Drive joints and use of said drive joint

The present invention relates to a drive joint for transmission of rotary motion between a drive unit and a propeller shaft with a propeller for propulsion of a boat, wherein the drive joint, comprises a flexible joint enclosed by a housing and provided for handling thrust forces from the propeller during operations. Further the invention relates to a use of said drive joint.

Various embodiments of drive joints are already known for use as drive joints in front wheel drive cars. These are known as constant velocity drive joints. The issue with "constant velocity" is that the traditional universal joint with a cross shaft leads to a non-constant velocity which relates to the different angle between the incoming and the outgoing part of the joint. In a constant velocity joint this problem is eliminated. In a front wheel drive car it is absolutely necessary to achieve a constant velocity since otherwise one would experience vibrations in the interior of the car when the car is springing or turning.

The above mentioned constant velocity joint is as mentioned earlier designed for use in cars. These joints can normally not be subjected to large thrust forces in more than one direction. This is not particularly a weakness in the mentioned application since the need for use of said thrust force in a drive shaft is not significant in the car industry. Axially operating forces in such a drive shaft is minimal.

The present inventor has found that a constant velocity joint of the present type can be adapted for use in small boats as a flexible joint between the propeller shaft and the gear box on board the boat. As far as one has been able to determine such joints have not earlier been conceived for use in the maritime field, that is for use in boat propulsion, thus will be a completely new application of the constant velocity joint.

It is therefore an object of the invention to provide a constant velocity joint suitable for use as a drive joint for propulsion of boats.

To achieve this objective it is provided a drive joint as described earlier which according to the invention is characterized in that to the exit shaft of the joint a locking ring is attached, provided at the inner or free end of the shaft and is dimensioned for handling thrust forces from the propeller during operations, where the housing outside the exit shaft's inner end is provided with an opening for direct access to the locking ring during assembly and dismounting of the drive joint.

Since this regards a new use of the drive joint it is according to the invention also provided a use of a drive joint having a flexible joint for transmission of rotary motion, as a drive joint between a gear box and a propeller shaft on board a boat,

wherein the drive joint is constructed to handle both pushing and pulling thrust forces from the propeller during operations.

During operation of the drive joint for propulsion of boats it is essential that the joint can sustain thrust forces acting in both directions, that are pushing thrust forces created by the propeller when the boat is moving forward, and pulling thrust forces created by the propeller when the boat is moving astern. The purpose of the joint is to transmit a rotary motion of a given rotary momentum with continuous small angular changes between the entering and exiting parts of the shaft due to the movement of the boat at sea during operations. When the boat is moving forward and the propeller thrusting forward due to the pressure from the propeller, this force will cause a small change in angles. Same relationship in the opposite direction is present when the boat is moving astern. In a boat without any kind of flexible element this would result in significant vibrations. With the drive joint according to the invention this problem is eliminated. A vary significant advantage of this joint is also that the angular deviation can be up to 7 or 8 degrees which is quite unique in this relationship.

The invention will here be disclosed in details with an exemplary embodiment with references to the drawings wherein

Figure 1 shows a longitudinal cross section of a drive joint according to the invention across the line I-I on figure 2, Figure 2 shows a cross section of the drive joint seen in the direction of the arrow A on figure 1 ,

Figure 3 shows a corresponding axial cross section as shown in figure 1 where the cross section is in a plane where the balls of the joint are not visible, and

Figure 4 shows a cut-away perspective of the drive joint with the same cross section of planes as shown in figure 1.

As a starting point the drive joint according to the invention is an industrialized version of a drive joint for a car where the joint has been modified in order to sustain thrust forces in both directions and is simultaneously designed for easy assembly and disassembly on board a boat. As is shown by the drawings drive joint 1 comprises an external housing 2 which encloses a flexible joint 3 which is designed to transmit a rotational momentum and simultaneously sustain push or pull thrust forces caused by the propeller during operations, while the joint permits angular deviations between the entering and exiting parts of the joint. The construction of the joint 3 will be disclosed in further details later.

The drive joint further comprises an exit shaft 4 which at its outer end is provided with a coupling head 5 with a depression for attachment of a clamping ring 6 for clamping of a propeller shaft for the propeller (not shown). At the other end of the drive joint the housing 2 is provided with a flange 7 with four holes 8 for bolts for

attachment of the drive joint to an exit shaft (not shown) from a drive unit which in this case is a gear box on board the actual boat.

Between the outer housing 2 and the exit shaft 4 of the drive shaft a closing rubber bellows 9 is provided, said bellows being attached to the shaft 4 at on end and attached to the housing 2 at the other end via a closing cover 10.

In the disclosed embodiment the flexible joint 3 comprises six balls 11 that are arranged in corresponding openings in a ball holder in the form of a so called ball grid 12, similarly to a ball bearing. The balls can move along a transverse outer and inner curved tracks while simultaneously transmitting rotational momentum. In this way outer curved tracks 13 are provided in the outer housing 2 and inner curved tracks 14 are provided in the inner ring 15. The inner ring 15 are rotationally fixed attached to the exit shaft 4 since the ring is provided with an inner set of longitudinal teeth ,(not shown on the drawings) that meshes with corresponding teeth (not shown) that are provided on the surface of the shaft. The curvature of the inner and the outer tracks are adapted to each other in such a way that the balls 11 continuously faces both the inner and the outer track at different angular deviations between the housing 2 and the exit shaft 4. The tracks are surface treated and honed, in order to minimize the friction between the balls and the tracks.

As mentioned earlier the drive joint is constructed in such a way that it sustains both push and pull thrust forces from the propeller during operations. When the boat is moving forward the thrust force from the propeller are sustained by the balls 11 since these are forced against the ball tracks due to the mutually converging motion of said tracks in the forward direction. When the boat moves astern, pull forces from the propeller are sustained by the balls 11 and with a locking ring 16 attached to a peripheral track in the exit shaft provided at said shaft's free or inner end, wherein the locking ring is facing an adjacent side edge of the inner ring 15. The locking ring is dimensioned sufficiently strongly in order to handle the pulling forces from the propeller. The locking ring can advantageously be a seeger ring as shown on figure 4.

When transmission of forces takes place when the drive joint has a certain angle between the entering and exiting parts, said parts adjust to the size of the angle while a part transmission is not changed at all. Depending on the size of the angles the balls will wander back and forth in their tracks while being forced towards the ball tracks when the propeller exerts a thrust force or pulling force on the joint.

As shown by the drawings, the outer housing 2 is provided with an opening 17 just above the free or inner end of the exit shaft 4. Due to this opening one achieves direct access to the locking ring 16 and thus convenient assembly or disassembly of the drive joint.

The drive joint according to the invention will in many ways represents a revolution in the boat market. A boat manufacture will, using this joint, be able to

attached engine and gear in relationship to the propeller shaft in a significantly shorter period than earlier while the result is improved. Furthermore, later adjustment will not be necessary since the joint will sustain motions that will occur. Large boats will further have a certain movement in the hull. All these issues have traditionally been a problem in all boats with propeller propulsion. These problems are eliminated using the present drive joint.