Planetary gear transmission systems or components – Nonplanetary variable speed or direction transmission... – Nonplanetary transmission is friction gearing
Reexamination Certificate
1999-09-24
2001-07-03
Marmor, Charles A (Department: 3681)
Planetary gear transmission systems or components
Nonplanetary variable speed or direction transmission...
Nonplanetary transmission is friction gearing
Reexamination Certificate
active
06254504
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a power transmission apparatus for helicopters whose speed change ratio can be continuously varied by a traction transmission mechanism.
2. Description of the Related Art
Recently, the demand for commuter helicopters capable of taking off and landing on a heliport in an urban district has been increased. Reduced noise level is a requirement for such a helicopter, and one of of effective measures to reduce the noise level is to reduce the rotational speed of the main rotor.
Japanese Unexamined Patent Publication JP-A 8-198192 (1996) of the same applicant as that of the present invention, discloses a power transmission apparatus comprising a traction transmission mechanism of continuously variable speed change ratio, coupled to an output shaft of an engine, for making the rotational speed of the power transmission apparatus variable. For the purpose of reducing noise of helicopters, the apparatus is designed to reduce only the rotational speed of the main rotor under the condition that the rotational speed of the tail rotor is maintained constant as well as the number of rotations of the engine.
The traction transmission mechanism includes input and output disks which are oppositely disposed so that their rotation shafts coincide with each other; a transmission roller which transmits the rotational power of the input disk to the output disk; and an actuator which changes tilt angle of the transmission roller. Lubricating oil is interposed between the disks and the roller, so that the power is transmitted by means of the shearing resistance of the lubricating oil. The transmission roller is disposed so as to be tilted by the actuator. By continuously displacing the actuator, the speed change ratio can be continuously varied.
In a conventional power transmission apparatus for helicopters, having no traction transmission mechanism, the number of rotations of the engine is reduced with a constant speed change ratio. Hence, the number of rotations of the main rotor is constant, which causes the problem of noise generation.
On the other hand, simple incorporation of such a traction transmission mechanism into a helicopter causes an increase of control gain during high-speed rotation, which is a cause of a generation of large tilting force. As a consequence the tilt angle is suddenly changed, and therefore a slide occurs between the disks and the rotor. When a slide occurs, power transmission ability is lost and the torque of the main rotor is rapidly lowered.
Among traction transmission mechanisms, for example, a toroidal CVT (Continuously Variable Transmission) has power transmission efficiency of only about 90%. Even when such a CVT is combined with a differential gear transmission, the power transmission efficiency of about 97% is obtained at the highest.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a power transmission apparatus for helicopters, capable of continuously varying the rotational speed of a main or tail rotor under the condition that the number of rotations of an engine is maintained constant, ensuring safety even in the case where a slide of a traction transmission mechanism occurs, and achieving high power transmission efficiency when transmission is not required.
The invention provides a power transmission apparatus for helicopters, comprising a traction transmission mechanism, capable of continuously varying speed change ratio by the traction transmission mechanism. The apparatus comprises a coupling switching mechanism for changing over a coupling state among an input shaft, an output shaft, and the traction transmission mechanism to carry out switching of the operation mode between a variable mode (in which the speed change ratio is made variable by branching power from the input shaft into power to be transmitted to the traction transmission mechanism, and into power to be joined with power from the traction transmission mechanism to be transmitted to the output shaft) and a fixed mode (in which the speed change ratio is made fixed by directly transmitting the power from the input shaft to the output shaft).
According to the invention, in the variable mode, the rotational speed of the main or tail rotor can be continuously varied by the traction transmission mechanism under the condition that the number of rotations of the engine is maintained constant.
For example, in the case of a flight over an urban district, the helicopter is operated in the variable mode, so that the number of rotations of the main rotor can be lowered to suppress the generation of noise. On the other hand, the operation is shifted to the fixed mode in a suburb so that power transmission efficiency can be increased to enhance fuel efficiency. In this way, the variable mode in which branched power is transmitted to the traction transmission mechanism, and the fixed mode in which no power is transmitted to the traction transmission mechanism are selectively used. Thus, both noise reduction and enhanced fuel efficiency can be attained.
Furthermore, the shift of operation mode between the variable mode and the fixed mode prevents occurrence of slide between a disk and a roller and lowering of power transmission efficiency.
For example, the coupling switching mechanism for the variable mode and the fixed mode in the invention can be realized as shown in
FIG. 1
or
4
. Furthermore, the invention provides a power transmission apparatus for helicopters, comprising a traction transmission mechanism and a planetary transmission mechanism. Power from an input shaft is branched into power which is transmitted to the traction transmission mechanism and power which is transmitted to the planetary transmission mechanism together with power from the traction transmission mechanism. The power from the planetary transmission mechanism is transmitted to an output shaft. The traction transmission mechanism includes an input disk, an output disk, and a transmission roller which is tiltably interposed between the input and output disks.
The planetary transmission mechanism includes a sun gear fixed to the output disk, planetary gears which meshes with the sun gear, and a ring gear having internal teeth that mesh with the planetary gears, and the ring gear transmits transmitting the power from the input shaft.
According to the invention, the combination of the traction transmission mechanism and the planetary transmission mechanism enables the rotational speed of the main rotor or the tail rotor to be continuously varied under the condition that the number of rotations of the engine is maintained constant. Therefore, noise reduction and enhanced power transmission efficiency can be attained. Since the sun gear of the planetary transmission mechanism is fixed to the output disk of the traction transmission mechanism, the power of the traction transmission mechanism can be directly transmitted to the planetary transmission mechanism. Consequently, an additional mechanism for coupling the mechanisms together is not required, and hence the apparatus can be miniaturized.
The structure of the invention in which the sun gear is fixed to the output disk can be realized by either a speed change apparatus
10
shown in
FIG. 4
, having a coupling switching mechanism, or a speed change apparatus
90
shown in
FIG. 8
, having no coupling switching mechanism.
Furthermore, in the invention it is preferable that the apparatus further comprises slide detecting means for detecting a slide in the traction transmission mechanism, and switching controlling means for, when a slide is detected, switching the coupling switching mechanism from the variable mode to the fixed mode.
According to the invention, a helicopter usually flies in the variable mode in which the branched power is transmitted to the traction transmission mechanism to reduce noise. When a slide in the traction transmission mechanism is detected, the mode is switched to the fixed mode in which the power from the input shaft is not branched to the traction transm
Goi Tatsuhiko
Kawakami Kouji
Yamakawa Eiichi
Advanced Technology Institute of Commuter-Helicopter, Ltd.
Marmor Charles A
Pang Roger
Wenderoth , Lind & Ponack, L.L.P.
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