EP1876341A1

EP1876341A1 - Method for shutting down an internal combustion engine

Info

Publication number: EP1876341A1
Application number: EP06116533A
Authority: EP
Inventors: Urs Christen; Simon Petrovic; Rainer Schloer
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2006-07-04
Filing date: 2006-07-04
Publication date: 2008-01-09

Abstract

A method for shutting down an internal combustion engine in such a way that a crankshaft of the internal combustion engine stops in a defined angular range is disclosed. The method according to the invention is solely based on the behaviour of the internal combustion engine itself. External devices like an electrical starter motor are not used actively to ensure the rotary position of the crankshaft for an optimized restart. This ensures a cost effective and also a reliable rotary positioning of the crankshaft.

Description

The present invention relates to a method for shutting down an internal combustion engine in such a way that a crankshaft of the internal combustion engine stops in a defined angular range.
For vehicles with stop/start functionality (hybrid vehicles, for instance), the angular position of the engine, in particular of pistons connected to a crankshaft in the internal combustion engine, at engine stop is important for a fast restart. This is especially true for diesel engines whose restart time is constrained by three factors: fuel pressure build-up in a fuel injection system, in particular in a common rail injection system, compression of the air in the cylinder and synchronization of the fuel injection system with the position of the piston belonging to the cylinder in which the air/fuel mixture has to ignite first during the starting procedure. The synchronization is realized with a flywheel connected to the crankshaft and having a plurality of circumferentially arranged equally spaced teeth. The teeth are used to assess the position of the cylinders such that the fuel injection can be timed correctly. A known Diesel engine has a flywheel with 60 teeth (with an interval of 6 degrees from falling edge to falling edge), of which two are missing in order to form a gap. This gap is the reference for absolutely positioning the engine, since the teeth of the flywheel can be read by means of a non-contact proximity switch, which communicates with an electronic control unit (ECU) which is responsible for controlling the internal combustion engine, in particular the injection system.
When the non-contact proximity switch detects the gap, the absolute rotary position of the crankshaft is available for the ECU. For a known four cylinder engine, for instance, the first falling edge after the gap may be at 66° after top dead centre (TDC) of cylinder 1 (cylinders are numbered from 0 to 3). In order to assess the angular position of the crankshaft and to synchronize the fuel injection at engine start, a few teeth need to be seen before the gap is detected; once the gap has been detected, the angular position of the crankshaft is known and fuel injection can be enabled if the fuel pressure is high enough. In worst case, it may take up to 400 degrees of crankshaft rotation until the angular position of the crankshaft is known.
To ensure an appropriate restart of the internal combustion engine with a minimum amount of starting energy to be provided by a battery to an electrical starter engine and to ensure an optimized restart time for instant readiness of the combustion engine for a car acceleration, the crankshaft has to be in a predeterminable rotary position after the shut down of the internal combustion engine is completed.
US 6,453,864 B1 discloses a method of controlling engine crankshaft motion in a hybrid electric drive system having an internal combustion engine and a motor-generator operatively connected to a crankshaft of the engine. The method includes monitoring the crankshaft position, forecasting a crankshaft stall position; comparing the forecasted stall position with a target range. If the forecasted crankshaft stall position is outside the target range, the motor-generator is operated to modify the forecasted stall position to be within the target range to properly position the crankshaft for initiating engine restart. The method further includes a calculation of an effective lube interval time once the crankshaft speed is zero; a comparison of the effective lube interval time to a critical time; and if the effective lube interval time is greater than the critical time, a pulsation of the motor-generator to rock the crankshaft for a pulse time to redistribute a lubricant film.
US 6,192,847 B1 discloses a control assembly for use within a vehicle having an engine and which selectively controls the speed of the engine in order to increase fuel efficiency and to affect relatively smooth starting and stopping of the engine. A control assembly cooperatively operates with a starter/alternator assembly and is adapted for use with hybrid vehicles employing a start/stop power train assembly, wherein fuel efficiency is increased by selectively stopping engine operation when the vehicle has stopped.
US 2005/0149249 A1 discloses a system for determining engine stop position and includes an engine tracking subsystem and a throttle control subsystem. The engine tracking subsystem is coupled to the engine and determines the engine position by sensing rotation of the crankshaft. Once the engine controller receives an engine shutdown signal, the throttle is controlled to lower the air pressure in the intake manifold of the engine. Lowered as such, the resulting reversal torque caused by compression of air in the cylinders is smaller than the friction torque of the engine and engine reversal is eliminated or substantially reduced. When the engine has stopped, the engine tracking system stores the last engine position for use during the next engine start-up.
Therefore it is an objective of the present invention to reduce the worst case angular interval the engine has to travel before the position is known and to increase comfort and exhaust characteristics of a start-stop system for an internal combustion engine.
This objective is achieved by a method according to claim 1.
Preferred embodiments of the invention are subject of the dependent claims.
According to claim 1, a method for shutting down an internal combustion engine at a predeterminable angular crankshaft position of the engine at engine stop is provided. The method comprises the steps of receiving an engine shutdown request from engine management; lowering an intake air pressure in at least one portion of an intake manifold by throttling the at least one intake portion and cutting fuel as soon as the crankshaft passes a predeterminable crankshaft rotary position TDC j_cut. TDC j_cut is the top dead centre closest to the crankshaft rotary position after which the fuel supply must be cut to ensure proper rotary positioning of the crankshaft after shutting down of the internal combustion engine has been completed. The engine shutdown request is provided by the engine management, in particular by the ECU, in which a stop/start strategy is implemented. The engine management is used for controlling the internal combustion engine in an optimized mode with respect to fuel consumption and/or battery loading conditions. As soon as the engine management decides that the internal combustion engine has to be shut down, the air pressure in at least one portion of an intake manifold is lowered.
Thus an intake resistance for the pistons of the internal combustion engine is increased and the kinetic energy of the rotating crankshaft is reduced. As soon as the crankshaft passes a predeterminable rotary position which can be detected by the non-contact proximity switch, the engine management generates the information that the internal combustion engine is ready to cut fuel supply to the cylinders. By cutting off fuel supply, the predeterminable angular crankshaft position of the engine at engine stop can be ensured. Thus, the fuel supply is cut off and the crankshaft rotates to a rotary position optimized for a restart of the internal combustion engine.
This procedure ensures that the engine stops such that the gap is located close to the non-contact proximity switch, but with a few teeth before passing the non-contact proximity switch in the restart procedure. Thus it is ensured that the non-contact proximity switch detects a few teeth before the gap is seen during the start procedure, and the gap is seen after 200 deg. of crankshaft rotation the latest. In this way, the worst case travel needed to synchronize the engine at start can at least be halved (from approx. 400 degrees to approx. 200 degrees). By reducing the guaranteed synchronization time to half a revolution, earliest possible fuel injection is enabled. The limiting factors then are either fuel pressure or waiting for the first cylinder with full compression.
So the present invention comprises among others two aspects which basically could also be implemented independently from each other, but are used preferably together: First the aspect that the engine is stopped within a predetermined crankshaft rotary position window in order to get an early synchronising signal from the gap on engine restart. Second the aspect to decelerate the engine rotation in a controlled manner by lowering intake air pressure.
The method according to claim 1 of the invention is solely based on the behaviour of the internal combustion engine itself. External devices like an electrical starter motor are not used actively to ensure the rotary position of the crankshaft for an optimized restart. This ensures a reliable rotary positioning of the crankshaft, which is also cost effective.
In a further development of the invention the intake manifold pressure is throttled to a predeterminable intake manifold pressure. The throttling or restricting of the intake manifold pressure to a predeterminable pressure, which can be determined with a pressure sensor in the intake manifold, allows reducing the kinetic energy of the internal combustion engine with respect to the engine shutdown request provided by the motor management.
In a further development of the invention, the fuel is cut after a predeterminable manifold pressure has been reached AND the crankshaft passes the predeterminable crankshaft rotary position (TDC j_cut ). This allows exactly controlling the shut down behaviour of the internal combustion engine with respect to the internal friction of the engine and ensures a precise rotary positioning of the crankshaft.
In a further development of the invention, the intake manifold pressure is throttled for a predeterminable time (t_delay) and the fuel is cut after the predeterminable time has passed AND the crankshaft passes the predeterminable crankshaft rotary position (TDC j_cut ). With this embodiment of the invention a pressure sensor in the intake manifold is not necessary to ensure the rotary position of the crankshaft and therefore the implementation of the method according to the invention can be realized more cost effectively.
In a further development of the invention, the crankshaft rotary position for cutting fuel is made dependent on a measurement of the intake manifold pressure. This gives the method more flexibility to react, e.g., on environmental circumstances like absolute air pressure, density of the air related to height above sea level, humidity, etc. Circumstances related to the internal combustion engine like the engine temperature, etc. can also be taken into account. In a preferred embodiment of the invention, the intake pressure can be influenced with a valve device arranged in at least a portion of the intake manifold, which is used to restrict the resistance for the air-flow in the intake manifold and can be used in the manner of an open-loop or closed loop control, which may be provided by the engine management.
In a further development of the invention, the intake throttle is opened, when the engine has stopped. This ensures the readiness of the internal combustion engine for restart in a short period of time.
In a further development of the invention - which could also be implemented independently from the special stop procedure according to the invention as described above - a predeterminable crankshaft rotary position j_cut is dynamically adapted by comparing the stop position j_stop to the desired stop position j_stop,des according to the algorithm: if j_stop <> j_stop,des, then j_cut = ((j_cut + 1) mod n_cyl/2), whereby

j_stop: is the real rotary position of the crankshaft after complete shut down of the internal combustion engine and
j_stop,des: is the crankshaft rotary position, which would be most efficient for an engine restart procedure.

If there is a significant difference (to be defined in advance and stored, e. g., in the ECU) between j_stop and j_stop,des, the value for j_cut is increased by 1 and then is input into a modulo-operation to calculate a whole-numbered value or integer value with respect to the number of cylinders divided by 2. With the aforementioned algorithm, long term changes of the characteristics of the internal combustion engine, like a change of internal friction and/or a change of power consumption of external devices connected to the internal combustion engine, in particular an electric generator, a water pump, an air conditioning compressor, etc. can be taken into account to ensure proper long term behaviour of the method according to the invention.
In a further development of the invention, the pressure dependence for j_cut may be introduced by creating a lookup table where individual j_cut values are associated with small subintervals of the full intake manifold pressure range. This allows shutting down the internal combustion engine with a precise, pressure-dependent timing for the cut of the fuel supply. The lookup table can be arranged like a matrix or an engine operating map and may be stored within the ECU. It allows an assignment of intake manifold pressure to j_cut in small steps and therefore with a high resolution.
In a further development of the invention - which could basically also be implemented in engine stop algorithms distinct from the invention as described above - the crankshaft rotary position for fuel cut off (j_cut) is made dependent on engine parameters such as an engine temperature and/or an idle speed of the engine and/or a power consumption of additional equipment, in particular of a compressor for an air conditioning device. This allows a further refinement of the shut down method and ensures a minimum deviation between the real rotary position of the crankshaft and the desired crankshaft position.
In a further development of the invention, additional equipment, in particular a compressor for an air conditioning device is being deactivated before shutting down the engine. This allows to normalize circumstances of subsequent shut down procedures, since some of the additional equipment, e.g. the compressor for the air conditioning, consumes a significant amount of power if activated, but is not necessarily activated with each shut down of the internal combustion engine. The method according to the invention can be made more robust with respect to a minimum deviation between j_stop and j_stop,des, if the circumstances for all shut down procedures are at least the same or very similar.
Further advantages and characteristics of the invention can be taken from the following description of preferred embodiments of the invention according to the drawings.

Fig. 1: illustrates a schematic overview of an internal combustion engine;
Fig. 2: illustrates a schematic view of a flywheel of the internal combustion engine according to Fig. 1, and
Fig. 3: shows a signal flow diagram according to an exemplary embodiment of the invention.

Fig. 1 shows a schematic overview of an internal combustion engine 1 with an engine block 2, comprising vertically movable pistons 3 which are rotatably connected to a crankshaft 4. The crankshaft 4 transmits the vertical movement of the pistons into a rotational movement of a shaft 5. The shaft 5 is connected to a flywheel 11 and a clutch 12 and also may drive an air condition compressor 14 with a belt drive 16. The shaft 5 also may drive other, not illustrated additional devices like a water pump or an electric generator. The clutch 12 allows a separable transmission of the engine power to a gearbox 13, being connected to wheels of a car, which are not illustrated. An intake manifold 6 is arranged at the top of the engine block 2 and comprises an adjustable throttle 17 and a pressure sensor 15. The adjustable throttle 17 allows a restriction of the air flow to the pistons 3 by partially blocking the intake manifold 6. Each piston 3 has its own injector 7 to inject fuel. The injectors 7 are connected by a common rail fuel line 8 with a fuel pump 9, capable of delivering pressurized fuel to each of the injectors 7. The fuel pump 9, the intake manifold pressure sensor 15 and the throttle 17 are connected to an electronic control unit ECU 10, which coordinates the function of the aforementioned devices.
The flywheel 11, which is illustrated in fig. 2 in more detail, is equipped with a not illustrated non-contact proximity switch (e.g. a Hall Sensor assembly), serving as a sensor to detect the teeth 18 and the gap 19 of the flywheel 11. The information generated by the non-contact proximity switch is provided to the ECU 10 to synchronize the position of the crankshaft 4 and the pistons 3 with the injection of fuel by injectors 7.
According to Fig. 3, the shut down of the internal combustion engine 1 is realized with the following procedure according to a preferred embodiment of the invention:
The automatic engine shutdown in stop/start operation controlled by ECU 10 occurs when internal combustion engine 2 is warmed-up and at idle speed such that the engine friction is well predictable. This is important for the internal combustion engine 2 to have a consistent stopping behaviour. For this reason, additional devices like an air conditioning compressor may be disconnected from the internal combustion engine before shut down.
Shake of the internal combustion engine 2 at shutdown is reduced by closing the intake manifold 6 by means of the throttle 17. This reduces "gas spring" forces from the compressed air in the cylinders and thus the oscillating gas forces compared to the friction forces. Engine reversals at the end are avoided or reduced, and the driver feels less shake.
The intake manifold pressure for shutdown can be controlled to a defined value according to the 2nd step: "wait for intake manifold pressure to reach set point" or the intake manifold 6 can be throttled for a predeterminable period of time t_delay.
Hence, it is possible to calibrate a shutdown strategy to cut fuel after TDC j_cut such that the stop will occur after TDC j_stop. Since it is irrelevant whether stopping occurs after TDC 0 or TDC 2 for a four cylinder engine, all these TDC numbers should be taken modulo 2 (In general: modulo n_cyl/2 for engines with an even number of cylinders).
As soon as the predeterminable intake manifold pressure is reached or the predeterminable period of time t_delay has passed, the ECU 10 may set an injection_off_flag as soon as(j mod n_cyl/2) = j_cut (i.e., cut fuel for all the following engine cycles until engine stop). After the fuel injection to the injectors 7 is stopped and in the case of a gasoline engine there is no further ignition, the internal combustion engine 1 stops turning and the crankshaft 4 rests in a predeterminable rotary position. After the rotation of the crankshaft 4 has stopped, the intake throttle 17 is opened again to ensure readiness for restart of the internal combustion engine 1. Opening the throttle also makes sure that no energy is wasted for keeping it closed against the spring (default open position).
For robustly compensating engine to engine differences in friction or change in friction over time due to wear, j_cut can be adapted automatically. At each engine stop, the stop position j_stop is compared to the desired stop position j_stop,des. If these positions are not equal, j_cut is incremented (modulo n_cyl/2). Thus, at the end of the procedure described above, the following step is executed: $If (j_{stop} < > j_{stop, des}), {then j}_{cut} = ((j_{cut} + 1) {mod n}_{cyl} / 2) .$
If the intake throttle is closed for a certain period of time before fuel is cut, j_cut can be made intake manifold pressure dependent (with or without adaptation as described in the previous paragraph).
The procedure with adaptation then reads:

• Receive engine shutdown request from stop/start strategy,
• Close the intake throttle and wait for t_delay seconds,
• Measure intake manifold pressure, p_i,cut,
• Set the injection_off_flag as soon as (j mod n_cyl/2) = j_cut(p_i,cut), (i.e., cut fuel for all the following engine cycles until engine stop),
• Open the intake throttle when the engine has stopped.

If (j_{stop} < > j_{stop, des}), {then j}_{cut} (p_{i, cut}) = ((j_{cut} (p_{i, cut}) + 1) {mod n}_{cyl} / 2) .

The pressure dependence for j_cut may be implemented by creating a lookup table where individual j_cut values are associated with small subintervals of the full intake manifold pressure range.
Robustness with respect to engine friction may be improved by making j_cut dependent on engine temperature, T_eng (oil or coolant temperature) - instead or in addition to the pressure dependence. Similarly, if variations in idle speed can occur because the set point for the idle speed is increased under certain conditions, j_cut may be idle speed dependent as well.
It may happen that at some particular idle speed subinterval or some particular intake manifold pressure subinterval, the stopping position is not robust such that, even if keeping j_cut constant, j_stop varies randomly. This may be counteracted by deliberately changing the set point for either the speed or the intake manifold pressure at the time of shutdown.

Abbreviations and Dimensions:

j: TDC last passed (in direction of normal travel; numbered from 0 to n_cyl-1)
j_cut: TDC after which fuel must be cut off
j_stop: TDC after which the engine stops (in direction of normal travel)
j_stop,des: desired TDC after which the engine should stop
n_cyl: number of cylinders
p_i,cut: [kPa] intake manifold pressure at the time fuel is cut
T_eng: [deg. C] engine temperature
t_delay: [s] delay between closing the intake throttle and cutting fuel

Reference numbers

1. Internal combustion engine
2. Engine block
3. Pistons
4. Crankshaft
5. Shaft
6. Intake manifold
7. Injector
8. Fuel line
9. Fuel pump
10. ECU
11. Flywheel
12. Clutch
13. Gearbox
14. Air condition compressor
15. Pressure sensor
16. Belt drive
17. Throttle
18. Teeth
19. Gap

Claims

A method for shutting down an internal combustion engine (1) at a predeterminable angular crankshaft position of the engine at engine stop,
characterized by the steps of:
Receiving an engine shutdown request from a engine management (10);

Lowering an intake air pressure in at least one portion of an intake manifold (6) by throttling the at least one intake portion, and

Cutting fuel as soon as the crankshaft (4) passes a predeterminable crankshaft rotary position (TDC j_cut).
The method according to claim 1,
characterized by
the additional step of throttling the intake manifold pressure to a predeterminable intake manifold pressure.
The method according to claim 2,
characterized in that
the fuel is cut after the predeterminable intake manifold pressure has been reached and the crankshaft (4) passes the predeterminable crankshaft rotary position (TDC j_cut).
The method according to one of claim 1,
characterized by
the additional step of throttling the intake manifold pressure for a predeterminable time (t_delay) and cutting the fuel after the predeterminable time has passed and the crankshaft (4) passes the predeterminable crankshaft rotary position (TDC j_cut ).
The method according to claim 4,
characterized by
the additional step of making the crankshaft rotary position for cutting fuel dependent on a measurement of the intake manifold pressure.
The method according to one of the precedent claims,
characterized in that
the intake throttle (17) is opened after the engine has stopped.
The method according to one of the precedent claims,
characterized in that
a predeterminable crankshaft rotary position j_cut is dynamically adapted by comparing the stop position j_stop to the desired stop position j_stop,des according to the algorithm: if j_cut <> j_stop,des, then j_cut = ((j_cut + 1) mod n_cyl/2).
The method according to one of claims 5 to 7,
characterized in that
the pressure dependence for j_cut is related to a lookup table where individual j_cut values are associated with small subintervals of the full intake manifold pressure range.
The method according to one of the precedent claims,
characterized by
the additional step of making the crankshaft rotary position for fuel cut off (j_cut) dependent on engine parameters such as an engine temperature and/or an idle speed of the engine and/or a power consumption of additional equipment, in particular of a compressor for an air conditioning device (14).
The method according one of the precedent claims,
characterized by
the additional step of deactivating additional equipment, in particular a compressor for an air conditioning device (14), before shutting down the engine.