TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for determining the reliability of an estimated value of the elasticity of a fluid system for a pressurised fluid as well as a fluid system according to the preamble of the appended claim directed thereto.

Said pressurised fluid may be a gas or a liquid, and it may by way of example be mentioned that such a method is interesting to carry out in fluid systems of a motor vehicle, such as for feeding fuel to an internal combustion engine thereof or AdBlue to an exhaust gas catalytic converter, without restricting the invention to these applications.

BACKGROUND ART

Especially in a fluid system for dosage of pressurised fluid to for instance an injector for injecting the fuel into a chamber, such as in a cylinder of an engine, it may be of importance to have a fairly exact value of the elasticity of the fluid system or a conduit of the fluid system connecting a pump to the injector for ensuring that the feed of fluid in the system, such as to the injector, will be as requested. Thus, the value of the elasticity of the system or a said conduit may be utilized for proper regulation of a pump or diagnosis, such as disclosed for instance in US 8 875 498 B2. Furthermore, in a fluid system having filters and other constrictions in the pressurised part of the system cloggings may influence the elasticity felt by the system. This may in certain cases be an advantage, which is disclosed in for instance WO 2014/200413 A1 , but this may in some cases cause problems, such as when an incorrect regulator parameter is calculated on the basis of the elasticity felt, which is not the real elasticity of the system , causing undesired behaviours of equipment.

Accordingly, for being able to use an estimated elasticity value obtained through measurements on the fluid system in critical applications, such as for regulations, it is necessary to decide whether the elasticity is representative for the entire fluid system or if it has been influenced by for instance a clogging.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for determining the reliability of an estimated value of the elasticity of a fluid system for a pressurised fluid addressing the problem discussed above as well as a fluid system enabling to address this problem.

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

Thus, by controlling an arrangement, which may be a pump, to feed a pressurised fluid in the system, determining how much power is needed to obtain a determined flow at a determined pressure of fluid in the system or which flow and pressure may be obtained by a determined power of the arrangement and comparing such a measurement value with a stored expected corresponding value for a proper function of the fluid system it may be determined whether it may be relied upon estimated values of the elasticity of the fluid system obtained through measurements carried out on the fluid system or not. This means that it will be known whether the estimated elasticity values may be used to for instance determining parameters of a regulator of the fluid system. This means that the risk for secondary effects of cloggings (for instance errorounesly selected regulator parameters) may be minimized.

According to an embodiment of the invention the arrangement is in step a) controlled to obtain a determined flow and pressure of said fluid in the system and the power consumption of said arrangement necessary for obtaining said determined flow at said determined pressure is measured in step b) . This constitutes a simple and reliable way of obtaining a said measurement value indicative of the condition of the fluid system .

According to another embodiment of the invention it is a pump configured to pump said fluid in the system that is controlled in step a) . The power consumption of said arrangement may then be measured by measuring the supply of electricity to the pump in accordance with another embodiment of the invention.

According a still other embodiment of the invention it is the power of a displacement pump of said arrangement that is controlled in step a) and the flow obtained through the operation thereof is measured by measuring the number of revolutions per minute of the pump. The number of revolutions per minute may of course be indirectly measured by measuring the number of revolutions per any time unit, such as a second. This constitutes a simple and reliable way of obtaining an accurate measurement value of the fluid flow in the system .

According to another embodiment of the invention said threshold value divided by said expected value is in the range of 0.05-0.5, 0.05-0.30, 0.05-0.20 or 0.05-0.10. Thus, when the measurement value deviates less than 5% from the expected value it may be concluded that there are no cloggings or leakages and the measurement value may be used for determining if the fluid system is in good order and it may be relied upon estimated values of the elasticity of the system obtained through other measurements and if such values may be used for instance to calculate a parameter of a regulator used to control the pump of the system.

According to another embodiment of the invention an alarm member is activated if said difference exceeds a determined value being higher than said threshold value. Attention is then brought to the fact that cloggings of a certain dignity are present in the fluid system and may cause any action, such as replacement of any component of the system.

According to another embodiment of the invention the method is carried out for a fluid system in a motor vehicle, which constitutes a preferred application of the method, since the value of the elasticity of a fluid system in a motor vehicle may be of importance for regulating components, such as pumps, of the system. The fluid system may then for instance be in the form of a fuel feed system or a system feeding AdBlue to an exhaust gas catalytic converter of the motor vehicle.

The object of the invention is with respect to the fluid system obtained by providing a fluid system of the type defined in the preamble of the appended independent claim directed thereto with the features listed in the characterizing part of that claim . The function and advantages of such a fluid system and of the embodiment thereof defined in the dependent claim appear clearly from the above discussion of the method according to the invention and the embodiments thereof.

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

Further advantages as well as advantageous features of the invention will appear from the description following below.

BRIEF DESCRIPTION OF TH E 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 fluid system according to the invention applied to an internal combustion engine for feeding fuel thereto and upon which the method according to the present invention is applicable,

Fig 2 is a flow chart illustrating the steps carried out in a method according to an embodiment of the invention, and

Fig 3 illustrates schematically an electronic control unit according to the invention .

DETAILED DESCRI PTION OF AN EMBODIMENT OF THE INVENTION

Fig 1 illustrates schematically a fluid system in the form of a fuel feed system 1 according to the invention for feeding fuel from a fuel tank 2 to injectors 3 for injecting fuel into cylinders 4 of an internal combustion engine 5. The internal combustion engine 5 is here arranged in a motor vehicle 6.

The fuel feed system comprises a pump 7 configured to feed fuel in a conduit 8 to the injectors. The pump 7 is controlled by an electronic pressure regulator 9. The regulator 9 is configured to determine a control signal to be sent to the pump for control thereof on the basis of a value of the elasticity of the conduit 8. Furthermore, the fuel feed system has a control unit 10 in which the pressure regulator may be implemented as a code, configured to control the pump 7 to obtain a measurement value to be sent to the regulator 9 enabling the latter to know if an estimated value of the elasticity of the fluid system obtained through other measurements may be used for determining how the regulator shall control the pump in operation o the engine 5. This is here done in the following way: the fuel feed system comprises an assembly 16 with a member 15 configured to measure the flow and pressure of fuel in the conduit 8 and send information thereabout to the control unit 10. The control unit 10 is configured to control the pump 7 to obtain a determined flow at a determined pressure of the fluid in the conduit. The power consumed by the pump 7 for obtaining this is recorded by the control unit, which compares this power measurement value with a stored expected corresponding value for a proper function of the fluid system. The control unit is configured to determine that it may be relied upon estimated values of the elasticity of the fluid system obtained through measurements carried out on the fluid system if the difference of said measurement value and said expected value is below a threshold value and otherwise not. The threshold value is for instance 1 0 % of said expected value. The control unit 10 will send information about said comparison to the regulator 9 which is configured to use the estimated value of the elasticity of the conduit determined through said other measurements when said difference is below said threshold value and to use a reasonable default value of the elasticity of the conduit if said difference is equal to or above said threshold value, for determining the control signals sent to the pump. In the case the pump 7 is a displacement pump, the flow measuring member 15 is not needed, since a value of the flow may be obtained by measuring the number of revolutions per minute of the pump. As an alternative the control unit 1 0 may instead be configured to control the pump to operate at a predetermined power consumption , and said measurement value used for determining the elasticity of the conduit 8 may then be obtained by said assembly by measuring the flow and pressure of fuel in the conduit 8 obtained by said power consumption of the pump 7. Furthermore, an alarm member 20 may be activated if the difference between said measurement value and said expected value exceeds a determined level being higher than said threshold value and making this important to know.

Fig 2 illustrates a flow chart of a method according to an embodiment of the present invention carried out for a fluid system of the type shown in Fig 1 . The method is started with a step Si of controlling the pump to operate followed by a step S2 of measuring the flow of fluid in the fluid system. The pump is in a step S ₃ controlled to obtain a predetermined value of said flow, and the measured flow value is in a step S ₄ compared with a stored expected value. The question“is determined flow value obtained?” is then in a step S5 asked, and the steps S ₂ -S ₅ are repeated until the answer to this question is “Yes”, whereupon the power consumption of the pump for delivering the flow value is in step S ₆ measured. The measured flow value is then in a step S7 compared with a stored expected corresponding value. In a step Ss the question is asked: “Is difference of measured flow value and expected flow value below a threshold value?”. When the answer to this question is“Yes” it is in a further step Sg determined that the system is in good order and it may be relied upon estimated values of the elasticity thereof obtained through other measurements. When the answer to this question is“No” it is in a step S _{1 0} determined that the fluid system does not function properly and said estimated values may not be used.

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 . 3 illustrates very schematically an electronic control unit 10 comprising an execution means 1 1 , e.g. a central processor unit (CPU), for execution of computer software. The execution means 1 1 communicates with a memory 12, e.g. of the RAM type, via a data bus 13. The control unit 10 comprises also a non-transitory data storage medium 1 4, e.g. in the form of a flash memory or a memory of the ROM, PROM, EPROM or EEPROM type. The execution means 1 1 communicates with the data storage medium 14 via the data bus 13. 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. 2, is stored on the data storage medium 14.

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 regulator may be implemented as a code in the control unit. The estimated value of the elasticity may be subjected to other use than to set regulator parameters, such as for diagnosis of injectors.