Abstract:
A lawn mower comprises a cutting deck 2 mounted on at least first and second wheel assemblies. The first and second wheel assemblies comprise, respectively, first and second height adjustment mechanisms 22. The first height adjustment mechanism 22 comprises a first pivoting mechanism 22 pivotal about a first axis for adjustment of the height of the deck above the first wheel assembly. The second height adjustment 22 mechanism comprises a second pivoting mechanism 22 pivotal about a second axis, parallel to the first axis, for adjustment of the height of the deck above the second wheel assembly. A connection or bar 38 is formed between the first and second pivoting mechanisms for pivoting the first and second pivoting mechanisms in opposite directions about the first and second axis, respectively. Each of the pivoting mechanisms 22 raise the height of the deck 2 by substantially equal mounts when pivoted through any part of their full range of pivotal movement.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to lawn mowers and more particularly to height adjustment mechanisms for such mowers. 
     Household lawn mowers comprise a cutting deck upon which is mounted a motor. The motor can be either an electric motor powered by either a main electricity supply or a battery or an internal combustion engine. The motor rotatingly drives a cutting blade mounted below the cutting deck about a substantially vertical axis. The cutting blade cuts the grass beneath the deck as it rotates. The cutting deck is commonly mounted on wheels or rollers. The wheels can either have a fixed direction of travel so that the lawn mower moves over the lawn in a forward and reverse direction, or can be castor wheels which are able to freely swivel so that the mower can travel over the lawn in any direction of travel. 
     It is desirable to have the height of the cutting blade adjustable in relation to the surface of the lawn. This allows the grass to be cut to differing heights. One common way of achieving this is by having the cutting deck of the lawn mower mounted on the wheels or rollers in such a manner that the height of the deck, and hence the height of the cutting blade, is adjustable relative to the wheels. 
     Such mechanisms include mounting the axles of the wheels or rollers on the ends of levers which are pivotally mounted onto the deck and which are capable of being releasably locked into a plurality of angular positions. The height of the cutting deck in relation to the wheels or rollers is dependent upon the angle of pivot of the levers. Interconnecting bars can be added between the levers to ensure that the levers pivot in unison so that the height adjustment of the wheels is uniform. 
     In one type of mower, the forward and rear axles are mounted on the end levers which are pivotally mounted on the cutting deck which are parallel and are interconnected by a bar so that they pivot in unison. However, the forward rear axles pivot about their axes in the same direction. U.S. Pat. No. 4,835,952 shows a mower having a typical design of height adjusting mechanism. In U.S. Pat. No. 4,835,952 the front axle is mounted on to arms of two bell cams which are pivotally mounted onto the body of the mower at their apexes. The second arm of the bell cams project in a generally upward direction. The rear axle is mounted in a similar fashion. Two interconnecting bars interconnect between the second arms of the front and rear bell cams. As the front bell cams pivot, the rear bell cams also pivot in the same direction thus lowering or highering the body of the mower uniformly. 
     However, such designs are bulky taking up valuable space on the mower because it is necessary for the interconnecting bars to project beyond the wheels. In addition, the length of the interconnecting bars has to be approximately the same as the distance between the front and rear wheels if the rate which the height of the deck rises above each wheel is to be constant. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a lawn mower comprises a cutting deck mounted on at least first and second wheel assemblies. The first and second wheel assemblies comprise, respectively, first and second height adjustment mechanisms. The first height adjustment mechanism comprises a first pivoting mechanism pivotal about a first axis for adjustment of the height of the deck above the first wheel assembly. The second height adjustment mechanism comprises a second pivoting mechanism pivotal about a second axis, parallel to the first axis, for adjustment of the height of the deck above the second wheel assembly. A connection is formed between the first and second pivoting mechanisms for pivoting the first and second pivoting mechanisms in opposite directions about the first and second axis, respectively. By constructing the height adjustment mechanisms in this fashion, it can provide a compact construction. It can also enable the height adjustment mechanism to be located between the wheel assemblies thus reducing the amount of mechanical linkage required. 
     Preferably, each of the pivoting mechanisms raise the height of the deck by substantially equal amounts when pivoted through any part of their full range of pivotal movement. 
     Preferably, the first pivoting mechanism is pivotally connected at a first point away from its (“first”) pivot axis to an end of an interconnecting bar. The second pivoting mechanism is pivotally connected at a second point away from its (“second”) pivot axis to the other end of the interconnecting bar. This can provide a simple and reliable construction. 
     The length of the interconnecting bar can be less than the distance between the axes of pivot of the pivoting mechanisms. This provides the advantage that the points of articulation at the ends of any interconnecting bar joining the pivoting mechanisms can lie between the pivoting mechanisms while allowing substantially equal vertical movement of the different height adjustment mechanisms. 
     Preferably, the first point connection of the bar to the first pivoting mechanism is spaced from the first axis in a first direction parallel to a plane extending though the first and second axes. And the second point connection of the bar to the second pivoting mechanism is spaced from the second axis in a second direction opposite the first direction. This can enable the length of the interconnecting rod to be reduced so that it is less than the distance between the axes of pivot. In addition, the interconnecting bar does not have to project pass any of the wheel assemblies when moved through its full range of positions and thus avoids taking up valuable space. 
     Each pivoting mechanism can be pivotally connected to the interconnecting bar via a rod which is rigidly attached to the pivoting mechanism and which preferably projects perpendicularly away from the axis of pivot of the pivoting mechanism. In a direction perpendicular to the plane which passes through both axes of pivot of the pivoting mechanisms, the two rods ideally project in opposite directions to each other and preferably in a direction parallel to a plane which passes through both axes of pivot, towards each other. 
     Each pivoting mechanism can comprise at least one lever pivotally mounted on the cutting deck and connected with the wheel assembly. And ideally, the lever of each mechanism are configured to move as a mirror image of each other in the plane located equidistantly between the two axes of pivot of the levers. The levers can project from their axis of pivot in a direction parallel to a plane which passes through both axes of pivot away from each other. This can result in a very compact yet simple height adjustment mechanism. The whole of the interconnecting mechanism is located between the wheel assemblies throughout its fill range of movement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A lawn mower according to the present invention will now be described by way of example with reference to the following drawings of which: 
     FIG. 1 shows the cutting deck of a lawn mower mounted on four castor wheels; 
     FIG. 2 shows the central mount of a castor wheel; 
     FIGS. 3A and 3B show the pivotal lever from above and in perspective respectively; 
     FIG. 4 shows a vertical section of the height adjustment mechanism, the cutting deck and the caster wheel when the height of the deck is at its maximum; 
     FIG. 5 shows a vertical cross section of the height adjustment mechanism, the cutting deck and the castor wheel when the height of the deck is at its minimum; 
     FIG. 6 shows a perspective view of the front pair of castor wheels together with corresponding pivotal levers to the ends of an interconnecting rod; and 
     FIGS. 7A and 7B show the deck of the mower in its lowered and raised positions respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, the cutting deck  2  or frame of the lawn mower is mounted on four castor wheels  4  located near to the four comers of the deck  2 , upon which is mounted an electric motor not shown and a hood not shown which encloses the motor. The motor rotatingly drives a cutting blade not shown mounted below the deck on the output drive spindle of the motor about a substantially vertical axis in known fashion. A grass chute  6  is mounted on top of the cutting deck  2  which directs the grass cuttings from the cutting blade to a grass box not shown which attaches to the rear of the cutting deck  2 . A height adjustment mechanism is attached to the mower which raises or lowers the height of the cutting deck  2  in relation to the castor wheels  4 , hence lifting or lowering the height of the cutting blade in relation to the ground below the mower. 
     Each of the four castor wheels  4  of the mower and its corresponding height adjustment mechanism are preferably constructed and operate in the same manner. Other variations will be apparent to those skilled in the art. 
     As can be seen in FIG. 1, each castor wheel  4  comprises two wheels  8  of equal dimensions which are mounted on a central mount  10  adjacent to each other and which have the same axis of rotation. FIG. 2 shows the central mount  10  which comprises a vertical sleeve  12 , a vertical triangular flange  14  attached to the side of the base of the sleeve  12  and two shafts  16  of circular cross section which project perpendicularly from the sides of the triangular flange  14  in opposite directions. The sleeve  12  forms a bore  18  of circular cross section which is sealed at the base end. The two horizontal shafts  16  form axles upon which the two wheels  8  are mounted. The wheels  8  are retained upon the axles  16  by means of a clip not shown and are able to freely rotate about the axles  16 . The central mount  10  is formed from a low friction plastic in a one piece construction. 
     Each castor wheel  4  is mounted on a metal rod  20  which is rigidly attached to and projects vertically downwards from the underside of the cutting deck  2  as best shown in the cross sectional drawings shown at FIGS. 4 and 5. The metal rod  20  has a circular cross section having a diameter which is slightly less than that of the bore  18  of the central mount  10 . The metal rod  20  is located within the bore  18  of the central mount  10 , the central mount  10  being able to freely slide along and rotate about the metal rod  20 . 
     The height adjustment mechanism for each castor wheel  4  comprises a lever  22  which is pivotally mounted on the cutting deck  2  about an axis of pivot  24 . FIGS. 3A and 3B show the pivotal lever  22 . The lever is slidably attached to the sleeve  12  of the castor wheel  4  and acts as a cam, sliding the central mount  10  back and forth along the rod  20  as the lever  22  pivots in either direction, as shown in FIGS. 4 and 5. 
     A collar  26  is formed around the top of the sleeve  12  of each castor wheel  4  as best shown in FIG. 2. A groove  28  is formed around the outer periphery of the collar  26 . The pivotal lever  22  is trough shaped as best shown in FIG.  3 B. An elongate slot  30  is formed along the length of the lever  22  in the base of the trough. At one end of the elongate slot  30 , towards the axis of pivot  24  of the lever  22 , a large aperture  32  has been formed resulting in an overall key shaped slot. The diameter of the large aperture  32  in the lever  22  is greater than that of the outer circumference of the collar  26 . The width of the elongate slot  30  is less than the diameter of the outer circumference of the collar  26  but less than the diameter of the circumference of the groove  28 . 
     The sleeve  12  of the central mount  10  of the castor wheel  4  is attached to the lever  22  by passing the top end of the sleeve  12 , having the entrance to the bore  18 , through the large aperture  32  until the groove  28  formed around the collar  26  becomes aligned with the elongate slot  30  in the lever  22 . The thickness of the lever  22  around the edge  34  of the elongate slot  30  is less than the width of the groove  28 . The collar  26  is moved along the length of the lever  22 , the edge  34  of the elongate slot  30  entering into and sliding through the groove  28 . The sleeve  12  is, therefore, able to slide back and forth along the lever  22  within the elongate slot  30 . The groove  28  acts as a cam follower, sliding along the edge  34  of the elongate slot  30  as the lever  22  pivots. However, the collar  26  is prevented from being moved perpendicularly to apart from the slight movement due to the thickness of the edge  34  of the elongate slot  30  being less than the width of the groove  28  or withdrawn from, and hence detached from the lever  22  whilst the collar  26  is located within the elongate slot  30 . 
     When the lawn mower is fully assembled the metal rod  20  is located within the bore  18  formed by the sleeve  12  and the collar  26  is located within the elongate slot  30  in the lever  22 , such that the edge  34  of the elongate slot  30  are located within the groove  28  around the collar  26  as best shown in FIGS. 4 and 5. 
     The height of deck  2  above the castor wheel  4  is at its maximum when the lever  22  is pivoted in downward position, as best shown in FIG.  4 . In this position the collar  26  is located at the end of the elongate slot  30  furthest away from the large aperture  32  and the axis of pivot  24  of the lever  22 . The rod  20  is of sufficient length that part of the rod  20  still remains within the bore  18  of the central mount  10  when the deck  2  is at its maximum height. Sufficient overlap is provided between the rod  22  and the bore  18  i.e. the amount of rod  20  still located within the sleeve  12  when the central mount  10  is extended away from the cutting deck  2  by its maximum amount to provide a strong and sturdy interconnection between the sleeve  12  and the metal rod  20 , particularly when the forces are applied to the castor wheel perpendicularly to the vertical axis of swivel. 
     When the height of the cutting deck  2  above the castor  4  is to be reduced, the lever  22  is pivoted in an upward direction, as best shown in FIG.  5 . This moves the sleeve  12  and hence the central mount  10  along the rod  20 , a greater proportion of the length of the rod  20  being located within the bore  18  of the sleeve  12 . As the central mount  10  moves along the rod  20 , the groove  28  slides along the sides  34  of the elongate slot  30  in the lever  22 . 
     When the height of the cutting deck  2  above the castor is at its minimum as best shown in FIG. 5, the whole of the metal rod  20  is located within the bore  18  of the central mount  10 . In this position the collar  26  of the central mount  10  is located towards the end of the elongate slot  30  closest to the large aperture  32 . The large aperture  32  is located in such a position that the collar  26  is unable to slide far enough along the elongate slot  30  in order to enter into the large aperture  34  from the elongate slot  30  while the castor wheel  4  is adjusted through its full range of height positions. 
     The height of deck  2  above the castor wheel  4  is fixed by locking the angular position of the lever  22 . 
     Because the groove  28  is formed around the full circumference of the collar  26 , the central mount  10  and hence the castor wheel  4  is able to freely rotate about the rod  20  whilst the collar  26  is located within the elongate slot  30  within the lever  22 . 
     The two levers  22  which are connected to the front two castors  4  on the mower are rigidly attached in parallel to the two ends of a rod  36  perpendicularly to longitudinal axis of the rod  36  as best shown in FIG.  6 . The rod  36  is mounted onto the underside of the cutting deck  2  by means of resilient clips not shown which wrap around and hold the rod  36 . The clips are configured to allow the rod  36  to rotate about its longitudinal axis, thus enabling the two levers  22 , attached to its ends, to pivot in unison about the longitudinal axis of the interconnecting rod  36 . 
     The two levers  22  attached to the two rear castors  4  on the mower are similarly attached to the ends of a second rod  37  which is mounted in parallel to the first rod on the underside of the cutting deck  2  by resilient clips. Thus, the two rear levers  22  pivot in unison about the longitudinal axis of the second rod  37 . 
     An interconnecting bar  38  is pivotally attached between a one of the front levers  22  connected to one of the front castors via a rod  21  rigidly attached to to the front lever  22  and b one of the rear levers  22  connected to one of the rear castors via a second rod  23  rigidly attached to the rear lever  22  so that all four levers  22  pivot in unison. The levers  22  attached to the front castor wheels  4  project forward in the opposite direction to the levers  22  attached to the rear castor wheels  4  which project rearward. The first rod  21  points in a general upward direction. The second points in a general downward direction. The interconnecting bar  38  pivotally attaches to the ends of the rods  21 ,  23  and is arranged so that clockwise rotation of the forward levers  22  results in an anti-clockwise rotation of the rear levers  22 . This enables the height of the deck above all four castors to be kept constant, and that the height of the deck is adjusted in uniform manner above the four castor wheels. FIG. 7A shows the mower with the cutting deck  2  in its lowest position, FIG. 7B shows it in its highest position. 
     A handle  40  (not shown) preferably extends perpendicularly from one of the interconnecting rods. Pivotal movement of the handle by an operator pivots all four levers and this adjusts the height of the cutting deck and hence the cutting blade above the ground. 
     The height of the mower is maintained at the desired height by locking angular positions of the levers  22  by locking the angular position of the handle  40  in well known manner. 
     It is clear from the description that design of interconnecting bar  38  used in conjunction with the two rods  21 ,  23  can be utilized on a mower mounted on wheels having their axles attached to the ends of pivotal levers in a similar manner to that described in U.S. Pat. No. 4,835,952 and arranged so that the levers attached to the front axle of the front wheels pivot in the opposite direction to the levers on which the rear axle for the rear wheels is attached. 
     While the invention has been explained by reference to a preferred embodiment, those skilled in the art will appreciate that various modifications and variations can be made without departing from the spirit and scope of the invention. Thus the present invention is intended to cover all such modification and variations provided they are covered by the appended claims and their equivalents.