Device for rotating and simultaneous hardening by electric induction

The invention relates to the rotary and simultaneous electroinductive hardening of the bearing surfaces (2a; 3a) of crank pins (2; 3) of a crankshaft (1) disposed immediately one beside the other and offset in relation to one another in the axial direction (D), having inductors (10; 11) which each engage around the crank pins (2; 3) by a maximum of 180.degree. and which each have two inductor branches (12, 13; 14, 15) arranged in parallel and following the curvature of the bearing surfaces (2a; 3a), of which one branch is associated with the overlapping zone (5) of the crank pins (2; 3), the other branch being associated with the particular other edge zone (2b; 3b) of the crank pin (2; 3) associated therewith, the inductor branches (12, 13; 14, 15) of each inductor (10; 11) having in the axial direction (D) a distance (A) increased in relation to half the total width (B) of the crank pins (2; 3). According to the invention such a device is characterised in that the inductors (10; 11) engage around the crank pins (2; 3) substantially from the same direction (R) and the zone of increased distance (A) of the inductor branches (12, 13; 14, 15) of each inductor (10; 11) is limited to that portion (12c; 14c) of the inductor branch (12; 14) associated with the overlapping zone (5) which does not in any rotary position of the crankshaft (1) penetrate the corresponding portion (14c; 12c) of the inductor branch (14; 12) of the particular other inductor (11; 10) associated with the overlapping zone (5).

BACKGROUND OF THE INVENTION 
The invention relates to a device for the rotary and simultaneous 
electroinductive hardening of the bearing surfaces of crank pins of a 
crankshaft disposed immediately one beside the other and offset in 
relation to one another in the axial direction, having inductors which 
each engage around the crank pins by a maximum of 180.degree. and which 
each have two inductor branches arranged in parallel and following the 
curvature of the bearing surfaces, of which one branch is associated with 
the overlapping zone of the crank pins, the other branch being associated 
with the particular other edge zone of the crank pin associated therewith, 
the inductor branches of each inductor having in the axial direction a 
distance increased in relation to half the total width of the crank pins. 
In crankshafts having crank pins disposed offset immediately one beside the 
other, also known by the term "split pin crankshafts", there is the basic 
problem that with the individual hardening of each bearing surface the 
previously hardened immediately adjacent bearing surface is annealed by 
the heating of the following hardened bearing surface. For this reason, 
for example, German Patent Specification DE 42 36 921 C1 suggests that the 
hardening of the immediately adjacent bearing surface of a split pin 
crankshaft should be performed simultaneously. Associated with each crank 
pin is an inductor, the inductors being disposed substantially 
diametrically opposite. This diametrically opposite, offset arrangement 
has the advantage that the space available on both sides of the crankshaft 
can be used for the arrangement of supply and control devices for the 
operation of the inductors. Another advantage of the diametrically 
opposite arrangement of the inductors is that it enables the width of the 
individual inductors--i.e., the distance between the inductor branches--to 
be so selected that the sum of the width of two inductors is greater than 
the total width of two bearing surfaces to be hardened. The radially 
opposite arrangement ensures that even though they overlap in the axial 
direction because of the increased width, the inductors do not collide 
when the crankshaft rotates. 
Another problem in the electroinductive hardening of immediately adjacent 
bearing surfaces of a crankshaft is that as a rule cheeks are formed which 
are constructed laterally of the crank pins disposed directly one beside 
the other and which cheeks have a larger volume of material than the crank 
pins disposed therebetween. 
When the bearing surfaces become heated, the accumulation of material in 
the zone of the cheeks results in a reduction in heat in the zone of the 
bearing surface edge zones associated with the cheeks. To obviate this 
problem German Patent Application 195 30 430 suggests that the inductor 
branch associated with the cheek side edge zone of the bearing surface to 
be hardened should be constructed longer than the inductor branch disposed 
in the overlapping area of the crank pins. This achieves a uniform 
temperature distribution in the electroinductive heating of bearing 
surfaces. 
The afore-explained devices have proved themselves in practical trials, but 
it has been found that it is technically very expensive so to guide the 
diametrically opposite inductors and keep them bearing against the bearing 
surface to be hardened that on the one hand any damage to the bearing 
surface is impossible, while on the other hand the close electroinductive 
coupling of the inductor and the bearing surface is ensured necessary for 
the effective heating of the bearing surface. 
Neither could the cost of guiding the inductors be reduced by the 
rearrangement of the electric supply elements, as also known from 
practice, to enable the inductor casings to be jointly brought in from one 
direction from above. Even with inductors thus supplied from above, each 
of the inductor branches operative during heat generation had to be 
disposed substantially diametrically opposite, to prevent them from 
colliding when the crankshaft rotated. 
It is an object of the invention to provide a device of the kind specified 
in which the technical cost of guiding the inductors is reduced, while at 
the same time an optimum heating and hardening result is ensured. 
SUMMARY OF THE INVENTION 
This problem is solved according to the invention by the features that, 
the inductors engage around the crank pins substantially from the same 
direction, and 
the zone of increased distance of the inductor branches of each inductor is 
limited to that portion of the inductor branch associated with the 
overlapping : zone which does not in any rotary position of the crankshaft 
penetrate or brush over the corresponding portion of the inductor branch 
of the particular other inductor associated with the overlapping zone. 
According to the invention the inductor branches engage around their 
associated bearing surfaces from the same direction. This means that the 
inductor branches operative for heating are advanced jointly with the 
inductor casing from one direction to the bearing surface to be hardened 
and, disposed immediately adjacent, engage from the same direction around 
the bearing surfaces when placed thereon. This eliminates expensive 
mechanisms for applying diametrically opposite inductor branches to the 
bearing surface. At the same time the inductors' own weight can be used to 
generate the force necessary for the proper fitting of the inductors on to 
the bearing surfaces, while the actual force applied can be metered by 
simple means, for example, by resilient elements. 
Since according to the invention the branches of each inductor have only 
over a certain portion a distance increased in relation to the width of 
the bearing surface to be hardening, the inductors are reliably prevented 
from colliding when the crank shaft rotates, even though they are disposed 
lying closing adjacent one beside the other. At the same time, the limits 
of the portion of increased distance--i.e., the zone in which the inductor 
branches overlap in the axial direction--is fixed by the ends of that 
portion of the inductor branch associated with the overlapping zone 
between which and the corresponding portion of the inductor branch of the 
other inductor associated with the overlapping zone no meeting takes 
place, viewed in the axial direction of the crankshaft, during a rotation. 
The limitation of the zone in which the inductor branches of the! inductors 
associated with the overlapping zone of the crank pins overlap one another 
in the axial zone of the crankshaft not only enables the inductors to act 
on the bearing surfaces from the same direction without any risk of 
collision. Such limitation also allows for the fact that the heat supplied 
to the overlapping zone must be lower than the quantity of heat which must 
be supplied to the other edge zone of the bearing surface, which is as a 
rule associated with a cheek. In this way the inductor construction 
according to the invention can reliably prevent damage due to the 
overheating of the bearing surfaces to be hardened. 
In addition, the demand that different quantities of heat should be 
introduced into the various zones of the bearing surface to be hardened is 
met by the feature that the inductor branch associated with the 
overlapping zone is shorter than the other inductor branch of the 
inductor. Alternatively, or in addition to this step, different quantities 
of heat can be introduced into the overlapping zone and the other edge 
zone of the bearing surface by the feature that the inductor branch 
associated with the overlapping zone is substantially inoperative in the 
zone in which it is at a smaller distance from the other inductor branch 
of the inductor. 
In principle it is also possible that the inductor branch associated with 
the overlapping zone can be substantially constructed only in the portion 
of increased distance. 
Also advantageously a guide shoe is associated with each free end of the 
inductor branches. Such supporting elements make it particularly simple to 
support the particular inductor on the bearing surface to be hardened, 
without incurring any risk that the bearing surface may become damaged. 
As regards the construction of the device according to the invention, 
conveniently at least one of the inductor branches, but preferably both 
branches of each inductor are divided. This not only enables the electric 
connecting wires to approach and be taken away in an optimum manner, but 
it also enables at least one guide shoe to be disposed between the 
component portions of the inductors.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings, a crankshaft 1 has a first crank pin 2 offset in 
relation to its axis of rotation D and having a bearing surface 2a. The 
first crank pin 2 immediately adjoins a second crank pin 3 which has a 
bearing surface 3a and is also disposed eccentrically in relation to the 
axis of rotation D of the crankshaft 1 and is also offset in relation to 
the first crank pin 2. A overlapping zone 5 in which the crank pins 3, 2 
merge into one another is formed therebetween. Via their edge 2b, 3b 
opposite the overlapping zone 5 the bearing surfaces 2a, 3a each adjoin 
cheeks 6, 7 which have a substantially identical thickness and a 
considerably larger diameter than the diameter of the crank pins 2, 3. 
To heat the bearing surfaces 2a, 3a of the crank pins 2, 3, inductors 10, 
11 are applied from the same direction from above on to the crank pins 2, 
3, each of the inductors 10, 11 being associated with one of the bearing 
surfaces 2a, 3a. The inductors 10, 11 each have two inductor branches 12, 
13, 14, 15 which engage from the same direction R around the bearing 
surfaces 2a, 3a and are each divided into component branches 12a, 12b, 
13a, 13b, 14a, 14b, 15a, 15b. Each of the inductor branches 12, 14 of the 
inductors 10, 11 is associated with the overlapping , zone 5, while the 
other inductor branch 13, 15 is associated with the other edge zone 2b, 3b 
of the bearing surface 2a, 3a associated with the cheeks 6; 7. 
Via their first component portion 12b, 13b; 14a, 15a the inductor branches 
12, 13; 14, 15 engage around the associated bearing surface 2; 3 by 
approximately 90.degree., while via their other portion 12a, 13a; 14b, 15b 
they each engage around the bearing surface 2a; 3a by a smaller angular 
amount. Guide shoes 16, 17, 18, 19 are disposed at each free end of the 
component portions of the inductor branches 12a, 12b, 13a, 13b, 14a, 14b, 
15a, 15b. An additional pair of guide shoes 20, 21 is disposed centrally 
between the component portions 12a, 12b, 13a, 13b, 14a, 14b, 15a, 15b. 
Each of the component portions 12a, 13b; 12b 13.sub.b of the inductor 
branches 12, 13 and the portions 14a, 15a; 14b, 15b of the inductor 
branches 14, 15 are electrically connected to one another via connecting 
branches 22, 24; 25, 23. 
The component portions 12b, 14a of each of the inductor branches 12, 14 of 
the inductors 10, 11 associated with the overlapping zone 5 each have a 
portion 12c, 14c which is disposed at a distance A from the particular 
other inductor branch 13, 15. The distance A is greater than the distance 
a between the other portions of the particular inductor branch 12; 14 and 
the particular other inductor branches 13, 15. The remaining portions in 
question are formed by the remaining part of the portions 12b, 14a and the 
particular second portion 12a, 14b. The portions 12c, 14c of the inductor 
branches 12, 14 each merge in an inclination into the remaining portion 
more closely adjacent to the particular other inductor branch 13, 15. 
The distance A is such that the sum of the distances A of the two inductors 
10, 11 is greater than the total width B of the bearing surfaces. By this 
dimensioning of the distance A, the portions 12c and 14c of the inductor 
branches 12, 14 overlap one another in the axial direction. The limit at 
which the portions 12c, 14c of increased distance A merge into the portion 
of smaller distance a corresponds to the limit of that zone of the 
inductor branches 12, 14 which, when the crankshaft 1 rotates, does not 
stand opposite the corresponding zone of the other inductor 14, 12 in the 
axial direction of the crankshaft in any rotational position thereof. The 
position of the portions 12c, 14c is made clear by FIGS. 3a-3h, which 
shows how the hatched portions 12c, 14c of increased distance A do not 
stand directly axially opposite one another viewed in the axial direction 
of the crankshaft 1, in any position of a rotation thereof. 
In contrast with the component portions 12b, 13a, 13b of the branches 12, 
13 of the inductor 10 and the component portions 14a, 15a, 15b of the 
branches 14, 15 of the inductor 11, the component portions 12a, 14b of the 
inductor branches 12, 14 are constructed unlaminated with sheet metal, so 
that they are substantially without effect in the heating of the bearing 
surfaces 2a, 3a. This prevents any overheating of the zones of the crank 
pins 2, 3 adjoining the overlapping zone 5. 
At the same time, the fact that the length of the inductor branches 13, 15 
associated with the cheeks 6, 7 which is effective as regards heating is 
greater than that of the inductor branches 12b, 14a operative in the 
overlapping zone 5 compensates for the higher heat transfer in the 
transitional zone between the cheeks 6, 7 and the adjoining crank pins 2; 
3. 
Alternatively to the embodiment shown in the drawings, the component 
portion 12a; 14b can also be connected directly to the outer end of the 
adjacent component portion 13a and 15b respectively of the inductor branch 
13, 15 associated with the edge zone of the bearing surface 2a, 3a. It is 
also possible to completely eliminate the component portion 12a; 14b of 
the inductors 12, 14 associated with the overlapping zone 5 and to 
construct the inductor 12; 14 associated with the overlapping zone 5 only 
over the length of the portion 12c; 14c of increased distance A.