JPH04116243A - Control method for fuel injection device - Google Patents

Abstract

PURPOSE:To invariably maintain the fuel injection quantity at a desired value by opening a fuel injection valve in the succeeding compression stroke for the cumulative time in which the fuel injection quantity cumulative value calculated from the inner pressure of each cylinder and the fuel pressure reaches the target fuel injection quantity. CONSTITUTION:A pressure detector 8 detecting the cylinder inner pressure of a combustion chamber 11 and inputting the detected pressure to a control circuit 3 is provided on a cylinder head 1. The inner pressure of each cylinder is inputted at every preset time in the preceding compression stroke, and the fuel injection quantity at every preset time is calculated from the difference between the inner pressure of each cylinder and the fuel pressure. The time in which the cumulative value of the calculated fuel injection quantity reaches the target fuel injection quantity is accumulated, and a fuel injection valve 2 is opened for the accumulated time in the succeeding compression stroke. The desired target fuel injection quantity is realized even if the cylinder inner pressure is changed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a control method for a fuel injection device, and particularly to a control method that can reliably adjust the amount of fuel injected in a fuel injection device that performs direct cylinder injection. .

[Prior Art] Instead of supplying atomized fuel using a conventional vaporizer, fuel injection devices are often used in which an electromagnetic fuel injection valve directly supplies the necessary atomized fuel depending on the engine operating condition. Among these, the direct injection type, which has a fuel injection valve in the cylinder head and supplies atomized fuel directly into the engine combustion chamber, can reduce valve overlap to improve filling efficiency.
It is attracting attention because it can reduce emissions of unburned gas.

[Problems to be Solved by the Invention] Incidentally, the amount of fuel injected by an electromagnetic fuel injection valve is adjusted by expanding or contracting the valve opening time for fuel supplied at a constant pressure, regardless of the engine operating state. This is based on the premise that in conventional devices that inject fuel into the intake pipe, the difference between the fuel pressure and the internal pressure of the intake pipe does not vary significantly.

However, when direct injection is employed, the pressure inside the cylinder (in-cylinder pressure) changes significantly during the compression stroke that constitutes fuel injection, and the amount of change also varies depending on the operating state of the engine. Therefore, even if the valve opening time is the same, the difference between the fuel pressure and the cylinder pressure may vary greatly depending on the injection timing during the compression stroke and the engine operating state, and the desired fuel injection amount may not be obtained.

That is, the fuel injection amount q is expressed by the formula (■), and the valve opening time Δt
Even if q is kept constant, if the differential pressure between the fuel pressure Pf and the cylinder pressure Ps fluctuates, the fuel injection amount q will not be constant.

q=CA g γ・Pf−Ps)・Δt...■ Here, C: flow coefficient, A: valve opening area, g: gravitational acceleration, and γ: fuel specific gravity.

In addition, Fig. 5 shows an example of temporal changes in fuel pressure and in-cylinder pressure during the compression stroke before TDC (top dead center). It is known that the difference between

This problem arises because, for example, in the fuel injection device described in Japanese Patent Publication No. 1-51893, the injected fuel pressure is made as low as possible in order to reduce the size and weight of the fuel injection nozzle, and the fuel injection is performed when the fuel injection nozzle is close to the top dead center. (late injection).

Therefore, in order to solve this problem, we
Publication No. 79 proposes a device that controls the operation of a regulator to constantly change the injected fuel pressure to follow the in-cylinder pressure, but it is difficult to make the injected fuel pressure accurately follow rapid changes in the in-cylinder pressure. In addition, it is necessary to provide the regulator with a control section that uses an external signal, which inevitably increases costs.

The present invention solves this problem, and provides a method for controlling a fuel injection device that can constantly maintain the amount of injected fuel at a desired value in response to fluctuations in cylinder pressure, and does not cause a large increase in cost. The purpose is to

[Means for Solving the Problems] The present invention will be described in detail as a fuel injection system comprising a fuel injection valve that directly injects constant pressure fuel into an engine cylinder, and a pressure detector that detects the in-cylinder pressure of the engine cylinder. A control method of the device, in which cylinder pressure is input at predetermined time intervals in the preceding compression stroke, and the fuel injection amount is calculated for each predetermined time period from the difference between each cylinder pressure and fuel pressure, and the calculated fuel injection amount is The time required for the integrated value to reach the target fuel injection amount is integrated, and the fuel injection valve is opened for the integrated time in the subsequent compression stroke.

[Effect] The cylinder pressure fluctuates greatly during the compression stroke of the engine.

In this case, since the preceding and succeeding compression strokes appear at relatively short time intervals, the change in cylinder pressure detected at predetermined time intervals in the preceding compression stroke almost coincides with the change in cylinder pressure in the subsequent compression stroke.

Therefore, by calculating the difference between the constant fuel injection pressure and the in-cylinder pressure at each predetermined time period, the fuel injection amount for each predetermined time period is predicted and calculated using the formula 0 described above, and the cumulative value of this fuel injection amount is the target fuel. The cumulative time until the injection amount is reached is approximately equal to the time required for the target fuel injection amount of fuel to be actually injected.

Therefore, if the fuel injection valve is opened for the above cumulative time in the subsequent compression stroke, the desired target fuel injection amount can be achieved even if the cylinder pressure changes.

According to such a method, it is possible to always perform accurate fuel injection even if the in-cylinder pressure changes rapidly, and there is no need for external signal control of the regulator as in the conventional method.
It does not lead to an increase in costs.

[Example] FIG. 1 shows an example of an apparatus configuration for implementing the method of the present invention. The cylinder head 1 of the engine has a combustion chamber 11 at its tip.
An electromagnetic fuel injection valve (injector) 2 is provided, and the valve is opened at a predetermined timing for a predetermined time by a valve opening pulse signal from a control circuit 3 containing a microcomputer, and fuel is directly injected into the combustion chamber 11. Inject.

Fuel to the injector 2 is supplied from the fuel tank 5 to the regulator 6 and the common rail piping 7 by the fuel pump 4.
is supplied at a constant pressure. The cylinder head 1 is also provided with a pressure detector 8 for detecting the cylinder pressure in the combustion chamber 11, and the detected pressure is input to the control circuit 3.

In the figure, 12 is a piston, and 13 is a spark plug.

The operation of the control circuit will be explained using the flowchart of FIG. 2 with reference to FIG. 3. In step 101, from the start of injection in the preceding compression stroke, the cylinder pressures PcO, Pc1, . . .
, Pcn are read at every fixed time Δ, initial settings are made in step 102, and then the fuel injection amount Δq is calculated every fixed time (step 103). This calculation is based on the fuel pressure Pf
The above cylinder pressures read as PcO, Pcl,...
The difference from Pcn is taken and the equation 0 described above is used.

In step 104, the calculated fuel injection amount for each fixed period of time is integrated, and the integrated time T up to that point is calculated. In step 105, it is checked whether the cumulative value q of the fuel injection amount has reached the target fuel injection amount, and if it has, the valve opening time Ti is set as the cumulative time T at this time plus the invalid injection time TV. Step 106, FIG. 4), the time taken Ti
A valve-opening pulse that lasts for 20 seconds is output in the subsequent compression stroke. As a result, fuel is injected during the time Ti, and the target fuel amount is accurately injected regardless of changes in the cylinder pressure.

[Effects of the Invention] As described above, according to the control method for a fuel injection device of the present invention, it is possible to directly inject fuel by the target fuel injection amount accurately in the compression stroke where the in-cylinder pressure changes greatly, and the engine It is possible to improve exhaust emissions while maintaining good operation.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of an apparatus for carrying out the method of the present invention, Fig. 2 is a flowchart of the control circuit, Fig. 3 is a graph showing changes in cylinder pressure, and Fig. 4 is a graph showing the cumulative fuel value and valve opening time. The graph showing the relationship, FIG. 5, is a time chart. 1... Cylinder head 11... Combustion chamber 2... Electromagnetic fuel injection valve 3... Control circuit 4... Fuel pump 6... Regulator 7... Common rail vibe 8... Pressure detector Figure 3 Figure 4 Figure 5 DC Valve opening pulse i -11-1-111

Claims (1)

[Claims] A method for controlling a fuel injection device comprising a fuel injection valve that directly injects constant pressure fuel into an engine cylinder, and a pressure detector that detects the in-cylinder pressure of the engine cylinder, the method comprising: controlling the in-cylinder pressure for a predetermined period of time in a preceding compression stroke; calculate the fuel injection amount for each predetermined time from the difference between each cylinder pressure and fuel pressure,
A method of controlling a fuel injection device, characterized in that the time required for the calculated cumulative amount of fuel injection amount to reach the target fuel injection amount is integrated, and the fuel injection valve is opened in the subsequent compression stroke for the cumulative amount of time. .