Valve gear
The valve train design with an inclined cam surface addresses cam protrusion and wear issues by reducing contact concentration, maintaining intake air volume, and preventing friction, ensuring efficient engine operation.
Patent Information
- Application Number
- JP2024010418
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-01-26
- Publication Date
- 2025-08-07
AI Technical Summary
Conventional valve trains in internal combustion engines suffer from cam protrusion and excessive wear of the valve lifter due to the cam's pointed shape, which concentrates contact and leads to premature wear.
The valve train design includes a camshaft with an inclined cam surface that tapers as it extends, overlapping with a circular valve lifter, reducing contact concentration and preventing protrusion while maintaining cam lobe height.
This design effectively suppresses wear on the valve lifter and prevents cam protrusion, ensuring efficient operation and intake air volume without increasing friction or reducing cam lobe height, thus supporting high-speed engine rotation.
Smart Images
Figure 2025115777000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a valve train for an internal combustion engine. [Background technology]
[0002] A known example of a conventional valve train related invention is a cam device for a valve train of an internal combustion engine, as described in Patent Document 1. The cam of this valve train cam device has a shape in which the cam width becomes smaller as it approaches the nose of the cam lobe, which prevents the cam from protruding from the valve lifter. [Prior art documents] [Patent documents]
[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 63-38601 Summary of the Invention [Problem to be solved by the invention]
[0004] Incidentally, in the cam device for operating a valve of an internal combustion engine described in Patent Document 1, the cam has a pointed shape, which causes the cam to come into contact with a portion of the valve lifter in a concentrated manner, making the valve lifter prone to wear.
[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a valve train that can prevent the cam from protruding from the valve lifter while also preventing the valve lifter from wearing. [Means for solving the problem]
[0006] A first aspect of the present invention is The valve train includes a valve, a valve lifter, and a camshaft. The valve includes a valve head and a valve stem, The valve stem extends in a first direction from the valve head portion, the valve lifter has a circular shape when viewed in the first direction and overlaps with an end of the valve stem in the first direction when viewed in the first direction, the camshaft is rotatable about a central axis extending in the second direction and includes a cam; the cam has a cam surface that contacts the valve lifter, The shape of a cross section of the cam perpendicular to the second direction is defined as a cam cross-sectional shape, The cam surface is inclined with respect to the central axis, so that the cam cross-sectional shape becomes smaller as it goes in the second direction, The center of the cam surface in the second direction is located further in the second direction than the center of the valve lifter. It is a valve train.
[0007] A second aspect of the present invention is the cam surface forms an inclination angle with the central axis, The angle formed between the first direction and the second direction is 90° plus the tilt angle. 1 is a valve train according to a first aspect of the present invention; [Effects of the Invention]
[0008] According to the present invention, it is possible to suppress wear of the valve lifter while suppressing the cam from protruding from the valve lifter. [Brief explanation of the drawings]
[0009] [Figure 1] FIG. 1 is a schematic diagram of a valve train 10. [Figure 2] FIG. 2 is a view of the valve lifter 16a viewed in the opposite direction d11. [Figure 3] FIG. 3 is a view of a valve lifter 316a in a valve gear 310 according to a comparative example, viewed in the opposite direction d11. [Figure 4] FIG. 4 is a view of a valve train 310 according to a comparative example, viewed in the second direction d2. [Figure 5]FIG. 5 is a graph showing the calculation results using the first model. [Figure 6] FIG. 6 is a graph showing the calculation results using the second model. [Figure 7] FIG. 7 is a graph showing the calculation results using the third model. DETAILED DESCRIPTION OF THE INVENTION
[0010] (Embodiment) [Valve train structure]
[0011] The structure of a valve train 10 according to one embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a schematic diagram of the valve train 10. The direction in which the valve stem 122 extends from the valve head portion 121 is defined as a first direction d1. The direction in which the camshaft 20 extends is defined as a second direction d2.
[0012] The valve train 10 is used, for example, in an internal combustion engine of an automobile. The valve train 10 according to this embodiment is used in an internal combustion engine having four valves per cylinder. The four valves include two intake valves and two exhaust valves. The valve train 10 operates the two intake valves. As shown in FIG. 1 , the valve train 10 includes valves 12a, 12b, valve guides 14a, 14b, valve lifters 16a, 16b, springs 18a, 18b, a camshaft 20, and a cylinder head 22.
[0013] The camshaft 20 can rotate about a central axis Ax extending in the second direction d2. The camshaft 20 includes a shaft 201 and cams 202a and 202b. The shaft 201 is a rod-shaped member extending in the second direction d2.
[0014] The cam 202a has a cam surface Sa. The cam surface Sa is the outer peripheral surface of the cam 202a. The cam surface Sa faces in a direction perpendicular to the second direction d2. However, as will be described later, the normal to the cam surface Sa is slightly inclined with respect to the direction perpendicular to the second direction d2.
[0015] In addition, the distance from the central axis Ax to the cam surface Sa is not uniform. As a result, the cam 202a has a cam lobe 203a. The distance from the central axis Ax to the cam surface Sa at the cam lobe 203a is longer than the distance from the central axis Ax to the cam surface Sa at a portion other than the cam lobe 203a.
[0016] Here, the shape of a cross section of the cam 202a perpendicular to the second direction d2 is defined as the cam cross-sectional shape Xa. Because the cam surface Sa is inclined with respect to the central axis Ax, the cam cross-sectional shape Xa becomes smaller as it moves in the second direction d2. The cam surface Sa forms an inclination angle θ with the central axis Ax. Specifically, the area of the cam cross-sectional shape Xa becomes smaller as it moves in the second direction d2. As a result, the distance from the central axis Ax to the cam surface Sa becomes shorter as it moves in the second direction d2. Therefore, the cam 202a has a tapered shape when viewed in a direction perpendicular to the second direction d2. Furthermore, the cam surface Sa has a linear shape when viewed in a direction perpendicular to the second direction d2.
[0017] The valve 12a includes a valve head portion 121 and a valve stem 122. The valve stem 122 is a rod-shaped member. The valve stem 122 extends from the valve head portion 121 in a first direction d1. The angle formed between the first direction d1 and the second direction d2 is 90° plus the inclination angle θ.
[0018] The valve head portion 121 has a circular shape when viewed in the first direction d1. The valve head portion 121 opens and closes an intake port of an internal combustion engine by reciprocating in the first direction d1 and a direction d11 opposite to the first direction d1.
[0019] The valve guide 14a has a cylindrical shape with a central axis extending in a first direction d1. The valve stem 122 passes through the valve guide 14a. This allows the valve 12a to be supported by the valve guide 14a. The valve 12a can reciprocate relative to the valve guide 14a in the first direction d1 and the opposite direction d11. The valve guide 14a is supported by the cylinder head 22.
[0020] The valve lifter 16a has a cylindrical shape with a central axis extending in the first direction d1. However, the end of the valve lifter 16a facing the first direction d1 is closed, and the end facing the opposite direction d11 is open. As a result, the valve lifter 16a has a circular shape when viewed in the first direction d1. Hereinafter, the end of the valve lifter 16a facing the first direction d1 will be referred to as a circular portion 161a. The main surface of the circular portion 161a facing the first direction d1 will be referred to as a first main surface S1. The main surface of the circular portion 161a facing the opposite direction d11 to the first direction d1 will be referred to as a second main surface S2. The first main surface S1 of the valve lifter 16a is located in the opposite direction d11 of the cam 202a. The cam surface Sa of the cam 202a is in contact with the first main surface S1 of the valve lifter 16a.
[0021] The valve lifter 16a covers the end portion in the first direction d1 of the valve stem 122. As a result, the circular portion 161a of the valve lifter 16a overlaps the end portion in the first direction d1 of the valve stem 122 when viewed in the first direction d1. The circular portion 161a of the valve lifter 16a is fixed to the end portion in the first direction d1 of the valve stem 122.
[0022] The valve lifter 16a is provided in a hole Ha provided in the cylinder head 22. The hole Ha has a cylindrical shape with a central axis extending in a first direction d1. The valve lifter 16a can reciprocate within the hole Ha in the first direction d1 and the opposite direction d11 relative to the cylinder head 22. Therefore, the valve 12a can also reciprocate in the first direction d1 and the opposite direction d11 relative to the cylinder head 22.
[0023] The spring 18a has a spiral shape with a central axis extending in the first direction d1. Both ends of the spring 18a are in contact with the second main surface S2 of the circular portion 161a and the first surface S11 of the cylinder head 22, respectively. The valve stem 122 passes through the spring 18a. The spring 18a pushes the valve lifter 16a in the first direction d1. As a result, the valve 12a receives a force from the spring 18a in the first direction d1 because the valve stem 122 is fixed to the valve lifter 16a.
[0024] In the valve train 10 described above, one rotation of the camshaft 20 generates a first period during which the cam surface Sa of the cam lobe 203a contacts the valve lifter 16a, and a second period during which the cam surface Sa of a portion other than the cam lobe 203a contacts the valve lifter 16a. During the first period, the cam 202a pushes the valve lifter 16a in the opposite direction d11. As a result, the valve 12a is moved in the opposite direction d11 by the cam 202a. This opens the intake port. On the other hand, during the second period, the cam 202a does not push the valve lifter 16a in the opposite direction d11. As a result, the valve 12a is moved in the first direction d1 by the spring 18a. This closes the intake port.
[0025] The positional relationship between the cam 202a and the valve lifter 16a will now be described with reference to Figure 2. Figure 2 is a view of the valve lifter 16a viewed in the opposite direction d11. In Figure 2, contact area Aa is the area where the cam 202a contacts the valve lifter 16a. The center C0 of the cam surface Sa in the second direction d2 is located further in the second direction d2 than the center C1 of the valve lifter 16a.
[0026] Note that the valve 12b, valve guide 14b, valve lifter 16b, spring 18b, and cam 202b have structures symmetrical to those of the valve 12a, valve guide 14a, valve lifter 16a, spring 18a, and cam 202a in FIG. 1, and therefore a description thereof will be omitted. However, for the valve 12b, valve guide 14b, valve lifter 16b, spring 18b, and cam 202b, a first direction d1', a second direction d2', and an opposite direction d11' are used instead of the first direction d1, the second direction d2, and the opposite direction d11. The first direction d1', the second direction d2', and the opposite direction d11' are symmetrical to the first direction d1, the second direction d2, and the opposite direction d11 in FIG. 1. Therefore, the second direction d2' is the opposite direction of the second direction d2.
[0027] [effect] According to the valve train 10 described above, it is possible to prevent the cam 202a from protruding from the valve lifter 16a while also preventing wear on the valve lifter 16a. Fig. 3 is a view of the valve lifter 316a in a valve train 310 according to a comparative example, viewed in the opposite direction d11. Fig. 4 is a view of the valve train 310 according to the comparative example, viewed in the second direction d2. For ease of explanation, the left-right direction in Fig. 3 will be simply referred to as the left-right direction, and the up-down direction in Fig. 3 will be simply referred to as the up-down direction.
[0028] As shown in FIG. 3, in the valve gear 310, the inclination angle θ is 0°. Therefore, the cam surface Sa is not inclined with respect to the central axis Ax. However, the center C0 of the cam surface Sa in the second direction d2 is located further in the second direction d2 (to the right) than the center C1 of the valve lifter 316a. As a result, the area over which the contact area Ba overlaps with the right half of the valve lifter 316a is larger than the area over which the contact area Ba overlaps with the left half of the valve lifter 316a. The contact area Ba applies a force to the right half of the valve lifter 316a that rotates the valve lifter 316a clockwise, and also applies a force to the left half of the valve lifter 316a that rotates the valve lifter 316a counterclockwise. In this case, the force that rotates the valve lifter 316a clockwise is greater than the force that rotates the valve lifter 316a counterclockwise. As a result, the valve lifter 316a rotates clockwise. As a result, the cam 402a is prevented from contacting a portion of the valve lifter 316a in a concentrated manner, thereby suppressing wear on the valve lifter 316a.
[0029] However, when the center C0 of the cam surface Sa in the second direction d2 is located further in the second direction d2 (to the right) than the center C1 of the valve lifter 316a, the upper right corner of the contact area Ba significantly protrudes upward from the valve lifter 316a. Hereinafter, the length by which the upper right corner of the contact area Ba protrudes upward from the valve lifter 316a is defined as the protrusion amount D1. The distance between the center C0 and the center C1 is defined as the offset amount D2. As the offset amount D2 increases, the protrusion amount D1 also increases. In other words, when wear of the valve lifter 316a is suppressed, the protrusion amount D1 is likely to increase.
[0030] However, the design of the valve train 310 requires that the protrusion amount D1 be smaller than a predetermined value. Therefore, in order to reduce wear on the valve lifter 316a and reduce the protrusion amount D1 to be smaller than the predetermined value, the cam lobe of the cam 402a must be lowered. In other words, the maximum contact length D3 in FIG. 4 becomes shorter. As shown in FIG. 3, the maximum contact length D3 corresponds to half the vertical length of the contact area Ba.
[0031] Incidentally, there is a demand for increasing the amount of intake air into the internal combustion engine in the valve train 310. One way to achieve this is to make the cam lobe of the cam 402a higher. This increases the valve lift of the valve train 310, thereby increasing the amount of intake air into the internal combustion engine. However, this increases the protrusion amount D1. Therefore, if the amount of intake air into the internal combustion engine is increased, it becomes difficult to reduce wear on the valve lifter 316a and reduce the protrusion amount D1 below a predetermined value.
[0032] 3, if the center C0 of the cam surface Sa in the second direction d2 is located further in the second direction d2 (to the right) than the center C1 of the valve lifter 316a, the upper right and lower right corners of the contact area Ba will significantly protrude upward from the valve lifter 316a. In other words, if the upper right and lower right corners of the contact area Ba are prevented from significantly protruding upward from the valve lifter 316a, the protrusion amount D1 can be reduced.
[0033] Therefore, in the valve train 10, the cam surface Sa is inclined with respect to the central axis Ax, so that the cam cross-sectional shape Xa becomes smaller in the second direction d2 (rightward). As a result, in the valve train 10, the upper right corner and the lower left corner of the contact area Aa are prevented from significantly protruding from the valve lifter 16a. In other words, the protrusion amount D1 is reduced.
[0034] Furthermore, when the cam surface Sa is inclined with respect to the central axis Ax, and the cam cross-sectional shape Xa becomes smaller in the second direction d2 (rightward), the length of the left side of the contact area Aa shown in FIG. 2 can be maintained the same length as the length of the left side of the contact area Ba shown in FIG. 3. Therefore, the vertical length of the contact area Aa (hereinafter, the maximum contact length D3) is unlikely to become short. In other words, the cam lobe 203a is unlikely to become low. Therefore, a decrease in the valve lift of the valve train 10 is suppressed, and a decrease in the intake amount of the internal combustion engine is suppressed. For the above reasons, the valve train 10 can suppress the cam 202a from protruding from the valve lifter 16a while suppressing wear of the valve lifter 16a. Furthermore, the valve train 10 suppresses a decrease in the intake amount of the internal combustion engine.
[0035] Furthermore, in order to reduce the protrusion amount D1 while maintaining the height of the cam lobe of the cam 402a, for example, the radius r of the valve lifter 316a can be increased. However, if the radius r of the valve lifter 316a is increased, the mass of the valve lifter 316a increases. As a result, a spring with a large spring constant is required, which increases the friction generated in the valve train 310. This also hinders the internal combustion engine from rotating at high speed.
[0036] On the other hand, in the valve train 10, as described above, the protrusion amount D1 is reduced while maintaining the height of the cam lobe 203a. Therefore, the spring 18a with a large spring constant is not required, and the friction generated in the valve train 10 is unlikely to increase.
[0037] The inventors performed the following calculations to determine the preferred offset amount D2 and the preferred tilt angle θ. First, the inventors created a first model with the following conditions: The cam center speed v is the length in the front-to-rear direction at the center of the left-to-right direction of the cam 202a, as shown in Figure 2.
[0038] First model Valve lifter 16a radius r: 13.6825 mm Cam width b: 9mm Inclination angle θ: 5° Cam center speed v: 13.26 mm
[0039] In the first model, the offset amount D2 was varied within a range of 0.5 mm to 1.5 mm. Then, the protrusion amount D1 of the upper right corner of the contact area Aa and the protrusion amount D4 of the upper left corner of the contact area Aa were calculated. Figure 5 is a graph showing the calculation results using the first model. The vertical axis represents the protrusion amounts D1 and D4, and the horizontal axis represents the offset amount D2.
[0040] The protrusion amount needs to be kept to 0.73 mm or less. According to the graph in Fig. 5, if the offset amount D2 in the first model is 0.5 mm or more and 1.5 mm or less, the protrusion amounts D1 and D4 will be smaller than 0.73 mm.
[0041] Next, the inventors of the present invention created the following second and third models.
[0042] Second model Valve lifter 16a radius r: 13.6825 mm Cam width b: 9mm Cam center speed v: 13.26 mm Offset amount: 0.5 mm
[0043] Third model Valve lifter 16a radius r: 13.6825 mm Cam width b: 9mm Cam center speed v: 13.26 mm Offset amount: 1.5mm
[0044] In the second and third models, the tilt angle θ was varied within a range of 2° to 8°. Then, the protrusion amount D1 of the upper right corner of the contact area Aa and the protrusion amount D4 of the upper left corner of the contact area Aa were calculated. Figure 6 is a graph showing the calculation results using the second model. Figure 7 is a graph showing the calculation results using the third model. The vertical axis represents the protrusion amounts D1 and D4, and the horizontal axis represents the tilt angle θ.
[0045] 6 shows that when the offset amount D2 is 0.5 mm, if the tilt angle θ is between 2° and 7°, the protrusion amounts D1 and D4 will be less than 0.73 mm. On the other hand, according to FIG. 7, when the offset amount D2 is 1.5 mm, if the tilt angle θ is between 3° and 8°, the protrusion amounts D1 and D4 will be less than 0.73 mm. From the above calculations, it can be seen that if the offset amount D2 is between 0.5 mm and 1.5 mm and the tilt angle θ is between 3° and 7°, the protrusion amounts D1 and D4 can be set to appropriate values.
[0046] (Other embodiments) The valve train according to the present invention is not limited to the valve train 10, and can be modified within the scope of the invention.
[0047] The valve train 10 may operate two exhaust valves. [Explanation of symbols]
[0048] 10: Valve train 12a: Valve 14a: Valve guide 16a: Valve lifter 18a:Spring 20: Camshaft 22: Cylinder head 121: Valve head 122: Valve stem 161a: Circular section 201: Shaft 202a: Cam 203a: Camrob Aa: Contact area Ax: Central axis line Ha: hole S1: First main surface S11: 1st page S2: 2nd principal surface Sa: Cam surface
Claims
1. The valve train includes a valve, a valve lifter, and a camshaft. The valve includes a valve head and a valve stem, The valve stem extends in a first direction from the valve head portion, the valve lifter has a circular shape when viewed in the first direction and overlaps with an end of the valve stem in the first direction when viewed in the first direction, the camshaft is rotatable about a central axis extending in the second direction and includes a cam; the cam has a cam surface that contacts the valve lifter, A cross-sectional shape of the cam perpendicular to the second direction is defined as a cam cross-sectional shape, The cam surface is inclined with respect to the central axis, so that the cam cross-sectional shape becomes smaller as it goes in the second direction, The center of the cam surface in the second direction is located further in the second direction than the center of the valve lifter. Valve train.
2. the cam surface forms an inclination angle with the central axis, The angle formed between the first direction and the second direction is 90° plus the tilt angle. The valve train according to claim 1 .
Citation Information
Patent Citations
JP1988038601U