RESISTANCE-RUBAN A VENTILATION EXTERNE AVEC GRANDE CAPACITE DE CHARGE

EXTERNALLY VENTILATED STRIP-RESISTANCE UNIT HAVING A HIGH LOAD-CARRYING CAPACITY

Abrégé anglais

Abstract
Disclosed is an externally-ventilated, high-load-carrying-
capacity strip resistance unit which consists of a copper-free, meander-
pattern resistance strip, the deflecting locations on one end of which
are held resiliently to a frame. The deflecting locations on the other
end consist of welded-on, copper-containing, U-shaped brackets to which
connecting bolts, made of a material containing a larger proportion of
copper, are welded. The graduated amounts of copper in the brackets
and connecting bolts prevents intercrystalline corrosion of the copper-
free resistance strips. Each connecting bolt has a square section which
fits into a square recess in an insulating cup, the square outside
contour of which projects through a corresponding square aperture in the
frame to which it is secured by means of screws, so that the deflecting
locations, together with the connecting bolts, are held rigidly and
secure against rotation in the frame. Thus when the connecting cables
are tightened to the necks of the connecting bolts, there is no turning
of the deflection locations and no contact between adjacent welded-on
resistance strips.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An externally ventilated, high-load-carrying-capacity strip-
resistance unit having resistance paths arranged in a meander pattern and
held to, but insulated from, a frame, the said resistance paths consisting
of resistance strips with deflection locations at opposite ends of the frame,
those at one end having no electrical connections and being resiliently
flexible, while those on the other end are welded to the said resistance
strips, contain copper, and are held rigidly, but detachably, to the said
frame by means of connecting bolts also used for resistance stages and
passing through insulating elements supported on the said frame, so that
the entire resistance path lies fully exposed in a flow of cooling air,
characterized in that the copper-containing deflection locations welded to
the copper-free resistance strips are in the form of U-shaped brackets made
of an alloy containing less copper than the connecting bolts each consisting
of a bolt head, a square part, and a threaded bolt neck, and in that the
head of each connecting bolt, passing through its associated bracket, rests
upon the transverse portion of the bracket and is welded thereto, is held by
its square part which is located outside the said bracket, secured against
rotation in an insulating cup, also secured against rotation, resting upon
the frame and having a square external contour and a square recess, and rests
upon the insulating cup by means of an attachment nut screwed to the neck of
the bolt.
2. A unit according to claim 1, characterized in that the brackets
are made of a 40% copper alloy, the connecting bolts of a 70% copper alloy,
and the resistance strips of a chrome-nickel alloy.
3. A unit according to claim 1 or 2, characterized in that half-
brackets are provided for terminal connection locations and are welded to

the resistance strips and to the connecting bolts.
4. A unit according to claim 1, characterized in that sections of
the resistance strips having the same length are of different cross section
between two adjacent electrical connecting bolts.

Description

47~3~7
This invention relates to an externally ventilated strip-
resistance unit having a high load-carrying capacity, arLd with resistance
paths arranged in a meander pattern and held to, but insulated from, a
frame, the said resistance paths consisting of resistance strips with
deflection locations, those on the one side having no electrical
connections and being resiliently flexible, while those on the other side
are welded to the said resistance strips, contain copper, and are held
rigidly, but detachably, to the said frame by means of connecting bolts
also used for resistance steps and passing through insulating elements
supported on the said frame, so that the entire resistance path lies
fully exposed in the flow of cooling air.
In the strip-resist~lce unit disclosed in German Public
Inspection Text 1,~65,915, the meander-pattern resistance paths, mounted
to allow unimpeded heat expansion, consist of straight-profile resist-
ance strips with separate deflection locations, preferably made of
copperj welded to the ends thereof. Connecting bolts are connected
mechanically and electrically to the easily accessible deflection
locations situated on one side, the said bolts forming, in conjurlction
with the insulating elements through which they pass, rigid screwable
means for retaining the resistance paths to the frame. The
de M ection locations free of electrical connections, situated on the
other side, are held resiliently to the frame. All of the deflection
locations are in the form of complex, copper-containing castings
adapted to the profiles of the resistance strips, so that in addition
to the expense of the castings themselves, a correspondingnumber of
such welded castings is required, regardless of the number of electrical
connection locations. Satisfactory, long-lasting welds in copper
castings require the use of copper-containing resistance strips, but
these have a lower load-carrying capacity than resistance strips
.~'P~
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containing no copper.
When the connecting cables are screwed to the connecting bolts,
the latter, together with the castings and welded-on resistance strips may
be inadvertently rotated, so that impairment o-f the cooling or even contact
between adjacent resistance strips is possible.
In the known resistance unit, in order to prevent the castings
from rotating, mechanical retention is separate -from electrical connection
and is achieved by means of separate bolts passing insulatedly through *he
castings, thus adding to the expense of the said castings.
It is the purpose of the invention, in the case of resistance paths
havlng a particularly high load-carrying capacity~ to restrict the number of
deflection locations to be welded to the resistance strips to the deflection
locations provided with connection locations, and to manage with deflection
locations which are o-f simple configuration, are easily and permanently
weldable, and can be secured to the frame so that they are easily detachable
and cannot be turned.
This purpose is achieved, according to the invention, in that the
copper-containing deflection loccations welded to the copper-free resistance
strips are in the form of U-shaped brackets made of an alloy containing
less copper than the connecting bolts each consisting oE a bolt head, a
square part, and a threaded bolt neck, and in that the head of each
connecting bolt passing through its associated bracket rests upon its
transverse part and is welded thereto, is held by its square part, which is
located outside the said bracket, secured against rotation in an insulating
cup, also secured against rotation, resting upon *he frame, and having a
square external contour and a square recess, and rests upon the insulating
cup by means of an attachment nut screwed to the neck of the bolt.
The in~ention will now be further described in conjunction with
the accompanying drawings, in which:

7~37
Figure 1 is a side elevation of a strip--resistance unit in
longitudinal section;
Figure 2 is a cross section of the object in Figure l;
Figures 3 and 4 are details of the unit in plan view and cross
section
Two substantially indentical meander-pattern resistance paths are
arranged, in the direction of flow o th~ cooling air, one behind the other,
and spaced from each other, in a rigid square frame 1 consisting of a
~ plurality of straight frame parts la, lb,-~e-j ld welded toge-ther. The
meanders of resistance strips 2 of each resistance path are held to, but are
insulated from, relevant frame parts la and lb, at upper and lower deflection
locations 3 and 4, by retaining means 5,6. Upper deflection locations 3,
which have no electrical connections, have apertures through which insulating
tensioning bolts 6a are passed from inside to outside, so that appropriately
shaped, lower bolt heads 6b lie snugly against resistance strips 2 at the
said deflection locations. Bolt sleeve 6c projects through insulating cup
11 which has a square external contour and is seated, secured against rotation,
in a corresponding aperture in frame part la, resting thereupon by means of
an external shoulder lla. Arranged within insulating cup 11 is an internal
projection llb with which an annular, disc-shaped abutment 6g arranged
around bolt neck 6c engages. Arranged between abutment 6g and a second
abutment 6c is a spring 6f which bears against an abutment 6d located by
means of a clamp 6e at the end of the bolt neck, and which presses abutment
6g against the said internal projection llb. Lower deflection locations 4,
which have no electrical connections, are also secured to frame part lb in
the manner described above.
Certain lower deflection locations are provided with e:Lectrical
connection locations 7, and these are also retained by insulating cups 11
described above~ but in this case insulating bolts 6a are replaced by

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electrically conducting bolts 9 which are held rigidly to insulating cups 11
by means of the attachment nuts 10 for the electrical cables. Under heads
9a, bolts 9 have a square part 9c which holds the bolt securely against
rotation in the square recess in insulating cup 11. Square part 9c is
followed by threaded bolt nect 9b on which, as already stated, attachment
nut 10 is screwed.
Connecting bolts 9 are made of a material having a lower value of
electrical resistance-than resistance strip 2 in order to avoid any over-
heating of the cables and consequent damage to the insulation thereof. Since
a direct welded connection between a predominently copper-containing connect-
ing bolt and a resistance strip free of copper can lead to :intercrystalline
corrosion, a bracket 8 made of a material different from that of connecting
bolts 9 and resistance strip 2 is welded to each deflection location ~
requir~ng a connection, transverse portion 8a of each bracket being welded
to bolt head 9a. Bracket 8 contains less copper than the connecting bolts,
thus ensuring a satisfactory and lasting joint between the material of the
resistance strip and the connecting bolts, the specific resistance of
connecting bolt 9 being the lowest, and that of the bracket being lower than
that of the resistance strip. For example, the latter may be made of a ~
Ni-Cr alloy, the bracket may be made of a ~0% Cu alloy, and the connecting
bolt may be made of a 70% Cu alloy. Connecting locations 7' at the
beginning and end of the strip have only half brackets 8' of the type
mentioned.
Where use is made of one-piece resistance strips2, only specific
resistance stages are possible with meanders of given geometrical dimensions.
The use of brackets 8 makes it possible to use strip material of different
resistance value between individual connection locations 7,7', i.e.
between the connecting bolts thereof. For example, sections 2a and 2b may
be made of the same strip material but of different cross section, so that

~fD47~!L37
although the meanders are of the same length and the connection locations
are fixed, any desired resistance steps are available at the said connection
locations, as required for the driving and braking resistances of electrical-
ly-driven vehicles. Since the heads of the bolts are flat and are narrower
than the internal dimensions of the relevant deflection locations in the
meanders and brackets, they do not materially impede the flow of cooling airO
In order to provide easy installation and removal of the resistance
units, the frame and resistance-strip design described above constitute an
assembly unit which is held in, and insulated from, a structure common to all
assembly units. Depending upon the side from which the connection locations
are to be accessible, the spring-loaded resilient deflection locations may
also be arranged at the bottom instead of at the top as shown, in which case
all connection locations will be accessible from the top instead of from the
bottom.