Variable valve timing system

Abstract

To suppress noise when switching a valve lift amount, and improve durability.SOLUTION: A variable valve device (20) can change a valve lift amount in a cylinder head. The variable valve device is provided with a camshaft (21) on which a plurality of cams (23, 24) with different valve lift amounts is formed, a switching mechanism (40) that switches a cam that moves the valve (12) between the plurality of cams; and an oil control valve (60) that controls oil pressure for the switching mechanism. Oil starts to be supplied from the oil control valve to the switching mechanism at valve lift end timing or in a zero section where no valve lift occurs.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a variable valve device.

Background Art

[0002] Conventionally, a variable valve device that changes the valve lift amount according to the engine speed is known (see, for example, Patent Document 1). In the variable valve device described in Patent Document 1, the valve is moved via a rocker arm by the rotation of a camshaft. A pair of cams with different lift amounts are formed on the camshaft, and a pair of rocker arms are provided corresponding to this pair of cams. By switching the connection state of the pair of rocker arms by a switching mechanism of the variable valve device, the cam that lifts the valve is switched and the valve lift amount is changed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such a variable valve device, the switching operation of the cam is performed by a switching mechanism regardless of the phase of the camshaft. When the switching operation of the cam is performed during valve lift, abnormal noise may occur due to a defect in the switching operation, and the durability of the variable valve device may be reduced. The same problem occurs not only during the cam switching operation using a rocker arm but also during the cam switching operation using a shift cam.

[0005] The present invention has been made in view of this point, and an object thereof is to provide a variable valve device capable of suppressing abnormal noise and improving durability when switching the valve lift amount.

Means for Solving the Problems

[0006] A variable valve timing device according to one aspect of the present invention is a variable valve timing device in a cylinder head that can change the amount of valve lift, comprising: a camshaft having a plurality of cams with different valve lift amounts formed thereon; a switching mechanism for switching the cam that moves the valve among the plurality of cams; and an oil control valve for controlling the hydraulic pressure to the switching mechanism. A plurality of rocker arms that contact the plurality of cams to move the valve, Equipped with, The switching mechanism includes a connecting pin that connects the plurality of rocker arms, and a hydraulic piston that moves the connecting pin, and the cam is switched by switching the connection state of the plurality of rocker arms by the connecting pin, and a part of the oil passage from the oil control valve to the switching mechanism is formed by the oil groove of the camshaft, At the end of the valve lift or during the zero section where no valve lift occurs, oil begins to be supplied from the oil control valve to the switching mechanism. The oil groove is formed in such a way. This solves the above problem. [Effects of the Invention]

[0007] According to one embodiment of the variable valve timing device of the present invention, oil is supplied from the oil control valve to the switching mechanism at the end timing or zero section of the valve lift, so that the cam switching operation is not hindered by the valve lift. Therefore, the generation of abnormal noise caused by malfunctions in the cam switching operation is suppressed, and the durability of the variable valve timing device is improved. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view of the variable valve timing device of the first embodiment. [Figure 2] This is a schematic top view of the variable valve timing device of the first embodiment. [Figure 3] This is an example of the cam switching operation of a variable valve timing device in a comparative example. [Figure 4] This is a schematic diagram of the variable valve timing device of the first embodiment. [Figure 5] This is a schematic diagram of the working passage and shortcut passage of the first embodiment. [Figure 6] This is an explanatory diagram of the movement operation of the hydraulic piston in the first embodiment. [Figure 7] This is an explanatory diagram of the coupling operation of the variable valve timing device of the first embodiment. [Figure 8] This is a perspective view of the variable valve timing device of the second embodiment. [Figure 9] This is an explanatory diagram of the switching operation of the variable valve timing device in the second embodiment. [Figure 10] This is an explanatory diagram of the switching operation of the variable valve timing device in the second embodiment. [Modes for carrying out the invention]

[0009] A variable valve timing device according to one aspect of the present invention is installed in a cylinder head and changes the amount of valve lift. Multiple cams with different valve lift amounts are formed on the camshaft, and the cam that moves the valve is switched between the multiple cams by a switching mechanism. The hydraulic pressure supplied to the switching mechanism is controlled by an oil control valve, and oil is supplied from the oil control valve to the switching mechanism at the end of the valve lift or in the zero section where no valve lift occurs. Therefore, the switching operation of the cam is not hindered by the valve lift. Thus, the generation of abnormal noise caused by malfunctions in the switching operation of the cam is suppressed, and the durability of the variable valve timing device is improved. [Examples]

[0010] <First Example> The variable valve timing device of the first embodiment will be described below with reference to the attached drawings. Figure 1 is a schematic cross-sectional view of the variable valve timing device of the first embodiment. Figure 2 is a schematic top view of the variable valve timing device of the first embodiment. Figure 3 is an example of the cam switching operation of a comparative variable valve timing device. Note that the cylinder head and cylinder head cover are omitted in Figure 2.

[0011] As shown in Figures 1 and 2, the cylinder head 10 is provided with four intake valves 12 that open and close the intake port 11, and four exhaust valves 15 that open and close the exhaust port 14 (only two of each are shown in Figure 2). The intake valves 12 are pressed in the closing direction by valve springs 13, and the exhaust valves 15 are pressed in the closing direction by valve springs 16. A cylinder head cover 17 is attached to the upper surface of the cylinder head 10, and the cylinder head 10 and the cylinder head cover 17 form a valve train chamber 18. A variable valve train 20 that changes the valve lift amount in the cylinder head 10 is mounted in the valve train chamber 18.

[0012] The variable valve timing device 20 is provided with a camshaft 21 common to both the intake and exhaust sides, and intake and exhaust rocker shafts 27 and 28 parallel to the camshaft 21. The camshaft 21 is rotatably supported by the cylinder head 10. The camshaft 21 is installed between the intake valve 12 and the exhaust valve 15, and a low-speed cam 23, a high-speed cam 24, and an exhaust cam 25 are formed on the outer circumferential surface of the camshaft 21. Each cam 23-25 ​​is formed in a plate shape with a cam lobe protruding from a part of the base circle. The cam lobe of the high-speed cam 24 is higher than that of the low-speed cam 23 so that the valve lift amount of the high-speed cam 24 is greater than that of the low-speed cam 23.

[0013] The intake and exhaust rocker shafts 27 and 28 are attached to the cylinder head 10 above the camshaft 21. Two types of rocker arms 31a and 31b are pivotably supported on the intake rocker shaft 27 (only one of each is shown in Figure 2), and a pair of rocker arms 35 are pivotably supported on the exhaust rocker shaft 28 (only one is shown in Figure 2). The intake rocker arm 31a and the exhaust rocker arm 35 are formed in a seesaw shape with a point of force application and a point of load application, but the intake rocker arm 31b is formed to be the point of force application for the rocker arm 31a.

[0014] At one end of the intake-side rocker arm 31a, a roller 32a that rolls on the low-speed cam 23 is rotatably supported, and at the bifurcated other end of the rocker arm 31a, a pair of intake valves 12 are connected. At one end of the intake-side rocker arm 31b, a roller 32b that rolls on the high-speed cam 24 is rotatably supported, and the intake valve 12 is not connected to the other end of the rocker arm 31b. At one end of the exhaust-side rocker arm 35, a roller 36 that rolls on the exhaust cam 25 is rotatably supported, and at the bifurcated other end of the rocker arm 35, a pair of exhaust valves 15 are connected. The rocker arms 31a and 31b are formed to be connectable.

[0015] During low and medium engine speeds, the rocker arms 31a and 31b are not connected. Therefore, the rocker arm 31a is swung by the low-speed cam 23, and the rocker arm 31b is swung by the high-speed cam 24. Since a pair of intake valves 12 are connected to the rocker arm 31a, the pair of intake valves 12 are moved according to the rotation of the low-speed cam 23. Since the cam peak of the low-speed cam 23 is low, the valve lift amount of the pair of intake valves 12 is low. Since the intake valve 12 is not connected to the rocker arm 31b, the rocker arm 31b idles according to the rotation of the high-speed cam 24.

[0016] During high engine speed, the rocker arms 31a and 31b are connected. Therefore, the rocker arms 31a and 31b are integrally swung by the high-speed cam 24. Since a pair of intake valves 12 are connected to the rocker arm 31b via the rocker arm 31a, the pair of intake valves 12 are moved according to the rotation of the high-speed cam 24. Since the cam peak of the high-speed cam 24 is high, the valve lift amount of the pair of intake valves 12 is high. Thus, by switching the connection state of the rocker arms 31a and 31b, the low-speed cam 23 and the high-speed cam 24 that move the intake valve 12 are switched.

[0017] The variable valve timing device 20 is provided with a switching mechanism 40 that switches between the connected and disconnected states of rocker arms 31a and 31b by hydraulic pressure. The rocker arms 31a and 31b have housing holes, and a connecting pin 41 is installed in the housing hole of rocker arm 31b. The rocker arms 31a and 31b are connected via the connecting pin 41 when a portion of the connecting pin 41 enters the housing hole of rocker arm 31a from the housing hole of rocker arm 31b. The connection between the rocker arms 31a and 31b is released when a portion of the connecting pin 41 is pushed back from the housing hole of rocker arm 31a into the housing hole of rocker arm 31b.

[0018] As shown in Figure 3(A), in the comparative example variable valve timing device 100, the connecting pin 102 is moved regardless of the phase of the camshaft 101. Therefore, when switching from the low-speed cam 103 to the high-speed cam 104, if the connecting pin 102 protrudes from the housing hole of the rocker arm 106b just before the valve lift of the intake valve 105, the connecting pin 102 may not be able to fully enter the housing hole of the rocker arm 106a. As shown in Figure 3(B), if the connecting pin 102 comes out of the housing hole of the rocker arm 106a and the connection is released during the valve lift by the high-speed cam 104, the rocker arm 106a will collide with the low-speed cam 103, generating an abnormal noise and causing a decrease in the durability of the variable valve timing device 100.

[0019] Therefore, the variable valve timing device 20 of this embodiment performs the switching operation between the low-speed cam 23 and the high-speed cam 24 while taking into consideration the phase of the camshaft 21. When switching from the low-speed cam 23 to the high-speed cam 24, the connecting pin 41 is pushed from the housing hole of the rocker arm 31b to the housing hole of the rocker arm 31a, avoiding the valve lift period when the housing holes of the rocker arms 31a and 31b do not align. The connecting pin 41 smoothly connects the rocker arms 31a and 31b, and the connection between the rocker arms 31a and 31b is not released during the valve lift period by the high-speed cam 24, thereby suppressing the generation of abnormal noise.

[0020] The variable valve timing device of the first embodiment will be described below with reference to Figures 4 to 6. Figure 4 is a schematic diagram of the variable valve timing device of the first embodiment. Figure 5 is a schematic diagram of the operating passage and shortcut passage of the first embodiment. Figure 6 is an explanatory diagram of the movement operation of the hydraulic piston of the first embodiment.

[0021] As shown in Figure 4, in the variable valve timing device 20, an oil supply passage 71 extends from the oil pan 70 to the oil control valve 60. An oil pump 72 located along the oil supply passage 71 pumps oil from the oil pan 70 and supplies it to the oil control valve 60 through an oil filter 73. The oil control valve 60 is formed by a valve housing 61 that houses a valve spool (not shown) and a solenoid 62 that moves the valve spool forward and backward. The movement of the valve spool by the solenoid 62 switches the oil passage within the oil control valve 60.

[0022] The valve housing 61 has an input port 63, a low-speed port 64, a high-speed port 65, and a drain port 66. An oil supply passage 71 is connected to the input port 63, a dead-end passage 74 is connected to the low-speed port 64, an operating passage (oil passage) 75 is connected to the high-speed port 65, and a drain passage 76 is connected to the drain port 66. The output of the dead-end passage 74 is blocked, and the operating passage 75 extends from the oil control valve 60 toward the switching mechanism 40. The drain passage 76 extends from the oil control valve 60 toward the top of the oil pan 70, and oil is drained into the oil pan 70 from the outlet of the drain passage 76.

[0023] When the valve spool of the oil control valve 60 is moved, the input port 63 is connected to either the low-speed port 64 or the high-speed port 65, and the drain port 66 is connected to the other of the low-speed port 64 or the high-speed port 65. Oil is output from the oil control valve 60 to either the dead-end passage 74 or the operating passage 75, and excess oil is discharged from the other of the dead-end passage 74 or the operating passage 75 to the oil control valve 60 (drain passage 76). In this way, the oil control valve 60 controls the hydraulic pressure to the switching mechanism 40.

[0024] A portion of the operating passage 75 leading from the oil control valve 60 to the switching mechanism 40 is formed by the oil groove 26 of the camshaft 21. As described above, the camshaft 21 has a low-speed cam 23, a high-speed cam 24, and an exhaust cam 25 (not shown in Figure 4), and the oil groove 26 is partially formed on the outer circumferential surface of the camshaft 21, which is supported by a cam housing (not shown). As the camshaft 21 rotates, the upstream passage 77a and the downstream passage 77b of the operating passage 75 alternately communicate and disconnect. As a result, oil is intermittently supplied from the oil control valve 60 to the switching mechanism 40 through the operating passage 75.

[0025] Furthermore, a shortcut passage (another oil passage) 78 branches off from the upstream passage 77a of the operating passage 75. The shortcut passage 78 extends directly from the oil control valve 60 to the switching mechanism 40 without going through the oil groove 26 of the camshaft 21. As a result, oil is continuously supplied from the oil control valve 60 to the switching mechanism 40 through the shortcut passage 78. As will be described in detail later, the oil supply from the operating passage 75 is used as a trigger to move the hydraulic piston 52 of the switching mechanism 40, and the oil supply from the shortcut passage 78 is used to hold the hydraulic piston 52 in the pushed-out position.

[0026] As described above, rocker arms 31a and 31b are adjacent, but their upper parts face each other with a small gap C between them. The upper parts of rocker arms 31a and 31b have housing holes 33a and 33b, which are parallel to the camshaft 21. The diameters of the housing holes 33a of rocker arm 31a and 33b of rocker arm 31b are the same, and they are formed coaxially so that the housing holes 33a and 33b communicate when the rocker arm is not lifted. A connecting pin 41 is installed in the housing hole 33b of rocker arm 31b, and a return pin 44 is installed in the housing hole 33a of rocker arm 31a.

[0027] The housing holes 33a and 33b of the rocker arms 31a and 31b are formed straight, and flange pins are used as the connecting pin 41 and the return pin 44. A flange 42 is formed on one end of the connecting pin 41 that protrudes to one side from the rocker arm 31b, and a flange 45 is formed on the other end of the return pin 44 that protrudes to the other side from the rocker arm 31a. In this case, the flange 42 of the connecting pin 41 abuts against the rocker arm 31b, restricting the pushing of the connecting pin 41, and the flange 45 of the return pin 44 abuts against the rocker arm 31a, restricting the pushing back of the return pin 44.

[0028] A sliding chamber 51 is formed in the cylinder head 10 on one side of the rocker arm 31b, and a hydraulic piston 52 is installed in the sliding chamber 51. The pressing surface of the hydraulic piston 52 is in contact with the connecting pin 41, and the hydraulic piston 52 moves the connecting pin 41 to the other side. In addition, a sliding chamber 53 is formed in the cylinder head 10 on the other side of the rocker arm 31a. A spring pin 54 is installed in the sliding chamber 53. The pressing surface of the spring pin 54 is in contact with the return pin 44, and the spring pin 54 returns the return pin 44 to one side. A sensing arm 55 extends from the spring pin 54 to the other side.

[0029] In the switching mechanism 40, the connection state of the rocker arms 31a and 31b is switched by the movement of the connecting pin 41 by hydraulic pressure. As described above, when the rocker arms 31a and 31b are not connected, the pair of intake valves 12 are operated by the low-speed cam 23 via the rocker arm 31a. When the rocker arms 31a and 31b are connected, the pair of intake valves 12 are operated by the high-speed cam 24 via the rocker arms 31a and 31b. Thus, in the switching mechanism 40, the connection state of the rocker arms 31a and 31b is switched by the connecting pin 41, which switches the cam that operates the pair of intake valves 12.

[0030] The variable valve timing device 20 is also equipped with an ECM (Engine Control Module) 57, an engine angle sensor 58, and a switching sensor 59. The engine angle sensor 58 detects the engine speed, and when it exceeds a predetermined speed, the ECM 57 outputs a coupling command signal to the solenoid 62, and when it falls below the predetermined speed, the ECM 57 outputs a release command signal to the solenoid 62. The switching sensor 59 detects the switching between the coupled and uncoupled states of the rocker arms 31a and 31b from the movement of the tip of the sensing arm 55. The command signal from the ECM 57 and the detection signal from the switching sensor 59 are compared to determine if there is a malfunction in the variable valve timing device 20, such as a switching malfunction.

[0031] As shown in Figure 5, the upstream passage 77a of the operating passage 75 extends from the oil control valve 60 toward the camshaft 21, and the downstream passage 77b of the operating passage 75 extends from the camshaft 21 toward the hydraulic piston 52 of the switching mechanism 40. The downstream end of the upstream passage 77a and the upstream end of the downstream passage 77b are located on the same circumference on the outer surface of the camshaft 21. An oil groove 26 is formed in the circumferential direction on the circumference of the outer surface of the camshaft 21. Both the upstream passage 77a and the downstream passage 77b of the oil groove 26 function as operating passages 75 that supply oil to the hydraulic piston 52.

[0032] Oil is supplied from the oil control valve 60 to the hydraulic piston 52 only while the upstream passage 77a and the downstream passage 77b are in communication via the oil groove 26. At this time, the oil groove 26 is formed such that the upstream passage 77a and the downstream passage 77b are in communication at the end of the valve lift, and separate before the start of the valve lift. In other words, the oil groove 26 is formed such that oil is supplied from the oil control valve 60 to the hydraulic piston 52 at the end of the valve lift, and the supply of oil to the hydraulic piston 52 is completed before the start of the valve lift.

[0033] Since oil is supplied to the hydraulic piston 52 at the end of the valve lift, the coupling operation of the rocker arms 31a and 31b is not hindered by the valve lift. Also, since the coupling operation of the rocker arms 31a and 31b is completed before the start of the valve lift, the rocker arms 31a and 31b are not coupled in the middle of the valve lift. Therefore, as the camshaft 21 rotates, oil is intermittently supplied from the oil control valve 60 to the hydraulic piston 52 through the operating passage 75, and the rocker arms 31a and 31b can be smoothly coupled via the coupling pin 41.

[0034] Furthermore, a shortcut passage 78 extends directly from the oil control valve 60 to the hydraulic piston 52. The shortcut passage 78 is shorter than the operating passage 75. A stepwise oil supply structure to the hydraulic piston 52 is formed so that oil is supplied to the hydraulic piston 52 from the shortcut passage 78 after oil is supplied to the hydraulic piston 52 from the operating passage 75. If only intermittent oil is supplied from the operating passage 75, there is a risk that the hydraulic piston 52 will move, but the direct supply of oil from the shortcut passage 78 keeps the hydraulic piston 52 stably held.

[0035] As shown in Figure 6(A), a hydraulic piston 52 is installed in a cylindrical sliding chamber 51 of the cylinder head 10. The downstream end of the operating passage 75 (downstream passage 77b) is open on the inner bottom surface of the sliding chamber 51, and the downstream end of the shortcut passage 78 is open on the inner circumferential surface of the sliding chamber 51. The direction of oil supply from the operating passage 75 to the hydraulic piston 52 is in the direction of the hydraulic piston 52's advance, and the direction of oil supply from the shortcut passage 78 to the hydraulic piston 52 is in the radial direction of the hydraulic piston 52. When the hydraulic piston 52 is in the retracted position, the downstream end of the shortcut passage 78 is blocked by the outer circumferential surface of the hydraulic piston 52.

[0036] As shown in Figure 6(B), as the engine speed increases from low to high, oil is supplied to the sliding chamber 51 from the downstream end of the working passage 75. Since the direction of oil supply from the working passage 75 is directed in the direction of the hydraulic piston 52's advance, the hydraulic piston 52 moves smoothly in the advance direction. As shown in Figure 6(C), when the hydraulic piston 52 moves in the advance direction, the downstream end of the shortcut passage 78 is opened, and oil is supplied to the sliding chamber 51 from the downstream end of the shortcut passage 78. The oil from the shortcut passage 78 holds the hydraulic piston 52 in the advanced position protruding from the sliding chamber 51.

[0037] In this way, as the hydraulic piston 52 is moved from the retracted position to the extended position, the intermittent oil supply to the hydraulic piston 52 from the operating passage 75 is switched to a continuous oil supply from the shortcut passage 78. Since the shortcut passage 78 is formed to be shorter than the operating passage 75, oil is smoothly supplied from the shortcut passage 78 to the hydraulic piston 52, and the hydraulic piston 52 can be held stably. Since the downstream end of the shortcut passage 78 is opened and closed by the hydraulic piston 52, the number of parts can be reduced and the variable valve timing device 20 can be made compact.

[0038] The coupling operation of the variable valve timing device will be explained with reference to Figure 7. Figure 7 is an explanatory diagram of the coupling operation of the variable valve timing device of the first embodiment. Also, in Figure 7, the reference numerals from Figure 3 will be used as appropriate for ease of explanation.

[0039] As shown in Figure 7(A), at low engine speeds, oil is not supplied from the oil control valve 60 to the hydraulic piston 52. No pressing force is applied from the hydraulic piston 52 to the connecting pin 41, and the spring force of the spring pin 54 is acting on the return pin 44. The flange 45 of the return pin 44 abuts against the rocker arm 31a, positioning the return pin 44 in its initial position. At this time, the other end 43 of the connecting pin 41 is in contact with one end 46 of the return pin 44 at the non-connected position P1 of the gap C between the rocker arms 31a and 31b. The other end 43 of the connecting pin 41 is located outside the rocker arm 31b, and the rocker arms 31a and 31b are separated.

[0040] As shown in Figure 7(B), when the engine speed increases above a predetermined speed, oil is supplied from the oil control valve 60 to the hydraulic piston 52. As the camshaft 21 rotates, the upstream passage 77a and the downstream passage 77b of the operating passage 75 are intermittently connected through the oil groove 26, and oil is intermittently supplied from the operating passage 75 to the hydraulic piston 52. At this time, the oil is supplied at the timing when the valve lift of the intake valve 12 ends, so as not to hinder the coupling operation of the rocker arms 31a and 31b. As a result, the hydraulic piston 52 is smoothly pushed out in the advance direction by the oil from the operating passage 75.

[0041] The hydraulic piston 52 pushes in the connecting pin 41, and the connecting pin 41 moves the spring pin 54 to the other side via the return pin 44. The other end 43 of the connecting pin 41 moves to the other side from the unconnected position P1 to the connected position P2 of the rocker arm 31a. A portion of the connecting pin 41 fits into the housing hole 33a of the rocker arm 31a, thereby connecting the rocker arms 31a and 31b via the connecting pin 41. The movement of the hydraulic piston 52 opens the downstream end of the shortcut passage 78, and the position of the hydraulic piston 52 is maintained by the continuous oil supply from the shortcut passage 78.

[0042] As shown in Figure 7(A), when the engine speed drops below a predetermined speed, oil is returned from the hydraulic piston 52 to the oil control valve 60 (drain passage 76). The hydraulic piston 52 releases the push of the connecting pin 41, and the spring pin 54's repulsive force pushes the return pin 44 in, pushing the connecting pin 41 back to one side. The other end 43 of the connecting pin 41 moves to one side from the connected position P2 to the unconnected position P1. Then, a part of the connecting pin 41 comes out of the housing hole 33a of the rocker arm 31a, releasing the connection between the rocker arms 31a and 31b.

[0043] As described above, with the variable valve timing device 20 of the first embodiment, oil is supplied from the oil control valve 60 to the switching mechanism 40 at the end of the valve lift timing. Therefore, the coupling operation of the rocker arms 31a and 31b is not hindered by the valve lift, and the rocker arms 31a and 31b are properly coupled by the coupling pin 41. Thus, the coupling state of the rocker arms 31a and 31b is not released in the middle of the valve lift, the generation of abnormal noise is suppressed, and the durability of the variable valve timing device 20 is improved.

[0044] <Second Example> Next, the variable valve timing device of the second embodiment will be described with reference to Figures 8 to 10. The variable valve timing device of the second embodiment differs from the variable valve timing device of the first embodiment in that the cam that moves the intake valve is switched by a shift cam. Therefore, the description of the configuration of the second embodiment that is the same as that of the first embodiment will be omitted. Figure 8 is a perspective view of the variable valve timing device of the second embodiment. Figures 9 and 10 are explanatory diagrams of the switching operation of the variable valve timing device of the second embodiment.

[0045] As shown in Figure 8, in the second embodiment, a shift cam 83 is slidably and integrally rotatably mounted on the shaft body 82 of the camshaft 81. Guide grooves (not shown) are formed axially on the inner circumferential surface of the shift cam 83, and guide rails 85 that fit into the guide grooves are formed axially on the outer circumferential surface of the shaft body 82. Low-speed cams 86a, 86b and high-speed cams 87a, 87b are formed on the outer circumferential surface of the shift cam 83, as well as switching grooves 88a, 88b for sliding the shift cam 83 relative to the shaft body 82. In addition, a single oil groove 89 is formed on the outer circumferential surface of the shift cam 83, connecting oil passages 91a, 91b.

[0046] A pair of intake valves 90 are provided corresponding to the low-speed cams 86a and 86b and the high-speed cams 87a and 87b, and a hydraulic changeover switch (changeover mechanism) 95 is provided corresponding to the changeover grooves 88a and 88b. The changeover switch 95 is provided with changeover pins 96a and 96b that enter the changeover grooves 88a and 88b by hydraulic pressure, and the shift cam 83 slides and the cam is switched when the changeover pins 96a and 96b enter the changeover grooves 88a and 88b. When the changeover pin 96a enters the changeover groove 88a, the cam is switched to the high-speed cams 87a and 87b, and when the changeover pin 96b enters the changeover groove 88b, the cam is switched to the low-speed cams 86a and 86b.

[0047] A portion of the oil passages 91a and 91b, leading from the oil control valve 80 to the switching pins 96a and 96b, is formed by an oil groove 89. An upstream passage 92aa of the oil passage 91a extends from the oil control valve 80 toward the shift cam 83, and a downstream passage 92ab of the oil passage 91a extends from the shift cam 83 toward the switching pin 96a. The downstream end of the upstream passage 92aa and the upstream end of the downstream passage 92ab are located on the same circumference 97a on the outer surface of the shift cam 83. When the low-speed cams 86a and 86b are in use, the oil groove 89 is located on the circumference 97a.

[0048] An upstream passage 92ba of the oil passage 91b extends from the oil control valve 80 toward the shift cam 83, and a downstream passage 92bb of the oil passage 91b extends from the shift cam 83 toward the switching pin 96b. The downstream end of the upstream passage 92ba and the upstream end of the downstream passage 92bb are located on the same circumference 97b on the outer surface of the shift cam 83. When the high-speed cams 87a and 87b are in use, an oil groove 89 is located on the circumference 97b. The communication state of the oil passages 91a and 91b is controlled by one oil groove 89 through the sliding of the shift cam 83.

[0049] When the oil groove 89 is positioned on the circumference 97a, the upstream passage 92aa and the downstream passage 92ab are intermittently connected through the oil groove 89. At this time, the oil groove 89 is formed such that the upstream passage 92aa and the downstream passage 92ab are connected at the end of the valve lift, and separated before the start of the valve lift. In other words, the oil groove 89 is formed such that oil is supplied from the oil control valve 80 to the switching pin 96a at the end of the valve lift, and the supply of oil to the switching pin 96a ends before the start of the valve lift.

[0050] Since oil is supplied to the switching pin 96a at the end of the valve lift, the switching operation of the shift cam 83 is not hindered by the valve lift. Also, since the switching operation of the shift cam 83 is completed before the start of the valve lift, the shift cam 83 is not switched in the middle of the valve lift. When the oil groove 89 is positioned on the circumference 97b, the upstream passage 92ba and the downstream passage 92bb are intermittently connected through the oil groove 89. Even when oil is supplied to the switching pin 96b, the switching operation of the shift cam 83 is performed while avoiding the valve lift.

[0051] As shown in Figure 9(A), at low engine speeds, oil is not supplied from the oil control valve 80 to the selector switch 95. The selector pins 96a and 96b of the selector switch 95 are pressed in the retraction direction by an internal spring. Since the selector pins 96a and 96b are disengaged from the selector grooves 88a and 88b, no force is acting on the shift cam 83 in the sliding direction. At this time, the low-speed cams 86a and 86b of the shift cam 83 are positioned in front of a pair of intake valves 90, and the pair of intake valves 90 are valve-lifted by the low-speed cams 86a and 86b. Also, the oil groove 89 is positioned on the circumference 97a.

[0052] As shown in Figure 9(B), when the engine speed increases above a predetermined speed, oil is supplied from the oil control valve 80 to the changeover switch 95. As the camshaft 81 rotates, the upstream passage 92aa and the downstream passage 92ab of the oil passage 91a are intermittently connected through the oil groove 89, and oil is intermittently supplied from the oil passage 91a to the changeover pin 96a. The changeover pin 96a enters the changeover groove 88a, and the shift cam 83 slides to the other side. Since the oil is supplied at the timing when the valve lift of the intake valve 90 ends, the sliding of the shift cam 83 is not hindered by the valve lift.

[0053] As shown in Figure 10(A), the supply of oil from the oil control valve 80 to the changeover switch 95 is stopped, and the changeover pin 96a disengages from the changeover groove 88a due to the repulsive force of the internal spring, ending the sliding of the shift cam 83. Since the changeover pins 96a and 96b are disengaged from the changeover grooves 88a and 88b, no force is acting on the shift cam 83 in the sliding direction. At this time, the high-speed cams 87a and 87b of the shift cam 83 are positioned on the pair of intake valves 90, and the pair of intake valves 90 are valve-lifted by the high-speed cams 87a and 87b. Also, the oil groove 89 is positioned on the circumference 97b.

[0054] As shown in Figure 10(B), when the engine speed drops below a predetermined speed, oil begins to be supplied from the oil control valve 80 to the changeover switch 95. As the camshaft 81 rotates, the upstream passage 92ba and the downstream passage 92bb of the oil passage 91b are intermittently connected through the oil groove 89, and oil is intermittently supplied from the oil passage 91b to the changeover pin 96b. The changeover pin 96b enters the changeover groove 88b, causing the shift cam 83 to slide to one side. Since the oil supply begins at the timing when the valve lift of the intake valve 90 ends, the sliding of the shift cam 83 is not hindered by the valve lift.

[0055] As described above, with the variable valve timing device 99 of the second embodiment, oil is supplied from the oil control valve 80 to the changeover switch 95 at the end of the valve lift timing, so the cam cannot be switched in the middle of the valve lift. Therefore, the generation of abnormal noise is suppressed and the durability of the variable valve timing device 99 is improved.

[0056] In the first and second embodiments, the valve lift termination timing is not limited to the timing when the valve lift has completely finished, but also includes the timing immediately before termination when the valve lift can be considered to have finished.

[0057] Furthermore, in the first and second embodiments, the oil supply from the oil control valve to the switching mechanism (hydraulic piston, changeover switch) begins at the timing of the end of the valve lift. However, the timing of oil supply is not limited to the timing of the end of the valve lift. Oil may also begin to be supplied from the oil control valve to the switching mechanism during the zero section in which no valve lift occurs. Even with such a configuration, it is possible to prevent the cam switching operation from being hindered by the valve lift.

[0058] Furthermore, in the first and second embodiments, the oil groove is formed so that the supply of oil to the switching mechanism (hydraulic piston, changeover switch) via the oil passage is completed before the start of the valve lift. However, the oil groove may be formed to be longer. For example, the oil groove may be formed so that the supply of oil to the switching mechanism via the oil passage is completed from the end of one valve lift to the start of the next valve lift. This configuration ensures a longer oil supply time to the switching mechanism through the oil passage, thereby stabilizing the cam switching operation by the switching mechanism.

[0059] Furthermore, although flange pins are used for the connecting pin and return pin in the first embodiment, straight pins may also be used for the connecting pin and return pin.

[0060] Furthermore, while a seesaw-type rocker arm was exemplified in the first embodiment, the type of rocker arm is not particularly limited, and a finger-follower type rocker arm may also be used.

[0061] Furthermore, in the first embodiment, a pair of rocker arms are provided on the intake side of the variable valve train, but it is also acceptable for the variable valve train to have multiple rocker arms on the intake side. For example, the variable valve train may have three or more rocker arms on the intake side.

[0062] Furthermore, in the first embodiment, multiple rocker arms are adjacent to each other, but multiple rocker arms may be spaced apart.

[0063] Furthermore, in the first embodiment, an operating passage and a shortcut passage are formed in the cylinder head, but it is sufficient for the cylinder head to have at least an operating passage.

[0064] Furthermore, the exhaust system of this embodiment is not limited to the engine of the saddle-type vehicle described above, but may be used in the engines of other vehicles. Also, the saddle-type vehicle is not limited to motorcycles, but can be any vehicle equipped with an engine. Moreover, the term "saddle-type vehicle" is not limited to all vehicles in which the driver sits straddling a seat, but also includes scooter-type vehicles in which the driver does not sit straddling a seat.

[0065] As described above, the variable valve timing device (20) is a variable valve timing device that can change the amount of valve lift in the cylinder head (10), and comprises a camshaft (21, 81) on which a plurality of cams with different valve lift amounts (low-speed cams 23, 86a, 86b, high-speed cams 24, 87a, 87b) are formed, a switching mechanism (40, changeover switch 95) that switches the cam that moves the valves (intake valves 12, 90) between the plurality of cams, and an oil control valve (60, 80) that controls the hydraulic pressure to the switching mechanism, and oil is supplied from the oil control valve to the switching mechanism at the end timing of the valve lift or in the zero section where no valve lift occurs. With this configuration, since oil is supplied from the oil control valve to the switching mechanism at the end timing of the valve lift or in the zero section, the switching operation of the cam is not hindered by the valve lift. Therefore, the generation of abnormal noise caused by malfunctions in the switching operation of the cam is suppressed, and the durability of the variable valve timing device is improved.

[0066] In a variable valve timing device, there are multiple rocker arms (31a, 31b) that contact multiple cams to move the valve. The switching mechanism includes a connecting pin (41) that connects the multiple rocker arms and a hydraulic piston (52) that moves the connecting pin. The connecting pin switches the connection state of the multiple rocker arms, thereby switching the cams. A portion of the oil passage (operating passage 75) from the oil control valve to the switching mechanism is formed by an oil groove (26) on the camshaft. The oil groove is formed so that oil is supplied from the oil control valve to the switching mechanism at the end of the valve lift or in the zero section where no valve lift occurs. With this configuration, because an oil groove is formed on the camshaft, oil is intermittently supplied from the oil control valve to the switching mechanism through the oil passage as the camshaft rotates. Since oil is supplied from the oil control valve to the switching mechanism at the end of the valve lift or in the zero section, the multiple rocker arms are properly connected by the connecting pin without the connection operation of the multiple rocker arms being hindered by the valve lift. Therefore, the connection between multiple rocker arms is not released during the valve lift, thus suppressing the generation of abnormal noises.

[0067] In a variable valve timing device, another oil passage (shortcut passage 78) extends directly from the oil control valve to the switching mechanism. After oil is supplied to the hydraulic piston from the oil passage, oil is supplied to the hydraulic piston from the other oil passage. With this configuration, there is a risk that the hydraulic piston may move if only intermittent oil is supplied from the oil passage, but the direct supply of oil from the other oil passage allows the hydraulic piston to be held in place.

[0068] In a variable valve timing device, other oil passages are formed to be shorter than the other oil passages. With this configuration, oil can be smoothly supplied from the other oil passages to the hydraulic piston, and the hydraulic piston can be held stably.

[0069] In a variable valve timing device, the direction of oil supply from the oil passage to the hydraulic piston is aligned with the direction of the hydraulic piston's advance, and the direction of oil supply from another oil passage to the hydraulic piston is aligned with the radial direction of the hydraulic piston. When the hydraulic piston is in the retracted position, the downstream end of the other oil passage is blocked by the outer surface of the hydraulic piston, and when the hydraulic piston moves in the advance direction, the downstream end of the other oil passage is opened. With this configuration, since the direction of oil supply from the oil passage is aligned with the direction of the hydraulic piston's advance, the hydraulic piston can be moved smoothly in the advance direction. In addition, since the downstream end of the other oil passage is opened and closed by the hydraulic piston, the number of parts can be reduced and the variable valve timing device can be made compact.

[0070] In a variable valve timing device, the camshaft includes a shift cam (83) with multiple cams formed thereon, and a shaft body (82) on which the shift cam is mounted so as to be slidable and integrally rotatable. The shift cam has multiple switching grooves (88a, 88b) formed thereon that allow the shift cam to slide relative to the shaft body. The switching mechanism is provided with multiple switching pins (96a, 96b) that enter the multiple switching grooves by hydraulic pressure. The shift cam slides as the multiple switching pins selectively enter the multiple switching grooves, thereby switching the cams. A portion of the oil passage (91a, 91b) from the oil control valve to the switching mechanism is formed by the oil groove (89) of the shift cam, and oil is supplied from the oil control valve to the switching mechanism at the end of the valve lift timing or in the zero section where no valve lift occurs. With this configuration, because the shift cam has oil grooves, oil is intermittently supplied from the oil control valve to the switching mechanism through the oil passage as the shift cam rotates. Because oil is supplied from the oil control valve to the switching mechanism at the end of the valve lift or in the zero-pressure section, the cam cannot be switched midway through the valve lift, thus suppressing the generation of abnormal noise.

[0071] In a variable valve timing device, an oil groove is formed such that the supply of oil to the switching mechanism via the oil passage is completed before the start of valve lift. With this configuration, the cam switching operation is completed before the start of valve lift, so the cam is not switched during valve lift.

[0072] In a variable valve timing device, an oil groove is formed such that the supply of oil to the switching mechanism via the oil passage is completed between the end of one valve lift and the start of the next. This configuration ensures a longer oil supply time to the switching mechanism through the oil passage, thereby stabilizing the cam switching operation by the switching mechanism.

[0073] Although this embodiment has been described, other embodiments may include combinations of the above embodiment and its modifications, either entirely or partially.

[0074] Furthermore, the technology of the present invention is not limited to the embodiments described above, and may be modified, substituted, or transformed in various ways without departing from the spirit of the technical idea. Moreover, if the technical idea can be realized in a different way by advances in the technology or by other derived technologies, it may be implemented by that method. Accordingly, the claims cover all embodiments that may fall within the scope of the technical idea. [Explanation of symbols]

[0075] 10: Cylinder head 12, 90: Intake valve (valve) 20, 99: Variable valve timing devices 21, 81: Camshaft 23, 86a, 86b: Low-speed cam (cam) 24, 87a, 87b: High-speed cam (cam) 26, 89: Oil groove 31a: Rocker arm 31b: Rocker arm 40: Switching mechanism 41: Connecting pin 52: Hydraulic piston 60, 80: Oil control valve 75: Operating passage (oil passage) 78: Shortcut passage (other oil passage) 82: Shaft body 83: Shift Cam 88a, 88b: Switching groove 91a, 91b: Oil passages 95: Changeover switch (changeover mechanism) 96a, 96b: Switching pins

Claims

1. A variable valve timing device in a cylinder head that can change the valve lift amount, A camshaft having multiple cams with different valve lift amounts, A switching mechanism for switching the cam that moves the valve between the plurality of cams, An oil control valve that controls the hydraulic pressure for the switching mechanism, The system comprises a plurality of rocker arms that contact the plurality of cams to move the valve, The switching mechanism includes a connecting pin that connects the plurality of rocker arms, and a hydraulic piston that moves the connecting pin. The cam is switched by switching the connection state of the multiple rocker arms using the connecting pin. A portion of the oil passage from the oil control valve to the switching mechanism is formed by the oil groove of the camshaft. A variable valve timing device characterized in that the oil groove is formed such that oil begins to be supplied from the oil control valve to the switching mechanism at the end of the valve lift timing or in the zero section where no valve lift occurs.

2. Another oil passage extends directly from the oil control valve to the switching mechanism. The variable valve timing device according to claim 1, characterized in that oil is supplied to the hydraulic piston from the other oil passage after oil is supplied to the hydraulic piston from the oil passage.

3. The variable valve timing device according to claim 2, characterized in that the other oil passage is formed to be shorter than the oil passage.

4. The direction in which oil is supplied from the oil passage to the hydraulic piston is oriented in the direction in which the hydraulic piston advances. The direction in which oil is supplied from the other oil passage to the hydraulic piston is directed in the radial direction of the hydraulic piston. The variable valve timing device according to claim 2 or 3, characterized in that when the hydraulic piston is in the retracted position, the downstream end of the other oil passage is blocked by the outer circumferential surface of the hydraulic piston, and the hydraulic piston moves in the advance direction to open the downstream end of the other oil passage.

5. A variable valve timing device in a cylinder head that can change the valve lift amount, A camshaft having multiple cams with different valve lift amounts, A switching mechanism for switching the cam that moves the valve between the plurality of cams, The system includes an oil control valve that controls the hydraulic pressure to the switching mechanism, The camshaft comprises a shift cam on which the plurality of cams are formed, and a shaft body on which the shift cam is installed so as to be slidable and integrally rotatable. The shift cam has a plurality of switching grooves formed therein that allow the shift cam to slide relative to the shaft body, and the switching mechanism is provided with a plurality of switching pins that enter the plurality of switching grooves by hydraulic pressure. The shift cam slides as the multiple switching pins selectively engage with the multiple switching grooves, thereby switching the cam. A portion of the oil passage from the oil control valve to the switching mechanism is formed by the oil groove of the shift cam. A variable valve timing device characterized in that the oil groove is formed such that oil begins to be supplied from the oil control valve to the switching mechanism at the end of the valve lift timing or in the zero section where no valve lift occurs.

6. The variable valve timing device according to claim 1 or 5, characterized in that the oil groove is formed such that the supply of oil to the switching mechanism via the oil passage is completed before the start of valve lift.

7. The variable valve timing device according to claim 1 or 5, characterized in that the oil groove is formed such that the supply of oil to the switching mechanism through the oil passage is completed between the end of one valve lift and the start of the next valve lift.

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