Abstract:
An oil pressure control apparatus for a valve driving system for an internal combustion engine, in which a main oil supply passage feeds oil to a hydraulic actuator of the engine valve driving apparatus. A control valve is provided for closing the oil supply passage. A bypass oil passage bypasses the control valve continuously. The control valve, when closed, regulates the oil pressure to below a predetermined value and the oil pressure is insufficient to actuate the hydraulic actuator. When the control valve is opened, responsive to an engine operating condition such as engine speed, oil pressure is above the predetermined value, and the hydraulic actuator is actuated rapidly to shift the valve driving system from low speed to high speed operation.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an oil pressure control apparatus for an internal combustion engine, and more particularly to an oil pressure control apparatus for an engine valve driving system capable of selecting one of a plurality of cams for driving an intake valve and/or an exhaust valve in accordance with engine operating conditions. 
     BACKGROUND OF THE INVENTION 
     Engine valve driving systems are known which have a plurality of cams for driving an intake and/or exhaust valve to change valve timing and/or the quality of the valve lift in accordance with an engine operating condition. One such engine valve driving system is described in unexamined Japanese Utility Model Publication No. 58605/1986. This system provides a first rocker arm pivotally mounted on a rocker shaft for driving an intake valve under low speed engine operating conditions, in accordance with the movements of a low speed cam having a cam lobe suitable for low speed engine operation. Beside the first rocker arm is a second rocker arm pivotally mounted on a rocker shaft for driving the intake valve under high speed engine operating conditions, in accordance with the movements of a high speed cam having a cam lobe suitable for high speed cam operation. Engaging means engages the second rocker arm with the first rocker arm under high engine RPM and disengages the second rocker arm from the first rocker arm under low engine RPM. 
     An operating oil supply system for another type of engine valve driving apparatus is described in unexamined Japanese Patent Publication No. 59-231118 (U.S. Pat. No. 4,537,165). This reference discloses an operating oil supply system for a valve actuating mechanism having a stopping function, with a plunger selectively positioned by operating oil pressure controlled by an oil pressure control valve, which is actuated in response to engine operating conditions. 
     However, utilizing the above-mentioned systems requires rapid shifting of the plunger between an inoperative and operative position, and it is usually necessary to shift into the operative position several times before the oil supply passage is filled and the plunger beings to work, which can be relatively time-consuming. 
     In order to overcome this problem, an accumulator or similar mechanism is used with the oil pressure control apparatus. However, in an internal combustion engine, it is still difficult to raise the oil pressure to a sufficient level, especially when the engine is running at low speed. Nor does lowering the operating pressure of the plunger serve as an appropriate correction, since such action would require weakening the force of a return spring for the plunger, thereby requiring even more time to shift the plunger from the operative to inoperative position. Further, where the oil passage serves both as an operating oil and lubricating oil supply passage, it is difficult to lower the set pressure of the plunger below that of a predetermined limit value for preventing insufficient oil supply. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention is designed to solve the above-described problem by way of a novel oil pressure control apparatus which is able to respond quickly when shifting the plunger in systems where the oil passage serves as both a lubricating oil supply and operating oil supply passage. This is accomplished by the provision of a novel oil pressure control apparatus, in which a control valve has a bypass passage for bypassing the control valve. An oil pressure regulating valve is provided to allow a small amount of oil to flow to the engine valve driving apparatus, even when the control valve is in its closed position, at the same time preventing the bypassed oil from interfering with the operating pressure of the hydraulic actuator. In this inventive apparatus, the hydraulic actuator rapidly engages in operation when the control valve shifts from the closed to the open position. In systems where the operating oil supply passage also serves as a lubricating oil supply passage, lubricating oil pressure is available, even when the control valve is in the closed position. 
     Other objects, advantages, and features of the invention will become apparent from the following detailed description of a preferred embodiment, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a portion of the inventive engine valve driving apparatus. 
     FIG. 2 is a top plan view of the inventive engine valve driving apparatus of the invention. 
     FIG. 3 is a cross-sectional side view taken along line III--III of FIG. 2. 
     FIG. 4 is a side view, partially in cross-section, taken along line IV--IV of FIG. 2. 
     FIG. 5 is a cross-sectional side view taken along line V--V of FIG. 2. 
     FIG. 6 is a cross-sectional top view taken along line VI--VI of FIG. 5. 
     FIG. 7 is a cross-sectional view of the novel control valve in the closed position. 
     FIG. 8 is a cross-sectional view of the novel control valve in the open position. 
     FIG. 9 is a cross-sectional side view of a cam shaft unit. 
     FIG. 10 is a schematic of the hydraulic circuit of the invention. 
     FIG. 11 is a top plan view of an engine valve driving apparatus showing another embodiment of the invention. 
     FIG. 12 is a side view taken along line XII--XII of FIG. 11, upon which a schematic of the hydraulic circuit has been imposed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1-9 show a preferred embodiment, in which an engine valve driving apparatus is provided with the novel oil pressure control apparatus of the present invention. This engine valve driving apparatus is similar to the apparatus disclosed in nonpublished Japanese Application No. 61-186246, filed Aug. 8, 1986, and U.S. patent application Ser. No. 082,621, filed Aug. 7, 1987, owned by assignee and now U.S. Pat. No. 4,794,893. 
     Multi-cylinder engine 1 is of a V-8 configuration. It has two intake valves, two exhaust valves (not shown) for each cylinder 1, 2, etc., and a pair of cam shafts 14 (only one being shown) rotatably supported on cylinder head 13 by bearing portions 13a. 
     As shown in FIG. 1, low speed cams 15 and high speed cams 16 are mounted on cam shaft 14. Each intake or exhaust port of the engine requires a valve, and a pair of cams 15, 16 operate each valve. Since all valves and cams are of the same structure, only one valve and its associated operating cams will be described herein. 
     Low speed cam 15 has a smaller cam profile than high speed cam 16, and both are fixed to rotate with cam shaft 14. High speed cam 16 slidably fits onto cam shaft 14 and is adapted to be shifted axially relative to cam shaft 14 by a spline joint. Engine valve 33 is positioned beneath and in operative relationship to cams 15 and 16 and is provided with a tappet 33a, which engages continuously with cam 15 and intermittently with cam 16. Located below the tappet 33a is valve stem 33b having a valve head at its lower end to control a port to the combustion chamber of a cylinder. 
     FIGS. 1, 2, 3, and 9 show a valve driving apparatus which operates in cooperation with hydraulic actuator A for controlling the axial shifting or movement of high speed cam 16. Actuator A includes: a plunger 17 disposed in an oil pressure chamber 17a, common oil supply passage 20 and oil supply passage 20a extending therefrom formed in cam shaft 14, counter plunger 19 provided in bore 19a, and a return spring 18 biasing plunger 19. The oil supply passage 20 is connected to an oil pressure control apparatus 3 at an end portion of cam shaft 14 through line 22 and passage 21. 
     When the engine is driven at a low speed range, oil pressure in the oil pressure chamber 17a is kept at about 0.8 kg/cm 2  by oil pressure control apparatus 3 so that engine valve 33 is driven only by the low speed cam 15, the high speed cam 16 being shifted by the bias of spring 18. When the engine is driven at a high speed range, operating oil from the oil pump is fed directly to the oil pressure chamber 17a through oil supply passages 20, 20a. Oil pressure is thereby raised above 2.0 kg/cm 2  so that plunger 17 is forced toward cam 16, shifts the cam 16 from an inoperative to operative position, and engine valve 33 is driven by the high speed cam. 
     FIG. 10 shows a schematic for the novel hydraulic circuit for an internal combustion engine valve driving apparatus. Engine 1 has valve driving apparatus 2, which includes hydraulic actuators A as previously described. Oil from the oil pump P, taken from line 32 leading from reservoir R, is fed to the engine valve driving apparatus 2 through pressure control apparatus 3. Oil from pump P is fed through conduit 28 to the port of fitting 27. Ball check valve 29, which allows oil into--but not out of--passage 4, establishes a predetermined hydraulic pressure of greater than 2.0 kg/cm 2  in accumulator 5. Passage 4 connects with accumulator 5, while passage 4b leads from accumulator 5 to control valve 8. Passage 6 leads from control valve 8 to valve driving apparatus 2 in engine 1 via fitting 31 and conduit 22. Conduit 28a leads from valve driving apparatus 2 to pump P. 
     Piston 5b is mounted in accumulator 5 for reciprocation and is biased or urged by spring 5a downwardly against the oil in the accumulator. Passage 7 connects control valve 8 with a one-way pressure relief valve 10. Hydraulic pressure relieved by valve 10 is returned to reservoir R by line 7a. Valve 10 includes a ball element 10b urged against a valve seat by spring 10a to establish a predetermined relief value of 0.7 kg/cm 2 , which is substantially lower than the predetermined pressure value of 2.0 kg/cm 2  required to actuate hydraulic actuators A. A small diameter bypass line 9 connects accumulator 5 with passage 6, thereby bypassing control valve 8. 
     Control valve 8 comprises a spool element 8b driven by actuator 8a, which is preferably an electric actuator. Spool element 8b essentially has two positions. One is a shown in solid lines in FIG. 10, wherein passage 4b is blocked and passage 6 is connected to passage 7. In this position, since passage 6 receives oil at the higher pressure via bypass 9, the connection to passage 7 relieves the higher pressure to the lower pressure, which is passed to valve driving apparatus 2. The second position is shown in dotted lines in FIG. 10, wherein passage 7 is blocked and passages 4b and 6 are connected, allowing the higher pressure to be passed to valve driving apparatus 2. 
     Referring to FIGS. 2 and 4 through 6, oil pressure control apparatus 3 has a casing 25, which is fixed to a side surface of the cylinder head 13 by stays or brackets 25, 25a. A cover plate 26 closes casing 25 and supports a fitting 27 connected to a conduit 28 which, in turn, is connected to oil pump P. Control valve 8 is mounted within casing 25 suspended from cover 26. Electric actuator 8a is mounted on the control valve body and is operatively connected to valve element 8b by means of a shiftable sleeve or spool. 
     Conduit 28 carries oil from pump P and is connected to fitting 27, which is supported by cover 26. Fitting 27 includes one-way ball check valve 29 having a ball element biased by a spring to effect the higher pressure. Fitting 27 also defines accumulator 5 and passage 4 leading horizontally from the bottom of valve 29 to a vertical inlet to accumulator 5. 
     Within accumulator 5, piston 5b is biased by spring 5a for vertical reciprocation. Passage 4b extends horizontally and connects accumulator 5 with one end of control valve 8. Passage 6 extends vertically from an intermediate position of control valve 8 through fitting 31 carried by cover 26 and connects with conduit 22 leading to passage 21 in cylinder head 13. Bypass conduit or channel 9 is defined by the block of fitting 27 and connects passage 6 with passage 4b, where it meets with control valve 8. Passage 7 leads from the other end of control valve 8 through relief valve 10 into the space within casing 25 which serves as the reservoir R. 
     Referring now to FIGS. 7 and 8, valve element or body 8b of the control valve 8 is shown in the form of a sleeve 30 mounted for axial shifting or movement within valve 8. Sleeve 30 defines an inlet portion 30a connected to the passage 4b, an outlet port 3b connected via passage 6 to the oil supply passage 20 in the cam shaft 14, and a relief port 30c connected via passage 7 to the chamber of the casing 25, which serves as reservoir R. Outlet port 30b is connected to oil supply passage 21 of the cylinder head 13 through oil supply passage 6, connector or fitting 31, and an outlet pipe 22. Return pipe 32 connects the chamber of the casing 25 to pump P directly or via an oil pan. Bypass oil passage 9 has a smaller diameter than that of oil supply passage 4 and bypasses the control valve 8 to continuously supply oil to oil supply passage 6. 
     When the engine is driven in a high speed range, an engine speed sensor sends an appropriate signal to actuator 8a. Actuator 8a then moves the valve body 8b toward the left, as shown in FIG. 8, placing inlet port 3a and outlet port 30b in communication and thereby connecting the oil supply passage 4 and the oil supply passage 6. When the engine is driven in a low speed range, the engine speed sensor sends an appropriate signal to actuator 8a, and actuator 8a moves body 8b toward the right, as shown in FIG. 9. Outlet port 30b and relief port 30c are in communication, thereby connecting oil supply passage 6 and relief oil passage 7. 
     As shown in FIGS. 1 through 10, when the engine is driven in a low speed range, valve body 8b is shifted so that oil from the oil pump is fed to the oil supply passage 6 only through bypass oil passage 9. Even though oil passages 20, 21 are filled with oil, the oil pressure in the oil pressure chamber 17a will not rise above 0.7 kg/cm 2  by virtue of relief valve 10 being in communication with passage 6 via valve 8. The high speed cam 16 is forced into its inoperative position by return spring 18, and valve 33 is driven only by low speed cam 15. Relief oil from the relief valve 10 is returned to the oil pan or pumped through the chamber of the casing 25 and the return pipe 32. Further, since oil pressure changes in accordance with the engine RPM, one-way valve 29 mounted in the fitting or connector 27 prevents backflow of oil in the accumulator 5, even if the engine speed decreases. 
     When engine speed increases to a high speed range, actuator 8a moves valve body 8b to the opened position, and the plunger 17 forces, by oil pressure directly applied from the accumulator 5 and the oil pump, the high speed cam 16 to axially slide into its operative position, and valve 33 is driven by the high speed cam 16. In this embodiment, oil inlet pipe 28 is connected to an upper portion of the oil pressure control apparatus 3 in order not to introduce air from the oil pump. 
     Another embodiment is shown in FIGS. 11 and 12, where the engine valve driving apparatus is a rocker arm type apparatus, as proposed by nonpublished Japanese Application No. 61-24684, filed Oct. 16, 1986, in the name of assignee. In FIGS. 11 and 12, one cylinder of an internal combustion engine is shown having a plurality of cylinders and a cylinder head 41. Each cylinder has two intake valves 42a and 42b for opening and shutting, respectively, intake ports and one exhaust valve 43 for discharging exhaust gas from the cylinder. 
     Above cylinder head 41, a cam shaft 44 is mounted between the intake valves 42a, 42b and the exhaust valve 43. Cam shaft 44 has mounted thereon in spaced relation one pair of low speed cams 45a, 45b and a high speed cam 46 located substantially in the center of the spacing between low speed cams 45a and 45b. The high speed cam 46 has a cam lobe which is larger than that of the low speed cams 45a and 45b. The high speed cam 46 provides greater cam lift and allows the cam to remain open longer than the low speed cams 45a and 45b. A cam 47 for driving the exhaust valve 43 is provided between low speed cam 45b and high speed cam 45. 
     A rocker shaft 48 is mounted on the side of intake valves 42a and 42b parallel to the cam shaft 44. A rocker shaft 49 is mounted on the side of the exhaust valve 43b parallel to the cam shaft 44. Rocker arms 50a and 50b drive intake valves 42a and 42b, respectively, and are pivotally mounted on the rocker shaft 48. Rocker arms 50a and 50b are disposed to engage with the stems of the intake valves 42a, 42b, respectively, at one end thereof and, at the other end, to engage with low speed cams 45a and 45b, respectively. At one end of each rocker arms 50a and 50b, a hydraulic lash adjustor 51 is provided so that the end of each rocker arms 50a and 50b engages with the stem of its associated intake valves 42a and 42b, without any lash therebetween. At the other end of each of rocker arms 50a and 50b are roller cam followers 52 for reducing sliding friction between the associated end of each of rocker arms 50a, 50b and low speed cams 50a, 50b. An oil passage 48a is formed in rocker shaft 48 for feeding oil from the oil pressure control apparatus 3 to the hydraulic lash adjustor 51, the lubricated parts, and an hydraulic actuator (explained below). 
     Reference numeral 65 designates an oil passage in communication with oil passage 48a for feeding oil to the hydraulic lash adjustor 51. Rocker arm 53 is mounted for transmitting the movement of the high speed cam 46 to the respective rocker arms 50a and 50b and is pivotally mounted on the rocker shaft 48 at substantially the center position between the rocker arms 50a and 50b. Arm 53 is engaged with the high speed cam 46 at one end thereof. A spring 66 is mounted for pressing the end of the rocker arm 53 against the high speed cam 46 and preventing the rocker arm 53 from hitting the high speed cam 46 at low engine rpm. At the end of the rocker arm 53, there is provided a roller arm follower 54 for reducing sliding friction between the end of the rocker arm 53 and the high speed cam 46. The axial length of roller cam follower 54 is larger than that of roller cam follower 52. Moreover, a rocker arm 55 for transmitting the movement of the cam 47 for driving the exhaust tappet 43 connected to the exhaust valve 43 is pivotally mounted on the rocker shaft 44 and has at one end thereof a roller cam follower 56 for reducing sliding friction between the end of the rocker arm 55 and the cam 47. 
     A pair of hydraulic actuators 57 releasably connect the rocker arms 50a and 50b and the rocker arm 53. Each of the actuators 57 comprises a cylinder bore 57a formed integrally in the rocker arm 53, a plunger 57b slidable in each cylinder bore 57a, and an oil pressure chamber 57c formed by the cylinder bore 57a and the plunger 57b. Wall 57d separates the oil pressure chamber 57c of one actuator 57 from that of the other. An oil passage 57e for feeding oil to the oil pressure chambers 57c feeds into wall 57d and opening 64 therein. The oil passage 57e communicates with the oil passage 48a formed in the rocker shaft 48. Preferably, oil passage 57e is formed by a drill to be oblique toward the upstream direction of the oil passage 48a, so that oil can be easily introduced into the oil pressure chamber 57c. 
     Bores 61 for receiving the plungers 57b are formed integrally in the respective rocker arms 50a and 50b. Relatively sliding end walls 62 of the respective bores 61 provide surfaces for respective plungers 57b to abut and engage. In each of the bores 61, there is a spring 63 which biases the plunger 57b outwardly through the slidable end wall 62. At low engine speed, oil pressure in the oil pressure chamber 57c is kept low by oil pressure control apparatus 3. The plungers 57b are forced toward each other, retracting from bores 61 under the urging or bias of springs 63. At this time, plungers 57b lie entirely within cylinder bores 57a. The rocker arm 53 is disengaged from the rocker arms 50a and 50b. 
     On the other hand, at high engine speed, oil pressure in the oil pressure chamber 57c will be high as received from the oil pressure control apparatus 3. The plungers 57b will be pushed away from each other and into the bores 61 of the rocker arms 5a and 50b against the force of springs 63. The rocker arm 53 will be engaged with the rocker arms 50a and 50b. An air relief passage for the oil pressure chamber 57c of the rocker arm 53 is provided to relieve the air in the oil pressure chamber 57c. 
     According to the above-described embodiment, since the rocker arm 53 is not engaged with the rocker arms 50a and 5b at low engine speed, the movement of the low speed cams 45a and 45b is transmitted to the intake valves 42a and 45b by the rocker arms 50a and 50b, and the intake valves 45a and 45b are driven by the low speed cams 45a and 45b. On the other hand, at high engine speed, since the rocker arm 53 is engaged with the rocker arms 50a and 50b, the movement of the high speed 4b is transmitted to the intake valves 42a and 42b through the rocker arm 53 and the rocker arms 50a and 50b and the intake valves 42a and 42b are driven by the high speed cam 46. 
     In this embodiment shown in FIGS. 1 and 12, oil passage 57e is communicated to both the lubricated portion of the engine valve driving mechanism and the hydraulic lash adjustor 51, even if the control valve 8 is in the closed position, oil pressure still exists for feeding oil to the hydraulic lash adjustor and the lubricated parts. 
     The present invention has been shown and described with reference to specific embodiments. However, it should be noted that the present invention is in no way limited to the details of the described arrangements, but changes and modifications may be made without departing from the scope of the appended claims. For example, the novel oil pressure control apparatus can be used with the engine valve driving system as a means of providing a stopping function.