Electrical braking and energy storage for moving vehicles

A system for electrical braking and the storage for reuse of the braking energy is disclosed using alternating current (AC) rather than direct current (DC) generators coupled to the wheels of the vehicle to be braked. Upon braking, the AC generators feed the primary coil of a transformer whose secondary coil can be tapped at one of a number of different turns. Means are provided for changing the tap points so as to increase the number of turns in the secondary as the speed of the braked wheel declines. The output from the secondary is fed to a rectifier and thereafter the direct current is fed to a battery energy storage device. By increasing the turns of the secondary as the wheel speed drops, more energy can be fed and stored in the battery and the range of effective braking by the alternating current generator can be extended to lower speeds.

FIELD OF THE INVENTION 
The present invention relates to electrical braking and energy storage for 
wheeled vehicles. 
BACKGROUND OF THE INVENTION 
Conventional vehicles are stopped by means of conventional brakes such as 
disc brakes or drum brakes which are essentially two surfaces rubbing 
against each other. When stopping, the mechanical energy of the vehicle is 
completely converted to heat. Conventional automobiles, buses and trucks 
currently use such mechanical braking almost exclusively. 
Electrical braking has been proposed, (mainly for railroad engines) 
however, which uses a direct current (DC) generator to slow down and stop 
a vehicle. These systems often employ an electrical load, such as a 
resistor, to dissipate the electrical energy as heat, or a battery to 
store the electrical energy. The electrical load at the output of the DC 
generator is translated as a mechanical counter torque which is in 
opposition to the direction of shaft rotation. Electrical resistance is 
converted to mechanical resistance. 
The reverse is true for an electric motor. The greater the mechanical load 
placed on its rotating shaft (counter-torque), the greater the current 
that is drawn from the electric power supply. The law of conservation of 
energy must be obeyed, and there are slight losses as heat for both the 
generator and the motor. 
Examples of electrical braking and battery storage can be found in the 
following references: 
______________________________________ 
5,642,023 J. C. Journey June 24, 1997 
5,578,911 J. C. Carter, et al. 
November 26, 1996 
5,466,998 S. Kinoshita, et al. 
November 14, 1995 
5,350,985 H. Konrad, et al. 
September 27, 1994 
4,908,553 L. O. Hoppie, et al. 
March 13, 1990 
4,671,577 D. H. Woods 
June 9, 1987 
4,427,928 S. Kuriyama, et al. 
January 24, 1984 
4,330,742 E. Reimers 
May 18, 1982 
4,186,333 M. Kremer 
January 29, 1980 
______________________________________ 
Also of possible interest is U.S. Pat. No. 5,428,551 to J. T. Trainor, et 
al. (issued: Jun. 27, 1995). 
In such prior art electric braking DC electric energy often charges the 
battery. In such systems a problem exists in that when the brake switch is 
applied and the vehicle starts to slow down (because the battery is an 
electrical load) generator voltage decreases. When generator voltage drops 
down to battery voltage, the battery won't charge anymore. The energy 
capacity (voltage times current times time) is still present in the 
generator, but it cannot enter the battery, because battery charger 
voltage must be greater than battery voltage in order to charge it. 
The other alternative is to use a generator with a voltage rating much 
higher than battery rated voltage at the driving speed right before the 
brakes are applied. The reasoning is that when the vehicle has slowed down 
to almost a complete stop, generator voltage is still slightly higher than 
battery voltage, conserving all of the energy into the battery. 
Unfortunately, this method presents a real physical hazard: extremely high 
current forced into the battery can severely shorten the battery's life, 
or it can cause a physically dangerous situation such as a battery 
explosion. 
There is thus a need for a system that prevents the stopping of battery 
charging at a slow speed (wasting energy) or quickly overcharging the 
battery (physically dangerous). In other words, there is a need to keep 
generator voltage slightly higher than battery voltage throughout the 
braking process. 
SUMMARY OF THE INVENTION 
The invention, together with further advantages and features thereof, may 
best be understood by reference to the following description taken in 
connection with the accompanying drawings, in the several figures of 
which, like reference numerals identify like elements.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to the drawings and initially to FIG. 1, there is depicted a 
vehicle 10 having a front 12 and a rear 14. The vehicle 10 has a pair of 
front wheels 16 and 18 mechanically driven by a prime mover 20 which may 
be a conventional internal combustion engine or an electric motor. The 
front wheels 16 and 18 are driven by a conventional drive chain including 
drive axles indicated schematically by shafts 22 and 24. Conventionally, 
means for turning the front or steering wheels 16 and 18 are provided but 
not shown to simplify the depiction. The vehicle 10 also has a pair of 
rear wheels 30 and 32. The wheels 16, 18, 30, and 32 are provided with 
conventional (mechanical) braking means controlled by a brake pedal 34 
which means and e.g. conventional hydraulic lines are also not 
illustrated. These can be the same as employed in conventional passenger 
cars, but are designed to work in conjunction with an electric braking 
system of the present invention to provide back up and supplemental 
braking as the vehicle slows down and stops. 
In accordance with the present invention, each of the wheels 16, 18, 30 and 
32 are mechanically coupled to an alternating current (AC) generators 34, 
36, 38 and 40. The outputs of each of these AC generators is fed, 
respectively, as indicated by lines 42, 44, 46 and 48 to a variable 
transformer and rectifier unit 50. (Shown in detail in FIG. 2.) The output 
of this unit 50 is a direct current voltage which is fed as indicated by 
the line 52 to a battery 60 which may also serve as the source of stored 
electrical power for the prime mover 20 as indicated by the line 62 and to 
provide power to a control unit 70 as indicated by the line 64. A signal 
developed from the brake pedal 34 is also fed, via the line 66, to the 
control unit 70. 
In addition, the vehicle 10 includes a tachometer 80 coupled to the drive 
shaft 24. The tachometer 80 develops a signal proportional to the speed of 
the wheel 18 and feeds that signal as indicated by the line 68 to the 
control unit 70. Since all of the wheels of the vehicle are usually 
turning at the same approximate speed only one tachometer may be, for 
economy, engaged. However, if desired, separate tachometers may be 
provided at each wheel and separate controllers 70 provided for each 
wheel. And alternately, the AC frequency output of the AC generators could 
be used to devise the tachometer signal. The control unit 70 serves to 
control the unit 50 as best explained with reference to FIG. 2. 
In FIG. 2 only one wheel, the wheel 32 are one alternating current 
generators (the generator 36) are illustrated, it being understood that 
the arrangement for the other wheels and generators would be substantially 
the same. The output of the generator 36 is a sinusoidal wave produced 
between lines 44A and 44C. This AC power is fed by the lines 44A and 44C 
through a pair of relay switches 71A and 71C to an input coil 52 of a 
transformer 54 whose output coil 56 is tapped at one end by a line 58 and 
at a plurality of points along the output coil. These taps range from all 
of the turns of the coil at line 82 to about half of the turns at line 91 
with lines 82, 83, 84, 85, 86, 87, 88, 89 and 90 in between. Each of these 
lines are contacted to successive points 101, 102, 103, 104, 105, 106, 
107, 108, 109, 110 and 111 to tap changer 92 whose blade 115 is connected 
to a line 116. The relay switches 71A and 71C are normally open to 
deactivate the AC generator 36, but are closed upon braking by a braking 
signal provided by the controller 70 as indicated at 70A. This signal 
operates a relay coil 71R to closed switches 71A and 71C and couples the 
transformer 54 to the generator 36. 
During braking the AC output of the transformer is presented across lines 
58 and 116 and fed to a full wave rectifier 120 whose direct current 
output is fed between lines 52D and 52C to the battery 60. 
The blade 115 of the tap changer 92 is mechanically moved, as indicated by 
the dashed-line 72 by the controller 70. The controller 70 is basically a 
speedometer driven by the signal via lines 66 and 68 from the tachometer 
and brake in a manner so as to have the blade 115 tap point 111 at the 
start of the braking and to move the blade 115 sequentially through the 
points 111 to 101 as the speed of the wheel drops. 
On pressing the brake pedal, a back emf is presented to the AC generator 36 
and provides electrical braking. That is, the AC generator 36 takes energy 
from the wheel and converts it into alternating current electrical energy 
which is fed to the input coil 52 of the transformer 54. This energy is 
fed from the output coil 56 to the rectifier 120 to the battery 60 were it 
is stored. As the speed of the wheel 16 drops, the controller moves the 
blade 115 progressively along the points 111-101 and thus increases the 
effective number of turns for the output or secondary coil 56 of the 
transformer 54. This increases the voltage output of the transformer to 
continue to feed energy to the battery. That is, at a high speed the 
voltage output from point 111 would produce a voltage over that of the 
battery 60 and thus easily transfer power from the generator 36 to the 
battery 60. As the speed of the wheel drops the output of the generator 36 
would also fall and eventually reach a rectifier output that would no 
longer be able to overcome the battery 60 voltage brake level (e.g. 
12+v.). Before this occurs, the blade 115 would move clockwise to a higher 
turn point and as the speed of the wheel drops further moved still further 
clockwise by the controller so as to continue to provide electrical 
braking to the wheel 16 and to store more energy in the battery 60. 
Eventually as the speed of the wheel drops still further, conventional 
braking is provided to completely stop the vehicle 10. 
Although only one wheel and generator is shown in FIG. 2, a similar 
arrangement is provided for each wheel with each providing electrical 
output to either a separate primary coil for the transformer 54 (in which 
case it would have four primary coils like the coil 52 wound on the same 
core but only one secondary coil 56) or to a set of transformers like that 
transformer controlled in tandem by the controller 70. If preferred, as 
mentioned above, separate controller 70 and tachometers such as the 
tachometer 80 can be provided, one for each wheel. In any case, the AC 
generator provides power that is stored in the battery 60 and which can be 
used either directly by the prime power mover 20 (if it is an electric 
motor) or to operate other components of the vehicle 10. 
As the brakes are applied, the electronically controlled tap changer 
changes the transformer's primary-to-secondary turns ratio (which is the 
voltage ratio) so that the transformer's secondary voltage is fairly 
constant while the generator's voltage is dropping. The transformer's 
output should be constant until the vehicle is almost completely stopped 
and then it should suddenly drop to zero. 
Of course, this system should increase the efficiency (range-of-travel) for 
an electric automobile, especially in bumper-to-bumper traffic. The 
electric car's main battery pack can accept the braking energy directly, 
or the braking system can use a separate (smaller) battery, and the energy 
can be transferred from one battery to another by a switching mechanism. 
While one embodiment of the invention have been shown and described, it 
will be obvious to those in the art that changes and modifications may be 
made without departing from the invention and, therefore, the aim in the 
appended claims is to cover all such changes and modifications as fall 
within the true spirit and scope of the invention. 
For example, a resistive load can be employed either in leu of or in 
supplement to the rectifier and battery without departing from the spirit 
of the invention, at least in its broader aspects. And, although a switch 
blade and multi-contact mechanism is depicted for the tap changer, such 
may also be achieved using solid circuit switching.