JPH0643823B2 - Fuel pressure control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel pressure control device for a fuel injection engine, and more particularly to a fuel pressure control device with improved startability during hot start.

2. Description of the Related Art In an electronically controlled fuel injection engine, a pressure regulator is provided to adjust the pressure of fuel sent to a fuel injection valve by a fuel pump, and this pressure regulator has a built-in spring load and intake air. By using the pipe negative pressure, when the supplied fuel pressure becomes high, a part of the fuel is returned to the fuel tank side, whereby the supplied fuel pressure is adjusted and the differential pressure from the intake pipe negative pressure is kept constant. It is generally designed to keep the value.

As described above, the normal pressure regulator uses the intake pipe negative pressure as a control parameter.Therefore, when the intake pipe negative pressure sharply rises at the same time when the engine starts, the pressure regulator operates to return the fuel to the fuel tank. As a result, the fuel pressure in the fuel passage sharply drops. Therefore, when starting at a high engine temperature, such as during hot restart after high-speed traveling, there is a problem that vapor may be generated in the fuel passage due to the rapid decrease in the fuel pressure, causing vapor lock. .

In order to solve this problem
According to the publication, a hot start sensor is constituted by a cooling water temperature sensor or an engine atmosphere temperature sensor and an AND circuit of a timer that holds a starter signal for a predetermined time, and the operation of the pressure regulator is released for a predetermined time determined by the hot start timer. A fuel pressure control device that controls so as to increase the fuel pressure in the fuel supply system has been proposed.

Problems to be Solved by the Invention However, the fuel pressure control device described in the above-mentioned publication has the following problems. In other words, the deactivation time of the pressure regulator is uniformly set by the timer.If this time is too long, if the vapor in the fuel supply pipe disappears after the hot start and the operating state of the engine becomes normal. In addition, the operation of the pressure regulator is released, and the air-fuel ratio becomes overrich, resulting in deterioration of fuel consumption and / or emission.

On the contrary, if the holding time set by the timer is too short, the time during which the pressure regulator is deactivated will be too short, and vapor will be generated in the fuel supply pipe and the idle will become unstable. Engine stall may occur.

As described above, in the fuel pressure control device described in the above-mentioned publication, it is very difficult to determine the optimum release time of the pressure regulator, and it is not possible to sufficiently cope with the ever-changing operating state of the engine. was there.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a fuel pressure control device that controls the release time of the pressure regulator according to the amount of vapor generated in the fuel supply pipe.

Means for Solving the Problems In order to solve the above-mentioned problems of the prior art, the present invention relates to a pressure regulator that controls the fuel injection pressure of a fuel injection valve according to the intake pipe pressure, and an intake air to the pressure regulator. A switching valve provided in a passage for guiding the pipe pressure, and the fuel injection pressure of the fuel injection valve is increased by activating the switching valve at the time of high temperature start to release the operation of the pressure regulator. In the configured fuel pressure control device, the cooling water temperature detecting means and the intake air temperature detecting means detect the cooling water temperature and the intake air temperature, and when the starting time detecting means detects the engine start time, the cooling water temperature and the intake air temperature are equal to or higher than a predetermined temperature. In this case, from the fuel pressure control starting means for activating the switching valve to release the operation of the pressure regulator, and the specific component concentration in the exhaust gas, An air-fuel ratio sensor that detects the air-fuel ratio, an air-fuel ratio feedback correction coefficient setting means that sets an air-fuel ratio feedback correction coefficient based on the output of the air-fuel ratio sensor, and determines whether the air-fuel ratio feedback correction coefficient is less than a predetermined value. And a fuel pressure control ending unit for reactivating the pressure regulator by turning off the switching valve when the air-fuel ratio feedback correction coefficient is determined to be less than a predetermined value by the determining unit. A fuel pressure control device is provided.

During normal operation, the intake pipe negative pressure is guided to the pressure regulator via the switching valve, and the fuel injection pressure of the fuel injection valve is controlled according to the intake pipe negative pressure so that the differential pressure from the intake pipe negative pressure is constantly maintained. The fuel pressure is controlled so as to reach a predetermined pressure. When restarting after high-speed and high-load operation, vapor is generated in the fuel supply pipe, the air-fuel ratio becomes over lean, and idle rotation becomes unstable.

Therefore, the present invention detects the cooling water temperature and the intake air temperature by the cooling water temperature detecting means and the intake air temperature detecting means, and detects the fuel pressure when the cooling water temperature and the intake air temperature are equal to or higher than a predetermined value when the engine starting time is detected by the starting time detecting means. The control start means introduces atmospheric pressure into the pressure regulator through the switching valve to release its operation, increase the fuel injection pressure of the fuel injection valve, and prevent instability of idle due to vapor generation.

When the high-temperature restart fuel pressure control is started, the air-fuel ratio is still lean, so it is necessary to increase the fuel injection amount by feedback control, and the air-fuel ratio feedback correction coefficient is set to a large value. If the fuel pressure control is continued, the lean degree of the air-fuel ratio becomes smaller, and the air-fuel ratio feedback correction coefficient also becomes gradually smaller. According to the present invention, when the air-fuel ratio feedback correction coefficient becomes less than the predetermined value, the fuel pressure control at the time of high temperature restart is controlled. That is, the present invention focuses on the point that the base air-fuel ratio becomes rich because the fuel injection pressure is controlled to be higher than normal when the normal state is restored without the occurrence of vapor or the like during the fuel pressure control, and the air-fuel ratio feedback When the correction coefficient is less than the predetermined value, the fuel pressure control at the time of high temperature restart is configured to end,
The optimum fuel pressure control is always achieved according to the engine condition.

Embodiment An embodiment of the present invention will be described with reference to the drawings.

FIG. 2 shows an example of a schematic configuration of an internal combustion engine to which the fuel pressure control device of the present invention is applied.

In the figure, 1 is an internal combustion engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is a spark plug, 7 is an intake valve, 8 is an exhaust valve, and 9 is an exhaust manifold 10. An oxygen sensor for detecting the oxygen concentration in the exhaust gas, 15 is a water temperature sensor for measuring the cooling water temperature, 16
Is an ignition switch, and 21 is a battery power source.

In the intake system, the intake amount of intake air taken in from the air cleaner 24 is measured by the air flow meter 25, the intake temperature is measured by the intake temperature sensor 26, and the intake is performed by the throttle valve 28 that opens and closes according to the stroke of the accelerator pedal 27. A predetermined amount of air is sent to the intake manifold 30. The throttle body 31 is provided with a throttle sensor 32 for detecting the opening degree and the fully closed position of the throttle valve 28 interposed therein.

In the fuel system, a fuel injection valve 38 for injecting and supplying a predetermined amount of fuel pumped by a fuel pump 37 from a fuel tank 35 through a passage 36 is attached near the intake valve 7 and is applied to the fuel injection valve 38. The fuel pressure is adjusted by the pressure regulator 39. That is, during normal operation, the negative pressure switching valve (VSV) 45 introduces an intake pipe negative pressure into the diaphragm chamber of the pressure regulator 39 so that the fuel pressure applied to the fuel injection valve 38 is always higher than the intake pipe pressure by a predetermined value, for example, 2.55 kg / cm 2. It is set to be higher by ² , and excess fuel is returned to the fuel tank 35 through the passage 46. At the time of high temperature starting, the negative pressure switching valve (VSV) 45 introduces atmospheric pressure into the diaphragm chamber of the pressure regulator 39 to increase the fuel pressure applied to the fuel injection valve 38 regardless of the intake pipe pressure, thereby increasing the temperature at the time of high temperature starting. The startability is being improved.

Then, in the ignition system, the high voltage generated in the ignition coil 40 is supplied to the distributor 41, and the high voltage is distributed and supplied to the ignition plugs 6 of the respective cylinders at a predetermined timing while performing a predetermined ignition timing control by the distributor 41. I am trying to do it. The distributor 41 is provided with a rotation speed sensor 43 that detects a rotation angle and a rotation speed from a rotation position of a distributor shaft 42 that rotates in synchronization with a crankshaft (not shown). The sensor 43 outputs a pulse signal 24 times for every two rotations of the crankshaft, and outputs a pulse signal once at a predetermined angle for each rotation of the crankshaft.

Further, in the exhaust passage 47 on the downstream side of the oxygen sensor 9, a three-way catalytic converter 48 for simultaneously purifying three harmful components HC, CO, and NO _x in the exhaust gas is provided.

The control device 50 is, for example, a microcomputer operated by a battery power source 21, and in the microcomputer, as shown in FIG. 3, a central processing unit (CPU) 51 and a read only memory (ROM) 52 are provided.
A random access memory (RAM) 53, and a backup random access memory (RAM) 54 that retains memory even when the ignition switch 16 is off. Of these, the ROM 52 stores programs such as a main routine, a fuel injection amount control routine, an ignition timing control routine, and various fixed data and constants necessary for these processes. Further, in the microcomputer, an A / D converter 55 having a multiplexer
And an I / O device 56 having a buffer memory are incorporated, and these 55 and 56 are connected to each other by 51 to 54 and a common bus 57.

In the A / D converter 55, the output signals of each sensor such as the air flow meter 25 and the intake air temperature sensor 26 are input to the multiplexer via the buffer, and these data are input to the A / D converter.
Converted and instructed by the CPU 51, the CPU 5 at a predetermined time
1 and the RAM 53 or 54. As a result, the latest detection data such as the intake air amount, the intake air temperature, the water temperature, etc. are fetched into the RAM 53, and these data are stored in the predetermined area. Further, in the I / O device 56, detection signals of the sensors such as the throttle sensor 32 and the rotation speed sensor 43 are input, and these data are output to the CPU 51 and the RAM 53 or 54 at a predetermined time according to a command from the CPU 51. ing.

The CPU 51 calculates the fuel injection amount based on the data detected by each of the sensors according to the program stored in the ROM 52, and outputs the pulse signal based on the calculated fuel injection amount to the I / O.
Output to the fuel injection valve 38 via the device 56. That is,
Basically, the basic fuel amount is calculated from the intake air amount detected by the air flow meter 25 and the engine speed detected by the rotation speed sensor 43, and this is corrected according to the detected intake air temperature and cooling water temperature. A pulse signal corresponding to the amount is sent from the drive circuit (not shown) in the I / O device 56 to the fuel injection valve 38.

That is, the fuel injection amount TAU is determined based on the equation TAU = TP × FAF × K + TV. Where TP is the intake air amount Q
/ Basic injection amount determined from the engine speed N, FAF is an air-fuel ratio feedback correction coefficient determined based on the output of the oxygen sensor 9, K is another correction coefficient, and TV is an invalid injection time due to the operation delay of the fuel injection valve. is there.

Next, one embodiment of the fuel pressure control system of the present invention will be described in detail with reference to the flowchart of FIG.

The flow chart of FIG. 4 is a flow chart showing the operation of one embodiment of the fuel pressure control system of the present invention. First, at step 101, it is judged if the engine is in a starting state, that is, if the starter is on, and it is turned on. In this case, the routine proceeds to step 102, where it is determined whether the engine cooling water temperature THW detected by the water temperature sensor 15 is a predetermined value or more, for example, 95 ° C. or more in the present embodiment. When the cooling water temperature is 95 ° C. or higher, the routine proceeds to step 103, where the intake air temperature sensor 26
Whether the intake air temperature THA detected by
For example, it is determined whether the temperature is 60 ° C. or higher. When the intake air temperature is 60 ° C. or higher, the routine proceeds to step 104, where the negative pressure switching valve VSV
Is turned on to introduce atmospheric pressure into the diaphragm chamber of the pressure regulator to execute fuel pressure control during hot start, and to increase fuel pressure to prevent over lean of the air-fuel ratio at hot start due to vapor generation. .

Next, the routine proceeds to step 105, where it is judged if the air-fuel ratio feedback correction coefficient FAF is 0.85 or more. In a device that executes feedback control of the air-fuel ratio using the output voltage of the oxygen sensor using a three-way catalytic converter as in this embodiment, for example, the feedback width is set to ± 20%, so air-fuel ratio feedback correction is performed. The coefficient is 1.
It varies from 0.8 to 1.2 centered on 0. At the time of high temperature restart, the air-fuel ratio is usually over lean due to the generation of vapor in the fuel supply pipe, etc., so it is necessary to increase the fuel injection amount by feedback control.
The air-fuel ratio feedback correction coefficient FAF is normally set to the upper limit value of 1.20. Therefore, the air-fuel ratio feedback correction coefficient FAF is 0.8 for a while after the high temperature restart.
Since the state of 5 or more continues, the routine proceeds to step 106, where a set value, for example, 100 (corresponding to 2 seconds) is set in the counter CFAF of the air-fuel ratio feedback correction coefficient.

This routine is a fixed time routine that is repeated every 20 ms, for example, and executes the processing of this routine every 20 ms.
During that time, the air-fuel ratio gradually becomes rich due to the fuel pressure control. Therefore, the air-fuel ratio feedback correction coefficient FAF becomes less than 0.85 after a certain time has elapsed after the start of the fuel pressure control.

In this way, when the air-fuel ratio feedback correction coefficient FAF becomes less than 0.85 in step 105, the routine proceeds to step 107, where the counter value CFAF of the air-fuel ratio feedback correction coefficient is decremented by one, for example. Next, the routine proceeds to step 108, where it is judged if the counter value CFAF of the air-fuel ratio feedback correction coefficient is zero. Initially, the counter value is decremented from 100, so step 108 is a negative judgment, and this processing routine is once ended.

However, this processing routine is, for example, 20 ms as described above.
Since it is repeated every time, after the counter value CFAF of the air-fuel ratio feedback correction coefficient is set to 100 in step 106, the counter value CFAF in step 108 becomes zero when about 2 seconds have elapsed. In this case, the routine proceeds to step 109, where the negative pressure switching valve VSV is turned off, the intake pipe pressure is introduced into the diaphragm chamber of the pressure regulator to restart the operation of the pressure regulator, and the fuel pressure applied to the fuel injection valve 38 is reduced. The intake pipe pressure is controlled according to fluctuations so that the differential pressure is always a constant value.

That is, in this embodiment, the negative pressure switching valve VSV is turned off at step 109 about 2 seconds after the air-fuel ratio feedback correction coefficient FAF becomes less than 0.85 because the air-fuel ratio feedback correction coefficient FAF is 0. This is because it is determined that it is certainly lower than 85.

The embodiment described in FIG. 4 will be described in more detail with reference to the time chart in FIG. When the fuel pressure control at the time of high temperature restart is executed, the air-fuel ratio is over lean, so that the fuel injection amount is controlled by feedback control so as to increase. As described above, the air-fuel ratio feedback correction coefficient FA
Since F is set so as to fluctuate within a range of 0.8 to 1.2 around 1.0, the state where the air-fuel ratio feedback correction coefficient FAF remains 1.20 for a certain time continues. When time elapses and becomes t ₁ , the lean degree of the air-fuel ratio becomes small and the air-fuel ratio feedback correction coefficient FAF becomes the control region within the feedback width, and gradually becomes smaller and approaches 1.0.

When the time t ₂ has elapsed, the air-fuel ratio feedback correction coefficient FAF becomes 1.0. Since the fuel injection pressure of the fuel injection valve is set higher than that in the normal state by the fuel pressure control to make the base air-fuel ratio rich, the fuel injection amount is reduced from this point. At time t ₃ , the air-fuel ratio feedback correction coefficient FAF becomes about 0.85, and the amount of increasing fuel by the fuel pressure control is almost corrected. Therefore,
Since it is considered that there will be no problem if the fuel pressure control is stopped when the air-fuel ratio feedback correction coefficient FAF reaches 0.85, FAF = 0.85 is adopted as the determination reference value in this embodiment.

In the present embodiment, further, Δ from time t _{3 to} t _4.
Although the fuel pressure control is continued for t (2 seconds), this is to reliably determine that the air-fuel ratio feedback correction coefficient FAF is less than 0.85. In this way, when the FAF continuously reaches t ₄ which is less than 0.85 for Δt seconds, the fuel pressure control is stopped. At this point in time, the generation of vapor in the fuel supply pipe has been completely eliminated, so if the fuel pressure control is stopped and fuel injection is executed at normal fuel injection pressure, the air-fuel ratio feedback correction coefficient FAF will be around 1.0. It becomes a value.

As described in detail above, the present invention is configured to determine the end time of the fuel pressure control at the time of high temperature restart by the air-fuel ratio feedback correction coefficient, so that at the time of high temperature restart, the optimum time fuel increase is always achieved. In addition, it is possible to reliably prevent the unstable state of the idle due to over lean, and to effectively prevent the deterioration of fuel consumption and / or the deterioration of emission due to overrich.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a fuel pressure control device of the present invention, FIG. 2 is an overall schematic configuration diagram of an engine to which the fuel pressure control device of the present invention is applicable, and FIG. 3 is a control circuit composed of a microcomputer. FIG. 4 is a block diagram showing an example, FIG. 4 is a flow chart showing the operation of one embodiment of the fuel pressure control system of the present invention, and FIG. 5 is its time chart. 1 ... Internal combustion engine body, 6 ... Spark plug, 9 ... Oxygen sensor (air-fuel ratio sensor), 15 ... Water temperature sensor, 21 ... Battery power supply, 28 ... Throttle valve, 38 ... Fuel injection valve, 39 ...... Pressure regulator, 45 …… Negative pressure switching valve (VSV), 48 …… Three-way catalytic converter, 50 …… Control device.

Claims (1)

[Claims] 1. A pressure regulator for controlling a fuel injection pressure of a fuel injection valve according to an intake pipe pressure, and a switching valve provided in a passage for guiding the intake pipe pressure to the pressure regulator. In a fuel pressure control device configured to increase the fuel injection pressure of the fuel injection valve by operating the switching valve and releasing the operation of the pressure regulator, a cooling water temperature is detected by a cooling water temperature detecting means and an intake air temperature detecting means. And the intake air temperature is detected, and when the engine start time is detected by the start time detection means, if the cooling water temperature and the intake air temperature are equal to or higher than a predetermined temperature, the switching valve is operated to release the operation of the pressure regulator. Means, an air-fuel ratio sensor for detecting the air-fuel ratio from the concentration of a specific component in the exhaust gas, and an air-fuel ratio sensor based on the output of the air-fuel ratio sensor. Air-fuel ratio feedback correction coefficient setting means for setting the feedback correction coefficient, determination means for determining whether the air-fuel ratio feedback correction coefficient is less than a predetermined value, and the determination means determines the air-fuel ratio feedback correction coefficient is less than the predetermined value. And a fuel pressure control ending means for turning off the switching valve and reactivating the pressure regulator.