GB2535470A

GB2535470A - Vehicle drivetrain and method of operation therefore

Info

Publication number: GB2535470A
Application number: GB1502554.7A
Authority: GB
Inventors: Brunetti Gianmarco; Giraudo Gabriele; Cancellieri Angelo
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2015-02-16
Filing date: 2015-02-16
Publication date: 2016-08-24
Anticipated expiration: 2035-02-16
Also published as: GB201502554D0; GB2535470B; CN105888867A

Abstract

Disclosed is a drivetrain for a vehicle, comprising an internal combustion engine 1, a sensor 3 for monitoring rotation of a crankshaft 16 of the combustion engine and a clutch 12 coupling the combustion engine 1 to an output shaft 13 of the drivetrain. An engine controller 8 controls fuel injectors 4 associated with cylinders 2 of the combustion engine 1 based on operating parameters. An update controller 11 is provided for setting the operating parameters based on the output of the crankshaft sensor 3. A clutch controller 14 controls torque transmission from the combustion engine 1 to the output shaft 13 by said clutch 12. The controllers 8, 11, 14 support a drive mode in which the engine is on while the clutch 12 is closed, a sailing mode in which the engine is off while the clutch 12 is open, and a switchover from the drive mode to the sailing mode or vice versa, said switchover comprising a transition phase in which at least one of the Injectors 4 supplies fuel to its respective cylinder 2 while the clutch 12 is partially open. The update controller 11 is configured to set the operation parameters of the fuel injectors 4 based on data obtained by the sensor 3 during the transition phase. The arrangement provides a smooth engagement of power when transitioning between engine modes. An associated method is also disclosed

Description

Vehicle drivetrain and method of operation therefore

Description

The present invention relates to a drivetrain for a vehicle, comprising a combustion engine such as a Diesel engine or a direct-injection spark-ignition engine.

Such an engine comprises injectors which inject fuel into its cylinders.

The response of these injectors to a given control signal, in particular the amount of injected fuel and the injection timing, may vary from one injector to another due to manufacturing tolerances, causing the rotation speed of a crankshaft of the engine to vary periodically. The frequency of these variations can be half the crankshaft rotation frequency and integer multiples thereof. It is known to detect these variations and to use them for controlling the operation of the engine. A method therefore is described e.g. in DE 100 55 192 Al.

Variations of the engine load also affect the rotation speed of the crankshaft, and distinguishing such variations from the effects of the injectors is not straightforward. Therefore, a good time to detect rotation speed variations caused by the injectors is in a coasting mode, in which accelerator pedal of the vehicle is not depressed, and the engine is moved by torque supplied to it by an output shaft.

If at times when the accelerator pedal is not depressed, a sailing mode is entered in which the engine is shut down and a clutch coupling the engine to the output shaft is opened, fuel can be saved, but there is also no more opportunity to monitor the rotation speed and to adjust the operation of the injectors.

An object of an embodiment of the invention is to provide a drivetrain which supports a sailing mode while maintaining the possibility to adjust the operation of the injectors. -2 -

This object is achieved by a drivetrain for a vehicle, the drivetrain comprising a combustion engine, a sensor for monitoring rotation of a crankshaft of the combustion engine, a clutch coupling the combustion engine to an output shaft of the drivetrain, an engine controller for controlling fuel injectors associated with cylinders of the combustion engine based on operating parameters set by an update controller based on the output of the sensor, and a clutch controller for controlling torque transmission from the combustion engine to the output shaft by said clutch, wherein the controllers are configured to support a drive mode in which the engine is on, i.e. running, while the clutch is closed, a sailing mode in which the engine is off, i.e. not running, while the clutch is open, and a switchover from the drive mode to the sailing mode (or vice versa, i.e. from the sailing mode to the drive mode), said switchover comprising a transition phase in which at least one of the injectors supplies fuel to its respective cylinder while the clutch is partially open, and the update controller is configured to set the operation parameters of the fuel injectors based on data obtained by the sensor in said transition phase.

Since such a transition phase can be included in all switchovers, preferably those from drive mode to sailing mode but also from sailing mode to drive mode, sufficient opportunity remains for collecting the data needed for appropriately setting the operation parameters.

In each transition phase the update controller may select a first subset of injectors to supply fuel to their associated cylinders and a second subset of injectors which do not supply fuel to their associated cylinders. If the choice of subsets changes from one transition phase to the subsequent transition phase, information can be derived selectively on individual cylinders.

Deriving such information is easiest if in each transition phase the first subset comprises just one injector, i.e. if only one cylinder receives fuel during said transition phase.

There may be transition phases in which fuel is not injected at all, or a transition phase may comprise a time interval in which said selected fuel injectors supply fuel to their associated cylinders and a time interval in which no fuel is supplied at all. In a time interval in which no fuel is supplied the rotation speed of the crankshaft varies according to a predetermined pattern due to compression and -3 -expansion of air in the cylinders, i.e. the rotation speed is not constant but has a spectrum which comprises harmonics of the rotation frequency, the amplitude and phase of which depend on the design of the engine and can be measured. Rotation speed data from the sensor may suggest that the crankshaft speed does fluctuate according to a pattern different from the expected one. Such deviations are caused by systematic noises e.g. crank wheel mechanical tolerances (e.g., errors in the teeth angular width, inaccuracies of the sensor or of its mount) and unbalancing due to the gas pressure torque and/or the reciprocating inertia torque. Therefore, the time interval in which no fuel is injected can be used by the update controller to to learn how the crankshaft speed deviates from an expected pattern, and to take account of these deviations when controlling fuel injection in drive mode.

The switchover from the drive mode to the sailing mode or vice versa should comprise the transition phase, since a switchover to the drive mode will usually occur when drive torque is required, and availability of the torque should not be delayed by the transition phase.

A switchover to sailing mode can be triggered by the driver releasing at least an accelerator pedal. A release of the brake pedal may be a further zo condition for the switchover.

The transition phase may have a duration of at least 0,1s, in order to comprise a sufficient number of crankshaft revolutions for a reliable measurement. Unnecessary wear of the clutch can be avoided if the transition phase lasts for less 25 than 5s. A duration of approximately 3s is a good compromise.

The opening degree of the clutch may vary continuously throughout the transition phase, so as to provide a smooth transition without jolts which is comfortable for the occupants of the vehicle. Further, rotation speed measurements may thus be carried out under diverse opening degrees within a single transition phase, so that more information can be derived.

Furthermore, a method of controlling a drivetrain is disclosed, which comprises the following steps -providing, in a switchover from a drive mode in which a combustion engine is on and a clutch is closed so as to transmit torque from the combustion engine to an output shaft of said drivetrain, to a sailing mode in which the clutch is open while the engine is off, or vice versa in a switchover from the sailing mode to the drive mode, a transition phase in which the clutch is partially open controlling, in the transition phase, at least some injectors of the engine to supply fuel to their associated cylinders while the clutch is partially open deriving operating parameters for the injectors based on monitoring rotation of a crankshaft of the combustion engine during said transition phase, and - operating the injectors based on the derived operating parameters.

Also disclosed is a computer program which enables a computer, in particular the controllers mentioned above, to carry out the method as described above. In this regard, the controllers can be said to be configured to support the above drive mode and sailing mode, to provide the switchover as stated above and to update operating parameters as explained above.

Another aspect of the disclosure relates to a computer readable data carrier having program instructions stored on it and which enable a controller to 20 carry out the method explained above.

A control apparatus may comprise means for controlling a switchover between a drive mode in which a combustion engine is on and a clutch is closed so as to transmit torque from the combustion engine to an output shaft of said drivetrain, and a sailing mode in which the clutch is open while the engine is off, and for inserting in said switchover a transition phase in which the clutch is partially open; means for controlling, in the transition phase, at least some injectors of the engine to supply fuel to their associated cylinders while the clutch is partially open - means for deriving operating parameters for the injectors based on monitoring rotation of a crankshaft of the combustion engine during said transition phase, and means for operating the injectors based on the derived operating parameters.

Further features and advantages of the invention will become apparent from the subsequent description of embodiments thereof referring to the appended drawings.

Fig. 1 is a block diagram of the drivetrain; Fig. 2 is a time diagram of operating parameters of the drivetrain during a switchover from drive mode to sailing mode and back.

The drivetrain of Fig. 1 comprises a combustion engine 1 having a plurality of cylinders 2 formed in it. The cylinders 2 drive a crankshaft 16, the angular position and/or rotation speed of which is monitored by a crankshaft sensor 3. Each cylinder 2 has a fuel injector 4 associated with it for injecting fuel from a common rail 5. The common rail 5 is pressurized by a fuel pump 6 which draws fuel from a tank 7.

An engine controller 8 is data connected to crankshaft sensor 3, to an accelerator pedal sensor 9 and to the fuel injectors 4. In a drive mode, engine controller 8 controls injection timings of the injectors 4 based on crankshaft angle readings from crankshaft sensor 3 and controls injection amounts based on position readings of accelerator pedal 10 from sensor 9. Both timings and injection amounts are corrected individually for each injector 4 based on operating parameters provided by an update controller 11. Among these operating parameters there may be timing offsets and correction factors for the injection quantity which take account of the fact that response delays of the various injectors may be slightly different, and that the fuel quantities injected in response to a command specifying a same injection quantity may vary from one injector 4 to another, too.

Since these variations can depend on circumstances such as fuel and injector temperatures which are hard to control, the operating parameters have to be updated repeatedly. The update controller 11 does this based on data from crankshaft sensor 3.

In a transition phase, when the clutch is neither fully engaged nor fully disengaged, and vehicle inertia is still partly dragging the engine 1, engine -6 -controller 8 may decide to have one of injectors 4 inject fuel into its associated cylinder, or not to inject fuel at all. In the first case, the selected injector 4 is controlled to inject a predetermined amount of fuel by energizing it during a predetermined period of time. The update controller 11 processes the crankshaft speed signal from crankshaft sensor 3 so as to obtain signals or data representative of the amplitude of a predetermined harmonic component of the crankshaft speed signal, and calculates the power of said harmonic component. This power is a function of the amount of fuel injected, and based on the knowledge of this function, the update controller 11 calculates an estimate of the amount injected. The difference between this estimate and the predetermined amount mentioned above is stored as an update value, and is afterwards, in drive mode, retrieved by engine controller, in order to correct the duration of the energizing periods of said one injector so that the actually injected amount of fuel is precisely the predetermined one.

If engine controller 8 decides not to inject fuel at all, there may still be a small amount of background harmonics in the crankshaft speed signal that are due to mechanical imperfections of the engine 1 or the crankshaft sensor 3. These background harmonics can be determined by the update controller 11, in order to subtract them from the harmonics detected in other transition phases in which fuel is injected, and thus to obtain an background-free measurement of the harmonic power caused by fuel injection.

A clutch 12 is provided between the crankshaft of engine 1 and an output shaft 13. When the drivetrain is built into a motor vehicle, the output shaft 13 drives wheels via a gearbox, not shown. A clutch controller 14 is provided for opening the clutch 12 whenever gears have to be shifted in the gearbox or when the drivetrain enters a sailing mode.

Clutch controller 14, update controller 11 and engine controller 8 may be implemented as individual microcomputers, each having a microprocessor and associated computer readable memory for executing a specific operating program. As an example, engine controller 8 can be an electronic control unit commonly found in vehicles such as passenger cars and mainly governing the operation of the engine. The clutch controller 14 can be a transmission control unit mainly governing the operation of the transmission. The update controller 11 can be a separate controller, e.g. a controller embedded in the clutch. It is also possible that engine controller 8 and clutch controller 14 are one and the same controller, but that the update controller is different. In the alternative, different programs or program modules can be executed concurrently in the same microcomputer 15, e.g. from the engine controller 8.

Fig. 2 illustrates the time behaviour of various parameters of the drivetrain, namely vehicle speed V, rotation speed R, the amount of injected fuel F and the clutch status C during a switchover into sailing mode and back into drive to mode.

Prior to a time instant tO, the drivetrain is in drive mode. At tO, a switchover to sailing mode is triggered by a release of the accelerator pedal 10. Engine controller 8 then either shuts down all injectors 4, in order to measure the background harmonics, or selects one of the injectors 4 to inject a small amount of fuel, as illustrated by section F' in Fig. 2, during a transition phase lasting till time instant t1. This fuel injection causes the rotation speed of the crankshaft 16 to fluctuate at one half of the rotation frequency. The amount of the fluctuation and its phase are detected by crankshaft sensor 3 during the transition phase from tO to t1.

The frequency is too high for the fluctuation to be discernible in crankshaft rotation speed curve R; what the curve R does show is a gradual decrease of the average rotation speed due to the fact that the amount of fuel supplied to said one selected cylinder is insufficient to keep the engine running. Since the energy for moving the engine 1 is taken from the kinetic energy of the vehicle, vehicle speed V decreases noticeably.

In the transition phase, clutch controller 14 gradually decreases the clutch capacity, i.e. the maximum torque which clutch 12 would be able to transmit without slipping. Clutch controller 14 controls the speed of operation of clutch 12 so that an instant t1, when disks of clutch 12 lose contact with each other, and the clutch capacity drops to zero, occurs approximately 3 seconds after tO. At t1, engine controller also shuts down the selected injector 4, so that the decrease of rotation speed R becomes steeper after t1. Soon, the rotation speed R becomes zero, and the engine 1 is completely off. The drivetrain has reached sailing mode. No fuel is consumed until at time instant t2, the driver presses accelerator pedal 10 again, and the controllers 8, 11, 14 revert to drive mode. Since no more kinetic energy is -8 -consumed in the engine, deceleration is less than in the transition phase, as shown by curve V. While in the sailing mode, update controller 11 estimates the actual injection amount and its timing based on the data collected by sensor 3 in the transition phase, and supplies these to engine controller 8 when drive mode starts again at t2.

The next time a switchover to sailing mode is triggered, another to injector 4 is selected, so that if n is the number of cylinders of engine 1, operating parameters of each injector 4 are updated once in every n transition phases.

In a more sophisticated embodiment of the invention, there are, in addition to the transition phases described above, transition phases in which no fuel is supplied to any of the cylinders. If the sensor 3 did not suffer from manufacturing tolerances, it would deliver a train of evenly spaced impulses if the crankshaft rotates at constant speed. In practice; impulses from sensor 3 jitter. If e.g. the sensor comprises a sprocket wheel comprising n sprockets mounted to the crankshaft and a Hall sensor for detecting the passage of the sprockets, so that each impulse emitted by sensor 3 corresponds to the passage of a sprocket before the Hall sensor, eccentricity of the sprocket wheel may cause time intervals between impulses to fluctuate in a deterministic way. While the crankshaft rotates idly, time intervals between pulses can be measured, and the update controller 11 records a relative duration for each gap between subsequent sprockets. Later, when the engine is under load, time intervals between subsequent sprockets can be corrected by dividing by their associated relative durations.

Alternatively, transition phases can be divided into a portion in which fuel is supplied to a selected cylinder, in order to carry out the measurements described above referring to Fig. 2, and a portion in which no fuel is supplied at all, and said relative durations are measured.

It should be understood that the above detailed description and the drawings disclose specific embodiments of the invention, but that they are intended only for illustration purposes and must not be construed as limiting the scope of the invention. Various modifications of the described embodiments can be made within -9 -the scope of the appended claims and their range of equivalents. In particular, from the description and the drawings, features may become apparent which are not mentioned in the claims. Such features may appear in other combinations besides those specifically disclosed here. The fact that several such features may be mentioned in the same sentence or in some other kind of contextual relation must not lead to the conclusion that they can only appear in the combination specifically disclosed; rather, it should be assumed that among such a plurality of features, one or more features can be left away or modified, as far as this does not jeopardize the correct operation of the invention.

Claims

-10 -Claims 1. A drivetrain for a vehicle, comprising a combustion engine (1), a sensor (3) for monitoring rotation of a crankshaft (16) of the combustion engine (1), a clutch (12) coupling the combustion engine (1) to an output shaft (13) of the drivetrain, an engine controller (8) for controlling fuel injectors (4) associated with cylinders (2) of the combustion engine (1) based on operating parameters, an update controller (11) for setting said operating parameters based on the output of the sensor (3), and a clutch controller (14) for controlling torque transmission from the combustion engine (1) to the output shaft (13) by said clutch (12), wherein the controllers (8, 11, 14) support a drive mode in which the engine (1) is on while the clutch (12) is closed, a sailing mode in which the engine (1) is off while the clutch (12) is open, and a switchover from the drive mode to the sailing mode or vice versa, said switchover comprising a transition phase (t0-t1) in which at least one of the injectors (4) supplies fuel to its respective cylinder (2) while the clutch (12) is partially open, and the update controller (11) is configured to set the operation parameters of the fuel injectors (4) based on data obtained by the sensor (3) in said transition phase (t0-t1).
2. The drivetrain of claim 1, wherein the update controller (11) is configured to select, in at least some of said transition phases (t0-t1), a first subset of injectors (4) to supply fuel to their associated cylinders (2) and a second subset of injectors (4) which do not supply fuel to their associated cylinders (2), and wherein the subsets of subsequent transition phases are different.
3. The drivetrain of claim 2, wherein the first subset comprises just one injector (4).
4. The drivetrain of any of the preceding claims, wherein at least some of said transition phases (t0-t1) comprise a time interval in which no fuel is injected.
5. The drivetrain of any of the preceding claims, a switchover from the drive mode to the sailing mode comprises the transition phase (t041).
6. The drivetrain any of the preceding claims, wherein the controllers (8, 11, 14) are configured to switch over to sailing mode when the driver releases an accelerator pedal (10).
7. The drivetrain of any of the preceding claims, wherein the transition phase (t0-t1) has a duration between 0,1s and 5s.
8. The drivetrain of any of the preceding claims, wherein the opening degree of the clutch (12) varies continuously throughout the transition phase (t0-t1).
9. A method of controlling a drivetrain, which comprises the steps of in a switchover between a drive mode (<0) in which a combustion engine (1) is on and a clutch (12) is closed so as to transmit torque from the combustion engine (1) to an output shaft (13) of said drivetrain, and a sailing mode (t1-t2) in which the clutch (12) is open while the engine (1) is off, inserting a transition phase (t0-t1) in which the clutch is partially open; in the transition phase (t0-t1), controlling at least one injector (4) of the engine (1) to supply fuel to its associated cylinder (2) while the clutch (12) is partially open; deriving operating parameters for the injectors (4) based on monitoring rotation of a crankshaft (16) of the combustion engine (1) during said transition phase (t041), and operating the injectors (4) based on the derived operating parameters.
10. A computer program comprising program code means which enable a at least one of the controllers (8, 11, 14) in the drivetrain of any of claims 1 to 8 or to carry out the method of claim 9.
11. A computer-readable data carrier, having program instructions stored on it which enable at least one of the controllers (8, 11, 14) in the drivetrain of any of claims 1 to 8 or to carry out the method of claim 9.