Assembly formed by an electromagnetic retarder and its electric supply means

An assembly is provided formed by an electromagnetic vehicle retarder and its electric supply means, where the retarder has a rotor (2) mounted on the output shaft of the gearbox of the vehicle and a stator (13) cantilevered on the casing of this gearbox. The armature (5) of the retarder forms part of the stator and is cooled by water and its inductor (4), which forms part of the rotor, is fed electrically by an alternator whose rotor (13) and stator (14) are secured respectively to the rotor (2) and the stator (3) of the retarder.

The invention relates to assemblies formed by an electromagnetic retarder, 
intended to brake a vehicle transmission shaft, and its electric supply 
means, which assemblies comprise a stator through which the shaft passes, 
which is centred in this stator by appropriate guide means and a rotor 
fastenable with the shaft so as to present an external cylindrical face in 
the vicinity of an internal cylindrical face of the stator with 
interpositioning of an airgap of small thickness, the rotor comprising an 
inductor, with electric wire coils, capable of generating, when 
electrically energized, a magnetic field with alternate distribution in an 
annular ferromagnetic part of the stator forming the armature and 
associated with a liquid cooling circuit, the electric supply for the 
coils being provided by means of a multiphase alternator, particularly 
three phase, whose armature forms part of the above rotor and is connected 
to said coils by means of a rectifier also forming part of said rotor. 
Such an assembly has been described in the French patent 1 467 310. In this 
assembly, the retarder is mounted on a section, of the vehicle 
transmission shaft concerned, relatively distant from the engine; this 
section is itself mounted between two ball bearings carried by two 
transverse flanges defining the axial ends of the stator, then in the form 
of a cylindrical box, and is connected to the rest of the shaft by two 
homocinetic joints. 
The rotor of the apparatus is then in the form of a solid core fixed to 
said central shaft portion and extended radially outwardly by the inductor 
coils, small in number (typically six). 
Such a construction does not lend itself to direct cantilever mounting on 
the output of the gearbox of the vehicle, wherein the stator is 
cantilevered on the casing of the gearbox and the rotor is cantilevered on 
a stub shaft extending from said gearbox, this rotor being further fast 
with a cardan coupling element for connecting it to the rest of the 
transmission shaft. 
Now, such cantilevered mounting, which has been described in the U.S. Pat. 
No. 3,496,396, is particularly precious since it makes possible the use of 
an electromagnetic retarder on a very short transmission such as those 
equipping semi-trailer tractors or coaches with advanced cabin. 
The purpose of the present invention is especially to make retarders of the 
above kind such that they lend themselves to such cantilevered mounting. 
For this, in accordance with the invention, the number of inductor coils of 
the retarder and that of the inductor poles of the alternator are both 
greater than or equal to twelve, the stator ring formed by the inductor 
poles of the alternator surrounds the rotor armature of this alternator 
with a small clearance and the two rotor rings formed respectively by the 
inductor coils of the retarder and by the armature of the alternator are 
juxtaposed axially on the external face of a same inner sleeve of 
relatively large inner diameter extended on the inside by a transverse 
connection flange. 
This flange lends itself to direct connection to a plate or similar fast 
both with the output shaft of the gearbox of the vehicle and with a cardan 
coupling element, which may itself be housed at least partially in the 
large space inside the sleeve. 
As for the stator assembly, it is relatively light since it no longer 
comprises relatively bulky and long retarder inductor coils: it lends 
itself then quite well to cantilever fitting on the casing of the gearbox. 
It may be further observed that the above mounting makes it possible to 
place the stator armature of the retarder, to be cooled by liquid, very 
close to the engine of the vehicle and in particular to the normal water 
cooling circuit thereof. 
In preferred embodiments, recourse is further had to one and/or other of 
the following arrangements: 
the axial end of the rotor of the retarder, the furthest from the rotor of 
the alternator, is extended axially by a finned structure for ventilation 
of the retarder stator, 
the two stator rings formed respectively by the liquid cooled retarder 
armature and by the inductor poles of the alternator are juxtaposed 
axially on the internal cylindrical face of the same cylindrical casing 
coaxial with the internal sleeve, 
the number of inductor coils of the retarder is equal to 18 and the number 
of inductor poles of the alternator is equal to 24. 
The invention comprises, apart from these main arrangements, certain other 
arrangements which are preferably used at the same time and which will be 
more explicitly discussed hereafter.

In what follows, one embodiment of the invention will be described with 
reference to the accompanying drawings in a way which is of course in no 
wise limitative. 
FIG. 1 of these drawings shows schematically the assembly, constructed in 
accordance with the invention, of an electromagnetic vehicle retarder and 
its electric energization means. 
FIG. 2 shows the same assembly in a perspective view, with parts cut away. 
FIG. 3 shows schematically the fitting of such a retarder to the gearbox of 
the vehicle. 
The electromagnetic retarder considered is intended to slow down the 
rotating shaft of a vehicle, preferably of the "heavy vehicle" type. 
In a way known per se, this retarder comprises a rotor 2 fast for rotation 
with the output shaft 1 of the gearbox 30 of the vehicle and a stator 3 
cantilevered on the casing 31 of this gearbox. 
But contrary to what is usually contemplated, it is here the inductor which 
is mounted for rotation, the armature being fixed. 
In other words: 
the electric wire windings or coils 4 which conduct the electric current 
for energization of the retarder and which, with radial cores 4' which 
they surround, define a ring of inductor poles with alternating polarities 
step by step, form part of rotor 2, 
and the ferromagnetic material annular piece 5 which forms the armature and 
in which the eddy currents are generated which cause braking and heating 
form part of stator 3. 
This annular piece 5 is formed by a cylindrical drum surrounding the 
inductor with interpositioning of a cylindrical air-gap E. 
Since this piece 5 is here fixed, it may be readily cooled by a liquid 
stream since it is not necessary to use special joints for sealing at the 
level of connections between two parts in relative movement. 
For this, a liquid circuit 6 is provided comprising a section 7 which 
extends directly along the face, of the induced piece 5, opposite the 
air-gap E. 
More precisely, said section 7 is here formed by a duct extending helically 
about the drum 5, which duct is ended at its ends by two inlet 8 and 
outlet 9 connections. 
To improve the heat exchange between drum 5 and the liquid flowing in duct 
7, hollows or reliefs such as annular or helical ridges 10 may be provided 
on the face of the drum defining a wall of said section. 
Such hollows or reliefs may also be provided on the other walls of said 
section. 
In a variant, the circuit section 7 is formed by a simple annular water 
jacket defined by two coaxial cylindrical walls joined together at their 
ends by two transverse washers and by a radial longitudinal dividing wall 
separating the inlet from the outlet. 
Cooling circuit 6 comprises, in addition to section 7, a drive pump 11 and 
an external heat exchanger 12, such as a finned radiator, for dissipating 
to the outside the heat carried by the flowing liquid. 
This liquid is advantageously formed by water to which an anti-freeze is 
added. 
Pump 11 and exchanger 12 are advantageously the water pump and the radiator 
which form part of the normal cooling circuit of the engine of the 
vehicle: it should in fact be noted that, during operation of the 
retarder, the engine releases little heat so that its cooling needs are 
then reduced; in addition, because the retarder is mounted on the gearbox 
of the vehicle, it is very close to said normal cooling circuit. 
The axes of coils 4 which define the inductor poles here extend radially 
about the axis of the apparatus. 
Since this inductor is rotary, it is advisable to provide special means for 
supplying its coils 4 with electric current. 
For this, a rotary electricity generating machine is used whose rotor is 
fast with that 2 of the retarder. 
As a matter of fact, when a need exists for slowing down shaft 1, the 
latter is rotating: unused energy corresponds to such rotation of shaft 1 
and a portion of this energy is here transformed into the electric current 
required for feeding the inductor of the retarder. 
The two following advantages are thus obtained at one and the same time: 
the inductor of the retarder is supplied with power with a very small 
supply of external electric energy, this energy being limited to that 
required for supplying the energizer of the generator with power: in the 
present case of a vehicle retarder, the energization energy taken from the 
battery of the vehicle is of the order of 30% only of that required for 
supplying the retarder in the usual constructions and may even be 
appreciably lower, 
the generation of the electric current for feeding the inductor of the 
retarder itself consumes a certain mechanical energy which is taken from 
the shaft to be slowed down: such consumption therefore itself contributes 
to braking said shaft. 
In the preferred embodiment illustrated, the generator is an alternator 
comprising: 
a three phase rotor 13 forming the armature of this alternator, 
and an inductor stator 14 with multiple poles surrounding the rotor 13 with 
a small clearance forming an air-gap e. 
The electromagnetic connection between this rotor 13 and stator 14 is 
provided exclusively through this air-gap e, without any mechanical 
contact of the ring and brush type. 
The multiple poles of the stator are created by a ring of small 
electromagnets of alternating polarities connected to a DC source 15 such 
as the battery of the vehicle. 
This connection is provided through a regulation circuit 16 for adjusting 
at will the intensity of the energization current of inductor 14 and 
consequently the intensity of the electric current generated by the 
alternator, and finally the braking torque applied to the rotor of the 
retarder and so to shaft 1. 
This circuit 16 advantageously comprises a manual control member 17. 
The alternating current collected at the terminals of rotor 13 is rectified 
by an appropriate bridge 18 before being applied to the coils 4 of the 
retarder. 
Of course, the assembly of components 18 forms part of the rotor 2 just as 
coils 4 and armature 13. 
As can be seen in FIG. 2, this armature 13 is secured to the coils 4 of the 
retarder, the assembly of these elements being mounted on a same sleeve 18 
extended inwardly by a transverse flange 20 itself formed with fixing 
holes 21 and forming a flange for connection to a plate 32 fast with shaft 
1. This sleeve 19 may form a single piece with the cores 4' and with 
flange 20. 
Plate 32 is in its turn secured to one of the two jaws 33 of a cardan 
coupling whose other jaw 34 is fast with the main section 1' of the 
transmission shaft: as can be seen in FIG. 3, these two jaws 33 and 34 are 
freely housed inside the tube formed by sleeve 19. 
The stator 14 is mounted inside a fixed sleeve 22 defining the outside of 
the above duct section 7: it is this sleeve 22 which is cantilevered to 
casing 31 of gearbox 30 by means of an apertured frame in the form of a 
bell 35 such as a ring of arms. 
Of course, the output shaft 1 of the gearbox is strictly centred therein, 
more particularly by means of bearings 36, 37, so that the rotor 2 and 
stator 3 are centered with respect to each other and so that the above 
annular air-gaps E and e are formed therebetween. 
In FIGS. 2 and 3, a finned structure 23 can be seen forming a ventilator 
and fixed to the axial end, of rotor 2, the furthest away from armature 13 
: this structure makes it possible to feed a stream of cooling air between 
the coils 4 of the retarder, which contributes to the removal of the heat 
generated by drum 5. 
The number of inductor coils 4 and that of poles 14 of the generator is 
relatively high, namely at least 12, so as to free inside the machine a 
large diameter space for the passage of the shaft 1 to be slowed down : in 
fact, the higher these numbers, the easier it is to give small radial 
lengths to the corresponding coils and poles ; these two numbers are for 
example here respectively 18 and 24. 
Following which, and whatever the embodiment adopted, an electromagnetic 
retarder is finally obtained whose construction follows sufficiently from 
the foregoing. 
The operation of this retarder is very readily controlled by simple 
energization of the fixed inductor 14 of the generator, which energization 
is preferably controlled by means of member 17. 
Said retarder has numerous advantages with respect to those known 
heretofore and in particular the following : 
its cantilevered mounting on gearbox 30 makes it possible to use it even 
for very short transmissions, 
cooling of the fixed armature 5 of the retarder, by a liquid stream, is 
easy because of its proximity to the normal water circuit of the vehicle 
and it is extremely efficient, which makes it possible to obtain an 
excellent retarding torque at cruising speed since this torque is all the 
higher the lower the temperature of the armature, 
the energy taken from battery 15 or another DC source is relatively low 
since this energy is limited to that required for feeding the inductor 14 
of the generator, the power supply for the inductor coils 4 of the 
retarder being integrally generated from rotationn of shaft 2; in 
practice, this energy taken from the battery is generally less than a 
third of that required for constructions with rotating armature, 
energization of the retarder is progressive and continuous, which results 
in a similar variation of the braking torque exerted by said retarder on 
the shaft to be braked. 
As is evident, and as it follows moreover already from what has gone 
before, the invention is in no wise limited to those of its modes of 
application and embodiments which have been more especially considered ; 
it embraces, on the contrary, all variants thereof, particularly : 
those where the alternator (13, 14) is a multi-phase type other than three 
phase, particularly of the two phase or six phase type, 
those in which the inner face of the inner sleeve (19) is not cylindrical, 
being for example bell mouthed towards its end opposite the gearbox (30), 
those where the external face of the external sleeve (22) is not 
cylindrical, being for example convergent or divergent towards its end 
opposite the gearbox (30), 
those where one and/or other of the two sleeves (19, 20) is formed of 
several elements fixed axially one on the other, e.g. by mutual fitting 
together as shown in figure 3.