Other variable valve timing control mechanisms are a variable phase control mechanism for varying the operation angle phase (i.e., maxim lift phase) of the intake and exhaust valves, an operation angle varying mechanism for varying the operation angles and valve lifts of the intake and exhaust valves and a valve stop mechanism for temporarily stopping the intake and exhaust valves of some of the cylinders. 
     SUMMARY OF THE INVENTION 
     In this connection, in case two hydraulic operating mechanisms which are operated independently by oil pressure of a common oil pressure source e used in an internal combustion engine, there is a possibility of causing the following problems. Namely, In case the operating conditions of both of the hydraulic operating mechanisms are changed simultaneously, particularly at a low-speed engine operating condition where the oil pressure produced by the oil pump is low, there is a possibility that the hydraulic operating mechanisms become poor in responsiveness due to a lack of the oil pressure supplied thereto. To prevent such deterioration of the responsiveness, it is considered to use an oil pump, accumulator or the like for the hydraulic operating mechanisms&#39; exclusive use. However, in this instance, a hydraulic circuit of the hydraulic control system becomes complicated in structure, thus causing a possibility of increasing the weight and the cost. 
     Particularly, in case the two hydraulic operating mechanisms are variable valve timing control mechanisms for varying the lift characteristics of the intake and exhaust valves, it is highly necessitated to change the operating conditions of the variable valve timing control mechanisms at the same timing so as to attain the required lifts which vary largely in accordance with the operating conditions of the engine at idling or at full-throttle operation. 
     For example, in case a variable phase control mechanism for varying the operation angle phase of an intake valve and a valve stop mechanism for temporarily stopping the intake and exhaust valves of some of the cylinders are used, it is desirable, when the valve stop mechanism is operated to stop the intake and exhaust valves of some of the cylinders, to advance the operation angle phase of the intake valve by the variable phase control mechanism so that a predetermined torque can be attained by the remaining cylinders. In this instance, the delay of the responsiveness of the valve stop mechanism becomes a particularly large problem. Namely, in the cylinders where the intake and exhaust valves are stopped, it is necessitated to inhibit injection of fuel. If there is a difference between the period during which the intake and exhaust valves are actually stopped and the period during which injection of fuel is actually inhibited, it is possible that fuel is injected during the time of the valves being stopped. This is particularly not desirable. 
     It is accordingly an object of the present invention to provide a hydraulic control system for an internal combustion engine, which has two hydraulic operating mechanisms operated independently by oil pressure of a common oil pressure source and which is simple in structure and has an improved responsiveness. 
     To accomplish the above object, there is provided according to an aspect of the present invention a hydraulic control system for an internal combustion engine comprising a first hydraulic operating mechanism, a second hydraulic operating mechanism, the first hydraulic operating mechanism and the second hydraulic operating mechanism being operated independently by oil pressure of a common oil pressure source, and a circulation line that supplies pressure oil discharged from the first hydraulic operating mechanism to the second hydraulic operating mechanism. 
     According to another aspect of the present invention, there is provided a hydraulic control system for an internal combustion engine comprising an oil pressure source, an oil sump, a first hydraulic operating mechanism, a second hydraulic operating mechanism, a first hydraulic control valve for selectively communicating the first hydraulic operating mechanism with one of the oil pressure source and the oil sump thereby controlling an operation of the first hydraulic operating mechanism, a second hydraulic control valve for selectively communicating the second hydraulic operating mechanism with one of the oil pressure source and the oil sump, a control line fluidly connecting between the second hydraulic control valve and the second hydraulic operating mechanism for conducting pressure oil supplied to and discharged from the second hydraulic operating mechanism, and a circulation line connecting between the first hydraulic control valve and the control line for supplying pressure oil discharged from the first hydraulic operating mechanism to the second hydraulic operating mechanism. 
     According to a further aspect of the present invention, there is provided a hydraulic control system for an internal combustion engine comprising a phase control mechanism for varying a phase of an intake valve, a valve stop mechanism for temporarily stopping intake and exhaust valves of some of cylinders, the phase control mechanism and the valve stop mechanism being operated by oil pressure of a common oil pressure source, and means for supplying pressure oil discharged from the phase control mechanism to the valve stop mechanism in addition to pressure oil supplied from the oil pressure source to the valve stop mechanism when the phase of the intake valve is advanced by the phase control mechanism and the intake and exhaust valves of some of the cylinders are stopped by the valve stop mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a hydraulic control system for an internal combustion engine according to an embodiment of the present invention; 
     FIGS. 2A to  2 C are schematic views for illustrating operations of a variable phase control mechanism and a hydraulic control valve for phase control, which are used in the hydraulic control system of FIG. 1; 
     FIG. 3 is a perspective view of a valve stop mechanism used in the hydraulic control system of FIG. 1; 
     FIGS. 4A and 4B are schematic views for illustrating operations of a hydraulic control valve for valve stop, used in the hydraulic control system of FIG. 1; and 
     FIGS. 5A and 5B are graphs for showing an advanced valve timing operation range and a part cylinder operation range, respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1, a hydraulic control system for an internal combustion engine includes first hydraulic operating mechanism  12  and second hydraulic operating mechanism  14  that are fluidly connected to oil pump  10  serving as a anon oil pressure source. In this embodiment, hydraulic operating mechanism  12  and  14  are embodied in valuable valve timing control mechanisms capable of varying lift characteristics of at least one of an intake valve and an exhaust valve of each cylinder. More specifically, hydraulic operating mechanisms  12  and  14  are embodied in a variable phase control mechanism for continuously varying the phase of an intake valve and a valve stop mechanism for temporarily stopping the intake and exhaust valves of some (e.g., a half) of the cylinders, respectively. 
     Further, the hydraulic control system includes hydraulic control valve  16  for phase control, that controls oil pressure supplied from oil pump  10  to variable phase control mechanism  12 , and hydraulic control valve  18  for valve stop, that controls oil pressure supplied from oil pump  10  to valve stop mechanism  14 . 
     Variable phase control mechanism  12  is of the type having been already proposed and described briefly with reference to FIGS. 2A to  2 C. Variable phase control mechanism  12  includes outer circumferential side gear potion  22  rotatable together with cam sprocket  21  which is in turn rotatable in timed relation with a crank shaft (not shown), inner circumferential side gear portion  24  disposed concentrically with and inside of cam sprocket  21  and rotatable together with intake cam shaft  23 , annular piston  25  meshed with the inner and outer circumferential surfaces of outer circumferential side gear portion  22  and inner circumferential side gear portion  24  by means of splines, and return spring  26  for urging piston  25  toward the retard side. 
     The opposite ends of piston  25  are associated with retard side oil pressure chamber  27  and advance side oil pressure chamber  28 , respectively. By axial movement of piston  25  in response to oil pressures in oil pressure chambers  27  and  28 , the phase of intake camshaft  23  relative to cam sprocket  21  is varied thereby varying the phase of the intake valve continuously. 
     Details of such a phase control mechanism are disclosed in Japanese Patent Provisional Publication Nos. 2000-073797, 2000-145487 and 2000-234533. 
     Valve stop mechanism  14  is of the type having been already proposed and described briefly with reference to FIG.  3 . When the oil pressure in valve stop oil pressure chamber  31  is low, coupling  33  is urged by the bias of a spring (not shown) disposed inside thereof so as to protrude into a position where it contacts auxiliary rocker arm  36   a  having roller bearing  34 . This causes rotational power to be transmitted to the intake and exhaust valves by way of auxiliary rocker arm  36   a , coupling  33  and rocker arm  36  thereby causing all the cylinders to operate. On the other hand, when a predetermined oil pressure is supplied to valve stop oil pressure chamber  31 , piston  38  pushes coupling  33  against the bias of the spring disposed inside coupling  33  and causes coupling  33  to move apart from auxiliary rocker arm  36   a . This shuts off transmission of power from auxiliary rocker arm  36   a  to coupling  33  thereby performing a part cylinder operation where the intake and exhaust valves of some of the cylinders are stopped. Details of such a valve stop mechanism are disclosed in Pages 56 to 58 of Auto Motor and Sport (German car magazine) No. 15, published on Jul. 14, 1999. 
     Referring to FIGS. 1 to  4 A and  4 B, a hydraulic circuit of the hydraulic control system will be described. The hydraulic circuit includes first supply line  41  for supplying oil pressure from oil pumps  10  to hydraulic control valve  16  for phase control, second supply line  42  for supplying oil pressure fan oil pump  10  to hydraulic control valve  18  for valve stop, retard side control line  43  connecting between control valve  16  and retard side oil pressure chamber  27 , advance side control line  44  connecting between control valve  16  and advance side oil pressure fiber  28 , valve stop control line  45  connecting between control valve  18  and valve stop oil pressure chamber  45 , retard side drain line  46  for conducting pressure oil discharged from control valve  16  to oil sump or oil pan  11 , and drain line  47  for valve stop for conducting pressure oil discharged from control valve  18  to oil pan  11 . 
     In the embodiment, circulation line  48  is provided which is fluidly connected at one end to retard side oil pressure chamber  27  of phase control mechanism  12  and at another end to valve stop oil pressure chamber  31  of valve stop mechanism  14  so as to supply pressure oil discharged from retard side oil pressure chamber  27  to valve stop oil pressure chamber  31 . More specifically, circulation line  48  is connected at one end to control valve  16  so as to communicate with retard side oil pressure chamber  27  of phase control mechanism  12  by way of retard side control line  43  and at another end (downstream side) to valve stop control line  45  so as to communicate therethrough with valve stop oil pressure chamber  31  of valve stop mean  14 . Namely, circulation line  48  is constructed so that it can supply pressure oil discharged from retard side oil pressure chamber  27  not through control valve  18  but directly to valve stop oil pressure chamber  31 . 
     In circulation line  48  is disposed check valve  49  for preventing reverse flow of pressure oil from valve stop mechanism  14  to phase control mechanism  12 . Further, control valve  51  is disposed in advance side drain line  50  branching off from circulation line  48  at a location upstream of check valve  49  (i.e., on phase control mechanism  12  side of check valve  49 ) and extending up to oil pan  11 . The valve opening pressure of check valve  49  is set at a value lower than that of control valve  51 . For example, the valve opening pressure of check valve  49  is set at about 0.1 kgf/cm 2  and the valve opening pressure of control valve  51  is set at about 0.3 kgf/cm 2 . 
     The operation of the hydraulic control system will now be described. 
     Phase control mechanism  12  supplies a duty signal to a solenoid (not show) for driving spool  16   a  of control valve  16  thereby feedback controlling the operation angle phase of the intake valve corresponding to the position of piston  25 . 
     More specifically, upon retard, i.e., when the operation angle phase of the intake valve is retarded, spool  16   a  of phase control valve  16  is placed in the position shown in FIG.  2 A. This causes the oil pressure from oil pump  10  to be supplied to retard side oil pressure chamber  27  by way of first supply line  41  and retard side control line  43 , while causing pressure oil in advance side oil pressure chamber  28  to be discharged through retard side drain line  46  into oil pan  11 . As a result, piston  25  is pushed toward the retard side (i.e., to the left-hand side in FIG.  2 A). In the meantime, in FIG. 2A are shown the lift characteristics of the intake and exhaust valves that are retarded maximumly. 
     Upon advance. i.e., when the operation angle phase of the intake valve is advanced, spool  16   a  is placed in the position shown in FIG.  2 B. This causes oil pressure to be supplied to advance side oil pressure chamber  28  by way of first supply line  41  and advance side control line  44 , while causing pressure oil in retard side oil pressure chamber  27  to be discharged through retard side control line  43  and circulation line  48 . As a result, piston  25  is pushed to the advance side (i.e., to the right-hand side in FIG. 2B) . In the meantime, in FIG. 2B are shown the lift characteristics of the intake and exhaust valve that are advanced maximumly. 
     When the operation angle phase of the intake valve is to be held at any given phase, spool  16   a  is placed in the position shown in FIG. 2C to close both of the ports connected to retard side control line  43  and advance side control line  44 . By this, the oil pressure in both oil pressure chambers  27  and  28  is confined therewithin, thus allowing piston  25  to be held at the present position, i.e., making it possible to hold piston  25  at any given position. 
     Valve stop mechanism  14  performs switching between full cylinder operation with all cylinders in operation and part cylinder operation with some of the cylinders kept out of operation, by switching the positions of spool  18   a  of control valve  18  according to the operating condition of the engine as shown in FIGS. 4A and 4B. Specifically, at the time of full cylinder operation. spool  18   a  of control valve  18  is placed at the position shown in FIG.  4 A. This causes pressure oil in valve stop oil pressure chamber  31  to be discharged through valve stop control line  45  and valve stop drain line  47  into oil pan  11 . On the other hand, at the time of port cylinder operation, spool  18   a  is placed at the position shown in FIG. 4B thereby causing oil pressure of oil pump  10  to be supplied through second supply line  42  and valve stop control line  45  to valve stop oil pressure chamber  31 . 
     In case oil pressure is supplied to valve stop mechanism  14  to start part cylinder operation at the time of advance, i.e., under the condition where pressure oil is discharged from retard side oil pressure chamber  27  into circulation line  48 , pressure oil is supplied through circulation line  48  to valve stop oil pressure chamber  31  rapidly. Namely, in addition to pressure oil supplied from oil pump  10  to valve stop oil pressure chamber  31  by way of second supply line  42 , control valve  18  and valve stop control line  45 , pressure oil is supplied from retard side oil pressure chamber  27  to valve stop oil pressure chamber  31  by way of circulation line  48 . Accordingly, retard side oil pressure chamber  27  functions as a kind of accumulator, so that it becomes possible to improve the responsiveness of valve stop mechanism  14  without using an additional accumulator or the like. As a result, it becomes possible to make longer the time of part cylinder operation and therefore it becomes possible to further improve the fuel consumption. 
     In other words, if the responsiveness of valve stop mechanism  14  is lowered, fuel will possibly be injected into a cylinder whose valves are stopped and therefore will possibly deteriorate the exhaust efficiency. However, since valve stop mechanism  14  starts part cylinder operation with an improved responsiveness, such a deterioration of the exhaust efficiency can be effectively suppressed. 
     Particularly, at low-speed engine operation, the oil pressure supplied by oil pump  10  is low so that the responsiveness of valve stop mechanism  14  tends to be lowered. However, according to the present invention, additional pressure oil is supplied from retard side oil pressure chamber  27  thereby enabling valve stop mechanism  14  to attain a good responsiveness even in an operation range where the oil pressure supplied to valve stop mechanism  14  is low. 
     Further, circulation line  48  is joined to valve stop control line  45  connecting between control valve  18  and valve stop oil pressure chamber  31  and is therefore constructed so as to supply pressure oil not through control valve  18  but directly to valve stop oil pressure chamber  31 . 
     Further, as seen from FIGS. 5A and 5B, the region H 2  where pressure oil is supplied to valve stop mechanism  14  to perform part cylinder operation with some of the cylinders kept out of operation is nearly included with the region H 1  where the operation angle phase of the intake valve is advanced from the maximumly retarded phase by phase control mechanism  12  thereby performing an advanced timing engine operation. Namely, when part cylinder operation is performed, it is desirable to advance the operation angle phase of the intake valve thereby retaining a predetermined torque by means of the remaining cylinders, while increasing an internal EGR thereby improving the fuel consumption and reducing the NOx emission. Accordingly, when oil pressure is supplied to valve stop mechanism  14  to start part cylinder operation, it is highly possible that phase control mechanism  12  is in a state of operation where the operation angle phase is advanced. 
     As indicated by arrows A 1  in FIGS. 5A and 5B, under an engine operating condition where the engine speed increases from the low-speed low-load range, the operating condition of phase control mechanism  12  is switched to the advance side simultaneously with switching to part cylinder operation. Further, as indicated by arrows A 2 , under an engine operating condition where the engine speed decreases from the high-speed low-load range, switching to the part cylinder operation is started during switching of phase control mechanism  12  to the advance side. Further, as indicated by arrows A 3 , even under an engine operating condition where the torque decreases from the high load range, switching to the part cylinder operation is started during switching of phase control mechanism  12  to the advance side. In this manner, when part cylinder operation is started, it is highly possible that phase control mechanism  12  has been switched to the advance side, i.e., it is highly possible that pressure oil is supplied through circulation line  48  to valve stop oil pressure chamber  31 , so that it becomes possible to make effectively higher the responsiveness of the hydraulic control system at the time of start of part cylinder operation. 
     In the meantime, in case phase control mechanism  12  is switched to the advance side under a condition where the oil pressure downstream of check valve  49  is high so that check valve  49  cannot be opened, such as the case where part cylinder operation is performed continuously, control valve  51  is adapted to open to enable pressure oil in retard side oil pressure chamber  27  to be discharged through advance side drain line  50  to oil pan  11 . 
     Further, at the time of full cylinder operation, the valve opening load of check valve  49  is lower than that of control valve (check valve)  51  and the oil pressure downstream of check valve  49  is low, so that when phase control mechanism  12  is switched to the advance side only check valve  49  is opened. Accordingly, pressure oil in retard side oil pressure chamber  27  is discharged through circulation line  48 , valve stop control line  45  and valve stop drain line  47  to oil pan  11 . 
     The entire contents of Japanese Patent Application P2001-12557 (filed Jan. 22, 2001) are incorporated herein by reference. 
     Although the invention has been described above by reference to a certain embodiment of the invention, the invention is not limited to the embodiment described above. Modifications and variations of the embodiment described above will occur to those skilled in the art, in light of the above teachings. For example, a flow restriction or orifice that generates a differential pressure can replace control valve  51 . The scope of the invention is defined with reference to the following claims.