WO2008119588A1 - Method for the diagnosis of a shut-off valve - Google Patents

Abstract

The invention relates to a method for the diagnosis of a shut-off valve (400, 500, 510) in a fuel line (50), wherein the shut-off valve is disposed in the fuel line between at least one reservoir and at least one injection valve (70), wherein the shut-off valve is closed for the diagnosis, and fuel is removed via an injection valve for the operation of an internal combustion engine. The shut-off effect of the shut-off valves is determined to be insufficient if the pressure in the fuel line does not drop in an unexpected manner.

Description

 description

title

Method for diagnosing a shut-off valve

State of the art

The invention relates to a method for diagnosing a shut-off valve in a fuel line according to the preamble of the independent claim and a fuel supply system.

Compressed gas (CNG) systems typically include a series connection of a tank shut-off valve, a pressure regulator shut-off valve, a pressure regulator module, and a low-pressure relief valve. Often, the pressure regulator module itself also has a valve function which shuts off the low-pressure region from the high-pressure region if the pressures are too high in order to prevent the injection valves or injection valves from reliably opening when the pressures are too high.

Due to legal requirements in particular Tankabsperrventile are prescribed. An error in the shut-off function, ie internal leaks, does not affect normal vehicle operation. If the shut-off devices do not close sufficiently in the event of a malfunction, there is a risk that the entire tank contents may escape into the environment. Therefore, there is a particular interest the shut-off effect of the shut-off devices / valves in

It is preferable to check the apron routinely and to initiate a warning or a fault reaction if there is a lack of blocking effect.

From the unpublished DE 10 2005 048 456 a method is already known in which downstream of a shut-off valve, a low fuel pressure is set, with a closed shut-off and insufflation ü checks whether the fuel pressure rises downstream of the check valve. In an increasing fuel pressure insufficient blocking of the shut-off valve is detected.

From US Pat. No. 6,427,670 B2, a CNG system is known by way of example in which fuel is stored under pressure in a tank and conducted via a fuel line to injection valves. After switching off the internal combustion engine and closing the tank valves, it is provided to check the fuel pressure in the fuel line, with an external leakage - ie a leak of the

Fuel system out to the environment - is detected when the fuel pressure drops faster than expected.

Disclosure of the invention

The inventive method with the features of the independent method claim has the advantage that a shut-off valve, which is arranged in a fuel line between at least one tank and at least one injection valve, in a few steps with typically already existing sensors or measuring means on its shut-off - ie internal leakage - can be checked. For this purpose, the shut-off valve is closed and monitored the fuel pressure downstream of the closed shut-off valve, wherein further fuel is admitted via a blow-in valve for operating an internal combustion engine in a combustion chamber. Starting from the introduced fuel mass, a downstream of the shut-off valve expected fuel pressure is determined, the shut-off of the valve is not recognized as sufficient if the fuel pressure downstream of the shut-off valve from the expected fuel pressure deviates or does not decrease as expected.

Further, a fuel supply system having the features of the independent apparatus claim is equally advantageous. In this case, a control device with an adjusting means and a monitoring means is provided, wherein the control device and the device means are arranged for carrying out the method according to the invention. The measures listed in the dependent claims advantageous refinements and improvements of the method specified in the independent claim are possible.

The shut-off is also recognized as insufficient if the fuel pressure downstream of the shut-off valve exceeds the expected fuel pressure and / or the fuel pressure deviates from an expected pressure profile.

In a further advantageous embodiment, it is provided to carry out the diagnosis of the shut-off valve when switching off the internal combustion engine, wherein the internal combustion engine is operated until the completion of the diagnosis.

Furthermore, it is advantageous to take into account in the measurement of the pressure in the fuel line, a variable which indicates a temperature of the fuel.

Thus, in an advantageous manner, a fuel mass in the system can be determined from the pressure and the temperature, and the shut-off effect of the valve can be recognized as insufficient if the fuel mass in the fuel line downstream of the shut-off valve does not fall below an expected fuel mass.

drawing

An example of a fuel supply system according to the invention is shown in FIG.

description

Figure 1 shows schematically a fuel supply system for the operation of an internal combustion engine with LPG or compressed gas, for example o- the hydrogen or natural gas. In the exemplary embodiment shown, the fuel is stored under pressure in a first and second tank 100, 110. Of the Pressure of the fuel in the first and second tanks 100, 110, and thus indirectly also the fuel level, is monitored in each case via a first and second tank pressure sensor 200, 210. The two tanks 100, 110 are connected to a common fuel line 50, which leads the fuel to a pressure control valve 300 and downstream of the pressure control valve 300 to four injection valves 700. Between the common fuel line 50 and the tanks 100, 110, a Tankabsperrventil 500, 510 is arranged in each case. Upstream of the pressure regulator 300, a shut-off valve 400 is provided and between the pressure regulator 300 and the shut-off valve 400, a third pressure sensor 220 and between the pressure regulator 300 and the injection valves 700, a fourth pressure sensor 230. To fill the fuel system, a filler neck 600 is arranged at one end of the common fuel line 50 ,

In normal operation of the fuel supply system, for example, hydrogen is stored in the two tanks 100, 110 under a pressure of up to 300 bar. The Tankabsperrventile 500, 510 and the check valve 400 in the fuel line 50 are open. In this respect, in the common fuel line 50 to the pressure regulator, the tank pressure of, for example, <300 bar and is measured via the third pressure sensor 220. The pressure regulator 300 reduces the applied pressure, so that downstream of the pressure regulator 300, for example, a pressure of 2 to 6 bar is applied in the fuel line. With this low pressure, the fuel is then blown into the combustion chamber of an internal combustion engine, not shown, via the injection valves 700.

In the event of a malfunction or under special operating conditions, it is planned to close the shut-off valves 500, 510, 400. For example, if there is a leakage of the injection valves 700 or the fuel line, so escape of the fuel is avoided in the environment. Due to the high safety relevance of the shut-off valves, it is desirable to check the shut-off effect of the shut-off valves routinely.

To check the shut-off or the tightness of a shut-off valve, it is provided according to the invention to close the shut-off valve 400 and to monitor the fuel pressure downstream of the shut-off valve 400, wherein the injection valve 700 is further actuated to operate the internal combustion engine. Starting from the known operating conditions such as pressure and possibly temperature in the fuel line and the injection duration of the injection valve 700, a fuel mass can be determined, which flows into the combustion chamber. The injected fuel mass reduces the fuel mass in the fuel line and leads, in a closed and tight-fitting shut-off valve 400, to a pressure reduction in the fuel line. If the pressure reduction does not occur in the expected manner, it can be assumed that fuel will flow into the fuel line via the shut-off valve.

Each injection process also reduces the expected fuel pressure in the fuel line downstream of the closed shut-off valve. As the number of injections increases, the differential pressure between the upstream and downstream sides of the shut-off valve thus increases.

Therefore, according to the invention, it may also be provided to monitor the differential pressure across the shut-off valve.

Furthermore, it may also be provided to set a threshold above the expected fuel pressure at which the blocking effect of the shut-off valve 400 is still tolerated as sufficient. The threshold value has to be tracked in accordance with the fuel mass flowing out via the injection valve.

In order to further improve the accuracy of checking the shut-off effect, it is possible to check the pressure downstream of the pressure regulator with the fourth pressure sensor 230. For this purpose, the pressure downstream of the closed shut-off valve 400 to be tested is lowered by blowing out the fuel via the injection valves 700 to a pressure below the pressure control threshold. If the pressure control threshold of the pressure regulator 300 is, for example, 6 bar, the pressure would be below 6 bar, for example 2 bar. Under these conditions, the pressure regulator 300 is fully open and the

Pressure sensor 230 thus measures the pressure directly on the downstream side of the shut-off valve 400. This procedure has the advantage that, on the one hand, the differential pressure at the shut-off valve 400 becomes as large as possible and, on the other hand, the fourth pressure sensor 230 reacts more sensitively in the low-pressure region than through the smaller measuring range the third pressure sensor 220 in the high pressure Area. The accuracy and reliability of the measurement thus increases. To improve the accuracy, an additional calculation of the mass increase in the observed volume can be carried out by an additional temperature detection. The temperature can be measured with a temperature sensor at the observed volume or a tank temperature sensor.

Of course, other embodiments of a fuel supply system according to the invention are conceivable. For example, can be dispensed with a first and second pressure sensor 200, 210 and the fuel pressure in other ways or for example via the third pressure sensor 220 can be determined.

It may also be provided to operate only one fuel tank or more than two fuel tanks.

The method according to the invention is furthermore not limited to the diagnosis of a shut-off valve 400. In particular, the two tank valves 500, 510 can be examined for their shut-off.

If the diagnosis is carried out, for example, at high load, there is the risk that the fuel pressure with a large gradient downstream of the closed shut-off valve falls below a critical pressure and operation of the internal combustion engine is no longer possible. In order to avoid this, a pressure threshold is expediently provided below which the diagnosis is not carried out, or a load threshold above which the diagnosis is not carried out.

If there is a low load request, the shut-off valve is closed until the fuel pressure downstream of the shut-off valve has noticeably dropped. This allows the further operation of the internal combustion engine as well as the implementation of the diagnosis. During the closed shut-off valve, the injected fuel mass is accumulated and compared to a maximum value defined for that shut-off valve at which a pressure drop is detectable. The defined permissible maximum value of the accumulated injected fuel mass can be determined, for example, in advance and, if necessary, stored in maps for retrieval. If the stored permissible maximum value is exceeded, the shut-off valve is detected as faulty.

Alternatively, a suitable maximum permissible opening time of the shut-off valve can also be stored. Furthermore, it is also possible to provide a second pressure threshold, from which the shut-off valve is closed again. It is also conceivable to operate the shut-off valve periodically.

Furthermore, it may be provided to store the blocking effect of the shut-off valve, which is not recognized as sufficient, in a fault memory.

Furthermore, it may be provided to carry out the diagnosis at fixed intervals or after a defined time. In this case, it can also be provided, for example, that the shut-off effect is only recognized as insufficient if this has been established in several diagnoses.

In addition, it may be provided that further diagnoses during the leak diagnosis, in particular electrical diagnostics of the shut-off valve, are carried out, such as a diagnosis for line interruption or short-circuit to the supply voltage. By such a procedure, a fault differentiation between the power amplifier and component (valve) is possible in a simple manner.

Claims

claims A method of diagnosing a shut-off valve (400, 500, 510) in a fuel line (50), wherein the shut-off valve (400, 500, 510) in the fuel line (50) between at least one tank (100, 110) and at least one inflation valve (70) is arranged, wherein a fuel pressure downstream of the check valve (400, 500, 510) is detected, wherein fuel is introduced via a blow-in in a combustion chamber, wherein the check valve (400, 500, 510) is closed for diagnosis in that a fuel mass introduced via the blow-in valve is determined, that a fuel pressure which is to be expected downstream is determined on the basis of the introduced fuel mass and that the blocking effect of the shut-off valve (400, 500, 510) is not recognized as sufficient if the fuel pressure downstream of the shut-off valve (400, 500, 510) deviates from the expected fuel pressure. 2. The method of claim 1, wherein the shut-off of the shut-off valve (400, 500, 510) is recognized as insufficient when the fuel pressure downstream of the shut-off valve (400, 500, 510) exceeds the expected fuel pressure and / or expected Pressure course deviates. 3. The method according to at least one of the preceding claims, wherein when stopping the internal combustion engine, the shut-off valve (400, 500, 510) is closed, and the internal combustion engine is operated until the diagnosis is completed. 4. The method according to at least one of the preceding claims, wherein in the measurement of the pressure in the fuel line (50) is taken into account a size that indicates a temperature of the fuel. 5. The method according to at least one of the preceding claims, wherein from pressure and temperature, a fuel mass in the fuel line (50) is determined, and the shut-off of the shut-off valve (400, 500, 510) is recognized as insufficient if the fuel mass in the fuel line (50) does not decrease according to the embedded fuel mass. 6. Fuel supply system with at least one tank (100, 110), a Einblasventil (70) and a shut-off valve (400, 500, 510) and a control unit, characterized in that the control unit for diagnosis, the shut-off valve (400, 500, 510) a Adjusting means and a monitoring means, wherein the adjusting means are configured such that the adjusting means for diagnosing a shut-off valve (400, 500, 510) closes the shut-off valve (400, 500, 510), - wherein the monitoring means is adapted that there is a force monitored fuel pressure downstream of the shut-off valve (400, 500, 510), and depending on an inset via a blow-in in a combustion chamber fuel mass an expected fuel pressure determined and a lack of Absperrwirkung the check valve (400, 500, 510) detects when the fuel pressure downstream of the Stop valve (400, 500, 510) exceeds the expected fuel pressure.