JPS641459Y2 - - Google Patents

Description

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

Engines with wet liner type cylinders tend to suffer from cavitation, especially when the cooling water is at a low temperature. Cavitation is air bubbles generated in the cooling water in contact with the outer periphery of the cylinder liner, and is caused by a drop in water pressure due to engine vibration. These bubbles are generated in the low-pressure area with microscopic depressions on the liner surface as nuclei, and collapse instantly when the next high pressure is reached. At this time, high-frequency water pressure fluctuations are generated inside the cooling channel, causing the depressions on the liner surface to form. cavitation erosion occurs, 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 piezoelectric element used to detect cavitation detects not only pressure fluctuations associated with cavitation, but also vibrations in the engine body caused by other factors, resulting in extremely poor cavitation detection accuracy and low reliability. It is something.

In addition, in the case of this type of prevention device previously proposed by the present applicant in Utility Application No. 127521/1980, the air chamber is constantly in communication with the water pump suction side via the air passage, so cavitation is prevented. Air may be mixed in even when the cooling water is at a high temperature, which is unlikely to occur, and there is a concern that cooling efficiency will be impaired. Furthermore,
In this device, air is always mixed in when the cooling water temperature is low and the thermostat is closed, so when the cooling water temperature is low, air is mixed in regardless of whether cavitation occurs or not, so it cannot necessarily be said to be efficient. .

This idea was made in view of the above circumstances.
It is an object of the present invention to provide a cavitation erosion prevention device that is more efficient and reliable than conventional devices by having a configuration in which air is mixed only when the engine is in an operating state where cavitation is likely to occur.

An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, when the coolant temperature is low, such as during startup, the coolant warmed by the engine body 1 does not flow into the water pump 5 via the bypass passage 4 because the thermostat 2 is closed. The fuel is supplied to the engine body 1, and is then sent under pressure to the engine body 1, where it is circulated through these cooling systems to promote warm-up.

On the other hand, when the coolant temperature exceeds a predetermined temperature and the thermostat 2 is opened, the coolant in the engine body 1 flows into the radiator 3, where it is cooled and then is pumped to the engine body 1 via the water pump 5.
The engine body 1 is cooled by circulating through these cooling systems so that the temperature of the cooling water does not exceed a certain value.

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

In this embodiment, in addition to the cooling system configured in the same manner as in the conventional art described above, an air passage 10 is provided which communicates the air chamber 8A in the upper part of the water tank 8 with the suction side of the water pump 5. A passage opening/closing valve 11 is interposed which is driven to open and close based on a signal from a control unit 20.

The control unit 20 has a built-in microcomputer (hereinafter referred to as microcomputer), and the microcomputer stores in advance an operating range where cavitation is likely to occur based on the load and rotation speed, as shown in FIG. has been done.
In FIG. 2, A indicates an area where cavitation may occur, and B indicates an area where cavitation will definitely occur.

The control unit 20 includes a rotation speed sensor 13, a load sensor 12, and a water temperature sensor 14.
The signals S ₁ , S ₂ , and S ₃ from the controller are input, and based on these signals, it is determined whether the operating state is in the cavitation generation region or not, and a signal based on the determination result is output to the passage opening/closing valve 11. It's summery. 15 is a pressure valve for releasing air to the outside when the air pressure in the water tank 8 becomes abnormally high.

Next, the action will be explained.

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 pump 8 and the suction side pressure of the water pump 5 increases. In this state, if the operating state corresponding to the output signals S ₁ and S ₂ of the load sensor 12 and the rotation speed sensor 13 is within the region A where cavitation may occur as shown in the second figure, the control unit 2
0, a valve opening signal is issued to the passage opening/closing valve 11, and the passage opening/closing valve 11 opens. As a result, the air in the air chamber 8A of the water tank 8 is sucked into the suction side of the water pump 5 through the air passage 10 and mixed into the cooling water, producing bubbles. These bubbles reduce water pressure fluctuations in the cooling water passage around the cylinder liner based on elastic deformation of the bubble volume, thereby reducing pressure fluctuations and effectively suppressing cavitation that occurs during pressure fluctuations.

On the other hand, when the operating state is outside the region A, the control unit 20 outputs a valve closing signal and the passage opening/closing valve 11 is closed, so that the mixing of air into the cooling water is stopped.

After that, when the cooling water temperature rises and the thermostat 2 opens, the cooling water flows through the radiator 3 instead of the bypass passage 4, and the pressure on the suction side of the water pump 5 increases accordingly.
The difference between the pressure inside A becomes smaller and the air suction force disappears. Therefore, when the cooling water is at a high temperature where cavitation does not occur, the mixing of air is stopped regardless of the operating state. Therefore, the cooling efficiency of the cooling water is not impaired, and the engine body 1 due to heat load can be reduced.
damage can be avoided. In this embodiment, in order to reliably prevent air from entering the cooling water when the temperature is high, when the water temperature sensor 14 detects that the cooling water has exceeded a predetermined temperature, the output signal S ₃ of the water temperature sensor 14 is used. Control unit 20
A valve closing signal is output from the passage opening/closing valve 11 so that the passage opening/closing valve 11 is closed regardless of the operating state. Therefore, the reliability of air entrainment control is improved.

Note that the supply source of air mixed into the cooling water is not limited to the air chamber of the water tank, but a separate air tank may be provided, or a structure may be adopted in which outside air is introduced.
Furthermore, in addition to the load and rotational speed, fuel injection timing or the like may be used as a detection element for the operating state.

As described above, according to the present invention, air is mixed in only during operating conditions where cavitation occurs, so there is no needless air mixing, and cavitation can be efficiently prevented and erosion of cylinder liners etc. Can be effectively suppressed. Furthermore, it is possible to reliably prevent air from entering the cooling water when the temperature is high, and it is possible to prevent damage to the engine body due to heat load without impairing cooling efficiency. Therefore, the durability and reliability of the engine can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a simplified configuration diagram showing one embodiment of the present invention;
FIG. 2 is a diagram showing the relationship between engine operating conditions and cavitation occurrence regions. 1...Engine body, 2...Thermostat,
3...Radiator, 5...Water pump, 10
... Air passage, 11 ... Passage opening/closing valve, 12 ... Load sensor, 13 ... Rotation speed sensor, 20 ... Control unit.

Claims (1)

[Scope of utility model registration request] In a water-cooled engine equipped with a wet type cylinder liner, an air passage is provided on the water pump suction side of the cooling system to introduce air into the cooling system, and a detection means for detecting the engine operating state is provided, and a detection means for detecting the engine operating state is provided. and a passage opening/closing valve that is interposed in the air passage and is driven to open or close in accordance with the output of the determination means. Cavitation erosion prevention device.