FI ELD OF THE I NVENTION

The present invention pertains to a method for fu nction control of a high pressure pump in a system for fuel injection in a combustion engine, where the system comprises an independent feed ing pump, controllable by the combustion engine, for the supply of fuel in a low pressu re part of the system to the h igh pressu re pump, which comprises at least one pu mp element con nected between said low pressure part and an accumulator tan k for fuel injection to the combustion engine, and wh ich has a cylinder with a pu mp chamber with a movable piston inside for purposes of pumping and i n the con necting open ing in th is cylinder an inlet valve to the low pressure part, which is controllable for pu rposes of controlli ng the flow of fuel into the pump chamber, and a device accord ing to the preamble to the enclosed independent device claim.

Thus the invention is not limited to any specific type of combustion engine or fuel , and diesel and ethanol may be mentioned as a couple of non-exhaustive examples of fuel . Also, the invention pertains to function control of a high pressure pump for supply of fuel to combustion engi nes designed for all types of use, such as in i ndustrial applications, crushing machines and in various types of motor vehicles, even though the invention is particularly applicable to wheeled motor vehicles, especially commercial vehicles, such as trucks and buses, and will for th is reason sometimes be discussed in th is application with the objective of elucidating , but not l imiting , the invention .

Further, the invention is, with respect to the low pressure part in a system for fuel i njection in a combustion engine, applicable to systems in which said feeding pump is controllable independently of the combustion engine, which is advantageously achieved since the pump is d riven by an electric engine, which may be controlled totally independently of the combustion engine's fu nc- tion . I n other respects, the low pressure part of the system may have any appearance.

BACKGROUN D TECHNOLOGY I n order to ensure a secure and efficient operation of a said system, it is desirable to be able to discover impaired performance ability in said high pressure pu mp early, in order to be able to take suitable measures for the pump to fu nction optimally agai n , or in order to replace the pump. Herei n , li mited performance abil- ity of the high pressure pump may be due to the occu rrence of a leak in one or several of said pump elements between the inlet valve and the pump chamber's connecting open ing to the low pressure part, e.g . because of a somewhat damaged valve, or leakage between the piston and pump chamber wall because of wear particles getting caught in the fuel and damaging said wall .

US 7 431 018 describes a method for detecting faults in a h igh pressure pump by measuring the fuel pressure in the area of said accu mulator tan k and comparing this with reference values. Th is is done with the help of a pressure regulator and pressure fault sensor, and the method described therein consists of a relatively blunt instrument for function control of a high pressure pu mp, and is more focused on discovering larger faults in the fu nction of the same.

SUMMARY OF THE I NVENTION

The objective of the present invention is to provide a method and a device of the type defined above, which are improved in at least some respect in relation to prior art methods and devices of this type, with respect to ach ieving a reliable function control of a said high pressu re pump.

This objective is ach ieved with respect to the method by provid- ing such a method with the features listed i n the characterising portion of claim 1 .

The invention is thus based on the insight that i n stationary operati ng conditions of the combustion engine, with a constantly requested reference value of the fuel pressu re i n the accumulator tank, the feed ing pu mp may be controlled so that the fuel pressure in the low pressure part at the inlet to the h igh pressure pump is reduced . At the same ti me, the pressure in the accumulator tank is measured and compared to the requested reference value of the fuel pressure in the accumulator tank, in order to use the outcome of this comparison as an i ndication of the high pressure pump's functionality. It has been found that with such a method , the occurrence of both the above mentioned types of leakage, i .e. at the inlet valve and between the piston and the pump chamber wall , in the high pressure pump may be discov- ered. Thus, the function control only requires stationary operating conditions in the combustion engine for a brief period of time, in the range of one second, in order to be carried out. When the combustion engine is located in a wheeled motor vehicle, the method may for example be carried out with desired intervals, when the vehicle is driven on a substantially horizontal base at a substantially constant speed.

According to one embodiment of the invention, the reduction of the fuel pressure at said position in the low pressure part is carried out toward a predetermined minimum pressure, as of which the high pressure pump at normal functioning is incapable of delivering a fuel pressure in the accumulator tank which achieves said requested reference value, and the fuel pressure at said position in the low pressure part, at which the fuel pressure in the accumulator tank falls below said reference value is registered as a limit pressure. By deciding the value of said limit pressure and its size in relation to the size of said minimum pressure, a measure of the high pressure pump's functionality may be obtained.

According to one further development of this embodiment, the pressure reduction in step b) is made down to a pressure which is higher than or equal to said minimum pressure, and the fuel pressure in the low pressure part at which the comparison in step d) gives a measurable difference, is registered as said limit pressure and used to determine the pump's functionality. If, by carrying out this method, a limit pressure which is higher than said minimum pressure is confirmed, then the conclusion may be drawn that the high pressure pump functions inadequately in its compression phase, because of the occurrence of a leakage be- tween the piston and the pump chamber wall in one or several pump elements.

According to another embodiment of the invention, the pressure reduction is interrupted in said position, when the fuel pressure in the accumulator tank falls below said requested reference value by a predetermined difference value. This difference value may for example be 25-100 bar, 30-70 bar or around 50 bar, and when this occurs, the then prevailing pressure at said position may be determined as said limit pressure.

According to another embodiment of the invention, in step b) the feeding pump is controlled, so that said fuel pressure at said position falls until it is below a minimum pressure by at least 5%, 5- 20% or 5-10% when the high pressure pump is unable, during normal functioning, to deliver a fuel pressure in the accumulator tank in accordance with said requested reference value. By reducing the pressure in said position in the low pressure part down to this level, the occurrence of so-called self-pumping due to the occurrence of a leakage in one or several pump elements between the inlet valve and the pump chamber's connecting opening to the low pressure part may be discovered. Where such a noticeable leakage occurs, the fuel pressure in the accumulator tank will not fall below said reference value, even though the pressure is at or below the minimum pressure at said position.

Accordingly, by reducing the pressure in said position of the low pressure part down toward said minimum pressure, the leakage between the piston and the pump chamber wall may be detected, but said limit value is not reached until said minimum pressure has been reached , or if it has not been reached , the pressure may be reduced a little to determine whether the high pressure pump has optimal functionality (the pressu re in the accumulator tank should then fall ) or whether one of the inlet valves is dam- aged (the pressure in the accumulator tank in that case does not fall).

According to another embodiment of the invention , the method for a high pressure pump is carried out with several of said pump elements connected i n parallel between the low pressure part of the system and the accumulator tank, and in a said stationary operating mode of the combustion engine, at which one single of said pump elements is capable of deliveri ng a fuel pressure in the accu mulator tank accordi ng to the requested reference value alone, and steps a) - d) are carried out du ring the control of the high pressu re pump's elements, so that one single pump element delivers the fuel pressure requested in the accumulator tank in order to determine the functionality of such pu mp element. By carrying out the method according to the invention i n a stationary operating mode which only requi res the use of one pump element, a reliable functional ity control of such specific pump element may be carried out. It is pointed out that said minimu m pressure will thus be higher than in the event the fu nctionality control is carried out i n an operati ng mode with several pu mp elements operating simultaneously.

According to a further development of this embod iment, the steps a) - d) are carried out at intervals for all said pump elements during the control of the h igh pressure pump's pu mp elements, so that one single of these delivers a fuel pressu re in the accumula- tor tank alone, according to the requested reference value for the determination of the fu nctionality of all the pump elements. This embodiment thus facilitates the identification of a faili ng pump element, or a pump element with poorer functionality than nor- mal .

According to another embodi ment of the invention , the method comprises storage of data produced during the performance of the method steps, in order to provide the possibil ity of later as- sessment of the functional ity of the h igh pressu re pump or the high pressu re pump and its pump elements. Thus, du ring maintenance of the high pressu re pump the parts of the latter which so requi re, may be appropriately addressed . The invention also provides a device according to the preamble, which is equi pped with the featu res of the characterising portion of the enclosed independent device clai m. The advantages of such a device and the embodiments thereof defined in the non- independent device claims are made very clear in the discussion above, regarding the method accord ing to the invention .

The invention also pertains to a computer program with the features listed in claim 1 3, a computer program product with the features listed in claim 14, an electronic control device with the fea- tures listed in patent claim 15, and a motor vehicle accordi ng to claim 16 or 1 7.

Other advantageous featu res and advantages with the invention are set out in the description below. BRIEF DESCRIPTION OF THE DRAWINGS

Below are descriptions of example embodiments of the invention with reference to the enclosed drawings, in which:

Fig 1 is a schematic view illustrating the structure of a system for fuel supply to a combustion engine, comprising a device according an embodiment of the invention for the performance of a method according to the in- vention,

Fig 2 is a simplified view, illustrating the structure and function of a pump element in a high pressure pump in a system according to Fig 1,

Fig 3 and

Fig 4 are diagrams showing the pressure in the accumulator tank, and in said position in the low pressure part over time, at the performance of the method according to the invention according to two different embodiments,

Fig 5 is a flow chart showing a method according to one embodiment of the invention, and

Fig.6 is a diagram of an electronic control device for the implementation of a method according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS ACCORDING TO THE INVENTION Fig 1 shows a system for fuel injection in a combustion engi ne equipped with a device accord ing to the invention , and on which methods accord ing to the invention described below are appl ica- ble. The general structure of the system is prior art and comprises a fuel tank 1 , which is here d ivided into two containers, from which fuel , via a feeding pump 2 in a low pressu re part 3 with a pressu re of for example 2-6 bar, is fed to a h igh pressure part 4 of the system, which starts with a high pressure pump 5, which at a high pressure, for example in the range of 500- 2 500 bar, pumps fuel to an accumulator tan k 6 with nozzles 7 for injection of fuel into the cylinders of a combustion engine 8, which is here arranged in a motor veh icle identified with the digit 9. The components wh ich are drawn inside the frame M are here ar- ranged on the combustion engine.

The feeding pump 2 is operated by an electric engine 10, which is controlled by a control device 1 1 and is thus controllable independently of the combustion engine.

Reference is now made to Fig 2, with the hel p of which the structure and function of the high pressure pump 5 will be described in fu rther detail . The high pressure pu mp comprises one or several pump elements, usually 2-3 pump elements, but the number is arbitrary and may be for example 8, which are connected in parallel between the low pressure part 3 of the system and the accumulator tank 6 for fuel injection to the combustion engine. Fig 2 shows only one of these pu mp elements 12, but they all have the same design and are controlled in the same manner, and in the event there are several such elements, they each have a cylinder 13 with a pump chamber 14, with a moveable piston 15 for pumping therein, and an inlet valve 17 in the cylinder's connecting opening 16 to the low pressure part, which valve is controllable via an actuator 18 in order to control the flow of fuel into and/or out of the pump chamber 14. Specifically, the pumping of fuel is effected via a said pump element 12, through a lifter 19 connected with the piston 15 being impacted by a camshaft 20, which is mechanically connected to the combustion engine's crankshaft 21, so that the piston 15 will move forwards and backwards in the pump chamber 14 in accordance with the rotation of the engine crankshaft 21. The actuator 18 of the inlet valve 17 is controlled through control signals from a motor control device 22, which in its turn obtains information regarding the engine crankshaft's or the camshaft's instantaneous position, and thus the position of the piston 15, via the engine position sensors 23. The engine control device 22 also obtains information from an element 24 designed to measure the fuel pressure in the accumulator tank 6. Generally this means that when the piston 15 moves in Fig 2, seen in the downwards direction, and the pump chamber volume increases, the actuator 18 controls the inlet valve 17 so that it moves in the same direction, so that fuel may pass through the valve 17 in the connecting opening 16 and be sucked into the pump chamber 14. When the piston 15 then is in the region of its lowest position with maximum pump chamber volume, the actuator 18 controls the inlet valve 17, so that it moves upwards to abut against the walls defined in the connecting opening 16 and fit tightly against these, so that on subsequent piston upstrokes in the pump chamber existing fuel is compressed and pressed out past a check valve 25 toward the accumulator tank 6, i n order to be injected into the cylinders of the combustion engi ne via this tank. Thus, if there are several pu mp elements, these may each have a conduit to the accumulator tank or, as i ndicated in Fig. 1 , a joint conduit from the h igh pressure pu mp to the accumulator tank.

The function of a said pu mp element may be degraded mainly through two types of leakage. One is due to fuel leaking past the piston 1 5, as indicated with the arrows 26, since the piston does not seal tightly against the surrounding pu mp chamber walls. This may be due to wear particles having entered the fuel and damaged said walls. The other type of leakage is a leakage past the inlet valve 1 7, from the pump chamber to the low pressure part 3, when the piston 15 is in the fuel compression phase and the i nlet valve must fully close the connecting opening 16. This may be due to the valve being damaged , for example due to wear and tear. There follows a description of the characterisi ng features of the present invention . A device accordi ng to the i nvention , for fu nctionality control of the high pressure pu mp 5, comprises elements 27 designed to measu re the fuel pressure in a position in the low pressure part at the inlet to the high pressure pump. This pres- sure measurement element 27 is adapted to send information about the measu red fuel pressure to the control device 1 1 to control the feeding pump 2 , and to a device 28 arranged i n the engine control device designed to compare the pressure measured by the element 24 in the accumulator tank with a reference value for this, and , during the performance of the method accord ing to the invention , to carry out th is comparison in connection with a pressure reduction measu red at one of the elements 27.

How a method according to a first embodiment of the invention is designed to be carried out will be described below with reference also to the diagram in Fig 3, which shows the development of the fuel pressure P over time t. Thus, the u ppermost straight line P _B represents a requested reference value for the fuel pressure in the accu mulator tan k du ring a given stationary operating mode of the combustion engine, and th is may e.g . be 2 000 bar. The dashed l ine P _min shows the fuel pressure in said position in the low pressure part, as of wh ich the high pressure pu mp in normal functioning is incapable of delivering a fuel pressure in the accumulator tank wh ich reaches said requested reference value, and this pressure may for example be 3 bar. P _jn shows the pressure measured by the element 27 at the inlet to the h igh pressure pump, wh ich during normal operation in said stationary operating mode of the combustion engine could be 5 bar. The method accord ing to the invention is started at the point in time t ₀ , by the feed ing pu mp being controlled to reduce the fuel pressure P _in at the inlet to the high pressure pump. During th is pressure reduction the pressure P _s in the accu mulator tank is measu red and compared with the requested reference value P _B . The pressure reduction is made until a predetermined difference value Δ is achieved between P _B and P _s , wh ich may e.g . be 50 bar. This has occu rred at the poi nt in time t _{1 :} and the pressure which P _in has at this time is registered as a limit pressure P _G . Should this limit pressu re be substantially consistent with P _min , then this indicates a good functionality of the h igh pressure pump. I n the case d is- played , however, the limit pressure is substantially h igher than said minimum pressure, namely around 3.5 bar, which indicates a reduced functionality of the high pressure pump and that a leak between the piston and the pump chamber wall in one or several pump elements probably exists. The time lapsed between t ₀ and t _i: i.e. the time which is required to carry out the method according to the invention, may for example be around 500 ms.

Fig 4 shows the same type of diagram as Fig 3 for the performance of the method according to the invention, according to an- other embodiment of the invention. In this case, the pressure P _s in the accumulator tank does not fall below the requested reference value P _B before P _jn reaches P _niiri , and the feeding pump is therefore controlled to reduce the pressure in the inlet to the high pressure pump further by around 10%, and yet the pressure still does not fall in the accumulator tank, but rather increases somewhat. This indicates so-called self-pumping through inadequate sealing, due to damage of one or several inlet valves in the high pressure pump. Fig 5 shows a flow chart which illustrates a method according to one embodiment of the invention, for functionality control of a high pressure pump in a system for fuel injection in a combustion engine. In a first step Si it is determined whether a stationary operating mode prevails in the combustion engine. In the event of an affirmative answer to this question, a second step ensues S ₂ , in which the fuel system's feeding pump 2 is controlled to reduce the pressure at the inlet to the high pressure pump 4, and this step is carried out in parallel with step S ₃ of measuring the pressure at said inlet, and measuring the pressure P _s in the ac- cumulator tank 6 at a step S ₄ . In step S ₅ the pressure measured in the accu mulator tan k is compared with a reference value P _B for this, i n order to be used in a step Se for generating information about the h igh pressure pu mp's functionality, A computer program code for the implementation of a method accord ing to the invention is su itably i ncluded in a computer program , loadable into the internal memory of a computer, such as the internal memory of an electronic control device of a combustion engine. Such a computer program is suitably provided via a computer program product, comprising a data storage med ium readable by an electronic control device, which data storage medium has the computer program stored thereon . Said data storage mediu m is e.g. an optica! data storage medium in the form of a CD-ROM , a DVD , etc. , a magnetic data storage mediu m in the form of a hard disk d rive, a diskette, a cassette, etc. , or a Flash memory or a ROM , PROM , EPROM or EEPROM type memory.

Fig. 6 illustrates schematically an electronic control device 29 comprising execution means 30, such as a central processor unit (CPU ), for the execution of a computer software. The execution means 30 commu nicates with a memory 31 , e.g. a RAM memory, via a data bus 32. The control device 29 also comprises a data storage mediu m 33, e.g . in the form of a Flash memory or a ROM , PROM , EPROM or EEPROM type memory. The execution means 30 commun icates with the data storage means 33 via the data bus 32. A computer program, comprising computer program code for the implementation of a method accordi ng to the invention , for example in accordance with the embodiment illustrated in fig . 4, is stored on the data storage mediu m 33. The i nvention is obviously not limited in any way to the embod iments described above, but nu merous possible modifications thereof should be obvious to a person skilled in the area, without such person departing from the spirit of the invention as defined by the appended claims.

The appearance of the high pressure pump's pump element could be different than as illustrated schematically in Fig . 2. Is respect of the fuel , it would be fully possible to carry out the method on a combustion engine which is operated with a fuel which is gaseous at the pressure prevailing in the low pressure part, but which becomes liquid in the h igh pressure part, such as for example DM E (di methyl).

The methods could very well be carried out in the form of workshops tests. This also applies where the combustion engine is arranged i n a motor vehicle.