TECHNICAL FIELD OF THE I NVENTION

The present invention relates to a method for checking the functionality of individual pumping elements of a high-pressure pump in a high-pressure accumulator fuel injection system of an internal combustion engine, in which said system comprises:

a high-pressure accumulator, a high-pressure pump with a plurality of pumping elements connected in parallel to sequentially feed fuel to the high-pressure accumulator and at least one injector connected to the high-pressure accumulator for injecting fuel into a cylinder of the engine, as well as an arrangement for carrying out such a method according to the preamble of the appended independent arrangement claim.

The invention is not restricted to such methods carried out for a high-pressure accumulator fuel injection system for injection of any particular fuel, into a cylinder or cylinders of an internal combustion engine, but diesel and ethanol may be mentioned by way of examples. Furthermore, the invention relates to such systems for internal combustion engines designed for any type of use, such as in industrial applications, in grinding machines and all types of motor vehicles, although the invention is particularly applicable to utility vehicles, especially wheeled utility vehicles, such as trucks or lorries and buses. For proper function of the internal combustion engine it is vital that the pressure inside the high-pressure accumulator may be kept at a desired level, but when problems to obtain this occur there are multiple components in the fuel feeding system to which the high- pressure accumulator fuel injection system belongs that could cause these problems, such as a clogged fuel filter, a leaking IMV (Inlet Metering Valve), bad venturi, bad inlet valve of the high- pressure pump and lost high pressure pump capacity. This makes it hard to pinpoint which of these components that is causing the problem.

BACKGROUND ART

US 6 526 948 discloses a method of the type defined in the introduction through which measures are taken for detecting malfunctions of individual pumping elements of the high-pressure pump in a high-pressure accumulator fuel injection system of an internal combustion engine in a motor vehicle. This is done by measuring pressure changes in the high-pressure accumulator depending upon changes occurring in the individual pumping elements. An average pressure increase is determined for each individual pumping element and these pressure increases are compared with each other for determining any defect of any pumping element. These measurements are, however, rather complicated and it is a desire to improve the reliability thereof.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method and an arrangement of the type defined in the introduction being improved in at least some aspect with respect to such methods and arrangements already known.

This object is with respect to the method obtained by providing such a method with the features listed in the characterizing part of appended patent claim 1 .

Accordingly, by driving the high-pressure pump while demanding a high fuel flow therefrom and simultaneously controlling said at least one injector to be closed while measuring the pressure inside the high-pressure accumulator at a frequency resulting in a plurality of pressure measuring values during each stroke of each pumping element and comparing the development of pressure measuring values obtained during a pumping stroke of each pumping element with a corresponding development of pressure measuring values for the other pumping elements of the high- pressure pump, the functionality of each pumping element may be determined by determining that there is a malfunction of a pumping element having a said development of pressure measuring values increasing less than a predetermined proportion of the development of pressure measuring values of the pumping element having the development with the highest increase. Thus, the pumping element with a said development with the highest increase will then function as a reference. This method will deliver a highly reliable result, since each stroke of each pumping element properly functioning shall with the injectors closed result in substantially the same pressure increase inside the high-pressure accumulator, so that a stroke of a pumping element resulting in a pressure increase being less than a predetermined proportion of the pressure increase resulted from the stroke of the pumping element having the highest such increase will be a reliable indication that this pumping element does not function properly. Thus, by using this method it is possible to rule out, or pinpoint, certain issues with the high-pressure pump and rule out errors that will affect the pumping elements equally, such as temperature, leakage, bad venturi and so on.

According to an embodiment of the invention said predetermined proportion is 70 %, 80 %, 90 % or 95 %. If a pumping element does not function properly it should show a pressure increase inside the high-pressure accumulator caused by a stroke thereof being less than 80 % and in most cases less than 70 % of a pressure increase caused by a stroke of the pumping element functioning as reference. Already a minor defect of a pumping element, such as a reduced performance due to a large gap between barrel and plunger, will result in a said pressure increase being less than the predetermined proportion and by that detectable as a malfunction of that pumping element.

According to another embodiment of the invention it is a high fuel flow in the form of a maximum fuel flow that is demanded when driving the high-pressure pump. It is suitable but not necessary to demand a maximum fuel flow when carrying out the method according to the invention.

According to another embodiment of the invention said determining step comprises a determining that the pumping element having a said development of pressure measuring values increasing most functions properly, and said development of this pumping element is taken as a reference for evaluation of the function of each other pumping element.

According to another embodiment of the invention it is carried out on an engine of a motor vehicle, such as a wheeled motor vehicle, especially in the form of a truck or a lorry or a bus. The method according to the invention is particularly suitable to be carried out when such a motor vehicle is subjected to maintenance work for checking the proper function of the high-pressure pump of the high-pressure accumulator fuel injection system of said engine to replace a pumping element or any defect component thereof.

The object of the present invention is with respect to the arrangement for checking the functionality of individual pumping elements in a high-pressure accumulator fuel injection system of an internal combustion engine obtained by providing an arrangement according to the independent claim directed thereto. Advantages of such an arrangement and the embodiment thereof defined in the dependent claim appear clearly from the above discussion of the method according to the invention and embodiments thereof.

The invention also relates to a computer program, a computer readable medium, an electronic control unit, an internal combustion engine and a motor vehicle according to the appended claims directed thereto.

Further advantageous features as well as advantages of the present invention appear from the description following below. BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a specific description of an embodiment of the invention cited as an example.

In the drawings:

Fig. 1 is a simplified schematic view showing a motor vehicle with an internal combustion engine having a high-pressure accumulator fuel injection system upon which the method according to the present invention is applicable,

Fig. 2 is a graph of the pressure P measured inside the high-pressure accumulator of an internal combustion engine of the type shown in Fig. 1 versus time t while carrying out the method according to an embodiment of the present invention,

Fig. 3 is a graph illustrating the effect of the pumping strokes of the individual pumping elements on the pressure measured inside the high-pressure accumulator when carrying out the method according to said embodiment,

Fig. 4 is a flow chart illustrating the steps carried out in a method according to said embodiment of the invention, and Fig. 5 illustrates schematically an electronic control unit according to the invention .

DETAILED DESCRIPTION OF AN EMBODI MENT OF THE I NVENTION

A part of an internal combustion engine 1 in a motor vehicle 2 with a plurality (six) of cylinders 3 and a high-pressure accumulator fuel injection system to which a method according to the invention is applicable is very schematically illustrated in Fig. 1 . This system comprises a high-pressure accumulator 4 or a common rail with one injector 5 for each cylinder connected thereto for injecting fuel into a cylinder of the engine. A high-pressure pump 6 is configured to feed fuel to the high-pressure accumulator 4 and has for that sake two pumping elements 7, 8 connected in parallel and controlled by a control unit 9 to pump sequentially. Each such pumping element has a separate inlet valve 10, 1 1 controlled by said control unit 9 and connected to an I MV 12 of the pump connecting the pump 6 to a low pressure part of the fuel feeding system of the vehicle.

A sensor 13 is configured to measure the fuel pressure prevailing in the high-pressure accumulator 4 at a frequency resulting in a plurality of pressure measuring values during each stroke of each pumping element 7, 8 and send information thereof to a member 14 integrated with the control unit 9 and configured to evaluate the pressure measuring values obtained through the pressure sensor.

The method according to the present invention is directed to check the proper function of the individual pumping elements 7, 8 of the high-pressure pump, and this is done by driving the high-pressure pump while demanding a high fuel flow, in this case a maximum fuel flow, therefrom, and simultaneously controlling the injectors 5 to be closed. The pressure inside the high-pressure accumulator 4 is during this driving of the pump measured by the sensor 13 by high speed sampling , i.e. at a frequency resulting in a plurality, such as more than 20, measurements during a pump stroke of each pumping element. The graph shown in Fig. 2 shows the development of the pressure P inside the high-pressure accumulator 4 versus time t and how the pressure is increasing somewhat (A) during pump strokes of one of the pumping elements followed by an increase being more than twice as high (B) during a pump stroke of the other pumping element. By using one of the pumping elements, let say the pumping element 7 with pump strokes resulting in the highest increase of the pressure inside the accumulator 4, as the reference and comparing the development of the pressure caused by a pump stroke thereof with the pressure development during pump strokes of the other pumping element 8 it may be determined that there is a malfunction of the pumping element 8.

The graph shown in Fig. 3 shows the pressure increase Dr obtained through each pump stroke of the pumping element 7 (PS7) and the pumping element 8 (PS8) clearly pointing out that there is a malfunction of the pumping element 8.

Fig. 4 illustrates a flow chart of a method according to an embodiment of the present invention carried out for a high- pressure accumulator fuel injection system of an internal combustion engine of the type shown in Fig . 1 for checking the functionality of individual pumping elements of a high-pressure pump of said system. The method is started with the step Si of continuing to drive the high-pressure pump at a high fuel flow demand. While driving the pump the injector(-s) of the high- pressure accumulator is kept closed as defined as a step S ₂ . While driving the pump and keeping the injector(-s) closed the pressure inside the high-pressure accumulator is measured at high frequency during each stroke of each pumping element in a step S ₃ . In a subsequent step S ₄ the development of the pressure measuring values of each pumping element is compared with that of the other pumping elements. Then in a step S ₅ the question is asked: Has a pumping element during a pump stroke a development of pressure measuring values increasing less than a predetermined proportion of pressure measuring values of the pumping element having the development with the highest increase? When the answer to this question is yes it is in a step Se determined that there is a malfunction of the pumping element, and if the answer to the question is no it is in a step S ₇ determined that there is no malfunction of that pumping element.

Computer program code for implementing a method according to the invention is with advantage included in a computer program which can be read into the internal memory of a computer, e.g. the internal memory of an electronic control unit of a motor vehicle. Such a computer program is with advantage provided via a computer program product comprising a data storage medium which can be read by a computer and which has the computer program stored on it. Said data storage medium is for example an optical data storage medium in the form of a CD ROM disc, a DVD disc etc., a magnetic data storage medium in the form of a hard disc, a diskette, a cassette tape etc., or a flash memory or a memory of the ROM, PROM, EPROM or EEPROM type. Fig. 5 illustrates very schematically an electronic control unit 9 comprising an execution means 15, e.g. a central processor unit (CPU), for execution of computer software. The execution means 15 communicates with a memory 16, e.g. of the RAM type, via a data bus 17. The control unit 9 comprises also a non-transitory data storage medium 18, e.g. in the form of a flash memory or a memory of the ROM, PROM, EPROM or EEPROM type. The execution means 15 communicates with the data storage medium 18 via the data bus 17. A computer program comprising computer program code for implementing a method according to the invention, e.g. in accordance with the embodiment illustrated in Fig. 4, is stored on the data storage medium 18.

The invention is of course in no way restricted to the embodiments described above, since many possibilities for modifications thereof are likely to be obvious to one skilled in the art without having to deviate from the scope of invention defined in the appended claims.

The pump does not have to be a so-called IMV-pump with an Inlet Metering Valve at the inlet of the pumping elements, but it may be of any other conceivable type having at least two pumping elements, such as an AIM-pump having an actively controlled inlet valve for each pumping element subjected to Active Inlet Metering.