Alternator for vehicles

Abstract: An alternator (1) is provided having a pulley (9) mounted on a rotating shaft of a rotor through a one-way clutch (90) which transmits a driving power to the rotor during acceleration of a crankshaft and does not transmit the driving power to the rotor during deceleration of the crankshaft. The rotor has a plurality of magnetic poles surrounding a field coil, and an alternator control mechanism supplies a predetermined exciting current to the field coil upon sensing engine stop. Noise from the alternator (1) is prevented by reducing the rotating period of the alternator rotor during an engine stop while preventing early breakage or slip noise of the belt during ordinary vehicle driving.

Description: The present invention relates generally to a vehicle-mounted alternator, and more particularly, to a vehicle-mounted alternator that has reduced noise. In a belt-driven alternator for vehicles, there has been a growing demand for increasing the current output of the alternator in order to meet increased various electric loads adopted for improving driving safety and comfort in a vehicle. Actually the inertial force of the rotor has been increased with the upsizing of the alternator. There is, however, such a problem that since the inertial torque of the rotor is circulated to the crankshaft during engine deceleration when the vehicle is running, early belt failure and noise caused by belt slip will occur. To cope with this problem, the use of a pulley with a built-in one-way clutch (hereinafter referred to as the clutch pulley) has been known as disclosed in JP-A No. Hei 7-72585. According to the clutch pulley, the rotational power is transmitted to the alternator when the engine rpm increases, and reversely no inertial torque of the alternator is transmitted to the driving belt when the engine rpm decreases. On the other hand, for the purpose of environmental protection by reducing exhaust emissions and also as a link of enhancing fuel economy, there has been carried out an effort to stop engines when temporarily stopping a vehicle, particularly a shuttle bus for city driving, at an intersection according to a traffic signal. Also in the case of passenger cars and trucks in general, the adoption of an idle stop system for automatically stopping the engine at an intersection is being contemplated. When the clutch pulley disclosed in JP-A No. Hei 7-72585 is adopted in the alternator for vehicles, the rotor of the alternator runs idle with its own inertial force for some time even after the engine is decelerated to a stop and disconnected from the alternator rotor by the clutch pulley. During this period, the rotor rotating in the engine compartment is only the rotor of the alternator for vehicles. Besides, the rotor rotates in one body with the cooling fan, and generally the rotor of the alternator for vehicles has a Randale-type magnetic pole having a fan effect. When the engine is stopped, the engine noise does not occur. So, only such noises like a sound of rotation of the rotor and a wind sound made by the cooling fan and the magnetic poles in the engine compartment will be audible and grating to the ear. Furthermore, recent alternators for vehicles are provided with many air vents in the frame for improving cooling performance, and therefore the noise produced by the rotation of the rotor is hard to reduce and cannot be shielded from the alternator, thus becoming more and more grating to the ear. Furthermore, if the engine is frequently stopped in urban areas because of the adoption of the idle stop system, noise from the vehicle-mounted alternator is heard every time the engine stopped, which will further grate a listener, thereby substantially degrading the quality of the vehicle which is required to be pleasant for human senses. Alternators of the kind discussed here are also known from PATENT ABSTRACTS OF JAPAN; vol. 1999, no. 11, September 30,1999 and JP 11 164 517 A, June 18, 1999. In a view of the above-described problems, it is an object of this invention to provide an alternator for vehicles which operates calmly with improved reliability of the driving belt and enhanced fuel economy to improve environmental conditions. More particularly, it is another object of this invention to decrease noise form the alternator for vehicles that are equipped with the idle stop system, while preventing early breakage or slip noise of the belt by the clutch pulley. To accomplish the above-described object, an alternator for a vehicle is provided by the present invention having the features of appended claim 1. Thus, the present invention provides a pulley driven through a belt by the rotation of an engine crankshaft, a rotor connected to the pulley, a stator located oppositely to the rotor, a ventilating means rotating in one body with the rotor, and a frame with a plurality of cooling air vents as the ventilating means and holding the rotor and the stator. The pulley is mounted on a rotating shaft of the rotor through a one-way clutch which transmits driving power to the rotor during acceleration of rotational speed of the crankshaft and does not transmit the driving power to the rotor during deceleration of rotational speed of the crankshaft. And the rotor has a plurality of magnetic poles surrounding a field coil, and an alternator control mechanism which supplies a predetermined exciting current to the field coil upon sensing engine stop. The rotating period of the alternator rotor during engine stop can be reduced while preventing early breakage and slip noise of the belt during ordinary vehicle driving. Therefore it is possible to reduce a noise from the alternator. In another aspect, the alternator control mechanism previously stated has an engine stop signal input section, and sets the alternator voltage at a high value upon receiving the signal. It is, therefore, possible to reduce the idling time of the rotor by supplying the exciting current to the field coil when the engine is stopped. In another aspect, the alternator for vehicles has a pulley driven through a belt by the rotation of an engine crankshaft, a rotor connected to the pulley, a stator located opposite to the rotor, a ventilating means rotating in one body with the rotor, and a frame with a plurality of cooling air vents as the ventilating means and holding the rotor and the stator. The pulley is mounted on a rotating shaft of the rotor through a one-way clutch which transmits driving power to the rotor during acceleration of rotational speed of the crankshaft and does not transmit the driving power to the rotor during deceleration of rotational speed of the crankshaft. The rotor has a plurality of magnetic poles surrounding a field coil, and an alternator control mechanism which controls an exciting current supplied to the field coil. The alternator for vehicles is characterized in that the alternator control mechanism has a signal input section, which receives a signal from the engine control mechanism to stop engine rotation upon sensing a vehicle stop, and supplies a predetermined exciting current to the field coil after receiving an engine stop signal from the engine control mechanism. It is therefore possible to reduce the rotating period of the alternator rotor during engine stop while preventing early breakage and slip noise of the belt in ordinary vehicle driving. Particularly, in the idle stop system, it is possible to enhance decreasing noise from the alternator. In another aspect, the alternator control mechanism sets the alternator output voltage at a high value upon receiving an engine stop instruction signal. It is, therefore, possible to reduce the rotating period of the alternator rotor by supplying the exciting current to the field coil during engine stop. In another aspect, the invention has an alternator control mechanism which will stop the exciting current upon sensing a stop of the rotor. Thus it is possible to reduce the rotating period of the alternator rotor and prevent thermal deterioration by keeping a supply of the field current when the rotor is stopped. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In the drawings: Fig. 1 is a cross-sectional view and a block diagram showing the general constitution of an alternator for vehicles according to this invention; Fig. 2 is a circuit block diagram of the first embodiment; Fig. 3 is a perspective sectional view of a clutch pulley of the first embodiment; Fig. 4A is a schematic view showing the operation of the clutch pulley during engine acceleration in the first embodiment; Fig. 4B is a schematic view explaining the operation of the clutch pulley during engine deceleration in the first embodiment; Fig. 4C is a graphical view showing an outer race and a shaft rotating during acceleration and deceleration; Fig. 5 is a graphical view showing a difference in variation of rotor rpm between before and after an engine stop in the first embodiment; and Fig. 6 is a graphical view showing a difference in variation of rotor rpm between before and after an engine stop in the first embodiment and other embodiments. Preferred embodiments of the alternator for vehicles according to this invention will be explained with reference to the accompanying drawings. Fig. 1 show the first embodiment of this invention, of which Fig. 1 is a sectional view showing the general configuration of the alternator for vehicles according to this invention; Fig. 2 is a circuit block diagram; Fig. 3 is a perspective sectional view of a clutch pulley; Fig. 4 is a view explaining operation of the clutch pulley; and Fig. 5 is an explanatory view of a difference between this invention and conventional one, explaining rotor speed variations before and after the engine stops. The alternator 1 for vehicles is of such a design that the power from the engine is transmitted to the clutch pulley 9 through a belt (not shown), thereby turning the rotor 3 fixed on the clutch pulley 9 through the shaft 31. In this state, as the exciting current is supplied to the field winding 34 of the rotor 3 through the slip ring 35, the N and S poles are formed in the pole core 32, thus enabling generation of the ac voltage in the stator winding 21 and to take out the dc current through the rectifier 6 connected to the output end 21c of the winding. The amount of electric power to be generated is regulated by the regulator 9 which controls the exciting current flowing in the field winding 34 shown in Fig. 2. The rotor 3 and the stator 2 are oppositely arranged on a pair of frames 4; the stator 2 being held by a plurality of bolts 7 between the frames 4. Cooling air is drawn in through the opening 42 in the axial direction of the frame 4 by means of the cooling fans 11 and 12 secured on the pole cores 71 and 72. It is discharged at the opening 41 in the radial direction. In the clutch pulley 9, as shown in Fig. 3, a plurality of clutches 90 are disposed between an outer race 91 and an inner race sleeve 92. The clutches 90 are arranged and supported at a nearly equal pitch in the circumferential direction by a holder 95 and a spring member 94. The outer race 91 fixed by pressing into the inner periphery of the pulley 96 turns as one unit with the pulley 96, while the inner race sleeve 92 rotates as one unit with the shaft 31. Fig. 4A shows the outer race 91 and the inner race sleeve 92 during engine acceleration, and Fig. 4B shows the outer race 91 and the inner race sleeve 92 during engine deceleration. As shown in Fig. 4A, the clutch 90 is meshed with the lock portion 97 of the outer race 91 during engine acceleration, the rpm of the pulley 96 becoming equal to the rpm of the shaft 31. On the other hand, during engine deceleration, the clutch 90 is disengaged from the lock portion 97 as shown in Fig. 4B, and turns idle. Accordingly, the rpm of the shaft 31 is slowly decreased at higher rpm than the rpm of the pulley 96 by the inertial force of the rotor 3, although the rpm of the pulley 96 follows the rotation of the engine. Fig. 4C is a view showing the rotation of the outer race 91 and the shaft 31 during acceleration and deceleration of the engine. When the engine is under acceleration, the rpm of the outer race 91 increases in synchronization with the increase of the engine rpm. When the rpm of the outer race 91 exceeds the rpm of the shaft 31, the clutch 90 fits in the lock portion 97, causing the outer race 91 to turn as one unit with the shaft 31. During engine deceleration, the speed of the outer race 91 decreases synchronously with the decrease in engine rpm. On the other hand, the speed of the inner race sleeve 92 is slowly decreased during engine deceleration because of the inertial force. Therefore, the speed of the shaft 3 rotating as one unit with the inner race sleeve 92 makes a little slower decrease than the speed of the outer race 91. Fig. 5 is a view showing a variation in rotor rpm before and after the engine stops. As shown in Fig. 5, when the engine stops, the clutch idles. Therefore, between A and B in the drawing, the rpm of the rotor 3 makes a slow decrease due to the inertial force like during deceleration. And at the point B where the engine rpm reaches zero, the regulator 8 shown in Figs. 1 and 2 receives an engine stop signal from a sensor mechanism 80. Upon receiving the signal, the regulator 8 operates to supply the exciting current to the field coil 34. Therefore, the inertial force of the rotor 3 is consumed for the driving torque, and accordingly the rpm of the rotor 3 suddenly lowers as low as point C. If exciting current is not supplied, the inertial force of the rotor 3 is consumed for rolling friction of bearings and the rotational energy of the fans. Thus the rpm of the rotor slowly decreases as indicated by a two-dot chain line in Fig. 4, reaching the point D, at which the rotor comes to a stop. In ordinary vehicle driving, therefore, when the engine is decelerated, the clutch pulley is disconnected so as not to transmit the inertial force of the alternator rotor to the pulley. Early breakage of the belt or slip noise of the belt can be prevented. And, it is also possible to quickly stop the alternator rotor during engine stop, to thereby reduce noises from the alternator. [Other Embodiments] In the first embodiment the exciting current was supplied upon sensing the decrease of engine rpm to zero. It should be noticed, however, that a signal may be received directly from a control mechanism which stops the engine upon sensing a vehicle stop, and then, as shown in Fig. 6, the exciting current may be supplied in synchronization with the transmission of an engine stop instruction signal. In this case, since the alternator rotor can be more quickly stopped, it is possible to further reduce noises from the alternator. The effect of noise reduction can be improved particularly by combining the alternator with the idle stop system. Furthermore, it becomes possible to quickly stop the alternator rotor by supplying the exciting current through the control to set the regulated voltage of the alternator at a high value when the engine stop signal is received. Furthermore, it becomes possible to prevent thermal deterioration caused by the rise of field coil temperature, by combining with the alternator control mechanism which stops the supply of the exciting current upon sensing an alternator rotor stop. For sensing the rotor stop, it is enough to sense for example the presence or absence of one-phase voltage. The time to stop the exciting current may be preset in accordance with the inertial moment of the rotor. Furthermore, the clutch pulley in the first embodiment has a combination of a roller-type clutch, a spring member, a holder, an outer race, and an inner race sleeve, but may be of other constitution if provided with a one-way clutch function. Furthermore, an electromagnetic clutch may be used. Furthermore, the first embodiment shows the rotor having cooling fans on both sides in the axial direction. But if there is margin for air cooling, for example because of the adoption of water cooling, the cooling fan may be mounted only one side, or the magnetic pole rotating without a cooling fan may be used in place of the fan. While the above-described embodiments refer to examples of usage of the present invention, it is understood that the present invention may be applied to other usage, modifications and variations of the same, and is not limited to the disclosure provided herein, but instead its scope is to be determined by the appended claims.

Claims: An alternator (1) for a vehicle having a pulley (9) driven by a belt from rotation of an engine crankshaft, a rotor being connected to the pulley (9), a stator (2) located opposite to the rotor, a ventilating means rotating as one body with the rotor, and a frame with a plurality of cooling air vents cooperating with the ventilating means, the frame holding the rotor and the stator (2), wherein: the pulley (9) is mounted on a rotatable shaft of the rotor by a one-way clutch (90) that transmits driving power to the rotor during acceleration of the crankshaft and does not transmit driving power to the rotor during deceleration of the crankshaft; the rotor has a plurality of magnetic poles surrounding a field coil; and characterized in that an alternator control mechanism is provided, supplying a predetermined exciting current to the field coil upon sensing engine stop. An alternator (1) for a vehicle according to claim 1, wherein the alternator control mechanism has an engine stop signal input section that sets an output voltage of the alternator (1) at a higher level upon receiving the signal. An alternator (1) for vehicles according to claim 1, wherein an alternator control mechanism which stops the exciting current upon sensing a stop of the rotor, is provided.

Inventors: HAYASHI YOSHINORI, NAKAMURA SHIGENOBU, HAYASHI, YOSHINORI, NAKAMURA, SHIGENOBU
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 2001
Main classification: H02P9
IPC codes: F02D29, H02P9, H02K7, F16H7, H02K19