JP2017020451A - Cam structure of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cam structure of an engine that can suppress noise due to transfer of a cam.SOLUTION: The present invention relates to a structure of a cam which lifts a valve of an engine, the structure having: a base circle where a lift amount of the valve becomes 0; a first cam profile which determines lift characteristics of the valve; a ramp part connecting the base circle and the first cam profile; a second cam profile of lift characteristics different from the first cam profile; and a bent part where a lift speed of the valve change as the first cam profile and second cam profile cross each other to be bent. A quantity of variation in lift speed of the bent part is set to be equal to or less than a quantity of variation in lift speed of the ramp part.SELECTED DRAWING: Figure 3

Description

  The present disclosure relates to an engine cam structure.

Patent Document 1 discloses a cam with a roller having a base cam having a base circle part and a valve lift part, and a roller attached to the tip part of the valve lift part for valve lift. Such a cam with a roller generates a positive first valve acceleration peak at the rising edge of the valve lift, and generates a positive second valve acceleration peak at the falling edge of the valve lift. The valve acceleration characteristic is such that the valve acceleration is negative between the first valve acceleration peak and the second valve acceleration peak.
Such a cam with a roller is generated when the driven portion of the valve mechanism moves from the valve lift portion of the base cam to the roller body of the roller between the first valve acceleration peak and the second valve acceleration peak. Occurs when the driven portion of the valve mechanism moves from the roller body of the roller to the valve lift portion between the positive third valve acceleration peak, the first valve acceleration peak, and the second valve acceleration peak. The diameter and the mounting position of the roller body of the roller are set so that the positive fourth valve acceleration peak is smaller than the first valve acceleration peak and the second valve acceleration peak.
The cam with a roller disclosed in Patent Document 1 can suppress a third valve acceleration peak that occurs when the driven portion of the valve mechanism moves from the valve lift portion of the base cam to the roller body. Further, since the valve jump becomes small, a stable valve lift characteristic can be maintained.

Japanese Patent No. 5287648

  By the way, in a valve lift device for an engine that employs a cam with a roller, when the driven part (valve) of the valve mechanism moves from the valve lift part of the base cam to the roller body, the driven part (valve) of the valve mechanism suddenly moves. Noise will increase when a significant speed change occurs.

  In view of the above circumstances, an object of at least one embodiment of the present invention is to provide an engine cam structure that can suppress noise due to cam transfer.

  (1) An engine cam structure according to at least one embodiment of the present invention is a cam structure that lifts a valve of an engine, and has a base circle in which the lift amount of the valve is 0, and lift characteristics of the valve. A first cam profile to be determined; a ramp portion connecting the base circle and the first cam profile; a second cam profile having a lift characteristic different from the first cam profile; and the first cam profile And a bent portion where the lift speed of the valve changes when the second cam profile intersects, and the amount of change in the lift speed of the bent portion is less than the amount of change in the lift speed of the ramp portion Set to

  According to the configuration of (1) above, since the amount of change in the lift speed at the bent portion is set to be equal to or less than the amount of change in the lift speed of the ramp portion, it is possible to suppress a rapid change in the valve speed, and to change the cam. Noise due to can be suppressed.

(2) In some embodiments, in the configuration of the above (1), the cam is a roller cam provided with a rotating roller at a tip portion of the cam, and the roller cam includes the base circle and the first cam. It is comprised by the cam peak part which consists of a profile, and the roller part which consists of said 2nd cam profile.
According to the configuration of (2) above, it is possible to suppress a rapid speed change of the valve between the cam crest and the roller, and to suppress noise due to the cam transfer between the cam crest and the roller. can do.

(3) In some embodiments, in the configuration of the above (1) or (2), the bent portion is in a range of 30 degrees to 60 degrees on the open side or the closed side on the basis of the maximum displacement point of the valve. Is set.
According to the configuration of (3) above, the cam transfer is set in the range of 30 to 60 degrees on the open side or the close side with reference to the maximum displacement point of the valve. Therefore, the amount of change in the lift speed at the bent portion can be set relatively easily below the amount of change in the lift speed of the ramp portion.

(4) In some embodiments, in any one of the configurations (1) to (3), the speed of the ramp portion is a speed of a constant velocity section in the ramp portion.
According to the configuration of (4) above, since the speed of the ramp part is the speed of the constant speed section in the ramp part, the amount of change in the bent part due to the transfer of the cam can be clearly set.

  According to at least one embodiment of the present invention, a rapid change in the speed of the valve can be suppressed, and noise due to the transfer of the cam can be suppressed.

It is a mimetic diagram showing simply the composition of the valve lift device to which the roller cam of the engine concerning one embodiment of the present invention is applied. It is a perspective view which shows the external appearance of the roller cam of the engine which concerns on one Embodiment of this invention. It is a figure which shows the lift amount and speed of the valve | bulb driven by the roller cam of the engine shown in FIG. It is a figure which shows the detail of the A section shown in FIG. It is a figure which shows the detail of the B section shown in FIG. It is a figure which shows the detail of the C section shown in FIG. It is a mimetic diagram showing simply the composition of the valve lift device to which the cam of the engine concerning one embodiment of the present invention is applied. It is a schematic diagram which shows the state before a T lever and a rocker arm are united. It is a schematic diagram which shows the state after T lever and the rocker arm were united. It is a figure which shows the lift amount and speed of the valve | bulb driven by the cam of the engine shown in FIG.

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. Absent.
For example, expressions expressing relative or absolute arrangements such as “in a certain direction”, “along a certain direction”, “parallel”, “orthogonal”, “center”, “concentric” or “coaxial” are strictly In addition to such an arrangement, it is also possible to represent a state of relative displacement with an angle or a distance such that tolerance or the same function can be obtained.
In addition, for example, expressions representing shapes such as quadrangular shapes and cylindrical shapes not only represent shapes such as quadrangular shapes and cylindrical shapes in a strict geometric sense, but also within the range where the same effect can be obtained. A shape including a chamfered portion or the like is also expressed.
On the other hand, the expressions “comprising”, “comprising”, “comprising”, “including”, or “having” one constituent element are not exclusive expressions for excluding the existence of the other constituent elements.

(Embodiment 1)
FIG. 1 is a schematic diagram simply showing an engine valve lift device 2 to which a roller cam (cam structure) 3 for driving an engine valve according to an embodiment of the present invention is applied.
First, based on FIG. 1, the valve lift apparatus 2 of the engine to which the roller cam 3 which drives the valve 21 of the engine which concerns on one Embodiment of this invention is applied is demonstrated easily. Here, the valve lift device 2 referred to as a direct type or a direct drive type in which the valve 21 is directly driven by the roller cam 3 that drives the valve 21 will be described as an example, but the present invention is not limited to this.

  The valve lift device 2 for the engine is provided on the intake side and the exhaust side of the engine. The valve lift device 2 on the intake side and the valve lift device 2 on the exhaust side are driven by an engine crankshaft (not shown), and the valves (intake valve and exhaust valve) at an appropriate timing with respect to the piston (not shown). ) 21 is opened and closed. Thereby, the air-fuel mixture is supplied to the combustion chamber 11 of the engine, and the exhaust gas is discharged from the combustion chamber 11.

In the valve lift device 2 provided on the intake side of the engine, a valve (intake valve) 21 serves to close the combustion chamber 11 while feeding the air-fuel mixture into the combustion chamber 11 and is provided on the exhaust side of the engine. In FIG. 2, a valve (exhaust valve) 21 serves to close the combustion chamber 11 while exhausting exhaust gas from the combustion chamber 11.
The valve lift device 2 provided on the intake side of the engine and the valve lift device 2 provided on the exhaust side of the engine may differ in size of the umbrella (valve head), but are substantially the same except for the opening / closing timing. It is a configuration. Thus, in the following description, the valve lift device 2 provided on the intake side of the engine and the valve lift device 2 provided on the exhaust side of the engine will be described without distinction.

  As shown in FIG. 1, the valve lift device 2 of the engine includes a valve 21, a valve seat 22, a tappet 23, a valve spring 24, and a roller cam 3 that drives the valve 21.

  The valve 21 serves to open and close the combustion chamber 11 as described above, and a mushroom-type poppet valve is usually employed. The poppet valve includes a shaft portion and a circular umbrella portion provided at one end of the shaft portion. The shaft portion is called a valve stem, and the umbrella portion is called a valve head. The other end of the valve stem (the other end of the shaft portion) is referred to as a valve stem end. A groove or hole for attaching a valve cotter (not shown) is provided on the valve stem end side (the other end side of the shaft portion) of the valve stem.

  As shown in FIG. 1, a valve (valve stem) 21 is inserted through a valve stem guide 25 and attached to a combustion chamber (cylinder head) 11. The valve stem guide 25 is used for causing the valve 21 to perform an accurate linear motion, and a thick cylindrical member made of cast iron is usually attached to the cylinder head.

  The valve seat 22 is in close contact with the valve 21 to prevent compression leakage of the combustion chamber 11. When the cylinder head is made of cast iron, the valve seat 22 is provided directly on the cylinder head, and when the cylinder head is made of an aluminum alloy or the like. Only the valve seat 22 is made of cast iron or heat-resistant steel and is fitted into the cylinder head.

  The tappet 23 plays the role of opening and closing the valve 21 by converting the rotational motion of the roller cam 3 that drives the valve 21 into a linear motion, and is also referred to as a valve lifter. The tappet 23 is formed in a cylindrical shape with a bottom, and the contact surface with the roller cam 3 that drives the valve 21 made of special cast iron is subjected to surface hardening. Further, the center of the roller cam 3 and the tappet 23 that drive the valve 21 is offset, and the tappet 23 is rotated by the movement of the roller cam 3 that drives the valve 21 so as to prevent uneven wear of the contact surface.

  The valve spring 24 is for reliably opening and closing the valve 21 and is interposed between the tappet 23 and a valve spring seat 26 provided on the cylinder head side. The valve spring 24 is composed of one or two coil springs.

  The roller cam 3 that drives the valve 21 is for opening and closing the valve 21, and is fixed to the camshaft 27, and the valve 21 is opened and closed by reciprocating the tappet 23. The camshaft 27 is driven by a sprocket, a chain, or a gear fixed to an engine crankshaft (not shown).

  Next, the roller cam 3 that drives the valve 21 of the engine according to the embodiment of the present invention will be described in detail with reference to FIGS. FIG. 2 is a perspective view showing the external appearance of the roller cam 3 that drives the valve 21 of the engine according to one embodiment of the present invention. FIG. 3 is driven by the roller cam 3 that drives the valve 21 of the engine shown in FIG. It is a figure which shows the lift amount (lift curve) and speed (speed curve) of the valve | bulb 21 to be performed. 4 is a diagram showing details of the A portion shown in FIG. 3, and FIG. 5 is a diagram showing details of the B portion shown in FIG. FIG. 6 is a diagram showing details of the C section shown in FIG.

  The roller cam 3 for driving the valve 21 of the engine according to one embodiment of the present invention opens and closes the intake valve or the exhaust valve of the engine, and is composed of a plurality of cams as shown in FIG. In the roller cam 3 that drives the valve 21 according to the embodiment of the present invention, the plurality of cams include a cam 31 that constitutes the cam body, and a roller 32 that is provided at the tip of the cam 31 (lift portion 31b). Configured.

The cam 31 is a ramp that connects the base circle part 31a in which the displacement of the valve 21 is 0 (zero), the lift part (cam peak part) 31b that determines the displacement of the valve 21, and the base circle part 31a and the lift part 31b. Part 31c. The outer peripheral surfaces of the base circle portion 31a, the lift portion 31b, and the ramp portion 31c constituting the cam 31 constitute a cam surface that is continuous in the order of the base circle portion 31a, the ramp portion 31c, and the lift portion 31b.
Further, a recess 31 e for accommodating the roller 32 is provided at the tip end portion (cam top portion 31 d) of the lift portion (cam peak portion) 31 b of the cam 31. The recess 31 e is provided at the center of the cam 31 in the width direction with a width of one third of the width of the cam 31.
Further, a shaft hole 31 f that penetrates in the width direction of the cam 31 is provided at the tip end portion (cam top portion 31 d) of the lift portion 31 b of the cam 31. The shaft hole 31f is for supporting the shaft 33 that supports the roller 32 accommodated in the recess 31e, and the shaft 33 for supporting the roller 32 is fitted into the shaft hole 31f.
As long as the cam 31 is fixed to the camshaft 27, the cam 31 may be provided integrally with the camshaft 27 or may be provided separately. Moreover, although the cam 31 mentioned above is provided integrally, it is good also as what comprises combining several components.

  The roller 32 is for reducing friction (friction resistance) generated between the roller 32 and the tappet 23. The roller 32 is accommodated in a recess 31e provided at the tip end portion (cam top portion 31d) of the lift portion 31b of the cam 31 so that a part of the outer peripheral surface of the roller 32 protrudes from the lift portion 31b. The shaft 33 is supported rotatably. Thereby, the outer peripheral surface of the roller 32 forms a cam surface. The tappet 23 driven by the roller cam 3 that drives the valve 21 is brought into sliding contact with the cam surfaces of the base circle portion 31a, the ramp portion 31c, and the lift portion 31b of the cam 31, and the cam surface of the cam 31 at the lift portion 31b. From the cam surface of the roller 32 to the cam surface of the cam 31 in the lift portion 31b.

  An oil supply hole 27a is provided in the axial direction at the center of the camshaft 27. An oil supply hole (not shown) communicating with the oil supply hole 27a is provided in the roller cam 3 (cam 31) for driving the valve 21 in the radial direction. Is provided. Thereby, the lubricating oil supplied to the oil supply hole 27 a provided in the cam shaft 27 passes through the oil supply hole provided in the cam 31 and is supplied to the roller 32.

Incidentally, as shown in FIG. 3, the lift curve DL indicating the lift amount (displacement amount) of the valve 21 driven by the roller cam 3 that drives the valve 21 with a solid bold line and a two-dot chain thick line represents the valve 21. This corresponds to the cam profile that determines the lift characteristics of the roller cam 3 to be driven. Thereby, the lift curve DL is composed of a base circle region P corresponding to the base circle portion 31a, a lift region Q corresponding to the lift portion (cam peak portion) 31b, and a ramp region R corresponding to the ramp portion 31c. .
Then, with reference to the maximum displacement point T of the valve 21, the opening side (open side) displacement and the closing side (closed side) displacement of the valve 21 are shown in one lift curve DL. The lift amount of the valve 21 by the ramp portion 31 c of 31, the lift amount of the valve 21 by the lift portion 31 b of the cam 31, and the displacement amount of the valve 21 by the roller 32 are shown in the lift curve DL.

Further, as shown in FIG. 3, a speed curve VL, which shows a lift speed of the valve 21 driven by the roller cam 3 that drives the valve 21 with a solid line, is obtained by differentiating the lift curve DL with respect to time. Similar to the lift curve DL, the speed curve VL corresponds to a cam profile that determines the speed characteristics of the roller cam 3 that drives the valve 21. The speed curve VL shows the lift speed of the valve 21 by the ramp portion 31c of the cam 31, the lift speed of the valve 21 by the lift portion 31b of the cam 31, and the lift speed of the valve 21 by the roller 32.
The lift speed of the valve 21 by the ramp portion 31c of the cam 31 is set so that the impact of the collision generated by the valve clearance (the gap between the tappet 23 and the roller cam 3 (cam 31) that drives the valve 21) is reduced. The Further, as shown in FIG. 6, the ramp portion 31c of the cam 31 is composed of a constant acceleration section S1, a constant speed section S2, and a constant acceleration section S3.

As shown in FIG. 3, the lift curve DL of the roller cam 3 that drives the valve 21 according to the embodiment of the present invention described above is a lift curve (first cam profile) DL1 that shows the lift amount by the cam 31 with a solid line. The lift curve (second cam profile) DL2 indicating the lift amount by the roller 32 by a two-dot chain line is synthesized, and the lift curve DL1 by the cam 31 and the lift curve DL2 by the roller 32 intersect as shown in FIG. Has a bent portion Z.
Therefore, the cam profile of the roller cam 3 is composed of the first cam profile that determines the lift characteristic by the cam 31 and the second cam profile that determines the lift characteristic by the roller 32, and the first cam profile and the second cam profile are combined. When the cam profile intersects, it bends and the lift speed of the valve 61 changes.

  As shown in FIG. 3, the roller cam 3 for driving the valve 21 according to the embodiment of the present invention is from the cam 31 to the roller 32 in the range of 30 to 60 degrees on the open side with reference to the maximum displacement point of the valve 21. And a bent portion Z due to the transfer from the roller 32 to the cam 31 in the range of 30 to 60 degrees on the close side.

  In addition, the speed curve VL of the roller cam 3 that drives the valve 21 according to the embodiment of the present invention is similar to the lift curve DL, the speed curve VL1 indicating the lift speed by the cam 31, and the speed curve indicating the lift speed by the roller 32. VL2 and VL2 are combined, and as shown in FIG. 5, there is a speed change amount (speed difference) Vb at the intersection of the lift curves DL.

  As shown in FIGS. 5 and 6, the roller cam 3 that drives the valve 21 according to the embodiment of the present invention uses the change amount Vb of the speed at the intersection of the lift curves DL as the lift speed (ramp speed) in the ramp region R. The change amount Vc is set to be equal to or less than the speed of the constant speed section S2, for example. The speed change amount Vb at the intersection of the lift curves DL is set to be equal to or less than the lift speed change amount Vc in the ramp portion 31c because of the speed change amount (collision between the roller cam 3 driving the valve 21 and the tappet 23). Is made smaller than the impact of the collision due to the valve clearance (collision between the roller cam 3 (the lamp portion 31c) driving the bulb 21 and the tappet 23). Thereby, the hitting sound of the collision due to the speed change amount Vb can be made smaller than the hitting sound of the collision due to the valve clearance.

  According to the roller cam (cam structure) 3 that drives the valve 21 of the engine according to the embodiment of the present invention, the lift speed change amount Vb in the bent portion Z is set to be equal to or less than the lift speed change amount Vc in the ramp portion 31c. Therefore, a rapid speed change of the valve 21 can be suppressed, and noise (sounding sound) due to the transfer of the cam can be suppressed.

  Further, according to the roller cam 3 for driving the valve 21 of the engine according to the embodiment of the present invention, the valve between the lift part (cam peak part) 31b of the cam 31 and the outer peripheral surface (roller part) of the roller 32 is provided. An abrupt speed change can be suppressed, and noise (sounding sound) due to the transfer of the cam between the lift portion 31b of the cam 31 and the outer peripheral surface of the roller 32 can be suppressed.

  In addition, according to the roller cam 3 that drives the valve 21 of the engine according to the embodiment of the present invention, the cam transfer is 30 degrees on the open side or the close side with reference to the maximum displacement point T of the valve 21 (the tappet 23). Therefore, the lift speed change amount Vb at the bent portion Z can be set relatively easily below the lift speed change amount Vc of the ramp portion 31c.

  Further, according to the roller cam 3 that drives the valve 21 of the engine according to the embodiment of the present invention, the speed of the ramp part 31c is the speed of the constant speed section S2 in the ramp part 31c, and therefore the bent part due to the transfer of the cam. The amount of change in Z can be clearly set.

(Embodiment 2)
FIG. 7 is a schematic diagram simply showing a configuration of a valve lift device 6 to which a cam (cam structure) 7 for driving a valve 61 of an engine according to another embodiment of the present invention is applied. 8 is a schematic diagram (cross-sectional view) showing a state before the T lever 62 and the rocker arm 63 are combined, and FIG. 9 shows a state after the T lever 62 and the rocker arm 63 are combined. It is a schematic diagram (cross-sectional view) shown. FIG. 10 is a diagram showing the lift amount (lift curve) and speed (speed curve) of the valve driven by the cam 7 that drives the valve 61 of the engine shown in FIG.

  The engine valve lift device 6 to which the cam 7 for driving the engine valve 61 according to another embodiment of the present invention is applied will be described with reference to FIGS. Here, the valve lift device 6 that opens and closes the two valves 61 and 61 simultaneously will be described as an example, but the present invention is not limited to this. In the description, the description of the configuration common to the above-described embodiment (Embodiment 1) of the present invention will be omitted.

  An engine valve lift device 6 according to another embodiment (Embodiment 2) of the present invention varies the opening / closing timing and opening / closing strokes of the valves 61, 61. As shown in FIG. , A T lever 62, a rocker arm 63, and a cam 7 (low speed cam 71, high speed cam 72) for driving the valve 61.

The T lever 62 opens and closes the two valves 61 and 61 simultaneously by directly driving the two valves 61 and 61, and is formed in a T-shape in a plan view as shown in FIG. Is provided with a control shaft 62a (rocker shaft). The T lever 62 is provided with a cam follower 64 at the center thereof. The cam follower 64 provided on the T lever 62 is rotatably supported on a shaft provided in parallel with the control shaft 62a.
As shown in FIGS. 8 and 9, a hydraulic piston 65 is provided inside the T lever 62. The hydraulic piston 65 illustrated in FIGS. 8 and 9 is provided so as to be able to advance and retract in the radial direction of the control shaft 62a. The hydraulic piston 65 is housed in the control shaft by the spring 66 before the hydraulic pressure is supplied, and the spring 66 is elastically restored after the hydraulic pressure is supplied. It is provided so as to protrude from the control shaft 62a against the force.

  As shown in FIG. 7, the rocker arm 63 is rotatably supported by a control shaft 62 a provided on the T lever 62. The rocker arm 63 is provided with a cam follower 67 at its tip. The cam follower 67 provided on the rocker arm 63 is rotatably supported on a shaft (not shown) provided in parallel with the control shaft 62a, similarly to the cam follower 67 provided on the T lever 62. Further, the rocker arm 63 has a fitting hole 63 a into which a hydraulic piston 65 provided inside the T lever 62 is fitted. Thereby, the rocker arm 63 does not directly drive the valves 61, 61, but the hydraulic piston 65 built in the T lever 62 is fitted into the fitting hole 63 a provided in the rocker arm 63. The rocker arm 63 is combined with the T lever 62 to drive (indirect drive) the valves 61 and 61.

  The cam 7 that drives the valve 61 is for opening and closing the valves 61, 61. The cam 7 is fixed to the cam shaft 73 and presses the cam follower 64 provided on the T lever 62 and the cam follower 67 provided on the rocker arm 63. As a result, the valves 61 and 61 are opened and closed. The camshaft 73 is driven by a sprocket and chain or gear fixed to the crankshaft of the engine.

As shown in FIG. 7, the cam 7 that drives the valve 61 of the engine according to the embodiment of the present invention includes a low-speed cam 71 and a high-speed cam 72 that is provided coaxially with the low-speed cam 71. Has been.
Each of the low-speed cam 71 and the high-speed cam 72 includes a base circle portion, a lift portion, and a ramp portion, and each has a cam profile suitable for the operating state of the engine. For example, when the engine is operated at high speed, a longer valve opening time or a larger valve lift amount is required than when the engine is operated at low speed. The cam stroke of the high-speed cam 72 is set to be longer than the cam stroke of the low-speed cam 71.

  In the valve lift device 6 described above, when the engine is operated at a low speed, as shown in FIG. 8, the hydraulic piston 65 is accommodated in the control shaft, and the rocker arm 63 is operated in a free state. Therefore, the low speed cam 71 presses the cam follower 64 provided on the T lever 62 and the high speed cam 72 presses the cam follower 67 provided on the rocker arm 63. There is no transmission. Thereby, when the engine is operated at a low speed, power is transmitted from the low speed cam 71 to the T lever 62, and the valves 61 and 61 open and close the combustion chamber with a small stroke.

  On the other hand, when the engine is operated at high speed, as shown in FIG. 9, the hydraulic piston 65 protrudes from the control shaft 62 a into the fitting hole 63 a of the rocker arm 63, and the rocker arm 63 is joined to the T lever 62. Driven. Accordingly, the low speed cam 71 presses the cam follower 64 provided on the T lever 62 and the high speed cam 72 presses the cam follower 67 provided on the rocker arm 63. In the example shown in FIG. The valve opening time of 72 is the same as the valve opening time of the low-speed cam 71, and the cam stroke of the high-speed cam 72 is larger than the cam stroke of the low-speed cam 71. To the T lever 62 through the rocker arm 63. As a result, when the engine is operated at high speed, power is transmitted from the high-speed cam 72 to the T lever 62 via the rocker arm 63, and the valves 61 and 61 open and close the combustion chamber with a large stroke.

By the way, as shown in FIG. 10, the lift curve DL of the valve 61 driven by the cam 7 that drives the valve 61 has a bent portion when shifting from low speed to high speed and when shifting from high speed to low speed.
That is, the lift curve DL indicates a lift curve (first cam profile) DL3 that shows the lift amount by the low-speed cam 71 as a two-dot chain line and a solid line that shows the lift amount by the high-speed cam 72 when shifting from low speed to high speed. The lift curve (second cam profile) DL4 is synthesized and has a bent portion at the intersection of the lift curve DL3 due to the low speed cam 71 and the lift curve DL4 due to the high speed cam. Similarly, when the lift curve DL shifts from high speed to low speed, the lift curve DL4 indicating the lift amount by the high speed cam 72 and the lift curve DL3 by the low speed cam 71 are combined, and the lift curve DL4 by the high speed cam 72 and the low speed cam 72 are low speed. The cam 71 has a bent portion at the intersection with the lift curve DL3.

Further, a derivative of this lift curve DL with respect to time becomes a speed curve VL indicating the lift speed of the valve, and has a speed change amount (speed difference) at the intersection of the lift curves DL.
Therefore, the cam profile of the cam 7 includes the first cam profile that determines the lift characteristic by the low-speed cam 71 and the lift characteristic by the high-speed cam 72 when shifting from low speed to high speed and from high speed to low speed. When the second cam profile to be determined intersects, it bends and the lift speed of the valve 61 changes.

  The cam 7 that drives the valve 61 according to the embodiment of the present invention is the amount of change in speed at the intersection of the lift curves DL (the roller cam 3 that drives the valve 61 according to the above-described embodiment (Embodiment 1)). (Speed difference) is set to the amount of change in the lift speed (ramp speed) in the ramp portion, for example, equal to or less than the speed in the uniform speed section. The amount of change in speed in the lift curve DL is set to be equal to or less than the amount of change in lift speed in the ramp portion because the impact of the collision due to the speed change (collision between the cams 71 and 72 and the cam followers 64 and 67) depends on the valve clearance. It is to make it smaller than the impact of the collision. Thereby, the hitting sound of the collision due to the amount of change in speed can be made smaller than the hitting sound of the collision due to the valve clearance.

  According to the cam 7 that drives the valve 61 of the engine according to the embodiment of the present invention, the amount of change in the lift speed at the bent portion is set to be equal to or less than the amount of change in the lift speed at the ramp portion. The speed change can be suppressed, and the noise (sounding sound) due to the transfer of the cam can be suppressed.

  In addition, according to the cam 7 that drives the valve 61 of the engine according to the embodiment of the present invention, it is possible to suppress a rapid change in the speed of the valve during the transfer of the cam between the low speed cam 71 and the high speed cam 72. Further, it is possible to suppress noise (sound hitting) due to the transfer of the cam between the low speed cam 71 and the high speed cam 72.

  The present invention is not limited to the above-described embodiments, and includes forms obtained by modifying the above-described embodiments and forms obtained by appropriately combining these forms.

DESCRIPTION OF SYMBOLS 11 Combustion chamber 2 Valve lift device 21 Valve 22 Valve seat 23 Tappet 24 Valve spring 25 Valve stem guide 26 Valve spring seat 27 Cam shaft 27a Oil supply hole 3 Roller cam 31 Cam 31a Base circle part 31b Lift part 31c Lamp part 31d Cam top part 31e Recess 31f Shaft hole 32 Roller 33 Shaft 61 Valve 62 T lever 62a Control shaft 63 Rocker arm 63a Fitting hole 64 Cam follower 65 Hydraulic piston 66 Spring 67 Cam follower 7 Cam 71 Low speed cam 72 High speed cam 73 Camshaft DL, DL1, DL2, DL3 , DL4 Lift curve P Base circle area Q Lift area R Ramp area

Claims (4)

A cam structure for lifting an engine valve,
A base circle in which the lift amount of the valve is zero;
A first cam profile that determines lift characteristics of the valve;
A ramp portion connecting the base circle and the first cam profile;
A second cam profile having a lift characteristic different from the first cam profile;
A bent portion where the first cam profile and the second cam profile intersect to bend and the valve lift speed changes;
Have
A structure of an engine cam, wherein a change amount of the lift speed of the bent portion is set to be equal to or less than a change amount of the lift speed of the ramp portion. The cam is a roller cam provided with a rotating roller at the tip of the cam;
The roller cam has the base circle,
A cam nose comprising the first cam profile;
A roller portion comprising the second cam profile;
The engine cam structure according to claim 1, comprising:   The engine cam structure according to claim 1, wherein the bent portion is set in a range of 30 degrees to 60 degrees on an open side or a closed side with reference to a maximum displacement point of the valve.   The engine cam structure according to any one of claims 1 to 3, wherein the speed of the ramp portion is a speed in a constant velocity section in the ramp portion.

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