Power Transmission

Abstract: A power transmission comprising a drive shaft and a driven shaft connected to each other to be relatively rotatable within a predetermined range. The connection between the two shafts includes a cam member axially slidable on the driven shaft. The driven shaft carries a brake device interlocked with the cam member. When an accelerating force is transmitted from ground wheels to the driven shaft, the cam member slides axially of the driven shaft. This sliding movement causes the brake device to brake the driven shaft.

Description: TECHNICAL FIELD The present invention relates to power transmissions, and more particularly to a power transmission for a vehicle which prevents the vehicle from being accelerated by gravity when travelling down an inclined terrain. BACKGROUND OF THE INVENTION Conventionally, when an agricultural tractor, a passenger vehicle or the like is running, the wheels and engine are interconnected through a reduction system. When the vehicle travels down an inclined terrain, the engine brake is operable to suppress acceleration of the vehicle by gravity. Fig. 5 shows a commonly known transmission for a vehicle. This transmission comprises a propelling line for transmitting power from an engine 1 to a running device 3 through a hydraulic clutch 31 and a first transmission gearing 32, and a propelling line for transmitting power from the engine 1 to the running device 3 through a second transmission gearing 33, a one-way clutch 34 and a transmission shaft 35. With this transmission, when the hydraulic clutch 31 is disengaged, the power is changed into a plurality of speeds by the second transmission gearing 33 and transmitted to the running device 3 through the transmission shaft 35. When the hydraulic clutch 31 is engaged, the power is changed into a plurality of speeds by the first transmission gearing 32 for transmission to the running device 3. The first transmission gearing 32 provides higher rotational rates than the second transmission gearing 33. The one-way clutch 34 is mounted in the transmission to enable the different rotational rates. When, for example, the vehicle travels down an inclined terrain with the hydraulic clutch 31 disengaged, an accelerating force due to gravity is transmitted through the running device 3 to the transmission shaft 35. With this transmission, however, the one-way clutch 34, which is constructed to allow the higher rotational rates than those transmitted from the second transmission gearing 33, will allow the transmission shaft 35 to be accelerated by such a force. As a result, the vehicle will be accelerated without limitation. Thus, there is room for improvement from the safety point of view. Among the transmissions being developed recently is one shown in U.S. Patent 4,487,085, which steplessly changes the speed of power with a combination of a cam, a roller, a one-way clutch and the like. As disclosed in the above patent, the one-way clutch is connected in series to a propelling line. Such a transmission, as does the transmission shown in Fig. 5, has room for improvement from the safety point of view since the vehicle will be accelerated while traveling down an inclined terrain. It is conceivable to provide a transmission mechanism comprising a worm gear between the transmission and running device to prevent acceleration of the running device. However, a transmission having such a worm gear not only entails a substantial power loss during a normal run, but results in enlargement of the transmission per se. This construction too has room for improvement. It is to be noted that, in a transmission having a worm gear, the worm gear is meshed with a wheel gear, and use is made of the feature that the wheel gear is rotatable by rotation of the worm gear but not vice versa. A power transmission device of the kind defined by the precharacterizing features of the claim is known from the GB-A-869 859. This power transmission device is constructed to transmit power without any power loss during a normal run and restricts acceleration due to an external cause, thereby overcoming the disadvantage discussed above along Fig. 5. This known power transmission, however, has room for improvement concerning the transmission of the movement of the displacing means to the brake means. The FR-A-2 218 788 is concerned with a clutch brake comprising a lever mechanism for urging an axially movable cam means against an axially fixed cam means bearing a brake member. The lever mechanism is disposed between the axially movable cam means and an axially fixed elastomeric member, said axially movable cam means being adapted to engage the axially fixed cam means also in the case that the axially displaceable cam means is becoming displaced against the elastomeric member where the lever mechanism is engaged between the elastomeric member and the axially displaceable cam means, thereby strongly forcing the brake member on the axially fixed cam means against a support at the casing of the clutch brake. SUMMARY OF THE INVENTION It is the object of the present invention to improve the transmission of the displacement of the displacing means to the brake means of the power transmission defined by the precharacterizing features of the claim. This object is attained by the characterizing features of the claim. The invention features a lever type control arm having a transmission amplification function so that the axial sliding movement of the displacing means moves the pressure plate of the brake means between a pressurizing position and a released position. BRIEF DESCRIPTION OF THE DRAWINGS The drawings show transmissions according to the present invention, in which:- Fig. 1 is a sectional view of a transmission, Fig. 2 is a sectional view showing the shape of a cam mechanism, Fig. 3 is a sectional view of a transmission in a different embodiment of the invention, Fig. 4 is a section taken on line IV-IV of Fig. 3, and Fig. 5 is a schematic view of a conventional transmission. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1, a propelling transmission system of a vehicle comprises a change speed device 2 and a transmission A for transmitting power from an engine 1 to a running device 3 including ground wheels. The change speed device 2 is constructed to allow its output portion to rotate when a higher rotational rate than an output rotational rate is transmitted to the output portion. Acceleration of the vehicle is suppressed by the transmission A shown in Fig. 1. Referring to Figs. 1 and 2, the transmission A includes a first shaft 4 for receiving the power from the change speed device 2, and a second shaft 5 for transmitting the power to the running device 3. The first and second shafts 4 and 5 are coupled to each other through a connection B which allows variations in rotational phase within a predetermined range between the two shafts 4 and 5. This connection B includes a drive cam 6 splined to the first shaft 4, and a driven cam 7 splined to the second shaft 5. As shown in Fig. 2, the drive cam 6 defines a recess 6a and a stopper 6b continuous with the recess 6a. The driven cam 7 defines a projection 7a which is allowed to move circumferentially (in directions of rotation) only within a region in which the projection 7a contacts the stopper 6b. This movement causes the driven cam 7 to slide axially of the first and second shafts 4 and 5. The second shaft 5 carries a brake disk 8 splined thereto through a holder 9. The brake disk 8 is sandwiched between a friction plate 10 and a pressure plate 11. The pressure plate 11 is interlocked with the driven cam 7 through a release bearing 12 and a lever type control arm 13 having a transmission amplifying function, so that the axial sliding movement of the driven cam 7 moves the pressure plate 11 between a pressurizing position and a release position. Further, braking springs 14 are provided to apply a force to the pressure plate 11. The above is an outline of the transmission A. The brake disk 8, friction plate 10, pressure plate 11 and so on constitute a brake device C. The first and second shafts 4 and 5 are supported by a casing 16 of the transmission A through bearings 15. The friction plate 10 is supported directly by the casing 16. The control arm 13 is supported by the casing 16 through a support shaft 17. When a force is applied from the running device 3 to the second shaft 5 to cause an overrun of the latter, the driven cam 7 will slide closer to the drive cam 6. As a result, the brake device C applies a braking force resembling an engine brake to the second shaft 5. Figs. 3 and 4 show another embodiment of the present invention, which differs from the foregoing embodiment in the way in which a displacement of a cam 70 is transmitted to a brake device. The brake device of this embodiment comprises a plurality of disks. In this embodiment, a connection B is formed by splines 4a and 5a of the first and second shafts 4 and 5, respectively, with some freedom of movement allowed therebetween. The brake device C includes friction disks 21 attached to the casing, friction disks 22 mounted on the second shaft 5, and a control member 24 supported by the second shaft 5 through a shaft 23. The control member 24 is operable in a braking direction by a displacement of a cam member 70 in contact with a cam 25 on the first shaft 4. The present invention may be put to practice in various ways, such as with the brake device comprising the drum brake type, with the cam member comprising pins for contacting a cam surface, or with the cam member mounted on a shaft through a ball spline for smooth sliding movement of the cam member.

Claims: A power transmission comprising: a casing (16), a first shaft (4) acting substantially as a drive shaft, a second shaft (5) acting substantially as a driven shaft, a connection (B) provided in said casing (16) between said first shaft (4) and said second shaft (5), said connection (B) including connecting means (6, 7) for interconnecting said first shaft (4) and said second shaft (5) in a way to allow a relative rotational displacement therebetween, and axially displaceable displacing means (7) displaceable with the rotational displacement occurring between said first shaft (4) and said second shaft (5), and brake means (C) for braking said second shaft (5) in response to the displacement of said displacing means (7), characterized in that said connecting means includes a first cam (6) mounted on said first shaft (4) and having engaging teeth (6b) formed on a peripheral surface thereof, and a second cam (7) mounted on said second shaft (5) and having engaging teeth (7a) formed on a peripheral surface thereof, said engaging teeth (6b, 7a) of said first and second cams (6, 7) having contacting surfaces with spacing therebetween variable with a relative circumferential displacement between said cams (6, 7), said second cam (7) is splined to said second shaft (5) and acts as said displacing means (7) displaceable axially of said second shaft (5), said brake means (C) includes a brake disk (8) mounted on said second shaft (5) between a pressure plate (11) movable relative to said brake disk (8) and friction plate (10) supported by said casing (16) and interlocking means (13) for moving said pressure plate (11) in response to the axial displacement of said second cam (7), wherein said interlocking means comprises a lever mechanism (13) for amplifying a displacing force from said second cam (7) and transmitting the displacing force to said pressure plate (11).

Inventors: FUKUI TETSU SAKAI SEIZOSHO -BA, OOTA YOSHIMI SAKAI SEIZOSHO -B, FUKUI, TETSU, SAKAI SEIZOSHO, 64-BANCHI, OOTA, YOSHIMI, SAKAI SEIZOSHO, 64-BANCHI
Applicants: KUBOTA KK, KUBOTA CORPORATION
Application year: 1990
Main classification: F16D59
IPC codes: F16D59, B60T7, F16D67