Machine element or mechanism – Elements – Cranks and wrist pins
Patent
1991-06-17
1993-03-02
Scherbel, David A.
Machine element or mechanism
Elements
Cranks and wrist pins
74595, 74579E, 1231974, 123 9031, F16C 304
Patent
active
051899272
DESCRIPTION:
BRIEF SUMMARY
This invention relates to variable ratio drive transmissions and in particular to variable throw crank drives for incorporation in such transmissions.
British Patent 132628 describes a variable stroke crank drive, comprising a crank shaft having a plurality of axially spaced big-end journals each having at least one connecting-rod (con-rod) mounted thereon through the intermediary of eccentric mounting means, the said means all being adjustable in unison to permit the eccentricity of each con-rod big-end to be adjusted from a minimum value to a maximum value, and a rotatable operating shaft extending axially through the crank shaft and operable, while the crank shaft is running, to vary the eccentricities of the said eccentric mounting means in unison.
The drive disclosed does not, however, provide for preserving dynamic balance and would therefore be liable to substantial vibration at high operating speeds.
The present invention is mainly characterized in that the eccentric mounting means for each con-rod big-end comprises a journal mounted for radial displacement relative to the crank shaft, and that a corresponding counterweight is also mounted for radial displacement relative to the crankshaft, the journal and its counterweight being radially displaceable in opposite directions by cam means fast with the operating shaft and operatively coupled to the said journal and its counterweight. This arrangement provides for automatic counterbalancing of the shaft throughout the range of adjustment of the eccentricity of the eccentric mounting means.
The invention also provides a crank shaft, suitable for use in such a drive, fabricated from a plurality of components to facilitate its production.
These and other features of the invention will appear from the following description of a presently preferred form of drive transmission in accordance with the invention, given with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-section on the line 1--1 of FIG. 2;
FIG. 2 is a longitudinal cross-section through the axis of the crank on the line 2--2 in FIG. 1;
FIG. 2A is a scrap detail from FIG. 2, on a larger scale;
FIGS. 3A,3B; 4A,4B; 5A,5B; 6A,6B; 7A,7B; 8A,8B,8C; 9; 10A,10B; and 11A,11B,11C,11D, are sets of views of individual components of the drive transmission;
FIG. 12 is an axial section on a drive shaft; and
FIG. 13 is a scrap section showing an actuating means for the drive transmission.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The drive shown in the drawings is a continuously variable transmission for a tractor. It has a main crank axis CA and two parallel driven shafts DA 1 and DA 2. Each of these shafts carries three one-way clutches, in the form of sprag clutches whose outer races are all connected to different respective con-rods each driving its associated sprag-clutch and drive shaft for up to 65.degree. of arc whilst overriding the other two clutches on the same shaft. The two drive shafts are coupled to a common output.
The con-rods all have adjustable throw, and means are provided for adjusting the throws of all six con-rods from zero to maximum value. At zero throw, no drive is transmitted to the driven shafts and at maximum throw, the shafts are driven at their maximum speed relative to the speed of rotation of the crank shaft.
Turning now to the constructions in detail, FIG. 2 shows the length of the crank shaft on its axis CA. The crank shaft is of fabricated construction, comprising a forward end main bearing and cam housing component 10, three journal housings 11, two middle sections 12 alternating axially with the housing 11, and a rear end main bearing and cam housing component 13. These components are rigidly secured together to form the crank shaft proper and as will be explained below, they provide "big-end" journal supports for three pairs of con-rods 14A,14B, three of which can be seen in FIG. 2 connected at their small ends to respective spragclutch outer races 16 on one driven shaft DA 1.
The main components of the crank shaft a
REFERENCES:
patent: 1875180 (1932-08-01), Rider
patent: 1924562 (1933-08-01), Lower et al.
patent: 1986549 (1935-01-01), Woolson
patent: 2204514 (1940-06-01), Schlote
patent: 4078450 (1978-03-01), Vallejos
patent: 4085628 (1978-04-01), McWhorter
patent: 4319498 (1982-03-01), McWhorter
patent: 4467756 (1984-08-01), McWhorter
patent: 4505235 (1985-03-01), Mitchell
patent: 4622864 (1986-11-01), Fetouh
Scherbel David A.
Yip Winnie
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