Multi-plate clutch transmission and marine vehicle including a multi-plate clutch transmission

A multi-plate clutch transmission includes an arrangement for selectively engaging the clutch by moving the sleeve to cause one or more friction disks on a sleeve connected to a shaft to move into contact with one or more friction disks on a clutch basket connected to a gear driven by another gear and another shaft driven by a prime mover. An arrangement for selectively disengaging the clutch is provided that uses prime mover torque to move the one or more friction disks on the sleeve out of contact with the one or more.friction disks on the clutch basket.

BACKGROUND AND SUMMARY

The present invention relates generally to transmissions and, more particularly, to multi-plate transmissions.

In transmissions for marine vehicles, it is conventional to use dog clutches, cone clutches, and hydraulic plate clutches. A conventional cone clutch for a marine vehicle transmission is shown in U.S. Pat. No. 3,269,497, which is incorporated by reference. The cone clutch operates in three positions. In the neutral position, the cone rotation is stationary while bevel gearing is rotated in mesh via the input shaft to, e.g., a pinion connection. There is a gear above and a gear below the cone clutch and these gears rotate in opposite directions in mesh with the pinion. Each gear has a rigidly attached shift cup facing the cone clutch. As the cone is urged upward by the shift lug shown, it begins to touch the shift cup of the rotating upward gear. Once cup-to-cone contact is made, the resulting frictional forces encourage the cone to rotate in the direction of the adjoining gear. The cone is guided by the output shaft which utilizes a screw thread to pilot and constrain the motion of the cone. Once the friction induced rotation occurs, the screw thread forces the cone upwardly thereby driving it home into the cup of the gear above, thus fully engaging the cup and cone for full torque transmission from the input shaft through the bevel gear through the cup and cone to the output shaft.

When the cone is retracted from the cup by the downward motion of the shift lug, disengagement occurs and the neutral position is achieved. Similarly as the shift lug moves downward, engagement occurs with the lower gear in the same manner and torque transmission occurs in the opposite rotational direction. Careful selection of materials of the cup and cone, as well as specific angles for each, have been highly developed to optimize this type of shift system. The materials required in cone clutch shift systems are necessarily very rigid due to the extremely high axial and radial forces encountered with the cone and cup architecture. Through put torque is transmitted by the frictional forces developed through a normal (non-axial) force between the cone and adjoining cup which is created by the output shaft driving the cone upward or downward by the screw thread on the output shaft.

Due to the use of rigid materials to satisfy the high axial and radial forces inherent in this device, the speed at which engagement occurs, and the associated high accelerations of the gear train inherent with each engagement event of the cone to cup, each engagement is accompanied by an audible “shift clunk.” In the cone clutch type transmission, the non-axial normal force is developed by a helical thread between the cone and output shaft. The frictional forces that result from the non-axial normal force between the cone and cup interaction are responsible for transmitted torque.

Another form of transmission used in marine vehicles is a hydraulic transmission designed with multiple plate wet clutch assemblies to accomplish shifting in a quiet and smooth manner. These types of marine transmissions all utilize an oil pump and a control unit. The oil pump is continuously rotated by the input shaft, and two clutch units are usually rigidly affixed on the input shaft and rotated continuously. A hydraulic control block directs oil flow/pressure to one of the respective clutches rotating in a desired output shaft rotation direction.

In one form of such a hydraulic clutch, a common clutch drum is rigidly affixed to the input shaft which also continuously rotates the oil pump. The oil pump is in flow communication with the clutch drum via separate axial drillings in the input shaft. Oil flow/pressure from the oil pump to the clutch drum is controlled via hydraulic control valves. Two beveled gears are constrained with bearings on the input shaft and are allowed to rotate independently as directed by clutch engagement. The gears are connected in mesh with a common output gear to transmit torque out of the transmission.

The multi-plate wet clutch can be closed by oil pressure to either gear (independently) to accomplish forward or reverse functions. When oil flow/pressure is diverted from the clutch drum by the control valve, the clutch(s) open and neutral is accomplished. In neutral, gears on the input shaft and the output shaft are motionless, as the input shaft, clutch drum, and oil pump continue to rotate. In this manner the forward-neutral-reverse functions are accomplished by the hydraulic transmission.

In this type of hydraulic transmission system, the transmitted torque is directly proportional to the oil pressure that is imposed by the oil pump on the clutch system of given hydraulic piston area and clutch disk contact surface area. Further, a control valve system is required to coordinate clutch functionality. The output shaft remains stationary in the neutral position when oil flow/pressure is directed away from the clutch units leaving them in the “open” position. For forward or reverse functions oil flow/pressure is directed by the hydraulic control valve to either the forward or reverse clutch independently. The hydraulic clutches utilize only axial forces which are developed by the application of oil flow/pressure to the clutch unit. The axial force pushes the planar clutch disks together causing frictional forces to couple the gear to the output shaft for the conveyance of torque through the transmission. Torque transmitted is directly proportional to the oil pressure acting upon a hydraulic piston that in turn forces clutch disks of designed contact area to develop friction in order to transmit torque. Design tradeoffs exist between desired transmitted torque and the necessary size of clutch area and the required pressure of the oil pump. As oil pressure is increased, hydraulic losses increase and are unrecoverable. Quiet smooth shifting is accomplished with a wet clutch assembly at the expense of additional complications such as a dedicated oil pump and hydraulic control valve assembly balanced with the required clutch contact area.

DE1025927 relates to a reversing gear for a train in which torque is transmitted from a bevel pinion to one of two face wheels to a first cage attached to a first one of the face wheels on which clutch plates are provided to clutch plates on a sleeve that is mounted on a threaded part of an output shaft, and from the sleeve to the output shaft. To reverse direction of the output shaft, the system must be stopped. The sleeve is then moved so that clutch plates on a second cage attached to the second face wheel to the clutch plates on, the sleeve, and torque is transmitted from the bevel pinion to the second face wheel to the second cage to clutch plates on the sleeve, and from the sleeve to the output shaft.

It is desirable to provide a transmission that avoids the mechanical “clunk” of a cone clutch. It is also desirable to provide a transmission that can be easily shifted into and out of gear while the engine is running. It is also desirable to provide a transmission that can be efficient, mechanically simple, low weight, and compact and that can be produced at minimal cost.

In accordance with an aspect of the present invention, a multi-plate clutch transmission, comprises a first shaft, a first gear mounted on and non-rotatable relative to the first shaft, a second shaft, a second gear coaxially mounted on and rotatable relative to the second shaft, the second gear engaging with the first gear and being arranged to rotate in a first rotational direction when the first shaft rotates in an first shaft rotational direction, a clutch basket fixed to one of the first gear or the second gear and coaxially mounted on and rotatable relative to one of the first shaft or the second shaft, respectively, the one of the first or second shaft comprising an externally threaded portion with external threads, the clutch basket comprising one or more friction disks extending radially inward from an interior surface of the clutch basket, a sleeve comprising internal threads that mate with the externally threaded portion on the one of the first or second shaft and one or more friction disks extending radially outward from an exterior surface of the sleeve, and means for selectively engaging the clutch by moving the sleeve to cause the one or more friction disks on the sleeve to move into contact with the one or more friction disks on the clutch basket, and means for selectively disengaging the clutch using prime mover torque to move the one or more friction disks on the sleeve out of contact with the one or more friction disks on the clutch basket.

In accordance with a further aspect of the invention, the means for selectively engaging the clutch comprises a groove around a circumference of the sleeve, and an actuator arrangement, the actuator arrangement comprising an actuator body that is pivotable about an axis of rotation of the actuator body between a first position and a second position, a shoe extending from the actuator body, a longitudinal axis of the shoe being offset from the axis of rotation of the actuator body, wherein the shoe is received in the groove and, when the actuator body is in the first position, the shoe is disposed substantially in a center of the groove and the one or more friction disks on the sleeve are out of contact with the one or more friction disks on the clutch basket and, when the actuator body is moved to the second position, the shoe contacts a surface of the groove and moves the sleeve so that the one or more friction disks on the sleeve are moved into contact with the one or more friction disks on the clutch basket.

In accordance with a further aspect of the present invention, the selective disengaging means comprises a groove around a circumference of the sleeve, a longitudinal central axis of the groove being offset from a longitudinal central axis of the sleeve.

In accordance with a further aspect of the present invention, the selective disengaging means further comprises an actuator arrangement, the actuator arrangement comprising an actuator body that is pivotable about an axis of rotation of the actuator body between a first position and a second position, a shoe slidably mounted in and partially extending from a hole in the actuator body, a shoe portion of the shoe being disposed outside of the hole, the hole being offset from the axis of rotation of the actuator body, and a resilient member for urging the shoe away from the hole, wherein the shoe portion is received in the groove and, when the actuator body is in the second position, the shoe portion contacts a surface of the groove and the one or more friction disks on the sleeve are in contact with the one or more friction disks on the clutch basket, and, when the actuator body is urged to move to the first position, the shoe portion contacts an opposite surface of the groove and is urged into the hole and bottoms out relative to the actuator and, as the prime mover causes rotation of the sleeve to continue, contact between the groove and the shoe moves the one or more friction disks on the sleeve out of contact with the one or more friction disks on the clutch basket.

In accordance with yet another aspect of the present invention, a multi-plate clutch transmission comprises a first shaft, a first gear mounted on and non-rotatable relative to the first shaft, a second shaft, a second gear coaxially mounted on and rotatable relative to the second shaft, the second gear engaging with the first gear and being arranged to rotate in a first rotational direction when the first shaft rotates in an first shaft rotational direction, a clutch basket fixed to one of the first gear or the second gear and coaxially mounted on and rotatable relative to one of the first shaft or the second shaft, respectively, the one of the first or second shaft comprising an externally threaded portion with external threads, the clutch basket comprising one or more friction disks extending radially inward from an interior surface of the clutch basket, a sleeve comprising internal threads that mate with the externally threaded portion on the one of the first or second shaft and one or more friction disks extending radially outward from an exterior surface of the sleeve, and means for moving the sleeve to selectively cause the one or more friction disks on the sleeve to move into and out of contact with the one or more friction disks on the clutch basket, wherein a lead angle of the internal and external threads is selected as a function of pressure capacity of material of friction disks on the sleeve and the clutch basket and one or more of

a number of friction disks on the sleeve and the clutch basket,

inner and outer diameters of friction disks on the sleeve and the clutch basket,

a coefficient of friction between material on friction disks on the sleeve and material on friction disks on the clutch basket,

prime mover torque be transmitted,

a gear ratio between the first gear and the second gear, and

a relationship between clutch capacity and idle torque.

In accordance with still another aspect of the present invention, a method of providing a multi-plate clutch transmission is provided, the multi-plate clutch transmission comprising a first shaft, a first gear mounted on and non-rotatable relative to the first shaft, a second shaft, a second gear coaxially mounted on and rotatable relative to the second shaft, the second gear engaging with the first gear and being arranged to rotate in a first rotational direction when the first shaft rotates in an first shaft rotational direction, a clutch basket fixed to one of the first gear or the second gear and coaxially mounted on and rotatable relative to one of the first shaft or the second shaft, respectively, the one of the first or second shaft comprising an externally threaded portion with external threads, the clutch basket comprising one or more friction disks extending radially inward from an interior surface of the clutch basket, a sleeve comprising internal threads that mate with the externally threaded portion on the one of the first or second shaft and one or more friction disks extending radially outward from an exterior surface of the sleeve, and means for moving the sleeve to selectively cause the one or more friction disks on the sleeve to move into and out of contact with the one or more friction disks on the clutch basket. The method comprises selecting a lead angle of the internal and external threads as a function of pressure capacity of material of friction disks on the sleeve and the clutch basket and one or more of

a number of friction disks on the sleeve and the clutch basket,

inner and outer diameters of friction disks on the sleeve and the clutch basket,

a coefficient of friction between material on friction disks on the sleeve and material on friction disks on the clutch basket,

prime mover torque to be transmitted,

a gear ratio between the first gear and the second gear, and

a relationship between clutch capacity and idle torque.

DETAILED DESCRIPTION

FIG.1is a schematic view of a marine vehicle100including a multi-plate clutch (MPC) transmission21according to an aspect of the present invention.FIG.2shows an embodiment of an MPC transmission21according to an aspect of the present invention. The MPC transmission21includes an input shaft23connectable to a prime mover25such as an engine or an electric motor. An input gear27is mounted on and non-rotatable relative to the input shaft23.

The MPC transmission21further comprises an output shaft29, the output shaft comprising an externally threaded portion31with external threads33. An output gear35is coaxially mounted on and rotatable relative to the output shaft29. The output gear35engages with the input gear27and is arranged to rotate in a first rotational direction when the input shaft rotates in an input shaft rotational direction. For example, when the input gear27rotates in a clockwise direction (when viewed along a longitudinal axis ISA of the input shaft23from the input gear toward the prime mover25), the output gear35rotates in a counter-clockwise direction (when viewed in a direction D along a longitudinal axis OSA of the output shaft29from a first end37of the output gear toward a second axial end39of the output gear).

The input gear27and the output gear35(and gear135) can be bevel gears or other suitable types of gears. The input gear27and the output gear35(and gear135) can both be (but need not be) bevel gears, which is useful when it is desirable or necessary to output torque along a different axis than the axis along which torque is input. InFIG.2, for example, the input shaft23is substantially perpendicular to the output shaft29.

An output clutch basket41is fixed to the output gear35in a suitable manner, such as by being welded to or formed integrally with the output gear, and coaxially mounted on and rotatable relative to the output shaft29. The output clutch basket41comprises one or more friction disks43extending radially inward from an interior surface45of the output clutch basket. The friction disks43can be connected to the interior surface45of the output clutch basket41via spline connections or any other suitable arrangement.

A sleeve47is provided around the output shaft29and comprises internal threads49that mate with the external threads33on the externally threaded portion31on the output shaft. The sleeve47also comprises one or more friction disks51extending radially outward from an exterior surface of the sleeve. The sleeve47can be made as a single piece, or in multiple pieces that are attached to each other. The friction disks51can be attached to the exterior surface of the sleeve via spline connections or any other suitable arrangement.

Means is provided for selectively engaging the clutch by moving the sleeve47to cause the one or more friction disks51on the sleeve to move into contact with the one or more friction disks43on the output clutch basket41. The friction disks51and43will ordinarily be made of steel and may have a different, non-steel friction material attached to one or both sides of the disks. A presently preferred selective engaging means can comprise a shift actuator body55that is rotatable or pivotable about a longitudinal axis SAA, such as by moving a lever57(seen inFIGS.3-5) back and forth between at least a first position (FIG.2) in which the MPC transmission is in “neutral” and a second position (FIG.3) in which the MPC transmission is in what shall be designated “forward” for purposes of the present description. The selective engaging means can also include a shoe or lug59that is disposed on an end61of the shift actuator body55and is off-center relative to the shift actuator axis SAA so that, as the shift actuator body pivots about the shift actuator axis, the shoe will be moved relative to the longitudinal axis OSA of the output shaft29(up or down inFIG.2). The shoe59is received in a groove63in an exterior surface65(FIG.6) of the sleeve47so that, when the shift actuator body55is pivoted about its longitudinal axis SAA and the shoe is moved down (to the position shown inFIG.3), the one or more friction disks51on the sleeve move into contact with the one or more friction disks43on the output clutch basket41.

When the clutch is engaged as is seen inFIG.3, i.e. the one or more friction disks51on the sleeve47contact the one or more friction disks43on the output clutch basket41, and the prime mover25is running, torque transmitted from the prime mover to the input shaft23is transmitted from the input shaft, to the input gear27, to the output gear35, through the friction disks51and43, to the sleeve47, to the output shaft29. Resistance to turning of the output shaft29, such as is applied by water against a propeller102(FIG.1) attached to the output shaft, causes the sleeve47to be screwed downwardly along the external threads33on the output shaft and, in addition to keeping the friction disks51on the sleeve47in contact the one or more friction disks43on the output clutch basket41, prevents the friction disks on the sleeve from moving out of contact with the friction disks on the output clutch basket.

To assist in overcoming the force tending to keep the friction disks51on the sleeve47in contact the one or more friction disks43on the output clutch basket41, means is also provided for selectively disengaging the clutch using prime mover torque to move the friction disks on the sleeve out of contact with the friction disks on the output clutch basket. In a presently preferred embodiment of the selective disengaging means the groove63comprises a V-shaped groove around a circumference of the sleeve47, a longitudinal central axis GA of the groove being offset from a longitudinal central axis SA of the sleeve (which is usually coaxial with the longitudinal axis OSA of the output shaft29). It will be appreciated that the groove63need not necessarily be V-shaped and may, for example, be more U-shaped with walls that approach perpendicular to the axis of the sleeve47, however, it is presently believed that a V-shape will facilitate disengagement by facilitating sliding of the actuator shoe relative to the groove.

The selective disengaging means also comprises the actuator arrangement that comprises the shift actuator body55that is pivotable about an axis of rotation SAA of the actuator body between at least the first position and the second position. The shoe59can be slidably mounted in and partially extend from a hole69in the actuator body, a shoe portion59aof the shoe being disposed outside of the hole. The hole69is offset from the axis of rotation SAA of the actuator body55. A resilient member71such as a spring, is provided in the hole69for urging the shoe59away from the hole. The shoe portion59ais received in the groove63and, when the actuator body is in the second position (FIG.3), the shoe portion contacts a surface63a(FIGS.3and6) of the groove on the side of the groove to which the sleeve has been moved and the one or more friction disks51on the sleeve47are in contact with the one or more friction disks43on the output clutch basket41.

When, as seen inFIG.4, the actuator body55is urged to move from the second position (FIG.3) back to the first position, the shoe portion59acontacts an opposite surface63b(FIGS.4-6) of the groove63and, ordinarily due to the angle of the groove (and, usually, the angle of the shoe portion), the shoe portion slides up the opposite surface63bof the groove and the shoe is urged into the hole69and eventually bottoms out relative to the actuator body, usually either by the shoe bottoming out in the hole, or the shoe portion bottoming out against a surface55aof the actuator body. Meanwhile, the prime mover25causes rotation of the sleeve47to continue. Contact between the groove63and the shoe portion59amoves the one or more friction disks51on the sleeve47out of contact with the one or more friction disks43on the output clutch basket41.

To further explain, when the shift actuator body55is urged toward the neutral position as seen inFIG.4, the shoe59moves (upwardly inFIG.4) into contact with the opposite face63bof the (ordinarily V-shaped) groove63and the shoe portion59aslides up the surface of the groove against the force of the resilient member71toward the shift actuator body55until it bottoms out relative to the actuator body. When the sleeve47spins, the offset groove63pushes toward the right inFIG.4which, correspondingly, tries to push the shoe59toward the right, i.e. toward the actuator body55. The amount of offset between GA and SA can be relatively small, with a presently preferred offset being about 0.5 mm, however, this amount of offset means that the surface of the groove63moves in and out about 1 mm in a direction perpendicular to a longitudinal axis of the sleeve47about 1 mm each time the sleeve spins around its longitudinal axis. Because the shoe59is bottomed out relative to the actuator body55in this position, it is unable to move any further to the right. Under these circumstances, the only way for the system to resolve is for the sleeve47to move upward, pulling the MPC transmission out of forward gear into neutral gear (FIG.2) in which that the friction disks51on the sleeve47are moved out of contact with the friction disks43on the output clutch basket41, i.e. using prime mover torque.

U.S. Pat. Nos. 3,269,497, 3,915,270, 4,630,719, and 5,096,034 describe illustrative means for selectively disengaging a cone clutch using prime mover torque that are suitable for use as the means for selectively disengaging the multi-plate clutch according to the present invention using prime mover torque, and both are incorporated by reference herein.

The MPC transmission21will ordinarily also be provided with structure for rotating the output shaft29in the direction opposite the “forward” direction ofFIG.3, i.e. in what shall be designated for purposes of the present description as “reverse”, as shown inFIG.5. The structure for rotating the output shaft29in reverse is similar to the structure for rotating the output shall in the forward direction and comprises a second output gear135coaxially mounted on and rotatable relative to the output shaft29, the second output gear engaging with the input gear27and being arranged to rotate in a second rotational direction when the input shaft rotates in an input shaft rotational direction. For example, when the input gear27rotates in a clockwise direction (when viewed along a longitudinal axis ISA of the input shaft23from the input gear toward the prime mover25), the second output gear135rotates in a clockwise direction (when viewed along a longitudinal axis OSA of the output shaft29in the direction D). The first rotational direction (for “forward”) and the second rotational direction (for “reverse”) are ordinarily opposite to each other.

A second output clutch basket141is fixed to the second output gear135and is coaxially mounted on and rotatable relative to the output shaft29. The second output clutch basket141comprises one or more friction disks143extending radially inward from an interior surface145of the output clutch basket. When the friction disks143of the second output clutch basket141contact the friction disks51on the sleeve47, torque is transmitted from the sleeve to the output shaft29so that the output shaft rotates in “reverse”. The torque transmission is thus from the prime mover25to the input shaft23to the input gear27to the second output gear135to the output clutch basket143and the friction disks151on the output clinch basket to the friction disks51on the sleeve and the sleeve47, and then to the output shaft29.

Because less torque is typically transmitted in “reverse” than in “forward”, it may be possible to use fewer friction plates in the clutch basket and sleeve portion used to transmit torque in reverse than in the clutch basket and sleeve portion used to transmit torque in forward gear.

In substantially the same manner as described in connection with shifting between “neutral” and “forward” and back to “neutral”, the selective engaging means for selectively engaging the clutch is adapted to move the sleeve47(up inFIG.2) to cause the one or more friction disks51on the sleeve47to move into contact with the one or more friction disks143on the second output clutch basket141(i.e., from “neutral” to “reverse”), and the means for selectively disengaging the clutch using prime mover torque is configured to move the one or more friction disks on the sleeve out of contact with the one or more friction disks on the second output clutch basket (i.e. from “reverse” to “neutral”).

In a typical marine transmission application, the MPC transmission will be arranged as shown inFIGS.2-5, with the output gear35disposed below the output gear135. The input gear27and the output gears35and135will ordinarily be disposed in a case (not shown). The output gear35will typically be submerged in lubricating oil in the case, while the output gear135will typically be disposed above the liquid level of the lubricating oil, but will be lubricated by spray from rotating components in the case.

It will be observed that, in the “neutral” position (FIG.2) the friction disks51on the sleeve47float freely as the gears rotate the driven disks43and143in opposite directions. For forward gear, the sleeve47is moved downwardly to the position as seen inFIG.3by the selective engaging means until the friction disks'51proximity to the friction disks43is reduced to induce hydrodynamic drag force. This drag force, and resistance to turning of the output shaft29from water acting against the propeller102, in turn induces the output shaft's29screw thread33to drive the sleeve47downward causing an axial force utilized to clamp the friction disks51to the driven friction disks43for the transmission of torque through the transmission. Disengagement is accomplished by the upward motion of the sleeve47. “Reverse” is accomplished the sleeve47being moved upwardly to the position seen inFIG.5by the selective engaging means until the friction disks'51proximity to the friction disks143is reduced to induce hydrodynamic drag force. This drag force in turn induces the output shaft's29screw thread33to drive the sleeve47upward causing an axial force utilized to clamp the friction disks51to the driven friction disks143for the transmission of torque through the transmission.

Ordinarily, only axial forces are utilized to engage the friction disks51and43or143. Further, the disks are preferably not hard rigid surfaces so the shift event need not be characterized by, e.g., harsh contact of a cone and clutch. Additionally, an oil film is maintained between the friction disks51and the driven friction disks43and143and a controlled rate of acceleration of the gear train system is achieved. The friction disks43and143on the output clutch basket141can comprise a plurality of grooves73extending to an outside diameter of the disks as seen inFIG.7to facilitate removal of oil between the friction disks on the output clutch basket and the friction disks41on the sleeve47. The structure and composition of the clutch disks and the oil film characteristics work together to accomplish a controlled acceleration of the gear train for a silent shift event.

In the present invention, movement of the sleeve47longitudinally along the output shaft29is ordinarily primarily or, preferably, exclusively limited by contact between the friction disks51on the sleeve and the friction disks43or143on the first or second output clutch baskets41or141, which permits the MPC transmission21to involve a minimal number of components. Axial forces are utilized to engage the friction disks51and43and143.

When the MPC transmission21is in gear, the output shaft29is loaded by resistance to turning a propeller (FIG.1,102) on the output shaft from water and therefore the output shaft screw thread applies a clamp load on the friction disks51and43and143. The design and thread lead of the shaft lead screw thread must be chosen in such a way that that several different functions are not adversely affected:1. Torque capacity: The clamp load needs to be high enough to carry the torque of the engine at full load;2. Torque capacity: The clamp load needs to be high enough to carry the torque at low load (idle speed in gear);3. Clutch plate friction material durability: The clamp load cannot be so high that the friction material of the clutch plates is damaged; and4. Disengagement force: The clamp load needs to be low when disengaging the clutch.
In general, the larger the lead angle on the output shaft29and the sleeve47, the less force is applied on the friction disks, making the assembly less efficient at transmitting torque. Also, the larger the lead angle on the output shaft29and the sleeve, the easier it is to move between gears.

Accordingly, preferably, the lead angle Θ of the internal threads49(FIG.6) on the sleeve47and the external threads33on the output shaft29is selected as a function of pressure capacity of material of friction disks51and43and143on the sleeve47and the output clutch baskets41and141and one or more ofa number of friction disks on the sleeve and the output clutch basket. The larger the lead angle, the less force is applied on the friction disks and, therefore, more plates may be needed to transmit the desired torque if the lead angle is increased.inner and outer diameters of friction disks on the sleeve and the output clutch basket. The larger the lead angle, the less force is applied on the friction disks and, therefore, larger diameter plates may be needed to transmit the desired torque if the lead angle is increased.a coefficient of friction between material on friction disks on the sleeve and material on friction disks on the output clutch basket. The larger the lead angle, the less force is applied on the friction disks and, therefore, a higher coefficient of friction between the plates may be needed to transmit the desired torque if the lead angle is increased.prime mover torque to be transmitted. A larger lead angle applies less force on the friction disks, so a smaller angle is needed to transmit more torque.a gear ratio between the input gear and the output gear. The larger the lead angle, the less force is applied on the friction disks. At higher gear reductions, a higher torque capacity is needed.a relationship between clutch torque transmitting capacity and idle torque. The larger the lead angle, the less force is applied on the friction disks so the clutch has less torque transmitting capacity but is easier to shift out of gear. The smaller the lead angle, the more force is applied on the friction disks so the clutch has more torque transmitting capacity but is harder to shift out of gear.

The lead angle Θ of the internal and external threads is preferably between 1 and 90 degrees, more preferably between 15 and 70 degrees, and still more preferably between 30 and 50 degrees.

A pressure capacity of the material of the friction disks51and43and143on the sleeve47and the output clutch baskets41and141is preferably at least 5 MPa, more preferably at least 10 MPa, and still more preferably at least 20 MPa.

The friction disks41and43and143on the sleeve47and each output clutch basket41and141preferably each include between 1 and 25 friction surfaces, where friction surfaces are defined here as surfaces that are intended to be used to transmit torque and that may, but need not necessarily, be a specially adapted material attached to e.g., a steel disk, more preferably between 5 and 15 surfaces, and still more preferably between 6 and 8 surfaces. It will be appreciated that not all friction disks necessarily have friction surfaces on each side.

The coefficient of friction between material on friction disks on the sleeve and material on friction disks on the output clutch basket is preferably between 0.05 and 0.2, more preferably between 0.075 and 0.175, and, still more preferably between 0.1 and 0.15.

The gear ratio between the input gear and the output gear is preferably between 1:1 and 3:1, more preferably between 1:1 and 2:1, and still more preferably between 1:1 and 1.3:1.

The MPC transmission is an over running, i.e. one directional, clutch in the sense that the clutch only connects in the direction of the prime mover to the driven member, e.g., the propeller, not in the other direction. Reducing the prime mover rpm is independent of propeller rpm, while increasing prime mover rpm is dependent on the propeller rpm, as that is the main function of the clutch.

Via the MPC transmission according to the present invention, axial forces are utilized in the engagement of the clutch system to press the friction surfaces of the friction disks together, which can facilitate a smooth, gradual engagement of the gears, avoiding the “clunk” typically associated with certain types of transmissions that engage quickly.

The MPC transmission according to the present invention does not require an oil pump to generate pressures/forces for clutch operation, thus permitting the MPC transmission to be provided at relatively low cost.

Actuation forces to close the MPC transmission according to the present invention are generated by a helical thread on the output shaft engaged with the clutch actuator. This enables the clutch to carry engine torque without applying external axial force on the friction disks. The axial force is generated from the threaded connection.

The MPC transmission according to the present invention is within the gear mesh geometry of a convention bevel gearing system, i.e. the clutch can fit inside of an existing gear set and can be compact.

In the MPC transmission according to the present invention, forward and reverse clutch disk diameters can be less than the pitch diameter of the bevel gear system and can rotate continuously in opposite directions, facilitating production of an MPC transmission of small size.

In the MPC transmission according to the present invention, the clutch baskets can be affixed to bevel gears and face the center of gear mesh, facilitating production of a compact MPC transmission with few parts that is simple to manufacture and durable.

In the MPC transmission according to the present invention, a single clutch/shift actuator need not be fixed to the output shaft but, instead, is constrained to move axially with a helical screw thread. In a hydraulic clutch, the hydraulic pistons ordinarily spin with the shaft.

In the MPC transmission according to the present invention, a single, self-actuating sleeve moves axially on a single, central helix to accomplish F-N-R shift functions in opposing directions, facilitating production of an MPC transmission with minimal parts.

In the MPC transmission according to the present invention, a single sleeve is engaged simultaneously to both forward and reverse clutch disks with a linear spline where the clutch disks are equally spaced above and below the sleeve's center.

In the MPC transmission according to the present invention, the system can operate between vertically disposed clutches with each clutch basket rigidly attached to the facing side of bevel gearing where a single shift actuator (sleeve) can move vertically on a helix that creates engagement forces due to induced drag from the adjoining clutch disk surfaces.

In the MPC transmission according to the present invention, the sleeve is constrained with a helical screw thread at the extreme ends of the sleeve for concentric stability, where each thread can pilot the sleeve in close proximity to the clutch disks location for concentricity of the friction disks (constrained by the bevel gear face), providing for a simple construction.

In an aspect of the MPC transmission shown inFIGS.2-5according to the present invention, the input shaft is not connected to or constraining forward or reverse clutch systems.

The MPC transmission21shown in, e.g.,FIGS.2-5includes the input gear27non-rotatably mounted on the input shaft23. The input gear27meshes with two output gears35and135rotatably mounted on the output shaft29. Output clutch baskets41and141with friction disks43and143are fixed to the output gears35and135, respectively. The sleeve47provided with friction disks51and having internal threads49is mounted on an externally threaded portion31of the output shaft29and is moved along the output shaft by a shift actuator.

It will be appreciated that the MPC transmission according to the present invention can, alternatively, be arranged as shown inFIG.8. In the MPC transmission321ofFIG.8, the output gear335is non-rotatably mounted on the output shaft329. The output gear335meshes with two input gears327and427rotatably mounted on the input shaft323. Input clutch baskets341and441with friction disks343and443are fixed to the input gears327and327, respectively. The sleeve47provided with friction disks51and having internal threads (not seen inFIG.8) is mounted on an externally threaded portion331of the input shaft323and is moved along the output shaft by a shift actuator355to engage and disengage the clutch in the same manner as describe above with respect to the MPC transmission21shown inFIGS.2-5. The MPC transmission321can be substituted for the MPC transmission21shown inFIGS.2-5in the marine vehicle100shown inFIG.1.

In the present application, the use of terms such as “including” is open-ended and is intended to have the same meaning as terms such as “comprising” and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as “can” or “may” is intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such.

While this invention has been illustrated and described in accordance with a preferred embodiment, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims.