Title of Invention

AN IMPROVED AUTOMOTIVE ALTERANATOR

Abstract

An improved automotive alternator comprising a salient pole rotor assembly such as for example a claw pole rotor assembly; stator assembly provided with two sets of three phase stator windings; a three phase full bridge rectifierl assembly; three control switches; and an electronic controller for sensing the alternator speed and enabling the control switches to switch only one of the stator windings above a pre-determined alternator speed and to switch both the sets of stator windings below the said p.redetermined alternator speed; a voltage regulator to, maintain the battery voltage at a fixed value by controlling the rotor field current.

Full Text

This invention relates to an improved automotive alternator. In the proposed automotive alternator, the stator of the alternator has two sets of three phase windings interconnected appropriately. With the help of additional three electronic switches which could be MOSFET or IGBT or Thyristor or any other appropriate device, the stator windings taking part in generation of electric power are controlled by a suitable electronic controller depending on the operating speed of alternator to enhance its output and efficiency. While various systems using power electronic devices and new winding configurations are used to improve the performance of automotive alternators, the following disadvantages are typically exhibited. • The number of controllable switching devices required are large • The power rating of switching devices are close to the rating of maximum output of alternator • Control methods are complex and to switch in both the sets of stator windings below the said predetermined alternator speed; and a voltage regulator to maintain the battery voltage at a fixed value by controlling the rotor field current. This invention will now be described by reference to the accompanying drawings which illustrate in Fig. 1.0 the circuit diagram of the proposed alternator with two sets of three phase windings in stator and three additional control switches (control switches and top windings at positive supply side) and Fig. 2.0 the circuit diagram of the proposed alternator as in Fig. 1.0, but with control switches and top windings at negative supply side. As indicated in Fig.1.0, the two sets of stator windings namely a1, a2, a3 and a1-, a2-, a3- are connected in series and star connection is formed by the coils a1, a2 and a3. The windings a1, a2 and 33 will be henceforth referred as bottom windings and the windings a1-, 32- and a3" will be referred 3S top windings. Switch Si (i=l or 2 or 3) is closed when the line voltage Vk-j -j (k=l or 2 or 3; j=l or 2 or 3; k=i & j # k) is larger than battery voltage and the S1 is opened when Vk,-j is smaller than battery voltage. The control switch could be a thyristor or MOSFET or IGBT or any other control device. Whenever switch Si is closed, the winding ai- conducts. It may be noted that current flows through windings ai and ai- from neutral point N when switch Si is closed, then through battery / load and returns through diode Djb (j#i) and winding aj to neutral point N. This implies that two windings (one in each of top and bottom winding sets) in one phase and one of the bottom windings corresponding to other phases are active in voltage generation. If the switches Si are permanently turned off, then the windings ai (i = 1,2,3) alone take part in voltage generation and rectification is realized through diodes, Dib and Dit (i = l, 2,3). The effective number of turns taking part in rectification is hence controlled by enabling or disabling the switching of the control switches Si. When the switches are enabled, the number of turns involved in rectification would correspond to those in windings ai, ai- as well as aj (i = l or 2 or 3 & j #i) while the switches are disabled the rectification is realized by winding ai and aj {i = l or 2 or 3; j=l or 2 or 3; j #i) only. It could also be observed :hat the current flowing through the bottom windings ai is 3i-directional in nature while the current through the top windings ai- is uni-directional since the return path for current is always through bottom windings. Thus according to the invention, the effective number of turns of stator windings taking part in voltage generation is controlled by simply enabling or disabling the control switches Si. At low speeds, the switches are enabled so that the low speed output of alternator would be increased due to a large number of turns taking part in rectification process. At high speeds, the switches are disabled and the bottom windings (ai, i=l,2,3) are alone in action. Under this situation, the effective number of turns taking part in rectification process and the effective stator resistance are lower compared to the case when the switches are enabled leading to higher output current and higher efficiency. An alternative circuit diagram with the control switches connected at the negative supply side is shown in Fig. 2.0, as above, in which case also, the top windings carry uni¬directional current and the bottom windings carry bi directional current. Although in this specification, reference has been made to alternators with three phase stator windings it must be understood that what is described and claimed in this specification is equally appplied to alternators with polyphase stator windings. We Claim ; 1. An improved automotive alternator comprising a salient pole rotor assembly including a claw pole rotor -assembly: a stator assembly chracterised in that the stalor is provided with two sets of three phase slalor windings; a three phase full bridge rectifier assembly, three control switches; and an electronic controller for sensing the alternator speed and enabling the control switches to switch only one of the stator windings above a predetermined alternator speed and to switch both the sets of stator windings beiow the said predetermined alternator speed; a voltage regulator to maintain the battery voltage at a fixed value by controlling the rotor field current. 2, An inrprnved automotive allernator substantially as herein described With reference to, and as illustrated in. the accompanying drawings. Dated this the 24th July 2002

Documents:

0558-mas-2002 abstract.pdf

0558-mas-2002 claims-duplicate.pdf

0558-mas-2002 claims.pdf

0558-mas-2002 correspondence-others.pdf

0558-mas-2002 correspondence-po.pdf

0558-mas-2002 description (complete)-duplicate.pdf

0558-mas-2002 description (complete).pdf

0558-mas-2002 drawings.pdf

0558-mas-2002 form-1.pdf

0558-mas-2002 form-19.pdf

0558-mas-2002 form-26.pdf