JPH0410343Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a two-stroke engine with a mechanical supercharger having an intake valve and an exhaust valve.

[Prior art] Conventionally, in a two-stroke engine with a mechanical supercharger, the air sent out by the supercharger was guided into the combustion chamber through a scavenging hole provided in the cylinder bore via the crank chamber (for example, in the 48-71204).
As a result, oil mist in the crank chamber enters the combustion chamber and is burned, resulting in increased oil consumption.In addition, the piston ring is located at the corner of the scavenging hole, resulting in severe ring wear.

In order to solve this problem, the applicant first
A two-stroke engine with a mechanical supercharger that has both an intake valve and an exhaust valve was proposed (in 1983-
No. 149180). The intake and exhaust valves were placed above the combustion chamber to guide air into the combustion chamber without passing through the crank chamber, reducing oil consumption and piston ring wear.

[Problems to be solved by the invention] In the previously proposed two-stroke engine with a mechanical supercharger equipped with intake and exhaust valves, a bypass passage is provided in the mechanical supercharger provided in the intake passage. The bypass valve was opened and closed according to the load to control the amount of supercharging. In other words, at light loads, the bypass passage is opened, reducing boost pressure in the intake passage to reduce scavenging air, increasing residual gas and reducing NOx, and at high loads, the bypass passage is closed to increase scavenging air and increase output. That's what I was doing.

Under general conditions, there is no problem with the above control, but especially in diesel engines, when the engine is cold, the combustion chamber wall temperature and intake air temperature are low, so there is a problem with the ignitability of the fuel. In addition, when the compression ratio is increased to solve this problem, the combustion pressure increases at high loads, resulting in a problem that the output is reduced due to the combustion pressure reaching its limit.

The present invention aims to improve the ignition performance of a two-stroke engine when the engine is cold in order to alleviate the above-mentioned problems.

[Means for Solving the Problems] A two-stroke engine with a mechanical supercharger according to the present invention for achieving the above object is provided with an intake valve and an exhaust valve above the combustion chamber, and the intake valve is installed. A mechanical supercharger is provided in an intake passage that connects to the intake port without going through the crank chamber, and a bypass passage that bypasses the mechanical supercharger is provided, and the opening and closing of the bypass passage is controlled by a computer. A bypass valve is provided, and the bypass valve opening/closing control by the computer is such that the bypass valve is opened when the engine is cold and under light or medium load, and the bypass valve is closed after the engine is warmed up and when the engine is cold and under high load. Consists of the settings.

[Function] In the two-stroke engine mentioned above, when the engine is cold and under light or medium load, the bypass passage is opened, the boost pressure decreases, and the scavenging efficiency decreases, so high-temperature residual gas increases in the combustion chamber, and the fuel The ignitability of the fuel is improved. In addition, the bypass valve is closed after warming up and under high load even when the engine is cold, so the supercharging pressure increases and the output is improved.

[Embodiments] Hereinafter, preferred embodiments of the two-stroke engine with a mechanical supercharger according to the present invention will be described with reference to the drawings.

1 and 2 show an embodiment of the invention. In the figure, reference numeral 1 denotes a reciprocating two-stroke engine, which has an intake valve 2 and an exhaust valve 3 in a portion other than the piston sliding area, for example, in the cylinder head. An intake passage 4 that does not pass through the crank chamber is connected to the intake port to which the intake valve 2 is attached, and a mechanical supercharger 5 is disposed on the intake passage 4.
The mechanical supercharger 5 is mechanically connected to the crank pulley via a belt 7. In the intake passage 4,
A bypass passage 8 is provided that communicates the upstream and downstream parts of the mechanical supercharger 5 and bypasses the mechanical supercharger 5. A bypass valve 9 is provided in the bypass passage 8 . The bypass valve 9 includes a valve body 10 that opens and closes the bypass passage 8, a spring 11 that biases the valve body 10 toward the closing side, and a spring 1.
The valve body 10 has a solenoid 12 that opens the valve body 10 against the biasing force of the solenoid 12 . Opening and closing of the bypass valve 9 by excitation of the solenoid 12 is controlled by a computer 13. An air cleaner 14 is provided in the intake passage 4 on the upstream side of the mechanical supercharger 5.

A fuel injection valve 16 faces the combustion chamber 15 of the two-stroke engine, and the fuel injection valve 16 injects fuel metered and pressurized by an injection pump 18 into the combustion chamber in response to the timing of the vertical movement of the piston 17. Inject at 15. The figure shows an example of a diesel engine as a two-stroke engine, but the spark ignition type
It may also be a cycle engine.

The exhaust port to which the exhaust valve 3 is attached is connected to the exhaust manifold 19, and further communicates with the outside air via an exhaust pipe.

A signal from a load sensor, such as an accelerator opening sensor 20, and a signal from an engine temperature sensor, such as a water temperature sensor 21, are sent as input signals to a computer 13 that controls the opening and closing of the bypass valve 9.

FIG. 2 shows a flowchart of the functions provided to the computer 13. First, step 22
The process starts at step 23, and it is determined whether the coolant temperature Tw is large or small. If the engine coolant temperature Tw is less than a predetermined value a°C, the process proceeds to step 27, and if the engine coolant temperature Tw is greater than a°C. If so, proceed to step 25 and control the bypass valve 9 to close the bypass passage 8.

In step 23, it is determined that the engine water temperature Tw is below a℃ and the engine is in a cold state, and the process proceeds to step 27.
When the process advances to step 27, it is determined whether the accelerator opening θ is less than the predetermined opening b, and if the accelerator opening is less than b, it is in the light to medium load range, so the process proceeds directly to step 24 and bypasses. The passage 8 is opened, and in step 27, when the accelerator opening degree θ is greater than b, that is, in the high load range, the process proceeds to step 25, where the bypass passage 8 is closed, so that a large engine output can be ensured. From steps 24 and 25, the process advances to step 26, and the routine ends.

Next, the effect will be explained.

In the case of the two-stroke engine 1, the piston 17 is pushed down by combustion, and the exhaust valve 3 first opens and exhaust gas is guided from the exhaust manifold 19 to the exhaust pipe, but then the intake valve 2 opens and fresh air enters the combustion chamber 15. The combustion chamber 15 is filled with the exhaust gas, and the exhaust gas is expelled. This scavenging effect varies greatly depending on the pressure of the air sent to the combustion chamber 15; the higher the pressure, the less the amount of exhaust gas remaining in the combustion chamber 15, and conversely, the lower the pressure, the more residual gas.

In the above embodiment, when it is cold, that is, when the water temperature Tw is low and when the load is light or medium, the bypass valve 9 is opened and the bypass passage 8 is opened, so that the boost pressure decreases and a high temperature is generated in the combustion chamber. The residual gas increases, and the temperature of the compressed air increases by that amount, improving ignitability.

In addition, after warming up and even when the engine is cold, the bypass valve 9 is closed when the load is high, so that the entire amount of intake air is sent to the engine, increasing scavenging air and improving output.

[Effects of the invention] According to the two-stroke engine with a mechanical supercharger according to the invention, the bypass passage that bypasses the mechanical supercharger is opened when the engine is cold and at light or medium loads, so the scavenging efficiency is improved. The remaining gas at a lower temperature increases, and the temperature of the compressed gas increases, improving ignitability and starting performance. Further, since the bypass valve is closed during high load even after warming up and when the engine is cold, the boost pressure increases and the output during high load is maintained at a good level.

[Brief explanation of the drawing]

Figure 1 is a system diagram of a two-stroke engine with a mechanical supercharger according to an embodiment of the present invention, and Figure 2 is a system diagram of a two-stroke engine with a mechanical supercharger according to an embodiment of the present invention.
Computer control flowchart in fig.
It is. 1...2-cycle engine, 2...Intake valve, 3
...Exhaust valve, 4...Intake passage, 5...Mechanical supercharger, 8...Bypass passage, 9...Bypass valve, 13...Computer, 21...Water temperature sensor.

Claims (1)

[Scope of utility model registration request] An intake valve and an exhaust valve are provided above the combustion chamber, and a mechanical supercharger is provided in an intake passage that connects to the intake port where the intake valve is installed without going through the crank chamber, and the mechanical supercharger is bypassed. A bypass passage is provided, and a bypass valve whose opening/closing is controlled by a computer is provided in the bypass passage. A two-stroke engine with a mechanical supercharger, characterized in that a bypass valve is set to close after the machine and when the engine is cold and under high load.