FR2795454A1 - METHOD FOR DETECTING A LEAK FROM A FUEL INJECTION SYSTEM - Google Patents

Abstract

This method, according to which the fuel is taken from a tank (T) by means of an upstream pump (2) to be sent to a high pressure pump (8) which delivers it under pressure to an injection installation ( 16, 18), consists in detecting a volume flow of fuel taken from the tank, detecting the injection volume flow delivered by the pump (8), calculating a characteristic value from the two volume flows and delivering a leak signal when the characteristic value exceeds or falls below a limit value.Application in particular to fuel injection systems of internal combustion engines.

Description

A method for detecting a system leak

  fuel injection, according to which the fuel is taken from a tank via an upstream supply pump and is sent to a high pressure pump, from which the fuel placed under high pressure is delivered directly or indirectly to an injection installation, as well as a device for implementing the process, in which the fuel is withdrawn from a tank via an upstream supply pump and is sent to a high pressure pump, the speed of which is regulated and from which fuel under high pressure is supplied directly or indirectly to a

injection system.

  In modern combustion engines, an exi-

  gence essential is that the engine has a consumption-

  tion as low as possible and this for an opti-

  male of power and torque. In this regard, we were able to

  achieve significant progress, in particular thanks to the development

  development of efficient fuel injection systems.

  Thus, for example in the case of diesel and petrol engines, fuel injection systems of the so-called "common rail" type are used, in which the fuel is withdrawn from a tank via a upstream supply pump and is sent via a supply line for a high pressure pump. By means of the latter, the fuel is placed at a high pressure (up to 2.108 Pa and in the case of petrol engines up to 4.107 Pa) and is sent to a common rail, to which injection valves are connected . These can be controlled individually so that the amount of fuel injection from each cylinder is adjustable. Thanks to this individual control of the quantity of fuel injected into the cylinders, the criteria indicated can be optimized

  higher for the internal combustion engine.

  As high-pressure pumps, in the case of the fuel injection systems described above, radial piston pumps are frequently used, in which several pump units are driven by means of an eccentric shaft. This shaft is connected by means of a coupling to a shaft of the internal combustion engine, for example the camshaft or else is equipped with its own drive system. The volume flow of low pressure fuel discharged by the upstream supply pump is usually injected into the crankcase of the radial piston pump and is sent from there via the unit's suction valves pumps, in the delivery space and is delivered via pressure valves to a high pressure pipe connected to the

common rail.

  Due to the comparatively high pressure in the supply line, particular attention is paid to the construction of the sealing elements which seal the space of the

  high pressure pump crankshaft. Thanks to these elements

  sealing elements, the high pressure pump is closed in a sealed manner with respect to the environment, but also

  relative to the engine lubrication oil circuit.

  A special risk exists in the camshaft coupling area since at this point the engine lubricating oil circuit and the fuel circuit are separated from each other only by the

sealing elements.

  In the event of a failure of a seal

  chewiness, due to the high supply pressure there can be significant leaks, which can lead for example to dirtying / dilution of the engine lubricating oil or to environmental pollution by the fuel which s escapes outside.

  For this reason, it is essential to prevent

  expensive such a leak thanks to provisions from the construction point of view and, in the event of an accident, to take

  appropriate assistance arrangements.

  In principle, to detect leaks, you can

  Use the usual fuel sensors, by means of which the outgoing fuel is identified and a corresponding signal can be sent to the driver. However, such provisions can only be used

  limited since they assume that the cap-

  the engine is disposed at the leak location and also that a significant amount of fuel

escapes.

  On the contrary, the object of the invention is to indicate a method for detecting a leak as well as a device for implementing this method, using which the leaks can be identified with a technical expense.

  minimal from the device point of view.

  This problem is solved in accordance with the invention using a method of the type indicated above, characterized by the steps consisting in:

  - directly or indirectly determine a volumetric flow

  mnique of fuel taken from the tank, - detect directly or indirectly the volume flow of injection injected or driven by the high pressure pump, - calculate a characteristic value from the volume flow of fuel and the volume flow of injection, and deliver a leak signal in the case where the characteristic value exceeds a limit value by higher or lower values, or by a method of the type indicated above characterized by the steps consisting in: - determining directly or indirectly the rotation speed of the pump at high pressure, - determine the set pressure from a characteristic curve of the pump as a function of the speed of rotation of the pump, - directly or indirectly determine the actual delivery pressure, - calculate a characteristic value from the set discharge pressure and the actual discharge pressure, - issue a leak signal te in case the value

  characteristic exceeds a predetermined threshold value

  born, as well as by a device for implementing the method of the type indicated above, characterized by: - a sensor for determining directly or indirectly a volume flow of fuel between the tank and the high pressure pump;

  - a second sensor to detect directly or indirectly

  the injection volume flow; - a device for calculating a characteristic value from the volume flow of fuel and the flow

  injection volume and to compare the charac-

  teristic to a limit value, and - a signal delivery device for delivering a leakage signal in the case where the characteristic value is greater or less than the limit value, or by a device for implementing the method of the indicated type above, characterized by: a sensor for directly or indirectly determining the rotation speed of the high-pressure pump, the rotation speed of which is regulated, - a pressure sensor for directly or indirectly determining the actual delivery pressure of the pump at high pressure, - a device for calculating a set delivery pressure from the speed of rotation, - a comparator device for calculating a characteristic value from the set delivery pressure and the actual delivery pressure and for compare the characteristic value with a limit value, and - a signal delivery device for delivering a sig leakage nal in the case where the characteristic value

  is greater or less than the limit value.

  According to a first variant, a leak

  is determined by comparison of the volumetric flow of injections

  tion pumped back by the high pressure pump towards the injection system, at the volume flow pumped by

  the upstream drive pump, in which case when

  ment of a predetermined difference between the two volume flows indicated above, a control signal can be sent to the motor control unit, a signal which can lead, for example, to stopping the pump

upstream supply or motor.

  According to a second variant, we use as

  high pressure pump a pump whose rotational speed

  tion is set. The rotation speed of the high pressure pump is used to calculate a pressure of

  setpoint delivery from the characteristic curve

  pump tick. At the same time the actual discharge pressure of the high pressure pump is detected by a pressure sensor and compared to the set value. In the case where the actual value is lower, and this beyond a predetermined tolerance, at the set delivery pressure resulting from the set rotational speed, a leak signal is sent by the engine management unit to the engine control unit and

  corresponding arrangements are made.

  According to the invention, the setpoint and the actual value can be obtained directly or be derived from measured values, from which the setpoint and the actual value of the volume flow of

  backflow can be calculated.

  According to the invention, the volume flow of fuel or the discharge pressure of the high-pressure pump or another suitable characteristic value is compared with a set value and a leak signal is issued in the event of an overflow d 'a range of

  tolerance by higher or lower values.

  The invention therefore makes it possible to reliably detect a leak with a minimum expense from the technical point of view of measurement and regulation and to initiate timely appropriate measures to prevent

  environmental or engine damage.

  In a variant of the method according to the invention, the variation in the filling level of the reservoir is

  used to calculate the volume flow of fuel.

  Otherwise, the volume flow of fuel driven by the upstream feed pump and also the flow

  injection volume driven by high pressure pump

  can be determined directly from the pressure difference between two measuring points of the

  respective fuel circulation paths.

  In the case of common rail fuel injection systems, excess fuel is returned to the

  supply line via a

  pressure limiting valve and return line. In this case it is preferable that the measurement of the volume flow of fuel takes place in an area located upstream of the place where the return pipe opens

  in the supply line.

  In another exemplary embodiment, the limit values, from which a leakage signal is sent to the engine control unit, is arranged in a variable manner according to the operating parameters of the engine. According to another characteristic of the invention, the volume flow of fuel is determined by direct measurement in the area between the tank and the

high pressure pump.

  Other features and advantages of the

  present invention will emerge from the description given

  hereinafter taken with reference to the accompanying drawings, in which: - Figure 1 shows a block diagram of a fuel injection system of the common rail type; - Figure 2 shows a flowchart of a

  first example of implementation of a method for detecting

  ter a leak; and FIG. 3 represents a flowchart of another example of embodiment, according to which a high pressure pump is used, the speed of which

rotation is set.

  FIG. 1 shows a basic diagram of a common rail fuel injection system 1

for a petrol engine.

  Consequently, the fuel is sucked in by an upstream feed pump 2 from a reservoir of

  fuel T and is sent via a cana-

  supply line 4 to the suction connection 6 of a high pressure pump 8. A fuel filter 10 for separating impurities is provided in the pipeline

supply 4.

  The fuel is pressurized by means of

  the high pressure pump 8 and is sent via

  diary of a pressure connection 12 in a pressure line 14, by means of which the pressurized fuel is supplied to a common rail 16. To the common rail 16 are connected fuel injection valves 19, which are associated respectively to a cylinder of the internal combustion engine. The injection valves 18 are controlled via an engine control unit 20 so that the rate of injection into each cylinder can be controlled individually for a

  optimization of the combustion rate.

  The pressure in the common rail 16 is limited by a pressure limiting valve 22 which, when a predetermined maximum pressure is exceeded by the engine control unit 20, controls a connection leading to a return line 24, of way to

  return fuel from common rail 16 to the cana-

  feed supply 4, to reduce the pressure. In the embodiment shown, the return line 24 opens downstream of the fuel filter 10 in the

supply line 4.

  In the embodiment shown in Figure 1, the high pressure pump 8 is of the radial piston type, an eccentric shaft 26 driving the pump units not shown being coupled to the camshaft of the

drive motor.

  In the case of radial piston pumps, use

  usually found in injection systems

  burant, several and for example three pump units

  are housed in a pump housing, in which case an excess

  eccentric shaft 26 moves in a crankshaft space, eccentric against which are preloaded discharge members of the pump units so that the rotation of the eccentric is converted into a suction or compression stroke delivery devices. The fuel charged by the upstream discharge pressure of, for example, between 4 and 5 × 10 5 Pa, is introduced via the suction connection 6 into the space containing the crankshaft of the high pressure pump 8 and, from there , is sucked in via the suction valves of the

  pumps, in the respective delivery space. That is

  say that the fuel, which is present in the crankcase of the high pressure pump 8, is charged by the upstream supply pressure so that the seals of the crankcase of the high pressure pump 8 are subjected to high constraints. What is particularly critical is the junction area with the camshaft since in this part, the

  fuel system and the lubricating oil system

  engine cations are separated from each other only by shaft seals. In the beginning of

  the description we have already given indications concerning

  the risks in the event of a leak in the bass range

  pressures and in the high pressure range of the pump.

  According to the invention, to identify a

  fuel leakage, a leakage program, which is shown

  shown in a very simplified manner in FIG. 2, is implemented via the control unit 20

of the motor.

  During a first step, the volume flow of car-

  burant VK taken from tank T and sent via the

  supply line 4 to the fitting

  suction 6 of the high pressure pump 8, is detected.

  For the detection of the VK fuel volume flow, it

  there are a multitude of possibilities.

  Thus for the detection of the volume flow of

  VK fuel, for example the change in the level of

  tank crumpling per unit of time can be measured and the volume flow of fuel withdrawn can be calculated

  from the variation in the contents of the tank.

  Another possibility consists in determining the volume flow of fuel withdrawn, in a known manner directly from the difference between the two measurement points in the supply line 4. One can then calculate the volume flow as a function of this

pressure difference.

  Naturally, the volume flow of fuel VK can be detected directly or indirectly also with the aid of other flow measuring devices, for example active pressure flow measuring devices.

  (throttle devices), magneto-inductive flowmeters

  tifs, etc. What is essential is that the measurement means indicated above are arranged upstream of the mouth of the return pipe 24, so that the measurement value is not distorted by the quantity

fuel returned.

  In principle, however, the measurement point could also be provided downstream of this mouth area since the flow of fuel returned via the return line 24 is also detected and

  can be taken into account in the program described below.

  During a parallel step, the injection volume flow VE, which is predetermined during the same unit of time by the engine control unit and which can be calculated for example on the basis of the volume flow delivered

  by the high pressure pump 8, is detected.

  In a next step, the difference AV between the fuel flow VK and the injection fuel flow VE is calculated and a limit value V * is read from the memory of the engine control unit, value

  which is calculated according to function parameters

  engine operation. These parameters can be for example the variations of the speed of rotation or the

engine load.

  In a next comparison step, the difference

  The AV of the volume flows is compared with the limit value V *. In the case where the calculated difference AV of the volume flows is less than the limit value V *, the program returns to the starting point and the calculation indicated

  previously is executed again.

  In the case where the detected difference AV between the volume flows is greater than the associated limit value V *, a leak signal is delivered and the engine control unit triggers corresponding antagonistic provisions to prevent engine damage or pollution of the environment by the leak. This can

  include for example the issuance of a warning signal

  the driver, adjusting the power of the

  motor at a lower level, stopping the drive pump

  upstream 2 or the entire engine.

  In the case of a high-pressure pump, the speed of which is regulated, another program can be used to detect a leak - this program is shown in the flow diagram of FIG. 3. In the case of such pumps, the speed is set, the discharge pressure is set using the

pump rotation speed.

  This embodiment undoubtedly presupposes that the high pressure pump is equipped with a clean drive device, for example an electric one, so that no coupling is present at the camshaft. During a first step, the rotational speed np of the high pressure pump 8 is detected and a setpoint discharge pressure PCONSIGNE is determined by means of a programmed characteristic curve of the pump, as a function of the speed rotation detected np

of the pump.

  In addition to the detection of the

  setpoint discharge PCONSIGNE, the discharge pressure

  the actual PREELLE is detected via a pressure transmitter located in the pressure line 14 and then the difference AP between the value of

  setpoint and the actual value is calculated.

  This difference in pressure AP is then compared

  at the next step, to a limit value p *, which is calculated according to the parameters indicated above

  of the internal combustion engine.

  Correspondingly, as in the case of the embodiment shown in FIG. 2, in the case where the pressure difference Ap is less than the limit value p *, the program is repeated. In the case where the pressure difference AP exceeds the calculated limit value p *, the leak signal is again delivered, and the measures described above are triggered by

the engine control unit 20.

  In principle, there is a multiplicity of pos-

  sibilities of comparing the amount of delivery taken from the tank T to the amount of fuel delivered per unit of time towards the common rail 16 and injected via the injection valves 18 into the cylinders, so that the invention n is in no way limited to the measurement methods described above. Instead of the formation of the difference described above, one can also calculate characteristic values AV and Ap also for the formation of the

  quotient or some other way.

  On the other hand, the setpoint could also be determined on the basis of the current, which is necessary to drive the pump whose speed of rotation is regulated. From this value you can then determine the speed of rotation and, from there, the set delivery pressure. That is to say, as a basis for the calculations, any measurement value can in principle be used, from which the target values and the actual values of the delivery volume flow can be calculated. In the

  In the case of these indirect measurement methods, it is possible

  you should use existing sensors or measuring devices, so that no particular sensor to detect the speed of rotation or to measure the

debit is required.

  The limit values V * and p * can be equal

  predetermined as constants in cases

fairly easy to use.

  methods have been indicated for detecting a leak from a fuel injection system, in which a leak is identified when the volume flow of the fuel withdrawn from the tank T is greater, by a predetermined limit value, than the volume current of injection driven by a high pressure pump or injected into

  cylinders by injection valves.

Claims (8)

  1. Method for detecting a leak from a fuel injection system, according to which the fuel is withdrawn from a tank (T) via an upstream supply pump (2) and is sent to a high pressure pump (8), from which the fuel placed under high pressure is supplied directly or indirectly to an injection installation (16,18), characterized by the steps consisting in:   - directly or indirectly determine a volumetric flow   fuel mique (VK) taken from the tank (T), - detect directly or indirectly the injection volume flow (VE) injected or driven by the high pressure pump (8), - calculate a characteristic value (AV) from of the fuel volume flow (VK) and of the injection volume current VE, and - deliver a leak signal in the case where the characteristic value (AV) exceeds a limit value (V *) by   higher or lower values.   2. Method according to claim 1, characterized in that the volume flow of fuel (VK) is calculated on the basis of the variation of the level in the tank (T). 3. Method according to claim 1, characterized in that the determination of the volume flows (VK, VE) is carried out by measuring the pressure difference between two measuring points.   4. Method according to claim 1, characterized in that the volume flow of fuel (VK) is determined by direct measurement in the area between the tank   (T) and the high pressure pump (8).   5. Method according to any one of the claims   1 to 4, according to which the fuel loaded under pressure is sent to a common rail (16), to which injection valves (18) are connected, and according to which an excess quantity is introduced via a return line (24) in the supply line (4), characterized in that the fuel volume flow (VK) is measured upstream of the place where the return line (24) opens into the line supply (4).   6. Method according to any one of the claims   1, 2, 4 and 5, characterized in that the injection volume flow (VE) is calculated from the speed of rotation of a high pressure pump (8) whose speed rotation is set.   7. Method according to any one of the claims   1 to 6, characterized in that the limit value (V *, p *) is variable depending on the operating state of the motor. 8. Device for detecting a leak from a fuel injection system, in which the fuel is taken from a tank (T) via an upstream supply pump (2) and is sent to a high pressure pump (8), the speed of which is regulated and from which the fuel placed under high pressure is supplied directly or indirectly to an injection installation (16, 18), characterized by: a sensor for determining directly or indirectly a volume flow of fuel (VK) between the tank (T) and the high pressure pump (8);   - a second sensor to detect directly or indirectly   the injection volume flow (VE);   - a device (20) for calculating a characteristic value   tick (AV) from the fuel volume flow (VK) and the injection volume flow (VE) and to compare the characteristic value (AV) with a limit value (V *), and - a device (20) for signal delivery to deliver   a leak signal in the event that the character value   (AV) is greater or less than the value limit (V *).