Vehicular electric power generation apparatus and method

Abstract: In a vehicular electric power generation apparatus having an a.c. generator (1) and an engine (2), a rotation speed (N1) of the a.c. generator (1) at the idling rotation operation of the engine (2) is set to be higher than a rotation speed (Np), at which the driving torque of the a.c. generator (1) becomes a maximum (Tp). Thus, the rotation speed of the a.c. generator (1) does not changes through the rotation speed (Np) at which the driving torque of the vehicle a.c. generator (1) becomes a maximum, even when the rotation speed of the engine (2) is raised high for running of a vehicle. Thus, changes in the load applied to the engine (2) can be restricted.

Description: The present invention relates to a vehicular electric power generation apparatus and method, which may be used in passenger vehicles, truck vehicles and the like. It is a recent trend to control idling rotation speed of an engine electronically in vehicles. In this instance, the idling rotation speed is determined based on cold/hot condition of the engine, heaviness/lightness of electric load, on/off of an air conditioner and the like. The engine rotation is stabilized to a target idling rotation speed by feeding back the actual rotation speed of the engine during engine idling operation. The idling rotation speed of the engine is lowered to meet various social requirements, that is, improvement in fuel economy, lower noise at the time of engine idling, and environmental protection. It became a recent problem that the engine idling rotation speed at the time of engine idling operation does not stabilize, thus repeating hunting to higher and lower rotation speeds. The electric power output of a vehicular alternating current (a.c.) generator driven by the engine generally increases up to a certain rotation speed with an increase in its rotation speed and saturates after reaching the certain rotation speed. Further, the driving torque of the a.c. generator may be considered as the output per rotation of the a.c. generator. Thus, the relation between the rotation speed and the driving torque is in a monotonic increase until the output saturates relative to the rotation speed, and is in a monotonic decrease after the output saturation. As a result, as shown in Fig. 3, the a.c. generator generally has a maximum driving torque Tp at a rotation speed No. The maximum driving torque changes sharply at around the rotation speed No. The increase and decrease in the engine rotation speed is controlled by an idling speed control apparatus as described above, even in the range of engine idling operation in which the output torque of the engine is not sufficient. For this reason, when the rotation speed of the a.c. generator at the time of engine idling rotation and the rotation speed No, at which the a.c. generator requires a maximum driving torque Tp, generally coincide at the rotation speed No, a response delay of control or the like causes a hunting in which the engine idling rotation speed falls far below and rises far above the rotation speed No at which the driving torque Tp of the a.c. generator reaches a maximum. When the hunting occurs, sound of changes in the rotation speed of the engine and in rotation speeds of a number of devices driven by the engine become noisy, and changes in vibration caused by the changes in the rotation speed becomes sensible. Thus, users of vehicles are likely to feel uncomfortable. This will result in an unacceptable problem in recent passenger compartments, which have increased quietness. It is therefore desired in view of the foregoing problems to provide a vehicular a.c. generator, which requires a lower driving toque and does not have a sharp maximum driving torque characteristics. For decreasing the driving torque, reduction in inertial moment of a rotary body by down-sizing, improvement in efficiency by improving cooling and the like have been attained. However, those are not effective to restrict hunting of rotation speed. Further, as disclosed in JP-B2-6-38720, it is known to regulate an energization current under a cold state for restricting the cold state driving torque to the same level as the hot state driving torque, because the a.c. generator has a larger driving torque in the cold state than in the hot state. However, this method is still incapable of suppressing occurrence of hunting, because the a.c. generator requires the maximum driving torque in the hot state. Further, as disclosed in JP-A-10-4698, although it is proposed to flatten the maximum driving torque characteristics by restricting an electric power generation output at around the maximum driving torque, the generated power output is decreased. Further, as disclosed in the abstract of the Japanese patent application No. 08152176, there is a power generation controller for an internal combustion engine, that is provided with an alternator, a rotational speed sensor and a controller. The rotational speed sensor detects the rotational speed of a rotor, which is a state quantity associated with the torque and the temperature of the alternator. The controller detects the voltage of a battery, connected with the alternator, to control the energizing for a field coil, according to the value detected. When the rotational speed of the alternator reaches a torque over predetermined threshold value, the controller limits the energizing amount for the field coil, in order to decrease the maximum torque. It is therefore an object of the present invention to reduce chances where a vehicular a.c. generator operates at a rotation speed at which a driving torque of the a.c. generator becomes a maximum. It is another object of the present invention to restrict hunting by driving a vehicular a.c. generator at rotation speeds other than a rotation speed at which a driving torque of the a.c. generator becomes a maximum. According to the present invention, a rotation speed of a vehicular a.c. generator at the time of idling rotation operation of an internal combustion engine is set to be higher than a rotation speed at which a driving torque of the a.c. generator becomes a maximum. Thus, even when the rotation speed of the internal combustion engine is raised for vehicle running from the idling rotation speed, the rotation speed does not change through the rotation speed at which the driving torque of the a.c. generator becomes a maximum. As a result, changes of the load applied from the a.c. generator to the internal combustion engine can be reduced. According to the present invention, a range of rotation speed of a vehicular a.c. generator is set to a range of rotation speed in which the driving torque of the a.c. generator does not become a maximum. Thus, the rotation speed of the internal combustion engine does not become equal to the rotation speed at which the driving torque of the a.c. generator becomes a maximum. Preferably, a lowest rotation speed in the range of rotation speed of the a.c. generator is higher more than 100 rpm than the rotation speed at which the driving torque of the a.c. generator becomes a maximum in a maximum output condition under a cold state. Thus, even when the idling rotation speed of the internal combustion engine varies, the change in the load applied to the internal combustion engine is restricted because the rotation speed at the maximum of the driving torque is more than 100 rpm lower. In addition, the rotation speed at which the driving torque of the a.c. generator in hot condition becomes a maximum is lower than the rotation speed for the maximum driving torque in the cold condition, and the driving torque in the partial output condition is lower than the driving torque in the maximum output condition. Therefore, the maximum driving torque of the a.c. generator can be avoided by setting it as above in the cold maximum output condition. It is also possible to combine with a construction of an electric power generation control apparatus, which restricts the output in the cold condition to that in the hot condition. In this instance, as the maximum driving torque of the a.c. generator can be avoided, the change in the load applied to the internal combustion engine at around the maximum driving torque can be restricted. Fig. 1 is a plan view showing an electric power generation apparatus having a vehicular a.c. generator on an engine according to an embodiment of the present invention; Fig. 2 is a graph showing a driving torque characteristics of the a.c. generator used in the embodiment shown in Fig. 1; and Fig. 3 is a graph showing a driving torque characteristics of a conventional a.c. generator. A vehicular a.c. generator according to the present invention is described below with reference to an embodiment shown in Figs. 1 and 2. A vehicular electric power generation apparatus includes, as shown in Fig. 1, an alternating current (a.c.) generator 1 mounted on an internal combustion engine 2, so that it may be driven by the internal combustion engine 2 via a belt 3. The engine 2 has a crank pulley 21 mounted on a crankshaft (not shown) of the engine 2, which is used as a driving source for vehicle running. The a.c. generator 1 has a pulley 11. The belt 3 is wound around those pulleys, so that rotation of the engine 2 is transmitted through the belt 3 to the a.c. generator 1 as well as to a plurality of other auxiliary rotary devices such as a compressor and water pump for an air conditioner. This kind of rotation transmitting device is a serpentine type belt driving device. The a.c. generator 1 has a driving torque characteristics in the cold maximum output condition as shown in Fig. 2. In Fig. 2, N1 indicates a rotation speed of the a.c. generator 1 at the time of idling of the engine 2, and the a.c. generator 1 is used normally in the range of rotation speed above N1 in this embodiment. Here, the normally used rotation speed range of the engine 2 corresponds to the normally used rotation speed range of the a.c. generator 1. In this embodiment, the diameters of the crank pulley 21 of the engine 2 and the pulley 11 of the a.c. generator 1 are 190 mm and 50 mm, respectively, so that the pulley ratio is 3.8. As the idling rotation speed as the lowest rotation speed of the engine 2 is 600 rpm in this embodiment, the rotation speed N1 of the a.c. generator 1 at the time of engine idling is 2280 rpm. That is, the rotation speed N1 is set to be 180 rpm higher than 2100 rpm, which is the rotation speed Np at which the driving torque becomes a maximum (peak) Tp. Although this idling rotation speed of the engine 2 may be raised in response to air conditioner operation and the like, it is set to be 600 rpm at the lowest. Thus, the rotation speed of the a.c. generator 1 rises through the rotation speed Np, at which the a.c. generator 1 requires the maximum driving torque Tp, only temporarily at the time of starting the engine 2, and is not used in the normal operation of the engine 2 and the a.c. generator 1. For this reason, even when the rotation speed of the a.c. generator 1 changes over a wide range during normal operation of the engine 2, the driving torque of the a.c. generator 1 does not become the maximum during normal operation of the engine 2. Thus, changes in the inclination of torque increase and torque decrease around the maximum driving torque Tp can be avoided. As a result, a uniform characteristics can be provided, in which the driving torque decreases as the rotation speed increases during the normal operation of the engine 2. Thus, when the idling rotation speed of the engine 2 is controlled to a fixed speed by an idling rotation speed control apparatus in the known manner, its control stability is improved and a hunting of rotation speed is restricted. Further, as the rotation speed Np at which the driving torque becomes the maximum is set to be lower than the lowest rotation speed N1 which corresponds to the idling speed of the engine 2, the maximum driving torque can be avoided even when the idling rotation speed is changed to a higher rotation speed for driving an air conditioner. In setting the pulley ratio, the diameters of the pulley 21 and the pulley 11 are set in consideration of the angle of winding the driving belt 3. For instance, it is preferred to construct the pulley 21 large as much as possible and the pulley 11 relatively small. The pulley ratio between the a.c. generator 1 and the engine 2 is set to the fixed ratio in the first embodiment. However, the driving torque characteristics may be changed by increasing the number of turns of the stator winding of the a.c. generator 1, so that the rotation speed Np at which the driving torque becomes a maximum may be set to be lower than the lowest rotation speed N1 of the a.c. generator 1. Further, a control apparatus for controlling a field current which restricts a maximum of the driving toque may be used, jointly with the above power generation apparatus. In this instance, any disadvantage which would be caused by the maximum driving torque can be eliminated, even when the field current restriction control fails. In addition, the belt driving system shown in Fig. 1 may be replaced with a driving system which is a combination of a crank pulley having multi-stage grooves and a plurality of belts. Still further, a rotation transmitting device such as a gear driing device may be used.

Claims: A vehicular electric power generation apparatus comprising: an internal combustion engine (2); and an a.c. generator (1) driven by the internal combustion engine (2), characterized in that the rotation speed (N1) of the a.c. generator (1) at the time of idling rotation operation of the internal combustion engine (2) is set to be always higher than a rotation speed at which a driving torque of the a.c. generator (1) becomes a maximum. A vehicular electric power generation apparatus as in claim 1, wherein: the lowest rotation speed in the range of normal rotation speed of the a.c. generator (1) is set to be higher more than 100 rpm than the rotation speed (Np) at which the driving torque of the a.c. generator (1) becomes a maximum in a maximum output condition under a cold state. A vehicular electric power generation apparatus as in claim 1 or 2, further comprising: a rotation transmitting device (3, 11, 12) provided to transmit rotation of the internal combustion engine (2) to the a.c. generator (1). A vehicular electric generation power method comprising the steps of: driving an a.c. generator (1) by an engine (2) through a rotation transmitting device (3, 11, 12), the a.c. generator (1) being driven at a maximum driving torque (Tp) at one rotation speed (Np); and maintaining a rotation operation of the engine (2) after starting so that the a.c. generator (1) is driven at another rotation speed (N1)that is always higher than the rotation speed (Np) for the maximum driving torque. A vehicular electric power generation method as in claim 4, wherein: the the lowest rotation speed corresponds to an idling rotation operation. A vehicular electric power generation method as in claim 5, wherein: the another rotation speed (N1) is more than 100 prm higher than the one rotation speed (Np).

Inventors: HORIBE MITSUTOSHI, HORIBE, MITSUTOSHI
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 1999
Main classification: H02P9
IPC codes: B60R16, H02P9