System for operating an internal combustion engine with direct injection, specially in a motor vehicle

An internal combustion engine for a motor vehicle is described which is provided with an injection valve with which fuel can be injected directly into the combustion chamber either in a first mode of operation during a compression phase or in a second mode of operation during an induction phase. Furthermore, the engine is provided with means for feeding back the exhaust gas into the combustion chamber as well as with a control apparatus for controlling (open loop and/or closed loop) the quantity of the fed back exhaust gas. According to the invention, the quantity of the exhaust gas, which is fed back into the combustion chamber, can be controlled (open loop and/or closed loop) differently in the two modes of operation.

FIELD OF THE INVENTION
 The invention relates to a method for operating an internal combustion
 engine of a motor vehicle wherein the fuel is injected directly into the
 combustion chamber of the engine either in a first operating mode during a
 compression phase or in a second operating mode during an intake phase and
 the fuel is combusted in the combustion chamber. In the method, at least a
 portion of the exhaust gas, which is generated in the combustion, is fed
 back into the combustion chamber. Furthermore, the invention relates to an
 internal combustion engine especially for a motor vehicle. The engine has
 an injection valve with which fuel can be injected directly into a
 combustion chamber either in a first mode of operation during a combustion
 phase or in a second mode of operation during an intake phase. The engine
 also includes means for feeding back the exhaust gas into the combustion
 chamber and has a control apparatus for controlling (open loop/closed
 loop) the quantity of exhaust gas fed back.
 BACKGROUND OF THE INVENTION
 A system of this kind for operating an internal combustion engine having
 direct injection especially for a motor vehicle is generally known and is
 continuously further developed with respect to a further reduction of fuel
 and a reduction of exhaust gas.
 In this connection, a so-called stratified charge operation as a first
 operating mode and a so-called homogeneous operation as a second operating
 mode are distinguished. The stratified charge operation is especially used
 for small loads; whereas, the homogeneous operation is applied for larger
 loads applied to the engine. In the stratified charge operation, the fuel
 is injected into the combustion chamber during the combustion phase and is
 there injected in the immediate vicinity of a spark plug. The fuel can
 however also be injected further distant from the spark plug and can be
 conducted to the spark plug via a movement of air. This has the
 consequence that no uniform distribution of the fuel can take place in the
 combustion chamber. The advantage of the stratified operation is that the
 applied smaller loads can be handled by the engine with a very small
 quantity of fuel. Larger loads, however, cannot be satisfied in the
 stratified charge operation. In the homogeneous operation, which is
 provided for such larger loads, the fuel is injected during the intake
 phase of the engine so that a swirling and therefore a distribution of the
 fuel in the combustion chamber can still easily take place. To this
 extent, the homogeneous operation corresponds approximately to the
 operation of internal combustion engines wherein fuel is injected into the
 intake manifold in the conventional manner.
 In both modes of operation, that is, in the stratified load operation and
 in the homogeneous operation, the fuel quantity to be injected is
 controlled (open loop and/or closed loop) to an optimal value in
 dependence upon a plurality of input quantities with respect to a
 reduction of fuel, a reduction of exhaust gas and the like.
 Here it is advantageous for the reduction of the generated exhaust gas when
 the exhaust, which arises in the combustion in the combustion chambers, is
 not immediately discharged into the ambient and is instead fed back into
 the combustion chambers in order to again be conducted for combustion.
 SUMMARY OF THE INVENTION
 It is an object of the invention to provide an internal combustion engine
 having direct injection wherein further fuel reductions and exhaust gas
 reductions are possible with the aid of the exhaust-gas feedback.
 This task is solved in a method of the above-mentioned type or for an
 internal combustion engine of the above-mentioned type in that the
 quantity of exhaust gas, which is fed back into the combustion chamber, is
 differently controlled in both modes of operation with the control being
 open loop and/or closed loop.
 Accordingly, both modes of operation of the internal combustion engine
 having direct injection are considered in the control (open loop/closed
 loop) of the exhaust gas which is fed back. This means that especially in
 stratified charge operation, the exhaust-gas feedback is controlled (open
 loop and/or closed loop) differently than in homogeneous operation and the
 greatest reduction in fuel is achievable in stratified charge operation.
 Thus, in stratified charge operation, it is necessary to reduce the
 nitrogen oxide emissions which occur in this mode of operation via a
 corresponding exhaust-gas feedback as far as possible. Furthermore, and
 according to the invention, the transitions which are present between the
 two modes of operation, are controlled differently (open loop and/or
 closed loop). In total, a system for operating an internal combustion
 engine having direct injection is thereby achieved with which an optimal
 fuel reduction with simultaneous exhaust gas reduction is obtained based
 on the particular adapted control (open loop and/or closed loop) in each
 mode of operation.
 In an advantageous configuration of the invention, the quantity of feedback
 exhaust gas in the first mode of operation is controlled (open loop and/or
 closed loop) in dependence upon the rpm of the engine and/or upon the
 torque, which is to be outputted by the engine, and/or the fuel mass which
 is to be injected into the combustion chamber. Accordingly, in the
 stratified charge operation, a complex and complete control (open loop
 and/or closed loop) of the exhaust-gas feedback is carried out. In this
 way, it is achieved that nitrogen oxide emissions, which arise in the
 stratified charge operation, are reduced to a minimum with the aid of the
 exhaust-gas feedback. According to the invention, the reductions in fuel,
 which are possible in stratified charge operation, are achievable with a
 simultaneous reduction in exhaust gas.
 It is especially purposeful when the following are considered: the intake
 air temperature and/or the engine temperature and/or the ambient pressure
 and/or the degree of tank venting and/or the like. In the control (open
 loop and/or closed loop) according to the invention of the exhaust-gas
 feedback in layered charge operation, not only are the dynamic operating
 conditions considered such as the rpm of the engine but also the
 statistical operating conditions such as the engine temperature. In this
 way, the control (open loop and/or closed loop) is optimally adapted to
 the conditions of the internal combustion engine and an optimal reduction
 of the generated exhaust gas is thereby achieved.
 In an advantageous further improvement of the invention, the quantity of
 the exhaust gas, which is fed back into the combustion chamber, is
 controlled (open loop and/or closed loop) in dependence upon the
 intake-manifold pressure for a switchover into the first mode of
 operation. In this way, it is achieved that a transition as uniform as
 possible is present with the switchover from the homogeneous operation
 into the stratified charge operation. In this connection, it is especially
 purposeful when the exhaust-gas feedback is adapted to the dynamic of the
 intake manifold.
 In an advantageous embodiment of the invention, a constant quantity and
 especially a small quantity or even no exhaust gas is fed back in the
 second mode of operation. In the homogeneous operation, only a small or
 even no exhaust-gas feedback is therefore required. In this way, it is
 avoided in homogeneous operation that a feedback of exhaust gas which is
 too high leads to disturbances of the combustions in the combustion
 chambers.
 In an advantageous improvement of the invention, for a switchover into the
 second mode of operation, an actual switchover is only made after a
 pregiven time duration. Because of the dynamic of the exhaust-gas
 feedback, a larger quantity of exhaust is fed back after a switchover
 which is to be made. If, under these preconditions, a switchover were made
 into the stratified charge operation, this could lead to combustion
 misfires or the like. Therefore, the actual switchover into the stratified
 charge operation is delayed. In this way, combustion misfires are reliably
 avoided. During this delay, the exhaust-gas feedback is already adjusted
 to the value required for the stratified charge operation, that is, to a
 small quantity or even no feedback exhaust gas.
 In an advantageous embodiment of the invention, the quantity of the actual
 fed back exhaust gas is determined and is compared to the desired quantity
 of the fed back exhaust gas and a correction is carried out in dependence
 thereon. Thus, a desired/actual comparison is carried out on the basis of
 which the exhaust-gas feedback is then influenced. In this way, a rapid
 and precise adaptation of the exhaust-gas feedback to the changes, for
 example of the operating conditions of the engine, is achieved.
 In a further advantageous embodiment of the invention, the exhaust gas is
 fed back via an internal exhaust-gas feedback and/or via an external
 exhaust-gas feedback into the combustion chamber of the engine. For the
 external exhaust-gas feedback, it can be concerned with an exhaust-gas
 pipe which connects the exhaust-gas end of the engine to the intake end
 thereof. It is especially purposeful when an exhaust-gas feedback valve is
 provided in this exhaust-gas pipe which is adjustable for controlling
 (open loop and/or closed loop) the quantity of the exhaust gas fed back.
 In this way, it is especially possible in a simple manner to control (open
 loop and/or closed loop) the exhaust which is fed back via the external
 exhaust-gas return path. An internal exhaust-gas return path can, for
 example, relate to a displacing mechanism for the camshaft with which it
 can be achieved that the inlet and outlet valves, which are controlled by
 the camshaft, are at least opened simultaneously for a short time. An
 exhaust-gas feedback via the outlet and inlet valves can take place during
 this short time duration.
 In an advantageous further improvement of the invention, the quantity of
 the actual fed back exhaust gas is determined in dependence upon: the
 intake manifold pressure and/or the inducted air mass and/or the
 exhaust-gas temperature. It is especially purposeful when the position of
 the exhaust-gas return valve and/or the position of the camshaft is
 detected by the control apparatus. In this way, it is possible to rapidly
 and precisely determine the quantity of the actual fed back exhaust gas
 and to consider the quantity of the fed back exhaust gas in the control
 (open loop and/or closed loop).
 In a further advantageous improvement of the invention, the quantity of the
 exhaust gas, which is returned into the combustion chamber of the engine,
 is considered in the control (open loop and/or closed loop) of the fuel
 mass which is to be injected into the combustion chamber and/or of the
 ignition spark igniting the fuel in the combustion chamber. In this way,
 it is achieved that the effect of the fed back exhaust gas on the
 combustion leads to no change of the combustion process.
 The realization of the method of the invention in the form of an electric
 storage medium is of special significance. This storage medium is provided
 for a control apparatus of an internal combustion engine and especially of
 a motor vehicle. A program is stored on the electric storage medium which
 can be run on a computer apparatus (especially on a microprocessor) and is
 suitable for carrying out the method of the invention. In this case, the
 invention is realized by a program stored on the electric storage medium
 so that this storage medium, which is provided with the program, defines
 the invention in the same manner as the method for which the execution of
 the program is suitable.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
 In FIG. 1, a control 1 is shown for the exhaust-gas feedback for an
 internal combustion engine having direct injection. In this control, a
 desired value generation 2 is provided which makes available a desired
 value magrdes for the quantity of the exhaust gas to be fed back. This
 desired value generation 2 is explained in greater detail with respect to
 FIG. 2.
 Corresponding to FIG. 1, the desired value magrdes is supplied to a
 comparator 3 and a drive unit 4. In the comparator 3, the desired value
 magrdes is compared to an actual value magract of the quantity of the
 exhaust gas to be fed back and a corrective value dmagr is generated in
 dependence upon the difference and is likewise supplied to the drive unit
 4.
 The exhaust-gas feedback is influenced with the aid of the drive unit 4.
 Thus, it is possible that the drive unit 4 influences an external
 exhaust-gas feedback in that an exhaust-gas feedback valve 5 is adjusted
 by the control unit 4. In this way, so much more exhaust gas is fed back
 into the combustion chambers of the engine the more the exhaust-gas return
 valve is opened. Furthermore, it is possible that the drive unit 4
 influences an internal exhaust-gas feedback in that the camshaft 6 of the
 engine is shifted by the drive unit. Then, the exhaust gas is fed back
 into the combustion chambers for that time duration during which the inlet
 and outlet valves are simultaneously opened by the camshaft.
 The exhaust-gas feedback valve 5 and the camshaft 6 are influenced by the
 drive unit 4 in dependence upon the desired value magrdes and the
 corrective value dmagr. The desired value magrdes is therefore
 continuously corrected by the corrective value dmagr. The division of the
 total exhaust-gas feedback to the external and the internal exhaust-gas
 feedback can take place with respect to characteristic fields or other
 relationships.
 The position of the exhaust-gas feedback valve 5 and the position of the
 camshaft 6 can be detected with the aid of sensors. These signals are
 supplied to an actual value generator 7 which determines the actual value
 magract for the actual quantity of the fed back exhaust gas based on this
 signal as well as additional data such as the intake manifold pressure
 and/or the inducted air mass and/or the exhaust-gas temperature. The
 actual value magract is then supplied to the comparator 3 as already
 mentioned.
 With the aid of the control 1, which is shown in FIG. 1, the quantity of
 the exhaust gas, which is fed back into the combustion chambers of the
 engine, is controlled to the desired value magrdes. The desired value
 magrdes is pregiven by the desired-value generator 2 and is thereafter
 compared to the actual value magract and is then correspondingly
 corrected. The adjustment of the exhaust-gas feedback takes place with the
 aid of the drive unit 4 and the adjustment of the exhaust-gas feedback
 valve 5 and/or the camshaft 6.
 The desired-value generator 2 of FIG. 1 is shown in greater detail in FIG.
 2. There, a first value egr1 for a desired exhaust-gas quantity to be fed
 back is determined from the rpm of the engine nmot and the indicated
 torque Mi or the fuel mass mk, which is to be injected, via a
 characteristic field 8. This value relates to a theoretical or
 standardized operating state of the engine, that is, to a specific
 temperature of the engine for example. From this first value egr1, a
 second value egr2 is determined for the desired exhaust-gas quantity to be
 fed back in a block 9 while considering the actual operating state of the
 engine. For example, in the block 9, the following are, for example,
 considered: the inducted air temperature tans and/or the engine
 temperature tmot and/or the ambient temperature pu and/or the degree of
 tank venting and/or other data as to the actual operating state of the
 engine.
 The second value egr2 is thereafter distributed with the aid of switch 10.
 Switch 10 can assume four switching positions which can be selected with
 the aid of four binary signals.
 If there is a signal B_sh=1, then this means that there should be a
 switchover from stratified charge operation into the homogeneous
 operation. In this case, the second value egr2 is connected to the
 terminal "stratified.fwdarw.homogeneous". If the signal is B_hs=1, then
 this means that there should be a switchover from homogeneous operation
 into the stratified charge operation. In this case, the second value egr2
 is connected to a terminal "homogeneous.fwdarw.stratified". If the signal
 is B_sa=1 or the signal is a signal B_st=1, then this means that the
 engine is in a starting operation or is in overrun operation. In this
 case, the second value egr2 is connected to a terminal "start, overrun".
 In all other cases, the second value egr2 is connected to a terminal
 "other".
 Should there be a switchover from the stratified operation into the
 homogeneous operation, that is B_sh=1, then the second value egr2 is
 applied to a time-delay element 11 and a block 12. The desired value
 magrdes is formed for the quantity of the exhaust gas to be fed back by
 the block 12 which is constant in homogeneous operation. This applies also
 to magrdes=c wherein c is a smaller value or can even be zero. The value c
 can but need not be dependent from the second value egr2. This constant
 value c for the desired value magrdes is made immediately available. The
 time duration TAGRDYN of the time-delay element 11 is dependent upon the
 dynamic of the exhaust-gas feedback and the dynamic of the intake manifold
 of the engine. Only after the time duration TAGRDYN has elapsed, is a
 binary signal B_egrsh generated by the time-delay element 11 after which
 there is an actual switchover into homogeneous operation.
 Because of the time duration TAGRDYN, it is achieved that the exhaust gas,
 which is present in the exhaust-gas feedback and in the intake manifold,
 is still combusted during stratified charge operation and only then is
 there a switchover into the homogeneous operation with its lesser demand
 of exhaust gas to be fed back. Insofar, combustion misfires are therefore
 avoided which are caused by an excess of fed back exhaust gas.
 If there is to be a switchover from homogeneous operation into the
 stratified charge operation (that is, B_sh=1), then the second value egr2
 is applied to a block 13 with which the second value egr2 is adapted to
 the dynamic of the intake manifold of the engine. The desired value
 magrdes is therefore generated from the second value egr2 by a
 corresponding function. With this function, there can be, for example, a
 time-dependent adaptation so that the desired value magrdes corresponds
 essentially to the second value egr2 for the desired exhaust-gas quantity
 to be fed back at least in the steadystate condition. Accordingly, in
 stratified charge operation, the quantity of the exhaust gas, which is to
 be fed back is controlled to this desired value magrdes with the aid of
 the control 1 of FIG. 1. In this stratified operation, a quantity of
 exhaust gas, which is essentially different from zero, is fed back into
 the combustion chambers of the engine.
 If the engine is in a starting operation or in overrun operation, then the
 desired value magrdes is adjusted with the aid of block 14 to a constant
 value d. Here, the concern can be a small quantity or even no fed back
 exhaust gas. In all other cases, the desired value magrdes corresponds
 directly to the second value egr2.
 The combustion in these combustion chambers is influenced by the
 exhaust-gas quantity fed back into the combustion chambers of the engine.
 This is again compensated by corresponding corrections of the quantities
 which otherwise characterize the combustion. One such compensation is, for
 example, necessary in stratified charge operation because there, the most
 exhaust gas is fed back and this fed back exhaust gas therefore operates
 the most on the combustion.
 FIG. 3 shows how the desired value magrdes, which is generated by the
 desired-value generation 2, operates on other quantities which influence
 the combustion. Accordingly, the following are influenced in dependence
 upon the desired value magrdes especially via corresponding functions
 and/or characteristic fields 15, 16, 17, 18 and 19: the ignition angle
 zwegrs and/or the injection start asbegrs and/or the injection end aseegrs
 for the fuel to be injected and/or the fuel injection pressure pregrs
 and/or the intake manifold pressure psegrs and/or the injection quantity
 mkegrs. This influencing can furthermore be dependent also upon the rpm
 nmot of the engine.
 The exhaust-gas quantity, which is fed back into the combustion chambers of
 the engine during stratified charge operation and during homogeneous
 operation, is controlled (open loop and/or closed loop) by a control
 apparatus especially with respect to a low fuel consumption and/or a
 reduced exhaust-gas development. Especially the exhaust-gas feedback is
 controlled (open loop and/or closed loop) with a view to the least
 possible nitrogen oxide emissions. For this purpose, the control apparatus
 is provided with a microprocessor which has a program stored in a storage
 medium and especially in a read-only-memory. This program is suitable to
 execute the above-mentioned control (open loop and/or closed loop). The
 control apparatus is especially suited to execute the block diagrams shown
 in FIGS. 1 to 3 in the form of a sequence. For this purpose, input signals
 such as nmot, tans and the like are applied to the control apparatus.
 These input signals indicate operating states of the engine measured via
 sensors and the control apparatus generates output signals such as the
 adjustment signals for the exhaust-gas feedback valve 5 and/or the
 camshaft 6 with which the performance of the engine can be influenced via
 actuators in correspondence to the desired control (open loop and/or
 closed loop).