GB2059176A

GB2059176A - An electrical generator

Info

Publication number: GB2059176A
Application number: GB8028505A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-09-06
Filing date: 1980-09-04
Publication date: 1981-04-15
Also published as: JPS5646650A; FR2465345A1; IT8024505A0; DE2935929A1; IT1132683B; BR8005658A

Abstract

An electrical generator, particularly a three-phase generator without slip- rings, for motor vehicles is proposed in which the rotor shaft 15, 16 acts as a magnetically hard member in the magnetic circuit of the rotor, thereby facilitating the build-up of self- excitation. The rotor shaft is thus made of steel (three examples are given) and has mounted thereon a first pole wheel 17 which is connected by way of a non-magnetic ring 18 to a second pole wheel 19, which is thus not directly secured to the shaft 15. End plate 11 carries a mount 21 for the excitation winding 22. <IMAGE>

Description

SPECIFICATION An electrical generator The invention relates to an electrical generator.

The electrical generators having self excitation, there is always the problem that the excitation field might not build up. If the magnetisable material used in the excitation circuit is magnetically soft, the remanence induction is very low and, after the generator has been put into operation, selfexcitation of the generator does not occur, or occurs only at high rotational speeds. It is already known to build up self-excitation in three-phase generators in motor vehicles by means of a pre-excitation current which flows into the excitation circuit by way of a resistor or by way of the charging pilot lamp after the ignition switch has been actuated.It is also already known to improve the build up of self-excitation, that is to say, the starting behaviour of the generator, by introducing oxide magnets at a suitable location in the excitation circuit, particularly between the claws of three-phase generators having claw pole rotors.

However, these known measures have the disadvantage that there is a certain amount of expenditure on circuitry, or the disadvantage of low mechanical strength. In any event, there is an unfavourable relationship between the costs and the result achieved.

According to the present invention there is provided an electrical generator, for motor vehicles, having a stationary output winding and an excitation device for producing a rotating excitation field, which excitation device includes a magnetic circuit and an excitation winding, wherein the magnetic circuit incorporates at least one magnetically hard member in addition to soft magnetic members, the magnetically hard member being the shaft of the generator.

In contrast to the prior art, the generator in accordance with the invention has the advantage that the cost of manufacturing is very low and the build up of self-excitation of the generator is ensured in all cases. Circuit measures outside the generator are not required. A further advantage is that no additional component for the excitation device is required for manufacturing the generator.

Advantageous developments of, and improvements in the generator specified in the main claim are rendered possible by the measures set forth in the sub-claims. A special advantage is that the volume of the generator is not increased and no parts susceptible to failure are used. Moreover, high mechanical strength and satisfactory magnetic properties can be obtained.

The present invention will now be described further, by way of example only, with reference to the accompanying drawing which shows one embodiment of a three-phase generator in accordance with the invention.

A rotor shaft 15 isjournalled in bearings 13 and 14 in a cup-shaped generator housing which incorporates two bearing plates 11 and 12. The rotor shaft 15 has a central portion 16 of larger diameter than that portion of the shaftjournalled in the bearings. The central portion 16 carries a first pole wheel 17. The first pole wheel 17 is connected by way of a non-magnetic ring 18 to second pole wheel 19 which is thus not directly secured to the rotor shaft 15. The bearing plate 11 at the drive end carries a holding device 21 to which an excitation winding 22 is secured. A stator 23, carrying an output winding 27, is fitted in the housing of the generator comprising the portions 11 and 12 serving as bearing plates.The output of the output winding 27 is connected to a rectifier 24 which, in addition to supplying the load current, also supplies the excitation current by way of a voltage regulator 25 which is connected to the excitation winding 22 by way of the cable 26. The pole wheels 17, 19 are provided with claws 31.

It will be seen from the drawing that the entire central portion 16 and some of the other portions of the rotor shaft 15 are located in the magnetic flux in series with the soft magnetic parts, that is to say, the pole wheels 17, 19.

Three materials have proved to be particularly advantageous for use for the parts 15, 16, that is to say, the rotor shaft 15 and its central portion 16: - High-carbon steel which is machined and treated in a conventional manner; - Low-carbon, alloyed case-hardened steel, such as 16 MnCr 5, which is hardened without carburization and which is tempered to a higher degree than normally; - Unalloyed case-hardened steel, such as C15, which is case-hardened.

A three-phase generator without slip-rings, such as is used for operation in motor vehicles, has been chosen as the embodiment. However, the measures described can also readily be used in a generator which has slip-rings.

1. An electrical generator, for motor vehicles, having a stationary output winding and an excitation device for producing a rotating excitation field, which excitation device includes a magnetic circuit and an excitation windng, wherein the magnetic circuit incorporates at least one magnetically hard member in addition to soft magnetic members the magnetically hard member being the shaft of the generator.

2. A generator as claimed in claim 1, in which at least one of the magnetically hard members is located in the magnetic flux in series with the soft magnetic members.

3. A generator as claimed in claim 1 or 2 in which the shaft has a central portion of larger diameter.

4. A generator as claimed in claim 3, in which the central portion is dimensioned such that it at the same time serves as a core for the excitation device.

5. A generator of the claw pole type as claimed in any of the preceding claims, in which the central portion carries the pole wheels.

6. A generator as claimed in any of the preceding claims, in which a high-carbon steel is used as the magnetically hard material.

7. A generator as claimed in any of claims 1 to 5, in which the magnetically hard material is an alloy

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION An electrical generator The invention relates to an electrical generator. The electrical generators having self excitation, there is always the problem that the excitation field might not build up. If the magnetisable material used in the excitation circuit is magnetically soft, the remanence induction is very low and, after the generator has been put into operation, selfexcitation of the generator does not occur, or occurs only at high rotational speeds. It is already known to build up self-excitation in three-phase generators in motor vehicles by means of a pre-excitation current which flows into the excitation circuit by way of a resistor or by way of the charging pilot lamp after the ignition switch has been actuated.It is also already known to improve the build up of self-excitation, that is to say, the starting behaviour of the generator, by introducing oxide magnets at a suitable location in the excitation circuit, particularly between the claws of three-phase generators having claw pole rotors. However, these known measures have the disadvantage that there is a certain amount of expenditure on circuitry, or the disadvantage of low mechanical strength. In any event, there is an unfavourable relationship between the costs and the result achieved. According to the present invention there is provided an electrical generator, for motor vehicles, having a stationary output winding and an excitation device for producing a rotating excitation field, which excitation device includes a magnetic circuit and an excitation winding, wherein the magnetic circuit incorporates at least one magnetically hard member in addition to soft magnetic members, the magnetically hard member being the shaft of the generator. In contrast to the prior art, the generator in accordance with the invention has the advantage that the cost of manufacturing is very low and the build up of self-excitation of the generator is ensured in all cases. Circuit measures outside the generator are not required. A further advantage is that no additional component for the excitation device is required for manufacturing the generator. Advantageous developments of, and improvements in the generator specified in the main claim are rendered possible by the measures set forth in the sub-claims. A special advantage is that the volume of the generator is not increased and no parts susceptible to failure are used. Moreover, high mechanical strength and satisfactory magnetic properties can be obtained. The present invention will now be described further, by way of example only, with reference to the accompanying drawing which shows one embodiment of a three-phase generator in accordance with the invention. A rotor shaft 15 isjournalled in bearings 13 and 14 in a cup-shaped generator housing which incorporates two bearing plates 11 and 12. The rotor shaft 15 has a central portion 16 of larger diameter than that portion of the shaftjournalled in the bearings. The central portion 16 carries a first pole wheel 17. The first pole wheel 17 is connected by way of a non-magnetic ring 18 to second pole wheel 19 which is thus not directly secured to the rotor shaft 15. The bearing plate 11 at the drive end carries a holding device 21 to which an excitation winding 22 is secured. A stator 23, carrying an output winding 27, is fitted in the housing of the generator comprising the portions 11 and 12 serving as bearing plates.The output of the output winding 27 is connected to a rectifier 24 which, in addition to supplying the load current, also supplies the excitation current by way of a voltage regulator 25 which is connected to the excitation winding 22 by way of the cable 26. The pole wheels 17, 19 are provided with claws 31. It will be seen from the drawing that the entire central portion 16 and some of the other portions of the rotor shaft 15 are located in the magnetic flux in series with the soft magnetic parts, that is to say, the pole wheels 17, 19. Three materials have proved to be particularly advantageous for use for the parts 15, 16, that is to say, the rotor shaft 15 and its central portion 16: - High-carbon steel which is machined and treated in a conventional manner; - Low-carbon, alloyed case-hardened steel, such as 16 MnCr 5, which is hardened without carburization and which is tempered to a higher degree than normally; - Unalloyed case-hardened steel, such as C15, which is case-hardened. A three-phase generator without slip-rings, such as is used for operation in motor vehicles, has been chosen as the embodiment. However, the measures described can also readily be used in a generator which has slip-rings. CLAIMS

7. A generator as claimed in any of claims 1 to 5, in which the magnetically hard material is an alloy case-hardened steel in a blank-hardened state and at least one of the magnetically hard members is tempered to a higher degree than is custmary.

8. A generator as claimed in any of the claims 1 to 5, in which an unalloyed case-hardened steel is used as the magnetically hardened material, and at least one of the hard magnetic members is casehardened.

9. An electrical generator as claimed in any preceding claim in which the generator is a threephase generator and is not provided with slip rings.

10. An electrical generator constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.