JPS6140935Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an exhaust gas recirculation (hereinafter referred to as EGR) control device that reduces smoke immediately after engine startup.

In order to reduce NOx emitted from meat-combustion engines, EGR devices are known that recirculate part of the exhaust gas into the intake air to suppress the maximum temperature of combustion, but because diesel engines do not have intake throttle valves, However, the pressure difference between the intake system and exhaust system was small, making it difficult to secure the required high EGR. Therefore, an EGR device as shown in Figure 1 was proposed (Nissan Motor Service Manual 1981.DATSUN.810.DIESEL).

An intake throttle valve 1 is provided in an intake pipe 8, and a servo diaphragm 2 is linked to the intake throttle valve 1 via a link.

A three-way solenoid valve 6 is disposed in the middle of the negative pressure passages 5a and 5b that lead negative pressure from the vacuum pump 4 to the diaphragm chamber 3, and is operated by an electric signal to selectively switch between negative pressure and atmospheric air. Ru.

On the other hand, an EGR tube (pipe) 9 for introducing exhaust gas from the exhaust pipe 7 to the downstream of the throttle valve 1 of the intake pipe 8
An EGR valve 10 is disposed midway between a and 9b. a negative pressure passage 12a that guides negative pressure from the vacuum pump 4 to the diaphragm chamber 11 of the EGR valve 10;
A three-way solenoid valve 13 is disposed in the middle of the valve 12b, which is operated by an electric signal and selectively switches between negative pressure and atmospheric pressure in the same manner as described above.

The three-way solenoid valves 6 and 13 receive signals from a lever opening sensor 14 and an engine speed sensor 15 of a fuel injection pump (not shown), and operate the intake throttle valve 1 and the EGR valve 10, respectively, according to the magnitude of the signals. A signal from a control circuit 16 that adjusts the opening and closing is input.

In other words, when the intake throttle valve 1 is throttled during low load, the intake negative pressure increases, and when the EGR valve 10 opens, the EGR
When the load is high, the intake throttle valve 1 is fully opened to relatively lower the intake negative pressure and the EGR rate is lowered, and if the intake throttle valve 1 is fully opened and the EGR valve 10 is closed, the EGR rate will increase. EGR can be stopped.

By the way, the control circuit 16 includes a cooling water temperature sensor 1.
7 is input, and is configured to output a signal to the three-way solenoid valves 6 and 13 so as not to perform EGR when the engine is at a low temperature and has not reached a predetermined warm-up state.

This is because if EGR is performed before warm-up, combustion will not proceed normally, HC and smoke emissions will increase, and stable operation will not be possible.

However, when starting the engine, a large amount of fuel required for starting is burned during the cranking, initial explosion, and complete explosion processes, and a large amount of smoke-containing exhaust gas is introduced into the EGR tube, exhaust pipe, and combustion chamber. This has led to problems such as accumulation of soot, clogging of fuel injection nozzles, and contamination of soot into lubricating oil.

However, such conventional EGR devices are configured so that when the engine is restarted in a warm state, EGR is performed at the same time as the engine is restarted, so the above problems are likely to occur when the engine is restarted. In addition, there are some models that stop EGR only during the period when the starter switch is closed (starter switch is closed), but in any case, the problem arises after the complete explosion. Since the soot is generated, even if you cut off EGR only while the starter is running,
The effect is very small.

Therefore, this idea was developed to ensure that the starting process and the predetermined time after starting, regardless of whether the engine is warmed up.
By configuring so that EGR does not occur,
The purpose is to prevent exhaust gas containing a large amount of soot from being recirculated to solve the above problem.

Hereinafter, embodiments of this invention will be described based on the drawings.

In FIG. 2, parts that are substantially the same as those in FIG. 1 will be described using the same reference numerals. A timer circuit 22 for stopping EGR for a predetermined period of time after engine startup receives a signal from the starter terminal 21 of the engine key switch 20 as a timing start signal. The timing end signal of the timer circuit 22 is sent to the relay 23.
The signal is output to the base of the power transistor 24 that drives the signal. Output signals to the three-way solenoid valves 6 and 13 of the control circuit 16 are input to terminals 23a and 23d of the relay 23, respectively. Also, the terminals 23b, 23e
are connected to the input terminals of three-way solenoid valves 6 and 13, respectively. Terminals 23c and 23f of the relay 23 are open terminals. Relay 23 is connected to terminal 2 in the energized state.
3a, 23c, and 23f, and terminals 23a, 23b, and 23d, 23e in a non-energized state.

The timer circuit 22 is specifically configured as shown in FIG. 3, for example. RL is a normally open relay connected to starter terminal 21, OP1 is a capacitor C and a resistor.
The operational amplifier _Tr1 , which compares the potential between _R4 and _R3 , is a transistor that becomes conductive when the output of the operational amplifier _OP1 reaches the saturation voltage.

Note that D ₁ to _{D 3} are diodes, and r ₁ to _{r 8} are resistances.

When the key switch 20 is turned to the starter terminal 21 position for cranking, the relay RL is energized and both ends of the capacitor C are short-circuited, and the capacitor C is discharged. When the engine starts, the starter terminal 21 is turned off, so the capacitor C
Both ends of are opened, and charging begins with current flowing through resistor _R2 . Output voltage of operational amplifier OP ₁
Vop ₁ rises according to this charging and diode D ₂
When the forward voltage reaches , the voltage changes to saturation voltage.

As a result, the transistor Tr ₁ , which had been non-conductive, becomes conductive, and the output Vout of the timer circuit 22, which is input to the transistor 24 as shown in FIG. The transistor 24 is turned on by outputting +V for a time equal to the charging time T, but after that,
Vout goes to zero, turning transistor 24 off. Note that the charging time T is determined by the values of resistors R ₂ , R ₃ , R ₄ and capacitor C, etc.

Next, the operation will be explained according to FIG. When the key switch 20 is turned to the starter terminal 21 position to start cracking, the timer circuit 2
The output of power transistor 24 is turned on, and the output of power transistor 24 is turned on.
becomes conductive, and the relay 23 is energized. Therefore, since the terminals 23a and 23c and 23d and 23f are connected, the three-way solenoid valves 6 and 13 are not energized regardless of the signal from the control circuit 16. This state continues for a period of time T determined by the timer circuit 22 during cranking and after starting. Therefore, during this time, the intake throttle valve 1 is fully open and the EGR valve 10 is fully open.
remains fully closed and EGR is held in a stopped state.

After the time T has elapsed, the output of the timer circuit 22 becomes zero, so the relay 23 becomes de-energized, and the terminals 23a and 23b and the terminals 23d and 23e
conducts. Thereafter, the energization state of the three-way solenoid valves 6 and 13 is determined based on the original control of the control circuit 16, and EGR is performed according to the operating state.

Note that if the above functions are configured as a centralized electronic control circuit such as a microcomputer, the timer circuit can omit additional components such as relays. In this case, it is possible to measure the time using an internal clock, or it is also possible to integrate the signals generated each time the engine makes one revolution and use the integrated signal instead of the clock. (However, this would mean having an engine in which EGR is not performed for a predetermined cumulative number of revolutions after starting.) As described above, according to this invention, regardless of whether or not the engine is warmed up after starting, it will take a predetermined period of time. Since EGR is not performed until after the engine starts, the smoke (soot) that is emitted in a particularly large amount immediately after the engine starts is reduced.
There is no flow back to the intake system, and it is possible to reduce the accumulation of soot in the intake pipe, etc., the clogging of fuel injection nozzles, and the mixing of soot into the lubricating oil.

In the above embodiment, since the starter switch is also used as a means for detecting starting, the configuration is simple, and since the timer circuit starts counting from the moment the starter is turned off, it is possible to appropriately determine the elapsed time after starting. This has the additional effect of being

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of a conventional EGR device, Figure 2
3 is a schematic diagram showing an embodiment of the present invention, FIG. 3 is a circuit diagram of a timer circuit, and FIG. 4 is an explanatory diagram of the operation of the timer circuit. 1... Intake throttle valve, 2... Servo timer flam, 6, B... Three-way solenoid valve, 7... Exhaust pipe, 8...
...Intake pipe, 10...EGR valve, 16...Control circuit, 20...Key switch, 22...Timer circuit, 23...Relay.

Claims (1)

[Scope of utility model registration request] A diesel engine is provided with an exhaust gas recirculation passage that short-circuits an intake pipe and an exhaust pipe, and an exhaust gas recirculation valve is interposed in the middle of the exhaust gas recirculation passage. An exhaust recirculation control device for a diesel engine, comprising: a timer circuit that keeps the exhaust recirculation valve closed until the time period elapses.