Vehicle AC generator control system

Abstract: The invention concerns a vehicle AC generator control system (fig. 3), comprising: an AC-generator (1) having a field coil (102); a rectifier (2) for rectifying an AC-output of said AC-generator (1); a battery (4) connected to the output terminal (201) of said rectifier; and a voltage regulator (3) having a switching element (3170) connected in series to said field coil (102) and being operable to detect the terminal voltage of either said rectifier or battery, to control a field current with the aid of said switching element (3170), to regulate an output voltage of said AC-generator to a predetermined value and including a field current controller (3010, 3020, 3070, 3050, 3060, 3080, 3090, 3130, 3120, 3100, 3140) for controlling the amount of field current supplied to said field coil (102); wherein said field current controller performs an ON/OFF control of said switching element (311) of said voltage regulator (3) to adjust the rectified output voltage of said AC-generator to a first value lower than a voltage appearing across said battery, such that the generator power output becomes zero, during a predetermined period of time from the rise in output voltage at the start of power generation of said AC-generator; and to then adjust the rectified output voltage of said AC-generator to a second value higher than the battery output voltage after the predetermined period has elapsed, such that the generator power output becomes 100%.

Description: BACKGROUND OF THE INVENTION This invention relates to a vehicle AC generator control system. A vehicle AC generator is driven through a V-belt by the engine, to convert rotational energy into electrical energy. There has been a demand for provision of a high power vehicle AC generator for an increasing vehicle electrical load. The increase in output of the vehicle AC generator means the increase in load torque of the engine. Hence, the rotation of the engine is liable to become unstable when the explosion and combustion are unstable for instance immediately after the start of the engine. In addition, at the start of the engine, the generator provides its maximum output to charge the battery which has been discharged to operate the starter motor, and accordingly the load on the engine is increased as much; that is, the rotation of the engine becomes more unstable. This phenomenon occurs significantly when the ambient temperature is low. In order to overcome this difficulty, a control device has been proposed, for instance, by the US Patent No. 4,839,576 in which, when the rotation of the engine is unstable immediately after the start, the amount of current supplied to the field coil is limited for a certain period of time to decrease the engine load, thereby to stabilize the engine idling rotation. The above-described control device controls the field current for a certain period of time from the start of the engine, as was described above. Therefore, the generator output is suppressed, but it will not become zero (A). Hence, with the device, it is difficult to completely eliminate the generator drive load torque; that is, the rotation of engine cannot be sufficiently stabilized. In general, when it is cold, the V-belt and pulleys for driving a vehicle generator are not sufficiently engaged with one another. Therefore, in the case of the above-described conventional control device, when the generator produces drive torque, the belt slips thus producing noises (hereinafter referred to as "belt slip noises", when applicable). Furthermore, with the conventional control device, a certain period of time from the start of the engine the field current is abruptly increased, and accordingly the generator output is also abruptly increased; that is, the engine load is abruptly increased, so that the belt slip noise is liable to be produced. In addition, the abrupt increase of the engine load may adversely affect the rotation of the engine. SUMMARY OF THE INVENTION Accordingly, an object of this invention is to eliminate the above-described difficulties accompanying a conventional control drive for a vehicle AC generator. More specifically, an object of the invention is to provide a control device for a vehicle AC generator in which the generator drive load torque is completely eliminated which otherwise occurs immediately after the start of the engine, to stabilize the rotation of the engine, and the production of a belt slip noise is prevented when it is cold, and in which the production of a belt slip noise and the decrease in the speed of rotation of the engine are prevented which otherwise may be caused when the generator output is restored. The foregoing object and other objects of the invention have been achieved by the provision of a vehicle AC generator control system comprising an AC generator having a field coil, a rectifier for rectifying an AC output of the AC generator, a battery connected to the output terminals of the rectifier and a voltage regulator having a switching element connected in series to the field coil, the voltage regulator detecting the terminal voltage of either the rectifier or battery, to control a field current with the aid of the switching element, to adjust an output voltage of the AC generator to a predetermined value. The voltage regulator operates to adjust the output voltage of the AC generator to a first value lower than a voltage appearing across the battery during a predetermined period of time after the start of power generation of said AC generator and then to a second value higher than the battery output voltage after the predetermined period has.elapsed. Alternatively, the voltage regulator operates to control said switching element so as to have a first conduction rate for a predetermined period of time from the start of power generation by said AC generator, and then to control said switching element so as to have a conduction rate gradually increasing from the first conduction rate to a second conduction rate. With the vehicle AC generator control system according to the invention, the generated voltage is adjusted to a value lower than the battery voltage for the predetermined period of time from the start of power generation, and thereafter to a value higher than the battery voltage so that the usual charge output operation is carried out. The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 is a circuit diagram showing an example of a vehicle AC generator control system; Figs. 2(a) to 2(b) are graphical representations for a description of the operation of the control device; and Fig. 3 is a circuit diagram showing an example of a vehicle AC generator control system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION As shown in Fig. 1, an AC generator 1 has an armature coil 101 and a field coil 102, and is connected to a rectifier 2. The rectifier 2 has a main output terminal 201, an auxiliary output terminal 202, and a grounding terminal 203. Furthermore, a voltage regulator 3 is provided which comprises: a constant voltage source A including a resistor 301 and a Zener diode 302; a reference voltage circuit including voltage dividing resistors 303 and 304 for dividing the voltage of the constant voltage source A to provide a reference voltage; voltage dividing resistors 305 and 306 for detecting a generator output voltage; a comparator 307 for comparing a generator output voltage with the reference voltage; a control transistor 309 whose base is connected to the output terminal of the comparator 307 and through a resistor 309 to the constant voltage source A; a power transistor 311 to which a base current is applied through a resistor 310, the power transistor 311 being turned on and off by the control transistor 309; and a suppression diode 312 connected in parallel to the field coil to absorb surge current. In addition, a field current controller 4 is provided which comprises: a timer 401 connected to the voltage dividing resistors 305 and 306 which detect a generator output voltage, the timer 401 being started upon detection of the generator output; a reference voltage circuit including voltage dividing resistors 402 and 403; a diode 404; a time constant circuit including a resistor 405 and a capacitor 406; a triangular wave generator 407 for generating a triangular wave having a predetermined period; and a comparator 408 for comparing the voltage at the circuit point B in Fig. 1 which is the output triangular wave signal of the triangular wave generator 407 with the voltage at the circuit point C in Fig. 1 which is the output signal of the time constant circuit. The output terminal of the field current controller 4 is connected to the base of the power transistor 311 in the voltage regulator 3. The main output terminal 201 and the auxiliary output terminal 202 of the rectifier 2 are connected to a battery 5. One end of the field coil 102 is connected through a key switch 6 to the battery 5, and the other end is connected to the voltage regulator 3. In the voltage regulator 3, for the purpose of charging the battery 5 and supplying current to a load 8, the comparator 307 compares a generator output voltage with the reference voltage so that the generated voltage reaches a predetermined value. In the field current controller 4, the timer 401, after detecting the start of power generation of the generator, outputs a high level signal for a period of time T 1 (Fig. 2), and a low level signal thereafter. The generated voltage, controlled according to the result of comparison of the voltage at the circuit point C (hereinafter referred to as "a point C voltage", when applicable) which is determined by the voltage dividing resistors 402 and 403 with the voltage at the circuit point B (hereinafter referred to as "a point B voltage", when applicable) which is the triangular wave signal, is so set as to be lower than the battery voltage. In addition, the voltage at the circuit point C (hereinafter referred to as "a point C voltage", when applicable) is so set that it is lowered by the time constant circuit consisting of the capacitor 406 and the resistor 405 to a predetermined level in a predetermined period of time T 2 as indicated by the broken line in Fig. 2(a). The operation of the above-described embodiment will be described. When the key switch 6 is turned on, the generator 1 has not started its power generation yet, and therefore the output of the comparator 307 in the voltage regulator 3 is at low level, and the output of the timer 401 in the field current controller 4 is also at low level. Hence, the output of the comparator 408 in the field current controller 4 is at high level, so that the power transistor 311 is rendered conductive (on) to allow an initial exciting current to flow in the field coil 102 through an initial exciting resistor 7. When the generator 1 starts power generation being driven by the engine, the output of the timer 401 is raised to high level, so that a time measuring operation is carried out. For the predetermined period of time T 1 that the timer 401 is in operation, the point C voltage is at the level set by the voltage dividing resistors 402 and 403. The level thus set relates to the triangular wave signal at the circuit point B as indicated in Fig. 2(a). These values are subjected to comparison by the comparator 408 in the field current controller 4, and in response to the result of comparison the power transistor 311 is rendered on and off as shown in Fig. 2(b). In this operation, the percentage of conduction of the power transistor is minimum, and in this case the generated voltage is not higher than the battery voltage. Hence, the output of the generator 1 is zero (0) for the predetermined period of time T 1 as shown in the part (c) of Fig. 2. When the output of the timer 401 is set to low level in the predetermined period of time T 1 , the point C voltage is decreased to a predetermined level taking the time T 2 determined by the time constant circuit consisting of the capacitor 406 and the resistor 405 as shown in Fig. 2(a). In this operation, the waveform of conduction of the power transistor 311 operating in response to the result of comparison by the comparator 408 is as shown in Fig. 2(b). That is, the percentage of conduction of the power transistor 311 is gradually increased, and reaches the maximum value 100% in the predetermined period of time T 2 . During the period of time T 2 , the output of the generator is gradually increased from 0% to 100% as indicated by the solid line in Fig. 2(c). Thereafter, the original control is carried out according to the output of the comparator 307 in the voltage regulator 3. In Fig. 2(c), the solid line indicates the variations of the generator output with the conventional control device. With this control device for a predetermined period of time from the start of power generation by the AC generator immediately after the start of engine the generated voltage is set lower than the battery voltage so that the generator provides no output. Hence, the generator drive load torque can be completely eliminated to quickly stabilize the engine idling rotation. In addition, the production of a belt slip noise can be prevented at low temperatures. Furthermore, with the control device, the percentage of conduction of the switching element is gradually increased in the predetermined period of time, and therefore the engine load will not be abruptly increased. Accordingly, the production of belt slip noises and the reduction of the speed of rotation of the engine can be positively prevented which otherwise take place when the generator output is restored. An example of a control device for a vehicle AC generator according to this invention will be described with reference to Fig. 3. The field coil 102 is connected to a voltage regulator 3 which controls the field current thereby to control the output voltage of the AC generator. The voltage regulator 3 comprises: a constant voltage source A including a resistor 3010 and a Zener diode 3020; a reference voltage circuit including voltage dividing resistors 3030, 3040 and 3050 for dividing the output of the constant voltage source A to provide first and second reference voltages; voltage dividing resistors 3060 and 3070 for detecting an output voltage of the generator; a first comparator 3080 for comparing a generator output voltage with the first reference voltage provided by the reference voltage circuit; a second comparator 3090 for comparing a generator output voltage with the second reference voltage provided by the reference voltage circuit; a timer connected to the voltage dividing resistors 3060 and 3070, said timer being started upon detection of a predetermined output voltage; resistors 3110 and 3120 connected to the constant voltage source A; a control transistor whose base is connected through a diode 3130 to the resistor 3110 (connected to the constant voltage source A) and the output terminal of the first comparator 3080, and connected to the output terminal of the second comparator 3090, and connected through a diode 3140 to the resistor 312 (connected to the constant voltage source A) and the output terminal of the timer 3100; a power transistor 3170 to which a base current is applied through a resistor 3160, the power transistor 3170 being controlled by the control transistor; and a suppression diode 3180 connected in parallel to the field coil 102, to absorb surge current. The main output terminal 201 and the auxiliary output terminal 202 of the rectifier 2 are connected to a battery 4. One end of the field coil 102 is connected through an initial exciting resistor 7 and a key switch 6 to the battery 4, and the other end is connected to the voltage regulator 3. A vehicle electrical load 8 is connected through a load switch 9 to the battery 4. For convenience in description, it is assumed that the vehicle AC generator is of 12V. The battery voltage is 12V. The second comparator 3090 determines whether or not the generator output voltage reaches a first predetermined value such as 10V, while the first comparator 3080 determines whether or not the generator output voltage reaches a second predetermined value such as 14V. The timer 3100 is started when the generator output voltage reaches, for instance, 8V, the timer 3100 is started to outputs a high level signal for a predetermined period of time, for instance ten (10) seconds, and a low level signal thereafter. The operation of the control device thus organized will be described. When the key switch 7 is turned on, the generator 1 has not been started yet, and therefore the outputs of the first and second comparators 3080 and 3090 are at low level, and the output of the timer 3100 is also at low level. Accordingly, in this case, the control transistor 3150 is non-conductive (off), and therefore the power transistor 3170 is conductive (on). Hence, an initial exciting current flows in the field coil 102 through the initial exciting resistor 7. Soon the generator 1 starts power generation being driven by the engine. When the generated voltage exceeds 8V, the output of the timer 3100 is raised to high level, thus starting the measurement of time. When the generated voltage exceeds 10V during ten (ten) seconds for which the timer 3100 is in operation, the output of the second comparator 3090 is raise to high level. As a result, the control transistor 3150 is rendered conductive (on), and therefore the power transistor 3170 is rendered non-conductive (off), thereby to prevent the rise of the output voltage. When, in contrast, the generated voltage becomes lower than 10V, the output of the second comparator 3090 is set to low level. As a result, the control transistor 3150 is rendered non-conductive (off), and accordingly the power transistor 3170 is rendered conductive (on), thus preventing the fall of the output voltage. Thus, the generator output voltage is maintained at 10V for the ten seconds the timer 3100 is in operation. When the operation of the timer 3100 is ended; that is, in the ten seconds, the output of the timer 3100 is set to low level, so that the control transistor 3150 is rendered non-conductive (off) and the power transistor 3170 is rendered conductive (on). As a result, the exciting current is increased, and the generated voltage is also increased. When the generated voltage exceeds 14V, then the output of the first comparator 308 is raised to high level, as a result of which the control transistor 3150 is rendered conductive, and therefore the power transistor 3170 is rendered non-conductive, thus suppressing the field current to prevent the rise of the generated voltage. When, in contrast, the generated voltage becomes lower than 14V, then output of the first comparator 3080 is set to low level. As a result, the control transistor 3150 is rendered non-conductive, and therefore the power transistor 3170 is rendered conductive, thus increasing the field current to prevent the fall of the output voltage. Thus, the generated voltage is maintained at 14V. As is apparent from the above description, with the control device of the invention, the generated voltage is adjusted to 10V lower than the battery voltage for ten seconds from the start of power generation by the generator; that is, the generator 1 provides no output. When ten seconds passes after the start of power generation, the generated voltage is adjusted to 14V higher than the battery voltage, so that the usual charge output operation is carried out. In the above-described control device, the operating time of the timer 3100 is ten seconds; however, the invention is not limited thereto or thereby. That is, the operating time may be set to other values as the case may be. It goes without saying that the technical concept of the invention is applicable to vehicle generators of other than 12V. Accordingly, the generator drive load torque can be completely eliminated, to quickly stabilize the engine idling rotation. The complete elimination of the generator drive load torque allows the belt to sufficiently engage with the pulleys, whereby the production of belt slip noises is positively prevented. While there has been described in connection with the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be included within the scope of the invention as defined by the appended claims.

Claims: A vehicle AC generator control system, comprising: a) an AC-generator (1) having a field coil (102); b) a rectifier (2) for rectifying an AC-output of said AC-generator (1); c) a battery (4) connected to the output terminal (201) of said rectifier; and d) a voltage regulator (3) having a switching element (3170) connected in series to said field coil (102) and being operable to detect the terminal voltage of either said rectifier or battery, to control a field current with the aid of said switching element (3170), to regulate an output voltage of said AC-generator to a predetermined value and including a field current controller (3010, 3020, 3070, 3050, 3060, 3080, 3090, 3130, 3120, 3100, 3140) for controlling the amount of field current supplied to said field coil (102); wherein f) said field current controller performs an ON/OFF control of said switching element (311) of said voltage regulator (3) to adjust the rectified output voltage of said AC-generator to a first value lower than a voltage appearing across said battery, such that the generator power output becomes zero, during a predetermined period of time from the rise in output voltage at the start of power generation of said AC-generator; and to then adjust the rectified output voltage of said AC-generator to a second value higher than the battery output voltage after the predetermined period has elapsed characterized in that said field current controller comprises: a first comparator (3080) for maintaining the output voltage at the second value, a second comparator (3090) for maintaining said output voltage at said first value, and a timer (3100) for providing an output indicating the predetermined time period, the outputs of said first and second comparators (3090, 3080) and said timer (3100) being wired together and used to control said switching element (3170). A system according to claim 1, characterized in that said field current controller (3) is adapted for performing said ON/OFF control of said switching element, such that.said rectified output voltage of said AC-generator is 10V for ten seconds from the start of power generation by said generator and then to adjust said rectified output voltage to 14V after said ten seconds have elapsed. A system according to claims 2, characterized in that said voltage regulator (3) further comprises: a control transistor (3150) connected to said wired comparators (1080, 1090) and said timer (3100) for ON/OFF controlling said switching element. A system according to claim 3, characterized in that the battery voltage is 12V, said second comparator (3090) determines whether said generator output voltage reaches 10V, while said first comparator (3080) determined whether said generator output voltage reaches 14V and wherein said timer (3100) is started when said generator output voltage reaches 8V whereupon a high level signal is output to said control transistor (3150) for said predetermined period of time being 10 seconds.

Inventors: IWATANI SHIRO, WATANABE HIROFUMI, IWATANI, SHIRO, WATANABE, HIROFUMI, IWATANI, SHIRO, C/O MITSUBISHI DENKI K.K., WATANABE, HIROFUMI, C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1990
Main classification: H02J7
IPC codes: H02J7