(1) Field of the Invention
The present invention relates to lawn mowers, and more particularly, to rotary lawn mowers for cutting grass by rotating cutting blades housed in housings which open downward toward the grass.
(2) Background Information
This kind of rotary lawn mower includes (1) lawn mowers of a type for use in a so-called bagging mode for receiving grass cut by cutting blades in grass receptacles such as bags and (2) lawn mowers of a type for use in a so-called mulching mode for cutting grass cut by cutting blades more finely within housings and discharging the cut grass downward of the housings. The lawn mowers of type (1) can remove all cut grass clippings, providing a good finish of the cut grass, and are thus commonly used in golf courses or the like. The lawn mowers of type (2) can eliminate the need for dumping grass clippings by returning the grass clippings to the lawns, and are thus commonly used in parks or the like.
It is, however, inconvenient to selectively use the two types of lawn mowers for their respective suitable uses. In recent years, an art of allowing a single lawn mower to serve as both types (1) and (2) has been developed (e.g., Japanese Patent Laid-Open Publication No. SHO-64-3441 and U.S. Pat. No. 4,951,449).
SHO-64-3441 discloses that a grass discharge chute can be mounted on a top plate of a housing to set it as a bagging-mode housing. With this structure, a bag is attached to an outlet of the grass discharge chute so that grass cut by a cutting blade can be received in the bag (bagging mode).
The lawn mower of SHO-64-3441 can also remove the grass discharge chute and mount a cover plate on the top plate of the housing to switch it into a mulching-mode housing. With this structure, grass cut by the cutting blade can be discharged downward of the housing (mulching mode).
A lawn mower of U.S. Pat. No. 4,951,449 has a bagging-mode housing with a grass discharge chute extended rearward and upward from its top plate. The bagging-mode housing has a scroll portion for allowing grass cut by a cutting blade to swirl within the housing while directing it to the grass discharge chute. A chute plug blocking the grass discharge chute can be removed to attach a bag to the grass discharge chute, thereby to receive grass cut by the cutting blade in the bag (bagging mode).
The lawn mower of U.S. Pat. No. 4,951,449 can also block the grass discharge chute with the chute plug to discharge grass cut by the cutting blade downward of the bagging-mode housing (mulching mode).
The lawn mower of SHO-64-3441 is switched between the bagging-mode housing and the mulching-mode housing by manually changing parts. The mode switching every time requires manual change of parts, inefficiently involving time-consuming and troublesome parts-changing work.
The lawn mower of U.S. Pat. No. 4,951,449 can switch the bagging-mode housing between the bagging mode and the mulching mode only by mounting or demounting the chute plug to or from the grass discharge chute. The mode switching operation is thus relatively easy.
However, the bagging-mode housing is also used in the mulching mode without change. The bagging-mode housing has, as described above, a scroll portion for allowing grass clippings cut by the cutting blade to swirl within the housing while directing the grass clippings to the grass discharge chute.
In the mulching mode, grass clippings are cut more finely by the cutting blade while being caused to swirl within the housing, and the swirling grass clippings are discharged downward of the housing. The cross-sectional area of the housing is larger at a portion where the scroll portion lies and smaller at a portion without the scroll portion. The flow velocity of an air flow swirling grass clippings within the housing, that is, a swirling flow, can thus be largely changed between the portion with the scroll portion and the portion without the scroll portion. The rapid change of the flow velocity of the swirling flow can be a factor in the retention of grass clippings within the housing.
If the flow velocity is rapidly reduced near the rear end of the scroll portion, for example, grass clippings accumulate on the inner surface of the housing at that portion, or grass clippings accumulate at the inlet of the grass discharge chute. A certain amount of accumulation within the housing reduces the flow of a swirling flow. Suspending the grass cutting operation each time it occurs and removing accumulated grass clippings prevents continuous mowing operations. The resulting operating inefficiency leaves room for improvement.
Furthermore, partial accumulation of grass clippings within the housing prevents grass clippings from being evenly discharged downward from the housing. The return amount of grass clippings returned from the housing to the lawn is thus nonuniform, resulting in a reduced finished quality of the grass cutting.
Thus, desired is a lawn mower which increases operating efficiency in a mulching mode while securing operating efficiency in a bagging mode, thereby improving the finished quality of grass cutting.