Control for overrun cutoff of internal combustion engine

Abstract

A method for controlling an internal combustion engine operated with direct fuel injection may include, during a transition phase after the end of an overrun cut-off with resumption of fuel injection and normal operation of the internal combustion engine, shifting an injection start time (SOI) by an adaptation value (SOI) in relation to an injection start time (SOI) which lies later than an injection start time (SOI_Norm) determined during normal operation of the internal combustion engine.

Claims

1. A method for controlling an internal combustion engine operated with direct fuel injection, the method comprising: at a beginning of an overrun cut-off operating state, stopping a supply of fuel to combustion chambers of the internal combustion engine and starting a time counter incremented from zero in steps of a first magnitude as time elapses; entering a transition phase after the overrun cut-off operating state; at a beginning of the transition phase, reversing the time counter in decrements of a second magnitude as time elapses; during the transition phase, resuming fuel injection and retarding an injection start time in relation to a normal injection start time based on normal operation of the internal combustion engine; and when the time counter reaches zero, entering normal operation of the internal combustion engine.

2. The method as claimed in claim 1, wherein a magnitude of the retardation of the injection start time depends on a time duration of the overrun cut-off.

3. The method as claimed in claim 1, wherein the magnitude of the retardation of the injection start time depends on a value of the time counter.

4. The method as claimed in claim 3, wherein the magnitude of the retardation of the injection start time is greater the higher the value of the time counter is.

5. The method as claimed in claim 1, wherein the fuel mass to be metered in is injected in the form of multiple injections during the transition phase.

6. The method as claimed in claim 5, wherein a division factor for the multiple injections depends on a value of the time counter, and the lower the value of the counter is, the greater the fuel mass injected by a first injection of the multiple injections.

7. The method as claimed in claim 5, wherein the multiple injections are performed until the value of the counter reaches zero.

8. The method as claimed in claim 1, wherein the first magnitude and the second magnitude depend a magnitude of an air mass flow (MAF) in an intake tract of the internal combustion engine.

9. The method as claimed in claim 1, wherein the first magnitude and the second magnitude depend a speed (N) and a load of the internal combustion engine.

10. An internal combustion engine operated with direct fuel injection, the internal combustion engine comprising: at least one combustion chamber; a fuel injector metering fuel into the at least one combustion chamber; and a controller operable to adjust the timing and amount of fuel metered by the fuel injector, wherein the controller is programmed to: at a beginning of an overrun cut-off operating state, stop a supply of fuel to the at least one combustion chamber and start a time counter incremented from zero in steps of a first magnitude as time elapses; enter a transition phase after the overrun cut-off operating state; at a beginning of the transition phase, reverse the time counter in decrements of a second magnitude as time elapses; during the transition phase, resume fuel injection and retard an injection start time in relation to a normal injection start time based on normal operation of the internal combustion engine; and when the time counter reaches zero, enter a normal operation phase of the internal combustion engine.

11. The internal combustion engine as claimed in claim 10, wherein a magnitude of the retardation of the injection start time depends on a time duration of the overrun cut-off.

12. The internal combustion engine as claimed in claim 10, wherein the magnitude of the retardation of the injection start time depends on a value of the time counter.

13. The internal combustion engine as claimed in claim 12, wherein magnitude of the retardation of the injection start time is greater the higher the value of the time counter is.

14. The internal combustion engine as claimed in claim 10, wherein, upon, the fuel mass to be metered in is injected in the form of multiple injections during the transition phase.

15. The internal combustion engine as claimed in claim 14, wherein a division factor for the multiple injections depends on a value of the time counter, and the lower the value of the counter is, the greater the fuel mass injected by a first injection of the multiple injections.

16. The internal combustion engine as claimed in claim 10, wherein the first magnitude and the second magnitude depend on a magnitude of an air mass flow (MAF) in an intake tract of the internal combustion engine.

17. The internal combustion engine as claimed in claim 10, wherein the first magnitude and the second magnitude depend on a speed (N) and a load of the internal combustion engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and refinements of the present invention will emerge from the description of the following exemplary embodiment, which is illustrated in the drawing, in which:

(2) FIG. 1 shows, in a schematic illustration, a block diagram of an internal combustion engine which is operated with direct fuel injection and which has the control device according to teachings of the present disclosure, and

(3) FIG. 2 shows a flow diagram of the control of the transition between operation with overrun cut-off and normal operation of said internal combustion engine according to teachings of the present disclosure.

DETAILED DESCRIPTION

(4) FIG. 1 shows, in a schematic illustration, an Otto-cycle internal combustion engine 10 which has a fuel supply device 11 for injecting fuel KST directly into combustion chambers of cylinders Z1-Z4. The internal combustion engine 10 is supplied with the fresh air required for the combustion of the fuel-air mixture in the cylinders Z1-Z4 via an intake tract 12. The combustion exhaust gases flow through at least one exhaust-gas catalytic converter, which is arranged in an exhaust tract 13, and through a silencer into the surroundings.

(5) For the control of the transition between operation with overrun cut-off and normal operation of the internal combustion engine 10, an electronic control device 14 is provided. The control device 14 comprises a processing unit (processor) 15 which is coupled to a program memory 16, to a value memory (data memory) 17 and to a time counter 23. Inter alia, there is implemented in software form in the program memory 16 a characteristic map-based function FKT_SCH for the control of the transition between operation with overrun cut-off and normal operation of the internal combustion engine 10, which function will be discussed in more detail on the basis of the description of FIG. 2.

(6) In the value memory 17 there are stored, inter alia, parameters or threshold values SOI_Norm, SOI, ZS1,2, ZS_MAX, the meanings of which will likewise be discussed in more detail further below on the basis of the description of FIG. 2.

(7) The control device 14 is connected to various sensors which detect operating parameters of the internal combustion engine 10 and operating parameters of the motor vehicle that is driven by way of the internal combustion engine 10. The sensors are inter alia an accelerator pedal position sensor 18, which detects an accelerator pedal value FPW, that is to say detects the position of an accelerator pedal 19, an air mass sensor 20 which is arranged in the intake tract 12 and which serves as a load sensor and which detects a signal MAF corresponding to the load of the internal combustion engine 10, a throttle flap sensor 25 which detects a throttle flap opening angle DKW of a throttle flap 24 arranged in the intake tract 12, a crankshaft angle sensor 21, which detects a crankshaft angle of the internal combustion engine 10, to which an engine speed N is then assigned, and a temperature sensor 22, which detects a signal TEMP which is representative of the temperature of the internal combustion engine 10, generally the coolant temperature of the internal combustion engine 10.

(8) Said sensors are normally provided in any case, because the signals thereof may be used for the control program of the engine management system.

(9) Instead of the air mass sensor 20 as a load sensor, it is alternatively or additionally also possible for an intake pipe pressure sensor to be used.

(10) In some embodiments, the control program FKT_SCH for the control of the transition between operation with overrun cut-off and normal operation is not executed in a separate control device 14 but is contained as a sub-program in the management system of the engine controller. In this way, it is possible to dispense with additional hardware.

(11) The method for controlling the transition between operation with overrun cut-off and normal operation will be discussed on the basis of a flow diagram in FIG. 2.

(12) The method is started, in a step S1, whenever the fuel supply to the cylinders Z1-Z4 is shut off in overrun operation of the internal combustion engine 10, that is to say overrun cut-off operation is present.

(13) At the start of said overrun cut-off phase, the time counter 23 is started in a step S2, and, during the ongoing operation of the overrun cut-off phase, said time counter is incremented by a first value ZS1 per scan. The value of the increment ZS1 is dependent on the air mass flow MAF through the cylinder Z1-Z4 and is stored in a characteristic map of the value memory 17. In this way, the cooling of the internal combustion engine, in particular the cooling of the combustion chambers and of the pistons, owing to the air mass flow MAF can be allowed for. Said air mass flow MAF may advantageously be detected directly by the air mass sensor 20. Alternatively or in addition, the engine speed and the load may also be taken into consideration.

(14) The overrun cut-off operating range is maintained until, in a subsequent step S3, ending of the overrun cut-off operation, that is to say resumption of the fuel injection into the cylinders Z1-Z4, is detected.

(15) If the conditions for overrun cut-off operation are still met, then it is queried in a step S4 whether the counter status ZS of the counter 23 has reached a predefined maximum value ZS_MAX. The maximum value ZS_MAX is stored in the value memory 17 and defines the maximum time duration for which the shift of the injection start time in the retarding direction is used.

(16) The loop composed of the steps S2, S3 and S4 is run through until either the maximum value ZS_MAX has been reached or the overrun cut-off operating range has been departed from, for example because the driver of the vehicle that is operated by way of the internal combustion engine 10 has actuated the accelerator pedal 19.

(17) In the event of the accelerator pedal actuation, that is to say upon the departure from the overrun cut-off operation, the fuel injection is enabled in a subsequent step S5, and in a step S6, the time counter 23 is restarted and, during the ongoing fired operation of the internal combustion engine 10, is decremented by a second value ZS2 per scan. The value of the decrement ZS2 is dependent on the air mass flow MAF or on the engine speed N and the load, and is likewise stored in a characteristic map of the value memory 17.

(18) With the resumption of the fuel injection, the injection start time SOI is shifted by a value SOI in the direction of an injection start time SOI+SOI which lies at a later point in time than the injection start time determined from speed, load and temperature of the internal combustion engine. The value SOI may in this case be set in a manner dependent on the counter status ZS, wherein the value SOI is greater the higher the counter status ZS is.

(19) Alternatively, the injection start time SOI may also, regardless of the counter status ZS, be shifted by a constant value SOI in the direction of an injection start time SOI which lies at a later point in time. Said value is also stored in the value memory 17.

(20) After the shift of the injection start time SOI has been performed, it is queried in a step S7 whether the counter status ZS has already reached the value zero. If this is not yet the case, then a branch is followed back to step S6, and a further shift of the injection start time SOI is performed.

(21) If the counter status ZS has reached the value zero, no further shift is performed, and a value SOI_Norm is assumed which is determined from the present operating point of the internal combustion engine (engine speed, load, temperature) (step 8). Subsequently, the method is ended in a step S9.

(22) Furthermore, it is also possible, upon the resumption of the fuel injection in step S6, for the fuel mass to be metered in to additionally be introduced into the combustion chamber in the form of multiple injections in order to reduce the penetration of the fuel jet. The multiple injections are activated until the counter status ZS has reached the value zero. The division factor for the multiple injections may in this case preferably be defined in a manner dependent on the counter status ZS. The lower the counter status ZS is, the greater is the proportion of the divided total fuel mass to be metered in that is assigned to the first injection of the multiple injections.

LIST OF REFERENCE DESIGNATIONS

(23) 10 Otto-cycle internal combustion engine 11 Fuel supply apparatus 12 Intake tract 13 Exhaust tract 14 Electronic control device 15 Control unit, processing unit, processor 16 Program memory 17 Data memory, value memory 18 Accelerator pedal position transducer 19 Accelerator pedal 20 Air mass sensor, load sensor 21 Crankshaft angle sensor 22 Temperature sensor 23 Time counter 24 Throttle flap 25 Throttle flap sensor DKW Throttle flap opening angle FKT_SCH Control function, overrun cut-off operation FPW Accelerator pedal value KST Fuel MAF Air mass flow, load signal N Speed of the internal combustion engine SOI Injection start time, start of injection SOI Adaptation value for injection start time SOI_Norm Injection starting time for normal operation TEMP Internal combustion engine temperature Z1-Z4 Cylinders of the internal combustion engine ZS Counter status ZS1 Increment counter status ZS2 Decrement counter status ZS_MAX Maximum value of counter status S1-S9 Method steps