Abstract:
A marine transmission for connecting a driven shaft to a driving shaft is provided with first and second dog clutch members and first and second friction clutch members which are actuated, respectively, by first and second hydraulically actuated devices. Engagement of the friction clutch members with each other creates rotation in the driven shaft that approaches or equals the rotational speed of the driving shaft so that subsequent engagement of the first and second dog clutch members can be accomplished without significant relative rotational speed differences between the two dog clutch members.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a dog clutch transmission for a marine vessel and, more particularly, to a marine transmission which incorporates both friction and dog clutch mechanisms in cooperation with hydraulic actuators that at least partially synchronize the rotational speed of a driving shaft and a driven shaft prior to engagement of the dog clutch elements. 
     2. Description of the Prior Art 
     Dog clutches of various types are well known to those skilled in the art and are used in many different variations of marine transmissions. 
     U.S. Pat. No. 1,931,288 which was granted to Griswold on Oct. 17, 1933, describes a transmission with an improved device for synchronizing the gear elements and in which the operation of the synchronizing clutches are affected through rotating parts not subjected to high relative speeds. 
     U.S. Pat. No. 2,091,557, which was granted to Montgomery on Aug. 31, 1937, describes a marine power transmission with a clutch housing located between an engine and the transom of a marine vessel. This application is intended to adapt high speed automotive or industrial-type engines to marine use. 
     U.S. Pat. No. 3,563,354, which issued to Sigg on Feb. 16, 1971, describes an automatically engaging and disengaging dog clutch. The dog clutch is disposed between an input shaft and an output shaft and includes a first straight-toothed clutch boss, a second helical-tooth clutch boss, an axially slidable clutch spider and a synchronizing sleeve which is retained against axial movement in the clutch spider. 
     U.S. Pat. No. 3,919,964, which issued to Hagen on Nov. 18, 1975, describes a marine propulsion reversing transmission with a hydraulic assist. The transmission is located in a propulsion unit and connected to a drive shaft and to a propeller shaft. It is shiftable between neutral, forward drive, and rearward drive conditions. 
     U.S. Pat. No. 4,349,091, which issued to Miyake et al. on Sep. 14, 1982, describes a synchronized dog clutch. It comprises a clutch shaft, a coupling sleeve splined to the clutch shaft and dog claws at its end. A synchronizer ring is slidably fitted to the outer periphery of the coupling sleeve and has a conical face for friction engagement. 
     U.S. Pat. No. 4,811,825, which issued to Christian et al. on Mar. 14, 1989, describes a dog clutch with locking synchronization. A synchronizer body and a gear turning with a different rotational speed are coupled together with the aid of an axially displaceable, annularly shaped sliding sleeve when synchronized. 
     U.S. Pat. No. 5,170,872, which issued to Salicini on Dec. 15, 1992, describes a synchronizer for activating and deactivating a dog clutch, particularly in article wrapping machines. The outputs of a pair of intermittence devices operated in phase with a clutch driving shaft is described. Electromagnetic friction clutches allow outputs to be connected to the driven disc of the clutch. 
     U.S. Pat. No. 6,062,360, which issued to Shields on May 16, 2000, discloses a synchronizer for a gear shift mechanism for a marine propulsion system. A synchronized gear shift mechanism is provided for a marine propulsion system. Using a hub and a sleeve that are axially movable relative to an output shaft but rotationally fixed to the shaft and to each other, the gear shift mechanism uses associated friction surfaces to bring the output shaft up to a speed that is in synchronism with the selected forward or reverse gear prior to mating associated gear tooth surfaces together to transmit torque from an input shaft to an output shaft. The friction surfaces on the forward and reverse gears can be replaced to facilitate repair after the friction surfaces experience wear. 
     U.S. Pat. No. 6,460,425, which issued Bowen on Oct. 8, 2002, describes a twin clutch automated transmission. The transmission includes a first engine clutch operable to establish a releasable drive connection between the engine and a first input shaft, a second engine clutch operable to establish a releasable drive connection between the engine and a second input shaft, an output shaft and a gear trained for selectively establishing a plurality of forward and reverse speed ratio drive connections between the input shafts and the output shaft. 
     U.S. Pat. No. 6,672,180, which issued to Forsyth on Jan. 6, 2004, describes a manual transmission with upshift and downshift synchronization clutches. An automated multi-speed transmission includes an engine clutch operable to establish a releasable drive connection between the engine and an input shaft, an output shaft adapted to transfer power to the drive line, and a synchromesh gear train having a plurality of constant mesh gear sets that can be selectively engaged to establish a plurality of forward and reverse speed ratios. 
     U.S. Pat. No. 6,571,654, which issued to Forsyth on Jun. 3, 2003, describes an automated manual transmission with upshift ball ramp synchronizer clutch and downshift ball ramp synchronizer clutch. The transmission includes an engine clutch operable to establish a releasable drive connection between the engine and an input shaft, an output shaft adapted to transfer power to the drive line, and a synchromesh gear train having a plurality of constant mesh gear sets that can be selectively engaged to establish a plurality of forward and reverse gear speed ratios. 
     The patents described above are hereby expressly incorporated by reference in the description of the present invention. 
     In marine transmissions, dog clutches are commonly used to connect a driving shaft to a driven shaft in either a forward or reverse direction. It would be helpful and beneficial if a marine transmission could provide a means for diminishing the impact during initial contact between dog clutch surfaces that creates a noise when the transmission is shifted from neutral to either forward or reverse gears. 
     SUMMARY OF THE INVENTION 
     A marine transmission made in accordance with a preferred embodiment of the present invention comprises a driving shaft and a driven shaft, a first dog clutch member and a second dog clutch member, a first friction clutch member and a second friction clutch member, a first hydraulically actuated device configured to cause the first and second friction clutch members to move into torque transmitting relation with each other and a second hydraulically actuated device configured to cause the first and second dog clutch members to move into torque transmitting relation with each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more fully and clearly understood from a reading of the description of the preferred embodiment in conjunction with the drawing, in which: 
         FIG. 1  is a section view of the marine transmission of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a section view taken through a transmission in a preferred embodiment of the present invention along a central axis of its driving and driven shafts. A driving shaft  10  is connectable in torque transmitting association with a source of motive power, such as an engine. A driven shaft  12  is connectable in torque transmitting association with a propulsor, such as a propeller system of a sterndrive apparatus. A first dog clutch member  20  is shown attached to the driving shaft  10 . A second dog clutch member  22  is shown slidably attached to the driven shaft  12  by a configuration of axial splines which are identified by reference numeral  26 . Arrow A illustrates the possible axial motion of the second dog clutch member  22  which is made possible by the use of the splines  26  which connect the second dog clutch member  22  to the driven shaft  12  in such a way that the second dog clutch member  22  rotates in unison with the driven shaft  12 , but is able to slide axially relative to the driven shaft  12 , as indicated by arrow A. 
     With continued reference to  FIG. 1 , a first friction clutch member  30  is attached to the driving shaft  10 . A second friction clutch member  32  is attached to the driven shaft  12 . In the illustration shown in  FIG. 1 , the second friction clutch member actually comprises two backing plates which are identified by reference numerals  32  and  33 . A first hydraulically actuated device  40  is configured to cause the first and second friction clutch members,  30  and  32 , to move into torque transmitting contact with each other. In other words, when the first hydraulically actuated device  40  pushes the backing plates,  32  and  33 , of the second friction clutch member together, they move into frictional torque transmitting association with the first friction clutch member  30  which is disposed between them. Since the first friction clutch member  30  is attached to the driving shaft  10  and the second friction clutch member  32  (along with backing plate  33 ) are attached to the driven shaft  12  the frictional contact between these friction clutch members transmits torque between the driving shaft  10  and the driven shaft  12 . Although it is not intended that this frictional connection be sufficient to transmit the full torque from the engine to the propulsor under all conditions, it is sufficient to cause the driven shaft  12  to begin to rotate about its axis of rotation  50 . 
     With continued reference to  FIG. 1 , a second hydraulically actuated device  60  is configured to cause the first and second dog clutch members,  20  and  22 , to move into torque transmitting contact with each other. In other words, when the second hydraulically actuated device  60  is energized with hydraulic pressure, it pushes the second dog clutch member  22  toward the right in  FIG. 1  and engages it with the first dog clutch member  20 . Although not shown in the section view of  FIG. 1 , it should be understood that mating dog clutch teeth are provided on surface  70  of the first dog clutch member  20  and on surface  72  of the second dog clutch member  22 . When these two faces move toward each other and into contact with each other, torque can be transferred directly from the driving shaft  10  to the second dog clutch member  22  and, through the splines  26 , to the driven shaft  12 . 
     In the preferred embodiment of the present invention illustrated in  FIG. 1 , the axis of the driving and driven shafts,  10  and  12 , are coaxial with each other. This coaxial relationship is identified by reference numeral  50 . 
     Although two pistons are shown in  FIG. 1  to represent the second hydraulically actuated device, it should be understood that typically three or more pistons would be disposed around a circular path and contained within the driven shaft  12  in a preferred embodiment. Similarly, although two pistons are shown in  FIG. 1  to represent the first hydraulically actuated device  40 , three or more pistons would typically be distributed evenly around a circumferential pattern which is generally coaxial with axis  50 . A first port  81  is provided in the housing portion  86  of the transmission to conduct hydraulic fluid to the first hydraulically actuated device  40 . A second port  82  is used to conduct hydraulic fluid to the second hydraulically actuated device  60 . Seals  91 – 93  are located between the outer cylindrical surface of the driven shaft  12  and the inner cylindrical surface in the housing  86  through which the driven shaft extends. These seals,  91 – 93 , define first and second hydraulic fluid passages,  96  and  98 , which extend annularly around the outer surface of the driven shaft  12  between the seals,  91 – 93 . This allows hydraulic fluid to be conducted from the first port  81  and through conduit  101  to the first hydraulically actuated device  40 , which can comprise a plurality of individual pistons spaced around the driven shaft  12 . The second conduit  102  allows the second port  82  to be connected in fluid communication with the second hydraulically actuated device  60  to provide hydraulic fluid to those pistons. It should also be understood that the first and second hydraulically actuated devices could be annularly shaped pistons that are coaxial with the shafts and concentric with axis  50 . Either individually spaced pistons or single annular pistons can be used as either the first or second hydraulically actuated devices, or both. The specific shapes of the hydraulically actuated devices are not limiting to the present invention. 
     With continued reference to  FIG. 1 , a plurality of bearings  110  are provided between various surfaces of the driving shaft  10 , the driven shaft  12 , and the second dog clutch member  22 . A spring  12  is provided to urge the second dog clutch member  22  toward the left in  FIG. 1  against the actuated movement of the second hydraulically actuated device  60 . Ball bearings  130  are provided to support the driving and driven shafts,  10  and  12 , relative to the housing  86 . 
     In operation, when connection of the driving and driven shafts,  10  and  12 , is desired, the first hydraulically actuated device  40  is initially actuated by introduction of hydraulic fluid pressure at the first port  81  which causes the plurality of pistons of the first hydraulically actuated device  40  to move the second friction clutch members,  32  and  33 , into contact with the first friction clutch member  30 . This transmits a certain degree of torque through the first and second friction clutch members and, as a result, causes the driven shaft  12  to begin to rotate. When the driven shaft  12  is rotating sufficiently fast to provide a satisfactory degree of synchronization between the driving and driven shafts,  10  and  12 , the second hydraulically actuated device  60  is actuated by introducing hydraulic fluid under pressure at the second port  82  to energize the plurality of pistons of the second hydraulically actuated device  60 . This causes the second dog clutch member  22  to move toward the right against the force of the spring  120  and into engagement with the first dog clutch member  20  as the two opposing dog clutch tooth surfaces,  70  and  72 , move toward each other. When these surfaces engage each other, torque is transmitted from the driving shaft  10  through the first and second dog clutch members,  20  and  22 , to the driven shaft  12  through the spline connection  26 . At this time, the first hydraulically actuated device  40  can be relaxed by decreasing the pressure in conduit  101 . 
     As described above, the second dog clutch member  22  is slidably attached to the driven shaft  12  by a configuration of axial splines  26 . The first hydraulically actuated device  40  comprises a first plurality of hydraulically actuated pistons supported for rotation by the driven shaft  12  in a particularly preferred embodiment of the present invention. However, it should be understood that alternative embodiments of the present invention could incorporate the first hydraulically actuated device  40  as part of the driving shaft. Similarly, the positions and functions of the first and second dog clutch members,  20  and  22 , can be reversed. In a preferred embodiment of the present invention, the first and second hydraulically actuated devices,  40  and  60 , are independently operable to actuate the first and second friction clutch members and the first and second dog clutch members, respectively. 
     By connecting the driving and driven shafts,  10  and  12 , in torque transmitting association with each other through the first and second friction clutch members, rotational synchronization can be obtained between the driving and driven shafts prior to engagement of the opposing dog clutch surfaces,  70  and  72 . Therefore, when the second dog clutch member  22  is moved toward the right in  FIG. 1  to engage the first dog clutch member  20 , little or no relative rotational speed should exist between those mating dog clutch teeth on surfaces  70  and  72 . 
     In a preferred embodiment of the present invention, the speed of actuation of the hydraulically actuated devices can be moderated in response to changes in temperature. In other words, when the hydraulic fluid is cold, and therefore more viscous, the speed of actuation of the first hydraulically actuated device can accommodate this condition to avoid a high impact contact between the dog clutch teeth. As a result, the speed of actuation of the two hydraulically actuated devices can be controlled to avoid high impact shifting of the dog clutch under many different temperature conditions. 
     Although the present invention has been described in significant detail and illustrated to show a preferred embodiment, it should be understood that the relationships and positions of its components can be alternatively positioned on other devices. In other words, the first and second hydraulically actuated devices,  40  and  42 , can be attached and supported by the driving shaft  10  rather than the driven shaft  12  in alternative embodiments. Similarly, the first and second friction clutch members can be reversed in their association with the driving and driven shafts. The number of pistons used in both the first and second hydraulically actuated devices,  40  and  60 , are not limiting to the present invention. Although the present invention has been described in particular detail and illustrated to show a particularly preferred embodiment, it should be understood that alternative embodiments are also within its scope.