JPH0229203Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention relates to a camshaft for a small internal combustion engine, and in particular,
The present invention relates to a camshaft having a synthetic resin cam gear.

[Prior art and its problems]

A conventional camshaft with a synthetic resin cam gear is made of special cast iron with high wear resistance, and the part to which the cam gear is attached forms a boss part, and the shape of the boss part is as follows when viewed from the axis direction: Almost rectangular in shape,
A cam gear made of synthetic resin is attached to the boss portion to make the attachment strong against torque fluctuations occurring on the camshaft. The positions and shapes of the intake and exhaust cams are carved out using copy machining.
The reference for the processing is the substantially rectangular boss portion. However, the shape of the boss portion is
Because it is approximately rectangular, that is, it does not have a smooth rotating body shape, problems such as the gauge stylus of the cam's processing angle detection sensor jumping at the rectangular corners occur, which is not the standard for rotary processing. As a result, there has been an inconvenience that the machining accuracy of the cam is poor.

In addition, excessive stress may be generated in the rectangular corners of the boss portion in response to an increase in the torque transmitted from the cam gear to the intake/exhaust cams, which may cause a crack.

[Structure of the idea]

The present invention attempts to solve the disadvantages of the prior art by creating a camshaft for a small internal combustion engine in which an eccentric boss is formed on the cast iron camshaft, and a synthetic resin cam gear is attached to the outer periphery of the boss. It is something to do.

Hereinafter, the configuration of the present invention will be described in detail based on embodiments shown in the accompanying drawings.

Fig. 1 shows an embodiment of the present invention, in which a partially cutaway side view is shown, Fig. 2 is a side view seen from the axial direction of Fig. 1, and Fig. 3 is a model diagram of the casting process.

1 is a camshaft used for general-purpose air-cooled gasoline engines,
The total length is 8.6 cm, 2 is the exhaust cam of the camshaft 1, 3 is the intake cam, and 4 is the boss part, whose shape is eccentric from the center O of the camshaft 1, as shown in Figure 2. The boss 4 has a circular shape centered at O', and a cam gear 5 made of reinforced plastic material (6 nylon) is attached to the boss 4. Reference numeral 6 indicates a balance weight mounting hole provided in the rib of the cam gear 5.

Here, the camshaft 1 of this embodiment is cast using molds 7 and 8 with a parting line L as shown in FIG. ) and rotates while using it as a reference, and when the stylus of the sensor comes to the key groove 9, the rotation is stopped and the cams 2 and 3 are copied and cut. Note that the extension connecting the eccentric center O' of the boss portion 4 and the center O of the camshaft is defined as a parting line L, and the cam nose of the intake or exhaust cam 2 or 3 is directed onto this line L, and other The cam nose is directed approximately above the parting line L to eliminate undercuts and facilitate mold release. Therefore, the shape of the boss portion 4 is not limited to an eccentric circular shape as in this embodiment, but may be an eccentric, smooth rotating body shape, for example, an ellipse, and a shape that does not cause undercuts during mold release. Either is fine.

In summary, the present invention provides a camshaft for a small internal combustion engine in which a boss is formed on a cast camshaft and a synthetic resin cam gear is attached to the boss. On the other hand, since this is a camshaft for a small internal combustion engine that is eccentric to the cam nose side of either the intake or exhaust cam and has a smooth rotating body shape, it has the following effects.

[Effect of the invention] Since the boss part is shaped like a smooth rotating body, even if the boss part is used as a processing reference and the cam cutting process is performed,
It can be processed accurately and quickly, improving mass productivity and reducing costs.

Since the cam nose and eccentric position were matched,
No undercuts occur on cast camshafts.

An eccentric boss part is formed on the camshaft where torque fluctuations occur frequently, and the cam gear is attached to the boss part, so the torque can be transmitted from the cam gear to the intake and exhaust cams without compromising the strength of the cam gear attachment surface. This allows the camshaft to be made smaller and lighter.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of the present invention, in which a partially cutaway side view is shown, Fig. 2 is a side view seen from the axial direction of Fig. 1, and Fig. 3 is a model diagram of the casting process. 1...Camshaft, 2, 3...Cam, 4...Boss, 5...Cam gear, O...Camshaft center, O'...
...eccentric center.

Claims (1)

[Scope of utility model registration request] In a camshaft for a small internal combustion engine, in which a boss is formed on a cast camshaft and a synthetic resin cam gear is attached to the boss, the shape of the boss is aligned with the intake/exhaust cam with respect to the center of the camshaft. A camshaft for a small internal combustion engine characterized by being eccentric to one of the cam nose sides and having a smooth rotating body shape.