Device for Detecting Leakage in a Fuel Supply

The invention is based on a device for detecting a leak in a fuel supply system in an internal combustion engine.

In motor vehicles with an internal combustion engine the fuel is pumped out of the fuel tank by an electric fuel pump and carried via fuel lines to the injection valves. Excess fuel typically returns to the fuel tank via a return line. In engines with self-ignition, a further pump is connected to the electric fuel pump and generates a very high pressure in the region of the fuel supply that communicates with the injection valves.

In such fuel supply systems with the associated injection nozzles, there is the danger that if the valve of an injection nozzle seizes in the open position, fuel still be injected continuously into the associated combustion chamber. A leak to the outside is also possible. It has therefore been proposed for instance in German Patent DE 31 26 393 to provide means are provided which continuously measure the pressure in the high-pressure region of the fuel supply system. A drop in the pressure in the reservoir below a predetermined value leads to the detection of an error. Since in such a case fuel would be injected continuously into the engine, in the known apparatus once an error is detected the engine is shutoff or fuel pumping is terminated.

The device according to the invention having the characteristics of the main claim has the advantage over the known art that the entire high-pressure fuel supply system can be monitored for intactness. Also not only can it be detected whether an injection valve is continuously open, but a leak to the outside can also be detected. The simplicity of the device of the invention is especially advantageous.

This advantage is attained in that a pressure sensor that s pressure sensor that is present anyway in the high-pressure part of the fuel supply system, measures the fuel pressure continuously, and error detection is performed only whenever the engine control unit detects a predeterminable operating state, such as overrunning. After the detection of the overrunning, the overpressure valve disposed in the return part of the fuel supply system for regulation of, with the aid of which valve the fuel pressure, is the closed, and the resultant pressure and especially the resultant pressure change is compared with predeterminable values. An error detection is tripped if the measured pressure, or the measured pressure course, with the return valve closed does not behave as expected.

Once a leak is detected, the engine is advantageously shutoff, or the fuel supply is disrupted by turning off the high-pressure pump.

It is especially advantageous that such leak monitoring can be done whenever the control unit detects the pressure of the overrunning in that cases, no injection operations should be performed, and the injection valves remain closed. If in the process the return valve is likewise closed, then an unexpected pressure course can be caused only by a leak, which is thus unequivocally detectable. By evaluating the course over time of the pressure rise after the closure of the return valve, an especially unambiguous finding as to the presence of a leak can be made. Moreover, tolerances present in the system that are expressed as leakage are at a minimum.

The sole drawing figure schematically shows the essential components of a fuel supply system for internal combustion engines with self-ignition, or in other words Diesel engines with the leak detection performed according to the invention.

In the drawing, the components of a fuel supply system of an internal combustion engine with self ignition that are required for comprehension of the invention are shown. The fuel supply system has a fuel tank 10, a fuel pump 11, typically an electric fuel pump, and a check valve. The check valve 12 for instance is integrated with the fuel pump 11.

The fuel pump 11 carries the fuel to a high-pressure pump 13 connected with a high-pressure reservoir 14. From the high-pressure reservoir 14, the fuel reaches the injection nozzles 15, 16, 17, 18 disposed in a so-called common rail system 14a. The triggering of the injection valves 15, 16, 17, 18 is done by an electronic control unit 19 as well as suitable connections 26. Further signals that allow the operating conditions of the engine to be detected are supplied to the electronic control unit. The signals are furnished by corresponding sensors 20, 21, 22.

From the common rail 14a, a return conduit 23 leads back to the fuel tank 10 via a magnet valve 24. This magnet valve 24 can be triggered by the control unit 19 via the connection 27. The injection pressure in the common rail 14a is regulated by the magnet valve 24. The magnet valve 24 can be closed for leak detection by the control unit 19.

A pressure sensor 25 is associated with the common rail 14a. The pressure sensor 25 measures the fuel pressure in the common rail and carries signals accordingly to the control unit 19 via the connecting line 28.

In the fuel supply system shown in the drawing, which in principle is already known from German Patent 31 26 393, the leak detection according to the invention is performed. The requisite calculations are carried out by the control unit 19, which moreover takes on the control or regulation of the engine in a known manner. In the event that the electronic control unit 19 is an additional control unit, then an exchange of information with the engine control unit is necessary. Which evaluations or calculations will be done in which of the control units can be chosen in a suitable way.

The regulation of the pressure in the high-pressure region can also be performed by an independent pressure regulator or electronic unit. The .sub.------ pressure regulator or electronic control unit takes the place of the electronic control unit 19 and triggers the magnet valve 14 as a function of the injection pressure pE furnished by the pressure sensor 25.

In currently used Diesel injection systems, the pump 13 producing the high pressure operates continuously at an rpm that is equivalent to about half the engine rpm. Fuel is pumped continuously, and the resultant fuel or injection pressure is regulated, as already noted, by triggering the magnet valve 24. On actuation of the injection valves, the pressure briefly drops, since a certain amount of fuel has been dispensed from the common rail. In order that such a pressure fluctuation will not be a hindrance in leak detection, the leak detection is preferably performed whenever no fuel is being injected.

Such a condition exists whenever the engine is in the overrunning mode. The leak detection is therefore carried out when the control unit of the engine, by evaluating the available information furnished for instance by the sensors 20, 21, 22, detects that the engine is in the overrunning mode. Overrunning detection by evaluating the rpm and/or other load-dependent variables is already typical in modern engines, and the precise procedure will therefore not be described in further details here. No triggerings of the injection valves are then tripped. If when overrunning is detected the magnet valve 24 is closed by the control unit, then the pressure in the common rail must rise, since the pump 13 is continuing to pump fuel. How markedly the pressure rises or within what periods of time which pressure rises are to be expected can be estimated or determined empirically from given system conditions. In the electronic control unit, comparison are therefore performed. In the comparison the pressure course pE(t) measured by the pressure sensor 25 in overrunning is evaluated or compared with predeterminable values. If the electronic control unit finds that the pressure changes or the pressure rise does not ensue as expected, then the control unit 19 trips appropriate triggerings, for instance via the connection 29. The triggering of the appropriate triggerings cause the engine to be shut off or at least terminate the fuel pumping via the high-pressure pump 13.

The detection according to the invention of a leak in the high-pressure portion of the common rail system, or of an injection valve that persists in the open position, accordingly assumes that a pressure drop in the common rail, or implausibility between the engine operating point, or in other words the relationship between the rpm and the injection quantity, and the triggering of the pressure regulating unit indicates an error, and requires corresponding countermeasures in reaction.

In general, the response of the pressure regulating circuit to set-point value changes can be monitored under certain operating conditions. Advantageously, the response can be monitored in overrunning. Plausibility exists only whenever the pressure within a time slot reaches the adjustable set-point value. If an intended change in the triggering of the pressure regulating circuit is performed, then the system response can be evaluated. From this system response it can be decided whether a leak exists.

With this system, it is accordingly possible to monitor and evaluate the dynamic behavior of the system, which leads to considerably more reliable results compared with static observation.