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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric wheel-drive for motor
vehicles, especially for passenger cars with internal combusion engine,
with individual brushless polyphasic electric motors attached to the
wheels and electronically controlled in frequency.
2. Purpose of the Invention
Aim of the present invention is the simple, inexpensive and reliable,
nondestructive, mass-hybridization of motor vehicles with internal
combustion engine, in particular automobiles, through the additional
installation of 2 electric wheel-drives without modification of the
wheels, the axle, or of other parts of the car, the drives being energized
by a battery which is included for this purpose, resulting in two
independent propulsion systems.
3. Description of the Prior Art
In the Journal "Elektrotechnik und Maschinenbau" (Austria) No. 8 (August
1976) pp. 335-341 a special electric streetcar was disclosed with
large-diameter electric wheel-hub motors on two individual very large
wheels at the middle of the streetcar, one small support wheel in front,
and one in the back. The propulsion is exclusively electric, the motors
being fed by a generator driven in turn by an internal combustion engine,
with a battery also included. This system is not suitable for a
nondestructive mass-hybridization of conventional cars.
Through the British patent GB-PS1246354 a motor vehicle with wheels driven
in principle by electric motors was disclosed. The propulsion is
exclusively electric, and the electric motors are fed by a generator
driven by a gas turbine, or by a battery. This system also does not
provide any suggestions for a nondestructive mass-hybridization of
conventional cars in terms of two independent propulsion systems.
In the disclosure DE-OS 2802753 (F.R. Germany) a heteropolar synchronous
motor for vehicle propulsion was presented. Neither can a suggestion for
the problem of nondestructive mass-hybridization of motor vehicles with
internal combustion engine be found in DE-OS 2802753 nor can this be
accomplished with the synchronous motor described there.
Taking into account the considerable insecurity and fluctuation in the
gasoline supply, as well as polution control, energy conservation, and the
large waste of fuel on the daily short distance trips from home to work, a
reversible, non-destructive means of transforming the car into a
gasoline-electric (parallel-type) hybrid is definitely needed today, both
at the level of the car manufacturer and at the dealer shop ("while you
wait").
SUMMARY OF THE INVENTION
Accordingly, the task underlying the invention, and the object of the
invention, is to create a wheel-drive of the kind described in the
beginning, which is simple and robust in operation, easy and fast to
install, transferable among similar cars, and which reduces gasoline
consumption, even to zero for short-distance traffic corresponding to the
limitations in battery capacity.
This task is performed by the invention through homopolar multiple-airgap
axial field motors whose rotors replace the drum of the brake, or the
disks if disk brakes were present, and whose stator replaces the
brake-shoes and the splash plates of at least two wheels with the same
axle of a conventional car, and through the inclusion of an electronic
control system for the propulsion and braking operation modes of the
motors.
Such an axial-field motor is robust and can be installed very fast. The
axial-field motors replacing two of the brakes, and the control are put in
in very short time and connected with the battery. The transformation can
be reversed at any time. The car receives an independent second propulsion
system according to this invention. All-wheel traction, useful in snow
conditions, can be obtained by electrifying the non-motor wheels.
The rotor of the axial-field motor is appropriately composed of an axially
magnetized or nonmagnetic supporting tube located on bearings on the axle,
of a tubular permanent magnet of high-energy-density material with
essentially axial magnetization clad on it, of frontally adjoining forged
iron disks of which the one located at the external side of the wheel
carries the screws holding the wheel, and of pole-rings put on the
permanent magnet peripherically and comprising both stars of support arms
and axially-magnetized pole-pieces of high-energy-density material at the
free ends of the support arms. The tubular permanent magnet may be
composed of hollow-cylindrical sectors, and/or annular disks.
The stator of the axial-field motor is composed best of a pot-shaped casing
and of support-elements fixed inside, on the casing, and extending inward,
which carry flat ring-shaped coils located in the air-gaps between the
pole-pieces. This yields a particularly compact and stable body.
The permanent magnet and the pole pieces are suitably consisting of a
samarium-cobalt alloy.
The ring-shaped coils are profitably made of lamellar windings, or they are
bobbin-wound coils of ribbon conductor. In a particularly advantageous
embodiment the axial-field motor has five pole rings and six airgaps. The
number of pole rings (and airgaps) is determined for each vehicle by the
space available on the axle. The motor has preferably eight poles and a
tri-phase winding.
Hall-effect switches are suitably located in the motor for control. In the
case of an eight-pole axial-field motor with balanced three-phase winding,
the Hall-effect switches are mounted with an angle of 15.degree. between
them on the stator.
The electronic control system is profitably connected for the regulation of
the motor in three modes of operation: propulsion, regenerative braking,
and resistive braking.
Furthermore, the control preferably contains a programmable read only
memory (PROM) which receives various driving, state of the system, and
security signals and emits control signals.
In an advantageous embodiment the electronic control is constructed with
silicon controlled rectifiers (SCR).
The electronic control can be appropriately switched on with a 3 position
switch for forward operation, exclusively braking, and reverse operation
of the axial-field motors.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is further explained below in terms of examples of embodiment
with the help of drawings. In the drawings:
FIG. 1 is a schematic axial section view of an axial field motor according
to the invention;
FIG. 1A is a view in perspective of one illustrative motor vehicle in which
the motor of FIG. 1 finds application.
FIG. 2 is a frontal view of the rotor of the motor in FIG. 1 at a smaller
scale, with the Hall effect switches pointed out;
FIG. 3 is a schematic cross-section through a star of support arms with
pole-pieces of the motor in FIG. 1.
FIG. 4 is a lamellar (ribbon) winding of the ring-coils in FIG. 1;
FIG. 5 is a representation of the switching sequence and output signals of
the Hall switches in FIG. 2;
FIG. 6 is the scheme of a circuit with silicon controlled rectifiers (SCR)
the control of the axial-field motor in FIG. 1;
FIG. 7 is a schematic representation of the currents in the three phases of
the motor in FIG. 1;
FIG. 8 is a representation of the digital processor controlling the scheme
in FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The brushless homopolar axial-field motor represented in FIGS. 1 to 3 is
triphasic, has eight poles, and exhibits six about 8 mm wide airgaps. It
comprises a rotor 1 and a stator 2, the stator 2 being connected to a
source of electrical energy by suitable lead wires L, L', and L" as shown
in FIG. 1. The rotor 1 replaces the brake drum or brake disk, and the
stator 2 replaces the brake shoe assembly or brake pads together with the
brake back plate or brake splash shield, without changes in the wheel-axle
3.
The rotor 1 contains an axially magnetized, or non-magnetic, support tube
5. In the case of motor-driven wheels, the rotor 1 is solid with the
(rotating) axle of the wheel, and the bearings 4 are missing. A tubular
permanent magnet 6 of highest energy density and with predominantly axial
magnetization is set on the support tube 5. The permanent magnet 6 may be
composed of annular disks or annular sectors. It is suitably composed of a
samarium-cobalt (or similar) material with energy density of 2.10.sup.5
J/m.sup.3 or higher. Forged iron annular-stellar disks 7, for example, 1.9
cm thick, adjoin the permanent magnet 6 frontally. The forged iron disk
facing the external side of the wheel carries the screws 8 holding the
wheel, as indicated on FIGS. 1 and 2. The predominantly axially magnetized
permanent magnet 6 can exhibit, towards its ends adjoining the forged iron
disks, a gradually increased radial component of the magnetization,
pointing outward.
Five pole rings 9 shaped in the form of stars of support arms with axially
magnetized pole-pieces 11 of high energy density attached to the free ends
of the support arms 10, are set on the permanent magnet 6. The pole pieces
11 can also be made of samarium-cobalt material, or, e.g., of an
iron-aluminum-nickel-cobalt alloy (5.10.sup.4 J/m.sup.3). Between the
pole-rings 9, light metal plastic or poured resin rings can be applied as
additional fasteners. The support arms 10 themselves are made of
non-magnetic material and are slightly slanted to provide ventilation.
The stator 2 of the axial-field motor is composed of a pot-shaped casing 13
fastened on the wheel-axle and steering knuckle. Some openings are present
on the bottom of the pot-shaped casing for ventilation and cooling. In the
case of motor wheels the casing rests on the bearings which support the
(rotating) axle. Six ring-shaped support elements 14, each of them
carrying a flat ring-shaped coil 15 protruding into the airgap between the
pole-pieces 11, are fixed in the case, extending inwards. On the inner
side of the ring-shaped coils there are support rings 16. The support
elements 14 and the support rings 16 are fastened to the corresponding
flat ring-shaped coil 15 e.g., by pouring a hardening agent.
The ring-shaped bobbin-wound armature coil 15 can be made suitably of
lamellar windings 17 as shown in FIG. 4, with the use of ribbon conductor.
Each of the six ring-shaped coils 15 contains three phases spatially
displaced by 15.degree. from each other and connected for all six
ring-shaped coils in series such that only three power leads are leaving
the motor. The winding is connected preferably in star.
The axial-field motor is homopolar, since the lines of force are passing
through the pole-pieces 11 everywhere in the same direction. The magnetic
flux density in the airgap is about 0.8 Tests.
For a current of 250A the motor develops a torque of about 330 Nm. A power
of about 20 KW is thereby obtained at a frequency of 600 rotations/m which
corresponds to an applied voltage of 100 V. Usually there would be two
axial-field motors installed in any car at the otherwise not propelled
wheels, yielding 40 KW together. For a small car weighing 1000 Kg
(including the batteries), with a diameter of the wheels of 0.5 m the
speed developed is then about 100 km/h or 62.5 m.p.h. Due to the limited
available torque, the highest slope accessible to the car without use of
the internal combustion engine is about 15%. The acceleration time from
rest to 50 km/h (31 m.p.h.) is about 8 s.
A control system and a battery are needed for the operation of the
axial-field motor. The control system is constructed with solid-state
components and performs two main functions.
(a) Switching the current for the three phases in the right sequence, such
that all radially oriented conductors in the three-phase winding
contribute positively to the torque while they are in the airgap. This
switching process is triggered by three Hall-effect switches H1,H2,H3
(FIG. 2) placed on the stator 2 in spatial intervals of .alpha.=15.degree.
in order to sense the position of the rotor. The switching cycle of the
Hall switches is represented in FIG. 5.
(b) Control of the current absorbed by the motor and of the torque
generated in the motor. The torque is proportional to the current.
The battery contains, e.g., 18 lead or iron-nickel batteries of 6 V, or the
same number of 12 V-batteries, the first choice being particularly
favorable for the case of 120 V power outlets being used with a
transformerless charger for overnight recharging, or used without charger,
by simply switching from the motor M in FIG. 6 to the power outlet (not
shown). During driving or regenerative braking the batteries can be
switched automatically, depending on the frequency of the signals given by
the Hall switches H.sub.1 -H.sub.3 to the PROM, i.e., depending both on
motor speed and on whether the gas pedal or the brake pedal is depressed,
in six parallel groups of three batteries in series (18/36 V), in three
parallel groups of six batteries in series (36/72 V), in two parallel
groups of nine batteries in series, or all in series (108/215 V). The
batteries, located for instance in the trunk of the car, are weighing at
this time about 300 kg and provide the car with an action radius of about
80 km without the use of the internal combustion engine. The engine is to
be used for longer trips. With the battery taken out, only the resistive
braking mode of operation can be used. Removal of the battery is
recommended for extended, or trans-continental trips.
FIG. 6 shows a circuit in the power control, which allows for driving,
regenerative braking, and resistive braking operation of the axial-field
motor. The circuit is connected through an ammeter I and a main switch H
to the battery. The capacitor C is parallel to the entrance and reduces
the ripple. Then a second switch A follows. Parallel to the capacitor C is
the series connection of a transistor-diode chopper combination TM, DM, a
braking resistor and a transistor-diode chopper combination TB, DB. The
transistor-diode chopper combination TM, DM is for current limitation and
control in the driving mode, and the chopper TB,DB is for current
limitation and control in the resistive braking mode. Parallel to the
chopper TM,DM there is an inductor L and a safety-diode D which eliminates
possible high voltage transients.
After the circuit mentioned above, in FIG. 6 there follows a bridge of six
transistor-diode combinations T1D1,T2D2,T3D3,T4D4,T5D5 and T6D6 which are
connected with the motor M. These six transistor-diode combinations are
switched by the Hall-effect switches (through the PROM) and generate
triphasic current. During regenerative braking the six diodes D1, D2, D3,
D4, D5 and D6 work as a rectifier bridge and charge the battery B. The
transistors TM, TB, and T1-T6 are preferably silicon controlled rectifiers
(SCR). If n motors are present, this (bridge) part of the controller will
be duplicated n times in parallel.
A suitable choice of the currents J.sub.R J.sub.S and J.sub.T sent to the
motor in the three phases in FIG. 5 is shown in FIG. 7.
The steering of the control shown in FIG. 6 by the Hall switches H1, H2 and
H3, by the gas and brake pedals of the car, and by the respective level of
the motor current is performed advantageously through a PROM. The
connections of such a PROM are presented in FIG. 8. The PROM receives
signals from the Hall-switches H1, H2 and H3, a signal V/R corresponding
to the choice of forward or reverse driving, a signal AP/BP from a gas
pedal (accelerator) potentiometer or a brake pedal potentiometer, a signal
TJ indicating possible thermal overloads of the motor M and the transistor
TM, as well as a current level signal JV. From the output of the PROM
leave the control signals for the transistors T1 to T6. Two other signals
from the PROM control two oscillant circuits which determine the width and
frequency of the rectangular opening-pulses for the transistor-diode
chopper combinations TM and TB, respectively. In addition, the PROM emits
several battery-switching signals. Due to the most likely presence of two
motors (with independent phases) the upper part of the PROM in FIG. 8, and
the connections H1-H3, T1-T6, and TJ will be duplicated in practice. This
duplication is trivial and has been omitted in this text for the sake of
simplicity.
In the electric operation mode the driver controls the vehicle with the
help of the gas pedal, of the brake pedal, and of the three-position
switch for forward driving, exclusively (resistive, i.e., dynamical)
braking, and reverse driving. From the three-position switch the signal
V/R originates, depending on which position the switch is in. Braking is
possible in all three positions, resistive (i.e., dynamical) braking even
when the main switch H is open. The other parts of the control system are
set in operation by closing the main switch H. This is suitably done in
the "Garage" position of the ignition lock (which does not lock the
steering wheel, but has the ignition off).
In addition to their normal function, the gas and brake pedals are each
connected mechanically with a potentiometer which also has a contact at
the beginning of its way in the case of the gas pedal and a contact at the
middle of its way in the case of the brake pedal. With the main switch H
closed, if the gas pedal is depressed the switch A (FIG. 6) and the gas
pedal contact arm (which switches the AP/BP signal) will close themselves
after a short way of the pedal. In this position the gas potentiometer has
the largest value of its resistance, and consequently the PROM opens the
transistor TM only about 5% of the time (creep speed, to be adjusted at
the oscillant circuit next to the PROM). If the gas pedal is further
depressed, the width and repetition frequency of the rectangular
"on"-signals finally increase, e.g. up to 3.10.sup.-3 s and 300 Hz,
respectively and the transistor TM will be open for about 90% of the time.
At this point the transistor TM may be short-circuited by a direct switch
(not shown on FIG. 6). The control can also be performed by making the gas
potentiometer (or variable inductance), part of an oscillant circuit whose
frequency it determines, and which in turn determines the repetition
frequency and width of the "on"-signals for the transistor TM. The
"on"-signals are further limited in width and frequency by thermal
overload signals T1 which act on the oscillant circuit and are coming from
the stator-windings of the axial-field motors and from the support of the
transistor TM.
If the gas pedal is left free, the car moves freely by virtue of its
inertia. If the brake pedal is depressed, after a very short way a contact
is closed switching the battery (through the PROM) to the series-parallel
combination corresponding to the respective motor speed, similar to what
happens if the gas pedal is depressed, but with a slightly different
adjustment. Simultaneously, the switch A closes itself. Thereby the
battery will be charged through the six diodes D1 to D6 in regenerative
braking. At very low speeds, at which the battery can no longer be
switched down, the regenerative braking action vanishes gradually. If the
brake pedal is further depressed, both the hydraulic brakes (at the
non-electric wheels) and resistive (dynamical) braking are initiated
beyond a certain position S of the pedal. Resistive braking occurs,
similar to the electric action of the gas pedal, by the closing of the
brake potentiometer contact in the position S. At this initial position,
somewhat before the middle of the pedal way, the brake potentiometer (or
variable inductance) has its largest value, and therefore the PROM opens
the transistor TB only for about 5% of the time. Resistive braking occurs
with heat being generated mainly in the resistor R.sub.B, but also in the
motors M, the transistor TB and in the wiring in parallel, i.e.,
additionally to the hydraulic brakes. The energy appearing in the case of
stronger braking action is therefore distributed among battery, brake
pads, and the resistor R.sub.B connected in series with the chopper
combination TB, DB in FIG. 6.
The control of the resistive braking is again accomplished, e.g., by making
the brake potentiometer (or variable inductance) part of an oscillant
circuit connected to the PROM, thereby controlling the frequency of the
circuit, and indirectly the frequency and width of the "on" signals for
TB. However, these signals are not limited additionally by thermal
overload signals from the motors M and the support of the transistor TB,
but these thermal overload signals activate only a red brake overload
warning light in view of the driver on the dashboard. The ammeter I, with
red maximal current marks on both sides, indicates the battery discharge
current by deflection to the right and the charging current by deflection
to the left in regenerative braking.
The series-parallel battery-switching is controlled by the PROM both in
driving and regenerative braking on the basis of the motor speed
information derived from the Hall switches H1, H2 and H3, also taking into
account the signal AP/BP.
A different shaping of the axial-field motor, e.g. as disk motor, is
considered as a poorer execution of the invention. All other modifications
of mechanical or electrical nature within the framework of the claims are
included in the protected domain of the invention.
Obviously, numerous modifications and variations of the present invention
are possible in light of the above teachings. It is, therefore, to be
understood that within the scope of the appended claims, the invention may
be practiced otherwise than specifically described herein.
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