US1862997A - Tachometer jewel frame and drive shaft retainer - Google Patents

Description

E. F. BACON June 14, 1932.

TACHOMETER JEWEL FRAME AND DRIVE SEAFT RETAINER Filed. Feb. 16, 1929.

Patented June 14, 1932 UNITED STATES PATENT oFF-ICE ELBRIDG'E F. "BACON, T FLINT, MICHIGAN, ASSIGNOB TO A C SPARK 'IPLUG COMPANY,

OF FLINT, MICHIGAN, A COMPANY OF MICHIGAN TACHOMETER JEWEL FRAME AND DRIV-E SHAFT ZR JEITJZHNER Application filed February 16, I929. .Serial'No. 340 633.

This invention relates to tachometer-s.

An object of the invention is to improye the construction of such an instrument in order to secure accuracy of its readings.

5 Another and related object is to provide an improved means for securing the parts together and securing the instrument to its support.

Another object is to so constr'uctthe instrum ment as to provide agreater range of adj ustment-s for the hair spring and also to render the hair spring and adjacent parts more accessible. v

j Still another object is to improve the speed 15 disc so as to prevent warping and to obtain a more uniform'pull .upon the disc. v I

Other objects and advantages will be .understood from the following description:

In the drawing:

Figure 1 is a vertical front elevation of the instrument with the bezel removed and the dial broken away to show the internalmechanism.

'Figuref2 is a cross section substantially on 25 line 2-2 of Figure 1.

Figure 3 is asection substantially on line 3- 3 of Figure 2 Figure 4 is a section on line 4-4: of Figure 3.

Eigure'5 is a perspective of the rotor shaft retaining means.

Referring by reference characters .to the drawing, numeral 7 is the casing of the tachometer within which casing is a frame 9 carrying the mechanism of the instrument. Frame 7 is secured in the casing by four studs designated by reference characters 10 and 10', of which studs 10 are diametrically arranged vertically, and studs 10 are dia- 50 vided in the magnet. This secondary magmetrically arranged in a horizontal line.

net is of C shape, as shown in Figure 3, its, poles lying adjacent the left stud 10, one slightly .above and the other below the horizontal line joining the studs 10, 10'..

The .main magnet overlies the secondary magnet and isspaced therefrom. It rests on a shoulder of the frame, as is shown in Figures 2 and 4.. Its gap overlies the gap of the secondary magnet,as will be seen by an inspection of Figure '1. A jewel frame 13 rests upon the main magnet 15 and serves to hold it in position. The jewel frame .is a crescent shape and is held by clamps encircling three of the studs and by nuts 22. As shown in Figure 1,:the upper and lower studs 10 and the right hand studs 10 are used to secure the crescent shape, jewel frame inposition. A compensator o'f-kno'wn kind, and represented'by numeral 23, is arranged to cross the poles of magnet 15 adjacent the left stud 10. It "is of suflicient extent to engage the two poles and is held bya clamp 20 and nut 22'. Overthe clamp and underthe nut there may be used a magnetic calibrating member 24. By suitably bending this member calibration may be readily eifected.

The spider rotor 31 is secured to the end of rotor shaft 33, which "latter is journalled in a bore of the axial stem 35 constituting a part of the .frame 9. The rotor is shown as being located between the two magnets. A speed-disc 18is also located between the magnets.- Its periphery 'is flanged as at 37 to surround the edge of the rotor. The disc 18 is carried bya spindle 1.7,.one end of whichis. j ournalled in the open inner end oYf-the rotor shaft 33'. The jewe'l frame, as shown in Fig u'res 1 and 4, has a radial arm :14 bent out from the plane of the frame and ending in the axis of the spindle 17.. At-its end it is provided with means to serve as a journal for the other end of :thesp'indle. The usual hair spring 23" is associated with thespindle 17 and aregulat or 16. The indicator .needle is designated by .numeral 45.

To retain the rotor shaft 33 it has been the former practice to cut a slot in the stem .35 and project a disc through the slot into a grooveformedinthe shaft. As a substitute for'this arrangement there'isused in the prescut case a retaining member 25 which is seated in a recess in the bottom of the cup-shaped frame within the secondary magnet. This retaining plate 25 has a slot 26 whereby the plate may be extended into an annular groove 27 of shaft 33. The plate is to be riveted to the frame as by fastening means 28. Preferably the plate 25 will be so dimensioned and shaped that the fastening means 28 may pass between the legs of the spider rotor. This is well illustrated in Figure 3.

The front of the instrument is closed as usual with a dial plate, a glass and bezel.

As compared with the earlier construction where but three studs were usedto hold the magnet in position, the present instrument is an improvement in that the magnet is held more firmly in position in its relation to the frame, there being four studs serving to hold the magnet, these studs being arranged at 90 intervals. Two diametrically opposed studs are of additional length whereby these fastening studs may also serve to mount the instrument on its support.

The instrument in use occupies a position somewhat as in Figure 1. In former instruments of this type the magnet gap has been in the bottom. Any displacement of the rotor shaft out of the axis, which is at right angles to the plane of the magnet, tends to move the rotor so that its plane is no longer parallel with the plane of the magnet. Such movement, though slight, so disturbs the operation of the instrument as to render the readings inaccurate. Such a tilting or displacement of the rotor shaft and rotor tends to occur, because the flexible shaft connected to the rotor shaft 33 exerts a pulling effect, generally in a downwardly direction. This difficulty is the greater because in previous constructions the material cut out of the stem 35 for the reception of the retainer has so weakened the stem that there has been a tendency for the stem, itself, to take a position such that its aXis is no longer normal to the plane of the magnets. By placing the gap in the horizontal axis instead of the vertical axis any such distortion 'is rendered less harmful. Furthermore, the feature, whereby the retaining means which secures the rotor shaft is so arranged as not to weaken the stem of the casing, serves to effectively preventany such distortion of the stem of the frame, and in consequence of the position of the rotor shaft, and rotor, therefore, remains normal to the plane of the magnets. By these simple and inexpensive improvements better results are secured.

Instead of constructing the jewel frame as a bridge over the hair spring, as has been done heretofore, the jewel frame is made of crescent shape with a radial arm terminating over the speed disc spindle. This renders the hair spring and the parts related thereto much more accessible and it gives a greater range of movement for the regulator of the adjusting spring, as will be obvious from an inspection of Figure 1.

The added rigidity of the speed disc, accompanied by the provision of the flange 37, serves to prevent warping of the disc, and it also secures for the speed cup a more uniform magnetic drag.

I claim:

1. In a tachometer, a cup-shaped frame having an axial stem extended horizontally, a rotor shaft extended through said stem, a rotor carried by and in the plane at right angles to said shaft, means to retain said shaft comprisingia plate having a slot, said shaft having an annular groove to cooperate with said slotted plate, and means to secure said plate to the bottom of said cup-shaped frame over said stem.

2. The invention defined by claim 1, said rotor being of spider shape, and the retaining means being so dimensioned and shaped as to permit access to said fastening means between the legs of said spider rotor.

3. In combination, a cup-shaped frame having an axial stem extended horizontally, a rotor shaft within said stem, a magnet having poles adjacent the horizontal plane of the rotor shaft, means to secure said magnet to the bottom of the cup in a plane at right angles to the axis of said shaft, a second magnet in said cup parallel to and spaced from said first magnet, a rotor carried by said shaft, said rotor being located between said magnets in a plane parallel thereto, a crescent jewel plate overlying said second magnet, a plurality of fastening means securing said jewel plate and second magnet to said frame, a speed disc also between said magnets and in a plane parallel thereto, an indicating means carried by said speed disc.

4. The invention defined by claim 3 together with a retaining plate, said plate and shaft having inter-engaging parts to prevent relative axial movement, and means to secure said retaining plate to the bottom of said cupshaped frame.

In testimony whereof I affix my signature.

ELBRIDGE F. BACON.

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