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Pump and cleaning apparatus comprising said pumpRelated Patent Categories: Pumps, Three Or More Cylinders Arranged In Parallel, Radial, Or Conical Relationship With Rotary Transmission AxisPump and cleaning apparatus comprising said pump description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060110265, Pump and cleaning apparatus comprising said pump. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to an axial piston pump with variable flow rate. This pump is particularly suitable for processing a cleaning fluid in a cleaning apparatus, for example a high-pressure cleaner. The cleaning fluid may be water to which detergent substances may have been added. The invention further relates to a cleaning apparatus provided with said pump. [0002] In high-pressure cleaning machines axial piston pumps are usually used. Known axial piston pumps comprise a swash plate rotationally driven by a motor shaft which, during rotation, reciprocates a plurality of pistons inside respective cylinders. A pump of this type is for example disclosed in the European patent application EP 1435457, in which an elastic element is arranged below the swash plate. Owing to the elastic element, it is possible to vary the flow rate of the cleaning fluid depending on the dispensing pressure of said fluid, which is selectable by a user by means of a separate pressure-adjusting device. The elastic element in fact enables the angle between the swash plate and the motor shaft to be modified when the dispensing pressure varies. Thus, the stroke of the pistons is modified, i.e. the volume of cleaning fluid that the pistons are able to displace changes. [0003] A drawback of the pump disclosed in EP 1435457 is that, as will be explained in greater detail below, the flow rate of the cleaning fluid decreases very rapidly when the dispensing pressure selected by the user increases. The elastic element, which -is substantially parallel to the pistons, is in fact almost completely compressed when the dispensing pressure of the cleaning fluid exceeds a relatively low value. In this situation, the swash plate is almost perpendicular to the motor shaft, which implies that the stroke of the pistons is short and the volume of cleaning fluid displaced by the pump is low. [0004] A rapid decrease in the flow rate as pressure increases is not desired, because in certain applications it is preferable to combine a high pressure with a high flow rate. A high pressure ensures an effective cleaning action, whereas a high flow rate enables the cleaning fluid to reach zones that are relatively far away from the dispensing point. [0005] An object of the invention is to improve existing pumps and cleaning apparatuses. [0006] A further object is to provide an axial piston pump in which the flow rate of the fluid processed by the pump is as constant as possible as the dispensing pressure increases. [0007] In a first aspect of the invention, there is provided a pump comprising a plurality of pistons movable in a direction, a swash plate arrangement forming an angle with said direction so as to reciprocate said plurality of pistons in said direction, an elastic element interacting with said swash plate arrangement to enable said angle to be modified, wherein between said elastic element and said swash plate arrangement a transmission device is interposed for receiving a force from said swash plate arrangement and transmitting a fraction of said force to said elastic element. [0008] Owing to this aspect of the invention, it is possible to obtain a pump in which, when pressure increases, the flow rate decreases only to a limited extent. The transmission device in fact enables only a fraction of the force exerted by the swash plate arrangement to be transmitted to the elastic element. This force depends on the thrust exerted on the swash plate arrangement by the pistons, i.e. on the pressure of the processed fluid. At a preset dispensing pressure selected by the user, the elastic element is thus less stressed than the elastic element disclosed in EP 1435457 and is able to keep the swash plate arrangement in a more inclined position, in which the pistons perform relatively long strokes. Thus, relatively high flow rates of fluid can be processed. [0009] In a second aspect of the invention, there is provided a pump comprising a plurality of pistons movable in a direction, a swash plate arrangement forming an angle with said direction so as to reciprocate said plurality of pistons in said direction, said swash plate arrangement being oscillatable substantially around a point to modify said angle, wherein said swash plate arrangement is supported by a sliding element and a further sliding element movable along respective substantially rectilinear paths, said paths approximating to circumference arcs centred on said point. [0010] Owing to this aspect of the invention, it is possible to obtain a pump provided with a swash plate arrangement oscillating around a substantially stationary point, which can be constructed in a relatively simple and economical manner. It is not constructionally complicated to provide a sliding element and a further sliding element that are movable along respective substantially rectilinear paths. [0011] The invention will be better understood and carried out with reference to the attached drawings, which show an exemplifying and not restrictive embodiment thereof, in which: [0012] FIG. 1 is a schematic section of a portion of a pump according to the prior art; [0013] FIG. 2 is a schematic representation of the distribution of forces on an elastic element of the pump of FIG. 1; [0014] FIG. 3 is a schematic section taken along the longitudinal axis of an axial piston pump; [0015] FIG. 4 is a schematic section of a swash plate of the pump of FIG. 3 in a position of maximum inclination; [0016] FIG. 5 is a section like FIG. 4, showing the swash plate in a first intermediate position; [0017] FIG. 6 is a section like FIG. 4, showing the swash plate in a second intermediate position; [0018] FIG. 7 is a section like FIG. 4, showing the swash plate in position of minimum inclination; [0019] FIG. 8 is a section taken along the plane VIII-VIII of FIG. 4; [0020] FIG. 9 is a schematic representation of the forces applied to an elastic element of the pump of FIG. 4; [0021] FIG. 10 is a graph that shows how the flow rate varies depending on pressure for some pumps; [0022] FIG. 11 is a schematic representation showing the swash plate in the position of maximum inclination and in the position of minimum inclination; [0023] FIG. 12 is a section like FIG. 4, showing some dimensions of the swash plate; [0024] FIG. 13 is a section like FIG. 7, showing some dimensions of the swash plate; Continue reading about Pump and cleaning apparatus comprising said pump... 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