Marine propulsion system
BACKGROUND AND SUMMARY 
     This invention relates to a marine propulsion system, and more particularly to an inboard-outboard type marine propulsion system. 
     The invention is designed to reduce or eliminate noise and vibration from an inboard mounted engine. The invention further provides an outboard mounted gearcase and drive unit, and a system for transferring power from the inboard mounted engine to the outboard mounted drive unit. The drive unit is mounted so as to be pivotable about a horizontal tilt axis, and steerable about a vertical steering axis. 
     In accordance with the invention, a marine propulsion system for use in a boat includes an engine adapted for mounting in the aft portion of the boat adjacent the transom. The engine is oriented so that its axis is substantially transverse to the axis of the boat. With this orientation, the engine crankshaft extends substantially parallel to the boat transom. A drive unit is mounted to the exterior of the transom, and includes a propeller interconnected with power transfer means for driving the propeller in response to rotation of the engine crankshaft. Drive means is provided for drivingly interconnecting the engine crankshaft with the power transfer means. In one embodiment, the engine is mounted in a chamber at the aft end of the boat for isolating the engine from the interior of the boat. One wall of the chamber is defined by the transom. The engine is mounted in the chamber by resilient mounting means for isolating the boat from engine vibrations. The drive unit is rigidly mounted to the exterior of the boat transom, and the power transfer means includes means for accommodating movement of the engine crankshaft resulting from engine vibration. The power transfer means includes a rotatable shaft disposed in the upper end of the drive unit defining a tilt axis about which the drive unit is pivotable. The engine crankshaft is interconnected with a rotatable output means, such as a sprocket, and the rotatable shaft in the upper end of the lower unit is provided with rotatable input means, such as a sprocket. A chain is provided about the output and input sprockets for transferring power therebetween. The means for accommodating movement of the engine crankshaft is preferrably associated with the output sprocket interconnected with the engine crankshaft. In one embodiment, the means for accommodating movement of the engine crankshaft includes a drive shaft interconnected with the engine crankshaft through a first flexible joint, such as a universal joint. The drive shaft is connected at its other end to the rotatable output sprocket through a second flexible joint, such as a universal joint. With the provision of universal joints at both ends of the drive shaft, engine vibration is isolated from the sprocket and thereby has little or no effect on the operation of the drive unit. In one embodiment, the sprocket is an axially extending hollow member, and the drive shaft extends substantially coaxially in the interior of the sprocket. The drive shaft is connected to an end of the passage in the hollow sprocket, and the teeth of the sprocket are located about the outer periphery of the sprocket at its other end. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings illustrate the best mode presently contemplated of carrying out the invention. 
     In the drawings: 
     FIG. 1 is a partial side sectional view showing the general arrangement of the engine, lower unit and drive means of the present invention; 
     FIG. 2 is a partial sectional view taken generally along lines 2--2 of FIG. 1; 
     FIG. 3 is a partial sectional view taken generally along line 3--3 of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, a marine propulsion system for mounting in the aft portion of a boat 10 includes an internal combustion engine 12. Engine 12 is mounted in a compartment 14 formed in the aft end of the boat. Compartment 14 is defined by the transom 16 of boat 10, an upper wall 18, a front wall 20 and boat hull 22. Compartment 14 is constructed so as to isolate sound from engine 12 from the remainder of the interior of boat 10. 
     As shown in FIG. 1, engine 12 is mounted in compartment 14 so that its longitudinal axis is substantially perpendicular to the longitudinal axis of boat 10. With this orientation, the engine crankshaft (not shown) extends substantially parallel to boat transom 16. 
     Engine 12 is resiliently mounted in compartment 14 by means of resilient mounts, shown at 24, 26 (FIG. 1) and 28 (FIG. 2). Mounts 24-28 are similar to those used in automotive applications for isolating engine vibrations from the supporting structure. With this construction, vibrations from engine 12 are substantially isolated from boat 10. 
     A drive unit 30 is rigidly mounted to the exterior of transom 16. Drive unit 30 includes a depending lower unit 32 and a propeller 23. A substantially vertical drive shaft 36 (FIG. 3) extends through lower unit 32, and is interconnected with a substantially horizontal propeller shaft (not shown) to which propeller 34 is connected. As is known, rotary power is transferred from drive shaft 36 and through the propeller shaft to propeller 34. A suitable reversing transmission is typically provided in a torpedo 38 (FIG. 1), within which the propeller shaft is mounted, for providing forward and reverse rotation of propeller 34. 
     Drive unit 30 is rigidly fixed to the exterior of transom 16 by a mounting bracket or other suitable mechanism (not shown). 
     An upper jack shaft 40 is provided at the upper end of drive unit 30. Jack shaft 40 is substantially horizontal, and extends parallel to transom 16. As shown in FIG. 3, jack shaft 40 extends within a housing 41, and is provided at its rightward end with a bevel gear 42. Jack shaft bevel gear 42 is engageable with a drive shaft bevel gear 44 connected to the upper end of vertical drive shaft 36. Jack shaft 40 is provided at its leftward end with an input, or driven, sprocket 48, contained within a sprocket housing 50 mounted to the exterior of boat transom 16. 
     With drive unit 30 and sprocket 48 rigidly fixed to the exterior of boat transom 16, and engine 12 mounted within compartment 14 so as to isolate boat 10 from engine vibrations, a means must be provided for accommodating movements of the engine crankshaft resulting from engine vibration so as to isolate sprocket 48 and drive unit 30 from the effects of such vibration. To this end, a drive shaft 52 (FIG. 2) is connected at its rightward end through a flexible universal joint 54 to the engine crankshaft (not shown). Drive shaft 52 extends substantially parallel to jack shaft 40, and is connected at its leftward end to a second flexible universal joint 56, which is mounted to the interior of a drive, or output, sprocket assembly 58. Output sprocket assembly 58 comprises a hollow substantially frusto-conical member having an inner passage 60 extending axially throughout its length. As shown, the rightward end of output sprocket assembly 58, located closest to engine 12, has a diameter greater than the leftward end of sprocket assembly 58. Drive shaft 52 extends through passage 60 substantially coaxially with output sprocket assembly 58. Universal joint 56 is connected at the inner leftward end of output sprocket assembly 58, which is mounted through a bearing assembly 62 against lateral movement. A second bearing assembly 64 is provided at the rightward end of sprocket assembly 58 to brace sprocket assembly 58 against lateral movement. A series of teeth 66 are provided about the outer periphery of output sprocket assembly 58 at its rightward end. A chain 68 is provided about teeth 66 of output sprocket assembly 58, and engages a series of teeth 70 provided about the periphery of input sprocket 48. As an alternative means for transferring power from output sprocket assembly 58 to input sprocket 48, chain 68 may be replaced by a belt. 
     As is known, a tilt cylinder 72 is provided for effecting tilting movement of drive unit 30 about a tilt axis defined by upper jack shaft 40. A satisfactory steering mechanism is provided for effecting steering movement of lower unit 30 about a steering axis defined by vertical drive shaft 36. 
     With the described construction, vibrations of engine 12 are substantially isolated from the drive system. Universal joints 54 and 56 accommodate movements of the engine crankshaft resulting from such vibrations, thereby isolating sprocket assembly 58 from the effects of such movement. In this manner, movements resulting from engine vibration have little or no effect on the operation of the drive system. 
     Various alternatives and modifications are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the invention.