Abstract:
A one-way drive strap wrench having two strand parts ( 11 A,  11 B) and a shoe ( 15 ) for bearing against an oil filter ( 2 ). The shoe is pivotally mounted about a laterally offset axis ( 16 ). The wrench is particularly adapted for the fitting and removal of motor vehicle oil filters.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a strap wrench for turning an object of cylindrical overall shape in one direction. This type of wrench includes a part forming a handle, and a strap, particularly made of metal, in the form of a loop, the two opposite strand parts of which cooperate with two zones secured to the handle when the strap is wrapped tightly around the object. 
     The handle is equipped, between the two zones, with a shoe for pressing against the object. The pressing shoe is not connected to the strap and has a bearing face of cylindrical overall shape with its generatrices at right angles to the overall plane of the strap. 
     The invention applies particularly to oil filter wrenches for motor vehicles and, in what follows, reference will be made to this application. 
     2. Description of Related Art 
     Examples of such strap wrenches are described in FR-A-1,570,027 and in EP-A-0,618,045 in the name of the Applicant Company. 
     In these known strap wrenches, the shoe is secured rigidly to the handle. As a result, when the space available around the oil filter allows the wrench to be turned only by a limited amount, the operator has to perform repetitive manipulations of shortening/lengthening the useful length of the strap, using a knurled knob which forms part of a screw-nut mechanism for adjusting the strap. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to make strap wrenches easier to use in a particularly ergonomical way. 
     To this end, the subject of the invention is a strap wrench of the aforementioned type, characterized in that the shoe is pivot-mounted with respect to the handle so that it can pivot about a geometric axis associated with the handle and at right angles to the overall plane of the strap. This axis is located in such a way that when the shoe and the strap are both clamped tightly against the object, action on the handle exerted in a first direction causes the object to be turned and, exerted in the other direction, causes the shoe and the strap to slip on the object. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described with reference to the appended drawings, in which: 
     FIG. 1 depicts, in longitudinal section, a strap wrench according to the invention with the strap in position loosely around an oil filter that is to be unscrewed; 
     FIG. 2 is a similar view after the strap has been adjusted to fit tightly around the oil filter; 
     FIG. 3 is a similar view during the first phase of unscrewing the filter; 
     FIG. 4 is a similar view, during the subsequent phase of backing up the wrench; 
     FIG. 5 depicts, in longitudinal section, another embodiment of the strap wrench according to the invention, during the first phase in the unscrewing; 
     FIG. 6 is a partial view from an exploded perspective of another embodiment of the strap wrench according to the invention; 
     FIG. 7 is a face-on view from the outside of the strap wrench of FIG. 5; 
     FIG. 8 is a side-on view from the outside of the same tool; 
     FIGS. 9 and 10 are views from the outside of an alternative form of the strap wrench of FIG. 5, the strap not being depicted; 
     FIG. 11 is a view in longitudinal section, taken in the overall plane of the strap, of an alternative form; 
     FIG. 12 depicts an alternative form of the shoe; and 
     FIG. 13 is an enlarged view of detail XIII of FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The strap wrench  1  depicted in FIGS. 1 to  4  is intended mainly for unscrewing and, in addition, by turning the wrench over, for screwing on, objects  2  of cylindrical overall shape, especially oil filters, the diameters of which may vary across a broad range, for example, in the embodiment depicted, from 66 to 96 mm. 
     To describe the wrench  1  more conveniently, it will be assumed to be oriented as illustrated in the drawings, with the filter  2  with its axis O horizontal and situated above the wrench. 
     The strap wrench  1  comprises the following: 
     1) A rigid body  3  which comprises a base  4  from which there extends a yoke  5 , the legs of which are parallel to the plane of the drawing. 
     2) A threaded rod  6  which may be a multiple-start thread, the lower end of which bears a knurled operating knob  7  while its plain and smaller-diameter, upper end  8  rotates in a central hole  9  in the base  4 , while being prevented from translational movement in this hole. An example of such an arrangement is described in the aforementioned FR-A-1,570,027. 
     3) A nut  10  mounted on the rod  6 . 
     4) A band, especially made of metal,  11 , forming a strap, each end part of which passes with a copious amount of clearance through a lateral slot  12  in the base  4  and then, below this slot, is fixed to the nut  10  by means of a screw  13 . The strap is guided laterally in each slot  12  which, opposite the other slot  12 , has a surface  14  on which the strap can bear. The surfaces  14  diverge in the direction of the object  2  and may be domed. As an alternative, these bearing surfaces could be defined by the peripheral surface of two rollers, as described in the aforementioned French A-publication. 
     5) A shoe  15 , for pressing on the filter  2 , is articulated in the yoke  5  about a pin  16  the axis of which bears the same reference numeral. The pin  16  protrudes from the shoe on each side and rotates in two holes formed in the legs of the yoke  5 . The shoe is placed freely between the two strand parts of the strap  11 . 
     6) A hairpin spring  17  wound around the pin  16 . One end of this spring bears against the upper face of the base  4  and its other end bears under a second pin  18  secured to the shoe  15 . The pin  18  protrudes from the shoe on each side thereof, and its ends are housed in arcshaped slots  19  formed made in the legs of the yoke  5 . The arc-shaped slots are formed such that the axis of pin  16  is the center. 
     The upper face  20  of the shoe has a cylindrical overall shape with generatrices at right angles to the mean plane of the strap  11 , which is the plane of the drawing. The directrix of the cylinder may be circular, for example of a radius that corresponds to the smallest radius of the filters that are to be manipulated, as depicted, or as an alternative may be in the shape of a very open V. The face  20  is additionally shaped with sawteeth inclined to the right in the figures, in an attempt to gain a grip or purchase on the object  2  in a preferred direction, as will become evident later. 
     The assembly comprising the body  3  and rod  6  with its knob  7  is symmetric with respect to a plane P, which is parallel to the axis O or at right angles to the mid-plane of the strap, which passes through the axis X—X of the rod  6 . The axis  16  is offset to the right with respect to the plane P, and the axis of the pin  18  is offset to the left with respect to this plane. 
     Thus, at rest (FIG.  1 ), the spring makes the shoe  15  pivot about the axis  16  in the clockwise direction until the pin  18  comes into abutment against the upper end of the slots  19 . 
     The unscrewing of the filter  2  using the wrench  1  will now be described. 
     The strap is fitted loosely around the filter (FIG. 1) Next, the knob  7  is turned in the clockwise direction (FIG.  2 ). Because of the lateral guidance of the two strand parts of the strap in the slots  12 , this movement causes the nut  10  to descend along the threaded rod, and therefore shortens the useful length of the strap, that is to say its length emerging from the body  3 . 
     When the shoe is pressing against the filter, the strap begins to be tensioned, pressing against the zones  14  of the base  4 . Continuing to turn the knob  7  forces the body  3 /rod  6  assembly to pivot slightly in the clockwise direction (arrow F 1  in FIG. 2) about the axis  16 , compressing the spring  17 . The pin  18  therefore leaves the upper end of the slots  19 . 
     The operator feels a markedly increased resistance to the turning of the knob  7  as soon as this compression of the spring  17  begins. He can therefore stop operating the knob  7 , and the wrench will be in the position of FIG. 2 ready to turn the filter  2 . If he nonetheless continues to turn the knob  7 , the tension in the strap will be limited by the pin  18  coming into abutment against the lower end of the slots  19 . 
     The strap  11  now has two taut strand parts. One strand part  11 A, to the right in FIG. 2, lying between the point  21 A where, on this side, the strap leaves the filter  2  at a tangent, and the distal point  22 A of its region of contact with the right-hand zone  14 A (FIG.  5 ); and a left-hand strap part  11 B, defined in a similar way. The zone  14 A lies on the same side as the geometric axis  16  with respect to the axis X—X and the distal end  22 A is further from the axis X—X than is the geometric axis  16 . 
     The operator then pushes the rod  6 /knob  7  assembly in the counterclockwise direction (arrow F 2  in FIG.  3 ). The sawteeth on the bearing face  20  of the shoe get a firm grip on the filter, and this action causes the wrench and the filter to rotate as one about the axis O (FIG.  3 ). 
     This is because, by virtue of the offset position of the axis  16  with respect to the axis X—X, the axis  16  thus being closer to the point  22 A than to the point  22 B, the distance  21 A- 22 B tends to increase more than the distance  21 A- 22 A tends to decrease, which means that the strap  11  is more taut. 
     During this phase of pushing towards the right (arrow F 2  in FIG.  3 ), the resistance to the unscrewing of the filter may cause the handle to pivot slightly with respect to the shoe about the axis  16 , but this pivoting is limited by the tension in the strap or by the pin  18  coming back into abutment with the top end of the slots  19 . 
     It can thus be seen that if θ represents the algebraic angle between, on the one hand, the axis Z—Z parallel to the axis X—X and passing through the axis  16  and, on the other hand, the straight line Y—Y which connects the center O of the filter to the axis  16 , the positive direction being that of the force in the direction F 2 , (counterclockwise in the drawings), then: 
     during the phase of tightening the strap around the filter, θ increases, and 
     during the pushing in the direction F 2 , θ tends to decrease. 
     After the filter has been rotated counterclockwise through a certain angle, for example limited by surrounding engine parts, the operator pushes the rod  6 - knob  7  assembly in the opposite direction F 1  (FIG.  4 ). 
     The distance  21 B- 22 B tends to decrease more than the distance  21 A- 22 A tends to increase, which means the strap  11  is less taut. Bearing in mind, in addition, the orientation of the sawteeth on the shoe, the entire tool slips about the filter  2  in the clockwise direction. 
     The wrench  1  therefore has a “ratchet” effect, which allows the handle to be moved back and forth a number of times to unscrew the filter  2  through several successive angles. 
     In the example described, the two stops for the pin  18  limit the angle θ to the range of zero to 25°. For each diameter of filter, there is a range of tightening values, and therefore a range of values of θ after tightening (FIG.  2 ), for which the ratchet effect is obtained. In the example in question, the amplitude of this range is about 10 to 15°. It depends on the geometry and on the coefficient of friction between the shoe and the filter. 
     It is important to note that as the spring  17  constantly presses the shoe against the filter, the angular offset which occurs between the shoe and the handle during the return or “ratchet back” movement is instantly taken up as soon as the action in the direction F 1  stops. The tool is thus particularly ergonomic because it requires no significant twist of the wrist, after the return movement, to begin the next turning operation on the filter. 
     In the embodiment of FIG. 5, the handle is embodied by a tubular handle body  23 , for example made of plastic, especially filled with reinforcing fibers, fitted onto the base  4  at one end and onto the knob  7  at the other. The exterior surface thereof is an extension of that of the body  23 . 
     In addition, the bearing surfaces  14  are asymmetric with respect to the axis X—X, the surface  14 A on the drive side being further from the knob  7  than the opposite surface  14 B. As before, the axis  16  is offset with respect to the axis X—X of the handle and is closer to the point  22 A than to the point  22 B irrespective of the diameter of the filter  2  in the range of diameters envisaged. In other words, the axis  16  is offset (to the right in FIG. 5) with respect to the mid-line X′—X′ of the segment  22 A- 22 B, as before. The zone  14 A lies on the same side as the geometric axis  16  with respect to the straight line X′—X′, and the distal end  22 A is further from this straight line X′—X′ than is the geometric axis  16 . 
     In order to permit the strap to be changed, the body  23  comprises, near to the base  4 , two opposed orifices  24  which allow a screwdriver to access the screws  13  when the nut  10  is in its uppermost position. 
     In this embodiment, the shoe  15  is made of a stack of metal sheets riveted together at  25 . As an alternative, the two outermost sheets may be the two legs of a sheet bent into a U with one or more additional sheets forming spacer pieces inserted between them. 
     As an alternative, the surface  14 A may be closer to the knob  7  than the surface  14 B, provided that the axis  16  remains closer to the point  22 A than to the point  22 B. This has been depicted diagrammatically in FIG. 5 by a mid-line X″—X″ of the segment  22 A- 22 B which passes between the axis X—X of the handle and the axis  16 . 
     In another particularly simple embodiment (FIG.  6 ), the wrench according to the invention has neither any system for adjusting the strap nor any spring. The elements which correspond to the embodiment of FIGS. 1 to  4  and whose geometry remains the same, bear the same references, increased by 100. 
     The wrench consists of: 
     a rigid body  103  forming a handle  123 , base  104  with its bearing surfaces  114  and yoke  105 . This body may be molded as a single piece or may consist of two molded pieces assembled, for example by two screws, along a vertical plane of connection; 
     a pin  116  borne by the yoke  105  and on which the shoe  115  is freely articulated; and 
     a strap  111 , at least one end part of which has a number of aligned orifices  27 . 
     On each surface  114 , the base  104  has a protruding stub  28 , which can be received in an orifice  27 . Each pair of orifices corresponds to a predetermined diameter of filter. In addition, a pin  118  borne by the shoe and passing through two arc-shaped slots  119  in the yoke  105  limits the angular travel of the shoe, in both directions, about the pin  116 . 
     Such an embodiment is particularly well suited to repetitive work performed on filters which all have the same diameter. 
     Of course, as an alternative, the tool may be equipped with a set of straps, each having a single orifice  27  at each end, each strap corresponding to a predetermined filter diameter. 
     As an another alternative, at least one of the stubs  28  may be provided at the top of the handle  123 , as shown in chain line in FIG.  6 . 
     It will be understood that it is possible to add a spring  17  to this embodiment. 
     In another embodiment which has not been depicted, the axis of pivoting of the shoe may be purely geometric without being embodied by a pin such as  16 . For that, all that is required is for the lower surface of the shoe to have a convex cylindrical shape which in cross section is in the shape of an arc of a circle and to cooperate with a mating concave guide surface provided on the body  3 . 
     FIGS. 7 and 8 show the external appearance of the strap wrench of FIG. 5, associated with filters of minimum and maximum diameters. 
     It will be observed that over its main length, the body  23  has a roughly elliptical cross section with its major axis in the overall plane of the strap. This cross section gradually becomes a circular cross section in the distal end part of the body  23 , adjacent to the knob  7 . 
     The knob  7  has flutes  29  to make it easier to grasp, and the body  23  has a number of recesses  30  and bears an arrow  31  which indicates the direction of drive. The flutes  29  allow the operator to identify the knob  7  of the body  23  unsighted, this being an effect which may be enhanced by the use of a substance which has a markedly different feel. 
     It will be understood that in each of the embodiments, the strap wrench according to the present invention can be used for screwing or for unscrewing, simply by turning it over. 
     FIGS. 9 and 10 show the external appearance of a slightly modified version of the tool in which the shoe  15  has sawteeth only in its two circumferential end regions. Furthermore, this shoe is made by bending a metal sheet into the shape of a U and inserting spacer pieces  32 , as described earlier. 
     FIG. 11 depicts an alternative form in which the handle body  23  consists of two half shells  23 A,  23 B, for example made of lightweight alloy or made of plastic, particularly filled with reinforcing fibers. The front parts of these shells together form the base  4  and the yoke  5 , the base being defined by superimposed perforated respective projections  4 A,  4 B formed integrally with the half shells. The plain front part  8  of the rod  6  passes through the holes in these two projections and is held axially therein by a snap ring  33  located between the projections  4 A and  43  and which snaps into a groove  34  in the part  8 . The nut  10  is guided in its translational movement by longitudinal reliefs inside the half shells. The lower ends of the two half shells are held together by an end skirt  7 A of the knob  7  pushed over them. 
     Dismantling may be achieved simply by pulling the knob  7  downwards, or as follows. 
     The knob  7  is fully unscrewed, which causes the nut  10  to move right up until it butts against the projection  4 A. By continuing to unscrew, the rod  6  is pushed downwards, which parts the snap ring  33  and releases the rod. The knob-rod assembly can then be lowered, and the two half shells parted. 
     Likewise, assembly may be achieved either by pushing the tip of the rod directly through the projections  4 A and  4 B or by first of all closing the two half shells around the rod  6  and the nut  10  and then by screwing the knob  7 . The nut  10  therefore moves down, butts against an internal collar  23 C,  23 D of the half shells, then continued screwing causes the rod  6 /knob  7  assembly to rise so that the tip of the rod passes through the projections  4 A and  4 B. At the end of its travel, the snap ring snaps into the groove in the rod and the skirt  7 A of the knob fits into position. 
     In the alternative form of FIGS. 12 and 13, the sawteeth of the shoe  15  are distributed in two regions  20 A,  20 B of the bearing face  20 , with clearance between them. The surfaces  25 A,  25 B tangential to the teeth in each of these regions may be planar as depicted, but may also be convex cylindrical or concave cylindrical with a radius larger than the largest radius of filter  2 . The combination of the surfaces  25 A and  25 B is such that for the most common filters in the range, one tooth and one tooth alone  26 A,  26 B of each region is in contact with the filter. 
     As can be seen clearly in FIG. 13, each tooth  26 A,  26 B has a trapezoidal overall shape with, to the left, a surface  27 A,  27 B which forms, with the surface  25 A,  25 B a relatively large angle α, followed by a surface  28 A,  28 B which forms, with the surface  25 A,  25 B, a relatively small angle β. The right-hand flank  29 A,  29 B of the tooth is almost at right angles to the surface  25 A,  25 B and connects to the surface  28 A,  28 B of the next tooth via a rounded portion  30 A,  30 B. 
     The teeth  26 A,  26 B are cut in two shots, i.e. a first-shot to give the overall shape of the teeth, and the second shot to cut out the part  28 A,  28 B of the tooth. The second cutting operation is intended to leave a tooth arris, the width of which is equal to the tolerance on the accuracy of the second cut with respect to the first. 
     It will be understood that in each embodiment, the strap wrench according to the invention provides one-way drive of the wrench by virtue of a toggle joint effect. The point of articulation of this toggle joint is the axis  16  or  116 , one side is the segment  0 - 16  or  0 - 116 , and the other side is a segment which extends from the axis  16 ,  116  to a point secured on the handle of the wrench, which, in the examples described, is close to the axis of the handle and to the surfaces  14 ,  14 A- 14 B or  114 .