Internal-combustion engines – Starting device – Condition responsive control of starting device
Reexamination Certificate
2000-10-20
2002-09-24
Mancene, Gene (Department: 3747)
Internal-combustion engines
Starting device
Condition responsive control of starting device
Reexamination Certificate
active
06453863
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a method for starting an internal combustion engine, as well as a starter system for an internal combustion engine.
BACKGROUND OF THE INVENTION
It is known from practice that internal combustion engines (for example, in vehicles), cannot be started from their own power. They must initially be cranked by an external power source (the so-called starter), and accelerated to the engine speed required for starting of the internal combustion engine. Only then can they continue to run under their own power.
A battery-fed DC motor is often used as the electric starter in vehicles. This motor transfers the necessary starting torque to the crankshaft of the internal combustion engine via a drive pinion that engages in a toothed ring on the disk flywheel. A starter system with an electric starter motor, whose rotor sits directly on the crankshaft of the internal combustion engine and is connected to rotate in unison with it, is also known from DE 44 06 481 A1. With this type of arrangement, the weight of the rotor of the electric machine is simultaneously used as flywheel mass.
An improved starter system of this type is also known from EP 0 569 347 A2 and WO 91/16538.
The starting torque of an internal combustion engine and the minimum starting speed depend, among other things, on engine type, working volume, number of cylinders, bearing friction, compression and mixture preparation and, above all, on temperature. The section of the operating process, in which the cylinder or cylinders of the engine are situated during starting, is also significant for compression of an internal combustion engine and therefore for its readiness to start. Thus, for example, the compression of a cylinder situated in the compression stroke has an unfavorable effect on starting behavior, because it opposes the starter with increased torque right at the beginning of starting. Thus far in the prior art this variable has not been adequately considered. Known starters in each case had to be designed according to power, so that the internal combustion engine can be started under all conditions.
OVERVIEW OF THE DISCLOSED DEVICE
In the disclosed method for starting an internal combustion engine, the crankshaft of the internal combustion engine is accelerated at least to a speed (so-called starting speed) necessary for starting the internal combustion engine. An electric machine is used for this acceleration, whose rotor acts directly on the crankshaft or via a transmission connected in between. The crankshaft is also brought to a stipulated crank angle position or stipulated crank angle (hereafter “starting angle”) by means of the electric machine for the starting process and the internal combustion engine is started from this starting angle. The power required for starting is taken at least partially from a capacitor accumulator. The actual starting process of the internal combustion engine can then begin from a favorable starting angle and is additionally fed, at least partially, from the capacitor accumulator (not fully from a starter battery, as usual), which can deliver the necessary electrical starting power much more quickly than an ordinary battery. Moreover, a capacitor accumulator is much less temperature-sensitive than an electrochemical battery, so that, even at very low temperatures, problem-free starting is possible.
Charging of the capacitor accumulator can occur in different ways. One possibility comprises charging the capacitor accumulator only before starting from a starter battery. The command that triggers the adjustment process of the crankshaft starting angle is preferably simultaneously used as signal to charge the capacitor accumulator from the starter battery. Starting of the internal combustion engine can then occur without any waiting time.
A disclosed starter system for an internal combustion engine includes: an electric machine, whose rotor is connected directly to rotate in unison with the crankshaft of the internal combustion engine or via a transmission connected in between, in order to accelerate the internal combustion engine at least to a speed (starting speed) necessary for starting; means to record and/or derive the crank angle of the internal combustion engine; a control device that controls the electric machine, so that the crank angle of the internal combustion engine is brought to a stipulated starting angle for the starting process; and a capacitor accumulator (for example, a so-called intermediate circuit accumulator), which at least partially supplies the power required for starting. The capacitor accumulator can preferably also be a combination of electrical capacitor elements and electrochemical battery elements.
The inventors recognized that the position of the crankshaft at the beginning of starting is of considerable importance for the starting behavior of an internal combustion engine. Based on this recognition, the inventors further recognized that, by influencing the crank angle before the actual starting process, as well as the type of starting power supply, a significant improvement in starting behavior of an internal combustion engine can be achieved. By means of the electric machine (for example, a so-called crankshaft starter with a rotor connected to rotate in unison directly with the crankshaft), it is possible to apply the torques necessary for adjustment of a desired starting angle in both directions of rotation of the crankshaft and with high accuracy. In this manner, an unfavorable crankshaft position at the beginning of starting is avoided, for example, when one or more cylinders of an internal combustion engine compress right at the beginning, and starting can thus be achieved with reduced starting power. In terms of the device, the starter system has a control device for this purpose, which, knowing the instantaneous crank angle, controls the rotor of the electric machine (optionally with consideration of the transmission ratio between the rotor and crankshaft), so that the crankshaft is brought to the desired starting angle.
Use of the disclosed starter system is advantageous both in spark ignition engines and diesel engines (for example, four-stroke engines with manifold injection or with direct injection), which are designed for use in passenger cars.
In a preferred variant, the crank angle at which the starting torque to be applied by the electric machine is lower at the beginning of the starting process than in the known starter systems is chosen as the starting angle. In an internal combustion engine operating, for example, in the four-stroke method, the cylinder pressure, and therefore the compression to be overcome by a starter, increases during a compression stroke and reaches its maximum roughly in the region of top dead center. If, in a preferred variant for a four-stroke internal combustion engine, the crank angle for the next start is set at the end of the compression stroke, preferably in a region right after top dead center, at the beginning of starting, the starter need only overcome the relatively low-compression suction stroke of the internal combustion engine. Moreover, almost two full revolutions remain for the starter at the beginning of starting, in order to build up sufficient starting power to overcome the next compression stroke. This is particularly favorable in a cold start.
In another variant, the crank angle at which the starting time (i.e., the time from the beginning of starting to starting of the internal combustion engine), is reduced to a minimum is chosen as starting angle. In a four-stroke internal combustion engine with manifold injection, this is preferably the crank angle position at the beginning of the suction stroke, with particular preference in the intersection region between the exhaust and suction stroke. On the other hand, in a four-stroke internal combustion engine with direct injection, the crank angle position is preferably at the end of the suction stroke. If the internal combustion engine is also equipped with an ordinary sensor system comprisin
Pels Thomas
Rosskopf Franz
Castro Arnold
Continental ISAD Electronic Systems GmbH & Co. KG
Mancene Gene
Marshall Gerstein & Borun
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