US 3059500 A
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O 3, 1 2 A. SCHNEITER 3,059,500
PAWL AND RATCHET DEVICE Filed Sept. 9, 1960 Ayenls United States Patent 3,059,500 PAWL AND RATCHET DEVICE Ali Schneiter, Neuchatel, Switzerland, asignor to Ebauches S.A., Neuchatel, Switzerland, a firm Filed Sept. 9, 1960, Ser. No. 55,015 Claims priority, application Switzerland Sept. 12, 1959 6 Claims. (Cl. 74-575) The present invention relates to pawl and ratchet devices notably fOI' retaining a leverescapement wheel.
Pawl and ratchet devices of the type utilising a resilient blade for a pawl are well known. The blade engages the 'teeth of a ratchet Wheel and is adapted for preventing recoil of the wheel. In the design of the blade it is necessary to construct the same so that it is of saidcient rigidity to resist buckling when the recoil force of the wheel is applied thereto, while the blade must also be of suiiicient flexibility in order not to exert an excessive pressure on the teeth of the ratchet wheel to prevent norrmal rotation thereof. Heretofore, the blades were either excessively flexible or rigid, depending on the use to which the blade was put.
It is an object of the present invention to obviate the above disadvantage by providing a pawl and ratchet gear in which the buckling strength and the flexibility of the blade are substantially independent of one another, so that the blade can be made suitably rigid while exhibiting desired flexibility. A particular object of the invention is to provide a pawl and ratchet gear rod, which is able to resist without buckling substantial recoil forces of the wheel while exerting on the wheel pressure which is substantially unrelated to the strength of the rod necessary for resisting buckling.
The pawl and ratchet device is characterised by a bent rod or blade forming a pawl, and is supported at one of its ends and co-operates at its other end with a ratchet, the rod or blade also bearing, adjacent the bend thereof, against an abutment, the arrangement being such that the resilience of the pawl is furnished by the resistance to torsion of the section of the rod or blade which extends between the point of attachment and the bend. The resilience is independent of the resistance of the pawl to buckling, which resistance is inter alia a function of the length of the section of the rod or blade which extends between the bend and the end co-operating with the ratchet.
A preferred embodiment of the subject of the invent-ion is illustrated by way of example in the accompanying drawings.
FIGURE 1 is a plan view of a wheel and a lever of an escapement, the wheel being retained 'by the pawl and ratchet device according to the invention, and
FIGURE 2 is an elevational view of the structure in FIG. 1 shown in section.
Lever 1 has pallets 2 which co-operate with an escape wheel 3 having on its lower face teeth 3a extending therefrom. A section 4a of a resilient blade is adapted to cooperate with the teeth in a manner to be explained more fully hereinafter. The resilient blade has a second section 4b which is fixed at its end to an eye bolt 5, which is in turn mounted on a bridge 6 of the frame of the apparatus on which the device is mounted. The two sections 4a and 4b of the resilient blade are in skewed relation with respect to one another, for which purpose the blade has been twisted at 40. In addition the sections extend perpendicularly to one another by virtue of a right angle bed at 4d. An eccentric 7 bears against the section 4b of the blade, adjacent bend 4d.
Because of the above arrangement, the pawl consisting of the resilient blade is operating by virtue of torsion of Patented Oct. 23, 1962 section 4b. The force with which the pawl acts on the ratchet 3a is mainly a function of the length of the section 4b since the angle of twist at the end of section 4b adjacent bend 4d is substantially proportional to the length of section 4b. On the other hand, the retaining force of the pawl i.e. its resistance to buckling, is determined mainly by the length of the section 4a of the blade. Thus, by choosing suitable relative lengths of sections 4a and 4b, it is possible to establish, in accordance with requirements, the ratio between the retaining force of the pawl and ratchet gear and the pressure with which the pawl acts on the ratchet.
By turning the eccentric 7, the section 4a of the resilient blade is slightly displaced, by a slight bending of section 41), whereby it is possible to very accurately adjust the angular position of the wheel 3 when the same is stationary and in contact with the retaining paw-l.
The pawl and ratchet gear, which has many applications, will be particularly suitable for retaining escape wheels of lever escapements, these wheels often tending to recoil, since they are not urged to turn in a particular direction, as are ordinary escape wheels.
While only one embodiment of the invention has been shown and described in detail, it will be apparent to those skilled in the art that modifications such as different crosssections for the blade are possible which do not depart from the spirit of the invention as defined in the appended claims.
What I claim is:
l. A pawl for use with a ratchet wheel comprising an elongated blade including first and second ends, said blade including a bend dividing said blade into a first straight section which includes sa-id first end and a second straight section which includes said second end, means for rigidly supporting said first end, an abutment in contact with the first section adjacent said bend, and a twist in said second section adjacent said bend for urging said second end into operative contact with said ratchet wheel whereby the resilience of said pawl is provided by said first section and the buckling resistance of said pawl is provided by said second section.
2. The pawl of claim 1 wherein said abutment is positioned on the side of said first sec-tion remote from said second end.
3. Apparatus comprising: an escape wheel including a face and teeth extending from said face; means for pivotally mounting said escape wheel in a given plane; and a pawl including an elongated blade including first and second ends and sides, said blade having a bend dividing said blade into a first straight section which includes said first end and a second straight section which includes said second end; means for rigidly supporting said first end so that said first section is disposed in a plane parallel to and displaced from said given plane; an abutment in contact with the first section of said blade remote from said second end; and a twist in said second section whereby said second end is urged against the teeth of said escape wheel.
4. A pawl as claimed in claim 1, in which the position of the said abutment is adjustable.
5. A pawl as claimed in claim 1, in which the said abutment includes an eccentric.
6. A pawl as claimed in claim 1, in which said bend is about .Ensign et al. Aug. 7, 1956 Rodgers et a1. July 14, 1959