JPS5943441Y2 - Overhead cam engine - Google Patents

Description

[Detailed description of the invention] The present invention relates to overhead cam engines, and was proposed with the aim of making it possible to tighten the timing belt that drives the camshaft that opens and closes the intake and exhaust valves without reducing cooling performance. It's a long time.

In an overhead cam engine, the camshaft that opens and closes the intake and exhaust valves is driven from the crankshaft via a timing belt, but the timing belt is sensitive to heat and is placed on the upstream side of the cooling air to avoid receiving heat from the engine. It is located near the cooling fan of the engine because it is provided in This blocks the compressed cooling air from the cooling fan attached to the tip of the crankshaft, significantly reducing the engine's cooling performance or making it impossible to cool the engine.

Therefore, in order to sufficiently cool the overhead cam engine that drives the camshaft with the timing belt, we have developed a timing belt that is stretched between the camshaft and the balancer shaft, which is placed biased toward the camshaft from the crankshaft. This is what I did.

The present invention will be explained in detail below based on a specific embodiment shown in FIGS. 1 and 2.

1 is a cylinder, 2 is a cylinder cover, and 3 is a crankcase.

The piston 4 slides up and down within the cylinder 1 according to the combustion pressure of the combustion chamber 5, and is connected via a connecting rod I to a crankshaft 6 horizontally suspended within the crankcase 3.

9 cylinder Rad cover 2 is provided with an intake path control and exhaust path 8 that connects to the combustion chamber 5, and the intake path button and exhaust path 8
intake valve and exhaust valve 9 to open and close the combustion chamber side opening.
is provided.

A valve seat 10 is embedded in the opening of the intake and exhaust passages 8, and the intake and exhaust valves 9 are tappet valves that push their heads 9a into the combustion chamber 5 so that they can be seated on the valve seats 10. The valve stem 9b is inserted into the guide tube 11 embedded in the rad cover 2 into the cylinder so that it can freely slide, and the shaft end of the valve stem 9b is connected to the cylinder above the rad cover 2! Make it stand out.

A seat plate 12 is provided at the shaft end of the valve stem 9b, and a coil spring 13 is compressed between the cylinder and the rad cover 2 to urge the intake valve button and the exhaust valve 9 upward. A cap 14 is interposed and brought into contact with a cam 16 which is fixed to a camshaft 15 and rotates phantom, so that the valve can be opened by rotation of the camshaft 15.

Further, the ignition plug 17 is screwed onto the cylinder cover 2 so as to face the combustion chamber 5.

A cooling fan 18 is added to the tip of the crankshaft 6,
A baffle plate 21 is provided which has an air intensifier 19 at the front and an air outlet 20 at the rear and surrounds the entire outer periphery of the engine, and as the engine operates, a cooling fan 18 rotates to generate cooling air. 21, the engine is forcibly cooled using the guide gh.

A balancer shaft 22 for removing engine vibration is
Located at a position offset from the crankshaft toward the camshaft,
The gear 23 fixed to the balancer shaft 22 is connected to the crankshaft 6
It is driven to rotate by meshing with a gear 24 provided in the.

Pulleys 24 and 25 are provided on the balancer shaft 22 and the camshaft 15, respectively, and a timing belt 26 is stretched between the pulleys 24 and 25.

21 is a cover that covers this timing belt 26.

Next, in water-cooled two-stroke engines, as with air-cooled engines, sufficient consideration has been given to cooling performance.

In a water-cooled engine, a water pump pumps cooling water into the engine's cooling waterway.

This water pump drives the power of the crankshaft via a transmission belt, but if the transmission belt is cut or the current is cut off, it may stop and fail to perform its cooling function, causing engine components to overheat. It reduces its strength and lubrication, and eventually causes the engine to seize.

Therefore, as shown in FIG.
A hose 33 is connected to a water pump case 31 that covers an impeller 30 via a joint 32 to communicate with the cooling water passage of the engine, and one end of the crankshaft is used as a drive shaft for the water pump.

With this configuration, during engine operation, the crankshaft 2
The impeller 30 also rotates at all times together with the water pump 9, operating the water pump and pumping the cooling water.

Therefore, the water pump will not stop due to the transmission belt being cut or the current being cut off, and the engine will always be cooled while the engine is running, and the engine will never overheat. .

As mentioned above, this invention is designed to be used in an overhead cam engine in which the camshaft that opens and closes the intake and exhaust valves is driven by a timing belt. This is an overhead cam engine in which a timing belt is stretched between the balancer shaft and the camshaft, which are placed biased towards the camshaft side, and the timing belt is placed biased from the center of the cylinder and crankcase. In this case, the timing belt does not completely block the cooling air from the cooling fan, resulting in good engine cooling.

Since the timing belt is installed on the balancer shaft, which is placed biased toward the camshaft from the crankshaft, the distance between the pulleys around which the timing belt is wound is shortened, and the power transmission mechanism from the crankshaft to the camshaft is improved. It can be formed small, and the engine as a whole can have a certain size and shape.

[Brief explanation of the drawing]

Figure 1 shows a concrete example of the overhead cam engine of this invention.
FIG. 2 is a schematic side view of FIG. 1 with a portion cut away, and FIG. 3 is a cross-sectional view showing a water pump of a water-cooled two-cycle engine. 6...Crankshaft, 18...Cooling fan, 9...Intake/exhaust valve, 15...Camshaft, 26...Timing belt , 22...
・Balancer axis.

Claims (1)

[Scope of utility model registration request] The air is cooled by pressure fed by a cooling fan attached to the tip of the crankshaft, and the camshaft that opens and closes the intake and exhaust valves is driven by an overhead cam engine driven by a timing belt, and the center of the crankshaft is biased toward the camshaft side. An overhead cam engine characterized by a timing belt stretched between the balancer shaft and the camshaft.