US3605677A

US3605677A - Boat drive arrangement

Info

Publication number: US3605677A
Application number: US907A
Authority: US
Inventors: Karl Abdon Bergstedt
Original assignee: Volvo Penta AB
Current assignee: Volvo Penta AB
Priority date: 1970-01-06
Filing date: 1970-01-06
Publication date: 1971-09-20
Anticipated expiration: 1988-09-20
Also published as: SE356009B; JPS4948720B1; DE2100208A1; CA931435A; CA921335A; GB1293999A; FR2075237A5; FR2075238A5; JPS566918B1; GB1294190A; DE2100207C2; DE2100208B2; DE2100207A1; SE355542B; DE2100208C3

Abstract

AN INBOARD-OUTBOAD DRIVE FOR A BOAT WHEREIN THE OUTBOARD LEG IS OF A GENERALLY Z CONFIGURATION, IS MOUNTED ON A HORIZONTAL TILT AXIS REARWARDLY ADHACENT TO THE TRANSOM AND INCLUDES A DOWNWARDLY AND FORWARDLY INCLINED DRIVE SHAFT COUPLED AT ITS LOWER END TO A GENREALLY HORIZONTAL PROPELLER SHAFT. THE CONNECTION BETWEEN THE DRIVE SHAFT AND THE PROPELLER SHAFT IS THROUGH GEARING HAVING A RATIO EQUAL TO SUBSTANTIALLY THE COSINE OF THE ANGLE BETWEEN THE DRIVE SHAFT AND PROPELLER SHAFT. THE LOWER PORTION OF THE OUTBOARD HOUSING IS ARRANGED TO ROTATE FOR STEERING ABOUT THE AXIS OF THE DRIVE SHAFT. HYDRAULIC STEERING MEANS, ARE PROVIDED FOR ROTATING THE LOWER HOUSING, INCLUDING A DOUBLE ACTING HYDRAULIC CYLINDER AND PISTON MEANS, THE PISTON MEANS BEING PROVIDED WITH PORTS AND CHECK VALVES WHICH OPEN AUTOMATICALLY AT EACH EXTREME OF THE STEERING MOVEMENT TO PERMIT A FLOW OF HYDRAULIC FLUID THROUGH THE PISTON MEANS TO SCAVENGE AIR FROM THE SYSTEM.

Description

Sept. 20, 1971 K. A. BERGSTEDT 3,505,577

BOAT DRIVE ARRANGEMENT Filed Jan. 6, 1970 3 Sheets-Sheet 1 INVL' N TOR Karl fltabn Berystedz mam ATTORNEY Se t. 20, 1971 K. A. BERGSTEDT 3,505,577

BOAT DRIVE ARRANGEMENT Filed Jan. 6, 1970 3 Sheets-Sheet 2 ll/ll T I. "1255' iiunuuut nun INVENWR 16 lfarl 4bdon Berystedt Sept. 20, 1971 K. A. BERGSTEDT 3,605,677

BOAT DRIVE ARRANGEMENT Filed Jan. 6, 1970 3 Sheets-Sheet S FIQS IN Vf N 70R Karl A'fidm Beryszedt ATTORNEY United States Patent US. Cl. 11535 11 Claims ABSTRACT OF THE DISCLOSURE An inboard-outboard drive for a boat wherein the outboard leg is of a generally Z configuration, is mounted on a horizontal tilt axis rearwardly adjacent to the transom and includes a downwardly and forwardly inclined drive shaft coupled at its lower end to a generally horizontal propeller shaft. The connection between the drive shaft and the propeller shaft is through gearing having a ratio equal to substantially the cosine of the angle between the drive shaft and propeller shaft. The lower portion of the outboard housing is arranged to rotate for steering about the axis of the drive shaft. Hydraulic steering means are provided for rotating the lower housing, including a double acting hydraulic cylinder and piston means, the piston means being provided with ports and check valves which open automatically at each extreme of the steering movement to permit a flow of hydraulic fluid through the piston means to scavenge air from the system.

This invention relates to inboard-outboard drive units for boats of the type wherein the lower propeller-carrying portion of the outboard housing is steerable about the axis of an upwardly extending drive shaft in the housing and wherein the steering torque is minimized by providing a gear ratio between the drive shaft and the propeller shaft substantially equal to the cosine of the angle between said shafts. A drive unit in which steering torque is so minimized is shown and claimed in my US. Pat. No. 3,382,838 issued May 14, 1968, entitled Device on the Propeller Installation for Boats. The present invention further relates to hydraulic steering means for such drive units.

It is a general object of this invention to provide an improved drive unit of the aforesaid type. It is a more specific object of this invention to provide a compact drive of such type, wherein the propeller is located adjacent to the boat transom. It is a further object of the invention to provide an improved hydraulic steering system for rotating an outboard housing portion which carries the propeller and which is mounted for rotation on a steering axis. Other and further objects will be apparent from the following description when taken in connection with the drawings, in which:

FIG. 1 is a side elevational view of an inboard-outboard drive unit for a boat embodying my invention, portions of the boat being represented in phantom;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a sectional side view of the unit on an enlarged scale taken generall along line 3--3 of FIG. 2;

FIG. 4 is a sectional detail view on a further enlarged scale of a portion of the hydraulic steering system taken generally along line 4-4 of FIG. 3; and

FIG. 5 is a sectional view of parts of the portion shown in FIG. 4 taken along line 5-5 and on the scale of FIG. 4.

3,605,677 Patented Sept. 20, 1971 In the drawings, an inboard-outboard drive unit is shown in FIGS. 1 and 2 comprising an inboard engine, generally represented at 1, which is mounted in a boat 2 having a stern transom 3 with an opening 4 therethrough. The opening is closed by a shell 5 including a flange 6 engaging and sealed against the outer face 7 of the transom and bolted, such as by means of bolts 8, to the transom. The shell 5 includes arm portions 9 which project rearwardly of the transom and which journal pivot pin projections 10 from a hood-like portion 11 of outboard housing or leg 12. Housing 12 comprises an upper portion 13 and a lower steerable portion 14 which carries propeller 15 and which is provided with a skeg 16 and anticavitation plate 17, the propeller being shown in FIG. 2 by a representation of its turning circle.

A hydraulic trimming and tilting cylinder arrangement is provided at 18 to adjust the trim angle of the outboard housing, which is shown in position for normal straight ahead drive in the drawing. The hydraulic trim arrangement is operated from a suitable remote station through a flexible push-pull cable means 19 connected to valve lever 20, the arrangement being provided through the valve controlled by lever 20 with hydraulic fluid under pressure from a suitable source represented by and including conduit 21.

Conduits

22 and 23 extend from a suitable pump connected with a steering wheel to provide hydraulic fluid under pressure to the hydraulic steering mechanism embodied within the upper portion 13 of the outboard housing 12 as hereinafter more particularly described. It will be understood that the

conduits

22 and 23 are flexible between the transom and the outboard leg, whereby tilting of the leg on the horizontal axis of pivot pins 10 is permitted. The

conduits

22 and 23 extend inwardly through the transom, and they preferably extend and are sealed through the flange 6 of the mounting hell 5 and pass into the boat through opening 4. Bumper means 24 is arranged to limit the forward tilting movement of the outboard housing or leg so as to prevent the leg from tilting forward under any circumstances into a position in which the lower housing 13 would contact the lower edge of the transom. Maximum extension of the hydraulic cylinder and piston arrangement 18 tilts the leg about axis T preferably sufliciently to raise the propeller 15 above Water.

The drive unit is shown in section in FIG. 3, several parts as there shown being identified by the reference numerals as described above in connection with FIGS. 1 and 2.

The inboard engine 1 is provided with a forward and reverse transmission (not shown) which is operated by a lever 25 controlled by a suitable linkage mechanism 26 from the usual operators station in the boat, from which station the steering and tilt and trim arrangements are also operable. The engine drive shaft 27 is journalled in a hollow ring member 28 which is externally connected and sealed by means of suitable compressed rubber or the like rings 29 to shell 5. The shaft 27 terminates rearwardly in a universal joint 30 which is in turn connected to universal joint 31 and therethrough to a countershaft 32. It will be understood that suitable spline connections (not shown) are provided between at least one of the shafts and one of the joints to accommodate the necessary movement imposed by the geometry when the outboard leg is tilted. Joints 3t) and 31 together comprise an assembly commonly referred to as a double universal joint. The tilt axis for the outboard leg is identified by the letter T in FIG. 3, and it will be understood that this corresponds to the horizontal axis of the pivot pins shown in FIGS. 1 and 2. The tilt axis, which extends laterally of the boat center line, will be seen to substantially intersect the axis, if extended, of engine shaft 27 and to be substantially midway between the

universal joints

30 and 31. The position of the tilt axis with respect to the joints is selected to establish an appropriate working axis of the joints. It will further be seen that the countershaft 32 is at a small downward angle of substantially degrees with respect to shaft 27. It has been found that operation of double universal joints at a slight angle, such as an angle of 15 degrees, does not adversely affect the performance of the joints, while the downward inclination of the counter shaft 32 permits improved geometry of the upper end 33 of the upper housing portion 13 and increases the maximum permissible tilt angle for the leg, in that there is greater clearance between the upper end 33 and the flange 6 or the transom 3, and, since there is a maximum permitted angle for operation of universal joints, in that the greater angle of tilt does not exceed such maximum angle for the joints. Specifically, for example, the double

universal joint

30, 31 may be designed for satisfactory operation up to a maximum angle of approximately 60 degrees, and, since the countershaft is inclined downwardly by approximately 15 degrees with the outboard leg in normal trim position, the joints would then accommodate rearward and upward tilting of the leg up to about 75 degrees from its normal trim position. It is to be noted that the top of the upper housing inclines downwardly along and adjacently above the countershaft to provide optimal transom clearance upon tilting up, as well as a pleasing external configuration of the outboard leg.

The hood or bell-like portion 11 of the outboard housing, which has been previously described as carrying pivot pins 10, is arranged to swing into the bell 5 with tilting of the outboard housing. The ring member 28 includes a unitary, rearwardly extending, hollow, generally cylindrical inner portion 34, and the member 11 has a similar inner hollow cylindrical portion 35 extending forwardly toward portion 34. A flexible corrugated cylindrical boot 36 is clamped to and extends between portions 34 and 35 to enclose the

universal joints

30, 31 in a watertight compartment.

It will be seen that outboard housing portion 11 and bell 5 serve to protect the boot 36 against damage from external objects, and it will be further seen that bell 5 together with member 28 completely close the opening 4 in transom 3 against the entrance of water into the boat, although water may reach the outside of boot 36.

Countershaft 32 is supported on

roller thrust bearings

37 and 38 within upper portion 13 of the outboard housing, and it has keyed thereon a bevel gear 39 meshing with bevel gear 49 keyed on the upper end 41 of a jointed drive shaft 42. The drive shaft extends from its upper end in a downward and forwardly inclined direction. The drive shaft is supported for rotation or journalled by thrust bearings 43 and 44 in the upper housing portion 13 and by thrust bearing 45 in the lower housing portion 14. Joint means 46 permit the shaft to be separated between its ends for convenience in assembling and disassembling the outboard leg and to provide for length adjustment of the shaft to accommodate it to the bearing positions.

The lower housing portion 14 has an upwardly extending hollow neck member 47 bolted thereto by bolts 48 at its upper end 49. The hollow neck 47 extends upwardly into a downwardly opening generally tubular projecting portion 50 of the upper housing 13 and is rotatable therein on pin bearing 51 and on ball bearing 52 on an axis coincident with the axis of shaft 42. A sealing ring 53 interposed between projection 50 and the upper end 49 of the lower housing prevents the escape of hydraulic fluid from and the entry of water up into the projection and thus protects

bearings

43, 44, 51 and 52.

The outer surface of the hollow neck member 47 is provided between bearings 51 and 52 throughout a part of its periphery with pinion teeth 54 engaged with the teeth of a rack member 55, as hereinafter more particularly described, permitting steering of the lower portion 14 of the housing with respect to the upper portion 13. Movement of the rack 55 in a direction toward the viewer in FIG. 3 will cause the lower housing portion 14 to swing in a direction in which the propeller would move away from the viewer, that is to say, propeller 15 being a pusher propeller, in a direction to steer the boat to starboard.

The neck member 47 carries at its lower end, and at a location within lower housing portion 14, a roller thrust bearing 56 which journals the drive shaft just below coupling 46. The drive shaft 42 terminates downwardly in a bevel gear 57. Propeller shaft 58 is mounted in the lower housing portion by roller thrust bearings 59 and 60 and roller bearings 61, and it is provided with a crown gear 62- meshing with the bevel gear 57. Propeller 15 is preferably a pusher propeller and is, accordingly, mounted on the propeller shaft exteriorly and rearwardly of the housing portion 14.

The drive shaft 42 and propeller shaft 58 rotate in the same direction of rotation, that is, the teeth of gear 57 are in mesh with the teeth of gear 62 above shaft 42 and above shaft 58, and the gear ratio between these shafts is substantially equal to the cosine of the angle between the shaft axes to minimize the steering torque effect of shaft 42 on the lower housing in accord with the teachings of my US. Pat. No. 3,382,838.

The angle between the axis of drive shaft 42 and the axis of propeller shaft 58 in the arrangement shown in FIG. 3 is 58 degrees, or 122 degrees, and the cosine of this angle is substantially 0.53, whereby the gear ratio between drive shaft 42 and propeller shaft 58, or from gear 57 to gear 62, is 120.53. As so arranged, gear 62, being a crown gear, and gear 57, a bevel gear, the teeth are in engagement perpendicularly above the point of intersection of the drive shaft and propeller shaft axes. It will be found normally desirable that the gear ratio should not be substantially greater than 1:053 for modern gasoline engines and modern high speed propellers, in that a substantially greater reduction from shaft 42 to the propeller would require excessive shaft speeds or a low speed propeller. If the angle between the

shafts

42 and 58 were degrees, for example, the gear ratio would be substantially 120.34, while at degrees the ratio would be 1:0.26 or nearly 4:1, a ratio which would be under any usual circumstances unsatisfactory for a high speed planning boat or for a high speed propeller. Decreasing the angle to 50 degrees would permit a ratio of 110.64, while an angle of 40 degrees would permit a ratio of 1:0.77. While such gear ratios may be more desirable for a high speed propeller than a ratio of 120.53, the geometry of the outboard leg would be adversely affected by the smaller angle and, since the lower unit 14 steers about the axis of shaft 42, the propeller shaft would tilt up at an undesirable angle when the lower unit was swung away from normal straight ahead drive position. Accordingly, the minium satisfactory angle between the shaft axes would be approximateiy 45 degrees and the maximum satisfactory angle would be approximately 70 degrees, although with a low speed propeller angles of as great as about 75 degrees might be employed.

A downward and forward inclination of 58 degrees to the horizontal for shaft 42 provides an arrangement in which propeller 1S and anticavitation plate 17 may be desirably disposed close to the lower edge 3' or the transom, with the plate aligned at the level of or slightly below edge 3' and with the propeller sufficiently close to the transom as to be in compacted water rather than in the turbulent wake further astern, and with the plate and propeller in positions in which they tend to remain at desired depth upon pitching of the boat.

The hydraulic steering system is best understood with reference to FIGS. 4 and 5. As seen therein, the up standing neck member 47, which is rigidly attached to lower housing 14, is provided exteriorly throughout somewhat less than half of its periphery with teeth 54 meshing with teeth 63 of rack member 55. The rack member carries a piston at each end, piston 64 being disposed in a cylinder 65 and piston 66 being disposed in a cylinder 67. The cylinders have closed outer ends 68 and 69, respectively, and are provided with suitable connections to respective

hydraulic fluid lines

22 and 23, whereby the piston and cylinders constitute a double acting hydraulic cylinder and piston mechanism for moving the rack member back and forth.

The hydraulic system includes a pump 70 connected to steering wheel 71 operable to force fluid into conduit 22 and to permit return of fluid from conduit 23 in response to rotation of the wheel in one direction and vice versa in response to rotation in the opposite direction.

A hydraulic fluid supply or sump 72 is connected to the pump 70- to supply fluid for the original filling of the system as the air is scavenged therefrom, and to supply make up fluid thereafter.

The rack member has motion in each direction limited when one or the other of

pistons

64 and 66 meets the respective

cylinder end wall

68 and 69. The teeth 63 on rack 55 extend through a distance therealong, and the teeth 54 on neck member 47 extend around the periphery thereof, suflicicntly to accommodate the full extent of the permitted movement of rack 55. For example, the rack may be arranged to move sufl'lciently to rotate neck member 47 and lower housing 14 through a total of approximately 60 degrees, 30 degrees on each side of the dead center position corresponding to straight ahead steering position.

In the construction shown, rack member 55 is provided with a partially threaded reduced generally cylindrical end portion 73 which passes through piston 64 and onto which nut 74 is screwed up against the piston to hold the piston firmly against shoulder 75 of the rack member. The end portion is longitudinally bored at 76 into a cross-bored chamber 77 in the rack member. The projection 50 constitutes a fluid containing chamber and housing for the rack and pinion mechanism and the interior 78 of the housing chamber has communication through a check valve 79 into the chamber 77 within the rack member. The check valve 79 may include a light spring 90 seated on pin 91.

The cylinder 65 terminates at an edge 80 which, at cutaway portion 80, exposes a small part of the wall 81 of piston 64 when this piston is fully extended, that is, with piston 66 stopped by or very close to end wall 69. A port or passage 82 is drilled into this portion of the piston wall and communicates with the interior of cylinder 65 through groove 83 formed around portion 55 of the rack and through passage 84 drilled from piston face 89 to the grove.

The arangement associated with piston 66 will be seen to be identical to that associated with piston 64 as above described, including bore 85, port 86, check valve 87 and passage 88 corresponding, respectively, to bore 76, port 82, check valve 79, and passage 4.

The above described arrangement provides for selfbleeding and air scavenging of the system. Operation of pump 70 to force fluid through line 22 into cylinder 65 causes the piston 64 to move in a direction outwardly of the cylinder until piston 66 nearly meets wall 69, whereupon port 82 is exposed, through cut-away portion or notch 80', to the chamber interior 78. Whatever air may be in line 22 and cylinder 65 now passes together with hydraulic fluid into bore 76, through

passages

83 and 84 and through port 82 into the interior 78 of the housing chamber. The increasing pressure in the housing chamber opens the lightly loaded check valve 87 and first any entrapped air, and later hydraulic fluid, pass through the check valve and bore 85 into cylinder 67 and thence through line 23 and into sump 72. Operation of pump 70 in reverse direction forces piston 66 in a direction outwardly of cylinder 67 until port 86 is uncovered, whereupon hydraulic fluid and any remaining trapped air pass through

channels

88 and 86 into chamber 78 and thence through check valve 79 and bore 76 into cylinder 65 and finally through conduit 22 to the sump 72. The pump is thus operated back and forth to and beyond its full steering eflect in one and in the other direction a sufflcient number of times to insure complete bleeding or scavenging of the air from the system.

In operation, the steering wheel now controls the movement of rack 55 between full starboard and full port steering positions of the lower housing up to the point at which port 82 or port 86 is uncovered, whereafter continued movement of the wheel will force a small flow of hydraulic fluid through the chamber interior 7-8, as when the system is being bled. The lower housing may be turned slightly beyond the full normal port or starboard steering position by an external force until one or the other of

pistons

64 or 66 meets the respective

cylinder end wall

68 or 69. Such end play in the system, with prop erly proportioned components, will be small, such as less than one degree of swing of the lower housing. Thus port 82 should become uncovered only when piston 66 has approached very close to wall 69 at the maximum steering to port position of the pistons, rack and lower housing portion, while port 86 should become uncovered at the maximum steering to starboard position.

What is claimed is:

1. An inboard-outboard drive unit for a boat comprising an outboard leg comprising an upper portion disposed rearwardly of the stern of the boat and a lower portion, means tiltably mounting said upper portion on the boat for tilting on a generally horizontal lateral axis, a drive shaft disposed in said leg extending from within said upper portion inclinedly downwardly and forwardly into said lower portion, means rotatably connecting said lower portion to said upper portion for rotation of said lower portion about the axis of said drive shaft, steering means for rotating said lower portion with respect to said upper portion about said axis, means having support in said upper portion for driving said drive shaft, a propeller shaft mounted in said lower portion disposed generally horizontally and parallel to the axis of the boat when said lower portion is oriented for normal forward propulsion, a water reaction propeller carried by said shaft exteriorly of said lower portion, driving means in said lower portion drivingly connecting said drive shaft to said propeller shaft, the angle between the axes of said shafts being between substantially 45 degrees and 70 degrees, said connecting means driving said propeller shaft in the same direction of rotation as the direction of rotation of said drive shaft and at a ratio from said drive shaft to said propeller shaft equal to substantially the cosine of said angle.

2. The combination according to claim 1 wherein said means for driving said drive shaft comprises an inboard engine, a drive train including a power shaft extending rearwardly from said engine, a counter shaft rearward of said power shaft and flexible drive means interposed between and drivingly connecting said power shaft and counter shaft, said drive train extending through an opening in said stern of the boat, and a gear connection from said counter shaft to said drive shaft, said upper leg portion having bearings mounted therein rotatably supporting said counter shaft, said flexible drive means having a working center at substantially said tilt axis, whereby said drive train is operative to transmit power from said 7 engine to said countershaft when said leg is in normal trim position and in upwardly tilted position.

3. The combination according to claim 1 wherein said propeller shaft projects rearwardly from said lower portion and said propeller is a pusher propeller.

4. The combination according to claim 1 wherein the engine is provided with a forward and reverse transmission operative to drive said drive train selectively in one and the other direction of rotation and thereby to drive said propeller selectively for forward propulsion and for backing down.

5. The combination according to claim 2 wherein said counter shaft extends from said flexible drive means rearwardly with a downward inclination with respect to said engine power shaft when said leg is in normal trim position and with an upward inclination with respect to said power shaft when said leg is in an upwardly tilted position.

6. An inboard-outboard drive for a boat having a transom with an opening therethrough and an inboard engine with a generally horizontal drive shaft extending rearwardly alignedly toward said opening, said shaft terminating in a rearward end, said drive having a countershaft with a forward end disposed rearwardly of said rearward end, a double universal joint connecting between said shaft ends, a gear keyed on said countershaft, a drive shaft, a propeller shaft, when said drive is in normal drive position, said drive shaft extending downwardly below said countershaft at an angle to the vertical of between substantially 20 and 45 degrees and said propeller shaft being generally horizontally disposed, gear means drivingly connecting said drive shaft to said propeller shaft for rotation in the same direction and having a gear ratio substantially equal to the cosine of the angle therebetween, an upper housing journalling said counter shaft and said drive shaft therein, a lower housing rotatably supported by said upper housing on a rotational axis coincident with the axis of said drive shaft, said drive shaft entering said lower housing, said drive shaft and said propeller shaft being journalled in said lower housing, said propeller shaft extending outwardly of said lower housing, a propeller exteriorly of said lower housing carried by said propeller shaft, pivot means establishing a horizontal tilt axis extending laterally of the boat and between said shaft ends tiltably mounting said upper housing to said boat whereby said housings may tilt upwardly from said normal drive position upon the lower housing striking a submerged or floating object, and steering means connected between said upper and lower housing operable to rotate said lower housing on its said rotational axis selectively from and to its straight ahead drive position.

7. The combination according to claim 6 wherein said drive shaft, when said drive is in normal drive position, extends inclinedly downwardly and forwardly below said countershaft.

S. The combination according to claim 7 wherein said countershaft, when said drive is in normal drive position, extends rearwardly from its said forward end at a downward inclination of between substantially l and 30 degrees to the horizontal.

9. In an inboard-outboard drive unit for a boat comprising a generally upright outboard leg disposed rearwardly of the boat transom and having an upper housing portion attached to the boat, a lower housing portion and a drive shaft in said leg extending into and between said portions, said lower housing portion journalling a propeller shaft drivingly connected to said drive shaft, means rotatively mounting said lower housing portion to said upper housing portion on a steering axis coincident with the drive shaft axis, a double acting hydraulic piston and cylinder assembly, said assembly including cylinder means having opposed cylinder end chambers, means to apply pressure hydraulic liquid selectively into one and the other of said end chambers and to open the said end chamber opposite to the chamber being supplied with pressure liquid for the escape of fluid therefrom, piston means in said end chambers adapted to be forced back and forth inwardly of said one and outwardly of said other end chamber upon application of pressure fluid into said other end chamber and inwardly of said other and outwardly of said one end chamber in response to said application of pressure fluid to said one end chamber, said assembly being connected between said upper and said lower housing portions and operative, in response to movement of said piston means with respect to said cylinder means, to swing said lower housing portion between respective maximum steering positions, and scavenging valve means communicating between said end chambers, said valve means being opened in response to maximum steering travel of said piston means in the direction outwardly of said one cylinder end chamber thereby to provide fluid flow through said chambers in series.

10. In an inboard-outboard drive unit for a boat comprising a generally upright outboard leg disposed rearwardly of the boat transom and having an upper housing portion attached to the boat, a lower housing portion and a drive shaft in said leg extending into and between said portions, said lower housing portion journalling a propeller shaft drivingly connected to said drive shaft, means rotatively mounting said lower housing portion to said upper housing portion on a steering axis coincident with the drive shaft axis, a pair of spaced apart cylinders having open inner ends facing each other and closed outer ends, a piston in each cylinder, a rack connected between said pistons, a pinion engaged with said rack and having an axis coincident with said steering axis, said pinion being connected to one of said housing portions and said cylinders being connected to the other housing portion whereby back and forth movement of said pistons and rack with respect to said cylinders steeringly rotates said lower housing portion on said steering axis between opposite limit positions, a chamber located between said cylinders and pistons adapted to be filled with hydraulic fluid, a passage in one piston opening through the face thereof into the respective cylinder and opening through a portion of the side wall thereof which is covered by the cylinder wall when the piston is inwardly of the cylinder and exposed to said chamber when the piston has moved outwardly of the cylinder into a position corresponding to limit steering in one direction, a passage through said other piston opening into said chamber and through the face of the piston into the interior of its respective cylinder, a check valve for said last passage blocking flow of fluid therethrough in the direction from said cylinder interior into said chamber and freely passing flow in the opposite direction, and means to force pressure fluid into the cylinder for said one piston and to permit fluid flow from the other cylinder, said last means being operable to force said one piston into limit position thereby to uncover said passage opening in the wall of said one piston and thereafter to cause said fluid to flow through said chamber and into and through said other cylinder, thereby to scavenge air from said cylinders and chamber.

11. In an inboard-outboard drive unit for a boat comprising a generally upright outboard leg disposed rearwardly of the boat transom and having an upper housing portion attached to the boat, a lower housing portion and a drive shaft in said leg extending into and between said portions, said lower housing portion journalling a propeller shaft drivingly connected to said drive shaft, means rotatively mounting said lower housing portion to said upper housing portion on a steering axis coincident with the drive shaft axis, a steering system characterized in that said last means comprises a generally cylindrical neck portion of said lower housing portion extending upwardly therefrom into said upper housing portion and coaxial with said drive shaft, bearing means in said up- 9 per housing portion rotatively journalling said neck portion therein, gear teeth externally on said neck portion, a rack member in said upper housing portion engaged with said teeth, double acting hydraulic cylinder means fixed in said upper housing portion, piston means in said cylinder means connected to said rack member, and manually controlled hydraulic pressure fluid supply means connected to said cylinder means for reciprocating said piston means and said thereto connected rack member to References Cited UNITED STATES PATENTS Armantrout et al. 11535X Bergstedt 11535 Shirnanckas 11534 Ekman 1l535 Alexander 115-34 provide steering rotation of said lower housing portion 10 TRYGVE BLIX Primary Examiner on said axis.