JPH02215970A - Fuel injection system for two-cycle engine - Google Patents

Abstract

PURPOSE:To improve drivability and reduction in fuel consumption by detecting intake negative pressure when setting a fuel injection quantity on the basis of crankcase internal pressure fluctuations, and lowering a fuel pressure regulator the extent of fuel pressure against an increase of this detected intake negative pressure and thereby compensating the fuel injection quantity. CONSTITUTION:A pressure detector 66 is attached to a crankcase 18, detecting internal pressure P in a crank chamber 24, and a voltage signal (p) conformed to this detected value P is transmitted to a controller 72. An optimum fuel injection quantity is determined in response to this signal, thereby opening a solenoid valve of a fuel injection valve 44. A throttle valve 68 is opened or closed by lever operation of a driver, but negative pressure Q in an intake pipe 26 goes down with a decrease in opening of the throttle valve 68 and both diaphragms 48, 50 compress a spring 62, therefore the diaphragm 50 separates from a nozzle 64. Consequently, fuel in a fuel pressure chamber 58 flows back to a fuel tank 40 from the nozzle 64 causes a fuel pressure regulator 46 to lower fuel pressure, and thereby fuel pressure in the injection valve 44 goes down, decreasing the injection quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fuel injection device that determines the amount of fuel to be injected by detecting the pressure in the crank chamber of a two-stroke engine with preloaded crank chamber.

(Background of the Invention) There is a known fuel injection device that takes advantage of the fact that the amount of fluctuation in the crank chamber pressure of a two-stroke engine with preloaded crank chamber corresponds to the amount of intake air, and determines the amount of fuel to be injected based on the amount of fluctuation in the crank chamber pressure. Yes (see JP-A-58-98632 and JP-A-59-5875). However, this device is based on the premise that the amount of variation in crank chamber pressure corresponds correctly to the amount of intake air, and it has been found that in actual engines, it may not be possible to detect the correct amount of intake air.

For example, when the throttle valve is opened at a small opening, the amount of variation in the crank chamber pressure does not change depending on the engine speed, and if the fuel injection amount is controlled depending on this amount of variation, the optimal injection amount cannot be obtained. I understand.

The solid line in FIG. 2 shows the change in the actual injected fuel amount M with respect to the engine speed N, using the throttle valve opening θ as a parameter, and the broken line shows the change in the optimal required fuel amount M. (hereinafter referred to as MN characteristic).

As is clear from this figure, when the throttle valve is fully open (θ=
1/1), the actual injection amount M is the optimal required characteristic a
However, when the throttle valve is opened at a small opening, the injection amount becomes too large at high speed.1 For example, θ=
With respect to the characteristics of the required fuel amount M at 1/8 load, the determined injection amount is large (as shown by solid line C).In other words, at low loads, especially in high speed ranges, the fuel amount in the shaded area becomes excessive; Problems arise such as unstable engine operation and increased fuel consumption.The reason for this may be that there is a limit to the high-speed response of the injection valve, but it is not possible to increase the response of the injection valve. Decreased productivity and reliability of injection valves,
This is undesirable as it leads to an increase in costs.

(Purpose of the Invention) The present invention was made in view of the above circumstances, and is a two-cycle system that makes it possible to appropriately control the injection amount, especially during low-load, high-speed operation, without increasing the high-speed response of the injection valve. The purpose is to provide a fuel injection device for an engine.

(Structure of the Invention) According to the present invention, this purpose is to detect the crank chamber pressure,
A crank chamber prepressure type two-stroke engine that determines the fuel injection amount based on the amount of pressure fluctuation includes a negative pressure detection means that detects intake negative pressure and a fuel pressure regulator that controls the fuel pressure supplied to the fuel injection valve. , the fuel pressure regulator is achieved by a fuel injection device for a two-stroke engine, characterized in that the fuel pressure regulator corrects the fuel injection amount by lowering the fuel pressure in response to an increase in intake negative pressure.

(Example) FIG. 1 is an overall configuration diagram of an embodiment of the present invention.

In this figure, numeral 10 is a two-stroke internal combustion engine with preloaded crank chamber, 12 is a cylinder, 14 is a piston, 16 is a spark plug, 18 is a crankcase, 20 is a crankshaft, 22
is a connecting rod. A crank chamber 24 is formed within the crankcase 18 .

26 is an intake pipe, and this intake pipe 26 is connected to the intake boat 30 via a reed valve 28. 32 is an exhaust boat, and 34 is an exhaust pipe.

36 is a scavenging boat, and this scavenging boat 36 communicates with the crank chamber 24 through a scavenging passage 38.

40 is a fuel tank, and 42 is an electric fuel pump. 4
Reference numeral 4 denotes an electromagnetic fuel injection valve, and fuel pumped from a fuel pump 42 is supplied to this injection valve 44 .

Reference numeral 46 denotes a fuel pressure regulator, which adjusts the fuel pressure fed from the fuel pump 42 to the injection valve 44 to a predetermined pressure determined by the intake negative pressure. That is, when the fuel pressure supplied from the fuel pump 42 to the injection valve 44 exceeds a predetermined pressure determined by the intake negative pressure, a portion of the fuel is circulated through the vibrator 47 to the fuel tank 4o.

This regulator 46 has a large diameter first diaphragm 48.
and a second diaphragm 50 having a small diameter. The first diaphragm 48 partitions an intake negative pressure chamber 54 and an atmospheric pressure chamber 56 . A vibrator 52 that detects the negative pressure of the intake pipe 26 is communicated with the intake pressure chamber 54 as an intake negative pressure detection means. The atmospheric pressure chamber 56 communicates with the atmosphere. Also, the second diaphragm 5
0 partitions the atmospheric pressure chamber 56 and the fuel pressure chamber 58. Fuel pressure chamber 58
is connected to a vibro 0 that connects the fuel pump 42 and the injection valve 44, and the fuel pressure of the injection valve 44 is guided thereto. The centers of both diaphragms 48 and 50 are connected to each other by a connecting rod, and a compression spring 62 applies a return force to the first diaphragm 48 toward the fuel pressure chamber 58 side. Further, a fuel pressure adjustment nozzle 64 faces the second diaphragm 50 from within the fuel pressure chamber 58, and the diaphragm 50 itself acts as a flapper that approaches and separates from this nozzle 64.
A known flapper nozzle type pressure regulation mechanism is formed. The intake negative pressure increases and the diaphragm 48.50 moves to the spring 62.
When the fuel in the fuel pressure chamber 58 leaves the nozzle 64 while being compressed, the fuel in the fuel pressure chamber 58 is returned to the fuel tank 40 from this nozzle 64.

Reference numeral 66 denotes a pressure detector attached to the crankcase 18, which detects the internal pressure P of the crank chamber 24 and outputs an electrical signal of a voltage corresponding to this internal pressure P, that is, a voltage signal p.

Reference numeral 68 denotes a shutter type throttle valve that moves up and down from above within the intake pipe 26 to change the area of the intake passage. The throttle valve 68 is opened and closed, for example, in conjunction with the driver's operation of the throttle lever. 70 is a rotation speed detector that detects the rotation speed N of the crankshaft 20 and the ignition timing signal α.

Reference numeral 72 denotes a control device composed of a microcomputer, into which signals such as the above-mentioned crank chamber internal pressure p, rotational speed N, ignition timing signal α, etc. are input.

Further, various signals such as engine temperature T, engine acceleration/deceleration, engine brake, etc. may be input for control. The control device 72 determines the optimum fuel injection amount M corresponding to the operating state based on these various input signals, determines the injection time for this injection amount M, and opens the electromagnetic valve of the fuel injection valve 44. The control device 72 has a built-in memory 72A, and the optimum injection amount M shown in the broken line in FIG. 2 is stored in the memory 72A in advance.
The characteristic (M-N characteristic) is stored, for example, in the form of an arithmetic expression, the injection amount M is determined, and the injection time is determined. Based on this injection time, injection is performed intermittently once or multiple times during one rotation of the crankshaft in synchronization with the rotation of the crankshaft.

The injection time determined by the control device 72 is sufficiently short when the throttle valve opening θ is below a certain level and the load is medium to low, and as the engine speed further increases, this injection time becomes even shorter. Therefore, the injection valve 44 cannot respond to this short injection time, and as explained in FIG. 2, the actual injection amount (solid line) increases from the optimum amount (dashed line). However, according to this embodiment, in this case, the fuel pressure regulator 46 lowers the fuel pressure,
Decrease injection amount. That is, as the throttle valve opening θ decreases, the intake pipe negative pressure Q decreases, and accordingly, the diaphragm 48, 50 compresses the spring 62, and the diaphragm 50 separates from the nozzle 64. Therefore, the fuel in the fuel pressure chamber 58 flows back to the fuel tank 40 from this nozzle 64,
The fuel pressure applied to the injection valve 44 decreases. As a result, the injection amount will decrease.

In general, the intake pipe negative pressure Q changes as shown in FIG. 3, whereas the control characteristic of the injection amount M to be determined is shown by the broken line in FIG. Furthermore, the relationship between the injection amount M and the fuel pressure A is MCCA+/2. Therefore, since the fuel pressure is lowered at low load and high speed times when the negative pressure Q increases, the injection amount decreases accordingly.

Here, the regulator 46 uses diaphragms 48 and 50 with two different diameters, which utilize fuel pressure to operate correctly even with a small intake pipe negative pressure Q, and to adjust the intake pipe negative pressure Q and injection amount M. This is to obtain desirable control characteristics. That is, by applying fuel pressure to the diaphragm 50 on the fuel pressure chamber 58 side, a force in the direction of compressing the spring 62 is applied to the diaphragm 48 on the intake negative pressure chamber 54 side.

As a result, the pressure conversion ratio between fuel pressure and intake pipe negative pressure can be changed by changing the area ratio of both diaphragms 48.50,
It becomes possible to respond to a small intake pipe negative pressure Q.

Note that the fuel pressure regulator of the present invention is not limited to the one in this embodiment, but may be one that uses a single diaphragm, one that has a return spring with non-linear characteristics, or one that uses a diaphragm. Instead, the intake negative pressure Q may be converted into an electrical signal, and the electrical signal may be used to open and close a solenoid valve to control the fuel pressure.

Furthermore, in this embodiment, the negative pressure in the intake pipe 26 (intake pipe negative pressure Q
), but it is also possible to use a negative pressure equivalent to this, such as the crank chamber pressure P, the internal pressure of the scavenging passage 38, etc., and the present invention encompasses such a negative pressure.

Furthermore, in Japanese Patent Application No. 63-161019, the applicant of the present application detects the throttle valve opening and intake pipe negative pressure, determines the optimum injection amount for these using a microcombuque, and calculates the injection time for this optimum injection amount. , proposed one that opens and closes the injection valve. By applying the present invention to this existing proposal, it is possible to configure the fuel injection amount to be controlled by lowering the fuel pressure in a high-speed region exceeding the limit of the opening/closing response of the injection valve. Contain things.

(Effects of the Invention) As described above, the present invention uses intake negative pressure to correct the fuel pressure guided to the injection valve when determining the fuel injection amount based on the crank chamber pressure fluctuation. from,
The optimal fuel injection amount can always be determined in response to engine operating conditions, improving engine operating performance and fuel efficiency. In addition, if the negative pressure in the intake pipe and the fuel pressure are applied to two diaphragms with different diameters, and the fuel pressure adjustment nozzle is opened and closed by these diaphragms, the conversion pressure ratio of both positive forces can be adjusted by the diameter ratio of both diaphragms. In other words, it becomes possible to obtain optimal control characteristics with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is an overall system diagram of an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the injection amount M with respect to the rotational speed N, and FIG. 3 is a diagram showing changes in the intake pipe negative pressure Q. 44...Engine, 44...Fuel injection valve. 46...Fuel pressure regulator, 48.50...Diaphragm, 52...Pipe as negative pressure detection means, 54...Intake negative pressure chamber, 56...Atmospheric pressure chamber, 58...Fuel pressure chamber , 64...Fuel pressure adjustment nozzle. Patent applicant Yamaha Motor Co., Ltd.

Claims (2)

[Claims] (1) In a crank chamber pre-pressure type two-stroke engine that detects the crank chamber pressure and determines the fuel injection amount based on the amount of pressure fluctuation, there is a negative pressure detection means for detecting intake negative pressure and supplying it to the fuel injection valve. 1. A fuel injection device for a two-stroke engine, comprising: a fuel pressure regulator for controlling fuel pressure, wherein the fuel pressure regulator corrects the fuel injection amount by lowering the fuel pressure in response to an increase in intake negative pressure. (2) The fuel pressure regulator includes a first diaphragm that partitions an intake negative pressure chamber and an atmospheric pressure chamber, and a second diaphragm that partitions the atmospheric pressure chamber and the fuel pressure chamber, and is interlocked with both diaphragms that are connected to each other. 2. The fuel injection system for a two-stroke engine according to claim 1, wherein the flapper facing the fuel pressure adjustment nozzle.