GB1560298A - Alternator including voltage build-up and control circuit - Google Patents

Description

(54) ALTERNATOR INCLUDING A VOLTAGE BUILD-UP AND CONTROL CIRCUIT (71) We, SHELLER-GLOBE CORPORA TION, a corporation organised under, the laws of the State of Ohio, United States of America of P.O. Box 1270, Toledo, Ohio 44132, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement; The present invention relates to alternators and more particularly to circuits for energizing the field of an alternator.

The present invention is particularly suited for use in an alternator field control circuit in vehicle alternators, e.g. heavy duty trucks in which the alternating output current of the alternator is rectified by a rectifier circuit and in which the rectifier circuit is connected across the battery to supply load current to the battery and to electrical accessories of the vehicle. In this type of circuit, it is necessary for the alternating current output of the alternator to be above battery voltage before the alternator can supply a direct current output, i.e., before the rectifier circuit can supply load current.

Commonly, in this type of circuit, excitation current must be supplied to the field to enable the output of the alternator to build up at low engine speeds to the voltage necessary to supply load current from the rectifiers and to supply self-excitation current from the rectifiers to the field.

Illustrative of prior circuits for energizing the field when alternator output voltage is below a level at which the alternator is self-excited are the following patents: U.S.

Patent No. 3,522,508, issued August 4, 1970, to Gadd; U.S. Patent No. 3,611,112, issued to Lehinhoff October 5, 1971; and U.S. Patent No. 3,378,753, issued April 16, 1968, to Poppinger et al.

In another circuit, the alternating remanence voltage of the alternator has been used to provide a control signal to switch on a semiconductor device connected in series with the field to supply battery current to the field to cause the alternator to achieve a sufficient output potential to supply load current at low engine speeds. However, it has heretofore been found necessary to supply bleed current from the battery to the field to aid the remanence voltage in achieving the output necessary to overcome at low engine speeds the threshold voltages in the control signal circuit due to the presence of various semi-conductor components of the alternator.

The present invention provides an alternator having a field winding and output windings and a voltage build-up circuit comprising: first semiconductor controlled switching means having a conductive circuit connected in series with said field winding and having a control terminal; means for connecting said field winding and the conductive circuit of said controlled switching means in series across a direct current source; and a non-inductive voltage multiplier for multiplying the output voltage of the alternator and having input terminals connected across at least one of said output windings and an output terminal coupled to provide a potential to the control terminal of said first semiconductor controlled switching means to render said first semiconductor controlled switching means conductive in response to the multiplied remanence voltage of said alternator to supply current from the direct current source to said field winding. In use, the controlled switching means are connected in series with an alternator field winding for connection across a source of direct current (e.g, a vehicle battery) in addition to being connected across a source of self-excitation voltage (e.g. the alternator output).

Voltage derived from the alternator output windings is utilized to control the conductive state of the controlled switching means, and to enable this to be achieved, the non-inductive voltage multiplier is provided (e.g. a diode-capacitor voltage multiplier) with its output terminals connected across an output winding and providing a direct current output coupled to control the state of the controlled switching means.

Voltage provided by the voltage multiplier in response to remanence voltage is sufficient to turn on the controlled switching means and connect excitation current from the direct current source through the field coil without requiring the use of bleed current to enable the alternator to build up and supply load and self-excitation currents at relatively low engine speeds. Moreover the direct current source will be disconnected from the field coil when the engine does not rotate. The alternator may supply load rectifiers, but it is also contemplated that it may supply alternating current to a load.

In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying FIGURE, which is a schematic illustration of an alternator circuit constructed in accordance with the present invention.

The FIGURE is a schematic illustration of an alternator system constructed in accordance with the present invention. A source of direct current in the form of a battery 10 is provided for charging by the alternator system. However, at start-up, the battery 10 is utilized as a source of field excitation current, and may conveniently comprise a well-known storage battery such as is commonly found in a vehicle such as a truck or bus. The battery 10 is connected between a positive terminal 11 and a negative terminal 12. The terminals 11 and 12 are not necessarily meant to imply physical terminals of the battery 11, but rather are reference points in the present description.

An alternator 15 is provided having a field winding 16 and a delta-connected armature comprising windings 17a,17b, 17c.

Commonly, the armature 17 comprises the alternator stator. The windings 1 7a-1 7c may be Y, A or multiphase connected, if desired. The windings 17a-17c are the output windings of the alternator, and are hereinafter referred to as output windings 17. The field winding 16 is on the alternator rotor, and is driven by a vehicle engine (not shown). Where alternator speed is discussed, the term refers to the speed of the alternator rotor expressed in revolutions per minute as driven by the vehicle engine. In a conventional manner, current supplied through the rotating field winding 16 induces alternating current voltage across the output windings 17a-17c. Of course, the alternator 15 could be other than a three-phase alternator if desired.In order to connect the output voltage of the windings l7a-17c for rectifying, the output winding 1 7a is connected between first and second terminals 20 and 21; the output winding 17b is connected between the second terminal 21 and a third terminal 22; and the output 17e is connected between the terminals 20 and 22. Output voltages are rectified by diodes 24a-24e and 25a-25e. The diodes 24a, 24b and 24c each have a cathode connected to the terminal 11 and an anode respectively connected to the terminals 22, 21, and 20. Simliarly, diodes 25a, 25b and 25c are provided each having its anode connected to the terminal 12 and its cathode respectively connected to terminals 22, 21 and 20.A full wave rectified output is thus provided between the terminals 11 and 12, and the direct current output at the terminals 11 and 12 may be referred to as the alternator direct current output.

In the present embodiment, the field winding 16 is coupled across the alternator direct current output so that the alternator 15 of the present invention is self-excited.

A field discharge rectifier 27 may be connected across the field winding 16 to provide a current path for current induced by a collapsing magnetic field in the field winding 16. The field winding 16 is selectively connected or disconnected across the terminals 11 and 12 by the conductive circuit of a controlled switching means 30.

In the present embodiment, the controlled switching means 30 comprises a field current switching transistor 30, sometimes hereinafter referred to as the field transistor, having its collector connected to a lower terminal of field winding 16. An upper terminal of the field winding 16 is connected to the terminal 11. This manner of connection provides for selective connection of a direct current source other than the alternator output, i.e., the battery 10, across the field winding 16. The controlled switching means 30, i.e., the transistor 30, is controlled at a control terminal thereof, namely the base of the transistor 30. Control voltage is coupled to the base of the transistor 30 by a resistor 33 connected between the base of the transistor 30 and a terminal 36.

The control voltage is provided by a voltage multiplier 37, which is utilized to multiply voltage appearing across an output winding 17a, 17b or 17e by a significant factor, e.g. at least 1.5 to provide a control voltage for controlling the conductive state of the transistor 30. The voltage multiplier is a non-inductive voltage multiplier and in the preferred embodiment the voltage multiplier 37 comprises a well-known halfwave rectifying voltage doubler. The voltage multiplier disclosed is a network noninductively coupled between its input and output and providing a direct current output at a voltage which is approximately a multiple of the peak value of applied alternating voltage. (See IEEE Standard Dictionary of Electrical and Electronics Terms Wiley Interscience, New York, 1972 and H. Hickey and W. Villines Elements of Electronics, McGraw Hill, New York 1955 pp.277-281).The voltage multiplier 37 preferably operates as a voltage doubler and will hereinafter be so termed.

The voltage doubler 37 has input terminals connected across an output winding, in the present embodiment the output winding 17b, and has an output terminal, the terminal 36, coupled to control the conductive state of the transistor 30. In the voltage doubler 37, a capacitor 38 and diode 39 are connected in series between the terminals 21 and 36. A diode 40 is connected between the terminal 22 and diode 39, and a capacitor 41 is connected between the terminals 22 and 36. More rigorously stated, the output of the voltage doubler 37 actually appears across the terminals 36 and 22. The load circuit of the voltage doubler 37 is the resistor 33, the base-emitter circuit of the transistor 30, the collector-emitter circuit of the transistor 45 and the diode 25a.

However, by simply stating that the terminal 36 of the voltage doubler 37 is connected to control the transistor 30, a proper return potential path is implied to those skilled in the art. The voltage doubler 37 operates as a well-known conventional voltage doubler and serves to shift the voltage level of an input voltage wave peak above the zero potential level to achieve voltage doubling while providing a continuous direct current output.

A regulator 49 is provided including controlled switching means 45 in the form of a transistor 45 having its conductive circuit connected to control the state of the field transistor 30 in response to an alternator output voltage. In the present embodiment, this is accomplished by providing the transistor 45 having its collector connected to the base of the field transistor 30 and its emitter connected to the terminal 12. The base of the transistor 45, which is the control terminal of the controlled switching means 45, is coupled to voltage sensing means comprising a voltage divider including resistors 50 and 51 connected in series across the terminals 11 and 12 and having a terminal 52 intermediate the resistors 50 and 51. A Zener diode 57 is connected in the reverse direction between the terminal 52 and the base of the transistor 45.A biasing resistor 56 is connected across the baseemitter circuit of the transistor 45, and a smoothing capacitor 58 is connected across the resistor 51.

At the initiation of operation (before the alternator 15 rotates), no output voltage appears across any of the windings 17a-17c.

The field transistor 30 is off, and the field winding 16 is disconnected from sources of potential. It should be noted here that bleed current through the field winding 16 during periods of non-operation of the alternator 15 is eliminated. Upon initiation of alternator rotation, remanence voltage is induced across each of the windings 17a 1 7c due to residual magnetism of the alternator. The voltage doubler 37 multiplies the output voltage of the winding 17b and provides a direct current output at the terminal 36. The voltage at the terminal 36 is coupled to turn on the transistor 30. Therefore, current flows from the battery 10 through the field coil 16. Excitation current through the field coil 16 consequently increases, thus inducing increased output voltage across windings 17a-17c.Since there is a regenerative effect, the alternator 15 substantially immediately goes to full excitation. Full excitation of the alternator 15 thus occurs at a relatively low engine speed. Since the output of the voltage doubler 37 has a minimal number of volttage drops to overcome, namely the forward voltage drop of the base-emitter circuit of the transistor 30 and the forward voltage drop of the diode 25a, a relatively low voltage, e.g., 1.0 volts using typical components, provided across the output winding 17b at a low engine speed, is sufficient to initiate the above-described operation. It should also be noted that the charge on the capacitors 38 and 41 of the voltage doubler 37 tends to forward bias the diode 25a, further facilitating circuit operation.

Also, the voltage doubler 37 has a low impedance output, and loading on the base of the transistor 30 is thus relatively low. Suitable values of capacitors 38 and 41 are selected for desired operation. Since the input of the voltage doubler 37 is non-inductively coupled to its output, there is no core which can saturate at low speed as in the case of a transformer. Saturation of an inductive coupler would result in absence of a control voltage for coupling to the base of the transistor 30. Saturation of an inductive coupler might be avoided by using heavy wire and a sufficient number of windings. However, such a coupler would be bulky and expensive.

Once the alternator is self-excited, regulation is provided by controlling the con ductive state of the transistor 30 in response to alternator output voltage. The values of the resistors 50 and 51 are chosen such that at a nominal output voltage of the alternator 15, e.g. 12 volts, a predetermined potential level appears at the terminal 52.

This potential level is the voltage drop across the Zener diode 57 and resistor 56.

The values of these Zener diode 57 and resistor 56 are chosen such that the Zener diode is broken down and the potential across the resistor 56 is insufficient to turn the transistor 45 on.

When the alternator 15 is running at a speed sufficient to reach an alternator output overvoltage, e.g. 14 volts, the potential level at the terminal 52 is increased. Since the Zener diode 57 is in the breakdown mode, a constant voltage drop is maintained thereacross, and the voltage drop across the resistor 56 must increase, turning on the transistor 45. When the transistor 45 turns on, the base drive is shunted from the transistor 30 through the collector-emitter circuit of the transistor 45.

Consequently, the transistor 30 turns off, the field winding 16 is disconnected from sources of excitation current, and alternator output voltage decreases. The potentital at the terminal 52 thus decreases, resulting in the turning off of a transistor 45, whereby the transistor 30 again conducts.

Conventional hysteresis circuitry (not shown) is provided to prevent excessive cycling of the transistors 45 and 30. It should be noted that the control current for the field transistor 30 comprises the load current for the regulator transistor 45.

Thus it is seen that the method is to increase remanence voltage, use the voltage thus increased to control means for connecting a source of excitation current, e.g. the battery 10, through the field winding 16. Further, an overvoltage-responsive potential is utilized to remove the control voltage from the controlled switching means 30 in series with the field winding 16.

It is generally desirable that the step up be of a magnitude of at least 1.5 Voltage tripler or other multiplier circuits could be used. However, the efficiency of a higher order multiplier is less than that of a doubler. The voltage doubler is most advantageous to use in that it provides a minimal power loss between the output winding voltage and the control terminal of the field control switching means. The voltage doubler thus provides optimal impedance matching.

What is thus provided is an efficient system in which full excitation of a field winding is rapidly achieved in response to remanence voltage. The need for bleed current circuitry connected to a field coil is eliminated. Although the resistors 50 and 51 provide a path across the battery 10, in typical systems the resistors 50 and 51 will have values that the current drain therethrough is significantly less than nominal bleed current. Additionally known circuitry (not shown) may be utilized and may be controlled by potential derived from the voltage doubler 37 to isolate resistors 50 and 51 from the battery 10 when the alternator is not in operation.

The above-described circuitry may also be used in an alternator providing alternating current to a load. Many modifications in addition to those discussed above may be made in the specific circuitry disclosed.

WHAT WE CLAIM IS: 1 .An alternator having a field winding and output windings, and a voltage buildup circuit comprising: first semiconductor controlled switching means having a conductive circuit connected in series with said field winding and having a control terminal; means for connecting said field winding and the conductive circuit of said controlled switching means in series across a direct current source; and a non-inductive voltage multiplier for multiplying the output voltage of the alternator and having input terminals connected across at least one of said output windings and an output terminal coupled to provide a potential to the control terminal of said first semiconductor controlled switching means to render said first semiconductor controlled switching means conductive in response to the multiplied remanence voltage of said alternator to supply current from the direct current source to said field winding.

2. An alternator according to claim 1 further comprising a voltage regulator having second controlled switching means having a control circuit and having a conductive circuit coupled to control the state of said first controlled switching means such that said first controlled switching means is non-conductive when said second controlled switching means conducts; sensing means coupled to respond to the output voltage of said alternator; means coupling the control circuit of said second controlled switching means to said sensing means, said sensing means being such that said second controlled switching means is biased to conduct in response to a predetermined level of output overvoltage of said alternator to render said first controlled switching means non-conductive, whereby excitation current through said field winding is disconnected in response to an alternator output overvoltage.

3. An alternator according to claim 2 wherein said conductive circuit of said

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

Claims (10)

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

   ductive state of the transistor 30 in response to alternator output voltage. The values of the resistors 50 and 51 are chosen such that at a nominal output voltage of the alternator 15, e.g. 12 volts, a predetermined potential level appears at the terminal 52.

   This potential level is the voltage drop across the Zener diode 57 and resistor 56.

   The values of these Zener diode 57 and resistor 56 are chosen such that the Zener diode is broken down and the potential across the resistor 56 is insufficient to turn the transistor 45 on.

   When the alternator 15 is running at a speed sufficient to reach an alternator output overvoltage, e.g. 14 volts, the potential level at the terminal 52 is increased. Since the Zener diode 57 is in the breakdown mode, a constant voltage drop is maintained thereacross, and the voltage drop across the resistor 56 must increase, turning on the transistor 45. When the transistor 45 turns on, the base drive is shunted from the transistor 30 through the collector-emitter circuit of the transistor 45.

   Consequently, the transistor 30 turns off, the field winding 16 is disconnected from sources of excitation current, and alternator output voltage decreases. The potentital at the terminal 52 thus decreases, resulting in the turning off of a transistor 45, whereby the transistor 30 again conducts.

   Conventional hysteresis circuitry (not shown) is provided to prevent excessive cycling of the transistors 45 and 30. It should be noted that the control current for the field transistor 30 comprises the load current for the regulator transistor 45.

   Thus it is seen that the method is to increase remanence voltage, use the voltage thus increased to control means for connecting a source of excitation current, e.g. the battery 10, through the field winding 16. Further, an overvoltage-responsive potential is utilized to remove the control voltage from the controlled switching means 30 in series with the field winding 16.

   It is generally desirable that the step up be of a magnitude of at least 1.5 Voltage tripler or other multiplier circuits could be used. However, the efficiency of a higher order multiplier is less than that of a doubler. The voltage doubler is most advantageous to use in that it provides a minimal power loss between the output winding voltage and the control terminal of the field control switching means. The voltage doubler thus provides optimal impedance matching.

   What is thus provided is an efficient system in which full excitation of a field winding is rapidly achieved in response to remanence voltage. The need for bleed current circuitry connected to a field coil is eliminated. Although the resistors 50 and 51 provide a path across the battery 10, in typical systems the resistors 50 and 51 will have values that the current drain therethrough is significantly less than nominal bleed current. Additionally known circuitry (not shown) may be utilized and may be controlled by potential derived from the voltage doubler 37 to isolate resistors 50 and 51 from the battery 10 when the alternator is not in operation.

   The above-described circuitry may also be used in an alternator providing alternating current to a load. Many modifications in addition to those discussed above may be made in the specific circuitry disclosed.

   WHAT WE CLAIM IS: 1 .An alternator having a field winding and output windings, and a voltage buildup circuit comprising: first semiconductor controlled switching means having a conductive circuit connected in series with said field winding and having a control terminal; means for connecting said field winding and the conductive circuit of said controlled switching means in series across a direct current source; and a non-inductive voltage multiplier for multiplying the output voltage of the alternator and having input terminals connected across at least one of said output windings and an output terminal coupled to provide a potential to the control terminal of said first semiconductor controlled switching means to render said first semiconductor controlled switching means conductive in response to the multiplied remanence voltage of said alternator to supply current from the direct current source to said field winding.
2. 2. An alternator according to claim 1 further comprising a voltage regulator having second controlled switching means having a control circuit and having a conductive circuit coupled to control the state of said first controlled switching means such that said first controlled switching means is non-conductive when said second controlled switching means conducts; sensing means coupled to respond to the output voltage of said alternator; means coupling the control circuit of said second controlled switching means to said sensing means, said sensing means being such that said second controlled switching means is biased to conduct in response to a predetermined level of output overvoltage of said alternator to render said first controlled switching means non-conductive, whereby excitation current through said field winding is disconnected in response to an alternator output overvoltage.
3. 3. An alternator according to claim 2 wherein said conductive circuit of said

   second controlled switching means is connected across the control circuit of said first controlled switching means such that control current of said first controlled switching means comprises load current of said second controlled switching means.
4. 4. An alternator according to claim 1, 2 or 3 wherein said non-inductive voltage multiplier comprises a voltage doubler.
5. 5. A method for controlling the operation of an alternator, comprising the steps of deriving an output voltage from an output winding of said alternator, multiplying the output voltage to provide an increased voltage using a non-inductive voltage multiplier, and applying the increased voltage to semiconductor control means for controlling connection of a direct current source across the alternator field winding.
6. 6. A method as defined in claim 5 and further comprising the step of sensing alternator output voltage and removing the multiplied output voltage from the control means in response to a predetermined level of overvoltage.
7. 7. An alternator including a field winding and output windings and a voltage build up circuit comprising: means for coupling said field winding across a battery and across terminals connected to the alternator output; said means comprising a field transistor having a conductive circuit connected in series with said field winding and having a control circuit; a non-inductive voltage multiplier having input terminals connected across an output winding and having an output connected to the control circuit of said field transistor to apply a multiplied alternator remanence voltage to said field transistor whereby said field coil is disconnected from the battery when the alternator system is not operating and a potential is provided from said voltage multiplier which renders said field transistor conductive in response to rotation of said alternator.
8. 8. An alternator according to claim 7 further comprising a regulator transistor having a control circuit and having a conductive circuit connected across the control circuit of said field transistor and sensing means connected to sense the potential across the output windings, and means coupling the control circuit of said regulator transistor to said sensing means for rendering said regulator transistor conductive when the potential across the output windings is at a first predetermined level and non-conductive when the potential across the output windings is at a second predetermined level lower than said first predetermined level.
9. 9. An alternator according to claim 7 or 8 wherein said non-inductive voltage multiplier comprises a voltage doubler.
10. 10. An alternator substantially as hereinbefore described with reference to the accompanying drawings.

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