Abstract:
The self-engaging, solenoid-releasable with manual override, latch is designed for use in a variety of applications. As such, the latch accepts the striker peg of the load when misaligned, and the latch accommodates bouncing, sideways laoding, etc of the load, without springing open.

Description:
[0001]    This invention relates to a development of the technology shown in patent publication U.S. Pat. No. 5,738,176 (Gingerich, April 1998). 
     
    
     
         [0002]    [0002]FIG. 2 of that patent shows a latch mechanism, for hitching an accessory to a tractor. The mechanism is automatically self-latching, in that when the mechanism is lowered onto a latch pin or striker-peg of the accessory, the peg becomes hooked into the mechanism. When the mechanism is then raised, the latch peg is retained. The latch mechanism is operable to release the accessory from the tractor by means of a solenoid, and a driver-operated switch in the tractor.  
           [0003]    The present invention provides an improved latch mechanism for use in that application, and in applications requiring a similar kind of latch function.  
         THE INVENTION IN RELATION TO THE PRIOR ART  
         [0004]    Electric-release self-latching mechanisms are well-known. But the general point may be noted that latch designs tend to be specialised to the particular applications. That is to say, the particular latch product caters only for the manner of loading peculiar to the application. Also, generally, the particular latch product is structured so as to take advantage of the strength and rigidity of the structure to which the latch is to be attached.  
           [0005]    So, generally, when a given latch structure is used in an application other than that for which it was particularly designed, the latch proves inadequate in some way, whereby trying to adapt an existing specialised latch for general use proves impossible. Especially if the latch has to support heavy forces, side-loading, violent bouncing and shaking, etc, the latch may spring open, or give way, and that is not acceptable.  
           [0006]    It is an aim of the present invention to provide a latch design that is capable of supporting heavy and abusive forces within its own structure, without the need for extra rigidity to be provided by the structure to which the latch is attached.  
           [0007]    It is also an aim to provide a latch which caters for very many types of misalignments and abusive shaking and bouncing of the load, without ill-effects, and especially without the latch tending to spring open. Thus it is an aim of the invention to provide a latch structure that is suitable to be used in many different applications, and which can be expected to function effectively and safely, without the need for testing programs and modifications to the design in each new application.  
           [0008]    The invention also aims to provide a latch that combines electric-release and manual-release, and is easy to manufacture and assemble, and also which is easy to maintain, and the components are easy to service and replace. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0009]    By way of further explanation of the invention, exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which:  
         [0010]    [0010]FIG. 1 is an elevation of a latch mechanism which embodies the invention, the latch being shown in an engaged condition.  
         [0011]    [0011]FIG. 2 is the same elevation as FIG. 1, but shows the latch in a just-disengaged condition.  
         [0012]    [0012]FIG. 3 is the same elevation as FIG. 1, but shows the latch in a disengaged condition, and ready for re-latching.  
         [0013]    [0013]FIG. 4 is a pictorial view of the latch mechanism of FIG. 1.  
         [0014]    [0014]FIG. 5 is the same view as FIG. 4, but the components are exploded.  
         [0015]    [0015]FIG. 6 is a close-up of a latch-lever and associated components of a similar mechanism.  
         [0016]    [0016]FIGS. 7 a,   7   b  are cross-sections illustrating other pivot-pin constructions. 
     
    
       [0017]    The apparatuses shown in the accompanying drawings and described below are examples which embody the invention. It should be noted that the scope of the invention is defined by the accompanying claims, and not necessarily by specific features of exemplary embodiments.  
         [0018]    The latch mechanism  20  shown in FIGS.  1 - 5  includes a base-plate  23 , having fastening-holes  24 , by which the base-plate  23  can be fixed to an attachment-body. The function of the latch  20  is to enable an item to be attached to the attachment-body. As may be understood from U.S. Pat. No. 5,738,176, the attachment-body might be, for example, a small electric tractor, and the item to be attached might be a tractor accessory—for example a lawn-mower accessory. The accessory includes a striker-peg  25 , which is the component that actually engages into the latch  20 . Several accessories can be provided for the tractor, fitted with respective striker-pegs.  
         [0019]    Again as may be understood from U.S. Pat. No. 5,738,176, the operation of latching the accessory to the tractor makes use of an operable arm, which carries the latch  20 . The accessory rests on the ground, and the tractor, with the arm raised, is manoeuvred until the latch lies poised over the striker-peg  25 . The arm is arranged to be operated to move through an arc, so the latch  20  moves predominantly vertically downwards, onto the striker-peg  25 . The arm is then lowered, whereby the striker-peg enters the latch  20 , until the latch snaps closed onto the striker-peg.  
         [0020]    Once the tractor has been correctly manoeuvred over the accessory, the action of lowering the movable arm down onto the accessory is all that is needed to snag the accessory to the tractor. Raising the arm is then effective to raise the accessory off the ground, for moving the accessory, and for lowering the accessory down into contact with the ground, where the accessory can perform its function of grass-cutting, snow-blowing, etc. Thus, the tractor driver can carry out the operation of driving up to an accessory, latching the accessory to the tractor, raising the accessory, driving off, and then lowering the accessory to working height, all without leaving the seat.  
         [0021]    Often, in the general case where an item is secured in the latch  20 , provision must be made to prevent the item from swinging and rotating with respect to the latch. In other cases, and especially in the case of tractor accessories, the designer may actually require the accessory to swing about, say, the pitch axis of the accessory, in order for the accessory to follow the contours of the land. Indeed, sometimes, the accessory is required to swing universally, i.e to swing about both the pitch and roll axes.  
         [0022]    This requirement for the latch to permit the accessory to swing about two axes can place great demands on the latch. The designer should ensure that the latch will not accidentally release the item, under any circumstances. This requirement for the latch to remain latched is an especially demanding one when the accessory can swing with respect to the latch, and especially when the accessory can swing in a universal mode, i.e about two axes.  
         [0023]    The requirement is made even more demanding when the accessory is heavy, and when the terrain is such that the accessory, in addition to swinging, is also bouncing and rebounding, and is undergoing many different, and abusive, combinations of misalignments and side-loadings. The scope of the invention is not limited to the item hanging vertically from the latch, nor to cases where the item can swing about two axes, nor to cases where the item is heavy and is subject to violent bouncing; however, a latch that remains secure in those cases is likely to remain secure in all cases.  
         [0024]    The base-plate  23  includes a base-slot  26 . The base-slot has a closed upper-end  27 , and an open mouth at its lower end. The base-slot  26  has sides  29 , 30 , which define a peg-guide-path  32 , between the sides, along which the striker-peg  25  is guided, upon entering the base-slot.  
         [0025]    Mounted on the base-plate  23  is a latch-lever  34 . The latch-lever pivots about a latch-pivot-pin  35 . Also mounted on the base-plate is a pawl-lever  36 . The pawl-lever pivots about a pawl-pivot-pin  37 . An extension of the pawl-lever  36  is provided with a handle  38 .  
         [0026]    Also mounted on the base-plate is a solenoid unit  39 , having a plunger  40 .  
         [0027]    The latch-lever  34  includes a latch-slot  42 . The latch-slot is closed at one end  43 , and has an open mouth at its other end. The latch-slot  42  has a peg-strike-surface  46  and a peg-support-surface  47 . These sides of the latch-slot receive the striker-peg  25  therebetween;  
         [0028]    [0028]FIG. 2 shows the latch in its disengaged position, the striker-peg having just been released from the latch. FIG. 3 shows the latch again in its disengaged condition, in which the latch-lever  34  is turned anti-clockwise about the latch-pivot  35 . In this position, the mouth of the latch-slot  42  coincides with the mouth of the base-slot  26 . Thus, when the striker-peg  25  enters the base-slot  26 , it also enters the latch-slot  42 .  
         [0029]    The striker-peg  25  travels upwards relative to the base-slot  26 , along the peg-guide-path  32 . In doing so, the striker-peg contacts the peg-striker-surface  46 . This contact causes the latch-lever  34  to rotate clockwise about the latch-pivot  35 . The layout of the latch-slot  42  means that the striker-peg also travels into the latch-slot. Further upwards motion of the striker-peg into the base-slot  26  is accompanied by further clockwise rotation of the latch-lever, until a pawl-shoulder  48  on the latch-lever  34  clicks or snaps over a pawl-ledge  49  on the pawl-lever  36 .  
         [0030]    The latch-lever is now in its engaged position (FIG. 1) and the latch is in its engaged condition. The force driving the striker-peg upwards into contact with the peg-strike side  46  of the latch-slot  42  may now be taken away, whereupon the striker-peg  25  settles downwards into contact with the peg-support side  47 .  
         [0031]    At the engaged position of the latch-lever, the striker-peg is confined to left and right by the two sides  29 , 30  of the base-slot, is confined above by the closed end  27  of the base-slot, and is confined below by the peg-support-surface  47  of the latch-lever.  
         [0032]    The peg-support-surface  47  of the latch-slot  42  preferably should not form an acute angle with either of the sides  29 , 30  of the base-slot  26 . If such an acute angle were formed, the striker-peg might, under some conditions of violent rebound, become wedged (momentarily) into the angle, and might tend to pry the surfaces apart. Of course, the latch designer will see to it that the components of the latch are adequate for supporting the (shock) forces applied to the surfaces, during bouncing, and will apply a suitable safety factor. But the danger is that if the surfaces that locate the peg were angled so that the striker-peg might tend to pry them apart, the force on the surfaces would thereby be multiplied. One of the prime aims of the designer is for security against accidental release, so it is better for the surfaces that support the striker-peg to be perpendicular to each other. Thus, preferably, the peg-support-surface  47  should be horizontal, and the sides  29 , 30  of the base-slot should be vertical. In fact, the peg-support-surface  47  may be provided with a hollow or depression, so arranged that if the striker-peg should be displaced to left or right of the base-slot, the depression provides a slight bias, to restore the peg to the centre of the base-slot.  
         [0033]    It is not only when a load swings from side to side through a large angle, that disruptive forces can be applied to the latch. For example, one side of a hanging load might touch the ground, whereby the striker-peg  25  would be knocked sideways—impacting, perhaps violently, against the side of the base-slot.  
         [0034]    As shown in FIG. 3, when lifting the latch-lever  34 , the striker-peg  25  contacts the peg-strike-surface  46  at a peg-touch-point  50 . As the latch-lever rotates, the peg-touch-point  50  changes, i.e the new peg-touch-point appears at a different location along the peg-strike-surface  46 . For smooth operation of the latch to the engaged position, the designer should arrange that the cam configuration of the peg-strike-surface is such that, at each position of the peg-touch-point  50 , the peg-strike-surface at that point is horizontal, i.e is perpendicular to the peg-guide-path  32 . This helps ensure that the striker-peg remains in the centre of the base-slot, i.e does not rub against the sides  29 , 30  of the bases-lot, during latching.  
         [0035]    Generally, in the invention, at the latch-engaged condition, the latch-lever is prevented from rotating to its disengaged position by the engagement of the abutment-point on the latch-lever with the stop on the strut. In the embodiment of FIGS.  1 - 5 , the latch-lever  34  is held against rotation by the engagement of the pawl-shoulder  48  on the latch-lever against the pawl-ledge  49  on the pawl-lever  36 . The generality is that the latch moves to its disengaged condition when the strut collapses; in FIG. 2, the strut collapsed when the pawl-lever  36  moved to the left. The pawl-lever  36  forms a strut in that the loads in the pawl-lever arising from contact with the latch-lever pass down the pawl-lever to the pawl-pivot pin  37 , and thence to the base-plate  23 .  
         [0036]    (The term “strut” sometimes is construed narrowly, in the sense of a rod or bar that is a component of a framework; in the context of the invention, the term strut should be construed more broadly, as meaning any structure that does not collapse under a load force.)  
         [0037]    In the engaged condition of the latch, as shown in FIG. 1, and again in FIG. 6, it will be noted that the weight of the item attached to the striker-peg  25  is supported approximately halfway between the latch-pivot pin  35  and the pawl-ledge  49 . The distance from the latch-pivot to the abutment stop is the abutment-radius  52 , and the abutment-radius is approximately horizontal. That is to say, the abutment-radius  52  is more or less perpendicular to the (vertical) line  53  of the item-force acting through the striker-peg  25 , on the latch-lever  34 . This arrangement, where the abutment-radius  52  is perpendicular to the line  53  of the item-force, and the line of the item force lies midway between the latch-pivot  35  and the pawl-ledge  49 , is a preferred feature of the invention.  
         [0038]    It is not essential that the item-force-line  53  lies exactly halfway between the latch-pivot  35  and the pawl-ledge  49 . The important aspect is that the item-force-line falls between the latch-pivot and the pawl-ledge. Then, both the latch-pivot reaction force  54  and the abutment reaction force  56  are smaller in magnitude than the weight of the accessory hanging from the striker-peg. If the item-force-line  53  were to fall beyond one of those points  35 , 49 , i.e outside the abutment-radius  52 , one of those reaction forces would necessarily be larger than the weight of the accessory.  
         [0039]    It is not essential, either, that the abutment-radius  52  be exactly horizontal, i.e exactly perpendicular to the item-force-line  53 . If the abutment-radius were angled more than about say twenty degrees to the perpendicular to the item-force-line (angle  57  in FIG. 6), then again the latch-pivot reaction force  54  and the abutment reaction force  56  would, in aggregate, be larger than the weight of the accessory. But the arrangement, as shown, where the abutment-radius  52  is more or less perpendicular to the line  53  of the item-force, and the line of the item-force lies between the latch-pivot  35  and the pawl-ledge  49 , means that the reaction forces are at a minimum, i.e the aggregate of the reaction forces is not greater than the weight of the accessory.  
         [0040]    The latch must of course be designed to support the loads imposed on it, including the shock and abuse load—but with the depicted arrangement, the latch need not be designed to support a multiplication of those loads. Where the item is a lawnmower accessory, for example, suppose one end of the lawnmower housing should encounter an obstruction, whereby the angle of the lawnmower suddenly changes; now, there is a large momentary side force acting between the striker-peg and the side of the base-slot. A moment later, there may be a side force on the other side of the base-slot. After that, the lawnmower may be bounced bodily clear of the ground, and then rebound. The latch must stand up to these actions, not only of course without breaking, but without the latch springing open. The benefit of the arrangement where the hanging weight of the accessory is divided and distributed between the latch-pivot and the pawl-ledge, and the abutment radius is more or less horizontal, is that it can hardly be envisaged that forces could multiply unexpectedly and accidentally, or could act in unexpected directions, which might cause the latch to spring open. In the depicted design, forces substantially cannot be unexpectedly large.  
         [0041]    By spacing the latch-pivot  35  well away from the pawl/lever engagement point  49 , the weight from the load is always distributed between the two. The further they are apart, on a horizontal line, the more each one takes its own loads, and other is not affected, even if the load should be bouncing and swinging, or otherwise be misaligned. In the invention, preferably, as mentioned, the abutment-radius  52  should be within twenty degrees of horizontal; but also, where the striker-peg  25  is e.g one cm diameter, the abutment radius should be more than say two cm. When this is so, again it can hardly be imagined that an abusive condition could arise in which the forces between the striker-peg and the latch could accidentally and unexpectedly be high enough to spring the latch open.  
         [0042]    The solenoid unit  39 , when operated, exerts a force on the plunger  40  that pulls the pawl-lever  36  to the left, thereby disengaging the pawl-shoulder  48  from the pawl-ledge  49 , and collapsing the strut. It is preferred to have a lever ratio such that the force at the pawl-shoulder is higher than the force exerted by the solenoid, so the solenoid should lie further out on the pawl-lever than the pawl-shoulder, with respect to the pawl-pivot pin  37 .  
         [0043]    Similarly, for ease of manual disengagement of the latch, the handle  38  should be at a larger radius than the pawl-shoulder, and preferable at a larger radius than the solenoid.  
         [0044]    The structure of the solenoid unit  39  will now be described. The coil-unit  58  is a staple product, comprising a square form-tube  59  of plastic around which the coil is formed. The coil leads  60  are embedded in the plastic. A coil-cover  62  is made of folded sheet steel, and encloses the coil-unit  58 , except that the coil-cover is open at the bottom, whereby the coil-unit can simply be dropped into the coil-cover. A plug-nut  63  resides inside the hollow coil tube, and a bolt  64  therein secures the coil-cover to the coil-unit. The coil-cover is then bolted to the base-plate  23 .  
         [0045]    Thus the solenoid unit  39  is easy to manufacture and assemble, and is securely fixed mechanically to the base-plate. The coil-cover, and the base-plate to which it is bolted, complete the magnetic flux path around and underneath the coil. The front of the coil-cover is shaped and folded so as to leave front margins  65  around the plunger, and the metal of the front margins should be as close as possible to the metal of the plunger, without actually touching.  
         [0046]    Preferably, in line with the aim of the invention to provide a latch that can be used in many applications, the solenoid coil should be wound, not for a particular voltage, but to provide effective pull force when supplied with a range of voltages. Thus, the coil preferably should be set to operate over a range of say 12-48 volts DC, or AC.  
         [0047]    A screwed rod  67  is attached to the plunger  40 , whereby the travel of the plunger can be adjusted to provide a trouble-free pawl release operation.  
         [0048]    A spring  68  serves to bias the pawl-lever  36  to its support position, and to bias the latch-lever  34  to its disengaged position.  
         [0049]    The base-plate  23  is a single, thick, flat, steel plate. Preferably, the plate should be at least five mm thick for use of the latch on a small tractor, to pick up such accessories as lawnmowers etc, having a striker peg of ten mm diameter. The thickness provides not only basic strength and rigidity, but also provides bearing width, whereby the load between the striker-peg and the sides of the base-slot is spread over a large area, and so does not tend to cut a groove in the peg. The latch-lever  34  preferably is made of the same stock as the base-plate  23 .  
         [0050]    It is known for latches (and other moving-lever mechanisms) to be mounted, not from a single thick base-plate, but to be sandwiched between a pair of thinner plates. This construction, though not ruled out, is less preferred in the invention, in that the presence of two plates would make it much more difficult to service the unit.  
         [0051]    The thick base-plate also means that the pivot pins  35 , 37  can be cantilevered up out of the base-plate  23 . Thus, the pins can be easily replaced, often without unfastening the base-plate from the tractor.  
         [0052]    As shown in FIG. 7 a,  the pivot pin may be formed from a shoulder-bolt  70 , or (FIG. 7 b ) may be formed from an ordinary bolt and a tubular spacer  72 , which may be of a bearing material. In each case, lock-nuts or the like should be provided to ensure the pin cannot work loose with respect to the base-plate.  
         [0053]    The latch structure as described herein is intended for automatic engagement of a tractor accessory to the vertically-movable arm carried on the tractor. It is intended that automatic engagement will proceed even when the striker peg is only loosely aligned with the mouth of the base-slot, whether the peg is misaligned as to its pitch, roll, or yaw orientation, or as to its front/back or left/right position. Also, the described latch is intended to cater for misalignments between the tractor and the accessory being carried, as might tend to arise during operation. Thus, the described latch should be distinguished functionally from latches (for example vehicle trunk-latches) in which the components are fully aligned before engagement starts, and never move in any mode thereafter, during engagement.