JPH0148427B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a cam of a camshaft, and particularly to a hardened layer of the cam portion thereof.

(Background technology) The camshaft of an internal combustion engine installed in a vehicle is
A cam attached to this opens and closes the intake and exhaust valves in conjunction with engine operation.

The cam portion of such a camshaft is used to open and close the intake and exhaust valves through a rocker arm, etc. against a valve spring, and the engine speed has increased due to recent improvements in engine performance, and as high-speed operation is becoming more common. Therefore, various hardening treatments are performed to increase the surface hardness in order to improve the wear resistance, impact resistance, fatigue resistance, etc. of the cam portion.

As a surface hardening treatment for the cam portion of the above camshaft, remelting hardening treatment, so-called remelting treatment, has been put to practical use, and a camshaft that satisfies the above requirements has been obtained, and the entire circumference of the cam portion including the base circle has been remelted and hardened. is the current situation.

By the way, the cam of the camshaft is as shown in FIG. 2, and has a cam portion 72 that bulges outward in the radial direction on the circumference of a base circle 71. The cam top part 75 is sandwiched between the rising parts and has a radius of curvature smaller than the radius of curvature of the base circle 71. This is involved in the lifting movement of the Rocker arm.

Looking at the load surface pressure distribution of each part of the cam profile when the cam part 71 of the camshaft engages with the rocker arm involved in opening and closing the valve, it is as shown in the characteristic curve a in the figure, and one of the rising parts 74 of the cam part 71 is The surface pressure is slightly high at the beginning of the engagement lift, becomes low at the subsequent rise, reaches a maximum at the cam top 75 where the lift amount is the largest, and symmetrically decreases toward the other rise.

When considering this surface pressure distribution, the surface pressure at the rising part of the cam is low, and the surface pressure at the top of the cam is extremely high.Therefore, it is not necessarily necessary to have uniform hardness functionally over the entire circumference of the cam; Then, the surface hardening process is performed by setting the hardness to be uniform through the remelting hardening process, and in fact, setting the hardness in accordance with the top of the cam where the surface pressure is highest.

The above camshaft has the cam portion 72 as described above.
After the surface of the cam is hardened, it is necessary to grind it with a grindstone, and each part 73 to 75 of the cam part 72 needs to be ground. During such grinding, the cam top part 75 has a small radius of curvature, while the cam part has a large radius of curvature. In the rising portions 74, 74, when the camshaft and therefore the cam portion are rotated at a constant rate for machining, the contact arc of the grindstone becomes long, and the amount removed per unit time, that is, the removal (grinding) speed becomes excessive. Therefore, compared to when machining the cam top 75, the cam rising portions 74, 7
Currently, when machining 4, the angular speed is slowed down and the machining takes time. Therefore, the machining time becomes long, and since the camshaft usually has many cam parts, the cumulative time required for machining is long, which is disadvantageous in terms of time economy, and further impedes efficient camshaft manufacturing. It is disadvantageous in terms of cost, and the grinding wheel also tends to wear out quickly due to the above.
Improvements are also desirable in terms of increasing the life of the grinding wheel.

(Objective of the Invention) The present invention has been made in view of the above, and its purpose is to focus on the function of the cam portion of the camshaft, improve the workability of the cam portion to a level necessary and sufficient for the function, and realize mass production. Moreover, it is an object of the present invention to provide a cam which is advantageous in terms of cost and which can be designed while improving the life of the grindstone and the like.

(Structure of the Invention) In order to achieve the above-mentioned problems, the present invention has a cam portion that bulges outward in the radial direction from a base circular portion, a cam rising portion having a radius of curvature larger than that of the base circular portion, and a cam rising portion having a radius of curvature smaller than the cam rising portion. a cam top portion having a radius of curvature, the cam rising portion having a higher surface pressure than the base circular portion having the lowest surface pressure due to sliding with the cam engaging member, and the cam top portion having the highest surface pressure;
In a camshaft equipped with a cam having a hardened layer formed by a remelting hardening process, the hardened layer on the top of the cam is an alloy hardening layer formed by the remelting hardening process in which alloy powder is added, and the rising portion of the cam is made of a hardened layer formed by the remelting hardening process. It is characterized in that it is formed on the hardened layer by the remelting hardening process without adding powder.

(Embodiment) Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a cam 2 of a camshaft 1 according to the present invention.
In this explanatory front view, the cam 2 consists of a shaft part 3 formed by a base circle and a cam part 4 which bulges outward in the radial direction and occupies 1/2 of a circular arc in this particular embodiment.
The shaft portion 3 is formed by a base circle, and the cam portion 4 is formed by the shaft portion 3.
The cam is symmetrically provided with rising parts 5, 5 which bulge outward in the pot radial direction from a part of the outer periphery of the cam, and the rising parts 5, 5 are formed with a radius of curvature larger than the radius of curvature of the base circle diameter. , its proximal end 6,6
continues around the outer periphery of the shaft portion 3. Cam rising part 5,
A cam top 8 is continuously formed between the tips 7 and 7 of the cam, and the cam top 8 is formed with a radius of curvature that is smaller than the radius of curvature of the rising portion of the cam, and is actually smaller than the radius of curvature of the base circle. has been done.

The above profile of the cam portion 4 of the cam 2 lifts (swings) the valve rocker arm against the valve spring to open and close the intake and exhaust valves, and the surface pressure distribution of the cam portion 4 is As mentioned above.

In the above cam, the surface forming the cam profile of the cam portion 4 is remelted and hardened, but during the treatment, the surface hardness of the cam rising portions 5, 5 and the cam top portion 8 is treated to be different in height. do. That is, the cam rising portions 5 and 5 are treated as zones A and C with low hardness, and the cam top portion 8 is treated as zone B with high hardness. Specifically, when remelting and hardening zones A and C, for example, the supply of metal powder that is supplied together with the plasma arc is stopped, and the plasma arc is used to remelt and harden zones A and C.
C, that is, chilled layers 9, 9 are formed on the surfaces of the cam rising parts 5, 5, while in processing zone B, that is, the surface of the cam top 8, alloy powder is supplied into a plasma arc and melted. , an alloy layer 10 having higher hardness than the above is formed on the surface. As a result, the profile of the cam portion 4 is such that the hardness of the cam top portion 8 is high and the hardness of the rising portions 5 is lower than this.

In this way, a cam 2 having a surface hardness that follows the surface pressure distribution is obtained.

By the way, a specific example of the above-mentioned process will be explained with reference to FIGS. 3 to 5. Both ends of the camshaft 101 in the axial direction are supported by the chuck 11 and the center 12, and the pressure cylinder 13 is pressed in the axial direction. The motor 14 supports the camshaft 101.
Rotate. The camshaft 101 is equipped with a plurality of cam parts 104, and the nozzle 16 of the torch 15 faces above the surface of any one of the cam parts 104 to maintain a clearance.The nozzle 16 is, for example, as shown in FIG. A chip 18 is disposed within the cap 17, and a passage 19 for shielding gas made of inert gas or the like is provided between the cap and the chip.
Further, a working gas passage 20 made of argon gas or the like is formed in the center of the chip 18, a cooling passage 21 is formed around the passage 20, and an electrode 22 made of tungsten or the like is provided inside the passage 20. , the shield cap 17 has metal powder introduction pipes 23, 2.
3 is inserted and fixed so that the extension of its axis intersects the extension of the axis of the passage 20. torch 15
is a holder 25 provided on the base frame 24 so as to be movable up and down.
The base frame 24 is screwed onto a feed screw 26, and the feed screw 26 is rotationally driven by a motor 27. Therefore, the torch 15 is moved up and down by the holder 25, and when the cam portion 104 of the camshaft 101 rotates, the torch 15 is moved up and down to maintain a constant clearance between the front surface of the torch and the nozzle 16, and the feed screw 26 is moved by the drive of the motor 27. It moves in the axial direction of the camshaft through the camshaft, sequentially approaches a plurality of cam parts spaced apart in the axial direction, processes each cam part in turn, and reciprocates each cam part to meander as the camshaft rotates as shown in Figure 5. A processing trajectory b is formed. The metal powder introduction pipes 23, 23 are connected to the supply device 29 through the pipes 28, 28 and the vibration device 3.
A valve 31 is interposed in the pipes 28 and 28, and the motors 14 and 27, the holder 25, the vibration device 30, the valve 31, and the power source 32 of the torch 15 are controlled by a control device 33. .

In the above, when processing the cam portion 104, the torch 1 is
5, the supply of metal powder by plasma arc from the proximal end 6 to the distal end 7 is cut off by closing the valve 31 for melting processing, and from one distal end 7 to the other. The valve 31 is up to the tip 7 of the valve 31.
The valve 31 is opened to supply metal powder into the plasma arc as shown in FIG. 4 to form an alloy layer on the surface of the cam top 8, and the valve 31 is closed at the tip 7 connected to this to cut off the supply of the metal powder. The area from the tip 7 to the base end 6 of the other cam rising portion 5 is treated with plasma arc only.

The above processing method is not limited to this and is arbitrary.

(Effects of the Invention) As is clear from the above, according to the present invention, first, the hardness of the surface of the cam part is set to the hardness required for the rising part and the top part of the cam according to the surface pressure distribution of the cam, so it is functionally superior. In particular, since it has hardness according to the surface pressure distribution of each part, it is superior in terms of compatibility with the other party, such as a rocker arm, and compared to a conventional cam with a uniform high hardness, the rocker arm engaging part etc. Second, unlike conventional cams where the entire surface of the cam is uniformly hard, the hardness of the rising part of the cam with a long contact arc is lower than that of the top of the cam. There is no need to take measures such as reducing the angular speed, and grinding work can be performed while rotating the cam at a constant rotation that matches the top of the cam with a short contact arc.
In addition to speeding up the subsequent grinding process and manufacturing efficient, rational, and cost-effective cams,
Since the alloy powder only needs to be supplied to the top of the cam, it is also advantageous in terms of material economy.

As described above, the present invention has many advantages.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention; FIG. 1 is an explanatory front view of a cam, FIG. 2 is an explanatory diagram of the surface pressure distribution, and FIG. 3 is a schematic diagram showing an example of a remelting treatment method. FIG. 4 is a vertical sectional view showing an example of a nozzle, and FIG. 5 is an explanatory perspective view showing an example of a treatment method for a cam portion. In the drawings, 2 is a cam, 4 is a cam portion, 5 is a rising portion, and 8 is a top portion.

Claims (1)

[Scope of Claims] 1. The cam portion bulging outward in the radial direction from the base circular portion is composed of a cam rising portion having a radius of curvature larger than that of the base circular portion and a cam top portion having a smaller curvature radius than the cam rising portion, A cam in which a hardened layer is formed by remelting and hardening treatment on the rising portion of the cam, which has a higher surface pressure than the base circular portion, which has the lowest surface pressure due to sliding with the cam engaging member, and on the top portion of the cam, which has the highest surface pressure. In the camshaft, the hardened layer on the top of the cam is a high-hardness alloy hardened layer obtained by the remelting hardening treatment with addition of alloy powder, and the rising portion of the cam is formed by the remelting hardening treatment without adding the alloy powder. A cam of a camshaft formed on the hardened layer according to the invention.