Electricity: single generator systems – Automatic control of generator or driving means – Voltage of generator or circuit supplied
Reexamination Certificate
2002-11-22
2004-10-12
Ponomarenko, Nicholas (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Voltage of generator or circuit supplied
C322S036000
Reexamination Certificate
active
06803747
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to an alternator control apparatus designed to control generation of electrical power in an alternator for use in automotive passenger vehicles or trucks, and more particularly to an alternator control apparatus working to minimize an undesirable change in inertial torque of a rotor of the alternator.
2. Background Art
Most of modern automotive vehicles are so designed that many functions thereof are controlled electronically instead of mechanically. Electric power demands are, thus, increasing for various controls of the vehicles. This results in an increased size of automotive alternators serving as a power supply, which leads to an increased size of a rotor producing a magnetic field inside the alternator, thereby causing the moment of inertia thereof to be increased.
Additionally, an engine compartment is also required to be decreased in size for increasing the volume of a cabin. To this end, adoption of a serpentine belt drive system in which vehicle accessories including an alternator are driven through a single torque transmission belt is progressing in order to save a space in the engine compartment. Such a serpentine belt drive system uses an automatic belt tensioner (will also referred to as an auto-tensioner below) on a transmission line which absorbs a variation in tension of the belt to keep it constant. The use of such an auto-tensioner eliminates the need for a concern about a drop in tension of the belt with time. The tension of the belt is, thus, allowed to be set initially to a lower level.
There is a tendency to decrease the speed of an engine further during an idle mode of engine operation which does not contribute to driving the vehicle and is entered frequently for the sake of earth environmental protection such as decreases in exhaust emission and consumption of fuel. Moreover, a common rail fuel injection system working to elevate the pressure within a combustion chamber of diesel engines greatly is used increasingly for clearing exhaust gasses of the engine.
The above factors are usually combined, thus facilitating ease of occurrence of a variation in idle speed of the engine in synchronization with a power stroke of the engine. An essential problem is an increase in tension of the belt arising from a change in inertia torque of each accessory caused by the variation in idle speed of the engine. Particularly, automotive alternators, as described above, tend to increase the moment of inertia and are higher in pulley ratio than other accessories, which impinges upon the variation in tension of the belt greatly. In recent years, the accessories have increased their capacities and required great driving torques. The transmission of such a great driving torque to each accessory is preferably achieved with the serpentine belt drive system. The serpentine belt drive system requires an increased angle over which a belt is in contact with a pulley of each accessory and a compact layout of the pulleys within the engine compartment. In such a layout, an increased variation in tension of the belts will result in a great swing of the auto-tensioner, which may lead to collision with other accessories driven by the serpentine belt, thereby resulting in a decrease in service life of the auto-tensioner and the belt. Such a problem is posed notably, particularly in diesel engines because a variation in pressure within a combustion chamber is, as described above, great.
In order to avoid the above problem, Japanese Patent Second Publication No. 7-72585 and U.S. Pat. No. 4,725,259 teach use of a one-way clutch in a pulley of an automotive alternator which is designed to allow torque to be transmitted only in a single direction. Some advantages of the automotive alternator using such a one-way clutch will be described below in brief.
If a pulley having no clutch is used, the speed of the alternator decreases following a decrease in idle speed of the engine. The moment of inertia of a rotor of the alternator works as a motor to keep the speed of the alternator constant, thus loosening a rotation-stretched portion of the belt instantaneously, while stretching a rotation-loosened portion of the belt. The automatic belt tensioner, thus, swings to keep the tension of the belt constant.
If a pulley with a one-way clutch is used with the alternator, the clutch is disengaged by the moment of inertia of the rotor of the alternator when the speed of the engine is dropping (i.e., when the alternator works as a motor), and the speed of the rotor of the alternator is higher than the speed of the pulley, so that the speed of the pulley decreases slowly in synchronization with the speed of the engine. When the speed of the engine is increasing, the clutch remains disengaged until the speed of the pulley increases up to the speed of the rotor of the alternator. This avoids transmission of the inertia torque produced by the moment of inertia of the rotor of the alternator to the pulley, thereby decreasing the instantaneous decrease in tension of the stretched portion of the belt and the instantaneous increase in tension of the loosened portion of the belt, thus minimizing an undesirable change in tension of the whole of the belt.
Japanese Patent First Publication No. 6-207525 discloses a pulley with a bi-directional clutch. A coil spring which has an inner diameter greater than an outer diameter of a sleeve installed on a shaft of a rotor of the alternator is disposed between a pulley and the sleeve and joined at one end to the sleeve and at the other end to the pulley. The elasticity of the coil spring serves to absorb an instantaneous change in tension of the belt during a rise in speed of the engine as well as a drop thereof.
The one-way clutch, as taught in Japanese Patent Second Publication No. 7-72585, has a complex structure in which splines and a roller are engaged and disengaged selectively to establish and block transmission of torque between a pulley and a rotor, so that a large amount of stress is exerted on component parts of the clutch during connection or disconnection thereof. In design of such a type of one-way clutch capable of withstanding harsh conditions of use of the automotive alternator (e.g., a wide range of speed, acceleration, deceleration, and ambient temperature), the trade-off between reduction in size and increase in service life of the clutch is encountered. Specifically, in a case where the pulley ratio is increased to improve output of the alternator in a low-speed range of the engine, reduction in size of the pulley requires reduction in size of the clutch built in the pulley, thus resulting in a decrease in durability due to decreases in fatigue life and applied amount of grease. The manufacturing cost is also increased as compared with typical pulleys for ensuring desired accuracy of parts of the clutch and assembling thereof.
The bi-directional clutch pulley, as taught in Japanese Patent First Publication No. 6-207525, is so constructed that a load is exerted on the coil spring many times in a direction of rotation, thus posing a problem of durability of the coil spring and a spring support supporting ends of the coil spring. Increasing the rigidity of the coil spring to ensure desired durability requires increasing the size of the coil spring and the spring support, thus resulting in an increased size of the clutch pulley. This also makes it difficult to decrease the diameter of the pulley to increase the speed of thereof in order to increase an output power of the alternator meeting increasing electric power demands of automotive vehicles. In recent years, a clutch shoe has been proposed which is disposed between a coil spring and a pulley to decrease a mechanical load on the coil spring while improving the performance of the clutch in one direction. The clutch shoe works to slip to block transmission of the inertia torque of a rotor of the alternator during deceleration of the engine, but however, a difficulty is encountered in removing wear powd
Nakamura Shigenobu
Taniguchi Makoto
Cuevas Pedro J.
Denso Corporation
Ponomarenko Nicholas
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