A ROAD CLEANING MACHINE COMPRISING A CENTRIFUGAL FAN ASSEMBLY

Abstract

Disclosed is a road cleaning machine including a centrifugal fan assembly that includes a fan casing including a casing inlet and a casing outlet and an impeller mounted in the fan casing and rotatable about an axis of rotation for drawing fluid from the casing inlet and directing the fluid to the casing outlet, the impeller includes a splitter wall extending outwardly from the axis of rotation to define first and second blade chambers extending from first and second faces of the splitter wall respectively, the splitter wall including a splitter wall aperture, a plurality of blades being mounted in the first and second blade chambers the impeller being configured to, during rotation about the axis of rotation, direct fluid from the casing inlet through the first and second blade chambers to the fan casing outlet, the fluid being directed into the second blade chamber via the splitter wall aperture.

Description

TECHNICAL FIELD

The present disclosure is directed towards a road cleaning machine comprising a centrifugal fan assembly and a method of operating such a road cleaning machine.

BACKGROUND

Road cleaning machines (also referred to as road sweepers, street cleaners and the like) are commonly used to remove unwanted debris from streets. A typical road cleaning machine is disclosed in WO2015140546A1, which discloses a road cleaning machine comprising a debris collection arrangement. The debris collection arrangement comprises suction conduits providing a passageway for picking up debris from the road and delivering it to a container mounted on the vehicle chassis. The suction force in the suction conduits may be provided by a centrifugal exhauster fan that is arranged to create a negative pressure in the container. The suction force may draw the debris into the container via the suction conduits. Once in the container, the debris may be separated from the air by means of a separation system before the air is exhausted by the fan to the atmosphere.

A suitable centrifugal fan used in a typical road cleaning machine is disclosed in GB-A-2225814. The centrifugal fan comprises an impeller having circular front and back plates and a plurality of blades therebetween. The blades may each be joined at one end to a generally cylindrical hub. Means may be provided, commonly in the form of a motor or via a transmission from an engine of the road cleaning machine, for rotating the hub and thereby the impeller. The impeller may be housed in a casing having a volute portion and an air outlet. The sides of each blade may be welded to the back plate and front plate of the impeller. The front plate may comprise an air inlet to allow air to enter the impeller.

The centrifugal fan will have an associated pressure loss. The pressure loss corresponds to the amount of energy used by the fan which is wasted and not used for a suction force provided by the fan. A higher pressure loss across the centrifugal fan results in more input power being required by the fan for the same amount of suction force and thus results in a lower efficiency.

In electrical road cleaning machines, the range of the machine is limited by the electrical storage capacity of its battery and the efficiency of its components. With the increasing interest in electrical vehicles including electrical road cleaning machines (i.e. vehicles or machines which do not use an internal combustion engine to provide a driving force), there is an increasing need for efficiency of the components of such electrical vehicles and machines.

SUMMARY

An object of the present invention is to provide a centrifugal fan configured to reduce pressure losses across the fan and improve the efficiency of the fan.

The present invention therefore provides a road cleaning machine comprising a centrifugal fan assembly. The centrifugal fan assembly comprises a fan casing comprising a casing inlet and a casing outlet and an impeller mounted in the fan casing and rotatable about an axis of rotation for drawing fluid from the casing inlet and directing the fluid to the casing outlet. The impeller comprises a splitter wall extending outwardly from the axis of rotation to define first and second blade chambers extending from first and second faces of the splitter wall respectively. The splitter wall comprises a splitter wall aperture. A plurality of blades are mounted in the first and second blade chambers. The impeller is configured to, during rotation about the axis of rotation, direct fluid from the casing inlet through the first and second blade chambers to the fan casing outlet, the fluid being directed into the second blade chamber via the splitter wall aperture.

In addition, there is provided a method of operating a road cleaning machine. The road cleaning machine comprises a fan casing comprising a casing inlet and a casing outlet and an impeller mounted in the fan casing and rotatable about an axis of rotation for drawing fluid from the casing inlet and directing the fluid to the casing outlet. The impeller comprises a splitter wall extending outwardly from the axis of rotation to define first and second blade chambers extending from first and second faces of the splitter wall respectively. The splitter wall comprises a splitter wall aperture. A plurality of blades are mounted in the first and second blade chambers. The method comprises rotating the impeller about the axis of rotation such that fluid is directed from the casing inlet, through the first and second blade chambers to the casing outlet and the fluid is directed into the second blade chamber via the splitter wall central aperture.

Including the splitter wall to divide the impeller into first and second blade chambers may reduce a pressure loss across the centrifugal fan assembly when in use. The splitter wall may reduce the pressure loss by reducing a size of vortices present in a fluid flow inside the impeller. Vortices may be present in a fluid flow inside the impeller due to non-uniform velocity at the inlet of the impeller and inside the impeller. The vortices are an example of a secondary flow. A primary flow may be defined as a flow in a desired direction. With regards the centrifugal fan, the primary flow is a fluid flow perpendicular to the axis of rotation, typically described as a radial outflow, because this is the direction which directs fluid towards the outlet. Any other flow direction, especially a flow direction perpendicular to the primary flow direction can be defined as the secondary flow. The vortices are a secondary flow as they are in a direction other than the primary flow direction. All fluid motion may have an associated pressure loss due to friction. Therefore, the secondary flow, such as the vortices, have a pressure loss. The pressure loss of the secondary flow is unnecessary since it is associated with an undesired fluid motion. The splitter wall reduces the size of the vortices because it reduces the space available in which the vortices can develop in the secondary flow direction and restrict flow to the primary flow direction. Therefore, the splitter wall reduces the pressure loss across the centrifugal fan assembly.

A key advantage of this invention is improving the performance of the fan in a compact envelope whilst reducing the complexity (or maintaining the status quo) of manufacture by retaining flat faces as the front and back plates.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, embodiments of a road cleaning machine and a method of operating such a machine in accordance with the present disclosure are now described with reference to, and as shown in, the accompanying drawings, in which:

FIG. 1 is a side elevation view of a road cleaning machine comprising a centrifugal fan assembly in accordance with the present invention;

FIG. 2 is a cross-sectional side elevation of the centrifugal fan assembly of the present invention;

FIG. 3 is a perspective view of a impeller of the centrifugal fan assembly of FIG. 2 with a first and second wall hidden from view;

FIG. 4 is a perspective view of the impeller of the centrifugal fan assembly of FIG. 2 with the first and second wall shown;

FIG. 5 is a magnified perspective view of a central portion of the impeller of FIG. 2;

FIG. 6 is a cross-sectional side elevation of the splitter wall of the impeller of FIG. 2 in isolation;

FIG. 7 is a cross-sectional side elevation of the impeller of FIG. 2;

FIG. 8 is a magnified perspective view of a hub portion of the impeller of FIG. 2 with a splitter wall hidden from view; and

FIG. 9 is a perspective view of the impeller of the centrifugal fan assembly of FIG. 2 with the first and second wall shown and with blades shown in a staggered arrangement.

DETAILED DESCRIPTION

The disclosed invention relates to a centrifugal fan for a road cleaning machine configured to reduce pressure losses across the fan. The fan comprises a wall configured to split an impeller of the fan into first and second blade chambers. Splitting the impeller into two blade chambers limits a size of secondary vortices or eddies present in a fluid inside the impeller. Reducing the size of the vortices reduces a pressure loss across the fan and thus improves efficiency.

Road cleaning machines are commonly used to remove unwanted debris from streets. A road cleaning machine 10 comprising a centrifugal fan assembly 20 in accordance with the present invention is shown in FIG. 1. The road cleaning machine 10 in this instance is a four-wheeled Truck Mounter sweeper 10 in the form of a driver operated vehicle. The road cleaning machine 10 comprises a front axle and corresponding wheels 11 and a rear axle and corresponding wheels 12. An operator control station 13 is located towards the front of the vehicle. At the sides of the sweeper there are provided cleaning tools, such as cleaning brushes 14 and debris collection arrangement 15.

The debris collection arrangement 15 commonly comprises suction conduits providing a passageway for picking up debris from the road and delivering it to a container 17 mounted on the vehicle chassis 19. The suction force in the conduits is provided by the centrifugal fan assembly 20 that is arranged to create a negative pressure in the container 17. The conveyancing force draws the debris from the suction conduits into the container 17 and once in the container 17, the debris is separated from the air by means of a separation system before the air is exhausted by the centrifugal fan assembly 20 to the atmosphere.

FIG. 2 illustrates an embodiment of a part of a debris collection arrangement 100 comprising the centrifugal fan assembly 20 of the present invention. The centrifugal fan assembly 20 comprises a fan casing 24 and an impeller 26. The impeller 26 is mounted within the fan casing 24 and is rotatable about an axis of rotation 28 for drawing a fluid, particularly air, through the fan casing 24. The impeller 26 may rotate in rotation direction 29 to cause a fluid flow through the fan casing 24.

The fan casing 24 comprises a casing inlet 41 and a casing outlet 43. The casing inlet 41 is for the entry of the fluid, namely air, into the fan casing 24 when the centrifugal fan assembly 20 is in use. The casing outlet 43 is for the exit of the fluid from the fan casing 24 when in use. The casing inlet 41 and the casing outlet 43 are in fluid communication with each other via the impeller 26. Upon rotation of the impeller 26, the fluid is drawn from the casing inlet 41 and directed to the casing outlet 43 by the impeller 26. The casing inlet 41 may be in fluid communication with suction conduits of the debris collection arrangement 100 such that a suction force provided by the centrifugal fan assembly 20 conveys debris along the suction conduits.

The fan casing 24 may further comprise a first casing wall 45, a second casing wall 47 and a casing side wall 49. The first and second casing walls 45, 47 may extend substantially parallel to one another and the casing side wall 49 may extend between the first and second casing walls 45, 47 substantially around the impeller 26.

The casing inlet 41 may comprise a casing inlet aperture 41, which may be centred on the axis of rotation 28. The casing inlet aperture 41 may be in the first casing wall 45 and may be circular. The casing outlet 43 may comprise a casing outlet aperture 43 in the casing side wall 49.

Referring to FIGS. 3 to 8, the impeller 26 comprises a splitter wall 61 and a plurality of blades 63. The splitter wall 61 extends outwardly from the axis of rotation 28 to define a first blade chamber 65 and a second blade chamber 67. The splitter wall 61 further comprises a splitter wall aperture 69, which may be centred on the axis of rotation. The blades 63 are mounted in the first and second blade chambers 65, 67. The impeller 26 is configured to, during rotation about the axis of rotation 28, direct the fluid from the casing inlet 41 through the first and second blade chambers 65, 67 to the casing outlet 43. The fluid is directed into the second blade chamber 67 via the splitter wall aperture 69.

As shown in FIG. 4, the impeller 26 may further comprise a first impeller wall 103 and a second impeller wall 101. The second impeller wall 101 extends radially outwardly from the axis of rotation 28. The first impeller wall 103 is spaced apart from the second impeller wall 101 and comprises a first impeller wall aperture 105, which may be central and/or circular, for directing the fluid from the casing inlet 41 into the first and second blade chambers 65, 67. The first and/or second impeller wall 103, 101 may extend perpendicularly from the axis of rotation 28 and the first impeller wall 103 may be parallel to the second impeller wall 101.

The impeller 26 may further comprise a centre 71 and an impeller outer edge 72. The centre 71 may be coincident with the axis of rotation 28. The splitter wall 61, first impeller wall 103 and/or second impeller wall 101 may extend from, from adjacent and/or from proximal the centre 71 of the impeller 26 to the impeller outer edge 72. As illustrated, the splitter wall 61, first impeller wall 103 and/or second impeller wall 101 may all extend to the impeller outer edge 72. However, in other embodiments the splitter wall 61, first impeller wall 103 and/or second impeller wall 101 may extend partially to the impeller outer edge 72.

The first impeller wall 103 may be spaced apart from the second impeller wall 101 by an impeller depth 107. The impeller depth 107 may be between 75 mm and 155 mm. A larger impeller depth 107 results in a higher flow rate through the impeller 26 because the impeller 26 is able to do work on a larger volume of fluid. The impeller 26 may comprise an impeller diameter 74 comprising twice the distance from the centre 71 of the impeller 26 to the impeller outer edge 72 and the impeller diameter 74 may be between about 600 mm and about 1000 mm. The impeller depth 107 is in the range of from about 1/10 to about ⅛ or to about ⅙ of the impeller diameter 74.

The first impeller wall aperture 105 may be circular and may comprise a first impeller wall aperture diameter 113. As shown most clearly in FIG. 7, the first impeller wall aperture diameter 113 may be between 2 and 4 times the impeller depth 107

The first impeller wall aperture diameter 113 may also be between about ⅓ and about ½ of the impeller diameter 74. The ratio of the first impeller wall aperture diameter 113 to the impeller diameter 74 may characterise how much work is added to the air flow during use of the fan.

The first impeller wall aperture diameter 113 may be between about 350 mm and about 550 mm less than the impeller diameter 74. The first impeller wall aperture diameter 113 may be between about 300 mm and about 500 mm.

Increasing the first impeller wall aperture diameter 113 increases the flow rate through the impeller 26 because a larger fluid flow rate is able to enter the impeller 26 through the first impeller wall aperture 105 under the same conditions.

The impeller 26 may comprise a radial blade length 115. The radial blade length 115 may be defined as: radial blade length=(impeller diameter-first impeller wall aperture diameter)/2.

In the context of the present invention, the impeller 26 may be characterised by an impeller ratio 117. The impeller ratio 117 is the ratio of the impeller depth 107 to the radial blade length 115. The impeller ratio 117 may be calculated from: impeller ratio=impeller depth/radial blade length. The impeller ratio 117 may determine a size and a strength of vortices present within the impeller 26, if the impeller 26 were not to include the splitter wall 61. The impeller ratio 117 may determine the optimised axial location for the splitter wall 61.

As shown in the illustrated embodiment, the impeller ratio 117 may be between about ⅓ and about ½.

If the impeller ratio 117 is larger than ½ then the vortices may be of a size and a strength such that a single splitter wall 61 is not sufficient to direct the fluid in a desired flow direction. If the impeller ratio 117 is more than ½, the impeller 26 may further comprise a second splitter wall 61. The second splitter wall 61 may comprise all of the features described in relation to the splitter wall 61. If the impeller 26 comprises a second splitter wall 61, the impeller ratio 117 may be between ½ and ¾. If the impeller ratio 117 is larger than ¾, the impeller 26 may comprise further additional splitter walls each of which may comprise all of the features described in relation to the splitter wall 61.

In the context of the present invention, the impeller 26 may be further characterised by an impeller area ratio. The impeller area ratio is the ratio is defined as the ratio between the area of the first impeller wall aperture 105 and the area of a cylindrical surface of the impeller at the impeller outer edge 72. The area of the first impeller wall aperture 105, A_in, is defined as A_in=πd²/4 (where d is the first impeller wall aperture diameter 113) and the area of a cylindrical surface of the impeller at the impeller outer edge 72, A_out, is defined as A_out=πD h (where D is the impeller diameter 74 and h is the impeller depth 107). The impeller area ratio may be calculated as: impeller area ratio=A_in/A_out. The impeller area ratio may be between ⅓ and ½.

The splitter wall 61 defines the first blade chamber 65 extending from a first face 75 of the splitter wall 61 and defines the second blade chamber 67 extending from a second face 77 of the splitter wall 61. The first and second faces 75, 77 face in opposite directions. The splitter wall 61 may be disposed between the first impeller wall 103 and the second impeller wall 101. The splitter wall 61 may be parallel to the first and second impeller walls 103, 101. The first blade chamber 65 may extend between the first impeller wall 103 and the splitter wall 61, such as the first face 75 thereof. The second blade chamber 67 may extend between the second impeller wall 101 and the splitter wall 61, such as the second face 77 thereof.

If the impeller 26 comprises the second splitter wall 61, the second blade chamber 67 may extend between the splitter wall 61 and the second splitter wall 61. In addition, the impeller 26 may comprise a third blade chamber extending from the second splitter wall 61 and the second impeller wall. If the impeller 26 comprises further additional splitter walls the impeller may comprise additional blade chambers extending between these splitter walls.

The splitter wall 61 may be a solid wall. The splitter wall 61 may be configured such that air cannot flow through the splitter wall 61 from the first blade chamber 65 to the second blade chamber 67. The first and second blade chambers 65, 67 may be sealed from one another except for at the impeller 26 outer edge 72 and at splitter wall aperture 69.

The splitter wall 61 may be located between the first and second impeller wall 101s 103, 101 such that flow in the first and second blade chambers 65, 67 is substantially balanced. The splitter wall 61 may be located between about 40% and about 60% of the distance between the first and second impeller walls 103, 101.

Hence the splitter wall 61 may be located at a substantially equal distance from the first impeller wall 103 as from the second impeller wall 101 and may be located substantially midway across the impeller depth 107.

The splitter wall 61 may extend perpendicularly from the axis of rotation 28. In addition and/or alternatively, the splitter wall 61 may be parallel to the first impeller wall 103 and the second impeller wall 101. The splitter wall 61 may comprise a planar body and may also be referred to as a dividing wall and/or plate. The splitter wall 61 may comprise a disc and may be circular.

As shown in FIG. 5, the splitter wall 61 may comprise a splitter wall main body 121 and a splitter wall guide wall 123 extending from the splitter wall main body 121 to the splitter wall aperture 69. The splitter wall guide wall 123 is configured to guide fluid from the casing inlet 41 into the first and second blade chambers 65, 67. By guiding fluid into the first and second blade chambers 65, 67, the splitter wall guide wall 123 reduces the pressure loss across the impeller 26 by providing a path for the fluid to follow and helps the fluid to avoid separating, which would result in pressure losses. The splitter wall guide wall 123 may be annular and may have infinite rotational symmetry around the axis of rotation 28. The splitter wall main body 121 and guide wall 123 may be formed integrally with one another or may be formed separately and subsequently connected to one another.

FIG. 6 shows the splitter wall 61 in isolation from the rest of the impeller 26. As shown in the illustrated example, the splitter wall guide wall 123 may comprise a splitter wall ring portion 125 and a splitter wall curved portion 127. The splitter wall ring portion 125 may be cylindrical and may comprise an outer surface which is parallel to the axis of rotation 28. The splitter wall curved portion 127 may comprise an outer surface which is concave. The splitter wall ring portion 125 may extend from the splitter wall aperture 69 to the splitter wall curved portion 127 and the splitter wall curved portion 127 may extend from the splitter wall ring portion 125 to the splitter wall main body 121. The gradient of the splitter wall curved portion 127 may continuously decrease from the splitter wall ring portion 125 to the splitter wall main body 121. A surface of the splitter wall curved portion 127 may be parallel to the splitter wall ring portion 125 where it meets the splitter wall ring portion 125 and parallel to the splitter wall main body 121 where it meets the splitter wall main body 121 (for example without any step changes).

Referring again to FIG. 5, the splitter wall aperture 69 may be substantially circular. The splitter wall aperture 69 may comprise a splitter wall aperture diameter 131. As shown in FIG. 7, the splitter wall aperture diameter 131 may be between about 1.5 and about 2.5 times the impeller depth 107. The splitter wall aperture diameter 131 may be between about 0.25 and about 0.35 times the impeller diameter 74. The splitter wall aperture diameter 131 may also be between about 0.5 and about 0.9 times the first impeller wall aperture diameter 113. The splitter wall aperture diameter 131 may also be such that a ratio of the area of the splitter wall aperture 69 to the first impeller wall aperture 105 is between 0.25 and 0.8. The splitter wall aperture diameter 131 may also be between about 400 mm and about 600 mm less than the impeller diameter 74. The splitter wall aperture diameter 131 may also be between about 50 mm and about 130 mm less than the first impeller wall aperture diameter 113. The splitter wall aperture diameter 131 may also be between about 180 mm and about 300 mm. The splitter wall aperture 69 may be sized relative to the first impeller wall aperture 105 such that an equal amount of fluid may flow into each of the first and second blade chambers 65, 67.

The blades 63, particularly those on the first face 75, may extend from outer blade ends 62 adjacent and/or proximal to the outer edge 72 of the splitter wall 61 and impeller 26, along the splitter wall main body 121 to inner blade ends 64 at, adjacent to and/or proximal to the splitter wall guide wall 123. As shown in FIG. 3, the inner blade ends 64 may be adjacent to the splitter wall guide wall 123 (i.e. with no overlap) and there may be a gap between the inner blade ends 64 and the splitter wall ring portion 125.

However, as shown in FIGS. 10 and 11, the blades 63 may extend along the splitter wall main body 121 and across at least part of the splitter wall guide wall 123, such as across all or part of the splitter wall curved portion 127. As in FIGS. 10 and 11, the blades 63 may extend to the splitter wall curved or ring portions 127, 125 and the inner blade ends 64 may be at or adjoined to the splitter wall curved or ring portions 127, 125. Hence the blades 63 overlap the gap between the splitter wall guide wall 123 and the first impeller wall aperture 105 (i.e. such that the blades are visible through the first impeller wall aperture 105). As in FIG. 10, top blade edges 66 of the blades 63 may extend straight from the first impeller wall 103, at the same height as the first impeller wall 103, to the splitter wall ring portion 125. As in FIG. 11, the top blade edges 66 may curve downwardly, or towards the splitter wall 61, from the first impeller wall 103.

Upon rotation, the blades 63 apply a force to the fluid to cause it to flow from the casing inlet 41 to the casing outlet 43. The blades 63 extend from the splitter wall 61 into the first blade chamber 65 and extend from the splitter wall 61 into the second blade chamber 67. The blades 63 extends from the first face 75 into the first blade chamber 65 and from the second face 77 into the second blade chamber 67. The blades 63 may extend at least partially between the splitter wall 61 and the first and second impeller walls 103, 101. Preferably, the blades 63 extend continuously from the splitter wall 61 to the first impeller wall 103 and the blades 63 extend continuously from the second impeller wall 101 to the splitter wall 61.

As shown best in FIG. 3, the blades 63 may comprise eight blades 63. The blades 63 may also comprise five, seven, nine, eleven or any other suitable number of blades 63. The number of blades 63 affects the fluid flow rate of the impeller 26. Increasing the number of blades 63 may increase a flow rate of the impeller 26 because more blades 63 are imparting a force to the fluid. However, increasing the number of blades 63 may increase a torque required to rotate the impeller 26, and thus more energy will be required to operate the impeller 26, because there will be more friction between the impeller 26 and the fluid. As in the illustrated embodiment, the optimum number of blades 63 is in the range of seven to nine and is preferably eight.

Each blade 63 may, such as by its shape, be configured such that the fluid is directed from the centre 71 of the impeller 26 to the impeller outer edge 72 when the impeller 26 is rotated in the rotation direction 29 around the axis of rotation 28. Each blade 63 may be curved and may be continuously curved. Each blade 63 may be convex such that a chord of the blade 63 is behind a camber of the blade 63 in the rotation direction 29. The chord of each blade 63 defines a straight line from a leading edge 81 to a trailing edge 83 of the blade 63. The camber of each blade 63 is a line defining a distance from the chord of a mid-thickness point of the blade 63, along the chord of the blade 63. Each blade 63 may alternatively be straight.

The blades 63 may extend, in the direction of the chord of the blade shape, across about 50%, about 75% or about 90% of a radius of the impeller 26. The leading edge 81 of each blade 63 may be spaced from the splitter wall aperture 69 by a distance of 5%, 10%, or 15% of the radius of the impeller 26. The trailing edge 83 of each blade 63 may be at the impeller outer edge 72.

As shown in the illustrative example, the blades 63 may extend continuously through the splitter wall 61 and may extend from the same point of the splitter wall 61 on the first and second faces 75, 77. Alternatively, the blades 63 could be non-continuous through the splitter wall 61, such as by being mounted directly onto the first and second faces 75, 77. The blades 63 may therefore have the same or different orientations and/or layouts in each of the first and second blade chambers 65, 67. In particular, the blades 63 in each of the first and second blade chambers 65, 67 may be staggered or offset from one another. Thus a blade 63 on mounted onto the first face 75 may bisect the area between two adjacent blades 63 on the second face 77, as illustrated in FIG. 9.

The impeller 26 may further comprise a hub portion 90 and the hub portion 90 may be rotatably mounted to the fan casing 24. FIG. 8 shows the hub portion 90 more clearly with the splitter wall 61 hidden from view. The hub portion 90 comprises a boss 91 for mounting the impeller 26 onto a drive shaft (not shown) and extending towards the first impeller wall 103, towards the splitter wall 61 and/or through the splitter wall aperture 69. The hub portion 90 may further comprise a hub wall 93 extending from the boss 91 and to the second impeller wall 101. The hub wall 93 may blend into the boss 91 and may curve, such as in a concave curve, between the boss 91 and the second impeller wall 101. Alternatively, the boss 91 may be cone shaped and blend directly into second impeller wall 101 without the presence of the hub wall 93. The blades 63 may extend from the hub wall 93 and the leading edge 81 of the blades 63 in the second blade chamber 67 may be located adjacent to the hub portion 90. The boss 91 may comprise a mounting arrangement 95, such as internal splines as illustrated, for mounting to the drive shaft such that the boss 91, and therefore hub portion 90 and impeller 26, is rotatable with the drive shaft.

The hub portion 90 may be mounted onto a drive shaft which is connected through transmission to an engine. Alternatively, the hub portion 90 may be mounted onto an electric motor.

As best shown in FIG. 2, the casing inlet 41, the first impeller wall aperture 105, the splitter wall aperture 69 and/or the hub portion 90 may be aligned along the axis of rotation 28. The first impeller wall aperture 105 may be located in and/or adjacent to the casing inlet 41. The splitter wall aperture 69 may be located in and/or adjacent to the first impeller wall aperture 105. The splitter wall aperture 69 may also be located in and/or adjacent to the casing inlet 41. The hub portion 90 may extend through the splitter wall aperture 69 and may also extend through the first impeller wall aperture 105. By this arrangement, fluid may flow in the same direction, along the axis of rotation 28 through the casing inlet 41 and through the first impeller wall aperture 105 into the first blade chamber 65 and through the splitter wall aperture 69 into the second blade chamber 67.

As shown best in FIG. 4, the impeller 26 may be open at the impeller outer edge 72, i.e. the impeller 26 may not be enclosed by a wall perpendicular to the axis of rotation 28. The open impeller outer edge 72 allows direct fluid communication without obstruction between the first and second blade chambers 65, 67 and the casing outlet 43 located in the casing side wall 49. In particular, fluid can flow out of the impeller 26 between the blades 63 through the open impeller outer edge 72 and to the casing outlet 43. Therefore, fluid is able to flow from the first and second blade chambers 65, 67 to the casing outlet 43.

Referring again to FIG. 2, the road cleaning machine 10 may further comprise an inlet duct 150. The inlet duct 150 may be for conveying the fluid into the centrifugal fan assembly 20. The inlet duct 150 is in fluid communication with the casing inlet 41 of the fan casing 24 and may provide fluid communication between the centrifugal fan assembly 20 and the container 17 mounted on the vehicle chassis 19. The inlet duct 150 may be elongate along a duct longitudinal axis 151. The duct longitudinal axis 151 is nonparallel to the axis of rotation 28 of the centrifugal fan assembly 20.

The inlet duct 150 may comprise a fluid guide vane 153 disposed within the inlet duct 150 for directing fluid into the impeller 26 in a direction parallel to the axis of rotation 28 of the centrifugal fan assembly 20. Directing fluid into the impeller 26 in a direction parallel to the axis of rotation 28 increases the flow rate through the impeller 26 by ensuring the fluid is parallel upon entry to the fan casing 24. This distributes a velocity profile of the fluid more evenly throughout the casing inlet 41 and increases the flow rate by reducing regions of low fluid velocity in the casing inlet 41.

The fluid guide vane 153 may comprise a flat plate. The fluid guide vane 153 may extend across the entire width of the inlet duct 150 and may split the fluid flow through the inlet duct 150 substantially into two. The fluid guide vane 153 extends between a first vane end 155 and a second vane end 157. The second vane end 157 is closer to the centrifugal fan assembly 20 than the first vane end 155 and may be adjacent to the casing inlet 41. The first vane end 155 is opposite the second vane end 157 and is distal to the casing inlet 41 (i.e. closer to the container 17 mounted on the vehicle chassis 19). The fluid guide vane 153 may comprise a first vane portion 160 extending parallel to the duct longitudinal axis 151 from the first vane end 155, may comprise a second vane portion 161 extending parallel to the axis of rotation 28 from the second vane end 157 and may comprise a curved vane portion 162 between the first and second vane portions 160, 161. The curved vane portion 162 may be continuously curved and extend continuously from both the first and second vane portions 160, 161.

A method of operation of the road cleaning machine 10 is now described. The impeller 26 of the centrifugal fan assembly 20 is rotated in the rotation direction 29 around the axis of rotation 28 such that the fluid is directed from the casing inlet 41 through the first and second blade chambers 65, 67 to the casing outlet 43. The fluid is directed into the second blade chamber 67 via the splitter wall aperture 69. The fluid may be directed into the first and second blade chambers 65, 67 via the first impeller wall aperture 105.

The impeller 26 may be rotated by means of the drive shaft (not shown) upon which the impeller 26 is mounted. The impeller 26 may be rotated by rotating the drive shaft and therefore the hub portion 90 of the impeller 26 mounted thereupon. The drive shaft may be rotated by means of an electric motor or a transmission from an engine of the road cleaning machine 10. Alternatively, the impeller 26 may be mounted directly to the electric motor.

The centrifugal fan assembly 20 may be rotated at a service speed. The service speed may be the rotational speed at which the centrifugal fan assembly 20 is designed to operate and the rotational speed at which the centrifugal fan assembly 20 operates with minimum pressure losses. The service speed may be between 1800 rpm and 4000 rpm. The service speed of the centrifugal fan assembly 20 may be dependent upon the impeller diameter 74 such that a fan assembly with a larger impeller diameter 74 will have a lower service speed.

Directing fluid from the casing inlet 41 to the casing outlet 43 produces a suction force at the casing inlet 41. The suction force may convey air and debris along the suction conduits which are in fluid communication with the centrifugal fan assembly 20 and into the container 17 mounted to the vehicle chassis 19 of the road cleaning machine 10. Subsequently, the air may be separated from the debris by means of a separation system and the debris is stored in the container 17 while the air flows towards the centrifugal fan assembly 20.

The air may flow through the inlet duct 150. The air may flow along the inlet duct 150 in a direction substantially parallel to the duct longitudinal axis 151. The air may flow along the fluid guide vane 153 disposed within the inlet duct 150. When the air flows along the fluid guide vane 153 it substantially follows a shape of the fluid guide vane 153 due to fluid friction. Therefore, the air first mainly flows in a direction substantially parallel to the first vane portion 160, then substantially along the curved vane portion 162 and finally in a direction substantially parallel to the second vane portion 161. Therefore, the air may turn from a direction substantially parallel to the duct longitudinal axis 151 to a direction substantially parallel to the axis of rotation 28 before leaving the inlet duct 150.

The air subsequently enters the centrifugal fan assembly 20 by entering the casing inlet 41 in first casing wall 45. The air may subsequently enter the impeller 26 through the first impeller wall aperture 105. A first portion of the air enters the first blade chamber 65. The first portion of air may be the air which flows through the first impeller wall aperture 105 in an annular area location radially between the first impeller wall aperture 105 and the splitter wall 61. A second portion of air enters the second blade chamber 67 through the splitter wall aperture 69. The second portion of air may be the air which flows through the area located radially within the splitter wall aperture 69.

The impeller 26 may be configured such that the air which passes through the impeller 26 only passes through a single blade chamber 65, 67. A first portion of air may enter the first blade chamber 65 and leave the impeller 26 without entering the second blade chamber 67 at any time. The first portion of air may be exhausted from the road cleaning machine 10 to the atmosphere without entering the second blade chamber 67 at any time. A second portion of air may enter the second blade chamber 67 and leave the impeller 26 without entering the first blade chamber 65 at any time. The first portion of air may be exhausted from the road cleaning machine 10 to the atmosphere without entering the first blade chamber 65 at any time.

The air may be further guided into the first and second blade chambers 65, 67 by the splitter wall guide wall 123. The air may flow along the splitter wall guide wall 123. When the air flows along the splitter wall guide wall 123 it substantially follows a shape of the splitter wall guide wall 123 due to fluid friction. Therefore, the air first mainly flows in a direction substantially parallel to the splitter wall ring portion 125, then substantially along the splitter wall curved portion 127 and finally in a direction substantially parallel to the splitter wall main body 121. Therefore, the air may turn from a direction substantially parallel to the axis of rotation 28 to a direction substantially perpendicular to the axis of rotation 28 as it enters the first and second blade chambers 65, 67.

In the first and second blade chambers 65, 67, work may be done upon the air by virtue of the rotating blades 63. The shape of the blades 63 and the rotation direction 29 causes the air to move through the first and second blade chambers 65, 67 from the centre 71 of the impeller 26 to the impeller outer edge 72. The air may also move from the centre 71 of the impeller 26 to the impeller outer edge 72 due to centrifugal force. The air is moved in a circular direction by contact with the blades 63 and the rotation of the impeller 26 and, due to the mass of the air, the air experiences a centrifugal force driving the air towards the impeller outer edge 72.

Subsequently, the air may leave the first and second blade chambers 65, 67 of the impeller 26 via the open impeller outer edge 72. Upon leaving the impeller 26, the air continues to flow in the direction perpendicular to the axis of rotation 28 towards the casing side wall 49 and then leaves the fan casing 24 via the casing outlet 43. The air is subsequently exhausted from the road cleaning machine 10 to the atmosphere.

Claims

1. A road cleaning machine comprising a centrifugal fan assembly, wherein the centrifugal fan assembly comprises: a fan casing comprising a casing inlet and a casing outlet;an impeller mounted in the fan casing and rotatable about an axis of rotation for drawing fluid from the casing inlet and directing the fluid to the casing outlet, the impeller comprising: a splitter wall extending outwardly from the axis of rotation to define first and second blade chambers extending from first and second faces of the splitter wall respectively, wherein the splitter wall comprises a splitter wall aperture; anda plurality of blades mounted in the first and second blade chambers,wherein the impeller is configured to, during rotation about the axis of rotation, direct fluid from the casing inlet through the first and second blade chambers to the casing outlet, the fluid being directed into the second blade chamber via the splitter wall aperture.

2. The road cleaning machine of claim 1 wherein the impeller further comprises a hub portion rotatably mounted to the fan casing.

3. The road cleaning machine of claim 2 wherein the impeller further comprises: a first impeller wall comprising a first impeller wall aperture for directing fluid from the inlet into the first and second blade chambers and extending outwardly from the axis of rotation of the impeller; anda second impeller wall which is parallel to and spaced apart from the first impeller wall and is adjacent to the hub portion.

4. The road cleaning machine of claim 3 wherein the splitter wall is disposed between and/or parallel to the first and second impeller walls.

5. The road cleaning machine of claim 3 or 4 wherein the plurality of blades extend continuously from the second impeller wall to the splitter wall.

6. The road cleaning machine of claim 3 wherein the plurality of blades extend continuously from the splitter wall to the first impeller wall.

7. The road cleaning machine of claim 3 wherein the splitter wall is located substantially midway between the first and second impeller walls.

8. The road cleaning machine of claim 3 wherein the first impeller wall aperture and splitter wall aperture are centred about the axis of rotation.

9. The road cleaning machine of claim 3 wherein the first impeller wall aperture is located in and/or adjacent to the casing inlet.

10. The road cleaning machine of claim 3 wherein the splitter wall aperture is located in and/or adjacent to the first impeller wall aperture.

11. The road cleaning machine of claim 1 wherein the impeller comprises an open outer impeller edge through which the first and second blade chambers are in direct fluid communication with the casing outlet.

12. The road cleaning machine of claim 1 wherein the splitter wall comprises a splitter wall main body from which the plurality of blades extend and a splitter wall guide wall extending from the splitter wall main body to the splitter wall aperture, wherein the splitter wall guide wall is configured to separate fluid flowing from the inlet into the first and second blade chambers.

13. The road cleaning machine of claim 12 wherein the splitter wall guide wall is annular.

14. The road cleaning machine of claim 12 wherein the splitter wall guide wall comprises: a splitter wall ring portion; and/ora splitter wall curved portion,

15. The road cleaning machine of claim 14 wherein the splitter wall ring portion extends from the splitter wall aperture to the splitter wall curved portion, and/orthe splitter wall curved portion extends from the splitter wall ring portion to the splitter wall main body.

16. The road cleaning machine of claim 12 wherein the blades extend to adjacent to the splitter wall guide wall or extend at least partially across the splitter wall guide wall.

17. The road cleaning machine of claim 1 further comprising an inlet duct wherein the fan casing inlet is in fluid communication with the inlet duct.

18. The road cleaning machine of claim 17 further comprising a fluid guide vane disposed in the inlet duct and configured to direct fluid into the impeller in a direction parallel to the axis of rotation of the centrifugal fan assembly.

19. The road cleaning machine of claim 18 wherein: the inlet duct is elongate along a duct longitudinal axis wherein the duct longitudinal axis is nonparallel to the axis of rotation of the centrifugal fan assembly; andthe fluid guide vane comprises a first vane portion extending parallel to the duct longitudinal axis from a first vane end and a second vane portion extending parallel to the axis of rotation from a second vane end.

20. A method of operating a road cleaning machine wherein the road cleaning machine comprises: a fan casing comprising a casing inlet and a casing outlet;an impeller mounted in the fan casing and rotatable about an axis of rotation for drawing fluid from the casing inlet and directing the fluid to the casing outlet, the impeller comprising: a splitter wall extending outwardly from the axis of rotation to define first and second blade chambers extending from first and second faces of the splitter wall respectively, wherein the splitter wall comprises a splitter wall aperture; anda plurality of blades mounted in the first and second blade chambers,wherein the method comprises:rotating the impeller about the axis of rotation such that fluid is directed from the casing inlet, through the first and second blade chambers to the casing outlet and the fluid is directed into the second blade chamber via the splitter wall central aperture.