EP0374584B1 - Method for operating a direct current generator connected to an internal-combustion engine as starter motor, and device therefor - Google Patents

Abstract

In order to use a generator 2, which is connected to an internal-combustion engine 1 and drives an electric drive motor 5, as the starter for the internal-combustion engine 1 without providing additional auxiliary windings in the generator 2, it is proposed that current flow through the exciter winding 6 before flowing through the armature winding 8. While the voltage of the starter battery 13 remains essentially constant, it is thereby possible for the exciter field to be built up almost completely before a current flows through the armature winding 8 and produces a torque. A switching arrangement for such a method is also proposed.

Description

The invention relates to a method for operating a direct current shunt generator connected to an internal combustion engine and a circuit arrangement therefor.

For starting internal combustion engines, a special electric starter motor is usually used, which is fed by a starter battery and rotates the flywheel of the internal combustion engine, which is provided with a ring gear, by means of a pinion. In internal combustion engines that operate a powerful electric generator that feeds an electric drive motor, it is known to carry out the starting process via the generator, ie to use the generator as a starter, so that the special starter motor and the ring gear can be saved. For this purpose, the generator is provided with a special auxiliary winding. Such a method or such an arrangement is described in the book "Electric Power Vehicles", Volume 2, page 645, by K. Sachs described, whereby vehicles with diesel-electric drive are affected. The dimensions of the auxiliary windings are adapted to the starter battery. If a generator without auxiliary winding is used for starting and the excitation winding is switched to the starter battery at the same time as the armature winding, the voltage of the starter battery drops sharply during the switch-on process and the generator is only slightly excited. As a result, the torque delivered by the generator, which is proportional to the excitation (magnetic flux) and the armature current, becomes too small to start the diesel engine.

The invention has for its object to provide an inexpensive method and a suitable device for operating a DC shunt generator connected to an internal combustion engine as a starter, in which no auxiliary windings are necessary.

This object is achieved according to the invention by the features of claims 1 and 4, respectively. Because current flows through the excitation winding before the armature winding, a strong excitation field can therefore initially build up, so that as soon as current flows through the armature winding with a delay, there is sufficient excitation to generate sufficient torque. It is advantageous if current flows through the armature winding only after a time corresponding to twice the time constant of the excitation winding, because then over 85% of the possible excitation is reached. This time to build up the excitation field can be approximately 0.5 to 1 sec. After the starting process has been initiated by actuating an ignition key.

In order to keep the ohmic resistance in the armature circuit low, according to a further step of the invention, the reversing pole winding can be switched off during the starting process.

According to the invention, the described method is achieved by a circuit arrangement according to claim 4, in which a switch is arranged in a line connecting the armature winding to a voltage source, which switch is operatively connected to a timing element. The switch connects the voltage source and armature winding with a time delay, while the excitation winding is immediately connected to the voltage source, so that an excitation field can build up undisturbed. A starter battery is used as the voltage source, which is strong enough to easily feed the excitation winding and generate an excitation field and then provide a sufficient armature current. Only after the field of excitation has been set up does the switch close and current flows through the armature winding, whereupon a torque is generated and the rotor of the generator and the crankshaft of the internal combustion engine connected to it are set in rotation. The field of excitation is only slightly weakened.

In an advantageous development of the subject matter of the invention, the switch is connected to a contactor and the timer is arranged in a signal line connected to the contactor, which is connected to the voltage source during the starting process. As a result, a control current circuit can be formed which controls the generator during the starting process and is separated in terms of circuitry from a main current circuit which is active during the current generation of the generator.

If a switch controlled by a relay is arranged in the signal line and can be switched as a function of the direction of flow of the current, as soon as the internal combustion engine has started and runs independently, so that a connected alternator now generates electricity, the armature winding of the generator is automatically switched off the starter battery. For this purpose, it is expedient to connect the relay to an alternator regulator, as is known from automotive engineering.

Another favorable embodiment of the subject matter of the invention, in which the generator is connected to an electric drive motor and feeds it in normal operation, provides for a switch to be arranged in a line connecting the generator to the drive motor, which switch interrupts the line during the starting process. As a result, no current flows to the drive motor, so that the current from the starter battery is only available to the generator acting as a starter.

It is particularly advantageous to use the described method and an associated circuit arrangement for an industrial truck, in particular forklift truck, with one or more electric drive motors which receive their power supply from a generator driven by an internal combustion engine.

The invention will be explained in more detail with the aid of the following schematic examples of figures.

• Figur 1 ein Diagramm mit dem zeitabhängigen Verlauf von Anker- und Erregerstrom,
• Figur 2 eine Hauptstromschaltung,
• Figur 3 eine Steuerschaltung zur Verwendung des Generators als Anlasser.

Show it:

• FIG. 1 shows a diagram with the time-dependent course of armature and excitation current,
• FIG. 2 shows a main current circuit,
• Figure 3 shows a control circuit for using the generator as a starter.

In your diagram in FIG. 1, the time is plotted on the abscissa and the voltage of the starter battery in percent and the current flowing through the excitation winding and the armature winding in percent on the ordinate. The curve labeled A shows the voltage profile of a starter battery. The curve labeled B represents the course of the current flowing through the armature winding. C denotes the course of the current flowing through the field winding. The dashed line D shows the constant rise in the excitation current with constant battery voltage.

The battery voltage is 100% at the start of the start. The start of the start process is marked with 0 on the abscissa. If a current flows through the excitation winding and through the armature winding at the same time, the current flow in the armature winding increases very quickly. However, sufficient rotation cannot be demonstrated because the field of the exciter has not yet been built up. As a result of the high current consumption with simultaneous supply of excitation and armature windings, the battery voltage breaks down and drops, for example, to approx. 50%. As As a result, the excitation current increases very slowly and the armature current drops again. The battery voltage also slowly increases again, but without reaching the original level again. The excitation current and thus the excitation field are far from reaching their maximum. As a result of a lack of excitation, the torque delivered at the armature therefore remains small.

The dashed line D shows the increase in the excitation current in the case of constant battery voltage, which is only achieved with a very large battery capacity, but not with a starter battery, as is used for the starter motor normally used. The starter battery is sufficiently dimensioned for a starter motor because the starter motor acts on a toothed flywheel of the crankshaft of the internal combustion engine via a pinion and because of the large transmission ratio, the torque is increased accordingly. If such a starter battery is used to supply a generator that is not used as a starter and has no auxiliary windings, the battery voltage breaks down, as described.

This problem is solved by the excitation current flowing in time before the armature current according to curve E. At time 0, i.e. at the start of the starting process, over 85% of the excitation current can already flow, so that the excitation field is set up accordingly when the current Armature winding flows through. The excitation current will drop again, which is not shown in the diagram, but since the field at the time of the Release of the armature current is already and has a certain inertia, sufficient torque can be delivered to the armature immediately.

FIG. 2 shows an internal combustion engine 1, which is coupled to a generator 2, which is connected via lines 3 and 4 to an electric drive motor 5 and supplies the latter with electricity while the internal combustion engine 1 is running. The generator 2 is provided with an excitation winding 6, a reversing pole winding 7 and an armature winding 8. The motor 5 has an excitation winding 6a. The field winding 6 of the generator 2 is supplied with current via an output stage 9. The control of the output stage 9 takes place during the starting process via a start control 10 and during generator operation via a drive control 11. A switch 12, in this example designed as a double switch, enables a starter battery 13 to be connected to lines 3 and 4 via lines 14 and 15. A switch 16 is provided in line 3 so that drive motor 5 can be disconnected from generator 2.

FIG. 3 shows the basic structure of the drive control 11. A contactor 20 is connected to the starter battery 13 via lines 17 and 18 and a signal line 19 and supplies the armature winding 8 with current via the switch 12, that is, switches the generator on. A timer 21 is arranged in series with the contactor 20. Also in series with the contactor 20, a switch 22 is provided in the signal line 19, which switch is controlled by a relay 23, which is located in a line 24 a connecting an alternator regulator 24 to the line 17. The alternator regulator 24 is over an alternator 25, which is provided for charging the starter battery 13 and supplying the lighting network, and is connected to the line 17 again via a line 24b separately from the line 24a and to the line 18 via a line 24c. A switch 26 is in the line 24a arranged, which is controlled by a relay 27 which is connected in a line 19a. The line 19a is connected to the line 18 and connected to the line 17 via a line 17a and thus connected in parallel to the line 19. Also connected to the lines 17a and 18 and thus connected in parallel to the lines 19 and 19a is a line 19b in which there is a contactor 28 which supplies the excitation winding 6 with current via a switch 28a via the output stage 9. Furthermore, a line 19c is connected to line 18 and connected via a line 17b to line 17, that is to say connected in parallel to lines 19, 19a and 19b. A contactor 29, which is connected to the switch 16, is arranged in the line 19c. The switches, contactors and relays described so far are open in the normal position, i.e. they interrupt the respective line.

The lines 17a and 18 are finally connected by a line 19d which is connected in parallel to the lines 19a to c. A relay 30 is provided in the line 19d, which controls a switch 31 which is arranged in line with the contactor 29 in the line 19c. The switch 31 is closed in the normal position, ie when the contactor 29 is de-energized, so the line 19c is not interrupted.

The lines 17a and 17b can be connected to one another and to the line 17 via a starter switch 32. The starter switch 32 has three positions. The first position I is the rest position, in which the lines 17a and 17b are not connected to the line 17 and therefore no current flows. In the second position II, the line 17 is connected to the line 17b, whereby this is connected to the starter battery 13. The third position III of the switch 32 connects the line 17 to the lines 17a and 17b at the same time and thus energizes them. Positions I and II are permanent positions. Position III must be held during the starting process. When switch 32 is released, it automatically jumps back to position II.

When starting the switch 32 is pressed into position III. As a result, the relays 27 and 30 are actuated, which causes the switch 26 to close and the switch 31 to open. The switch 31 thus disconnects the line 17b, so that the contactor 29 remains de-energized and the switch 16 interrupts the line 3 between the generator 2 and the electric drive motor 5.

Furthermore, the contactor 28 is switched on without delay so that current can flow to the excitation winding 6.

Closing the switch 26 causes the contactor 20 and the timer 21 to be energized via the relay 23 and the switch 22. The contactor 20 therefore switches the generator 2 or its armature winding 8 to the starter battery 13 with a time delay, so that a torque is generated which sets the crankshaft of the internal combustion engine 1 in rotation until the latter starts and starts up. When the internal combustion engine 1 is running automatically, the alternator 25 outputs voltage, so that the direction of flow of the current in the line 24a is reversed and the relay 23, which switches depending on the direction of flow, opens the switch 22 in the signal line 19. The contactor 20 is then de-energized, as a result of which the switch 12 opens and the generator 2 is disconnected from the starter battery 13 again.

When switch 32 is then released, it automatically jumps back to position II, as a result of which relay 27 is de-energized and switch 26 opens. The contactor 28 is also separated from the starter battery 13 so that no more current flows from the starter battery 13 into the excitation winding 6. The excitation current is now generated by the alternator 25 itself and controlled by the drive control 11. Finally, the relay 30 is also de-energized, which causes the switch 31 to close and then the contactor 29 to tighten, so that the switch 16 reconnects the interrupted line 3 and the generator current can flow to the electric drive motor 5.

Claims (9)

1. A method of operating a d.c. shunt generator connected to an internal combustion engine, comprising an exciting winding (6) and an armature winding (8) as starter, characterised in that the exciting winding (6) is traversed by current at an earlier time than the armature winding (8).

2. A method as claimed in Claim 1, characterised in that the armature winding (8) is traversed by current on the expiration of a time corresponding to double the time constant of the exciting winding (6).

3. A method as claimed in one of Claims 1 or 2 for a generator with a commutator winding, characterised in that the commutator winding (7) is switched off when the internal combustion engine (1) is started.

4. A circuit arrangement for a d.c. shunt generator which comprises an exciting winding (6) and an armature winding (8) and which is connected to an internal combustion engine and can be operated as starter, characterised in that a switch (12) is arranged in a line (14) connecting the armature winding (8) to a voltage source (13), where said switch is actively connected to a timer (21) in such manner that when the generator is operated as starter, the exciting winding (6) is traversed by current at an earlier time than the armature winding (8).

5. A circuit arrangement as claimed in Claim 4, characterised in that the switch (12) is connected to a contactor (20), and the timer (21) is arranged in a signal line (19) which is connected to the contactor (20) and which during the starting process is connected to the voltage source (13).

6. A circuit arrangement as claimed in Claim 5, characterised in that a switch (22) controlled by a relay (23) is arranged in the signal line (19), where said relay (23) can be switched in dependence upon the direction of flow of the current.

7. A circuit arrangement as claimed in Claim 6, characterised in that the relay (23) is connected to a dynamo regulator (24).

8. A circuit arrangement as claimed in one of Claims 4 to 7, wherein the generator is connected to an electric drive motor, characterised in that a switch (16) is arranged in a line (3) connecting the generator (2) to the drive motor (5), which switch (16) interrupts the line (3) during the starting process.

9. The application of a method as claimed in one of Claims 1 to 3 and of a circuit arrangement as claimed in one of Claims 4 to 8 to an industrial truck, in particular a fork lift truck.

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