JPH0318655Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for preventing cavitation erosion in a water-cooled engine.

During operation, a water-cooled engine tends to cause cavitation in the cooling water surrounding the cylinder due to vibrations of the cylinder liner and cylinder block.

Cavitation is air bubbles generated in cooling water that comes into contact with the outer periphery of a cylinder liner, cylinder block, etc., and is caused by a drop in water pressure due to engine vibration. These bubbles are generated in the low-pressure area with minute depressions on the surface of the liner or block as nuclei, and collapse instantly when the next high pressure is reached. At this time, high-frequency water pressure fluctuations occur inside the cooling channel, causing the liner to collapse. Cavitation erosion occurs in the concave portions of the block surface, which reduces the durability of the engine. One way to prevent cavitation erosion is to mix air bubbles into the cooling water and use these bubbles to alleviate fluctuations in water pressure. A prevention device has been proposed (Japanese Patent Laid-Open No. 57-93619).

This device has an air passage that communicates the air chamber of the radiator with the cooling water passage on the radiator outlet side,
A flow control valve is provided in this air passage, and a piezoelectric element is attached to the engine body. This piezoelectric element detects the occurrence of cavitation, and this detection signal controls the flow control valve to control the amount of air mixed into the cooling water. It's starting to be controlled.

However, in this conventional device, the cavitation detection piezoelectric element senses not only the pressure fluctuations associated with cavitation, but also the vibrations of the engine itself, which has the disadvantage of poor cavitation detection accuracy and low reliability. be.

In addition, in the case of this type of prevention device proposed earlier by the present applicant in Japanese Utility Model Application Publication No. 58-33729, the air chamber is always in communication with the water pump suction side via the air passage. Erosion due to cavitation hardly occurs, and even when the cooling water is at a high temperature, where air entrainment is undesirable, there is a risk of air entrainment, which poses a problem in terms of reliability.

This idea was made in view of the above circumstances.
By providing a passage opening/closing valve in the air passage for mixing air provided in the cooling system, and by configuring the passage opening/closing valve to be controlled to open and close at a cooling water temperature lower than the operating temperature of the thermostat installed in the cooling system, It is an object of the present invention to provide a cavitation erosion prevention device that is more reliable than the conventional one.

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

In FIG. 1 showing one embodiment of the present invention, when the coolant temperature is low, such as during startup, the coolant heated in the engine body 1 does not flow into the radiator 3 because the thermostat 2 is closed, but instead flows into the bypass passage. The water is supplied to the water pump 5 via the water pump 4, and is again pressure-fed to the engine body 1, where it circulates through these cooling systems to promote warm-up.

On the other hand, when the cooling water temperature exceeds the valve opening temperature of the thermostat 2 (e.g. 82°C), the thermostat 2 opens and the cooling water of the engine body 1 is diverted to the radiator 3.
After being cooled there, it is pumped to the engine body 1 via the water pump 5 and circulated through these cooling systems. When the temperature of the cooling water drops to the valve closing temperature of the thermostat 2 (for example, 76° C.), the thermostat 2 closes again and switches the flow direction of the cooling water to the bypass passage 4 side. In this manner, during operation, the thermostat 2 opens and closes in accordance with the cooling water temperature as shown in FIG. 2, thereby maintaining the cooling water temperature within a substantially constant temperature range.

During operation, cooling water flows into the water tank 8 from the upstream side of the thermostat 2 and the upper part of the radiator 3 via the air pipes 6 and 7, where air and water are separated and the cooling water is returned to the water tank 8 via the cooling water passage 9. The pump 5 is designed to be returned to the upstream circulation path.

In this embodiment, in addition to the cooling system configured similarly to the conventional one, an air passage 10 is provided that communicates the air chamber 8A in the upper part of the water tank 8 with the suction side of the water pump 5. 10, the air passage 10 according to the cooling water temperature.
A passage opening/closing valve 11 is provided to open and close the passage. This passage opening/closing valve 11 has a temperature sensing part 11A filled with thermowax inserted into the thermostat housing, and when the cooling water temperature exceeds the set temperature, the thermowax expands and closes, and the temperature drops below the set temperature. When this happens, the thermowax contracts and opens. The set temperature is the valve closing temperature of thermostat 2 (76 in this example).
℃), and in this embodiment, it is set to, for example, 74°C. Cavitation erosion hardly occurs above this temperature (see Figure 3). 12 is a pressure valve for releasing air to the outside only when the air pressure in the cooling system becomes abnormally high.

Next, the effect will be explained.

During engine operation, vibrations of the cylinder liner and cylinder block cause water pressure fluctuations in the cooling water passage around the cylinder liner, causing cavitation. This cavitation occurs violently when the cooling water temperature is low. The relationship between the amount of cavitation erosion generated due to the occurrence of cavitation and the cooling water temperature is as follows.
It looks like the picture.

When the coolant temperature is low, the thermostat 2 is closed as described above, and the coolant is supplied to the water pump 5 through the bypass passage 4.

In this case, the pressure difference between the pressure in the air chamber 8A of the water tank 8 and the suction side pressure of the water pump 5 has become large, and the passage opening/closing valve 11 of the air passage 10 is in an open state, so that the air chamber 8A is in an open state. Since it is in communication with the water pump 5, air in the air chamber 8A mixes into the circulating cooling water through the air passage 10 based on the differential pressure, creating bubbles. These bubbles alleviate water pressure fluctuations based on the elastic deformation of the bubble volume in the cooling water passage around the cylinder liner, reducing pressure fluctuations and effectively preventing cavitation erosion that occurs during pressure fluctuations. suppress.

After that, the cooling water temperature rises, and the passage opening/closing valve 11
When the operating temperature of 74° C. is exceeded, the thermowax expands and the passage opening/closing valve 11 closes to close the air passage 10 and stop the mixing of air. Therefore, when the cooling water is at a high temperature where cavitation erosion is less likely to occur, air is not mixed in, so that the cooling efficiency for the engine body 1 can be maintained as in the conventional case.

Therefore, damage to the engine body 1 due to thermal load can be reliably avoided and reliability can be improved.
In this case, the amount of mixed air is equal to the amount of air present in the water tank 8 before the engine starts operating, so the amount of air can be specified.

Furthermore, in this embodiment, the operating temperature of the passage opening/closing valve 11 is set lower than the closing temperature of the thermostat 2, so as shown in FIG. Therefore, the number of opening/closing operations of the passage opening/closing valve 11 is significantly reduced. Therefore, the life of the passage opening/closing valve 11 can be extended, and the probability of foreign matter getting caught in the opening/closing valve 11 can be reduced, making it possible to further improve the reliability of air entrainment control. Further, when the thermostat 2 is open, the passage opening/closing valve 11 is closed and no air is mixed in, so that air mixing into the radiator 3 can be prevented and the radiator 3 will not be adversely affected.

As described above, according to the present invention, air is mixed into the cooling system of a water-cooled engine from the air chamber in the cooling system at low temperatures, where cavitation erosion is likely to occur. Cavitation occurring in the cooling water passage around the cylinder liner due to vibration can be prevented, erosion of the cylinder liner, cylinder block, etc. can be suppressed, and the durability of the engine can be increased. In addition, a valve is installed in the air passage for air mixing, and the air passage is closed by the valve when the cooling water is at high temperature, so air mixing can be reliably stopped when the cooling water is at high temperature, which improves cooling efficiency when the cooling water is at high temperature. damage to the engine body due to heat load can be avoided. Therefore, the reliability of the engine can be further improved. Furthermore, the on-off valve of the air passage is opened and closed at a temperature lower than the operating temperature of the thermostat, reducing the number of opening and closing operations of the on-off valve, which greatly improves the durability of the on-off valve. The reliability of air entrainment control can be improved.

[Brief explanation of drawings]

FIG. 1 is a simplified configuration diagram showing one embodiment of the present invention;
Fig. 2 is a diagram showing the opening/closing characteristics of the thermostat in the same embodiment, Fig. 3 is a diagram showing the relationship between the amount of cavitation erosion and the cooling water temperature, and Fig. 4 is a diagram showing the relationship between the thermostat and the passage opening/closing valve. It is a diagram showing the opening/closing operation relationship of. 1...Engine body, 2...Thermostat,
3...Radiator, 5...Water pump, 8...
...Water tank, 10...Air passage, 11...
Passage opening/closing valve.

Claims (1)

[Scope of utility model registration request] In a water-cooled engine, an air passage is provided that communicates the air chamber provided in the cooling system with the water pump suction side, and opens and closes depending on the cooling water temperature to connect the radiator side of the cooling system and the bypass passage side of the radiator. A cavitation erosion prevention device characterized in that a passage opening/closing valve that opens and closes at a cooling water temperature lower than the operating temperature of a thermostat for switching the cooling water is interposed in the air passage.