Patent Publication Number: US-3875822-A

Title: Lever-operated ratchet devices

Description:
United States Patent Erith et al. Apr. 8, 1975 [5 LEVER-OPERATED RATCHET DEVICES 3.003.359 10/196] Maasdam 74/142 [75] Inventors: Cyril Edward Charles Erith.  
  Gloucester; Gordon Charles Elkins, Cheltenham both f England Primary ExaminerSamuel Scott Assistant E.\&#39;am1&#39;ner--F. D. Shoemaker [73] Ass1gnee: Nlultl-Stroke Handbrake Controls Almmey Agem, or p y &amp; Thompson Limited, Tewkesbury. Gloucestershire, England [22] Filed: July 5, 1974 [2]] App]. No.: 486,201 [57] ABSTRACT [30] Foreign Application Priority Data A lever-operated ratchet device includes a ratchet Julv 10, 1973 United Kingdom 32/97/73 Wheel different Surfacg Pomtms which are engaged by holding and application pawls. The pawls can be [52] Cl 74/575; 74/577 M; 254/1310 12 interchanged to provide fresh surface portions for en- 1511 Int. Cl. Fl6d 41/12 gagemeht With the ratchet Wheel 50 that the effective [53] Field of Search U 74/575 R, 577 142; life of the pawls is doubled. The pawls are preferably 245/1316 12 identical but differently positioned depending on whether they are performing the holding or driving [56] References Cited funcnon&#39; UNITED STATES PATENTS 2.970490 8 Claims. 4 Drawing Figures 2/1961 Winland 74/142 LEVER-OPERATED RATCHET DEVICES This invention relates to lever-operated ratchet devices of the type in which reciprocation or stroking of the lever operates to turn a cable drum or the like associated with the ratchet wheel. Devices of this character are commonly used to tension the brake cables of parking brakes on commercial vehicles, particularly the brakes of semi and independent goods trailers, and I the invention is of more particular application to a socalled multi-stroke handbrake of this type. It will be appreciated that although devices of the type concerned normally act through cables these can be replaced by any suitable flexible members, for example, by chains, and reference herein to a cable drum is to be construed accordingly.  
  Multi-stroke handbrake control devices normally have a ratchet wheel which provides one side plate of the cable drum and which is engaged by a springloaded holding pawl and actuated by a spring-loaded application pawl mounted on a control lever which shares a common pivot axis with the ratchet wheel. After considerable use the pawls wear and have to be replaced, and the object of the invention is to provide a very considerably increased life for the pawls.  
  Accordingly to the invention a lever-operated ratchet device has holding and application pawls which have different surface portions engaging the ratchet wheel such that the pawls can be interchanged to provide fresh surface portions for engagement with the ratchet wheel. Thus the effective life of the pawls is doubled, and the pawls are preferably identical but differently positioned according to whether they are performing the holding or driving function.  
  Preferably the pawls have surface portions which interengage when the lever is moved fully in the nondrive or freewheeling direction, such interengagement moving both pawls to and holding them in a disengaged condition with respect to the ratchet wheel. The formation of the pawls is desirably such that interchanging the pawls brings different interengaging surface por tions into use. so that changing over the pawls renews all operative surfaces thereof, and a projecting portion of one pawl desirably meshes with a re-entrant portion of the other. The interengagement of the pawls&#39;desirably serves to limit movement of the lever in the nondrive direction so that the provision of the usual stop for this purpose is unnecessary.  
  Torsion springs which urge the pawls into engagement with the wheel preferably have spring arms which engage different abutment points positioned so that the appropriate spring loading is provided for the pawls, to this end the profile of each pawl providing two definite spring abutment points respectively engaged when in the holding and application positions of the pawl. This obviates the drilling of spring-engaging holes in the pawls, as is the present practice.  
  The pawls may be made from forgings, castings, or steel bar or strip suitably machined. However, they may be produced by a sintering process, using accurate dies and a material specification calculated to provide high efficiency and an adequate safety margin.  
  A ratchet device in the form of a multi-stroke handbrake control embodying the invention will now be described by way of example, and with reference to the accompanying drawings, in which:  
 FIG. 1 is a front view of the ratchet device,  
  FIG. 2 is a plan view, partly in section, corresponding to FIG. 1,  
  FIG. 3 is a corresponding vertical sectional view through the ratchet wheel axis, and  
 FIG. 4 shows a pawl profile utilised in the device.  
  A cable drum 1, one side of which is provided by a ratchet wheel 2, is rotatably mounted on an axle 3 which extends between a flat generally triangular backplate 4, in which it is fixed, and a triangular cranked cover plate 5 which is fixed to the backplate 4 by a stud 6 clear of the drum and fixed in a bore 7 in the backplate. An operating lever 8 of rectangular section and with a generally circular flat inner end portion 9 is freely pivotable on the axle 3 between the backplate 4 and the ratchet wheel 2. A spring washer 10 between the other side 11 of the drum and the cover plate 5, which covers a sector of the drum, presses the drum towards the backplate and against the lever end 9, and also provides a braking torque operative on the drum. A button-headed socket screw 18 passes through the cover plate 5 into the end of the axle 3.  
  A stud 6, on which the cover plate 5 is fixed by a nut 12, is stepped to provide a pivot bearing for a holding pawl 13 and, between this pawl 13 and the backplate 4, is surrounded by a torsion spring 14 urging the holding pawl 13 into engagement with the ratchet wheel 2. An application pawl 15 pivotally mounted on the lever 8 adjacent the ratchet wheel 2 is spring loaded into engagement with the latter by a torsion spring 16 which surrounds a pivot 17 on which that pawl is mounted.  
  The cranked section of the cover plate 5, as shown in FIG. 3, extends around and has a close clearance with respect to the adjacent side ll of the drum, i.e. the side opposite to the ratchet wheel, and the adjacent side edge of the ratchet wheel. In each case the clearance is less than the diameter of the cable used so that the latter cannot jump off the drum. The cover plate 5 performs the dual function of preventing the cable jumping off the drum 1 and oftying together the axle 3 and the holding pawl pivot stud 6, while also providing a seating for the spring washer 10. i  
  The two pawls l3 and 15 are of sintered form and identical, but employ entirely different operative machined edge surface portions so that they can be interchanged to bring a completely new set of surfaces into use. The shape of one pawl will now be described in some detail with reference to FIG. 4. A boss 20 projects each side of the pawl, to act as a spacer, and has a central pivot bearing bore 21. A toothed portion 22 projects to one side of the boss 20, this portion having a side tooth 23 for holding engagement with the ratchet wheel and an end application tooth 24 for driving engagement therewith. This end tooth 24 defines one side of a V-shaped notch of A tail portion 25 which projects to the other side of the boss 20 has mutually inclined end faces A and B with an included obtuse angle of 136, which is also the re-entrant angle between one side face C of the holding tooth 23 remote from the boss and an adjacent side face D of the toothed portion 22.  
  The pawls l3 and 15 are mounted on their pivots with the toothed portions 22 both leading in the driving sense, the formation being such that one pawl is merely turned over as compared with the other to bring the appropriate tooth 24 or 23 into operation. The torsion spring 14 of the holding pawl 13 has two limbs or tangs 14a and 14b of which tang 14a engages the edge of the backplate 4 and tang 14b engages a concave abutment region 26 of the corresponding pawl close to the boss 20 and on the edge of the toothed portion 22 on the opposite side to the holding tooth 23. The application pawl sprung 16 has one end limb 16a in the form of an inturned radial bar which locates in a cross slot in the corresponding pawl pivot 17. The other limb or tang 16b engages a concave abutment region 27 on the driving pawl provided at the apex of the re-entrant angle of 136 on the toothed portion 22. Thus a different spring abutment region is provided for each pawl position, in each position the correct spring force being obtained. This is essential to correct operation of the device.  
  Movement of the lever 8 in the freewheeling nondrive direction is limited by interengagement of the pawls l3 and 15, such engagement serving to release both pawls from the ratchet wheel and hence relieve the cable tension as the drum 1 is now unrestrained apart from the braking torque produced by said spring washer 10. To this end the tail portion of the application pawl meshes with the tooth portion of the holding pawl, the 136 angle between the end faces A and B of the tail portion of the driving pawl mating with the similar but re-entrant angle between the face C of the holding tooth and the adjacent side face D of the holding pawl. The formation of the pawl faces is such that they interengage with a mutual camming action whereby to turnthem to the release position.  
  The circular inner end 9 of the lever 8, which may be a stamping or pressing, provides a thrust bearing face for the drum 1, this face being in bearing contact with the adjacent side face of the drum. The opposite side 11 of the dum has a recess 30 in which a grease nipple 31 is positioned, this nipple feeding a grease passage 32 parallel to the drum axis and offset radially by an amount slightly less than an overall radius of the circular end 9 of the lever. This passage 32 breaks into the outer end of a radial slot 33 machined in the side face of the drum contacting the lever, this slot 33 extending radially inwardly to the centre bore through which the axle 3 passes. An axially directed slot 34 is machined in this bore, extending throughout the full axial width of the drum from the inner end of the radial slot 33. This provides a particularly advantageous greasing arrangement, as one application of a grease gun simultaneously lubricates the bearing surfaces of theratchet wheel 2 with the end 9 of the operating lever and the axle journal bearing, also the friction slipping surfaces at said spring washer 10. The grease pumped inwardly through said passage is constrained to pass radially along said radial slot, which is closed by the bearing surface on the lever, and then axially outwards along the axle to the outer face of the drum around the spring washer. At the same time the bearing of the lever on the axle is adequately lubricated.  
 What is claimed is:  
  1. A lever-operated ratchet device having holding and application pawls which have different surfaces portions engaging the ratchet wheel such that the pawls can be interchanged to provide fresh surface portions for engagement with the ratchet wheel.  
  2. A ratchet device according to claim 1, wherein the holding and application pawls are identical but differently positioned.  
  3. A ratchet device according to claim 1, wherein the pawls have surface positions which interengage when the lever is moved fully in the non-drive or freewheeling direction, such interengagement moving both pawls to and holding them in a disengaged condition with respect to the ratchet wheel.  
  4. A ratchet device according to claim 3, wherein interchanging the pawls brings different interengaging surface portions into use, so that changing over the pawls renews all operative surfaces thereof.  
  5. A ratchet device according to claim 3, wherein a projecting portion of one pawl meshes with a re-entrant portion of the other.  
  6. A ratchet device according to claim 3, wherein limitation of lever movement in the non-drive direction is provided by the interengagement of the pawls.  
  7. A ratchet device according to claim 3, wherein torsion springs for urging the pawls into engagement with the ratchet wheel have spring arms whichengage different abutment points positioned so that the appropriate spring loading is provided for the pawls, the profile of each pawl providing two definite spring abutment points respectively engaged when in theholding and application positions of the pawl.  
  8. A ratchet device according to claim 3, wherein the pawls are formed by a sintering process using precision dies.