Vehicle AC generator control system

Abstract: A control device for a vehicle AC generator (1) provided with a rectifier (2) and a battery (5) connected to the latter comprises a voltage regulator (3) with a switching element (311) connected to the field coil (102) of the generator (1), to adjust the output voltage of the generator to a predetermined value in which a field current is controlled to eliminate a load torque which otherwise occurs immediately after the start of the engine, to stabilize the rotation of the engine, and the production of belt slip noises is prevented at low temperatures, and, when the generator output is restored, the production of a belt slip noise is prevented, and the decrease in the speed of rotation of the engine is prevented.

Description: The invention relates to a vehicle generator control system comprising the preamble features of claim 1. Such a control system is known from JP-A-58-66538, which is further discussed below. In this control system, a resistor is inserted into a series connection with respect to a field coil for a predetermined period of five to fifteen seconds after an input time, when the terminal voltage of a battery exceeds a certain level, here 11V. US-A-4,651,081 describes a control apparatus for a vehicle charging generator, where the regulated output power of the generator is rendered zero so that the driving torque of the generator is removed from the load of the engine during an acceleration performance and an idling operation of the engine. US-A-4,636,706 describes a generator voltage regulating system having four different modes of operation, whereby a duty cycle control of a switching element is performed, which on/off controls the field current through a field coil. During a starting of the engine a maximum field coil current is permitted by cancelling a previous field current suppression mode. US-A-4,839,576 discloses a controller for an AC-generator in vehicles. Here it is shown, that the field current of the AC-Generator increases to the time constant of the field coil until it reaches a maximum field current. A field current controller has a time constant circuit whereby this time constant of roughly 2-4 sec. is sufficiently larger than that of the field coil. When the field current is gradually increasing, the pulse width of the control signal applied to a switching element controlling the field current gradually changes. However, the field current controller has no active control over the applied pulse width, but only reacts to the field current gradually increasing by itself due to the field coil time constant. EP-A-0 201 243 discloses a control system where a control signal having a variable ON/OFF rate is used when voltage control is switched from a lower level of 12.5 volts to a higher level of 14.5 Volts. 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. The above-described control device (JP-A-58-66538) 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 The object of the invention is to provide a control system for a vehicle AC generator which can achieve a stable rotation of the engine and can prevent the occurrence of belt slip noises when starting the engine. This object is achieved by the control system of claim 1. Further advantageous embodiments and improvements of the invention are listed in the dependent claims. According to the invention, 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 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. According to the invention as defined in claim 1, a vehicle AC generator control system comprises 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. 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; and Figs. 2(a) to 2(b) are graphical representations for a description of the operation of the control device. DETAILED DESCRIPTION OF THE INVENTION One example of a control device for a vehicle AC generator according to this invention will be described with reference to Figs. 1 and 2. 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 308 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 rectified 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 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 signal 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 (power) 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 at the end of 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 dashed line indicates the variations of the generator output with the conventional control device. With the control device according to the invention, for a predetermined period of time from the start of voltage 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 power 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. As is apparent from the above description, with the control device of the invention, the generated voltage is adjusted to be 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 power. Ten seconds after the start of power generation, the generated voltage is adjusted to be 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 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.

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 (5) connected to the output terminal (201) of said rectifier; and d) a voltage regulator (3) having a switching element (311) 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 (311), to regulate an output voltage of said AC-generator to a predetermined value; e) a field current controller (4) for controlling the amount of field current supplied to said field coil (102); characterized in that f) said field current controller (4) applies an ON/OFF control signal having a wave form with a variable ON/OFF rate to said switching element (311) of said voltage regulator (3) causing said switching element (311) to have a correspondingly variable conduction rate, to control said switching element (311) so as to have a first conduction rate for a predetermined period of time from the start of voltage generation by said AC-generator, wherein said first conduction rate is set so that the rectified output voltage is lower than the voltage appearing across said battery, such that the generator power output becomes zero; and to then control said switching element (311) so as to have a conduction rate gradually increasing from said first conduction rate to a second conduction rate, where the rectified generated voltage is higher than the voltage appearing across said battery, such that the generator power output gradually increases from zero to 100 %. A system according to claim 1, characterized in that said field current controller (4) is adapted for performing said ON/OFF control of said switching element such that said first conduction rate is maintained for ten seconds from the start of voltage generation. A system according to claim 1, characterized in that said field current controller (4) comprises a timer (401) detecting a divided rectified output voltage from said voltage regulator (3), said timer (401) being started upon detection of said generator output, a reference voltage circuit (402, 403), a time constant circuit (405, 406) having a predetermined time constant, a triangular wave generator (407) for generating a triangular wave having a predetermined period and a comparator (408) for comparing a voltage from said triangular wave with an output voltage of said time constant circuit (405, 406), wherein an output from said comparator (408) is used for performing said ON/OFF control of said switching element of said voltage regulator (3).

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