Caster Wheel Biasing Mechanism

The invention relates to caster wheels for mower decks and mechanisms that bias the caster wheel to particular locations.

Conventional mowing vehicles are often provided with caster wheels which support a mower deck during operation. The caster wheels pivot with respect to the mower deck when the mowing vehicle executes a turn. Conventional caster wheel mechanisms typically include an upright shaft which is pivotally held within a cylindrical opening. As the mower vehicle makes a turn the shaft pivots within the opening to allow the caster wheel to pivot during the turn. Pivoting caster wheels generally prevent turf from being scuffed or otherwise damaged during a turn.

When the mower deck is raised, many conventional caster wheels are allowed to spin about the axis defined by the shaft. The spinning caster wheel can be noisy. When the deck is lowered to the ground again, the caster wheel may be turned to either side, and may contact the ground at an angle to the direction of travel. The turf can be scuffed or damaged when the caster wheel contacts the ground when misaligned with the direction of vehicle travel.

Therefore, it would be desirable for such a mechanism to bias the castor wheel to a predetermined position such that when the deck is lowered to the ground the caster wheel will contact the ground in proper alignment with the direction of forward vehicle travel. It would be desirable to provide a caster wheel mounting mechanism which allows the caster wheel to pivot throughout a large range of motion as the mowing vehicle executes turns and thereby prevent turf from being damaged during turns. It would also be desirable for such a mechanism to hinder the caster wheel from spinning when the mower deck and caster wheel are lifted off the ground.

The present invention provides a caster wheel having a shaft pivotally mounted in an opening defined in a mounting member. A ball member is biased by a spring to engage the surface of the shaft. The shaft is generally cylindrical with a flatted portion. Abuttment of the ball against the shaft, particularly against the flatted portion, will hinder the shaft and caster wheel from spinning. As the ball abutts against the flatted portion, the ball will apply a force to the shaft that will urge the shaft to pivot to its straight forward position. At that position the ball exerts a force on the flatted portion that is generally aligned with the axis of the shaft, and therefore the shaft will not be urged to pivot from this position.

An alternative embodiment provides a ball and spring carried in the shaft. The ball abuts against the inner surface of a generally cylindrical opening having a relief portion. The force of the ball against the inner wall of the opening, and particularly against the relief portion, will tend to hinder the shaft and caster wheel from spinning. The ball will tend to "bottom out" in the relief portion, which causes the shaft and caster wheel to remain or return to their straight forward positions.

The present invention thereby provides a caster wheel mechanism which allows the caster wheel to pivot throughout a large range of motion as the mowing vehicle executes turns and thereby prevent turf from being damaged during turns. The present invention also hinders the caster wheel from spinning when the mower deck and caster wheel are lifted off the ground. The present invention also biases the castor wheel to a predetermined, straight forward position such that when the deck is lowered to the ground the caster wheel will contact the ground in proper alignment with the direction of forward vehicle travel without scuffing the turf.

FIG. 1 is a plan view of a vehicle with which the present invention is adapted for use.

FIG. 2 is a side view of the caster wheel biasing mechanism according to the present invention.

FIG. 3 is a top sectional view of the caster wheel biasing mechanism according to the present invention showing the wheel in its straight forward alignment.

FIG. 4 is a top sectional view of the present biasing mechanism showing the wheel turned.

FIG. 5 is a sectional view of the present biasing mechanism when the wheel is turned slightly from its straight forward alignment.

FIG. 6 is an alternative embodiment of the present invention.

Referring now to FIGS. 1-6, there is shown the present invention. FIG. 1 shows a caster wheel mounting mechanism 10 according to a first embodiment of the present invention. A tire 12 adapted for contacting the ground has a hub member 14 and axle 16 at its center. A fork member 18 is coupled with the axle 16 and extends upwardly therefrom. A pivot member or shaft member 20 extends upwardly from the fork member 18 and is received within a generally cylindrical opening 22 in a mounting member 24. The mounting member 24 is coupled via bolts 26 to beams 28 which form a four bar linkage between the mounting member 24 and a mower deck 30.

The present invention includes a mechanism for generally preventing the caster wheel 12 from spinning when lifted from the ground, and which generally biases the caster wheel 12 to its forwardly oriented position. The shaft 20 is generally cylindrical in shape, with a generally circular cross sectional portion 32, but includes a flatted portion 34 as seen in FIGS. 2-5. An abutment member or ball 36 is held within a threaded member 38, and is biased by a biaser or compression spring 40 into abutment with the shaft 20. The threaded member 38 is received within a threaded opening 42 in the mounting member 24. The threaded member 38 includes a central opening 44 within which the ball 36 and spring 40 are positioned. A nut member 46 generally encloses the central opening 44 and generally confines the ball 36 and spring 40 within the central opening 44.

Next, the operation of the embodiment shown in FIGS. 1-5 will be discussed in greater detail. During normal mowing operations the caster wheel tire 12 rolls in engagement with the ground surface. As the mowing vehicle executes a turn, the caster wheel 12 is allowed to pivot so that the tire 12 continues to roll across the ground and not mar or scuff the surface of the turf. When the caster wheel 12 pivots, the shaft 20 will pivot within the opening 22 in the mounting member 24. As the shaft 20 pivots from its forward position shown in FIGS. 2 and 3, the flatted portion 34 will press the ball 36 against the spring 40 and toward the nut member 46. The shaft 20 will continue to pivot until the ball 36 is in contact with the rounded cylindrical portion 32 of the shaft 20, as shown in FIG. 4. The shaft 20 is free to continue pivoting or pivot back to its straight forward position as shown in FIG. 3. The present invention thereby allows the caster wheel 12 to pivot through a wide range of motion during execution of a turn when the tire 12 is in contact with the ground.

The present invention also serves to restrain the caster wheel 12 from spinning and biases the caster wheel 12 to its straight forward configuration shown in FIG. 3. When the mower deck 30 is lifted and the tire 12 is out of contact with the ground, the tire 12 may encounter forces which urge the caster wheel 12 and shaft 20 to spin. If the forces encountered are great enough to cause the shaft 20 to spin, the abutment of the ball 36 against the shaft 20 serves to apply a force to the shaft 20 which resists spinning motion. The present invention also biases the caster wheel 12 to its straight forward position shown in FIG. 3. If the shaft 20 is pivoted slightly from the position shown in FIG. 3 to the position shown in FIG. 5, the flatted portion 34 will press outwardly on the ball 36 such that the spring 40 becomes slightly compressed. The spring 40 will continue to urge the ball 36 against the surface of the shaft 20. The ball 36 will apply a force normal to the surface of the flatted portion 34 along line A as shown in FIG. 5. The force A is offset from the central axis 48 of the shaft 20, and therefore this force A establishes a moment arm 50 which tends to pivot the shaft 20 back to its position shown in FIG. 3. When the shaft 20 returns to the position shown in FIG. 3, the force A applied to the shaft 20 by the ball 36 and spring 40 is aligned with, or in other words, intersects with or passes through the central axis 48 of the shaft 20, and therefore the shaft 20 will not be caused to pivot from this position by the force applied by the spring 40 and ball 36.

Referring now to FIG. 6, there is shown an alternative embodiment 52 of the present invention. An abutment member or ball member 36 and spring 40 are supported by the shaft 20. The spring 40 biases the ball 36 outwardly into abutment with the inner diameter 54 of the opening 56 in the mounting member 24. The opening 56 has a generally cylindrical portion 58, and includes a curved relief portion 60. When the mower executes a turn, the caster wheel 12 will pivot, causing the shaft 20 to pivot within the opening 56. Pivoting of the shaft 20 causes the ball 36 to be compress against the spring 40 as the ball 36 leaves the relief portion 60 and begins rolling across the cylindrical portion 58 of the opening 56. Spinning of the caster wheel 12 and shaft 20 is generally hindered by the friction between the ball 36 and the opening 56. Furthermore, as the shaft 20 and caster wheel 12 spin, the ball 36 must pass through the relief portion 60 which requires the spring 40 to extend and then be compressed. Compression of the spring 40 absorbs energy from the spinning caster wheel 12, thereby helping bring the caster wheel 12 to rest.

The embodiment shown in FIG. 6 also serves to bias the caster wheel 12 to its straight forward position. As the caster wheel 12 pivots slightly from the position shown in FIG. 6, the ball 36 is compressed against the spring 40 as it abuts the surface of the relief portion 60. The spring 40 will continue to press the ball 36 outwardly. As the ball 36 is pressed outwardly, the surface of the relief portion 60 applies a force to the ball 36 along a line that is offset from the axis 48 of the shaft 20. A moment arm is thereby established which urges the caster wheel 12 to pivot back to its straight forward position shown in FIG. 6. With the ball 36 bottomed out in the relief portion 60 as shown in FIG. 6, the surface of the relief portion 60 applies a force to the ball 36 that is generally aligned with the axis 48 of the shaft 20, and therefore the shaft 20 is not urged to pivot from that position. Therefore the shaft 20 and caster wheel 12 are biased to return to and remain in a predetermined, straight forward position.