Steering Control for Zero Turn Radius Mower

The field of the invention pertains to commercial size riding lawnmowers, and, in particular, to lawnmowers that have a zero turn radius and lever steering control for the operator. Such mowers will spin about a vertical axis equidistant between drive wheels when the drive wheels are driven in opposite directions with the same rotational speed.

Zero turn radius mowers are often constructed with the drive wheels approximately equidistant from the front and rear of the mower and a large caster wheel adjacent the back of the mower. Examples of such zero turn radius mowers are disclosed in applicant's previous U.S. Pat. Nos. 4,395,865 and 4,429,515 and these patents are incorporated herein by reference.

Zero turn radius mowers such as applicant's above are traditionally controlled for forward, reverse and steering by a pair of lever arms mounted on transverse pivots. The lever arms are to either side of the operator and therefore require the operator to use both hands on the levers to operate the mower.

Single lever "joy sticks" have also been used to control zero turn radius mowers. Joy stick control offers a full range of speed and steering control with one hand, however, full range control with a joy stick results in "hunting" for the right combination of speed and turn to reach a specific goal. Tracking the mower straight at high mowing speeds is important to doing a professional mowing job and, with the dual lever or joy stick control, bouncing over the terrain causes untoward motion of the levers and erratic steering control.

The invention comprises a constrained single lever mechanism to control both drive wheels of the zero turn radius mower. The lever handle is constrained to move about two, preferably perpendicular, axes to control forward, backward and steering of the mower. By this constraint to the movement of the lever handle, inadvertent movement of the lever handle is likely to occur when the mower is bouncing over uneven terrain. Thus, forward or backward movement of the lever handle is constrained about a single transverse axis. The second longitudinal axis is constrained to move in a single plane perpendicular to the transverse axis. When the lever handle is moved right or left about the longitudinal axis steering of the mower occurs.

As an option a second lever handle, constrained as the first lever handle and linked to the first lever handle may be provided for control from a second location. Thus, with a lever handle on each side of the operator the mower can be fully controlled with either hand.

The invention is most appropriately applied to zero turn radius mowers having two variable volume, reversible hydraulic pumps. Each pump individually supplies oil flow to a wheel motor which in turn is attached to a drive wheel to either side of the operator who generally sits in the center of the machine. The drive wheels are on the same geometric axis and a castor wheel is located toward the rear of the machine. Motion of the mower is regulated by the relative motion of the drive wheels. Equal forward or reverse motion of both wheels provides forward or reverse motion of the mower. When one wheel moves relative to the other wheel by reducing pump flow to one wheel relative to the other, the mower turns. When both pump flows are equal but drive the wheels in opposite directions, then the mower "zero turns" or spins in place. Such a mower, as described in applicant's above noted patents has superior maneuverability to non-zero turn mowers.

The lever mechanisms control the pump flows in a user friendly manner. Forward or reverse pivoting of the lever handle creates equal pull on the control rods or cables and causes straight forward or reverse motion of the mower. Left or right pivoting of the lever handle causes opposite travel of the control rods or cables and results in turning movement when the lever handle is also pivoted in forward or reverse. A zero turn results when the lever handle is pivoted right or left from neutral. The lever mechanism is preferably set for neutral when the lever handle is vertical. This vertical lever handle position can be a detent or "spring-to-center" position. The spring-to-center option permits the lever handle to operate as a "deadman's throttle" causing the mower to come to a stop in the event the operator is accidently thrown from the mower.

Thus, a single-hand lever control that is properly constrained to prevent untoward movements and hunting over rough terrain as disclosed below is superior to two-handed lever control or an all quadrant points unconstrained joy stick control.

FIG. 1 illustrates in perspective a single lever handle constrained mower control; and

FIG. 2 illustrates in perspective a dual lever handle constrained mower control.

FIG. 3 illustrates in perspective a dual joy stick mower control.

In FIG. 1 a single lever handle 10 extends generally vertically upward through an aperture 12 in a pivot box 14. The lever handle 10 is mounted on bearings 16 in the pivot box 14 for rotation about the x-axis relative to the pivot box. The pivot box 14 is, in turn, mounted on bearings 18 for rotation about the transverse y-axis relative to the frame of the mower (not shown).

Since the bearings 18 are mounted to the frame (not shown) at a location that places the upper end of the lever handle 10 convenient to one hand of the operator, movement of the lever handle about the y-axis can be forward and backward for forward and backward motion of the mower. Movement of the lever handle 10 about the x-axis therefore controls steering to the right or left by the operator. The operator of the mower can thereby effect complete forward, reverse and steering control of the mower with a lever handle 10 constrained to move only about two perpendicular axes x and y.

The linkage to control the variable volume hydraulic pumps is located below the pivot box 14. The lever handle 10 extends below the pivot box 14 to support a pivot axis in the form of a stud 20 extending parallel to the x-axis. Depending downward from the pivot box 14 to either side of the lever handle 10 are a pair of rotatable columns 22 and 24. The columns 22 and 24 are rotatable about a pair of rotation bolts 26 and 28 respectively to provide rotation about a pair of axes perpendicular to the y-axis.

Extending from each column 22 and 24 respectively are a first pair of plates 30 and 32 rigidly attached to the columns. Attached to the pair of plates 30 and 32 respectively are a second pair of pivot bolts 34 and 36 providing attachment for a pair of links 38 and 40 rotatable thereon respectively. The pivot bolts 34 and 36 provide for rotation of the links 38 and 40 about axes parallel to the axes of the column rotation bolts 26 and 28. The links 38 and 40 at their other ends are rotatably attached to the stud 20. Thus, movement of the lever handle 10 about the x-axis effects rotation of both columns 22 and 24 simultaneously in the same rotational direction.

Depending angularly downwardly and toward each other are a second pair of plates 42 and 44 respectively rigidly attached to the columns 22 and 24. At the lower ends of the plates 42 and 44 are attached a third pair of pivot bolts 46 and 48 providing for rotatable connection of a second pair of links 50 and 52. The links 50 and 52 connect to the flow controls of the pair of hydraulic wheel pumps (not shown). Thus, the simultaneous rotation of the columns 22 and 24 above effected by the lever handle 10 movement about the x-axis causes the links 50 and 52 to move in opposite directions and effect a change in flow of one pump relative to the other pump.

Movement over the lever handle 10 about the y-axis, however, causes no rotation of the columns 22 and 24 but does cause simultaneous movement of the links 50 and 52 in the same direction.

Illustrated in FIG. 2 is a modification that permits two lever handle controls to be linked for operation of the mower by either hand. Elements that correspond to elements in FIG. 1 are numbered the same. The lever handles 10' and 10" are positioned to either side of the operator for operation by either the right hand or the left hand. The only unique additional part needed is a slave bar 54 connecting the stud 20' of lever handle 10' to stud 20" of lever handle 10". With the movement of one lever handle, the other lever handle is constrained to move therewith.

Although described for a mower with a pair of hydraulic wheel pumps, the new lever handle control can be applied to mowers with mechanical clutches from a single engine, electric clutches from a single engine or electric drive wheel motors, for example. The lever handle control can be also applied to non-zero turn radius mowers that use a change in relative rotation of drive wheels to effect steering.

The advantage to the lever handle mechanism is in the constraint to two pivot axes for forward/reverse and steering. Joy stick controls allow free direct motion into and throughout all quadrants of operation. For example, the "upper" or forward and right quadrant of control provides forward motion with a right turn. With the lever handle control the lever handle is pivoted forward to the correct speed, then pivoted right, in the natural manner for operation of a machine (first begin to move forward, then correct course of forward motion). In contrast, the joy stick allows the operator to move the stick on a direct path to a desired speed and turn position, however, the result is some hunting for the correct speed and turn combination.

Tracking the mower straight at high mowing speeds is important. For conventional dual hand and lever control zero-turn-radius mowers, bouncing over the terrain causes inadvertent motion of the levers and erratic steering control. Joy stick control is more difficult since the joy stick can also move easily into any of the four quadrants of joy stick travel. In contrast, with constrained two axes control, the wrist can be locked to control unwanted side to side motions of the lever handle (minor forward and reverse fluctuations are not a problem).

One of the most important features of the new control is the simple means as shown in FIG. 2 above to extend the control for use with either hand of the operator. The new control combines the best of both the single hand control and the choice of operation from either hand. The ability to switch from right hand to left hand at will is useful when operating under over-hanging obstacles or on a steep hillside when the operator is leaning to one side. If continuous control fatigues one hand, then the other or both hands can be used. Also, if one arm or hand is temporarily or permanently disabled, the mower can still be operated.

FIG. 3 illustrates a pair of joy sticks 60 and 62 located to either side of the mower operator. Each joy stick 60 and 62 is connected to a pair of wire wrapped cables 64 and 66, and 68 and 70 respectively. The mower is equipped with a pair of hydraulic pumps 72 and 74 or other means for controlling as well as powering the drive wheels of the mower. Each pump 72 and 74 has an operating lever 76 and 78 respectively. Cables 64 and 68 are operably attached to lever 76 and cables 66 and 70 are operably attached to lever 78. Thus, each joy stick 60 or 62 can control both pumps 72 and 74 and therefore the mower forward, reverse, speed and direction can be completely controlled by either joy stick. With this configuration using wire wrapped cables, the unused joy stick is forced to follow the motion of the joy stick moved by the operator. This feature is important because the operator can switch hands and joy sticks quickly under difficult operating conditions such as low tree branches and over hanging hedgerows.