EP0831179A2

EP0831179A2 - Recirculation systems

Info

Publication number: EP0831179A2
Application number: EP97307334A
Authority: EP
Inventors: designation of the inventor has not yet been filed The
Original assignee: Schmidt UK Ltd; Schmidt Holding Europe GmbH
Current assignee: Schmidt Holding Europe GmbH
Priority date: 1996-09-20
Filing date: 1997-09-19
Publication date: 1998-03-25
Also published as: EP0831179A3; GB2317407A; GB9619716D0

Abstract

An air transfer system for a suction cleaning vehicle (10) is provided with an air recirculation system (34) which recirculates air and entrained matter from the pressure side of the fan (14) to the inlet region (40) of the matter-collecting tank (12) substantially without passing through the inlet duct to the tank. Dust and other entrained matter is thereby removed from the pressure discharge from the tank and re-enters the tank (12) for collection therein without the need to pass a second time through the nozzle or associated inlet duct of the cleaning vehicle.

Description

This invention relates to recirculation systems and is particularly but not exclusively applicable to recirculation systems for use in cleaning machines such as self-propelled street cleaning machines of the kind in which matter removed from a surface or location to be cleaned is delivered to a matter collection tank or chamber in which it is intended that the matter shall be deposited.

A problem which arises in relation to such systems is that it frequently happens that the matter delivered to the tank is not deposited on the floor of the tank but circulates within the tank and is then at least partially discharged from the tank with the tank exhaust air flow.

This problem arises from the fact that the matter handling system of most cleaning machines of this kind operates on the basis of a fan system which is connected at its suction side to a matter-receiving tank, this tank being connected by a duct to a ground-cleaning suction nozzle. The fan is connected at its pressure or discharge side to an upwardly-directed discharge duct. As a result, the matter delivered to the tank is received from the inlet duct at a relatively high velocity, and in the case of dust and the like there is a strong tendency for this matter to be circulated within the tank, or at least to do so for some time.

Attempts to minimise the discharge of matter from the tank through its exhaust duct (which effectively discharges the output of the pressure side of the fan) have included the provision of a fan screen downstream of the fan to screen matter out from the fan inlet connection. However, such a screen removes only the larger particles from the turbulent and/or high velocity air flow within the tank.

Further attempts to minimise discharge of matter with the output air flow from the tank have included the use of water recirculation systems in which a water spray is injected into the air and matter flow prior to its delivery to the tank so that the solid matter entrained in the air flow has a greater tendency to be deposited in the tank. However, such systems introduce substantial complications into the cleaning machine in terms of a requirement for substantial water storage and water screening systems.

It has also been proposed to recirculate some of the dust-laden air from the tank/chamber system to the nozzle region so that it has a second opportunity to be deposited in the tank. For this purpose, it has been proposed to lead such recirculated and dust-laden air back to the nozzle region through appropriate ductwork. According to one such proposal the recirculated air is injected directly into the nozzle itself. In another such proposal the recirculated air and associated dust is directed onto the ground in front of the nozzle so as to ensure efficient entry of the recirculated matter into the nozzle and so as to effect additionally a degree of positive displacement ground cleaning.

However, such an arrangement leads to unacceptable complications in terms of the substantial lengths of large diameter ductwork needed for the recirculated air, not to mention the impact of this ductwork on the space available for other components in a relatively restricted area of the machine.

Accordingly, an object of the present invention is to provide improvements in or relating to the shortcomings of the prior art as discussed above, or generally.

According to the invention there is provided apparatus and a corresponding method as defined in the accompanying claims. In the claims, the state of the art with respect to the two-part form of claim 1 takes the prior art as discussed above in relation to the prior proposals for recirculation of air as the starting point for the novelty of the invention.

In an embodiment described below, there is provided a self propelled cleaning machine comprising a matter-receiving tank or chamber. A power-driven fan assembly is provided. The suction side of the fan assembly is connected to the tank so that the tank is at below atmospheric pressure. The fan draws air from the tank through a fan screen. On the upstream side of the screen, the tank is connected to a suction nozzle through a large diameter suction duct. In use, matter is sucked into the nozzle from a surface to be cleaned and conveyed through the duct to the tank where some of the matter is deposited on the base of the tank and other parts of the matter, particularly the small particles and dust, pass through the fan screen and into the fan itself, from which the majority of the air is discharged upwards together with any entrained dust or the like.

In the embodiment, there is provided air return means operative to return air from the region of the fan to the tank to enable that air to enter the tank a second time and thereby have an opportunity for deposition. In the embodiment, the air return means comprises ductwork interconnecting the fan housing and a duct at the inlet region of the tank and leading directly to the tank. In this way, the recirculated air can pass direct from the fan to the tank and in the embodiment this is achieved substantially within the tank structure and/or the housing for the tank, and without the need for the provision of lengths of ducts external to the tank and leading to the nozzle and brush region of the cleaning vehicle. Indeed, in the embodiment, there is no requirement for the provision of any lengths of flexible duct and the air feed-back arrangement is particularly compact and convenient.

As a result, the provision of the air/matter feedback system can be readily provided within the tank structure so that by means of some simple sheet metal duct work there is provided a facility enabling repeated recirculation of dust laden air until the dust or other matter is deposited in the tank, and without the weight and expense and complication of corresponding water recirculation systems.

In the described embodiments the means for recirculating the air and entrained matter is provided in a form comprising the provision of interception means on the fan assembly whereby a portion of the air and entrained matter passing through the fan assembly is permitted to be intercepted in the course of its passage through the fan assembly and to be caused to leave its otherwise intended trajectory so that it then adopts a new path in which it is caused to pass to an inlet device associated with the matter collection tank or chamber.

The interception means on the fan is provided in the form of an outlet opening in the fan casing. The fan is of the kind in which a rotary impeller discharges air in a radial and/or circumferential direction while generating a sub-atmospheric pressure in the axis region of the fan. Such a fan assembly comprises what may be termed a centrifugal impeller rotating in a generally volute-shaped impeller housing or casing. The interception means is provided in the form of an opening in the casing which permits an outer laminar layer of the rotating air and dust load in the casing to exit through the opening. The opening extends across the full axial (with respect to the rotation of the impeller) width of the casing and has an opening depth of between 10 and 30 millimetres, preferably 18 to 22 millimetres, which may be varied according to requirements by means of an adjustable shutter.

In this way, there is provided a simple means for achieving an effective separation of a significant proportion of the unseparated dust from the remainder of the air, due to the fact that the air layer at the outer periphery of the fan casing contains a higher proportion of the dust and other solid matter than the remainder of the air flow. This is due to dynamic effects during rotation of the air within the fan casing.

In an embodiment the arrangement is such that the ductwork conveying the recirculated air and entrained matter feeds into the existing pneumatic conveying system at a location such that the returned entrained matter does not re-enter the inlet duct leading from the nozzle to the tank. In this way the returned matter is able to re-enter the system by a short direct route. Moreover, the recirculated matter is injected into the ductwork carrying the existing pneumatically-conveyed matter without effecting a substantial reduction in the vacuum effect which is relied-upon to effect conveying.

In previous proposals for recirculation of entrained matter in pneumatic conveying systems of this kind it has been considered essential to deliver the recirculated air and entrained matter to a location where its effect on the vacuum system for material transport is minimised. This has hitherto been effected by delivering the recirculated air and material to the suction nozzle region of the cleaning machine so that, effectively, the material is just re-inserted into the system at the inlet end so that the entrained matter joins the new matter being removed from a surface being cleaned and thereby can be expected to have little effect on the vacuum conveying system provided for material transport.

The described embodiments of the invention avoid the need for such wasteful recirculation through the nozzle and its associated inlet duct leading to the tank, by delivering the material direct to the inlet to the tank and in a manner such that the effect on the vacuum conveying effect is minimised. This is achieved by arranging for a balanced recirculation effect whereby the pressure differential between the relatively high pressure at the casing of the fan (from which the recirculated air and matter is taken) to the relatively low pressure in the suction conveying system at the inlet to the tank is co-ordinated with the required degree of feedback. By arranging for the cross-sectional areas to be appropriately balanced, the desired conveying effect is achieved.

The balancing of the feedback loop so that the desired proportion of feedback is achieved may be effected by selection of the appropriate dimensions for the inlet to the feedback loop from the fan casing, together with the corresponding design selection for the dimensions and dispositions of the parts of the injection means for injecting the feedback flow into the main flow through the cleaning apparatus. Means for adjustment of the flow resistance in the feedback loop may be provided, for example in the form of an adjustable shutter. In this way there can be achieved a balance between the desirable effect of achieving the required recirculation or feedback effect and the unrequired effect that the feeding of additional air into the ducts through which the main vacuum cleaning system exerts its vacuum cleaning effect has a tendency to reduce that cleaning effect. The invention is based, according to one aspect of it, on the technical step of avoiding the perceived necessity for feedback to the first stage input level of the vacuum conveying system, and providing instead the means to feedback conveniently to exactly the location at which the hitherto unachieved deposition (in the tank) of entrained matter from the airstream can be given a second opportunity to occur, without the necessity for a repetition of the inconvenient passage of the matter through the first stages of the vacuum conveying system.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which :-

Fig 1 shows a schematic representation of a system according to the invention including a matter receiving tank and as associated screen together with the fan and the matter-removing nozzle assembly;

Fig 2 shows a schematic diagram of the system of Fig 1 illustrating the connected interrelationship of the main components of the system;

Fig 3 shows a side elevation view of a self-propelled street cleaning machine and includes in partially-sectioned format a showing of certain parts of the machine relating to the air transfer system and associated structures; and

Fig 4 shows on a larger scale a view on arrow IV in Fig 3 showing the relative disposition of a fan assembly and an inlet duct.

In the accompanying drawings, there is shown an air transfer system for a suction cleaning vehicle. That vehicle may be of the kind described in our published GB application number 2244740A. Reference is hereby directed to the latter published application and we hereby incorporate the entire text and drawings of that published application into the present application for purposes of economical disclosure.

In the accompanying entirely diagrammatic Fig 2 of the drawings, there is shown a representation of a self-propelled vehicle 10 comprising a matter-receiving tank 12, a fan 14 connected at 16 to said tank to reduce the pressure therein, a nozzle 18 connected to tank 12 by an inlet duct 20, and the ground is represented at 22, from which nozzle 18 removes matter to be cleaned by suction applied therefrom, as indicated at 24.

Tank 12 and fan 14 are enclosed within a housing or superstructure 26 carried on vehicle 10. There is provided within tank 12 a screen 28 serving to screen-out from the connection 16 to fan 14, entrained matter within the air stream, which is larger than the mesh openings of the screen. It is intended that the majority of the solid matter deposited in tank 12 will be deposited in the portion 30 of the tank which is on the upstream side of screen 28.

All of the components and systems described thus far are generally conventional for self-propelled suction cleaning vehicles of this kind and examples of the construction of these parts are to be found in our above-mentioned prior published GB application.

Fan 14 discharges at its pressure side as shown at 32 and under dry conditions of cleaning and sweeping, substantial amounts of dust enter tank 12 and cannot immediately be deposited on the base of the tank due to the inevitable high velocity air flow through the tank arising from the fan and the requirement for the application of significant vacuum to inlet duct 20. As a result, in certain cleaning vehicles operating under dusty conditions there tends to be a plume of dust discharged upwards at 32 which is not acceptable.

With a view to achieving a reduction in the amount of entrained matter discharged at 32 from vehicle 10, there is provided a recirculation or feedback system indicated generally at 34. Prior proposals for such feedback systems are indicated at 36.

In accordance with the invention the feedback/recirculation system 34 comprises ducting 38 connecting between fan 14 and the inlet 40 to tank 12 so that the air and entrained matter is injected into the airstream into the tank substantially without passing through the inlet duct 20 of vehicle 10.

The prior art systems 36 provide long ducts from the tank/fan region to the nozzle/ground region, which cause the disadvantages discussed above.

Turning now to the embodiment of the feedback/recirculation system 34 of the present invention as shown in Fig 1, corresponding parts are numbered in Fig 1 accordingly.

Thus, inlet duct 20 from nozzle 18 is connected to tank 12 to discharge air and entrained matter into it. Feedback/recirculation system 34, including ducting 38, provides feedback of air and entrained matter from fan 14 to the inlet region 40 of tank 12 through injection means 42, which is shown in more detail in Fig 1A, which shows an axial section through injection means 42.

As shown in Fig 1A, injection means 42 comprises a housing 44 into which the air flow and entrained matter from fan 14 is received, and within which is located an inlet device comprising a central nozzle 46 extending into a larger diameter receiving tube provided by tank inlet 40 and these defining between them an annular orifice 50 through which the air and entrained matter from fan 14 can enter tank inlet 40 and hence tank 12.

Due to the short region of overlap between nozzle 46 and tank inlet 40, the air entering annular orifice 50 is obliged to travel in a direction generally axially of the nozzle/tank inlet axis.

Inlet duct 20 is connected to injection means 42 through a hinge assembly 52 permitting the duct 20 to be pivoted away to assist in demounting and in cleaning of the assembly.

As shown in Fig 1, nozzle 46 may be formed with a pattern of apertures 54 to assist in the air injection process. These apertures may be used instead of the annular inlet orifice 50 or in combination therewith.

In this embodiment, the ducting 38 interconnecting tank inlet 40 and fan 14 extends across the width of the sweeper from a short feedback duct 56 through a tubular transfer duct 58 and thus tc a tapering inlet duct 60 for injection means 42. Transfer duct 58 has removable end caps 62 which are provided for inspection and cleaning purposes.

Feedback duct 56 necessarily extends in the direction shown in Fig 1, due to the direction of fan rotation indicated at 64. In a modification (not shown), an oppositely-rotating fan is employed and inlet duct 60 then extends laterally in the opposite direction with respect to the direction F of forward travel of vehicle 10, so that this modified feedback duct 56 can extend almost directly into injection means 42.

Figs 3 and 4 show a practical embodiment of the system described above and in this embodiment parts corresponding to the parts described above have been numbered accordingly, including the indication of the overall machine 10 itself.

In this embodiment, the main area of practical difference from that shown in Figs 1 and 2 is the relative disposition of the fan 14 and the inlet duct 20 between which the recirculated air and entrained matter is transferred via feedback duct 56 and inlet duct 60. It will be seen that these ducts are in relatively close proximity and feed directly one into the other whereby the transfer of air and entrained matter is effected more simply and more effectively.

In the embodiment of Fig 3 it can be seen that inlet duct 20 is connected to a nozzle 100 into which air is drawn, as shown at 102 and proceeds upwardly at 104 with entrained matter and is directed rearwardly into tank 12 at 106 before the air passes at 108 through screen 28 and vents to fan 14 for discharge upwardly at 32.

Operation of the device is believed to be self-evident from the description above.

Amongst modifications which could be made in the above embodiments while remaining within the scope of the invention as defined in the claims are modifications to the exact location at which the feedback/recirculation air and entrained matter is caused to enter the flow of air into the matter collection tank 12. While in the above embodiment it is convenient to provide the injection means 42 at the discharge end of the inlet duct 20, there is no reason why the injection may not be effected into the tank without actually connecting to the inlet duct at all, and the person skilled in the art will be able to choose locations and directions of injection of the air flow into the tank which will promote an effective recirculation action.

Claims

An air transfer system for a suction cleaning vehicle comprising :-

a) a tank or chamber to receive matter from a surface or location to be cleaned;

b) a fan connected at its suction side to said tank or chamber to reduce the pressure therein;

c) an inlet duct connected to said tank or chamber and adapted to communicate suction from said tank or chamber to a surface or location to be cleaned and to deliver matter from said surface or location to said tank;

d) a discharge outlet connected to the pressure side of said fan to discharge air drawn by said fan from said tank or chamber; and

e) return means to transfer, in use, matter from the air flow through said discharge outlet to be recirculated through said air transfer system to said tank or chamber

characterised by

f) said return means comprising ducting providing a connection between said pressure side of said fan and said tank or chamber and comprising injection means to inject an air flow and entrained matter from said fan into said air flow from said inlet duct into said tank or chamber, and said injected air flow entering said air flow into said tank substantially without passing through said inlet duct.
An air transfer system for a suction cleaning vehicle characterised by return means to transfer recirculated air from the pressure side of a fan to the air flow into a matter collecting tank substantially without passing through the inlet duct for said tank.
A system according to claim 1 or claim 2 characterised by said injection means being located at the discharge end of said inlet duct.
A system according to any one of claims 1 to 3 characterised by said injection means comprising an annular injection port surrounding a central duct into which said port opens, said central duct serving in use to carry the main air flow and entrained matter into said tank.
A system according to claim 4 characterised by said injection means being adapted to cause air and entrained matter injected into said main air flow into said tank, to travel in the same direction as said main air flow as it is injected thereinto.
A system according to claim 5 characterised by said injection means comprising an injection housing surrounding a portion of a duct connected to said inlet duct.
A method of air transfer for a suction cleaning vehicle comprising :-

a) providing a tank or chamber to receive matter from a surface to be cleaned;

b) providing a fan connected at its suction side to said tank or chamber and causing said fan to reduce the pressure therein;

c) causing an inlet duct to communicate suction from said tank to a surface or location to be cleaned and to deliver matter from said surface or location to said tank;

d) discharging air from the pressure side of said fan through a discharge outlet;

e) recirculating air and entrained matter from said air flow to said discharge outlet to said air transfer system for passage therethrough;

characterised by

f) injecting said recirculated air flow and its entrained matter from said fan into said air flow into said tank or chamber substantially without passing through said inlet duct.
A method of air transfer for a suction cleaning vehicle characterised by recirculating air and entrained matter from a suction fan and injecting said air flow and entrained matter into the air flow to a matter-receiving tank or chamber substantially without passing through the inlet duct to said tank or chamber.
A suction cleaning vehicle comprising an air transfer system according to any one of claims 1 to 6.