EP1151193B1 - Pulse start method and pulse start device for an internal combustion engine - Google Patents

Description

The invention relates to a pulse starting method for an internal combustion engine according to the preamble of claim 1 and a pulse starting device according to the preamble of claim 12, as known from JP-A-58 124 066.

State of the art

A pulse starting method and a pulse starting device for an internal combustion engine are known. In the impulse start process, a flywheel is accelerated in rotation during a winding phase. This is done using an electrical starter. In this case, a pulse start clutch arranged between the internal combustion engine and the flywheel is opened. Mechanical work is saved by driving the flywheel. During a clutch phase in which the impulse start clutch is closed, this stored work, together with the drive torque of the starter, turns the internal combustion engine on. The advantage over a conventional start, in which the internal combustion engine is driven at a quasi-stationary speed over a relatively long period of time, is that during the pulse start a pulse-like speed curve with a steeply rising flank when the pulse start clutch is closed, so that a safe start of the internal combustion engine is achieved.

A disadvantage of the known pulse starting method or the known device is that the starting system must be designed for high performance. In particular, because a safe start must be guaranteed for every operating state of the internal combustion engine. This high starter power is required in particular with increasing cold, because the towing power to be applied by the starter increases and the starter battery power decreases. Compared to the conventional starter system, this problem is even more pronounced when starting the pulse, because the drag power to be applied by the electric starter also increases with the speed. The towing power also increases when an automatic transmission is provided for torque transmission in the drive train, so that additional towing power must also be applied for the converter input of the transmission. Known pulse starting methods or pulse starting devices are also designed with regard to output in such a way that a reliable start is to be achieved even when the crankshaft of the internal combustion engine is in an unfavorable rotational position. In the worst case, it may be necessary, for example, to turn the crankshaft by 400 ° in order to achieve synchronization of the internal combustion engine that is necessary for starting. During the synchronization, positions of the pistons or the valves in particular should be determined. Corresponding These positions must be used for fuel injection and ignition. In addition, when starting the pulse, care must be taken to ensure that the narrow time window for starting the internal combustion engine can be maintained even in the case of unfavorable starting operating positions or environmental parameters. This time window results in particular from the fact that when the impulse start clutch is closed, the rotational speed of the flywheel mass decreases very quickly and thus the rotational speed of the internal combustion engine remains lower, whereby the internal combustion engine must be started at the latest when the rotational speed of the internal combustion engine is below the minimum rotational speed for starting ability drops. As the drag torque increases at low temperatures, for example due to the lower viscosity of the lubricants, this time window is narrowed. To ensure a cold start, it must therefore be dimensioned for a very high starting power, in particular also because if the start is aborted, ignorance of the mixture condition of the intake manifold and the individual cylinders reduces the chances of a successful second attempt to start. An estimate of the starting power for a 3-liter 6-cylinder engine with automatic transmission, for example at an ambient temperature of -25 ° C, results in a necessary wind-up speed of approx. 1500 l / min with a drag torque of approx. 35 Nm to be applied. This results in the starter's mechanical output of approx. 5.2 kW and a battery output of approx. 6.6 kW.

Advantages of the invention

In contrast, the pulse starting method with the features of claim 1 and the pulse starting device with the features of claim 12 offer the advantage that a significant reduction in the starting power required to secure the start when starting the pulse is possible. In particular, by a speed observer evaluating the speed curve of the flywheel during the pull-up and / or the coupling phase, it can be determined whether the available starting power, which is reduced compared to the prior art, is sufficient to start the internal combustion engine on a first attempt to start. If this is not the case, the internal combustion engine is at least brought into an operating position which is favorable for a subsequent second attempt to start by means of the rotationally accelerated flywheel and / or the electrical starting device. In cold start conditions in particular, it has been shown that when the internal combustion engine is turned on for the first time, the towing power for a subsequent second attempt to start can be reduced, since lubrication of the moving parts in the internal combustion engine and / or the flanged gearbox is achieved as soon as the engine is turned on. Automatic transmissions in particular have shown that a few revolutions are sufficient to reduce the drag power at the converter input. Thus, less towing power is required for the second subsequent start attempt, so that a significantly lower one is also achieved by setting the favorable operating position of the internal combustion engine for the second start attempt Starting power must be applied, but a safe start can still be achieved. If the speed curve of the flywheel is evaluated during the winding phase, it can also be determined whether the starter battery can provide sufficient power. However, if it can be seen from the speed curve that the flywheel cannot be brought up to the required speed, the clutch phase can be initiated prematurely and the internal combustion engine can be brought into an operating position that is favorable for the second attempt to start. The first turning on the first attempt to start also reduces the drag torque here, so that the subsequent second attempt to start is also successful with less power.

The pulse starting method and the pulse starting device according to the invention also offer the advantage that no additional hardware components have to be provided. When starting an internal combustion engine, the pulse start clutch is usually only closed when the flywheel mass has reached a certain speed. A speed sensor is therefore provided anyway. Its signal can of course also be used to assess the speed curve in the method according to the invention or in the pulse starting device according to the invention. In order to be able to set or provide the favorable operating position of the internal combustion engine, existing sensors, in particular rotary angle sensors, are also provided on modern internal combustion engines, for example can detect the rotational position of the crankshaft and / or camshaft and / or the piston position. In modern internal combustion engines, these values are required to control or regulate the combustion process. The signal from these transmitters can thus also be advantageously evaluated in the pulse starting method according to the invention or in the pulse starting device.

In order to be able to assess the speed curve of the flywheel mass, provision is made during the winding-up phase to observe the gradient of the speed curve, the clutch phase being initiated, as mentioned above, if the gradient is too low, so that the internal combustion engine is still in the position which is favorable for the second attempt to start Operating position can be brought.

As an alternative or in addition, the speed of the flywheel mass can be recorded at definable points in time for the evaluation or assessment of the speed curve, the clutch phase also being initiated at a certain point in time if the speed is too low.

If the impulse start clutch is closed prematurely during the pull-up phase, preferably no attempt is made at all in the sense that the ignition is activated or an injection is carried out on the internal combustion engine. This ensures that there is in the intake duct do not set any uncontrolled mixture states on the internal combustion engine.

If a gradient of the speed curve that is too low and / or a speed of the flywheel mass that is too low is determined at a certain point in time during the clutch phase, the start attempt is stopped prematurely, i.e. the control of the electrical starter device is canceled, but preferably only when the internal combustion engine is running for the second attempt to start has taken a favorable operating position. It can therefore be provided that the electric starting device continues to drive or brake the flywheel during the coupling phase in order to be able to stop the internal combustion engine in a certain desired operating position or to bring it into a desired position.

According to a development of the invention, it is provided that at least the synchronization of the internal combustion engine takes place when the start is aborted, during which the piston position and / or the valve position of the internal combustion engine is determined. A rotation of the crankshaft by 200 ° is typically sufficient to be able to determine the piston and / or valve positions of the internal combustion engine. In an unfavorable case, 400 ° crankshaft rotation may also be necessary to carry out the synchronization.

In order to be able to improve the assessment or evaluation of the speed curve of the flywheel mass, additional start parameters are preferred considered. These include, for example, the ambient temperature, the operating temperature of the internal combustion engine and the state of charge of the starter battery.

For an improved second starting attempt, it can be provided that the starter battery is recharged between the first and second starting attempts via the on-board electrical system battery of a motor vehicle. This makes it possible to increase the power to be output by the electrical starting device.

In order to bring the internal combustion engine into the operating position that is favorable for the second starting attempt, it is particularly provided that the oscillation of the internal combustion engine is influenced. This is possible, for example, via the electrical starting device that drives the flywheel. In addition to its drive function, the electrical starting device can also have a braking function. The electrical starter is therefore preferably designed as a so-called starter generator which supplies the electrical system of the motor vehicle with electrical energy during operation of the internal combustion engine. For the favorable operating position, provision is made in particular for at least one piston to be brought into a stroke position from which combustion of this fuel can be achieved after a fuel has been introduced into the combustion chamber, i.e. a working stroke of the piston can be provided, so that a first supporting combustion in of the internal combustion engine can be reached, specifically before the speed of the internal combustion engine drops under the start limit condition, which can be estimated at approx. 80 l / min.

Further advantageous configurations result from the subclaims.

drawing

Figur 1

ein Blockschaltbild einer Impulsstartvorrichtung,

Figur 2

ein Ablaufdiagramm eines Impulsstartverfahrens,

Figur 3

einen Drehzahlverlauf einer Brennkraftmaschine bei einem zweiten Startversuch.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawing. Show it:

Figure 1

2 shows a block diagram of a pulse starting device,

Figure 2

a flowchart of a pulse start procedure,

Figure 3

a speed curve of an internal combustion engine in a second attempt to start.

Description of the embodiments

FIG. 1 shows a block diagram of an internal combustion engine 1, which can comprise at least one reciprocating piston (not shown here) with associated valves, the reciprocating piston driving a shaft, in particular crankshaft 2, of the internal combustion engine. A pulse start clutch 4 known per se is arranged between a rotatably mounted flywheel mass 3 and the crankshaft 2, so that the flywheel mass 3 can be coupled to the crankshaft 2. The flywheel 3 is driven by an electric starter 5. Between Inertia 3 and starter 5 can be arranged a starter gear 6, which is preferably designed in several stages. The starter 5 is preferably a so-called starter generator. In order to drive a motor vehicle, not shown here, a speed transmission means 7 is also provided, the drive input 8 of which can be connected to the crankshaft 2. The speed transmission means 7 is preferably designed as an automatic transmission. However, it can also be a known sound transmission.

The electric starter 5 is controlled by a starter control 9. The starter control 9 also controls the opening and closing of the pulse start clutch 4. Signals from sensors arranged in the internal combustion engine 1, which for example detect the rotational position of the crankshaft 2 and / or a camshaft (not shown) and / or the temperature of the internal combustion engine 1 detected by the starter control 9. The electric starter 5 and the starter control 9 form a pulse starting device 10, in which the electric starter 5 accelerates the flywheel 3 to a predeterminable speed n. If the speed n reaches a winding speed n n which _is necessary for the start of the internal combustion engine 1, the starter control 9 controls the impulse start clutch 4 so that it is closed and the crankshaft 2 is accelerated by the flywheel mass 3. The starter control 9 opens the pulse start clutch before a new winding process, that is to say an acceleration of the flywheel 3, is to take place.

During the winding phase of the flywheel mass 3 to the wind-up speed n _, an evaluation circuit 11, preferably assigned to the starter control 9 _, monitors the speed curve of the flywheel mass 3. The evaluation circuit 11 can determine the level of the rotational speed of the flywheel mass 3 at certain predeterminable times. However, it can also be provided that a speed curve is determined over time, in which case the gradient of the curve can be determined at definable times. The speed n of the flywheel mass 3 is preferably determined via a speed sensor 12 arranged in the starter 5, the measurement signal of which is detected by the evaluation circuit 11. At least one first starting process can be triggered manually via an activation input 13.

A pulse start of the internal combustion engine 1 with up to two winding phases is reproduced on the basis of FIG. 2 using the flow diagram shown. Start 14 is triggered via activation input 13. The starter control 9 activates the electric starter 5, which drives the flywheel 3 during the winding phase 15. During wind-up 15 monitors the evaluation circuit 11, the speed n of the flywheel 3 as to whether the rotational speed n _to n is less than the wind-up is. Alternatively or additionally, it is determined whether the gradient g of the speed curve is greater than a predeterminable minimum gradient g _min . If these two conditions listed in decision step 16 are met, it is decided in starter control 9 that the pull-up phase to be continued, as indicated by method step 17.

If it is determined via the speed sensor 12 that the speed n is greater than or equal to the wind-up speed (step 18), the wind-up phase is ended and the pulse start clutch 4 is closed, which is represented by method step 19. The evaluation circuit 11 also determines whether the gradient g of the speed curve is less than the predeterminable minimum gradient g _min . _{Is intended} is also the rotational speed n is less than the target speed n (Step 20) is also closed, the pulse start clutch 4, thus proceeding to the process to step 19. Method step 19 is followed by first coupling phase 21, in which synchronization is carried out on internal combustion engine 1. The positions of the pistons and the valves of the internal combustion engine 1 are determined during the synchronization. In the subsequent second coupling phase 22, the synchronization is achieved or ended. During the second clutch phase 22, extrapolation of the speed curve recorded by the evaluation circuit 11, possibly including the gradient g, estimates whether at least one combustion process above the startability limit (minimum speed at which a start can be expected) of the internal combustion engine 1 is possible. In this method step 23 it is estimated whether the speed n is greater than or equal to a minimum speed n _kmin , which represents a minimum speed during the clutch _phase . In addition, the gradient g can have a limit value for the gradient g _{km can be compared in} the speed _curve during the clutch phase. If the speed n or the gradient g is greater than the comparison _values n _kmin or g _kmin , the start is continued in method step 24. If the speed is too low or the speed drop (gradient) is too large, ie if the speed curve n (t) has a large negative slope, the first attempt to start is aborted in method step 25. When the internal combustion engine swings out, the crankshaft 2 is preferably stopped at a rotational position that corresponds to an operating position of the internal combustion engine 1 that is favorable for a second attempt to start. In the favorable operating position, it is preferably provided that at least one piston of the internal combustion engine 1 has a position such that a combustion process can be initiated or started immediately afterwards in its associated cylinder. If the internal combustion engine 1 has come to a standstill, the pulse start clutch 4 is opened during method step 25. A second start attempt (method step 26) can subsequently be initiated, that is to say a new pull-up phase 15 can begin. Since the internal combustion engine 1 is in a favorable operating position for the second start, fuel can be injected into a cylinder of the internal combustion engine immediately before the end of the second pull-up phase 15 and before the start of the second clutch phase 22, so that a safe start is brought about during the second clutch phase 22 , In the second attempt to start, method step 21, ie the synchronization of the internal combustion engine may be waived. It is also provided that no fuel injection and / or ignition takes place after the abort of the first start during method step 25.

If it is determined in method step 20 during the first start attempt that the gradient g or the rotational speed n is too low, provision can be made for the crankshaft 2 of the internal combustion engine 1 to continue to be rotated for a predetermined amount of time, a corresponding rotational speed also being maintained , which results, for example, from the starter speed under load. This ensures, in particular during a cold start, that the moving parts in the internal combustion engine and in the speed transmission means 7 are lubricated, as a result of which there is an overall reduction in the drag power that the electric starter has to apply. As a result, the friction loss in the internal combustion engine 1 and the speed transmission means 7 is reduced during the second starting process, so that both the wind-up speed and the speed of the internal combustion engine are increased when the pulse start clutch is closed, thereby increasing the starting reliability.

FIG. 3 shows two speed curves of the flywheel mass 3 over time t during a second start attempt. The upper curve of the speed curve was determined during the second starting process, the internal combustion engine 1 or its crankshaft 2 being driven until an engine was stopped Reduction in friction losses occurred. This additional measure was not carried out on the lower speed curve.

The course of the curves is described in more detail below: the winding phase 15 of the flywheel 3 takes place until the time t1. At time t1, the first clutch phase 21 is then initiated, in which the pulse start clutch 4 is closed. The curves show that when the pulse start clutch is closed at time t1, the speed of crankshaft 2 increases until time t2 or t2 'and the speed of the flywheel mass decreases. At time t2 or t2 ', there is no slippage between the clutch part on the crankshaft side and the flywheel-side clutch part, so that the impulse start clutch 4 is completely closed. Due to the fact that the flywheel mass 3 has given up its rotational energy to the internal combustion engine, the speed n of the flywheel mass 3 and thus also that of the crankshaft 2 drops. upper speed curve) the first supporting combustion is possible. It can thus be seen that the first auxiliary combustion at time t3 or t3 'can be activated even before the minimum speed n _{min of} the internal combustion engine 1 is reached, with the pre-injection of the fuel into the cylinder of the internal combustion engine being possible during the period t0 to t1. It can be seen that in both cases there is a sufficient safety distance between the first supportive Combustion and the minimum speed n _min is present, so that the internal combustion engine 1 can be started safely at least during the second attempt to start.

Claims (12)

1. Pulse-start method for an internal combustion engine, in which, during a wind-up phase, a flywheel mass is accelerated, in rotation, and subsequently, during a coupling phase, the rotating flywheel mass is coupled to a rotatably mounted shaft, preferable crankshaft, of the internal combustion engine for torque transmissions, characterized in that, during the wind-up phase (15) and/or the coupling phase (21, 22), the rotational-speed profile of the flywheel mass (3) is evaluated, in that, from this evaluation, it is derived as to whether a successful start of the internal combustion engine (1) is possible, and in that, insofar as a successful start is not expected, the internal combustion engine (1) is brought via the shaft (2) into an operating position favourable from a following second start attempt.
2. Pulse-start method according to Claim 1, characterized in that, during the wind-up phase (15), the gradient (g) of the rotational-speed profile (n(t)) of the flywheel mass (3) is used for evaluation, and in that, in the case of too low a gradient (g), the coupling phase (21, 22) is initiated.
3. Pulse-start method according to Claim 1, characterized in that, during the wind-up phase (15), the magnitude of the rotational speed (n) of the flywheel mass (3) is detected at definable time points (t) for evaluation, and in that, in the case of too low a rotational-speed magnitude, the coupling phase (21, 22) is initiated at a specific time point.
4. Pulse-start method according to Claim 1, characterized in that, during the coupling phase, the gradient (g) of the rotational-speed profile (n(t)) of the flywheel mass (3) is used for evaluation, and in that, in the case of too negative a gradient (g), the start attempt is discontinued and the internal combustion engine (1) is brought into the operating position favourable for the second start attempt.
5. Pulse-start method according to Claim 1, characterized in that, during the coupling phase, the magnitude of the rotational speed (n) of the flywheel mass (3) is detected at definable time points (t) for evaluation, and in that, in the case of too low a rotational-speed magnitude, the start is discontinued at a specific time point (t) and the internal combustion engine (1) is brought into the operating position favourable for the second start attempt.
6. Pulse-start method according to one of the preceding claims, characterized in that, in the case of the discontinuation of a start, at least the synchronization of the internal combustion engine (1) still takes place, during which the piston position and/or valve position is determined.
7. Pulse-start method according to one of the preceding claims, characterized in that, further start parameters, preferably the ambient temperature, the operating temperature of the internal combustion engine and/or the charge state of a starter battery, are taken into account in the evaluation of the rotational-speed profile (n(t)).
8. Pulse-start method according to one of the preceding claims, characterized in that no fuel injection and/or no ignition takes place while the internal combustion engine (1) is brought into the operating position favourable for the second start attempt.
9. Pulse-start method according to one of the preceding claims, characterized in that, insofar as a successful first start is not expected, the shaft (2) of the internal combustion engine (1) is driven at a predeterminable rotational speed (n) for a definable period of time, before the latter is brought into the favourable operating position.
10. Pulse-start method according to one of the preceding claims, characterized in that a recharging of the starter battery via the on-board battery of a motor vehicle takes place between the first and the second start attempt.
11. Pulse-start method according to one of the preceding claims, characterized in that, by the swing-down of the internal combustion engine (1) being influenced after the discontinuation of the start, the latter is brought into the favourable operating position.
12. Pulse-start device for an internal combustion engine, with an electrical starter (5) which drives a rotatably mounted flywheel mass (3), and with a starter control (9) which controls the starter (5) and a pulse-start coupling (4), in particular for carrying out a pulse-start method according to one of Claims 1 to 11, characterized by an evaluation circuit (11) which evaluates the rotational speed (n) of the flywheel mass (3) at specific time points and/or the gradient (g) of the rotational-speed curve (n(t)) over the time (t) and judges whether a successful start of the internal combustion engine (1) is possible.