Torque limiter

A torque limiter limits transmission of torque between a drive shaft and an output shaft. The torque limiter includes a first rotational plate connected to the drive shaft, a second rotational plate facing the first rotational shaft and connected to the output shaft to be movable along an axial direction thereof, a ball ramp portion provided between the first rotational plate and the second rotational plate, a ball retained in the ball ramp portion, and a spring portion for pressing between the first rotational plate and the second rotational plate. A ball channel is formed in at least one of the first rotational plate and the second rotational plate. The ball in the ball ramp portion falls in the ball channel when the torque between the drive shaft and the output shaft exceeds a predetermined value to shut off the transmission of the torque.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a power transmission system for a general industrial device and an aircraft. More specifically, the present invention relates to a torque limiter in which a coupling portion for transmitting a rotational force shuts off or separates when a load exceeds a predetermined value.

A movable wing surface forming a part of a flight control system of an aircraft is called a rudder surface (flying wing surface or moving wing), and includes an aileron provided on a main wing as a main rudder surface, and an elevator and a rudder provided on a tail wing. The movable wing surface also includes a slat, a posterior-border slap, a flight spoiler, a gland spoiler and so on provided on the main wing as an accessory rudder surface. The main wing is composed of a wing and respective rudder surfaces (slat, slow speed aileron, high speed aileron, flight spoiler, gland spoiler and posterior-border slap). An aircraft body is controlled through an operation of the rudder surfaces and the tail swing.

FIG. 3shows a high-lift system of an aircraft. The high-lift system is a system in which a rudder surface of a flap/slat provided in a main wing is operated in order to obtain lift of the aircraft when the aircraft takes off and lands. It is necessary to operate each rudder surface of the right and left wings simultaneously (left rudder surfaces33aand34a, and right rudder surfaces33band34b). A drive motor30is disposed in the middle portion of the aircraft for rotating right and left torque shafts32simultaneously through a gear box31. In view of safety, it is necessary to operate the right and left rudder surfaces symmetrically (left rudder surfaces33aand34a, and right rudder surfaces33band34b).

FIG. 4(a) is a view showing a high-lift system equipped with torque limiters (left wing torque limiter35aand right wing torque limiter35b). The high-lift system has power for operating the right and left rudder surfaces with one drive motor30. The torque limiter limits torque transmitted to the left and right sides only as necessary and prevents excess torque from being transmitted. With the torque limiters, it is possible to reduce a size and weight of a component at a downstream side of the torque limiter as the torque limiter limits the maximum output torque.

The torque limiter of the high-lift system needs to shut off torque greater than a required torque for driving one wing, and needs to rotate the right and left shafts symmetrically within a predetermined level. The torque limiter mainly includes one type in which a shaft is fixed to a case and the other type in which a shaft becomes free for shutting off torque. In the high-lift system, since it is necessary to operate the right and left wings symmetrically, the type in which a shaft is fixed to a case is used. In the torque limiter in which a shaft is fixed to a case, it is necessary to stop the shaft instantly. Accordingly, when the torque limiter is operated, a large surge torque is generated due to inertial energy of the drive motor30, so that a measure for controlling the surge is separately required.

FIG. 4(b) is a view showing a high-lift system equipped with a surge torque buffering apparatus36. In the high-lift system, a torque limiter in which a shaft is fixed to a casing is provided on an output shaft of each of left and right wings (left wing torque limiter35a, right wing torque limiter35b). The surge torque buffering apparatus36is provided for reducing the surge torque generated by inertial energy. The surge torque buffering apparatus36is formed of a spring and the like.

FIG. 5is a cross sectional view of a torque limiter in which an output shaft2is to be fixed. An input plate3connected to a drive shaft1is fitted in a bearing provided in a housing9. At an opposite side, the output shaft2is supported on a bearing provided in the input plate3and a bearing provided in a housing10. The input plate3is connected to the drive shaft1to rotate, and the output plate4is capable of rotating and moving on the output shaft2in an axial direction. An output plate4is fitted into the output shaft2to be movable back and forth. A ball ramp portion5is disposed between the input plate3and the output plate4, and has lamp channels wherein a ball6is retained. A preload spring7is provided for pressing the ball ramp portion5in an axial direction so that the ball ramp portions5is not activated up to a certain torque. A brake portion8increases a torque according to a load in an axial direction generated when the ball ramp portion5is activated.

FIG. 6shows a structure of the ball ramp portion5. An upper portion inFIG. 6is a side of the input plate3, and a lower portion inFIG. 6is a side of the output plate4. Lamp channels with smooth slopes are provided on both sides for sandwiching the ball6. The preload spring7presses the output plate4. A depth and a size of the lamp channel and a size of the ball6are determined such that the ball ramp portion5is not activated up to a certain torque.

When the input plate3rotates, the lamp channel at a side of the input plate3moves in the right direction inFIG. 6. As a result, a driving force (torque) acts in an arrow direction through the ball6, and a pressing force acts in an arrow direction on the output plate4. When a torque greater than a predetermined value is applied, the input plate3moves further in the right direction inFIG. 6. As a result, the ball6rolls against resistance of the output plate4pressed by the preload spring7with a certain force, and increases a distance between the both plates. Accordingly, the brake portion8stops the output plate4, thereby shutting off the torque to the output shaft2. As described above, when a rotating torque greater than a predetermined value is applied to the drive shaft1, the coupling portion for transmitting the rotational drive limits the torque transmission.

Another type of torque limiter is able to shut off a torque when an overload is applied and maintain a position of the shut off (for example, refer to Japanese Patent Publication (Kokai) No. 07-293576).

In the conventional torque limiter with the structure described above, when the transmitting torque exceeds a predetermined value, the torque limiter instantly stops the rotational shaft, thereby generating a torque surge due to inertia of the rotational body. In order to reduce the torque surge, it is necessary to provide the surge torque buffering apparatus36such as a slip clutch as shown inFIG. 4(b), thereby increasing cost and weight, and lowering reliability.

In the view of the problems described above, the present invention has been made, and an object of the present invention is to provide a torque limiter with low cost, light weight and high reliability, wherein a downstream portion of a system is not affected when the transmitting torque exceeds a predetermined value due to the torque surge and so on.

SUMMARY OF THE INVENTION

In order to achieve the objects described above, according to the present invention, a torque limiter includes a ball ramp portion having lamp channels for retaining a ball between a rotational plate of a drive shaft and a rotational plate movable on an output shaft in an axial direction; a spring portion for pressing the ball ramp portion in the axial direction to prevent the ball ramp portion from being activated up to a certain torque; and a torque transmitting portion wherein a torque increases according to a load in an axial direction when the ball ramp portion is activated. In the torque limiter, the ball channels are provided in the rotational plates for allowing the ball in the ball ramp portion to move from the lamp channels and fall therein against a force of the spring portion when the transmitting torque exceeds a predetermined value, so that the torque is not transmitted through a displacement in the axial direction when the ball ramp portion is activated.

According to the present invention, a torque limiter includes ball ramp portions provided on both sides of opposing rotational plates of a drive shaft and having lamp channels wherein a ball is sandwiched; and spring portions provided on both sides of the opposing rotational plates for pressing in an axial direction, so that when one of the ball ramp portions is activated, a load in the axial direction induces activation of the other of the ball ramp portions. As a result, the driving torque is simultaneously applied to both output shafts.

In the present invention, the torque limiter is structured as described above, and formed of the ball ramp portion having the lamp channels for retaining the ball; the spring portion; and the torque transmitting portion. When the transmitting torque exceeds a predetermined value, the ball moves over the lamp channels of the ball ramp portion against the preload spring force, and the ball falls in the ball channels provided separately. Accordingly, a length of the ball ramp portion in the axial direction is shortened, thereby reducing the load of the spring portion. As a result, a torque that the torque transmitting portion can transmit decreases, so that an upstream portion and a downstream portion of the system are separated.

In the present invention, the ball ramp portions including the lamp channels for retaining the ball and the spring portion for pressing in an axial direction are provided on the both sides of the opposing rotational plates of the drive shaft. When one of the ball ramp portions is activated, the load in an axial direction eliminates the restriction of the preload force. Accordingly, the torque transmitting portion moves in a direction that the ball moves off, so that the other of the ball ramp portions is induced to activate. As a result, the pressing force from the torque transmitting portion through the ball disappears, so that the driving torque is not transmitted to the both output shafts.

In the present invention, the torque limiter is structured as described above. When the transmitting torque exceeds a predetermined value, the ball in the ball ramp portion falls in the ball channels provided separately, and an upstream portion and a downstream portion of the system are separated. Accordingly, as compared with a conventional torque limiter, the shafts do not stop suddenly, thereby reducing the torque surge and limiting the torque. Further, not only the side wherein an abnormal torque is generated, but also the other side operates simultaneously to separate the upstream and downstream portions of the system, so that the torque surge can be prevented. Further, it is possible to prevent a situation where just one of rudder surface operates.

In the present invention, it is possible to easily manufacture the torque limiter merely by forming the ball channels in the ball ramp portion in addition to the lamp channels formed in the conventional structure. Accordingly, it is possible to provide a system with such a torque limiter with low cost, light weight and high reliability without providing a separate surge torque buffering apparatus and a brake portion.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

According to an embodiment of the present invention, it is possible to provide a torque limiter with low cost, light weight and high credibility in a power transmission system without providing a buffering apparatus for reducing a torque surge generated by inertia of a rotational body.

FIG. 1is a cross-sectional view of a torque limiter according to an embodiment of the present invention.FIG. 2is a cross-sectional view of a ball ramp portion15of the torque limiter according to the present invention. The torque limiter is composed of two rotational input plates13provided on a drive shaft11at both sides of a drive gear11athrough torque transmitting portions11b; right and left output plates14disposed in right and left output shafts12aand12bto be movable along an axial direction thereof; and ball ramp portions15having two channels, i.e. ball ramp channels21wherein balls6are sandwiched between the both plates, and ball channels22wherein the balls6fall in. With a torque above a predetermined value, the balls6move over the ball ramp channels21and fall in the ball channels22, so that a distance between the input plates13and the output plates14is shortened and a transmission system between the drive shaft11and the output shafts12aand12bis disconnected. The torque limiter is also composed of preload springs17for pressing the ball ramp portions15in an axial direction through the output plates14to prevent the ball ramp channels21from being activated up to a predetermined torque.

Differences between the torque limiter and a conventional torque limiter are as follows. As shown inFIG. 6, in the conventional torque limiter, lamp channels of the ball ramp portion5are formed of slopes with a certain degree. An axial directional component force available for the brake portion8shown inFIG. 5and a spring force of the preload spring7have a proportional relationship. When a torque exceeds a predetermined value, the brake portion8applies brake and stops the drive shaft1, so that the driving torque is not transmitted to the output shaft2.

On the other hand, as shown inFIG. 2, the torque limiter of the invention is provided with the ball channels22in the ball ramp portions15in addition to the ball ramp channels21, so that the balls6fall in the ball channels when the transmitting torque exceeds a predetermined value. When the balls6fall in, a load of the preload springs17is reduced, and a torque that the torque transmitting portion11bcan transmit decreases. Accordingly, a distance between the input plates13and the output plates14is shortened, and an upstream portion and a downstream portion of the system are separated. With this structure, it is possible to limit a torque and prevent the torque surge without the brake portion8shown inFIG. 5.

A configuration of each component of the torque limiter will be explained next. The drive gear11ais supported with bearings provided in housings19and20, and the input plates13are disk-shape plates corresponding to the output shafts12aand12band provided on left and right sides of the torque transmitting portion11bof the drive gear11a. The ball ramp channel21of the ball ramp portion15and the ball channel22are provided in one surface of the input plate13. The ball ramp portions15are located at a circumferential portion, so that a torque is transmitted with a force at an accurate angle.

The output plates14are disposed to be movable in an axial direction on inner circumferences of the output shafts12aand12bsupported by bearings provided in the housings19aand20a. The preload springs17press the output plates14from behind with a certain force, so that the ball ramp portions15are not activated up to a specific torque. The ball ramp portions15are provided at more than three positions on the opposing surfaces of the input plates13and the output plates14, so that the preload springs17press the ball ramp portions15in an axial direction uniformly with a certain force.

The balls6are sandwiched between the input and output plates13and14. The balls6roll in the ball ramp channels21and fall in the ball channels22. When a torque exceeds a predetermined value, the balls6move over the ball ramp channels21and fall in the ball channels22, thereby shortening a distance between the input plates13and the output plates14in an axial direction. As a result, the drive shaft11is separated from the output shafts12aand12bin terms of the torque transmission, and an upstream portion and a downstream portion of the system are separated. With this structure, it is not necessary to provide the brake portion8shown inFIG. 5, and the torque can be limited without generating the torque surge.

A plurality of the preload springs17is provided on the rear surfaces of the output plates14inside the output shafts12aand12balong a circumferential direction. The preload springs17push the output plates14uniformly with a certain force in an axial direction through intermediate metal fittings, so that the ball ramp portions15are pressed in an axial direction, thereby preventing the ball ramp channels21from being activated up to a predetermined torque.

An operation of the torque limiter will be explained next. The ball ramp portions15are respectively provided between the drive shaft11and the right and left output shafts12aand12bthrough the input plates13and the output plates14. When the drive gear11ais rotated, the drive torque is transmitted to the input plates13through the torque transmitting portion11b. The preload springs17apply preload to the ball ramp portions15from the right and left sides. The preload springs17push the output plates14with a certain force in an axial direction, so that the force is transmitted to the balls6in the ball ramp portions15and allows the output shafts12aand12bto rotate.

In a normal state, the torque limiter operates as described above. When a torque above a predetermined value is applied on one of the right and left output shafts12aand12b, the balls6in the ball ramp portion15of the one of the right and left output shafts12aand12bmove over the ball ramp channels21against the preload of the preload springs17, and fall in the ball channel22provided separately. As a result, a length of the ball ramp portion in the axial direction is shortened, so that the preload of the preload springs17decreases. At this time, since the torque transmitting portion11bdoes not receive the preload of the preload springs17, the torque transmitting portion11bmoves in a direction that the balls6move off by the preload of the preload springs17at the other side where the balls6are still held, so that the balls6at the other side also fall in the ball channel22. Accordingly, the torque transmitting portion11bno longer applies a pressing force through the balls6to the right and left sides, so that the drive torque is not transmitted to the output shafts12aand12b.

Namely, in case the output plate does not rotate in association with the input plate by generation of abnormal situation occurring at the output shaft or a portion to which the output shaft is connected to thereby cause an abnormal torque opposite to a rotational direction in the normal situation, the balls are disengaged from the groove. Incidentally, in the above embodiment, the balls in the ball channel22do not automatically return to the original position when the abnormal situation is eliminated. The torque limiter must be disassembled and set once again.

As described above, in the power transmission systems at the right and left sides, not only one power transmission system wherein an abnormal torque is generated shuts off the torque transmission, but also the other power transmission system simultaneously associates with the one power transmission system, so that the both power transmission systems shut the torque transmission. Accordingly, it is possible to prevent asymmetric operation of left and right rudder surfaces, which is critical especially in the aircraft.

The embodiments described above are applied to the torque limiter having the output shafts12aand12bin two directions. The invention is applicable to a torque limiter having an output shaft in one direction.

The disclosures of Japanese Patent Applications No. 2003-362487 filed on Oct. 22, 2003 and No. 2004-164156 filed on Jun. 2, 2004 are incorporated in the application.