Crankpin grinder and method

A method of grinding crankpin journals on a crankshaft in which the crankshaft is rotated about its central longitudinal axis. Abrasive belts are moved along paths substantially perpendicular to the crankshaft such that the abrasive surfaces of the belts grind the crankpin journals while the crankshaft rotates. The belts are guided independently of one another at the point of contact with the crankpin journals along a variable path according to the position of the crankpin journal around the central longitudinal axis of the crankshaft as the crankshaft rotates.

This invention relates generally to grinding apparatus and refers more 
particularly to a method and apparatus for grinding the crankpin journals 
on a crankshaft by abrasive belts. 
BACKGROUND 
In accordance with present practice, the crankpin journals of a crankshaft 
are ground one at a time. The operation is carried out by rotating the 
crankshaft about the axis of one of the crankpin journals and grinding the 
surface of that crankpin journal with a grinding wheel while the 
crankshaft rotates. Before the next journal can be ground, the crankshaft 
must be indexed so that the next journal is placed on the axis of 
rotation. The indexing of the crankshaft and grinding of the crankpin 
journals one at a time is both time-consuming and cumbersome. Also, 
rotation of the crankshaft about an offset journal axis creates an 
imbalance which causes wear and sometimes results in imperfectly ground 
crankpin journals. 
SUMMARY 
In accordance with the present invention, the crankshaft is mounted once 
and once only for rotation about its own central axis. Then several of the 
crankpin journals are no need to index the crankshaft and since the 
crankshaft turns about its own central axis, imbalance is eliminated. 
In accordance with a specific embodiment about to be described, a plurality 
of abrasive belts are supported adjacent to the crankshaft opposite 
several crankpin journals in positions to grind the crankpin journals 
while the crankshaft turns about its own central longitudinal axis. Each 
belt is individually guided at its point of contact with a crankpin 
journal along a variable path as the crankpin journal orbits around the 
central longitudinal axis of the crankshaft. The guiding of the belts is 
carried out by shoes which engage the back surfaces of the belts. Each 
shoe is moved toward and away from the crankshaft axis independently of 
the movement of the other shoes. Preferably, the rotative position of the 
crankshaft is monitored, and the shoes which guide the paths of the belts 
at their points of contact with the crankpin journals are CNC controlled 
so that the belts remain in constant contact with the crankpin journals as 
the crankshaft rotates. 
An object of this invention is to provide a versatile and efficient 
grinding machine having the above features and which is also rugged, 
durable and efficient and of relatively simple manufacture and ease of 
operation; also to provide an improved method of grinding two or more 
crankpin journals at the same time. 
Other objects, advantages and features of the invention will become more 
apparent as the following description proceeds, especially when considered 
with the accompanying drawings.

DETAILED DESCRIPTION 
Referring now more particularly to the drawings, the numeral 10 designates 
a grinding machine having a base 12 on which is mounted a slide assembly 
14 for supporting a workpiece which in this instance is a elongated 
crankshaft C. The slide assembly comprises a slide base 16 which is 
rigidly secured to the grinding machine base 12. Parallel waybars 18 on 
slide base 16 slidably support a table 20 for movement along the waybars 
18 by a ball screw drive 22 powered by a reversible motor 24. A headstock 
26 is mounted on one end of the table 20 by a bracket 28. A tailstock 30 
at the opposite end of the table is slidable on ways 32 mounted on a 
support 34 rigidly secured to table 20. The ways 32 are parallel to the 
waybars 18 to permit the tailstock to be adjusted toward and away from the 
headstock 26 by the servo motor 36 and ball screw drive 38. The ends of 
the crankshaft C are gripped by collet chucks 40 and 42 rotatably mounted 
on the headstock and tailstock, respectively A servo motor 44 mounted on 
the headstock drives collet chuck 40 to rotate the crankshaft C about its 
central, longitudinal axis. 
The crankshaft C is an elongated member having crank arms 46 equally spaced 
apart along the length thereof which extend radially outwardly from the 
central axis of the crankshaft at different angles. Each crank arm has 
parallel side plates 48 which support a cylindrical crankpin journal 50 
near the outer ends thereof. These crankpin journals 50 are cylindrical 
members whose axes are parallel to but radially offset from the central 
longitudinal axis of the crankshaft. 
The base 12 has a lateral extension 52 on which a plurality, three in this 
instance, of grinding units 54, 56 and 58 are mounted. The grinding units 
are provided for the purpose of grinding the cylindrical surfaces of the 
crankpin journals 50 of the crankshaft. 
Each grinding unit comprises a frame having a pair of laterally spaced 
parallel side plates 60 and 62 which are disposed in planes at right 
angles to the crankshaft C and to the waybars 18 supporting the table 20 
on which the crankshaft C is mounted. The side plate 60 of each grinding 
unit is rigidly mounted on a saddle 64 which moves in ways 66 that are at 
right angles to the waybars 18 for the table 20. This saddle 64 is moved 
along its ways 66 by a ball screw drive 68 powered by a servo motor 70. 
The grinding units 54, 56 and 58 will be seen to be parallel to one 
another and to move along parallel paths. 
The side plate 62 of each grinding unit is secured to the side plate 60 in 
the parallel relationship shown by suitable means including the spacer 
blocks 72. At the rear end of the side plates 60 and 62 of each grinding 
unit there is a shaft 74 which rotates in the side plates and also in a 
bearing block 76 mounted on the side plate 62. A belt pulley 78 is mounted 
on the shaft 74 between the side plates for rotation as a unit with the 
shaft and is held in place on the shaft by collars 80. At the upper front 
of each grinding unit there is a shaft 82 which rotates in the side plates 
60 and 62 and in a bearing block 84 on the side plate 62. A belt pulley 86 
is centered on shaft 82 for free rotation between collars 88. A similar 
shaft 90 at the lower front portion of each grinding unit rotates in the 
side plates 60 and 62 and also in a bearing block 92. On this shaft 90 is 
mounted for free rotation a belt pulley 94 centered between collars 95. An 
endless flexible abrasive belt 96 extends over the pulleys 78, 86 and 94, 
having an abrasive surface on the outer side and a non-abrasive backing 
surface on the inner side. The abrasive belt 96 is held under 
predetermined tension by a roller 98 mounted on the end of a leaf spring 
100 the opposite end of which is secured to a shaft 102 extending between 
the side plates 60 and 62. The abrasive belts are disposed in planes 
perpendicular to the crankshaft C and the belts of the three units 54, 56 
and 58 are spaced from each other a multiple of the distance between crank 
arms on the crankshaft, in this instance a multiple of 2. 
The power for driving the abrasive belts of the three grinding units is 
provided by a motor 104 mounted on the base extension 52. The motor 104 
rotates a shaft 106 supported for rotation on base extension 52 by the 
bearing blocks 108. Mounted at spaced points along the shaft 106 are three 
timing belt pulleys 110, 112 and 114 which are secured to the shaft and 
rotate as a unit therewith. The shaft 74 of each of the grinding units has 
an extension upon which timing belt pulleys 116, 118 and 120 are mounted. 
A timing belt is provided for each grinding unit. Thus a timing belt 122 
extends over pulleys 110 and 116, a timing belt 124 extends over pulleys 
112 and 118, and a timing belt 126 extends over pulleys 114 and 120. 
Associated with each timing belt is a belt tensioner comprising a roller 
128 mounted on an arm 130 carried by the side plate 60 and urged by spring 
tension into contact with the timing belt. In this manner, the motor 104 
provides the power for linearly moving the abrasive belts of all three 
grinding units in the direction of the arrow 131. 
A shoe 132 is provided for each grinding unit for guiding the abrasive belt 
at the point where it contacts the crankpin of the crankshaft. This shoe 
has a mounting portion 134 secured where indicated to the side plate 60 by 
a key 136 and has a projecting nose portion 138 which bears against the 
back side of the abrasive belt between the idler pulleys 86 and 94. 
The nose 138 is in the form of an elongated thin flat blade or plate which 
is disposed in the plane of the abrasive belt which it backs. The length 
of the nose 138 is greater than the diameter of the circle traversed by 
the journal pins when the crankshaft rotates so that the belt is backed by 
the nose 138 and held in contact with the journal pin continuously 
throughout the orbiting of the journal pin around the crankshaft axis. The 
front surface 140 of the nose is flat and perpendicular to the plane of 
the belt and contacts and guides the belt not only at its point of contact 
with the crankpin journal continuously throughout the orbiting thereof but 
also during the approach of the belt to the point of contact and its 
movement beyond the point of contact. The nose 138 has side surfaces 141 
extending from opposite side edges of the front surface 140 which are 
perpendicular to the front surface and spaced apart a distance less than 
the width of the abrasive belt. 
Two sets of idler rollers 145 and 147 above nose 138 are provided for each 
grinding unit to fold the abrasive belt as it approaches the nose 138 from 
the normal flat condition to a generally U-shaped cross-section so that 
the belt as it traverses the nose extends over the front surface 140 
thereof and its side edge portions are folded-back over the side surfaces 
141 as seen in FIG. 7. These rollers 145 and 147 are mounted for rotation 
on the side plates 60 and 62. Rollers 145 and 147 can be seen in FIGS. 4-6 
but have been omitted from FIG. 1 for clarity. 
It will be observed in FIG. 7 that the total width of the nose plus the 
folded-back side edge portions of the abrasive belt is somewhat less than 
the width of the crankpin journal. If it is necessary to grind the full 
length of the periphery of the crankpin journal, then it may be necessary 
to oscillate the table 20 and crankshaft C during grinding. Oscillating 
the table 20 also will cause the folded-back portions of the abrasive 
belts to grind the inner surfaces of the side plates 48 of the crank arms 
46. 
The rollers 145 are set at an angle such that their peripheries are at 
about 45.degree. to the abrasive surface of the belt as seen in FIG. 6 to 
begin the folding. The rollers 147 are set at an angle such that their 
peripheries are at about 90.degree., or preferably slightly more than 
90.degree., to the abrasive surface of the belt, completing the folding in 
which the side edge portions of the belt are folded back 90.degree. or 
slightly more than 90.degree. so that when the belt reaches the nose 138 
the side edge portions of the belt will have a slight gripping action and 
hug the sides of the nose. 
Two sets of idler rollers 148 and 150 (also omitted in FIG. 1) below nose 
138 are provided for each grinding unit to engage the abrasive belt after 
it moves beyond the nose 138. Rollers 148 and 150 are mounted for rotation 
on side plates 60 and 62. Rollers 148 are set at an angle such that their 
peripheries are at about 90.degree. to the abrasive surface of the belt. 
These rollers 148 assist rollers 147 in maintaining the belt folded over 
the nose 138. Rollers 150 are set at an angle such that their peripheries 
are at about 45.degree. to partially unfold the belt so that when the belt 
reaches roller 94 it will return to the normal completely flat condition. 
The motors 70 for moving the grinding units 54, 56 and 58 toward and away 
from the crankshaft C are preferably driven and controlled by a CNC 
numerical control. A feed back device 45 on the motor 44 for rotating the 
crankshaft feeds back to the numerical control information regarding 
rotation of ball screw drive and hence the rotative position of the 
crankshaft, so that the numerical control will make corrections as 
necessary and operate the motors 70 of the grinding units to keep the 
abrasive belts in continuous contact with the crankpin journals being 
ground during crankshaft rotation. 
In operation, the table 20 is moved by motor 24 to a position aligning 
three crankpin journals with the abrasive belts of the three grinding 
units 54, 56 and 58. The three grinding units are advanced by motors 70 to 
place the abrasive belts in contact with the crankpin journals. The 
crankshaft C is rotated by motor 44. Device 45 feeds back to the numerical 
control information regarding the rotative position of the crankshaft C. 
The numerical control individually drives the motors 70 of the three 
grinding units to maintain the abrasive belts in constant contact with the 
crankpin journals as the crankshaft rotates. 
Upon completion of the rough or finish grinding of three crankpin journals, 
the grinding units are backed off, the table 20 is shifted to align 
another three crankpin journals with the abrasive belts of the three 
grinding units and the process is repeated. 
If the crankpin journals are longer than the width of the folded abrasive 
belt, and it is desired to grind the full length of the crankpin journal, 
the table 20 may be oscillated during grinding.