Interrelated power delivery controls – including engine control – Transmission control – Continuously variable friction transmission
Reexamination Certificate
2000-05-30
2001-11-06
Marmor, Charles A (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Continuously variable friction transmission
C476S004000, C476S011000, C476S043000
Reexamination Certificate
active
06312358
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a constant speed drive apparatus for an airborne generator which drives an airborne generator with engine torque, and to an aircraft power generating apparatus including the generator. Furthermore, the invention relates to a traction speed change apparatus of continuously-variable speed change ratio.
2. Description of the Related Art
An aircraft has generators mounted thereon for supplying electric power to electrical equipment including instruments, communication devices, lighting, air-conditioners and anti-icing heaters. Each engine of a large passenger airplane, e.g., a twin-engined jetliner, is mounted with a large generator of the order of 100 kVA. The engine has an accessory drive shaft for dividing out turbine torque to drive various devices such as a hydraulic pump. This accessory drive shaft serves as a drive source of the generator.
The engine speed of an aircraft varies widely from idling conditions at the time of landing to acceleration conditions at the time of takeoff, and generally varies continuously over the range of 5,000 rpm to 10,000 rpm. On the other hand, an AC output of 400 Hz±7 Hz is specified for generators, and the drive shaft of the generator is required to rotate constantly at a rate of 12,000 rpm or 24,000 rpm. Thus, in the case where engine output is directly connected to the generator through an accelerating gear or the like, some compensation system is needed since otherwise the rotational frequency of the generator varies to excess.
The following compensation systems have been in wide use heretofore: 1) mechanical type: a hydromechanical CSD (Constant Speed Drive) having a stepless speed change mechanism with a combination of a hydraulic pump, a hydraulic motor and a differential gear, disposed between the accessory drive shaft and a generator to absorb variations in the engine speed and drive the generator at constant speed, and 2) electrical type: a VSCF (Variable Speed Constant Frequency) having a semiconductor device for switching generator output with frequency variations to convert the output into an AC output of fixed frequency.
The former, mechanical type requires a large number of components and a complicated mechanism. This type can achieve only a low transmission efficiency of about 65% due to losses in conversion to hydraulic pressure and the like, and is expensive at that.
The latter, electrical type, though increasingly used at present, becomes heated to a very high degree since it controls a large amount of electric power. Thus, a large cooling mechanism is required, whereby this type is heavier as a whole than the mechanical type. Moreover, since the semiconductor device is less reliable than the mechanical type, the mechanical type remains the preferred option in the case where priority is given to safety and weight reduction.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a constant speed drive apparatus for an aircraft generator and a power generating apparatus for aircraft which are small and lightweight and yet achieve high transmission efficiency.
Another object of the invention is to provide a small and lightweight traction speed change apparatus capable of achieving a high transmission efficiency.
The present invention provides a constant speed drive apparatus for an aircraft generator, in which the apparatus comprise an input shaft for receiving drive torque from an aircraft engine; a traction speed change mechanism having a continuously-variable speed change ratio, and which is coupled to the input shaft; an output shaft for supplying the aircraft generator with drive torque which is changed in speed by the traction speed change mechanism; and a rotational-frequency controlling mechanism for controlling the speed change ratio of the traction speed change mechanism so as to maintain the output shaft at a predetermined rotational frequency.
The traction speed change mechanism includes an input disk interlocked to the input shaft; an output disk interlocked to the output shaft; transmission rollers disposed between the input disk and the output disk; yoke members for supporting the transmission rollers so that they are pivotable about an axis perpendicular to an axis of rotation of each of the transmission rollers and the input disk; and an actuator for pulling the yoke members along the axis of rotation of the input disk and drawing the transmission rollers toward the input disk to generate a pressing force of the transmission rollers.
According to the invention, the traction speed change mechanism of continuously-variable speed change ratio is disposed between the input shaft and the output shaft, whereby a relationship between the rotational frequency of the output shaft and the rotational frequency of the input shaft can be continuously controlled. Further, the rotational-frequency controlling means is provided for controlling the speed change ratio of the traction speed change mechanism to perform a feedback operation for maintaining the output shaft at a constant rotational frequency, thereby to eliminate inconveniences due to variations in rotational frequency of the input shaft. Thus, even when the rotational frequency of the aircraft engine varies over a wide range, the aircraft generator may be driven with a constant rotational frequency. A mechanical feedback control or an electrical feedback control are applicable as the rotational-frequency controlling means. In the former the rotational motion of the output shaft is taken out for use as an input for controlling the traction speed change mechanism, and in the latter the rotational frequency of the output shaft is converted into an electrical signal once for use as an input for controlling the traction speed change mechanism.
In connection with the traction speed change mechanism, according to the invention, the mechanism for generating the pressing force of the transmission rollers may be provided separately from the axis of rotation of the disks. Moreover, the actuator is operable to draw the transmission rollers directly through the yoke members, which allows the pressing force of the rollers to be controlled easily and with high precision.
In a conventional traction speed change mechanism, an axial force generating mechanism adjacent an input disk generates an axial force, to control the pressing force of rollers indirectly through the input disk. Such a mechanism is complicated. Where the axial force generating mechanism has cam rollers disposed on two opposed cam surfaces to generate an axial force corresponding to a torque difference between the cam surfaces, a slight hysteresis property occurs between the torque difference and the axial force, which is due to rolling friction and the like of the cam rollers. Further, at the time of high-speed rotation, a strong centrifugal force acts on the cam rollers to increase friction at supports of the cam rollers, which could obstruct rolling thereof. When a counter torque acts to produce a negative torque difference on the cam surfaces, the transmission rollers move away from the input disk. To avoid such a situation, some bias axial force mechanism is provided. On the other hand, the above measure peculiar to the cam rollers can be eliminated by employing the construction in which the actuator directly drives the transmission rollers.
The traction speed change mechanism may be in the form of a half toroidal CVT (Continuously Variable Transmission) or a full toroidal CVT, which is a small, lightweight and yet low loss speed change mechanism. With such a traction speed change mechanism coupled to a transmission line rotating at high speed, e.g. engine output, a maximum permissible torque can be small, contributing to a reduction in size and weight of the entire apparatus.
The invention also provides a constant speed drive apparatus for an aircraft generator, in which the apparatus comprises an input shaft for receiving drive torque from an aircraft engine; a traction speed change mechanism of
Goi Tatsuhiko
Kawakami Kouji
Yamakawa Eiichi
Advanced Technology Institute of Commuter-Helicopter, Ltd.
Ho Ha
Marmor Charles A
Wenderoth , Lind & Ponack, L.L.P.
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