Method and system for the controlled shutting-off of an internal-combustion engine

A method and a system are disclosed for the controlled shutting-off of an internal-combustion engine. The engine system includes a fuel injection timing gear, an ignition control, an electric machine in the form of an electric motor and/or generator coupled directly or indirectly with the internal-combustion engine, and another control unit. In order to ensure a controlled shutting-off the control unit is operable to detect a shut-off signal for the internal-combustion engine, to interrupt the fuel injection while the ignition is simultaneously maintained, to maintain a defined rotational engine speed for a defined time or a defined number of crankshaft revolutions by means of the electric machine, and finally to stop the internal-combustion engine by means of the electric machine.

This application claims the priority of German application 198 52 228.2,
 filed Nov.12, 1998, the disclosure of which is expressly incorporated by
 reference herein.
 BACKGROUND AND SUMMARY OF THE INVENTION
 The invention relates to a method and a system for the controlled
 shutting-off of an internal-combustion engine which has a fuel injecting
 timing gear and an ignition control, and an electric machine in the form
 of one of a motor and a generator which is coupled directly or indirectly
 with the internal-combustion engine.
 Conventionally, when an ignition key is turned into the "ignition-off"
 position, the injection and/or the ignition of an engine is switched off.
 This prevents a further combustion and the engine runs out corresponding
 to its moment of inertia.
 However, in the case of such a shut-off operation, the problem arises that
 unburnt gasoline-air mixture still remains in the combustion space or the
 intake system. When the engine is started again, this effect results in
 poor emission values. With a view to future emissions laws, it is required
 to eliminate the unburnt gasoline-air fractions before the start of an
 engine.
 This may take place in that the timing gear switches off the injection
 after the "ignition-off" signal but continues to trigger the ignition.
 However, because of the residual gas quantities which must then still be
 burnt, the engine will then run out in an undefined manner. This is called
 an "afterdieseling".
 It is an object of the invention to ensure the removal of unburnt gas
 quantities in the engine while its running-out behavior is defined.
 With respect to the method and to the system, this object is achieved by a
 system operable to carry out the following steps: detecting a shut-off
 signal for the internal-combustion engine, interrupting the fuel injection
 while simultaneously maintaining the ignition in response to the shut-off
 signal, maintaining a defined rotational engine speed for a defined time
 period or a defined number of crankshaft revolutions after the shut-off
 signal by means of the electric machine, and subsequently stopping the
 internal-combustion engine by means of the electric machine.
 An important idea of the invention is the fact that, also after the
 ignition-off signal, the internal-combustion engine continues to be
 operated for a defined time period with a defined revolution and a
 switched-on ignition control. Since, according to the invention, the fuel
 injection is switched off in this time period, the unburnt gas quantities
 still situated in the intake system and the combustion space are burnt
 without residues. After the burning of the residual unburnt gas
 quantities, a rapid stopping of the internal-combustion engine is caused
 by acting upon the internal-combustion engine by means of the electric
 machine. A combined starter-generator arrangement, such as a crankshaft
 starter generator, is particularly suitable for use as the electric
 machine (starter, generator).
 Other objects, advantages and novel features of the present invention will
 become apparent from the following detailed description of the invention
 when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS
 The present embodiment represents a simple variant and should not be
 understood as a limitation of the invention.
 The illustrated embodiment according to FIG. 1 shows an internal-combustion
 engine 10 which transmits the torque generated by it by way of an output
 shaft 12 to a transmission 16 which follows. In the present case, a
 combined starter--generator 14 is arranged on the output shaft 12.
 This combined starter--generator may also be arranged at a different point
 in the case of the internal-combustion engine, for example, directly on
 the crankshaft. As an alternative, electric motors can be used which are
 indirectly coupled with the internal-combustion engine. However, a more or
 less rigid connection between the selected electric machine and the
 internal-combustion engine 10 is a prerequisite.
 The drive shaft continues to the transmission 16 which provides by way of
 an output shaft 18 the power generated by the internal-combustion engine
 10 to the driving wheels (not shown).
 The internal-combustion engine is controlled by a timing gear 24 which
 determines the injection as well as the ignition. The timing gear receives
 many different input signals which are schematically illustrated by the
 arrows having the reference number 26.
 In addition, another control 22 is provided which, among other devices, is
 connected with the ignition switch 20 and thus receives a signal as to
 whether the ignition is switched on or off. The control 22 is connected
 with the engine timing gear 24 and the starter--generator arrangement 14.
 In the following, the method of operation of the system according to the
 invention will be described.
 First, the ignition switch 20 is switched to "on" and normal engine
 operations take place. When the ignition switch 20 is finally switched to
 "off", this is registered by the control 22, and the control 22 acts upon
 the engine timing gear 24 such that the latter immediately interrupts the
 fuel injection but continues to trigger the ignition.
 Simultaneously, the starter--generator arrangement 14 is acted upon so that
 it maintains the internal-combustion engine for two crankshaft revolutions
 at the rotational speed which existed when the "ignition off" signal was
 received. In this time period, the unburnt gas quantities still existing
 in the intake system and the combustion spaces are now burnt without
 residue.
 After the two crankshaft revolutions, the starter--generator arrangement 14
 stops the internal-combustion engine 10 as fast as possible.
 As an alternative, this shut down operation may take place by means of a
 defined rotational speed or torque sequence.
 FIG. 2 shows an effect caused by the invention. In the upper part of FIG.
 2, engine rotational speed RS is depicted as a function of time T. The
 rotational engine speed sequence in the case of a conventional shut-off
 operation is shown by a frequently broken line I. When the ignition is
 switched to "off" (compare lower part of the diagram which shows the
 ignition switch position as a function of time T), the rotational engine
 speed is reduced corresponding to the moment of inertia of the engine. If
 the residual gases in the combustion spaces and the intake system are
 still to be burnt, this results in an "afterdieseling effect", which is
 shown by the long broken lines II. This leads to an undefined shut-off
 operation.
 By means of the above-described invention, a rotational speed sequence can
 be achieved which is illustrated by means of the solid line III in FIG. 2.
 For a certain time period or a certain number of crankshaft revolutions
 after the "ignition off" signal, the rotational engine speed is still
 maintained. Then the rotational engine speed drops abruptly, and, in a
 defined manner, earlier than in the case of the conventional shut-off
 operations--, the stoppage of the internal-combustion engine is achieved.
 In preferred embodiments, the time period for maintaining rotational engine
 speed after "ignition off" is between 50 to 500 ms (milliseconds), and
 preferably about 200 ms.
 On the whole, the method according to the invention ensures a reproducible
 shut-off action and low pollutant emission values. In addition, it should
 be pointed out that, as the result of the fast braking of the
 internal-combustion engine, the energy consumption for the prolongation of
 the idling rotational speed phase, caused by the holding of the rotational
 speed, is compensated. In addition, it is possible to rapidly pass through
 possibly existing resonance points below the idling rotational speed.
 The foregoing disclosure has been set forth merely to illustrate the
 invention and is not intended to be limiting.
 Since modifications of the disclosed embodiments incorporating the spirit
 and substance of the invention may occur to persons skilled in the art,
 the invention should be construed to include everything within the scope
 of the appended claims and equivalents thereof.