JP2013130158A - Fuel injection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection system that can generate a pseudo-signal fit for an output characteristic of an air-fuel ratio sensor by using an inexpensive processor.SOLUTION: The fuel injection system includes a liquid fuel injection control device for outputting a first driving signal, and a gas fuel injection control device for calculating a gas fuel injection amount, based on the first driving signal input from the liquid fuel injection control device, and for outputting a second driving signal, in response to a calculation result therein, to a gas fuel injection valve, the gas fuel injection control device includes, in the fuel injection system, the processor for outputting a pulse signal of a duty ratio in response to an output voltage of the air-fuel ratio sensor, and an output circuit for analog-outputting an average voltage of the pulse signals input from the processor as a pseudo-air-fuel ratio sensor output voltage to the liquid fuel injection control device and the processor, and the processor sets the duty ratio to make a difference between the pseudo-air-fuel ratio sensor output voltage input from the output circuit and the output voltage of the air-fuel sensor get small.

Description

 The present invention relates to a fuel injection system.

  Conventionally, as a technology for improving the fuel efficiency and environmental protection performance of a vehicle, there is a bi-fuel system that selectively switches between liquid fuel such as gasoline and gaseous fuel such as compressed natural gas (CNG) and supplies it to a single engine. Are known. This bi-fuel system is generally constructed by adding a new gas injection system to an existing gasoline injection system in order to reduce development costs (see Patent Document 1 below).

  In Patent Document 1 below, engine control information that is an output signal from an O2 sensor (air-fuel ratio sensor) provided in an exhaust pipe that is output from a gasoline control device to a non-gasoline fuel control device is used for non-gasoline fuel use. A technique is disclosed in which a signal is shaped by a predetermined waveform shaping means so as to be adapted to the control device and then input to the gasoline control device.

JP 2008-69637 A

  By the way, in the above-mentioned Patent Document 1, it is not specifically disclosed in what configuration the waveform shaping means is realized, but in general, in order to generate a pseudo signal of the air-fuel ratio sensor output, D / A conversion is performed. A method using a detector or a PWM output circuit is conceivable. However, a processor such as a microcomputer incorporating a high-accuracy D / A converter is expensive, and a processor that can output a PWM signal at various cycles according to the output characteristics of the air-fuel ratio sensor is also expensive.

 The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a fuel injection system capable of generating a pseudo signal suitable for the output characteristics of an air-fuel ratio sensor with an inexpensive processor.

 In order to achieve the above object, in the present invention, as a first solving means related to the fuel injection system, a liquid fuel injection amount is calculated based on an engine operating state, and a first drive signal corresponding to the calculation result is output. And a liquid fuel injection control device that calculates a gaseous fuel injection amount based on the first drive signal input from the liquid fuel injection control device, and a second drive signal corresponding to the calculation result is supplied to the gas fuel injection valve. In the fuel injection system comprising: a gaseous fuel injection control device that outputs a gas fuel injection control device, the processor that outputs a pulse signal having a duty ratio corresponding to the output voltage of the air-fuel ratio sensor; An output circuit that outputs an analog voltage of the pulse signal as a pseudo air-fuel ratio sensor output voltage to the liquid fuel injection control device and the processor; For example, the processor sets the duty ratio so that the difference is small between the output voltage of the pseudo-fuel ratio sensor output voltage and the air-fuel ratio sensor which is input from the output circuit, to employ a means of.

 In the present invention, as a second solving means relating to the fuel injection system, in the first solving means, the processor is configured to output the pseudo air-fuel ratio sensor output voltage inputted from the output circuit and the air-fuel ratio sensor. When the difference from the output voltage exceeds a specified value, a means is adopted in which the duty ratio is set to an upper limit value or a lower limit value.

 According to the present invention, the gaseous fuel injection control device generates a pseudo signal (pseudo air-fuel ratio sensor output voltage) suitable for the output characteristics of the air-fuel ratio sensor with an inexpensive processor and outputs the pseudo signal to the gaseous fuel injection control device. It becomes possible.

It is a schematic structure figure of fuel injection system A concerning this embodiment. 5 is a timing chart (b) showing a configuration (a) provided for generating a pseudo O2 sensor output voltage by the 2nd-ECU 4 and an operation for generating the pseudo O2 sensor output voltage by the 2nd-ECU 4. It is a flowchart which shows the PWM output process which MCU4a of 2nd-ECU4 implements.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a fuel injection system A according to the present embodiment. The fuel injection system A is a bi-fuel system that selectively switches between liquid fuel (for example, gasoline) and gaseous fuel (for example, compressed natural gas) and supplies it to a single engine (not shown). And a gaseous fuel supply system 2, a 1st-ECU (Electronic Control Unit) 3, a 2nd-ECU 4, and a fuel changeover switch 5.

 The liquid fuel supply system 1 includes a gasoline tank 11, a gasoline supply pipe 12, and a gasoline injector 13 (liquid fuel injection valve). The gasoline tank 11 is a corrosion-resistant container that stores gasoline as liquid fuel, and has a built-in pump and regulator (not shown) that sucks the gasoline and sends it to the gasoline supply pipe 12.

 The gasoline supply pipe 12 is a pipe for delivering gasoline from the gasoline tank 11 to the gasoline injector 13. The gasoline injector 13 is an electromagnetic valve (for example, a solenoid valve) mounted on the intake pipe so that the injection port is exposed toward the intake port of the engine, for example, and corresponds to a gasoline pulse signal input from the 2nd-ECU 4. A predetermined amount of gasoline is injected.

 The gaseous fuel supply system 2 includes a gas tank 21, a high pressure gas supply pipe 22, a shutoff valve 23, a regulator 24, a low pressure gas supply pipe 25, a gas injector 26 (gaseous fuel injection valve), and a low pressure side fuel pressure sensor 27. And a low-pressure side fuel temperature sensor 28.

 The gas tank 21 is a high pressure vessel filled with compressed natural gas (CNG) as gaseous fuel. The high-pressure gas supply pipe 22 is a high-pressure pipe for delivering high-pressure gas fuel from the gas tank 21 to the regulator 25. The shut-off valve 23 is an electromagnetic valve inserted in the middle of the high-pressure gas supply pipe 22 (position close to the gas tank 21), and opens or closes according to a shut-off valve drive signal input from the 2nd-ECU 4.

 The regulator 24 is a pressure reducing valve disposed on the downstream side of the shutoff valve 23, and decompresses the high pressure gas fuel supplied from the gas tank 21 to a desired pressure when the shutoff valve 23 is opened to the low pressure gas supply pipe 25. Send it out. The low-pressure gas supply pipe 25 is a low-pressure piping for delivering low-pressure gas fuel from the regulator 24 to the gas injector 26.

 The gas injector 26 is an electromagnetic valve attached to the intake pipe so that, for example, the injection port is exposed toward the intake port of the engine, and injects a predetermined amount of gas fuel according to a gas pulse signal input from the 2nd-ECU 4. To do. Thus, the high-pressure gas supply pipe 22 and the low-pressure gas supply pipe 25 correspond to a gaseous fuel supply path from the gas tank 21 to the gas injector 26.

 The low pressure side fuel pressure sensor 27 detects the low pressure side (downstream side) from the regulator 24, that is, the internal pressure (low pressure side fuel pressure) of the low pressure gas supply pipe 25, and outputs a low pressure side fuel pressure signal indicating the detection result to the 2nd-ECU 4. To do. The low-pressure side fuel temperature sensor 28 detects the internal temperature (low-pressure side fuel temperature) of the low-pressure gas supply pipe 25 and outputs a low-pressure side fuel temperature signal indicating the detection result to the 2nd-ECU 4.

 The 1st-ECU 3 (liquid fuel injection control device) is configured to inject a gasoline injection amount (liquid fuel) to be injected from the gasoline injector 13 to the engine based on various sensor signals input from various sensors (not shown) that detect the engine operating state. Injection amount) is calculated, and a gasoline pulse signal having a pulse width corresponding to the calculation result is output to the 2nd-ECU 4. Further, the 1st-ECU 3 is configured so that the air-fuel ratio becomes the target air-fuel ratio (theoretical air-fuel ratio or an air-fuel ratio appropriate for the engine operating state) based on the pseudo O2 sensor output voltage input from the 2nd-ECU 4. Air-fuel ratio feedback control is performed to correct the gasoline injection amount.

 The various sensor signals input to the 1st-ECU 3 include at least a crank pulse signal having a period during which the crankshaft rotates by a certain angle as one cycle, an intake air temperature signal indicating an intake air temperature, an intake air pressure signal indicating an intake air pressure, A throttle opening signal indicating the throttle opening, a cooling water temperature signal indicating the cooling water temperature, and the like are included.

 The 2nd-ECU 4 (gaseous fuel injection control device) includes a low pressure side fuel pressure signal input from the low pressure side fuel pressure sensor 27, a low pressure side fuel temperature signal input from the low pressure side fuel temperature sensor 28, and an O2 sensor (air-fuel ratio sensor). ) Output from the O2 sensor output voltage (voltage signal corresponding to the air-fuel ratio), a gasoline pulse signal input from the 1st-ECU 3, and a fuel switching signal input from the fuel switch 5 13. Energization control of the gas injector 26 and the shutoff valve 23 is performed.

 Specifically, when the 2nd-ECU 4 recognizes that gasoline is selected as the fuel to be used for engine operation based on the fuel switching signal input from the fuel switch 5 (that is, during gasoline operation), The gasoline pulse signal input from the 1st-ECU 3 is output to the gasoline injector 13 as it is.

 When the 2nd-ECU 4 recognizes that gas fuel is selected as the fuel to be used for engine operation based on the fuel switch signal input from the fuel switch 5 (that is, during gas operation), the shut-off valve 23 is opened to start the supply of gas fuel from the gas tank 21 to the gas injector 26, and the fuel should be injected from the gas injector 26 to the engine based on the gasoline pulse signal, the low pressure side fuel pressure signal and the low pressure side fuel temperature signal. A gas injection amount (gaseous fuel injection amount) is calculated, and a gas pulse signal having a pulse width corresponding to the calculation result is generated and output to the gas injector 26.

 Further, as shown in FIG. 2A, the 2nd-ECU 4 includes an MCU (Micro Control Unit) 4a and an output circuit 4b as a configuration for generating a pseudo O2 sensor output voltage to be output to the 1st-ECU 3. ing. The MCU 4a is a processor in which a CPU (Central Processing Unit) core, a memory, an input / output interface, and the like are integrated, and A / D-converts the O2 sensor output voltage input from the O2 sensor and reads it as a digital value. A pulse signal (PWM signal) with a duty ratio corresponding to the O2 sensor output voltage is output to the output circuit 4b.

 The output circuit 4b is an analog low-pass filter circuit, for example, and outputs the average voltage of the PWM signal input from the MCU 4a to the 1st-ECU 3 and the MCU 4a as a pseudo O2 sensor output voltage (pseudo air-fuel ratio sensor output voltage). The MCU 4a A / D converts the pseudo O2 sensor output voltage fed back from the output circuit 4b as a digital value, reads the pseudo O2 sensor output voltage, and the O2 sensor output voltage inputted from the O2 sensor. The function of setting the duty ratio of the PWM signal so that the difference between the two is small.

 The fuel change-over switch 5 is a switch that enables the fuel to be changed by a user's manual operation. Whether the liquid fuel is selected as the state of the switch, that is, the fuel used for engine operation, or the gaseous fuel is selected. A fuel switching signal indicating whether or not the fuel is being output is output to the 2nd-ECU 4.

Next, the operation of the fuel injection system A configured as described above will be described in detail.
<Gasoline pulse generation operation by 1st-ECU 3>
The 1st-ECU 3 should inject fuel into the engine at each fuel injection timing based on various sensor signals regardless of the state of the fuel switch 5 (that is, regardless of gasoline operation or gas operation) while the engine is operating. The gasoline injection amount (the energization time of the gasoline injector 13) is calculated, and a gasoline pulse signal having a pulse width corresponding to the calculation result is output to the 2nd-ECU 4.

 Specifically, the 1st-ECU 3 calculates the engine speed from the crank pulse signal, and calculates the gasoline injection amount based on the engine speed, the intake air temperature, the coolant temperature, the intake pressure, and the throttle opening. The 1st-ECU 3 also performs air-fuel ratio feedback control for correcting the gasoline injection amount so that the air-fuel ratio becomes the target air-fuel ratio based on the pseudo O2 sensor output voltage input from the 2nd-ECU 4.

 Here, in the air-fuel ratio feedback control, the 1st-ECU 3 associates the previously calculated air-fuel ratio feedback correction coefficient (coefficient for correcting the gasoline basic injection amount) with the engine operating state at that time in the internal memory in a timely manner. Remember and update. Thus, storing and updating the air-fuel ratio feedback correction coefficient calculated in the past in the memory in association with the engine operating state is called “learning”, and the air-fuel ratio feedback coefficient obtained by this “learning” is “learned”. Called “value”.

 That is, in the air-fuel ratio feedback control, the 1st-ECU 3 extracts a learning value corresponding to the current engine operating state from the learning values obtained by past learning, that is, an air-fuel ratio feedback correction coefficient, and the air-fuel ratio feedback. By multiplying the previously calculated gasoline injection amount by the correction coefficient, the gasoline injection amount to be finally injected into the engine is calculated.

<Generation Operation of Pseudo O2 Sensor Output Voltage by 2nd-ECU 4>
As described above, the pseudo O2 sensor output voltage is important engine information for the 1st-ECU 3 to perform air-fuel ratio feedback control. The 2nd-ECU 4 generates a pseudo O2 sensor output voltage by a process described below. First, the MCU 4a of the 2nd-ECU 4 generates the O2 sensor output voltage input from the O2 sensor and the pseudo O2 sensor output voltage input from the output circuit 4b at a constant cycle regardless of the state of the fuel changeover switch 5 during engine operation. Both voltages are monitored by A / D conversion and reading.

  As shown in FIG. 2B, the MCU 4a of the 2nd-ECU 4 uses the O2 sensor output voltage input from the O2 sensor as the output target voltage and the pseudo O2 sensor output voltage input from the output circuit 4b as the reference voltage. The duty ratio of the PWM signal is set so that the difference between the two voltages becomes small (for example, zero). The MCU 4a of the 2nd-ECU 4 outputs a PWM signal having the duty ratio set in this way to the output circuit 4b. As a result, the pseudo O2 sensor output voltage that matches the output target voltage (that is, the O2 sensor output voltage) is output from the output circuit 4b to the 1st-ECU 3.

  Here, for example, a case is assumed in which the difference between the output target voltage and the reference voltage is greatly changed due to factors such as fuel switching at time t1 shown in FIG. When the difference between the output target voltage and the reference voltage exceeds the specified value in this way, the MCU 4a of the 2nd-ECU 4 sets the PWM signal duty ratio to an upper limit value (for example, 100%) or a lower limit value (for example, 0%) for a certain period of time. ). FIG. 2B illustrates a case where the duty ratio of the PWM signal is set to the upper limit value.

  In this way, when the difference between the output target voltage and the reference voltage changes greatly due to factors such as fuel switching, the reference voltage (by setting the duty ratio of the PWM signal to the upper limit value or the lower limit value for a certain period of time is set. That is, the pseudo O2 sensor output voltage) can be quickly matched with the output target voltage (that is, the O2 sensor output voltage), and the response to the output change of the O2 sensor can be improved. Further, by reflecting the difference between the output target voltage and the reference voltage in the duty ratio of the next PWM signal, it becomes possible to cope with changes in the output characteristics of the O2 sensor due to temperature changes and hardware variations.

  FIG. 3 is a flowchart showing a PWM output process performed by the MCU 4a of the 2nd-ECU 4 in order to realize the feedback control of the pseudo O2 sensor output voltage as described above. The MCU 4a of the 2nd-ECU 4 repeatedly performs the PWM output process shown in FIG. 3 at a constant period regardless of the state of the fuel changeover switch 5 during engine operation.

  As shown in FIG. 3, when starting the current PWM output process, the MCU 4a of the 2nd-ECU 4 first reads a reference voltage (step S1), and from the read current reference voltage and the previous output target voltage, O2 An output correction coefficient for correcting an output characteristic deviation due to sensor hardware variation or aging deterioration is calculated (step S2).

  Subsequently, the MCU 4a of the 2nd-ECU 4 calculates the duty ratio (output duty) of the PWM signal from the difference between the current reference voltage and the current output target voltage (the O2 sensor output voltage read this time) (step S3). Then, the MCU 4a of the 2nd-ECU 4 outputs a PWM signal with a duty ratio of upper and lower limits from the difference between the current reference voltage and the current output target voltage in order to speed up the response to the output change of the O2 sensor. Time (upper and lower limit duty output count) is calculated (for example, map search) (step S4).

  Then, the MCU 4a of the 2nd-ECU 4 sets the upper and lower limit duty output count buffers calculated in step S4 with the upper and lower limit duty ratios, and sets the remaining buffers with the output duty calculated in step S3 ( Step S5). Then, the MCU 4a of the 2nd-ECU 4 updates the duty ratio of the PWM signal output to the output circuit 4b by reflecting the buffer value set in step S5 to the PWM output timer (step S6), and finally the output target. The previous voltage value is updated and the current PWM output process is terminated (step S7).

<Fuel Injection Operation by 2nd-ECU 4>
The 2nd-ECU 4 outputs the pseudo O2 sensor output voltage regardless of the state of the fuel changeover switch 5 as described above, while the fuel injection mode changes according to the state of the fuel changeover switch 5.

  That is, when the 2nd-ECU 4 recognizes that the gasoline operation is selected from the state of the fuel switch 5, the 2nd-ECU 4 enters the gasoline injection mode and outputs the gasoline pulse signal input from the 1st-ECU 3 to the gasoline injector 13 as it is. As a result, during gasoline operation, an amount of gasoline that is required for the current engine operating state and that is required to bring the air-fuel ratio to the target air-fuel ratio is supplied to the engine.

  On the other hand, when the 2nd-ECU 4 recognizes that the gas operation is selected from the state of the fuel changeover switch 5, the gas fuel injection mode is set, the shutoff valve 23 is opened, and the gas fuel from the gas tank 21 to the gas injector 26 is opened. Start supplying. Then, the 2nd-ECU 4 calculates the gasoline injection amount based on the gasoline pulse signal input from the 1st-ECU 3, and corrects the gasoline injection amount based on the low-pressure side fuel pressure and the low-pressure side fuel temperature. A gas injection amount required for the engine operating state is calculated.

  The 2nd-ECU 4 outputs a gas pulse signal having a pulse width corresponding to the calculation result of the gas injection amount to the gas injector 26. As a result, during gas operation, an amount of gas fuel required for the current engine operation state and the amount required to bring the air-fuel ratio to the target air-fuel ratio is supplied to the engine.

 As described above, according to the present embodiment, the 2nd-ECU 4 can generate a pseudo signal (pseudo O2 sensor output voltage) suitable for the output characteristics of the O2 sensor and output it to the 1st-ECU 3 with an inexpensive MCU 4a. It becomes possible.

  A ... Fuel injection system, 1 ... Liquid fuel supply system, 2 ... Gas fuel supply system, 3 ... 1st-ECU (Liquid fuel injection control device), 4 ... 2nd-ECU (Gas fuel injection control device), 4a ... MCU ( Processor), 4b ... output circuit, 5 ... fuel changeover switch, 13 ... gasoline injector (liquid fuel injection valve), 26 ... gas injector (gas fuel injection valve)

Claims (2)

A liquid fuel injection control device that calculates a liquid fuel injection amount based on an engine operating state and outputs a first drive signal according to the calculation result;
A gaseous fuel injection control device that calculates a gaseous fuel injection amount based on the first drive signal input from the liquid fuel injection control device and outputs a second drive signal corresponding to the calculation result to the gaseous fuel injection valve; In a fuel injection system comprising:
The gaseous fuel injection control device comprises:
A processor that outputs a pulse signal having a duty ratio corresponding to the output voltage of the air-fuel ratio sensor;
An output circuit for analogly outputting the average voltage of the pulse signal input from the processor as a pseudo air-fuel ratio sensor output voltage to the liquid fuel injection control device and the processor;
With
The fuel injection system, wherein the processor sets the duty ratio so that a difference between the pseudo air-fuel ratio sensor output voltage input from the output circuit and an output voltage of the air-fuel ratio sensor becomes small.   The processor sets the duty ratio to an upper limit value or a lower limit value when a difference between the pseudo air-fuel ratio sensor output voltage input from the output circuit and the output voltage of the air-fuel ratio sensor exceeds a specified value. The fuel injection system according to claim 1.

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