GB2369160A

GB2369160A - Improving the re-starting of an i.c. engine having a starter/generator

Info

Publication number: GB2369160A
Application number: GB0123865A
Authority: GB
Inventors: Wolf Boll; Petr Krenovsky; Andreas Schondelmaier
Original assignee: DaimlerChrysler AG
Current assignee: Daimler AG
Priority date: 2000-10-11
Filing date: 2001-10-04
Publication date: 2002-05-22
Anticipated expiration: 2021-10-04
Also published as: DE10050170A1; GB2369160B; GB0123865D0; FR2815087A1

Abstract

The engine has a starter/generator 1 which is connected to or comprises a flywheel 2 having teeth 4, or perforations, with a unique marker 6 readable by a sensor 5 to identify the rotational position of the crankshaft. In the case of a four-stroke engine, a camshaft sensor is also provided to identify which half of the four-stroke cycle a piston is in. The invention provides that when the engine is switched off, the crankshaft is brought to a predetermined rest position by braking or driving means such that, when the engine is started subsequently, an unambiguous determination of the rotational position of the crankshaft is possible in less than one complete rotation of the crankshaft. Thus a designated starting speed is attained prior to the marker 6 arriving at the sensor 5. The angle 8 between the predetermined rest position and the sensor 5 may be 90 degrees for a four cylinder engine or 60, 60+120 or 60+240 degrees for a six-cylinder engine. The driving and braking may be performed by the starter/generator 1; alternatively, the throttle valve, a load eg air conditioning compressor, ignition angle during the last working cycle or a mechanical brake may be used.

Description

1 23691 60

Device for starting an internal combustion engine The invention relates to a device for starting an internal combustion engine.

A device for starting an internal combustion engine has already been disclosed (WO 91/16538), in which an electric motor serving as generator and starter is coupled to a crankshaft. Prior to the internal combustion engine being started, the crankshaft is brought by means of the starter into an advantageous position in which the pistons are aligned in a row. The rotational position of the crankshaft is determined via a sensor which is provided.

In the case of conventional ignition or injection systems of four-stroke motors, sensors for identifying the top dead centre (TDC) of the pistons are provided on the flywheel of the starting motor, and a sectoridentifying means for the sectors O - 360 degrees and 360 - 720 degrees of the crankshaft is provided. So that a control unit which is connected to the ignition or injection system can then ascertain the current position of the crankshaft from the sensor signals, the starter has to rotate the crankshaft through more than one revolution, and up to a maximum of 660 degrees in the case of a six-

cylinder motor.

In the case of modern starting/stopping systems, it is now possible to reach the starting speed for the internal combustion engine after a rotational angle of the crankshaft of just 90 degrees. It is therefore disadvantageous that despite reaching the starting speed firing cannot be carried out, since the unambiguous relationship with respect to the current rotational position of the crankshaft or position of the pistons which is still required for this purpose is absent, but is demanded by the control unit before ignition takes place.

For exhaust emission reasons and to protect against vibration, the internal combustion engine is to be brought as rapidly as possible to the starting speed designated for starting the internal combustion engine. A rapid bringing-up to speed enables relatively high air velocities to be produced during the induction, which results in better preparation of the fuel injected at the start. Furthennore, the accumulator (starter battery) is overtaxed in terms of power and thermally by the hitherto customary, repeated rotation of the internal combustion engine before starting is initiated. In addition, the energy removed from the

accumulator has to be replaced again later, which results in a disadvantageous effect on the efficiency of the internal combustion engine.

According to the present invention there is provided a device for starting an internal combustion engine, having an electric machine which is adapted to be connected to a crankshaft of the engine and to be operable as a starter/generator unit, and having a means of determining the rotational position for the crankshaft and brake or driving means, wherein when the internal combustion engine is switched off, the braking or driving means bring the crankshaft into a predetermined rest position from which, in a subsequent starting of the internal combustion engine, an unambiguous determination of the rotational position of the crankshaft is possible in less than one complete rotation of the crankshaft.

For starting an internal combustion engine, the invention has the advantage that very reliable and rapid starting of the internal combustion engine can be carried out.

This advantageously results in the exhaust emission having fewer harmful constituents, particularly when the internal combustion engine is started cold. In addition, the starting of the internal combustion engine can be carried out in a manner which is barely perceptible for the driver, which can increase the acceptance of a starting/stopping device for internal combustion engines. It is particularly advantageous that a reliable direct starting of the internal combustion engine can be carried out with a conventional, and therefore cost-effective, determination of the rotational position of the crankshaft.

The measures listed in the subclaims make possible advantageous developments and improvements of the device for starting an internal combustion engine.

By means of the rapid rewing-up of the internal combustion engine in less than one complete revolution of the crankshaft, the crank case of the internal combustion engine can advantageously be prevented from slipping into a natural shaking frequency.

An exemplary embodiment of the invention is illustrated in a simplified manner in the drawing and explained in greater detail in the following description. In the drawing:

Figure 1 shows a front view of a device according to the invention for starting an internal combustion engine, and Figure 2 shows a diagram of a braking process carried out according to the invention, the speed of the internal combustion engine being plotted over the time and the crankshaft angle.

Figure 1 shows, in a schematically simplified manner, a front view of a device according to the invention for starting an internal combustion engine, which device comprises an electric machine 1 which can be operated as a starter/generator unit. The electric machine 1, which is indicated by dash-dotted lines in Figure 1, is connected to a flywheel 2 whose outer circumference is provided, for example, with a toothing arrangement 4. A position marking 6 of a crankshaft 3 which is connected to the electric machine 1 is provided in the toothing arrangement 4. The position marking 6 reproduces the rotational position of the crankshaft 3 and therefore the current position of the pistons of the internal combustion engine. The ignition in the combustion chambers of the internal combustion engine can be initiated at a suitable time by reference to the current position of the pistons. As a rule, a position of the piston before top dead centre in the compression stroke is designated for the ignition. The position marking 6 is brought about by a relatively large tooth spacing in the toothing arrangement 4, so that a position sensor 5 in the vicinity of the toothing arrangement 4, which sensor is designed, for example, in the form of a pulse counter or inductive pickup, identifies the rotational position of the crankshaft 3 when the position marking 6 rotates past the position sensor 5. If the signal of a camshaft sensor (not illustrated in greater detail in Figure 1) of the internal combustion engine is also added to this, then the position of the pistons can be determined exactly via the rotational position of the crankshaft. This makes it possible, for example, in the case of a spark-ignited internal combustion engine (Otto) to identify whether a piston is at the beginning of ignition or at the beginning of induction.

However, the invention is not restricted to spark-ignited internal combustion engines. In the same or modified manner, the invention is also suitable for self-igniting internal combustion engines (diesel).

Instead of the toothing arrangement 4, a perforated disc may also be used. The flywheel 4 and a rotor of the electric machine 1 may comprise one part. The toothing

arrangement 4 and the position marking 6 may also be fitted directly to the rotor of the electric machine.

According to this embodiment of the invention, during the switching-off process of the internal combustion engine, the stopping of the crankshaft 3 by braking or driving means is influenced in such a manner that the crankshaft 3 comes to a standstill in a predetermined rest position. This rest position is wherein in the case of a subsequent starting of the internal combustion engine and rewing-up by means of the electric machine 1, a designated starting speed is attained prior to the position marking 6 of the flywheel 2 arriving at the sensor 5. In the starting phase, an electronic control unit, which is connected to the sensor 5 and is not illustrated in greater detail, therefore obtains, even before the end of a complete revolution of the crankshaft, an unambiguous signal from the sensor 5 from which, in conjunction with the crankshaft sensor, the position of the crankshaft 3, and therefore of the pistons, can then be ascertained unambiguously. In this case, a position of a piston can be detected before the upper dead centre, whereupon, after the signal of the sensor 5 has been passed to the control unit, firing of the internal combustion engine is initiated immediately by injection of fuel and ignition thereof.

The choice of the rest position of the crankshaft 3 and of an angle 8 enclosed between the position marking 6 and the sensor 5 is to be selected such that it is only as large as is necessary, i.e. is as small as possible, in which case the velocity achieved by the flywheel during starting is precisely enough to enable an unambiguous signal to be produced as the position marking 6 passes the sensor 5. In the case of a four-cylinder engine, approximately 90 degrees are sufficient for this purpose. In the case of a six-

cylinder engine, angles 8 of 60 degrees, 60+120 degrees or 60+240 degrees are possible, for example. If, in the case of the six-cylinder engine, the starting distance of 60 degrees were too small in order to be able to produce an unambiguous signal at the sensor 5, which depends on the available torque of the electric machine 1, then an angle of 180 degrees could be provided as the rest position to be aimed at for the crankshaft 3.

In the present example, after the internal combustion engine is switched off the braking or driving means should preferably be used to ensure that the crankshaft 3 is stopped according to the invention in a rotational position with the position marking 6 at 180 degrees from the sensor 5.

s In this connection, the braking can be undertaken as follows. In Figure 2, a switching-

off process of the internal combustion engine with braking initiated is shown and is indicated by the line 11. In the diagram, the speed is plotted over the time and over the rotational angle of the crankshaft. A running-on (section 12 of the line 11) controlled by the control unit is first of all initiated by the driver via the ignition lock or in the starting/stopping mode in the case of automated switching off, said running-on then being followed by braking into the optimum rest position (line 11 and section 14) or into the vicinity of the optimum rest position. In contrast, the dashed line 15 shows, for comparison purposes, a conventional stopping of an engine without braking or driving means. A conventional generator (dynamo) having active commutation in the belt drive can be provided as the driving or braking means. In this case, the generator may briefly also be used as the drive.

Furthermore, a crankshaft starter generator (not illustrated in greater detail) of a starting/stopping device may be used as the driving or braking means. Crankshaft starter generators of this type are disclosed, for example, in DE 199 05 366 Al or EP O 311 688 B1. The crankshaft starter generator has the advantage of being able to move into any desired crankshaft position on account of its high torque, even without taking the momentary "swing" into consideration. In addition, the crankshaft starter generator already has a rotational-angle detecting device which comprises a sensor which determines the position of the crankshaft 3 on the rotor, for example. In this case, the rotor of the crankshaft starter generator replaces the flywheel of the starting motor. Via the braking of the crankshaft by means of the crankshaft starter generator a defined position of the crankshaft 3 optimum for the next start can then be moved to in the same manner, as already described. In a further modification of the invention, it is also possible to provide a belt-driven starter generator.

Further influencing means for braking or accelerating the crankshaft 3 may involve an adjustment of the throttle valve of the internal combustion engine. It is also possible to switch on and adjust the load of an air-conditioning compressor which is provided. The braking or accelerating of the crankshaft 3 can be undertaken by influencing the ignition

angle during the last working cycle, for example in the direction of retarded or very advanced (countertorque). In addition, it is conceivable to provide a mechanical braking device on the crankshaft 3, as is used, for example, in the case of a gear-synchronizing aid. The electronic control unit can store in its memory whether the correct and optimum rest position of the crankshaft 3 has actually been moved to or whether there has also been after-shaking on account of braking which is excessive or too soft. When a deviation from the "ideal landing" of the crankshaft 3 has been established, a self-

learning regulating means provided in the control unit can be used during the next switching-off process to reach the optimum rest position in a stepwise manner by changing the braking or accelerating parameters.

The designs provided to this point are equally applicable for two- and four-stroke engines. In the case of the four-stroke principle, an additional analysis has also to be made and stored in the memory of the control unit as to which position the camshaft is in, for the purpose of relating the ignition to the working cycle.

Claims

1. A device for starting an internal combustion engine, having an electric machine which is adapted to be connected to a crankshaft of the engine and to be operable as a starter/generator unit, and having a means of determining the rotational position for the crankshaft, and brake or driving means, wherein when the internal combustion engine is switched off, the braking or driving means bring the crankshaft into a predetermined rest position from which, in a subsequent starting of the internal combustion engine, an unambiguous determination of the rotational position of the crankshaft is possible in less than one complete rotation of the crankshaft.

2. A device according to Claim 1, wherein in the case of a four-cylinder internal combustion engine, the predetermined rest position of the crankshaft is approximately 90 degrees before top dead centre.

3. A device according to Claim 1, wherein in the case of a six-cylinder internal combustion engine, the predetermined rest position of the crankshaft is approximately 60 degrees, or approximately 180 degrees, or approximately 300 degrees, before top dead centre.

4. A device according to Claim 1, wherein the moment at which the injection of fuel into combustion chambers of the internal combustion engine is switched off is determined in such a manner that the subsequent, automatic stopping of the crankshaft brings the latter into the predetermined rest position.

5. A device according to Claim 1, wherein the electric machine of the starter/generator unit brakes the crankshaft so that it reaches the predetermined rest position.

6. A device according to Claim 1, wherein the electric machine of the starter/generator unit is a crankshaft starter generator.

7. A device according to Claim 6, wherein a device for detecting the rotational position of the crankshaft starter generator is used for determining the rotational position of the crankshaft.

8. A device according to Claim 1, wherein a sensor on a flywheel connected to the electric machine of the starter/generator unit is provided for determining the rotational position of the crankshaft.

9. A device according to Claim 1, wherein the braking or driving means includes means for adjustment of a throttle valve of the internal combustion engine.

10. A device according to Claim 1, wherein the braking or driving means includes means for adjustment of the load of a charge air-conditioning compressor of the internal combustion engine.

11. A device according to Claim 1, wherein in an engine having electric ignition, the braking or driving means includes means for adjustment of the ignition angle during the last operating cycle before stopping of the engine in the direction of retarded or very advanced.

12. A device according to Claim 1, wherein a mechanical braking device on the crankshaft is provided as the braking or driving means.

13. A device substantially as described herein with reference to and as illustrated in the accompanying drawings.