EP0280188B1 - Control device for a diesel engine - Google Patents

Description

The invention relates to a control device of a diesel internal combustion engine with an air intake line, at least one fuel injection pump and an exhaust line, and with a device for stopping the internal combustion engine.

There are a large number of devices with which the internal combustion engine is stopped, for example by interrupting the fuel supply, when a permissible maximum speed is reached. However, these devices are not able to switch off the internal combustion engine if the amount of fuel suddenly increases below the maximum engine speed without user intervention, which is the case in mechanical fuel injection systems, for example due to a defect in the controller (spring break etc.) or in electronic injection systems by the Failure of one or more electronic components can be caused. If such an internal combustion engine is installed as a drive machine in a motor vehicle, such an abrupt increase in speed and the acceleration of the vehicle caused thereby can lead to incorrect reactions.

From JP-A-61-55334 a regulator for the air-fuel ratio of an internal combustion engine is known, in which misfire and damage to a catalytic converter are to be prevented by the fact that when the engine speed is above a predetermined value and the throttle valve is not fully closed and a rich air-fuel ratio is displayed beyond a predetermined value or period of time, the fuel supply is cut or cut. Thereby When driving downhill, a rich mixture and misfiring caused by this should be avoided. A limitation of the speed of the internal combustion engine is not achieved, since the speed in push mode is determined by the driving speed.

EP-A-152870 describes a method for regenerating the exhaust gas particle filter in an internal combustion engine with a throttle valve, the throttle valve being controlled, inter alia, as a function of the oxygen concentration in the exhaust gas, on the one hand to reduce the air supply when the temperature of the particle filter rises dangerously, and on the other hand heat up the particle filter at the oxygen limit and then apply a high proportion of oxygen to it. The internal combustion engine can be a diesel internal combustion engine in which the oxygen content in the exhaust gas is measured continuously. A limitation of the speed of the internal combustion engine is not intended here.

The invention has for its object to provide a control device for a diesel internal combustion engine with which the unintentional injection of a fuel excess is determined in a simple manner and in this case the internal combustion engine is stopped.

According to a first proposal of the invention, this object is achieved by a λ-lean probe in the exhaust pipe and a comparison electronics which compares the oxygen content in the exhaust gas determined by the λ-lean probe with a setpoint and at a certain amount greater than zero below this setpoint lying oxygen content activates the device for stopping the internal combustion engine, the comparison electronics containing a curve with speed-dependent λ setpoints and receiving a speed-dependent signal for determining the comparison setpoint, the setpoint curve decreasing towards the lowest speeds.

According to a second proposal of the invention, the object is achieved by a λ-lean probe in the exhaust pipe and a comparison electronics, which compares the oxygen content in the exhaust gas determined by the λ-lean probe with a target value and at a value below this by a certain amount greater than zero Setpoint lying oxygen content activates the device for stopping the internal combustion engine, wherein a timer is provided which is activated by closing the starter switch of the internal combustion engine and the device for stopping the internal combustion engine for a certain period after closing the starter switch out of operation.

The invention is based on the knowledge that when an excess amount of fuel is injected, as can occur with a faulty injection system, the air ratio λ in the exhaust gas is reduced almost suddenly. By using a known λ-lean probe (see, for example, DE-C-3305706), an air number in the exhaust gas which is above λ = 1 can also be determined. If the λ target value stored in the comparison electronics, which differs from engine to engine and can be, for example, λ = 1.5, is undershot, this is evidence that an excessive amount of fuel has been injected, and the comparison electronics activates it Device for stopping the internal combustion engine. However, since, in particular in diesel internal combustion engines for driving motor vehicles for starting, an additional quantity of fuel is injected, which leads to a corresponding reduction in the λ value in the exhaust gas, unintentional stopping of the internal combustion engine must be avoided. In the first proposal, this is achieved in that the comparison electronics contain a curve with speed-dependent λ setpoints, so that despite the injection of a fuel excess and the like, at the low starting speeds Reduction of the oxygen content in the exhaust gas does not stop the internal combustion engine. In the second proposal of the invention, the timing element activated when the internal combustion engine is started prevents the internal combustion engine from being stopped for a certain period of time after starting, even if the actual λ value falls below the permissible λ setpoint value, that is to say an excess fuel quantity is present.

In the simplest and preferred case, the device for stopping the internal combustion engine is an electromagnetic shut-off valve in the fuel line, which is normally present in every diesel fuel injection system and is used to suddenly cut off the fuel supply when the starter switch is switched off and to switch off the engine. In this case, only one switch in series with the starter switch needs to be provided in the circuit of the shut-off valve, which is excited by the comparative electronics and interrupts the circuit of the shut-off valve or connects it to ground. Alternatively, the device for stopping the internal combustion engine can be formed by a shut-off valve arranged in the exhaust line or in the intake line of the internal combustion engine.

Fig. 1

ein Schaltbild einer erfindungsgemäßen Steuereinrichtung,

Fig. 2

ein Diagramm der Luftzahl Lambda über der Drehzahl n, und

Fig. 3, 4 und 5

Abwandlungen des in Fig. 1 dargestellten Ausführungsbeispiels.

Some embodiments of the invention are described below with reference to the drawings. It shows:

Fig. 1

2 shows a circuit diagram of a control device according to the invention,

Fig. 2

a diagram of the air ratio lambda over the speed n, and

3, 4 and 5

Modifications of the embodiment shown in FIG. 1.

In FIG. 1, 1 designates a diesel internal combustion engine which has an air intake line 2, at least one fuel injection pump 3 and an exhaust line. The injection pump 3 receives the fuel from a fuel pump 5 from a container 6 and conveys it through an injection line 7 in a time-controlled and quantity-controlled manner to the injection valves (not shown) of the diesel internal combustion engine 1. An electromagnetic shut-off valve 8 is arranged in line 7, which is actuated by a spring 17 is brought into the open position. In the power supply line 9 to the winding 8a of the shut-off valve 8 there is a starter switch 10 which is closed during operation of the internal combustion engine and in the closed state connects the winding of the shut-off valve 8 to a voltage source 11, whereby the shut-off valve 8 is brought into its closed position.

A lambda lean probe 12 is arranged in the exhaust gas line 4, which determines the oxygen content in the exhaust gas and feeds a corresponding signal through a line 13 to a comparison electronics 14, in which the probe signal is compared with a lambda target value. If the lambda setpoint falls below, for example, 1.5 (by a certain amount), the comparison electronics 14 outputs an output signal to the winding 15a of a relay 15 via a line 14a, which is connected in series with the starter switch 10 in the circuit 9 of the shutoff valve 8 lies, whereby its contact tongue 16 is brought from the normal position shown to the dashed position 16a, in which the circuit 9 is interrupted or connected to ground. Then the shut-off valve 8 is closed by the spring 17 and thus causes the internal combustion engine 1 to stop immediately.

Since the diesel internal combustion engine is normally injected with an excessive fuel quantity during starting, which can lead to a lowering of the air ratio in the exhaust gas, and since the permissible lambda value can fluctuate over the rotational speed, it is expedient to have a curve in the comparison electronics 14 save with speed-dependent lambda setpoints. Such a curve is shown in FIG. 2. By supplying a speed-dependent signal to the comparison electronics 14, the latter can now determine the corresponding lambda target value for each speed and compare it with the signal of the lambda lean probe 12. To this A faulty shutdown of the internal combustion engine 1 is avoided.

In the modification according to FIG. 3, the diesel internal combustion engine 1 is not stopped by shutting off the fuel supply, but rather by shutting off the air supply by means of a butterfly valve 21 arranged in the intake line 2 and actuated by an electromagnet 20, the electromagnet 20 of which by the comparison electronics 14 in Closing sense is excited when the described conditions are met.

4, an electromagnetically actuated shut-off valve 22 is arranged in the exhaust line 4 of the diesel internal combustion engine 1, which in turn is closed by the comparative electronics 14 when the corresponding requirements are met, so that the internal combustion engine 1 immediately is stopped.

In the embodiment according to FIG. 1, the permissible lambda values are determined in the comparison electronics 14 as a function of the rotational speed in order to prevent the internal combustion engine from stopping during starting and the fuel excess quantity being injected in the process. 5, an electromagnetic switch 25 is provided for this purpose in the control line 14a from the comparison electronics 14 to the relay winding 15a, the switching element 26 of which is normally held in the closed position by a spring 27, but is brought into the open position for the starting process is so that despite the presence of a fuel excess, the relay 15 is not energized and the shut-off valve 8 remains closed. The switch 25 has a winding 28 on, in the power supply line 29 a timer 30 is arranged, which is activated when the starter switch 10 is closed and for a certain period after the start, for example 1 minute, maintains the power supply of the winding 28, so that the switching element 26 is in its open position Position is brought. After this period, the line 29 is interrupted by the timer 30 and the switching element 26 is brought into the closed position by the spring 27. Now the comparison electronics 14 can be effective again and de-energize the winding 8a of the shut-off valve 8 via the relay 15 when the lambda value drops below the certain amount, so that the shut-off valve 8 is brought into its open position by the spring 17 and the fuel supply to Internal combustion engine 1 is interrupted.

Claims (4)

1. Control device of a diesel internal combustion engine comprising an air intake pipe, at least one fuel injection pump and an exhaust pipe, and with a device for bringing the engine to a standstill, with a) a lambda lean probe (12) in the exhaust pipe (4) and b) an electronic comparator circuit (14) which compares the oxygen contents within the exhaust gas determined by the lamba lean probe with a nominal value and which activates the device (8, 21, 22) for bringing the engine (1) to a standstill if the oxygen contents is below said nominal value for a predetermined amount greater than 0, and whereby the electronic comparator circuit (14) comprises a curve of speed-dependent lambda nominal values and receives a speed dependent signal for determining the comperative nominal value, whereby the curve of nominal values falls towards lowest speeds.
2. Control device of a diesel internal combustion engine comprising an air intake pipe, at least one fuel injection pump and an exhaust pipe and with a device for bringing the engine to a standstill, with a) lamba lean probe (12) in the exhaust pipe (4) and b) an electronic comparator circuit (14) which compares the oxygen contents with in the exhaust gas determined by the lambda lean probe with a nominal value and which activates the device (8, 21, 22) for bringing the engine (1) to a standstill if the oxygen contents is below said nominate value for a certain amount greater than 0, and whereby a timer (30) is provided, which is activated by closing the starter switch (10) and which deactivates the device (8) for bringing the engine to a standstill for a certain period of time after closing the starter switch (10).
3. Control device according to claim 1 or 2, characterized in that the device for bringing the engine to a standstill comprises a shut-off flap (22) arranged in the exhaust gas pipe (4).
4. Control device according to claim 1 or 2, characterizd in that the device for bringing the engine to a standstill comprises a shut-off flap (21) arranged within the air intake pipe (2).

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