Abstract:
The present invention relates to a forage harvester blower including a blower rotor having a plurality of generally radially extending rotor paddles which operate in a corresponding substantially cylindrical housing, characterised in that said housing is provided with adjustment mechanism for at least locally adjusting the diameter of the housing. The present invention further relates to a method for optimising the operation of a forage harvester blower and to a method for preventing damage to a forage harvester blower during operation.

Description:
FIELD ON INVENTION 
   The present invention relates to forage harvesters and more particularly relates to a forage harvester blower for receiving and delivering chopped forage. The present method also relates to an improved method for operating said forage harvester blower. 
   BACKGROUND OF INVENTION 
   Generally, forage harvesters chop crop material, such as grass or maize, into small particles for storage and subsequent feeding to livestock. Conventional harvesters comprise a rotating cutter head with a plurality of knives, which co-operates with a stationary shear bar to cut the crop material fed thereto into small particles and deliver it to discharge mechanism. It is well-known in forage harvesters to provide a blower for receiving chopped forage either directly from the cutter head or from kernel processing rolls or an impeller or other forage moving apparatus located between the cutter head and blower and for delivering the chopped forage to a forage collecting container such as the box of a wagon or truck, for example. 
   In an attempt to minimise plugging, designers have advantageously located the blower so as to receive the chopped forage in a relatively thin mat flowing along the outer periphery of the cylindrical blower housing where the forage is engaged and accelerated upwardly by blades or paddles extending generally radially from the blower rotor. 
   An important problem associated with conventional harvester blowers is that the blowers may be seriously damaged when a foreign object enters the blower. Sometimes, during field activities foreign objects can enter the blower area and cause serious damage to the blower rotor and blower housing. This phenomenon is called a ‘blow-up’. Most of the time it starts when a stone or other hard object enters the harvester, in particular the cutter head, and gets stuck between a knife of the rotating cutter drum and it&#39;s counter knife or shear bar. This causes the knife to break such that this piece gets stuck between a subsequent knife and counter knife. A chain reaction is the result. Parts that leave the cutter head area are thrown into the blower and can plug the blower by getting stuck between the rotor and the housing of the blower unit. In most cases, this results in a deformation of the shaft on which the blower rotor is mounted and/or in a deformation of the housing and a serious decrease in efficiency of the blower. Presence of foreign objects in the blower may induce considerable material damage and material loss such that deformed rotor and/or housing will have to be removed and replaced, which involves expensive repair costs and which is time-consuming. Furthermore, the blow-up phenomenon also involves serious risks from a security point of view, since the blower can break down during operation. 
   The present invention aims to provide a solution to the above-mentioned problem. It is therefore, an objective of the present invention to provide a blower showing improved security and wherein repair costs as a consequence of a blow-up phenomenon can be reduced. The present invention provides a solution to the above-mentioned problems by providing a blower unit having an adjustable housing. 
   SUMMARY OF INVENTION 
   In a first aspect, the present invention provides an improved forage harvester blower. The blower is suitable for receiving chopped crop materials either directly from a cutter head or from a processing unit in a forage harvester and for conducting said chopped material to a subsequent discharging unit. The terms “crop material” or “crop” are used herein as synonyms and refer to crops containing kernels, such as maize, as well as to kernel-free crops such as alfalfa or grass. 
   More specifically, the present invention provides in a first embodiment a forage harvester blower including a blower rotor having a plurality of generally radially extending rotor paddles which operate in a corresponding substantially cylindrical housing, characterised in that said housing is provided with adjustment mechanism for at least locally adjusting the diameter (D) of the housing. 
   The term “diameter D” as used herein refers to the working diameter of the housing: i.e. the diameter of the housing where the edges of the rotor paddles most closely approach the housing. 
   The present invention provides a solution to the above-mentioned problem of increased security hazards and considerable material loss of a harvester blower when a foreign object enters the blower by providing a blower capable of quickly and easily evacuating and removing a foreign object that has entered the blower. For that, the blower is provided with adjustment mechanism for at least locally adjusting the diameter (D) of the housing. By locally enlarging the diameter of the housing, e.g. when a foreign object gets stuck in the blower for instance between the rotor paddles and the housing, the present invention permits to reduce the risks of blow-up and expensive repair costs associated there with. 
   In addition, this solution has the additional effect of considerably improving blower efficiency. In conventional forage harvesters efficiency of the blowing unit decreases as the rotor blades or paddles wear out. When the rotor paddles wear out, the distance between the outer edges of the rotor paddles and the housing increases, which seriously reduces efficiency of the blower. It is required to frequently replace the worn out rotor paddles in order to maintain blower efficiency. However, this requires the blower unit to be dismantled and the rotor to be removed from the blower, which involves a substantial amount of work and which brings along serious additional costs. The present invention provides a solution therefore by providing a blower unit having a housing of which the diameter can be locally adjusted. According to the invention, the diameter of the housing can be adjusted such that the distance between the outer edges of the rotor paddles and the housing can be minimised. By doing so, the present invention thus provides a blower unit wherein blower efficiency is considerably improved. 
   In a preferred embodiment, the present invention provides a forage harvester blower wherein the adjustment mechanism comprises a wear plate having a position which is adjustable such that by adjusting the position of the wear plate the diameter (D) of the blower housing can be adjusted. In a preferred embodiment, the wear plate is provided between the inlet section and the outlet section of the blower. 
   The invention allows easy and accurate adjustment of the diameter of the housing by adjusting the position of a wear plate provided on the housing, either inwardly to the centre of the rotor or outwardly away from the centre of the rotor. For that purpose, in a preferred embodiment, the wear plate is pivotably hinged on the blower housing and movable such that the diameter (D) of the housing can be adjusted by pivoting the wear plate. In another embodiment, the wear plate is connected to the housing by mechanism of two adjustment assemblies, which are suitable for adjusting the position of said wear plate, whereby one assembly is provided on each side of said wear plate. More specifically, the wear plate is positioned in the blower in a way so it can pivot around its upper fixation (hinge) points, while the position of the wear plate can be adjusted by mechanism of the adjustment assemblies. The position of the wear plate can be adjusted in order to minimise the play between the outer edges of the rotor paddles and the inside of the blower housing. The invention ensures an optimal set up of the blower paddle distance to the wear plate and thereby ensures optimal blower efficiency. Furthermore, the distance of the housing to the outer edges of the rotor paddles can be easily adjusted in function of the wear and tear degree of the paddles. Replacement of worn out rotor paddles can be delayed and the rotor paddles can be used for a longer time. 
   In a further embodiment of the present invention each adjustment assembly comprises an active adjustment unit for manually adjusting the position of the wear plate and a passive adjustment unit for automatically adjusting the position of the wear plate. The active unit can be manually operated in order to manually position the wear plate on a certain desired distance from the rotor paddles. The passive adjustment unit can be automatically activated when the pressure F exerted on the wear plate exceeds a threshold value. The passive adjustment units can be automatically activated without intervention of an operator. More specifically, the passive adjustment unit comprises a security mechanism, which enables the wear plate to automatically retract outwardly when the pressure F exerted on the wear plate exceeds a certain threshold value. This may occur when a foreign object gets stuck in the blower, e.g. between the rotor paddles and the housing. The present invention thus permits to reduce the risks of blow-up and expensive repair costs associated there with. Automatic retraction of the wear plate facilitates the removal of foreign objects out of the blower unit and thus increases protection of the blower rotor from damage due to the action of these objects. The present invention thus provides a blower having improved security and facilitated handling. In a preferred embodiment, the active adjustment unit is provided on the housing and the passive adjustment unit is provided on the wear plate. In another preferred embodiment, the active adjustment unit is connected to the passive adjustment unit. 
   The present invention further provides the following advantages. The wear plate can be easily removed, creating easy access to the blower for an operator which needs to do maintenance work, e.g. replacing the blower paddles. Furthermore, the present invention enables to easily remove and replace the wear plate at minimal costs when it is worn. 
   In a second aspect, the present invention provides a method for optimising the operation of a forage harvester blower, said blower comprising a plurality of generally radially extending rotor paddles operating in a corresponding substantially cylindrical housing, comprising the step of adjusting at least locally the diameter (D) of the housing when the blower efficiency differs from a threshold value. The term “foreign object” as used herein refers to undesired, not crop-related objects, such as e.g. stones. In a preferred embodiment, the diameter (D) of the housing is adjusted by adjusting the position of an adjustment mechanism provided on the blower housing. Preferably, said adjustment mechanism comprises a wear plate, which is hinged on the blower housing and provided with adjustment assemblies to adjust its position on the housing. The method comprises the step of reducing the diameter (D) of the blower housing by adjusting the position of the adjustment mechanism on the blower housing such that the distance between the outer edges of the rotor paddles and the blower housing is minimal. The method may also comprises the step of increasing the diameter (D) of the blower housing by adjusting the position of the adjustment mechanism provided on the blower housing such that a foreign object can be removed from the blower. 
   A forage harvester blower in accordance with the present invention will now be described in greater detail, by way of example, with reference to the following drawings. 

   
     DETAILED DESCRIPTION OF THE FIGURES 
       FIG. 1  is a side view of a self-propelled forage harvester embodying a blower constructed in accordance with the present invention. 
       FIGS. 2 and 3  are detailed vertical sectional views of a blower constructed in accordance with the present invention. 
       FIG. 4  is a perspective view of a blower constructed in accordance with the present invention and illustrating the fixation of the wear plate to the blower housing. 
       FIGS. 5 and 6  are perspective views of an adjustment assembly constructed in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention will now be described with reference to certain embodiments and certain drawings but the invention is not limited thereto. The drawings are schematic. The terms “front”, “rear”, “forward”, “rearward”, “right” and “left” used throughout the specification are determined with respect to the normal direction of movement of the machine in operation and are not to be construed as limiting terms. 
   Referring to  FIG. 1 , there is shown a self-propelled forage harvester  1  which embodies the present invention. It being noted that the principles of the present invention could be applied to towed forage harvesters as well. The forage harvester  1  includes a main frame  2  supported on front and rear pairs of wheels  3  and  4 , of which only one of each pair is shown. The forage harvester is shown equipped with a crop collecting apparatus, in the form of a row crop attachment  5 , suitable for the harvesting of maize, but which can be replaced with a conventional windrow pick-up device or a conventional cutter bar attachment, depending on the type of crop to be harvested. Customarily, the crop collecting apparatus is provided for severing a crop, such as corn or the like, from the ground and directing it to be chopped into forage by knives of a transverse cylinder type cutter head  8 . Chopped forage is delivered rearwardly by the cutter head  8  to a blower  9  which, in turn, delivers the chopped forage upwardly into, and creates an air stream for expelling it through, a rearwardly extending discharge conduit or spout  10 . 
   The forage harvester may further be provided with a crop processing unit (not shown). When a crop processing unit is provided, the chopped material is thrown by the cutter head into the crop processor, which processes (cracks), the kernels and transfers the material into a blower, which in its turn ejects the crop into a trailer or container. Preferably, the crop processing unit can be moved into the stream of chopped material or removed there from according to arrangements as shown for example in EP-B-1 229 778. 
   A detailed arrangement of the cutter head  8  and the blower  9  in accordance with an embodiment of the present invention is shown in  FIG. 2 . The blower  9  is provided in between the cutter head  8  and the discharge spout  10 . The position of the blower  9  relative to the cutter head  8  and discharge spout  10  is thought to result in a structure for efficiently conveying crop from the cutter head  8  to a discharge spout  10  and further to a forage collection container. The illustrated cutter head  8  is a transverse cylinder type cutter head  8  provided with a plurality of radially extending knives  11 . Crop material is chopped into forage by the knives  11  of the cutter head  8  and delivered rearwardly by the cutter head  8  to the blower  9 . The spout  10  can be positioned by an operator to direct the cut crop material as required, normally into a wagon, which is moving alongside or behind the forage harvester. 
   Referring to  FIG. 3 , there is shown a detailed arrangement of a blower  9  which is representative of the present invention. The blower  9  includes a housing  13  having an inlet section  15  extending rearwardly and upwardly from a lower right quadrant of the cutter head  8 , to a lower right quadrant of a cylindrical section of the housing  13 , and an outlet section  16  extending upwardly between an upper right quadrant of the cylindrical section of the housing  13  and an entrance to the discharge spout  10  (not shown). Located within the substantially cylindrical section of the housing  13  is a rotary blower rotor  12  including a transverse axle  22  extending through and being journalled (not shown) in opposite end walls of the housing  13 . The rotor  12  and the housing  13  extend generally co-axially. The rotor is provided with air stream openings  20 . The blower rotor  12  comprises a plurality of generally radially extending blades or paddles  14 , which are preferably equidistantly connected to the rotor axle and which have outer edges that trace a cylindrical path  46  spaced closely to the housing  13 . The distance of the outer edges of the rotor to the rotor axle is indicated with r. It will be clear that this distance r may vary and be reduced as the outer edges of the rotor paddles  14  wear out. 
   Forage leaving the cutter head  8  is fed directly into the periphery of the blower housing  13 , at its lower right quadrant, approximately tangential to the outer diameter of the blower rotor  12  and in the same direction of movement as that of the rotor paddles or blades  14 . Each paddle  14  collects the crop at its outer end as it moves the crop along the blower housing  13  periphery to and then discharges it uniformly up through the outlet section  16  into and through the spout  10 . The impact of the rotor blades  14  against the incoming crop is minimised because they have approximately the same direction of movement and thus the energy required to impel the crop is reduced. 
   At the backside of the blower  9  a wear plate  17  is pivotally attached to the housing  13 . As illustrated the top of this plate  17  is hinged to the topside of the blower housing  13 , e.g. by mechanism of two removable pins  18 , of which one is represented in  FIG. 3 . It should be clear that a second pin is provided symmetrically at the other side of the wear plate  17  (see  FIG. 4 ). The wear plate  17  can pivot around these hinge points under an angle a inwardly  44  towards the rotor axle thereby reducing the diameter D of the housing  13 . The maximal inward movement  44  of the wear plate  17  is determined and restricted by the outer edges of the rotor paddles. The wear plate  17  may also pivot around the hinge points outwardly  45 , thereby enhancing the diameter D of the housing  13 . It will be clear from  FIG. 3  that outward movement of the wear plate is not limited and that the plate may be retracted outwardly under any angle, if required. The diameter D is the diameter of the housing where the outer edges of the rotor paddles lay most closely to the blower housing. Specifically, because the rotor paddles  14  wear out, the position of the wear plate  17  can be adjusted in order to minimise the distance between the outer edges of the blower rotor paddles  14  and the blower housing  13  such that the blower  9  operates under optimal efficiency. Optimal adjustment of the working diameter D of the housing  13  is especially done in the section of the blower located between the inlet  15  and the outlet  16 . Outwards movement  45  of the wear plate  17  can be induced when a pressure F is exerted on the wear plate  17 , which exceeds a certain threshold value, e.g. due to the presence of a foreign object in the blower unit. Outwards movement  45  of the plate  17  enables to remove foreign objects from the blower unit and permits to avoid possible crop blockage in the channel between paddles  14  and housing  13 . 
   The bottom of the wear plate  17  is fastened to the blower housing  13  by mechanism of adjustment assemblies  21 , of which one is represented in  FIG. 3 . It should be clear that a second adjustment assembly is provided symmetrically at the other side of the wear plate  17  (see  FIG. 4 ). 
     FIG. 4  illustrates into more detail the fixation of a wear plate  17  to the housing  13  of a blower unit  9 , which is representative of the present invention. Preferably, the plate is hinged at its top side, while adjustment assemblies  21  are provided at the bottom side of the wear plate  17  in order to connect the wear plate  17  to the housing  13 . However, it should be clear that also other fixation configurations of the wear plate  17  to the housing  13  could be applied. It should also be clear from the  FIG. 4  that connection of the wear plate to the housing is performed in a similar way, symmetrically on both sides of the plate. 
   For connecting the top side of the wear plate  17  to the housing  13 , a pair of pins  18  is provided, whereby one pin  18  is provided on each side of said wear plate  17 . These removable pins  18  enable to affix the wear plate  17  on the housing  13  such that the top side of the wear plate  17  is hinged on the topside of the housing  13 . The pins can be locked in axial way by two spring clips  19 , so that no tooling is required when this wear plate  17  needs to be replaced. However, it is clear that other fixation mechanism can be applied to hinge the wear plate to the housing  13 . 
   On its bottom side the wear plate  17  is connected to the housing  13  by mechanism of two adjustment assemblies  21 , whereby one assembly  21  is provided on each side of said wear plate  17 . Each adjustment assembly  21  is partly fastened on the housing  13  and partly fastened on the wear plate  17 . Preferably, each adjustment assembly  21  comprises an active adjustment unit  23  which can be manually operated and which is mounted on the housing  13 . Each adjustment assembly  21  also comprises a passive adjustment unit  24 , which is preferably mounted on the wear plate  17  and which is able to be activated automatically, in particular when the pressure F exerted on the wear plate  17  exceeds a threshold value. In a particularly preferred embodiment the active adjustment unit  23  is connected to the passive adjustment unit  24 . The adjustment assemblies  21  permit to move the bottom side of the wear plate  17  towards the centre of the blower rotor, thereby reducing the distance between the outer edges of the rotor paddles  14  and the wear plate  17 . In addition, these adjustment assemblies  21  also permit the wear plate  17  to move outwardly, away from the centre of the blower rotor, thereby increasing the distance between the outer edges of the rotor paddles  14  and the wear plate  17 . This movement is of particular importance in a situation when a foreign object enters the blower. The wear plate  17  swings out in order to provide extra space so that the foreign object can pass the blower unit without causing too much damage. 
     FIGS. 5 and 6  illustrate preferred embodiments of adjustment assemblies  21  which are used in accordance with the present invention to position the wear plate  17  on the blower housing  13 . The distance between the rotor paddle and the wear plate can be measured directly through an inspection door (not shown) and manually adjusted if required, for instance in function of the degree of wear and tear of the rotor paddles. Manual adjustment of the position of the wear plate is performed by mechanism of the adjustment assembly  21 . The active adjustment units  23  of the assembly  21  comprise a latch  30 , which is mounted on the housing  13 . The front side  25  of the latch is releasably mounted on the housing  13  and its backside  26  extends outwardly through the housing  13 . The front side  25  of the latch  30  is provided with two apertures  47 , through which bolts  27  can be provided for affixing the front side  25  of the latch  30  to the housing  13 . The bolts  27  can be manually loosened. The latch  30  is further connected to the housing  13  by mechanism of an adjustment rod  28  and plate  29 . Rod  28  is provided on one side with a thread  49  which extends outwardly through housing  13 . The thread  49  of rod  28  is threadably engaged by a nut  32  which itself is welded to housing  13 . The other side of rod  28  extends through an opening (not shown) in plate  29  and is held on the backside by a bolt (not shown) so the rod  28  can rotate freely in the opening of plate  29 . Optionally, a nut  31  may be further provided for fixing the rod to the housing  13 . 
   When the two bolts  27  are loosened and nut  31  is released, it is possible to move latch  30  relatively to housing  13  by rotating threaded rod  28 . Rotation of rod  28  can be effected by using e.g. a flat spanner which can be placed on the flattened ends of the threaded rod  28 . 
   Rotation of rod  28  in a first direction will move the threaded end  49  of rod  28  through welded nut  32 , thereby pulling on plate  29 . Plate  29 , which is rigidly connected to latch  30 , will pull on latch  30  so that the backside  26  of latch  30  will move through an opening in housing  13 . Conversely, rotation of rod  28  in the opposite, second direction, will move the threaded end  49  of rod  28  through welded nut  32 , thereby pushing on plate  29 . Plate  29 , rigidly connected to latch  30 , will push on its turn to latch  30  so that the backside  26  of latch  30  will move to the opposite side through an opening in housing  13 . So the distance between the rotor paddles and the wear plate can then be adjusted by turning the adjustment rod  28  in- or outwards and thereby moving the latch  30  back- or forward. 
   A passive adjustment unit  24  is mounted in connection to the active adjustment unit  23  on each side of the wear plate  17 . The passive adjustment units  24  enable the wear plate to retract outwardly, when a pressure exerted on this plate exceeds a certain threshold limit. Each passive adjustment unit  24 , essentially comprising a bracket  24  with a spring-loaded pin  40 , is welded on the wear plate  17  by mechanism of an upper  35  and a lower  36  guiding plate. These plates  35 ,  36  are preferably L-shaped and are welded on the wear plate  17 . The guiding plates  35 ,  36  are provided with two apertures  48 , through which bolts  37  can be provided for affixing the guiding plates  35 ,  36  to a bracket  34 . Additionally, an upper  38  and lower  39  protection plate, which are part of the bracket  34 , are generally attached intermediately between the guiding plates  35 ,  36 . The plates  38 ,  39 , and bracket  34  are fixed between the guiding plates  35 ,  36  by mechanism of the bolts  37 . The bolts  37  can be manually loosened. When the four bolts  37  are loose, it is possible to move the position of the bracket  34  and the protection plates  38 ,  39  to adjust the biasing force of the spring  41 . As described earlier, the guiding plates  35 ,  36  are affixed to the wear plate  17 . The wear plate  17  can be easily removed and replaced when the plate is worn. For that, the plate  17  with the guiding plates  35 ,  36 , rigidly fixed on the plate, are removed. The bracket  34  can be re-used. 
   Active and passive adjustment units are inter-connected as follows. The backside  26  of the latch  30 , which extends outwardly through the housing  13  is provided with a countersunk hole (shown on  FIG. 6 ). The bracket  34  holds a pin  40  loaded with a spring  41 . The pin  40  can be manipulated by mechanism of a handling element  42 , which is connected at one extremity of the pin. The other opposite extremity of the pin  40  is forced into the countersunk hole  33  provided at the backside of the latch  30  of the active adjustment unit  23 . The handling element  42  can be pulled against the spring tension and will thereby retract the pin  40  out of the countersunk hole  33 . The handling element  42  can be stored behind a protrusion  50  extending from the upper protection plate  38 . When both pins  40  of the adjustment assemblies  21  are locked behind the protrusions  50  of the protection plates  38 , the wear plate  17  can hinge freely as described above. 
   The passive adjustment units  24  are in connection with the active adjustment units  23  in such a way that operation of the passive units  24  overrules the operation of the active adjustment units. More specifically, one extremity of the spring-loaded pin  40  is forced into the countersunk hole  33  provided at the backside  26  of the latch  30  of the active adjustment unit  23 , as illustrated on  FIG. 6 . When the adjusting rod  28  of the active adjustment assembly  23  is rotated, the position of the countersunk hole  33  changes in relation to the housing, and will cause the wear plate  17  to move relatively to that housing  13 . The pin  40  which is forced into hole  33  can move when a sufficient force F is applied to the wear plate  17 , resulting in a movement of the wear plate. 
   The passive adjustment units are automatically activated when the pressure F on the wear plate gets above a threshold limit. A foreign object may enter the blower and get stuck between the rotor paddles and the wear plate. This obstruction will induce a pressure F onto the wear plate  17  (see  FIG. 3 ). The direction of this force is directed towards the backside of the blower. When this pressure F on the wear plate  17  exceeds a certain threshold value, the spring-loaded pin  40  will be forced backwards because of the taps geometry of the countersunk hole  33 . The pin  40  will be pressed out of the countersunk hole  33  and the wear plate  17  will move outwards. The wear plate  17  can be re-positioned into its original position by replacing the pin  40  into the position hole  33 , and will remain in the position hole  33  because of the force of spring  41 . A chamfer  43  on the end of the latch  30  guides the pin into its position hole  33 . This can be done manually using the handling element  42  but without the necessity to use any additional tools. Outward movement of the wear plate creates enough space to let a foreign object pass. This mechanism allows easy removal of foreign objects out of the blower housing. 
   Repositioning of the wear plate  17  in its operational position after a force F was applied to the wear plate  17 , can be done manually by pushing the wear plate back into place. The pins  40  of the passive adjustment units  24  are brought back into the countersunk holes  33  providing a secure locking of the wear plate under normal conditions. Manually replacing the wear plate  17  after being forced open has an additional advantage because an operator of the forage harvester  1  will be obliged to check if a foreign object has damaged a part of the blower assembly  9 . The wear plate  17  can also be automatically repositioned when e.g. a spring (not shown) is used. The spring can pull the wear plate back to its normal working position after the force F is sufficiently decreased. 
   In a preferred embodiment, a sensor  51  can be provided which detects movements of the wear plate. If the wear plate  17  is forced out of its normal position due to force F, a signal will be send by the sensor  51  to the cabin of the forage harvester  1 , alarming the operator of the problem with the blower assembly  9 . The signal from the sensor can also be used to shut down the machine, e.g. for safety reasons. The sensor  51  can be connected to the housing, e.g. at the backside of the blower housing  13  under the wear plate  17 . However it should be clear that the sensor  51  may also be positioned elsewhere on the housing, if required. 
   While the invention has been shown and described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes or modifications in form and detail may be made without departing from the scope and spirit of this invention as defined by the claims.