FIELD OF THE INVENTION
This invention relates to a vehicle electronic system. More particularly, the present invention relates to a single wetting current circuit for the vehicle electronic system.
BACKGROUND
Specific applications require switch input to perform certain functions. Various modes of operations can be classified with respect to the need and application. To select a particular mode of operation, specific switches that will make it feasible are required.
Similarly, in a two-wheeler an engine control unit (ECU) can be dependent on some switch inputs based on which the internal microcontroller unit (MCU) would perform a particular mode of operation. The switch closure and opening which indicate a start and stop function to MCU must be very precise and accurate.
To meet this requirement, one criterion is the health of a switch, which is nothing but how clean the switch contact surface is so that there is no dust or oxide layer formation. If so, the switch may not be absolutely close or cause excessive switch debouncing resulting in improper functioning, and as a result, a specific mode of operation cannot be achieved.
Wetting current also known as loop sealing current is the minimum amount of electric current required to keep a mechanical switch contact in good health. If a mechanical switch contact is operated with too little current, the contacts will tend to accumulate excessive resistance and may fail prematurely.
In applications where these switch inputs are critical to ECU functionality, the wetting current requirement needs to be taken care of, to avoid inaccuracy.

However, in applications where multiple switch inputs are desirable for different modes of ECU functionality; it is necessary to make sure that a proper wetting current requirement is met. Depending on the wetting current value, the circuit parameters are designed. In the present case we have considered a requirement as high as 100 mA of wetting current. To meet this requirement on each switch and having separate wetting current circuit requiring high wattage components then the printed circuit board (PCB) size and cost increases. Also, not all switches will be active at a time so most of these wetting switch circuits will be idle occupying space and increase the cost of the PCB.
There are many ways to meet the need based on applications and uses. One such circuit which is optimized in terms of ECU cost, battery load, and printed circuit board (PCB) spacing for applications where multiple input switches are used, is described.
DISCUSSION OF PRIOR ART
The method involving wetting current for multiple switches, related to the telecommunication, vehicle electronic system, electrical relays, determining the status of a plurality of switches, wetting relay contacts require circuits avoiding redundancy of wetting current circuit and reduced demand on battery, PCB space consumption, and heat dissipation. The arrangement for the implementation of such methods includes, reading of the switch status, wetting current and related hardware circuitry and a microcontroller unit to sense and perform the required functions.
US6600242B1 titled "Method and apparatus for determining switch status"
discloses a method where two sets of switches are used to ascertain the status of a said switch. In a sequence of switching, a switch in the first set of switches is briefly closed to send a pulse of wetting current to each of the associated said switch. The switch in the second set of switches associated with the first set of switches is closed substantially at the same time to determine the status of the said switch. The status of the said switch is determined and stored in a register. Before

the next sequence of switching, the register is switched by one register location. When the register is updated with the status of all the switches, the content is accessed by means of an electronic control unit.
US5621250A titled "Wake-up interface and method for awakening an automotive electronics module" employs a wetting current generator circuit to burn-off any oxide coating on the switch contacts.
EP1843566B1 titled "Method and devices for providing wetting current" avails wetting current through the line-capturing matrix in a network device. By connecting a wetting current circuit through the line-capturing matrix, one wetting current circuit supplies wetting current for lines of multiple ports. The wetting current circuit can be inbuilt or independent.
SUMMARY OF THE INVENTION
The present invention relates to a vehicle electronic system. More specifically, the present invention relates to a single wetting current circuit and an internal microcontroller unit (MCU) based control for meeting the wetting current requirement of multiple switches of the vehicle electronic system.
The primary object of this invention is to provide a method using a single wetting current circuit (high wetting current requirements such as 150mA) consisting of high wattage components which allows flow of high current for a small duration such as 100 millisecs through a closed switch and then automatically reduces it to low currents such as 10mA.
The method of enabling the single wetting current circuit and controlling its connection to a particular switch at a time (to meet the requirement of wetting current) is decided and done by an MCU based on some internal timer and process loops. The MCU may include but is not limited to a microprocessor, microcontroller and any integrated circuit that contain all functions of a computer.
The space, battery load and cost of printed of circuit board (PCB) are reduced by minimizing the number of wetting current circuits.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows the schematic diagram for the implementation of the proposed solution.
Figure 2 shows a single wetting current for enabling of the master control signal from MCU which is applicable to all switches.
Figure 3 shows the single wetting current circuit for the required 150mA for small duration wetting current circuit. The single wetting current circuit is applicable to all the switches.
Figure 4 shows the interface circuit where in the MCU signals or enables i connection of the wetting current circuit to a particular switch sensed as ON by the MCU. The MCU sends independent signals for different switch.
Figure 5 shows the circuit for the external switch input (CLOSED / OPEN) signal going to the MCU.
Figure 6 shows the switch circuit external to ECU when the rider selects this switch (closes), the battery voltage (12V) gets connected to the input pin inside the ECU.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 shows the schematic diagram for implementation of the proposed solution for multiple switches (presently Figure 1 shows the implementation of i proposed method on two switches out of which working of one switch (drive Mode) is explained in detail below and similar method of working is applicable to rest of the switches.
The switch circuit design with high wetting current enable, consists of vehicle ignition on input signal 100 by an MCU, a Master wet control signal 101 controlled by the MCU, a 2.2K resistor R9, a 47K resistor R5, a NPN transistor MMUN2231L Q2, a NPN transistor BC846A Q3, a 82R resistor R7, 560R resistor R8, a 2.2u capacitor C2, a NPN transistor Q6, a 10K resistor R3, a 2.2K

resistor R4, a PNP transistor Ql, an MCU generated input drive mode wetting current enable signal 102, an external switch input signal for drive mode 104, a 12V voltage source VI, a switch SI, a 33K resistor R2, a 47K resistor Rl, a 4.7n capacitor CI and a drive mode (On/Off) signal to MCU 103.
Figure 2 is the circuit to enable the master control signal from MCU, which is applicable to all switches. When the ignition switch is switched ON by a rider, this is sensed by the MCU and it makes the ignition on signal 100 high which is connected to the base of the transistor Q3. The base of Q3 remains high as long as the ignition switch is ON. The master wet enabled signal 101 is generated by the MCU and has the highest priority among all the signals produced by the MCU for this circuit. As a result, when this signal 101 is made high, irrespective of the status of the ignition on signal 100, the transistor Q3 is turned OFF, and the high wetting current circuit is disabled. Hence, even if the ignition is on and MCU senses some abnormality in any running loop, it can completely disable the wetting circuit.
By this way, the MCU takes a decision of making the high wetting current available for the switches.
In Figure 3 the resistors R7, R8, the capacitor C2 and the transistor Q3 form the wetting current circuit. When a switch input is sensed as closed by the MCU and it decides to allow a high wetting current through it, then with the present design initially, a high current of 150mA flows through the circuit till the capacitor C2 gets charged, and once the capacitor C2 is charged completely the current reduces to 20mA. Thus, fulfils the requirement of a high wetting current pulse for a short time and then minimum wetting current flowing through the switch as long as it is closed. Hence, maintaining the switch contacts in good health.
Figure 6 shows the switch circuit in which the external switches SI, S2 are monitored by the MCU. The ON/OFF status of the switches SI, S2 are according to a mode of operation selected by the rider. The mode of operation may include but is not limited to auto mode, manual mode, drive mode and crank switch mode.

By detecting the status of the external switches SI, S2 and based on its internal process loops the MCU enables or disables the flow of high wetting current through that switch.
Figure 4 is the interface circuit, when the MCU senses (through signal 103) that the external drive mode switch SI is closed and decides to allow the high wetting current through the drive mode switch, it ensures that the base of Q3 is high and sends a high signal to the drive wet enable signal 102 connected to base of Q6. By doing so, the high wetting current circuit gets connected to the drive switch and the circuit output is achieved.
Also, if MCU decides to disconnect the high wetting current circuit after some calculated time period, it has to send a low signal (102) to the base of Q6. The wetting circuit gets disconnected from the drive switch even if the switch continues to be closed. Simultaneously, if some other switch is turned ON, the MCU can decide to connect the wetting circuit to that switch according to the requirement.
The MCU has an internal timer to keep track of how many times a particular switch SI, S2, is ON and waits for the calculated time from the last time ON state of the switch SI, S2 and then connects the wetting current circuit to the specific switch SI, S2. When the switch SI, S2 inputs are ON simultaneously, then the MCU takes a call on to which switch the wetting current circuit needs to be connected. Since the wetting current circuit could not be connected to two switches simultaneously. The MCU checks the priority loop to execute the mode of operation selected by the rider and connects the wetting current circuit to that particular switch SI, S2 as per the priority. When a manual mode is selected, all the auto mode switch inputs are ignored, and only manual mode switch inputs are prioritised, similarly for auto mode.

WE CLAIM:
1. A vehicle electronic system, said system comprises:
a plurality of electronic control units (ECUs);
an internal micro-controller (MCU) adapted to receive signals from said plurality of electronic control units (ECUs);
wherein said vehicle electronic system further comprises a single wetting current circuit (200) having vehicle ignition on input signal (100), a Master wet control signal (101), an MCU generated input drive mode wetting current enable signal (102), an external switch input signal for drive mode (104), a drive mode (On/Off) signal to the MCU, a plurality of electronic switches, and a voltage source VI.
2. The vehicle electronic system as claimed in claim 1, wherein the vehicle ignition on input signal (100) is from a microcontroller unit (MCU).
3. The vehicle electronic system as claimed in claim 1, wherein the MCU controls the Master wet control signal (101).
4. The vehicle electronic system as claimed in claim 1, wherein said plurality of
electronic switches includes at least one transistor, at least one capacitor, at least one resistor, and at least one external switch.
5. The vehicle electronic system as claimed in claim 1 or claim 4, wherein said
at least one resistor is a 2.2K resistor R9, a 47K resistor R5, a 82R resistor
R7, 560R resistor R8, a 10K resistor R3, a 2.2K resistor R4, a 33K resistor
R2, and a 47K resistor Rl.
6. The vehicle electronic system as claimed in claim 1 or claim 4, wherein said at
least one transistor is a NPN transistor MMUN2231L Q2, a NPN transistor BC846A Q3, a NPN transistor Q6, and a PNP transistor Ql.

7. The vehicle electronic system as claimed in claim 1 or claim 4, wherein said at
least one capacitor is a 2.2u capacitor C2, and a 4.7n capacitor CI.
8. The vehicle electronic system as claimed in claim 1 or claim 4, wherein said at
least external switch is switch SI and switch S2.
9. The vehicle electronic system as claimed in claim 1, wherein the MCU discounts a wet enable signal (104) on a particular switch after a defined time, even if that switch is ON.
10. The vehicle electronic system as claimed in claim 1, wherein the decision of the MCU to connect the wetting current circuit to the external switches SI, S2is,
(i) When the external switches SI, S2 are ON simultaneously, the MCU does not connect the wetting current circuit and never enables base of the transistor Q6 to be ON at a time, said MCU checks priority loop to execute a mode of operation selected by a rider and connects the wetting current circuit to the external switch, either SI or S2 as per the priority; and
(ii) Whenever the MCU detects ON state of the switches SI, S2 the wetting current circuit to these switches is disconnected, the number of times the external switches SI, S2 are ON is tracked by the internal timer in the MCU and, waits for a calculated time from the last time ON state of the external switches SI, S2 and connects the wetting current circuit to the external switches SI, S2 accordingly.