DE19752025A1 - Method and device for regulating the fuel pressure in a fuel accumulator - Google Patents

Description

The invention relates to a method for regulating the force substance pressure in a fuel storage according to the Oberbe Handle of claim 1 and a device for regulating the fuel pressure in a fuel accumulator.

In fuel injection systems that have a fuel accumulator have, the control of the fuel pressure is special their importance because, on the one hand, the fuel pressure corresponds chend dynamics of the internal combustion engine must be changed and on the other hand too high a fuel pressure to lose energy and, for example, for heating the fuel tank leads.

DE 195 48 278 A1 describes a method for controlling a Internal combustion engine with high pressure injection known Fuel from a pre-feed pump to a high pressure pump is led, which compresses the fuel highly and to the Passes fuel storage. To regulate the fuel pressure in the fuel storage is the speed of the Pre-feed pump as a function of a pre-control value and second, depending on the difference between one Target value for the fuel pressure and a measured force regulated fabric pressure. There is also a fuel tank Pressure control valve is provided, which for rapid overpressure Lowering the fuel pressure is opened.

The object of the invention is a more precise procedure Ren to provide fuel pressure control.

The object of the invention is characterized by the features of the claim 1 and solved by the features of claim 11. A An essential advantage of the invention is that  Determination of the first control signal for the feeder first the injection quantity required for the injection is calculated and then from the injection quantity in Ab Dependency of parameters of the feeder a Steueri gnal is determined for the feeder, so the Zu the required injection quantity to the force feeds material storage. The determination of is thus required th injection quantity and the determination of the control signal for the feeder is separated, creating precise control of the fuel pressure.

Further advantageous embodiments of the invention are in the dependent claims specified.

The invention is explained in more detail below with reference to the figures purifies; show it:

FIG. 1, a common rail injection system,

Fig. 2 is a pressure regulating valve,

Fig. 3, the control behavior of the pressure regulating valve,

Fig. 4 shows a schematic structure of the control process,

Fig. 5 th a representation of the individual Regelungskomponen,

Fig. 6 is a dynamic control signal,

Fig. 7 shows the fuel pressure and other control signals for an injection process.

Fig. 1 shows schematically a common rail fuel injection system where the fuel from a fuel tank 1 via a supply pump 2, a fuel filter 3 and a throttle valve 4 is guided to a high-pressure pump 5. The high-pressure pump 5 is connected to a fuel accumulator 7 , on which a pressure control valve 6 is provided, which is connected to the fuel tank 1 via a return line 12 . The fuel accumulator 7 is connected to injection valves 9 , which are assigned to an internal combustion engine 16 . At the fuel storage 7 , a pressure sensor 8 is provided which is connected to a control unit 10 via a signal line. The control unit 10 is connected via a first control line 13 with the throttle valve 4, via a second control line 14 to the pressure regulating valve 6 and via third control lines 15 to the injectors. 9

In addition, the control device 10 is connected to a data memory 17 . The injection valves 9 have leakage lines 11 which lead to the fuel tank 1 . The control unit 10 is also connected to a pedal value transmitter 18 , which determines the driver's request. Furthermore, the control unit 10 is connected to a speed sensor 19 , which is assigned to the internal combustion engine 16 .

The control unit 10 is also connected to a voltmeter 35 of the supply voltage 34 , which reports the supply voltage to the control unit 10 . In addition, a state sensor 37 is assigned to the internal combustion engine 16 , which detects the operating state of the internal combustion engine, such as, for. B. start, idle or full load determined, and passes to the control unit 10 . Furthermore, a cooling system 33 for the internal combustion engine 16 is provided which has a temperature sensor 36 which measures the cooling water temperature TCO and passes it on to the control unit 10 .

. The arrangement of Figure 1 operates as follows: The control unit 10 detects the driver's request via the Pedalwertge about 18 and the speed of the internal combustion engine 16 via the speed timer 19. Depending on the driver's request and the speed of the internal combustion engine, the control unit 10 sets a corresponding fuel pressure in the fuel accumulator 7 and controls the injection valves 9 accordingly. In this way, the internal combustion engine 16 , depending on the driver's request and the speed of the internal combustion engine, is supplied with a predetermined amount of fuel over a determined injection period.

To control the fuel pressure in the fuel accumulator 7, the control unit 10 measures the fuel pressure in the fuel accumulator via the pressure sensor 8 and controls the pressure regulating valve 6 and the throttle valve 4 according to predetermined methods, which are stored in the data memory 17 . The amount of fuel that is supplied to the fuel accumulator 7 is determined in this embodiment by the degree of opening of the throttle valve 4 .

If the high-pressure pump 5, for example in the re speed running Gelbar, then also on the regulation of rotation 5 to the number of high-pressure pump, the fuel quantity is controlled who, which is supplied to the fuel reservoir 7 to.

If, for example, the pre-feed pump 2 is designed to be re-controllable in speed, the fuel quantity can also be controlled by regulating the number of revolutions of the pre-feed pump 2 , which is supplied to the fuel accumulator 7 . Various control options for the fuel supply to the fuel accumulator 7 are thus possible.

The invention is not limited to the arrangement shown in Fig. 1 to a feeder, which includes a Vorför derpump with constant speed, a throttle valve 4 and egg ne high pressure pump 5 , the speed of which is proportional to the speed of the internal combustion engine, but applicable to any feeder device that leads to fuel in the fuel reservoir.

The pressure in the fuel reservoir 7 is set directly by a corresponding control of the pressure control valve 6 , which opens as a function of a first control signal from a predetermined fuel pressure in the fuel reservoir 7 and returns fuel via the return line 12 from the fuel reservoir 7 to the fuel tank 1 .

Fig. 2 shows schematically the structure of the pressure control valve 6 , which has a housing 21 which limits a control chamber 23 be. The pressure control valve 6 is connected to the fuel accumulator 7 via a feed line 20 . The feed line 20 mün det via a valve opening 28 in the control chamber 23rd The control chamber 23 has a drain 24 which is connected via the return line 12 to the fuel tank 1 . The valve opening 28 is assigned a closing member 29 , which is arranged in the control chamber 23 and is pressed against a corresponding sealing seat 22 via a closing spring 25 . To the closing member 29 is connected to an armature 26 of an electric magnet. The armature 26 is a magnet coil 27 to which the second control line 14 is connected.

The pressure control valve 6 of FIG. 2 works as follows: The spring force of the closing spring 25 and a corresponding energization of the solenoid 27 , the closing member 29 is pressed with a corresponding force against the associated sealing seat 22 . Thus, a holding pressure is pregiven ben up to which the closing member 29 closes the supply line 20 ver. Exceeds the fuel pressure in the fuel storage 7 , ie the rail pressure the predetermined holding pressure, the closing member 29 is lifted from the sealing seat 22 and fuel flows from the fuel storage 7 via the drain 24 and the return line 12 back to the fuel tank 1 .

Fig. 3 shows the rail pressure P as a function of the pulse-width modulated second control signal S2 with which the control unit 10 controls the pressure control valve 6 . For example, a holding pressure of 800 bar is set at a duty cycle of 40%. This means that the pressure control valve 6 is closed up to a fuel pressure of 800 bar and only opens when the fuel pressure in the fuel tank 7 exceeds the holding pressure of 800 bar.

Fig. 4 shows schematically in the form of a block diagram the structure of the control method. A first control block 30 controls the high-pressure side actuator, which corresponds to the pressure control valve 6 in this embodiment. A second control block 31 controls the low-pressure side actuator, which speaks the throttle valve 4 ent in this embodiment.

In a further development of the invention, the delivery capacity of the supply pump 2 and / or the pressure between the pre-feed pump 2 and the high pressure pump 5, in addition to the throttle valve 4, for example by a further pressure regulating gelventil and / or the delivery rate of the high pressure pump 5 are controlled.

The first control block 30 , the speed N of the internal combustion engine, the calculated injection quantity MF, the rail pressure FUP, the coolant temperature TCO of the internal combustion engine, the supply voltage VB and a status signal ES for the operating state of the internal combustion engine are supplied. From these variables, the first control block 30 determines a third control signal HP for the actuator on the high-pressure side, which is fed to the injection system 32 . In addition, the first control block 30 determines a pressure setpoint FUPS, which is preferably supplied to the second control block 31 .

The second control block 31 , the speed N of the internal combustion engine, the calculated injection quantity MF, the rail pressure FUP and the supply voltage VB are supplied. The second control block 31 determines a fourth control signal VC from the supplied data, which is fed to the injection system 32 . The rail pressure FUP of the fuel accumulator 7 is measured in the injection system 32 and fed to the first and the second control block 30 , 31 .

Fig. 5 shows the exact functioning of the first and the second control block 30 , 31 , which are preferably implemented in the control device 10 . In the first control block 30 of the coolant temperature and the TCO be calculated injection quantity MF is calculated from the rotational speed N, calculating a pressure setpoint FUPS in a fifth calculation unit 56th

The calculated injection quantity represents the fuel quantity that is supplied to the internal combustion engine during the next injection process. The fuel quantity MF to be injected is calculated by the control unit 10 as a function of the rotational speed and the driver's request and as a function of an engine map that is stored in the data memory 17 . The calculation of the pressure setpoint FUPS takes place as a function of engine characteristics and control methods, which are stored in the data memory 17 .

The pressure setpoint FUPS is fed to a seventh addition unit 57 . In addition, the pressure setpoint FUPS is passed to a fourth calculation unit 53 .

The rail pressure FUP is also fed to the seventh addition unit 57 , the seventh addition unit 57 forming a pressure difference FUPD according to the following formula:
FUPD = FUPS - FUP. The seventh addition unit 57 passes the pressure difference FUPD on to a linearization unit 58 . The linearizing unit 58 uses known methods to determine a linearized control signal LS, which represents a current control intervention, from the speed N, the rail pressure FUP and the pressure difference FUPD. The linearizing unit 58 contains a linearized PI controller, the calculation rule for the linearized control signal LS is as follows:

LS (i) = LS (i-1) + K. (FUPD (i) - (1- (TA / TN)). FUPD (i-1)),
where with LS (i) the current control intervention at time i, with LS (i-1) the previous control intervention at time (i-1), with FUPD (i) the current control difference, with FUPD (i-1) the previous control difference is designated, the control difference corresponding to the pressure difference value FUPD (i). K is an amplification factor of, for example, 0.1% per gap gap, TN is a reset time of, for example, 80 ms and TA is a sampling time of, for example, 20 ms. The sampling time TA defines the time which lies between the time i and the time i + 1 at which the values ab are sampled.

The gain factor K compensates for the non-linear behavior of the pressure control valve 6 via the rail pressure FUP. The gain factor K is calculated using the following formula: K = K0.LF, K0 denoting a basic gain factor with a value of, for example, 0.1% per megapascal and LF a linearization factor of, for example, 1.5. The linearization factor LF is taken from a characteristic curve and depends on the rail pressure FUP.

The control intervention LS (i) calculated in the linearization unit 58 is then fed to a second limiting unit 59 . The second limiting unit 59 prevents overloading of control unit components when the operating voltage is high. In addition, the second limitation unit 59 is adapted to improve the control quality of the working range of the pressure regulator 6 to the temperature-dependent adjustment range of the pressure regulator 6 .

The effective control intervention LS is therefore preferably limited as a function of the engine operating state ES, the battery voltage VB and the coolant temperature TCO. The setting range limits are stored in maps in the data memory 17 , which are set up via the battery voltage VB and / or the coolant temperature TCO, with a separate map being stored for each engine operating state. The engine operating conditions are, for example, the start of the internal combustion engine, idling or full load operation.

The control intervention LSG limited in this way is then passed to a first multiplier 60 . The first multiplier 60 multiplies the limited control intervention LSG by a second correction factor KB, which depends on the battery voltage VB. The second correction factor KB, which achieves compensation of the actuating current at the corresponding actuator with respect to the supply voltage VB, is either taken from a corresponding characteristic in data memory 17 or, as shown in the exemplary embodiment, determined in a first calculation unit 40 according to the following approximation equation : KB = (VBR / VB), with VBR a predetermined reference voltage and VB the supply voltage of the actuator is denoted, the supply voltage approximately corresponds to the battery voltage in the motor vehicle and the actuator in this case is the pressure control valve 6 .

The first multiplier 60 determines a second control signal HP using the following formula: HP = LSG.KB. The second control signal represents the corrected, current control intervention, which is guided to the pressure control valve 6 via the second control line 14 . The second control signal is designed as a pulse-width-modulated control signal which, by means of its pulse duty factor, as shown in FIG. 3, specifies the pressure in the fuel accumulator 7 .

The second control block 31 determines a first control signal for the throttle valve 4 essentially as a function of the fuel mass flow, which must be supplied at least to the fuel tank 7 in order to maintain the desired rail pressure and to provide the injection quantity requested by the driver.

For this purpose, the injection mass flow MFI is calculated in a second calculation unit 42 from the injection quantity MF requested and calculated by the driver and the engine speed N and the number of cylinders Z of the internal combustion engine according to the following equation: MFI = ZNMF.0.5. The calculated injection mass MF is given in mg fuel mass per injection cycle, with only half of the cylinders performing an injection per injection cycle. The injection mass flow MFI is fed to a third multiplier 44 .

In addition, a leakage mass flow MFL is preferably determined as a function of the measured rail pressure FUP from a first map 41 and passed to a second multiplier 43 . The second multiplier 43 multiplies the leakage mass flow MFL by a first safety factor SL, which is read out from a first data field 54 of the data memory. The first safety factor SL was determined experimentally and has positive values that are greater than 1. The second multiplier 43 calculates a safety leakage mass flow ML using the following formula: ML = MFL.SL. The value of the safety mass flow ML is fed to a first adding unit 45 .

The third multiplier 44 reads a second safety factor SI from a second data field 55 of the data memory 17 and multiplies the injection mass flow MFI by the second safety factor SI and thus receives a safety mass flow MI which the third multiplier 44 passes on to the first adding unit 45 . The safety mass flow MI is calculated using the following formula: MI = MFI.SI. The second safety factor SI is determined experimentally and has a positive value greater than 1.

With the aid of the first and second security factor that more fuel is supplied to the fuel reservoir 7, is taken as the fuel reservoir 7 is ensured. The first and the second safety factors are preferably stored in a characteristic diagram which depends on the operating time of the internal combustion engine, whereby aging effects of the injection system are taken into account. The mileage of the motor vehicle can also be used instead of the operating time.

The first adding unit 45 calculates a fuel mass flow MR according to the following formula: MR = ML + MI. The fuel mass flow MR is then fed to a third calculation unit 47 . The third calculation unit 47 calculates a basic control signal VCB from the fuel mass flow MR and the engine speed N. For this purpose, the third calculation unit 47 determines the basic control signal VCB from a delivery characteristic map, which depends on the fuel mass flow MR and the engine speed N. The conveyor characteristic map depicts the never pressure-side delivery characteristic of the feed device, which depends on the components used. The conveyor map shows the relationship between the first control signal and the amount of fuel that is supplied to the fuel tank 7 when the feeder is controlled by the first control signal.

In the exemplary embodiment described, the low-pressure delivery characteristic is essentially determined by the throttle valve 4 , since the prefeed pump 2 runs at a constant speed and the high-pressure pump 5 runs at a speed proportional to the engine speed N. The funding map is determined experimentally.

When using a speed-controlled pre-feed pump or a speed-controlled high-pressure pump is the delivery indicator Adjust the field accordingly and / or in addition to the choke valve to re-feed the pre-feed pump or the high pressure pump apply. However, the control signals for the front feed pump and the high pressure pump only after determining the Mass flow of fuel from corresponding production maps certainly.

The basic control signal VCB is supplied to a fourth multiplier 49 . The fourth multiplier unit 49 multiplies the basic control signal VCB with a pressure correction factor CP and determines a pressure-corrected control signal VCP according to the following formula: VCP = VCB.CP. The pressure correction factor CP is determined on the basis of a second map 46 as a function of the measured rail pressure FUP.

The pressure correction factor CP is used because the delivery of the high pressure pump 5 depends on the rail pressure FUP and decreases with increasing rail pressure FUP. Therefore, at a higher rail pressure FUP, the throttle valve 4 for the promotion of the same fuel flow in the fuel accumulator 7 must be opened further than at a lower rail pressure FUP.

The corrected base signal VCP is fed to the fifth adding unit 50 . The fifth adding unit 50 sums the corrected base signal VCP and a zero point value AD and preferably a dynamic intervention VD to a first control signal VC. The zero point value AD is read from a third characteristic field 48 as a function of the coolant temperature TCO. The zero point value AD compensates for the change in the zero point of the throttle valve 4 as a function of the temperature of the throttle valve 4 . At a higher temperature, the resistance of the throttle valve 4 increases and, as a result, a higher actuating current for controlling the Drosselven valve 4 is necessary than at a lower temperature. Approximately, instead of the temperature of the throttle valve 4, the coolant temperature TCO of the internal combustion engine is used. In this way it is ensured that the Drosselven valve 4 has the desired degree of opening regardless of its temperature.

The dynamic intervention VD is determined with the aid of a fourth calculation unit 53 , which represents a limited DT1 control element. The calculation rule of the fourth calculation unit 53 is defined as follows:

where with VD (i) the current value of the dynamic intervention at time i, with VD (i-1) the previous value of dyna mix intervention at time (i-1), with FUPS (i) the actu All pressure setpoint, with FUPS (i-1) the previous pressure setpoint, with KD a gain factor of, for example 0.1% .sec / megapascal, with TA a sampling time of for example of 20 ms and with T1 a time constant of for example, 200 ms. The sampling time is that Time between the sampling time i and the sampling time point i + 1 lies.

The time constant T1 and the gain factor KD are preferably determined as a function of the engine operating state and the engine speed N. The task of the dynamic intervention is to increase or decrease the fuel supply on the low-pressure side disproportionately, in particular during the transition between engine operating states, so as to accelerate the pressure build-up or the pressure reduction in the fuel accumulator 7 .

In a fifth multiplication unit 51 , the first control signal VC is preferably multiplied by the second correction factor KB, which compensates the actuating current in relation to different supply voltages of the low-pressure side actuator, that is, in this embodiment, for example, in relation to the supply voltage of the throttle valve 4 , causes.

The sixth multiplier unit 51 thus determines an actuating signal VCP using the following formula: VCP = VC.KB. The control signal VCP is then fed to a first limiting unit 52 , which limits the control range of the control signal. The limitation of the operating range prevents overloading of the control unit components when the battery voltage is high. In addition, to improve the control performance of the Ar is adapted beitsbereich of the throttle valve 4 to the temperature-dependent adjustment range of the throttle valve. 4

The effective control intervention is limited as a function of the supply voltage, which approximately corresponds to the battery voltage. The setting range limits are stored in a map that is spanned via the supply voltage VB. The limited control signal V is from the first limiting unit 52 leads via the first control line 13 as the first control signal to the throttle valve 4 ge.

Fig. 6 shows the pressure setpoint FUPS and dynamic engagement VD as a function of time t. It can be clearly seen that the sudden increase in the pressure setpoint FUPS causes the dynamic intervention VD to increase disproportionately and then to return to zero.

Fig. 7 shows the calculated injection quantity MF, the rail pressure FUP, the pressure setpoint FUPS, the second control signal S2 of the pressure control valve and the first control signal S1 for the throttle valve plotted over time t. The high control quality and the rapid adjustment of the rail pressure to the pressure setpoint are clearly visible.

A major advantage of the invention is that first the fuel mass flow MR is determined and then the first control signal for the low-pressure side actuator is calculated depending on the fuel mass flow MR. The calculation of the fuel mass flow MR is thus decoupled from the calculation of the control signal. This enables more precise control. In addition, application expenditure is saved since the fuel mass flow MR is calculated as a function of operating parameters and then the corresponding first control signal is determined in the third calculation unit 47 depending on a conveying map that is adapted to the respective injection system.

Various feeding devices used for supplying fuel in the fuel accumulator 7, Thus, the control unit maps by respective different support, which are taken in the third taken into calculation unit 47, are fitted to the various feeders on. This allows the control function to be quickly and easily adapted to different injection systems.

In particular by taking the rail pressure into account Pressure correction factor CP, by taking zero into account point shift by the zero point value AD and by the Taking into account the supply voltage VB becomes a very precise regulation procedure provided.

Another significant advantage of the invention resides in that in the low-pressure control of the fuel supply the rail pressure FBD is not taken into account directly. Even with the dynamic intervention VD the rail pressure FUP, son The pressure setpoint FUPS is used to add fuel drove to settle. This is a rocking of the regulation of Rail pressure FUP safely avoided.

Claims (11)

1. Method for regulating the fuel pressure in a fuel accumulator ( 7 ) of an injection system for an internal combustion engine ( 16 ),
the fuel reservoir ( 7 ) being supplied with fuel via a feed device ( 2 , 4 , 5 ),
wherein fuel is discharged from the fuel accumulator via a pressure control valve ( 6 ),
wherein the pressure in the fuel accumulator ( 7 ) is determined, characterized in that
that an injection quantity (MR) for the internal combustion engine is determined as a function of the driver's request and the speed of the internal combustion engine ( 16 ),
that a first control signal (VCB) for the feed device ( 2 , 4 , 5 ), with which the feed device is controlled, is determined as a function of the injection quantity (MR),
that a second control signal (LS) for the pressure control valve ( 6 ) is determined with which the pressure control valve ( 6 ) is controlled depending on the speed of the internal combustion engine ( 16 ), depending on the pressure in the fuel accumulator ( 7 ) and depending on a set pressure (FUPS) becomes. 2. The method according to claim 1, characterized in that the first control signal depending on the supply voltage (VB) the feeder is corrected. 3. The method according to claim 1, characterized in that the second control signal is corrected depending on the supply voltage of the pressure control valve ( 6 ). 4. The method according to claim 1, characterized in that the first or the second control signal are limited to a predetermined range of values ( 52 , 59 ). 5. The method according to claim 1, characterized in that the injection quantity is corrected as a function of the pressure in the fuel accumulator ( 41 , 43 , 45 ). 6. The method according to claim 1, characterized in that the first control signal is corrected depending on the pressure in the fuel accumulator ( 7 ) ( 46 , 49 ). 7. The method according to claim 1, characterized in that the first control signal is corrected depending on the temperature of the feed device ( 48 , 56 ). 8. The method according to claim 1, characterized in that at least from the speed of the internal combustion engine, a pressure setpoint (FVPS) is determined for the fuel accumulator, and that the first control signal is corrected depending on the pressure setpoint ( 50 ). 9. The method according to claim 8, characterized in that depending on the change in the pressure setpoint Control signal is corrected disproportionately (VD, 50). 10. The method according to claim 1, characterized in that the first control signal is determined from a map ( 47 ) which depends on the fuel mass flow (MR) and the speed (N) of the internal combustion engine ( 16 ). 11. Device for regulating the fuel pressure in one Fuel storage system of an injection system using the method according to claim 1.