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1. GB103959 - Improvements in and relating to Regenerative Braking Systems for Electrically Driven Vehicles.

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[ EN ]
COMPLETE SPECIFICATION.
Improvements in and relating to Regenerative Braking
Systems for Electrically Driven Vehicles.
We, WALTER VICTOR TURNER, of 117, Biddle Avenue, Wilkinsburg, Allegheny County, Pennsylvania, United States of America, Engineer, and THOMAS HAROLD THOMAS, of Edgewood, Swissvale Station, Pittsburg, Allegheny County, Pennsylvania, United states of America, Engineer, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:-
In electric traction systems where direct current is employed for propelling the vehicles, it is well known that the motel's may serve as generators when driven by the momentum of the vehicle, and that such generated current, or a portion of it, may be returned to line conductor or source of supply if the current generated is at a voltage sufficiently greater than the line voltage, and that when operating in this manner, the generator also serves as a braking element for retarding the vehicle when descending grades or for deceleration when running on a level track. Such regenerative braking systems have not, however, heretofore proved to be very efficient either in braking or in the amount of current restored, on account of the comparatively limited time at which the vehicle is being driven by its momentum at a sufficiently high rate of speed to overcome the voltage of the line.
If a direct current motor when being driven by the momentum of the vehicle at a given speed is restoring a certain amount of energy to the line and thus acting as a braking generator to retard the vehicle, it is apparent that, as the speed decreases, the induced voltageof the motor also diminishes, and consequently less and less current is returned to the line until the induced voltage falls to that of the line when further regeneration is impossible, and the braking effect ceases. If, notwithstanding the diminishing speed of the vehicle, the regenerated voltagecould bemaintained above the line voltage, some current could be restored to the line, or distributing system, throughout a much longer period of time, and the braking effect could be utilised until the vehicle is brought nearly to a -complete standstill.
The object of this invention, therefore, is to provide means whereby the voltage generated by the motors acting as braking generators, and impressed on the distributing system, may be maintained within predetermined limits until a certain mimimum speed has been reached, at which time the air brakes may be employed to complete the stop.
Where a plurality of motors are employed, such as a four motor equipment.
for propelling the vehicle, and the motors are acting as generators driven by the momentum of the vehicle, the maximum) voltage for a given speed will be developed- when the machines are connected-in series, while only half this voltage will be developed at the same speed when they are connected in senes parallel and still less voltage when theytare. connected in full parallel. In order to compensate for the reduction in speed and maintain the higher voltage output from the machines, this invention contemplates the automatic changing of the motor connections from parallel at high speed to series-parallel instead of as has hitherto been proposed manually ejecting this operation,' and then to full series as the speed diminishes, whereby the high voltage may be kept up during the major portion of the stopping period.
The invention also comprises the use of a booster, in series with the generator circuit for raising the voltage therein to compensate for the diminishing speed of the generators during the respective periods that the same are connected either in parallel or in series-parallel, or in series, the booster being driven by any suitable means, and operating to automatically maintain the voltage either by varying the strength 'of its field, or by* varying the speed of the driving motor.
The air brake system is combined with the regenerative system to' produce certain results,, since it will be evident that when operating at slow speeds and when the regenerated current falls below a predetermined amount, as when completing a stop, it is desirable that the air brake be used, and the invention therefore also contemplates means for automatically : applying the air brake when the regenerated current falls to a certain minimum'.
As a feature of safety, it is desirable that'at the time of regeneration, there should be a limit to the maximum speed permissible upon certain grades; and at various points along the road, so that the maximum speed allowed at such points will be such that the air brakes alone could properly control "the train, if, for any reason, the regenerative system should fail..With this in view, this invention further contemplates a provision for automatically applying the air brakes in case the speed of the vehicle exceeds the desired maximum, 'at the time that the regenerative system is in operation,, and also means for manu- . ally adjusting this maximum 'allowable. speed according. to. the grade or other conditions of the track..,
The features of this invention are adapted to be carried'out in a variety of different forms, and it is therefore not limited to any specific arrangement or particular construction of the parts... ' . In the accompanying drawing the figure illustrates in diagram, one ,form of regenerative braking system embodying this invention and applied to a vehicle with a four motor equipment.
The electric connections, including the circuits, controllers, switches, etc. for controlling the motors in propelling the vehicle, are not shown in the draw- ing, and only a sufficient number of contacts representing a brake switch or controller 1 are shown connected to the local or regenerative circuits of the machines, as are necessary to illustrate the operations during the regenerative braking periods. The contacts of the brake switch 1 are indicated in the closed position, that is, the position to which this switch is moved to open the' pro- pelling circuits and connect up the motors to act as generators in the regenera- tive circuit for braking purposes and for restoring energy to the line.
It will be understood that the contacts for the brake switch .1 may be mounted upon or operated by the running controller, qr master controller when, turned to a certain braking.position, or may be.operated by a Separate switch'.handle, or be connected up to the propelling', system in any suitable or preferred manner, and it is not deemed necessary to further illustrate, the circuits; and control of said propelling system, since it is well understood by those familiar with the art as 'to how the regenerative system, as .heroin illustrated may be properly connected into the ptopolling system of the motors.
In the drawing, a four motor equipment is illustrated diagrammatically comprising 'armatures 2, 3, 4,5, connected by suitable leads 6, 7, 8, 9, 10, 11, 12 and 13 through contact bars on switch 1, with corresponding conduct fingers of a series-parallel regulating or change over switch' 14 and motor fields 15, 16, 17, 18 having leads 19, 20, 21, 22, 23, 24,25, 26.suitably connected through corresponding contact bars on switch 1 when in bracing position. The change over switch 14 may be operated by various forms of speed con trolled means which serve to shift the relation ot the generators according to certain variations in the speed of the vehicle, the means, as shown, comprising a centri-

fugal' governor 27, the shaft of wh'...ch may be driven from an axle of the vehicle and operate through lever 28 to open and close the valves, 29 and 30 for controlling the supply of fluid to and exhaust from the pistons 31 and 32 of cylinder 33. A partition 34 divides the cylinder into separate chambers for the respective pistons, the piston 31 being connected to actuate the switch, and having a spring 35 opposing the action of the flnid pressure.
When the vehicle is travelling at or above a certain speed, at which the governor raises the lever 28 to close the exhaust and open both valves 29 and 30,. to admit fluid to both pistons 31 and 32, the switch 14 is held in full parallel position as shown in tlie drawing. When the speed diminishes sufficiently to close one valve 29 and open the exhaust from piston 31, the spring 35 shifts the switch 14' to the series-parallel position, at which point the piston 31 engages piston 32 and is held until the speed is further reduced sufficiently for the governor to close valve 30 aud open the exhaust from piston 32, whereupon the spring moves both pistons and the switch to the series position'.
A booster 36 is employed for raising the voltage of the regenerated current, from the machines sufficiently above the line voltage to return current to the line, ancl'to maintain the regenerated voltage as the speed diminishes, the booster being driven by a motor 37 with current from the line through the wire 38 leading from the regenerative braking switch 1. One of the armature terminals of the booster is connected to the retuin lead 13 from the machines, 'the other armature terminal 'being connected by wire 39 with the line 40 through a contact bar on the regenerative switch 1. The field of the booster is :energised by current from the line through wire 38 and may be controlled by a rheostat 41 governed by the solenoid or magnet 42 inserted in the regenerative circuit wire 39, whereby the strength of the booster field may be auto- inatically adjusted by said regenerated current to maintain a substantially coil- stantcurrent regardless of fluctuations in line voltage or other conditions which might vary the output of the generators. The booster is also governed by the speed of the vehicle in order to compensate for the reduction in speed during the respective periods that the motors are connected up in their different relations by the change over switch 14. This may be conveniently done by inserting a rheostat' 43 in the field circuit of the motor 37, the rheostat being controlled by the speed governor 27. 'As shown in the drawing, a carbon rheostat is employed having a lever 44 for exerting a varying pressure on the carbon discs to vary the resistance in the'fields of the motor 37.' A spring 45 acts upon: lever 44, tending to diminish the pressure upon the carbon rheostat, and thereby increase the resistance, the force of the spring 45 being regulated by the movement of the weights of the governor 27. Another spring 4G acts on the lever 44; in the opposite direction and tends to increase the pressure on

the carbon rheostat. The enective pressure acting on the rheostat is, therefore, the difference between the force of the springs 45 and 46, and as the shifting of the governor weights, due to variation in speed, also varies the force of the spring 45. the resistance of the rheostat, and consequently the speed of the motor 37 is accordingly regulated to compensate for the diminishing speed of the machines. In order to continue this regulation through each period of regeneration for the different positions of the change over switch 14, other springs 47 and 48 are mounted to act on the lever 44, but are held out of operation 'by means of the pistons 49 and 50 when the change over switch is in full
parallel position, the valves 29 and 30 also controlling the supply of fluid to these pistons. When these valves are operated by the governor, to release fluid from the pistons 81 and 32, fluid is also released from pistons 49 and 50 thus throwing the force of the springs 47 and 48 onto the lever 44.
The coil of the magnet' valve 51 is inserted in the return wire 39, so that when the speed of the vehicle and the corresponding regenerated current has diminished to a predetermined low amount, this valve is automatically opened to vent air from a pipe of the air brake system, and cause an application of the air brakes to. complete the stop. Another vent valve 52 is arranged to be operated to likewise vent air from the pipe of the air brake system when the speed of the vehicle exceeds a predetermined maximum degree, such vent valve being conveniently actuated by the governor through a lever 53 and a rod 54 connecting the same with the lever 28. This maximum speed may be adjusted to auy point desired by means of the hand lever device 55 connected to shift the fulcrum of lever 53. It is preferred that this device be so adjusted as to cause an automatic applicatiou of the air brakes whenever the speed of the vehicle exceeds what may be safely controlled by means of the air brakes without the assistance of the regenerative braking system.
Communication from the pipe 56 of the air brake system to the vent valves 51 and 52 is preferably controlled by a valve 57 operated manually at the same time ,that the regenerative braking switch 1 is thrown, , and preferably attached thereto, whereby said communication is cut off when the brake switch is turned to the running position; and opened when the brake switch is thrown. to the position shown in the drawing for establishing the regenerative circuits.
For the purpose of cutting of! the regenerative circuits when the speed of the vehicle has reduced to the minimum at which the vent valve 51 is opened,a switch 58 is inserted in the return wire 13 from the generators, the switch being held closed by piston 59 and air admitted through valve 57 from the pipe. 56 of the air brake system when the brake switch 1 and valve 57 are turned to the position shown. When the vent valve 51 is opened, it also releases the air pressure from piston 59, and the spring 60 then automatically opens the circuit 13. The maximum speed vent valve 52 is, however, prefer- ably so connected as to reduce the air pressure for causing an application of the air brakes, but not to release the pressure from piston 59. The switch 58 thus remains closed at that time so that the combined braking effect from the regenerative system and the air brake system is produced. As soon as the speed is reduced to the predetermined safe amount for which the apparatus is adjusted,the vent valve 52 closes, and the air brakes are automatically released, thus limiting the speed of the vehicle during the regenerative period.
When the brako switch is in running -position, the vent valves 51 and 52 are cut off from the pipe of the air brake system by means of the valve 57, which turns with the brake switch, but in braking position, as shown, com- munication is established from the pipe 56 of the air brake system to both valves 51 and 52, and also from the fluid pressure piston 59 to the vent valve 51.
The regenerative circuit switch 58 is therefore normally held closed by the air pressure acting on piston 59.
When the vehicle is running, and it is desired to make a brake application, the brake switch 1 is thrown to braking position, thereby connecting up the motors to act as generators in the regenerative circuit, to restore current to the line 40. The change over switch 14 then occupies one of its positions depend- ing upon the speed of the vehicle and of the governor 27. The armature of the booster 36 is connected in series with the regenerative circuit through leads 13 and 39, while current from the line flows to the fields of the booster and to the armature and fields of the motor 37 through the wire 38. Dot us suppose tha,t the speed of the vehicle and governor 27 at this time is sufficiently great to hold the change over switch 14 in its full parallel position, as indicated, - the course of the regenerated current is then from one terminal of the arma-
tures 2,3, 4,5 of the generators in parallel to the return wire 13, switch 58, through the armature of the booster 36, wire 39, including the coils of the electro magnets, 42 and 51, to contact bar on brake switch 1 to line 40, and return by ground connection to the negative terminals of the armatures of the generators. As shown in the drawings, the fields 15, 16, 17 and 18 of the generators are at this time connected' in series between the line and the ground by the leads 19,20, 21, 22,23, 24,25, 26, and the contact bars on the brake switch, although the circuits may be connected in other ways, if preferred.
If the regenerated current rises higher than a certain amount the force of the magnetic pull of the core of the magnet 42 acting on the lever. 61 will be increased and the pressure of spring 62 on the carbon rheostat diminished, so that less current from the line will flow through the rheostat and the fields of the booster 36 will be correspondingly weakened, thus regulating the booster to decrease the amount of current flowing back to the line. This feature serves to keep the current flow properly balanced at all times. With the speed at the rate as above indicated, the weights of the governor 27 move out radially to a position in which the lever 28 clears the valves 29 and 30 and a certain tension is exerted upon the spring 45 and transmitted to the lever 44 acting upon the carbon rheostat 43. With the valves 29 and 30 'in the positions shown, the exhausts are closed, and fluid pressure is admitted to all of the pistons 31, 32,49 and 50, thereby relieving the lever 44 from the force of the springs 47 and 48, so that the effective pressure acting on the carbon rheostat 43 will be that which is produced by springs 46 and 45.
As the speed of the vehicle begins to diminish, due to the retarding effect produced by the generators in regenerating current and restoring same to the line circuit, the governor weights move inward, and thereby tend to increase the pressure of the spring 45. This has the effect of varying the pressure of lever 44 upon the carbon rheostat 43, and thereby regulating the motor 37 driving the booster 36, so as to compensate for the diminishing speed of the vehicle and the generators, and maintain the voltage of the regenerated current above that of the line circuit. As the speed continues to diminish, the further inward movement of the governor weights serves to depress the .lever 28 suffi iently to operate the valve 29 to close its supply port and open its exhaust port, vhcreupon the fluid is released from pistons 31 and 49. The spring 35 then moves the piston 31 downward against the stem of piston 32 and throws the switch 14 to its series-parallel position, whereby the voltage generated will be increased, and thereby compensate for the diminished speed of the vehicle. In order to make a corresponding reduction in the speed of the booster to maintain the voltage of the regenerated current substantially constant, the spring 47 is released and exerts its pressure on lever 44 and rheostat 43. The field of the motor 37 is thereby strengthened and the speed of the booster reduced the desired amount. The current will then be restored to the line throughout another period of further reduction in the speed of the vehicle, during which period the regulation of the motor 37 of the booster, by means of rheostat 43, spring 45 and governor,.will be repeated as before described.
As the speed continues to decrease, the governor weights move further inward, and depress the lever 28 to operate the valve 30, thereby releasing fluid from pistons 32 and 50. The spring 35 then moves the piston farther downward, and throws the switch 14 to'the full series position, thus again raising the voltage of the regenerated current. The spring 48 is released by the exhaust of fluid from the piston 50, and adds its force to that of springs 46 and 47 acting on the lever 44, thus again adjusting the rheostat 43 to reduce the speed of the motor 37 and booster 36 to correspond with the changed relation of the generators.
The voltage of the regenerated current is thus maintained high enough to now to the line circuit throughout nearly the full stopping period, but when the speed is reduced to such 1 low rate that the current fails to hold the magnet
valve 51 closed, the valve opens to vent air from the pipe 56 and effect an application of the air brakes to complete the stop. The fluid will also be released from the piston 59, at the same time, and the spring 60 operates .the switch 58 to open the regenerative circuit to prevent back flow of current from the line.
If, at the time the brake switch is turned, to braking position, the speed of the vehicle is in excess of the desired maximum, as determined by the adjust,. ment of the device 55, the vent valve 52 will be immediately operated by the governor to discharge air from the air brako system and effect an application of' the air brakes. The regenerative braking effect will also be ob,tained, and the combined action of the two braking systems will soon reduce the spend .to a safe amount.