GB2463701A - Homing pantograph - Google Patents

Abstract

The pantograph has an electronic system to control its contact relative to its base. Three Hall Effect Sensors, L, C and R are fitted underneath the contact to measure the magnetic field from a live overhead wire. The voltages from the sensors are fed into three voltage comparators, LC, RC and LR. The outputs from the voltage comparators control relay switches in the circuit of a two-way electric motor, which moves the pantograph contact from side to side to align it centrally underneath the live wire.

Description

Homing Pantograph

Description

Intended benefit This invention is intended for use by vehicles such as trolleybuses, which require a fixed-track overhead wire but do not follow a fixed-track road. Such vehicles currently require clips to keep contact between their pantographs and the overhead wires; the Homing Pantograph invention allows them to use low-friction beam contacts as used by railway locomotives.

The use of beam contacts allows easy connection and disconnection from the overhead wires. The connection process is also eased by the system described here, because it can position the pantograph below the wires before connection.

This will help in the operation of dual-mode buses, which can alternate between internal and direct overhead power supplies. Sections of urban bus routes can be electrified where convenient, while the buses can revert to diesel power everywhere else. The Massachusetts Bay Transportation Authority currently uses dual-mode buses like this, but the electrified sections are in a tunnel where the buses have to follow a narrow, straight track to ensure that contact with the overhead wires is maintained. This invention allows the use of electrified sections in open city streets, where the buses can take a variety of different lines and still stay connected to the overhead wires.

Other benefits This system will allow one trolleybus to overtake another with neither required to stop and disconnect its pantograph. The pantograph can connect and disconnect in motion, with only the flick of a switch required by the driver to activate or deactivate the system.

Problems such as junctions and low bridges will be easily tackled by removing the wires at those points: dual-mode buses can lower their pantographs approaching the junction, cross it using battery or diesel power, then reconnect afterwards without stopping.

This will also allow cities to use trolleybuses without expending vast sums of money on city-wide electrification schemes: only a small section needs to be electrified to run battery-powered buses, achieving a large drop in urban pollution at a low cost.

Electronic circuit Figure 1 describes the electronic circuit from the magnetic field around the wire at the top to the motor (M) at the bottom.

The sensors are linear Hall Effect sensors, supplied with a 4.5V DC voltage. Output will vary continuously with the strength of the magnetic field. The sensors L, C and R are positioned underneath respectively the left, centre and right parts of the beam contact, facing forward.

There are various examples of voltage comparators that would do the job required for this circuit; I have attached the design of a suitable one, US patent 4,446,385, for reference.

This produces a binary output signal, which is used to control a relay switch.

The three voltage comparators in figure 1 each have input pins 0 and 1, and the relay switches below them have output pins 0 and 1; a larger input voltage on pin 0 will set the corresponding switch to position 0, and a larger input voltage on pin 1 will set the switch to position 1.

The two outputs where Vc is the greater voltage are not used, because the motor is not required to turn in this case. The other four outputs are directed to bipolar junction transistors forming two AND gates that check the required conditions for the motor to turn. LAnd requires VL> V from sensor LC and VL> VR from sensor LR; RAnd requires VR> Vc from sensor RC and VR> VL from sensor LR.

The AND gates supply voltages to two relay switches, ML and MR, that control the motor circuit. These switches are both normally set to the negative terminal, so the motor does not turn unless a signal comes from one of the AND gates. The switches revert to negative when the signal ceases. Mechanical relay switches are used here because a substantially higher voltage will be used to turn the motor than anything used in the signal circuit.

LAnd triggers the switch ML, putting a positive current on the left-hand side of the motor in figure 1. RAnd triggers the switch MR, putting the positive current on the right-hand side.

The motor is connected such that it will move the pantograph towards the positive current in figure 1. Thus a change in the location of the live wire will very quickly trigger the appropriate movement of the pantograph contact.

Physical layout The three sensors are located in a straight horizontal line. They therefore measure the relative position of the overhead wire in that dimension only. This will allow the motor to position the pantograph contact directly under the live wire, regardless of vertical distance: so the system can work when the pantograph is raised, or when it is lowered and "homing" in on the wire.

The line of sensors is located directly under the contact beam for best accuracy.

Sensors L and R should be placed at the far ends of the beam if possible, to allow the largest possible dead zone in the centre where the motor will stay inactive; however, if a short beam is used it will be necessary to move sensors L and R towards the centre to give the motor sufficient time to respond before contact is broken.

The rest of the circuit in figure 1, including the voltage comparators, is located at the base. This allows the motor to control the direction of the pantograph booms, and to sweep them through an angle arbitrarily close to 1800, depending on the diameter of the booms.

Trolleybuses use a second wire for the ground contact; this cannot be detected by this system, so the two booms will be connected with loose hinges at either end to keep them a constant distance apart. The two overhead wires must also therefore be kept a consistent distance apart: this presents no obstacle since they are held up in the same catenaries. The ground contact beam can be made slightly longer than the live contact beam to allow some leeway in this distance.

Other features An extra circuit may be added to lift the pantograph automatically when the motor is not turning: when the strongest signal is from sensor C, denoting that the pantograph is directly underneath the wire.

Another extra circuit will lower the pantograph automatically when contact with the live wire is about to break, using contact sensors at either end of the contact beam. This is just a standard fuse circuit and not part of this application.

The key feature of this system is the direct control of the motor by the Hall Effect sensors in figure 1. This allows the pantograph contact automatically to follow the live wire.

That is the basis of this application.

Claims (9)

1. Homing Pantograph Claims 1. See circuit diagram, figure 1.
2. 2. A beam contact, typical of electric railway pantographs, has Hall Effect sensors L, C and R mounted at the far left, centre and far right respectively.
3. 3. The sensors output voltages that increase with the strength of the magnetic fields across them.
4. 4. The dominant magnetic field is that created by the current in the live overhead wire, so the sensors use the magnetic field to signal their proximity to the live wire.
5. 5. Three voltage comparators compare the signals VL, V and VR to determine the action of the motor, which controls the position of the pantograph contact.
6. 6. The movement of the motor is controlled by the direction of the current across it.
7. 7. The motor will only move the contact to the left if VL> V and VL> VR; and to the right if VR> Vcand VR> VL.
8. 8. The motor is mounted at the base of the pantograph and directs the pantograph booms towards the wire.
9. 9. This system will work if the pantograph is in contact with the wire; or if it is lowered, when it can detect the wire remotely and connect to it.