Field of the Invention

This invention relates to a "Charging System for an Electric Vehicle" and more particular to a safety mechanism to prevent the vehicle from being started while plugged for charging.

Background of the invention

Electric Vehicles use an electric motor to propel the vehicle. The energy required for driving the vehicle is generally obtained from battery packs. The electric motor converts the electrical energy generated by the battery into mechanical energy for rotating the wheels of the vehicle.

Rechargeable batteries are generally used in these Electric Vehicles. A battery charger is provided on the vehicle which when connected to the domestic power supply outlet recharges the batteries. The battery charger converts the domestic power supply voltage into a voltage suitable for recharging the batteries.

There is an anti-drive away interlock mechanism already known from the prior art (US Patent 3904947), which prevents the driver from starting the vehicle while it is plugged to the alternating - current power outlet. The connector for connecting to the alternating - current supply socket has a normally closed limit switch with a feeler arm adapted to engage with the socket face of the power outlet. When the connector is completely inserted into the power supply socket, the feeler arm moves inwardly to open the limit switch. When the limit switch is open, the battery cannot be connected to the electric motor and therefore the vehicle cannot be started. This mechanism requires special connectors with inbuilt limit switch.

There is also a running prohibiting unit already known from the prior art (US Patent 5931245) that prevents the driver from starting the vehicle if the charging cord is in an unsafe pulled-out state. A cord reel winds to house the charging cord in a cord case and the charging cord has to be pulled out and connected to the alternating - current supply outlet for charging the batteries. There is a normally closed contact switch provided on the cord case such that when the charging cord is pulled out from the cord reel, the contact switch opens. When the contact switch is in an open state, the battery cannot be connected to the motor for starting the vehicle. Such a system requires a special cord case with contacts and cord reel for winding the charging cord.

Also known is a "Safety device to prevent the starting of an Electric Vehicle" (EP0083036) wherein a circuit breaker is provided between an accumulator and a drive unit and at least one control element acts on the circuit breaker to allow starting of the vehicle only when a mains plug of an on board charging device is connected with an on board socket. The mains plug can be connected to a stationery electric mains system for charging the vehicle. But such a system is only applicable for electric vehicles with on board charging devices. There are electric vehicles with battery chargers removably connected with the vehicle for weight reduction and due to space constraints and this system cannot be used for such vehicles.

There is a requirement for a low cost, compact and reliable Electric Vehicle Charging system with a safety mechanism to prevent starting of the vehicle while the vehicle is plugged to the alternating - current supply outlet for charging. Such a system will reduce complexity and cost considerably.

Hence, the principal object of this invention is to provide a charging system for an electric vehicle that prevents starting of the vehicle while plugged for charging the batteries.
Another object of this invention is to provide a charging system for the electric vehicle which is low cost and does not require special connectors or cord reel for fully ensuring safety while the vehicle is plugged for charging.

Also another object of this invention is to provide a charging system for the electric vehicle without any constraint on the location of the charger with respect to the vehicle.

Brief description of the invention

Accordingly the invention provides a charging system for an electric vehicle consisting of an energy storing device fixed on the vehicle, an electric motor for driving the vehicle, a switching device for connecting the energy storing device to the electric motor through a controller and a charger for recharging the energy storing device which is characterized in that the charging plug of the charger has at least two terminals that are interconnected and there is an electric circuit that detects the mating of the charging plug with a charging socket on the vehicle and suitably controls the switching device to prevent starting of the vehicle while the charger is plugged to the vehicle.

Brief description of drawings

The invention and objects and features thereof will be more readily apparent from the following description and appended claims when taken with the drawing, in which:

Fig 1 is a block diagram showing a Charging System for an electric vehicle with respect to a first embodiment of the present subject matter.

Fig 2 is a block diagram showing a Charging System for an electric vehicle with respect to a second embodiment of the present subject matter.

Detailed Description:

Referring to Fig 1, charger (10) has input plug (20) that can be removably connected to AC power supply outlet (30). The charger (10) has a charging plug (40) for connecting to a charging socket (50) that is fixed in the electric vehicle. The charger (10) converts the alternating current power supply into a direct current suitable for charging a battery pack (60). The charging plug (40) has three terminals (42), (44) and (46) in which terminals (44) and (46) are interconnected.
The charging socket (50) has three terminals (52), (54) and (56) for mating with the respective charging plug - terminals (42), (44) and (46). Charging plug (40) is a 3 pin plug and charging socket (50) is a 3 pin socket. The charging socket terminal (52) is connected to the positive terminal of the battery pack (60) and the charging socket terminal (56) is connected to the negative terminal of the battery pack (60).

All electrical loads to the battery pack (60) are connected through a Main Circuit Breaker (MCB) (70) that disconnects the battery and the electrical loads in case of a short circuit. A 200A MCB (70) was used in the embodiment. Generally high voltage battery pack is used in electric vehicles to reduce the losses in the transmission conductors and generate high torque and power output from the electric motor. In the invention disclosed a 144V battery pack was used by connecting twelve 12V batteries in series. A DC -DC converter (80) is used to convert the high voltage at the battery pack (60) terminals to low voltages required for DC loads like relays, bulbs, horn etc. A 144V - 12V, 25A DC - DC converter (80) was used in the invention disclosed.

In addition to other DC loads, the DC - DC converter (80) also provides power supply to a switching device - an electromechanical relay (100) coil terminal (102). The electromechanical relay (100) has contact terminals (104) and (106). A 12V, 100A relay (100) was used in the invention. The relay contact terminal (104) is connected to the output of the MCB (70) and the contact terminal (106) is connected to a controller (110). The controller (110) converts the 144V DC voltage into 3 - phase voltages for driving a Brushless DC motor (120) if the relay (100) contacts (104) and (106) are connected. The contacts (104) and (106) are normally open and close when the relay (100) coil (108) is energized.

The relay coil terminal (109) is connected to the collector of an NPN transistor (130). The base of the transistor (130) is connected to charging socket terminal (54) and the collector of transistor (130) is connected to the 12V output from the DC - DC converter (80) through a resistor (140). The 12V output is also connected to the transistor (130) base through a resistor (150).

Resistor (140) was 2.2 kilo ohm and resistor (150) was 1.5 kilo ohm for operating the transistor (130) as a switch.

There is a manual start switch (160) that connects the negative terminal of the battery pack (60) to the controller (110) and DC - DC converter (80). The start switch (160) is mounted on the vehicle at a convenient location for the user to start the vehicle easily. The controller (110) and the DC - DC converter (80) will be disabled if the start switch (160) is open.

Since the charging socket terminal (56) is connected to the negative terminal of the battery pack (60) and since the charging plug terminals (44) and (46) are interconnected, the charging socket terminal (54) will be electrically floating (open connection) when charging plug (40) is not connected to the charging socket (50).

The base - emitter junction of the transistor (130) will be forward biased if the charging socket terminal (54) is electrically floating due to the 12V DC supply when start switch (160) is closed and because of resistor (150). If the base -emitter junction of the transistor (130) is forward biased then the transistor (130) acts as a closed switch due to which a low voltage (-0.2V) will be available across the transistor (130) collector and emitter. There will thus be a potential difference (-11.8V) across the relay (100) coil (108) terminals (102) and (109). The contact terminals (104) and (106) will be closed and the MCB (70) output will get connected to the input of controller (110). The controller (110) is disabled if the start switch (160) is open and the motor can be started only if the start switch (160) is closed. When the charging plug (40) is not connected to the charging socket (50), the vehicle can thus be started by closing the start switch (160).

Since the socket terminal (54) is connected to the base of transistor (130), the base will have electrical connection with the negative terminal of the battery pack (60) when charging plug (40) is connected with the charging socket (50). There is no forward bias of the base - emitter junction of the transistor (130) even when start switch (160) is closed. The voltage across the transistor (130) collector - emitter will be approximately 12V DC and thus 12V DC will be available at relay (100) coil terminal (109). The voltage at the relay (100) coil terminal (102) will be 12VDC when the start switch (160) is closed and thus voltage across relay coil (100) terminals (102) and (109) is 0V DC. The coil does not energize and the contacts (104) and (106) will be open thus preventing the user from starting the motor even when the start switch (160) is closed.

Thus the electric vehicle cannot be started if the charging plug (40) is connected to the charging socket (50) even if the ac supply outlet (30) is in 'OFF condition.

Referring to Fig 2, another embodiment of the charging system for electric vehicle is shown wherein charging plug (240) has four terminals (242), (244), (246) and (248). Two of these terminals (244) and (246) are interconnected. The charging socket (250) in the vehicle also has four terminals (252), (254), (256) and (258) for mating with the charging plug (240) terminals. The charging socket (250) terminal (254) is connected to the emitter of an NPN transistor (291) in electric circuit (290). The terminal (256) is connected to ground such that the emitter of transistor (291) will be connected to ground when the charging plug (240) is connected with the charging socket (250). The charging socket (250) terminal (252) is connected to the positive terminal of battery pack (60) and terminal (258) is connected to the negative terminal of the battery pack (60).

When the start switch (160) is closed, 12V DC will be available for the electric circuit (290) and if the charging plug (240) is connected with the charging socket (250) then the transistor (291) base - emitter junction will be forward biased due to resistors (293) and (295). 2.2 kilo ohm resistors were used as (293) and (295). The collector voltage of transistor (291) will be low (-0.2V) that is not sufficient to turn 'ON' another NPN transistor (297). The transistor (297) is also biased to operate as a switch using resistor (299). Resistor (299) was 1.5 kilo ohm. The collector voltage of transistor (297) will be 12V DC and hence 12V DC is available at the relay coil terminal (109). Since the start switch (160) is closed, 12V DC is available at the relay (100) coil terminal (102) and the potential difference between the relay (100) coil terminals is 0V. The coil (108) does not energize and relay contacts (104) and (106) will be open. Thus the user cannot start the vehicle if charging plug (240) is connected with the charging socket (250).

If the charging plug (240) is not connected to charging socket (250) then transistor (291) base - emitter junction will not be forward biased and 12V DC will be available at collector of transistor (291). The transistor (297) will be turned 'ON' and low voltage (-0.2V) will be available at relay (100) coil terminal (109). Voltage across relay coil terminals (102) and (109) will be approximately 11.8V DC which will energize the relay coil (108) and contacts (104) and (106) will close. Thus the MCB (70) output will be connected to controller (110) and the user can start the vehicle during start switch (160) closed condition.

The charging system disclosed herein is applicable for a plug in type hybrid vehicle also wherein an electric motor and battery pack are used to drive the wheel along with an internal combustion engine. Generally available plugs and sockets can be used with the above mentioned connections to provide a fully secure charging system for the vehicle. Since minimum number of components is used and since the components like transistors, resistors and relays are available at low cost - a low cost charging system with security against driving during plugged condition is provided. The electric circuit (90) or (290) occupies little space and hence a compact charging system with prevention of driving during plugged condition is provided.

The electric motor (120) can be a brushed motor or an induction motor also. Instead of an electromechanical relay, a solid state relay could also be used. A fuel cell or an ultra capacitor pack could also replace the battery pack (60). It is also possible for the charging plug (40) or (240) to have female terminals and the charging socket (50) or (250) can have male terminals. Instead of junction transistors (130), (291) and (297), other semiconductor devices like FETs or logic gates could also be used. The vehicle could be a two wheeler, three wheeler, four wheeler or even trucks that have an energy storing device and an electric motor to drive the vehicle. The interconnection between the charging plug (40) or (240) terminals could also be provided external to the plug, even inside the charger.

Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present invention as defined.

Claims:

We claim:

1. A charging system for an electric vehicle, which comprises:

a power input means connected with a current converting means;

a power storage means connected to positive terminal of power input means;

a voltage regulation means;

a circuit and power storage protection means along with a relay device characterised in that the relay device is connected to output of the said circuit and power storage protection device and a controller;

a switching device connected to power input means and voltage regulation means;

a start switching means connecting the negative terminal of power storage means to the said controller whereby the controller and voltage regulation means is disabled when the start switching means is open.

2. A charging system for an electric vehicle as claimed in claim 1, characterised in that the power input means comprises a charging plug and socket whereby one of the said charging socket terminal is connected to the positive terminal of the power storage means and another connected to the negative terminal of the power storage means.

3. A charging system for an electric vehicle as claimed in claim 1, whereby the power storage means is a high voltage battery pack.

4. A charging system for an electric vehicle as claimed in claim 1, characterised in that the said voltage regulation means is a DC-DC step down converter connected to battery pack whereby the said DC-DC converter supplies low voltage to DC loads and to the said switching device.

5. A charging system for an electric vehicle as claimed in claim 1, characterised in that the said circuit and power storage protection means is a circuit breaker along with an electromagnetic relay device.

6. A charging system for an electric vehicle as claimed in claim 1, characterised in that the said controller converts the DC voltage into three phase voltage for driving a brushless DC motor when the said relay contacts are connected.

7. A charging system for an electric vehicle as claimed in claim 1, characterised in that the said switching device is a NPN transistor whereby the base of the said transistor is connected to said charging socket terminal along with an output through a resistor and the collector of the said transistor is connected to output of the said DC-DC converter through a resistor.