Claims:We claim:
1. A time delay switching device for a vehicle comprising:
a light emitting device (102) configured to get actuated by a push button (103);
a delay circuit (107) electrically configured to said push button (110) to sense a mechanical push;
an ignition switch sense circuit (108) configured to sense a transition of a voltage in said delay circuit (107) and trigger said turn OFF threshold circuit (111) to provide a threshold voltage to a switching device.
2. The time delay switching device as claimed in claim 1, wherein said turn OFF threshold circuit (111) being configured to sense a voltage across a first capacitor (C1) set by a Zener diode (D1);
wherein, said turn OFF threshold circuit (111) being configured to discharge said first capacitor (C1) within a time limit set by a switch OFF time of said switching device;
wherein, said switching device being a MOSFET (M1).

3. The time delay switching device as claimed in claim 1, wherein said delay circuit (107) being configured to provide a turn OFF delay.
4. The time delay switching device as claimed in claim 1, wherein said capacitor (C1) charges through said push button (110) and a resistor (R1).
5. The time delay switching device as claimed in claim 1, wherein said MOSFET (M1) being configured to be switched based on a potential at a node (cap).
6. The time delay switching device as claimed in claim 1, wherein said transition of a voltage is sensed when an ignition switch (109) being turned OFF and ignition switch sense circuit (108) bypasses said push button (110) and charges capacitor (C1) of said delay circuit (107) through switching device (Q4);
wherein, said switching device (Q4) being controlled by a voltage at a base of said switching device (Q4) and resistor (R10, R13) being configured for biasing said switching device (Q4); and resistor (R12) provides pull down to a first end of a capacitor (C2).
7. The time delay switching device as claimed in claim 1, wherein said ignition switch (109) being connected to a node (IGS switch);
a diode (D3) configured to discharge capacitor (C2) to supply a voltage when potential at a second end of capacitor C2 is more than a supply voltage.
8. A method of operation of a time delay switching device for a vehicle comprising the steps of:
switching ON an ignition key to supply a constant voltage to a capacitor (C2);
switching OFF said ignition key to enable discharging of capacitor (C2) through a resistor (R12);
supplying a voltage (Vs) to a light switch in a delay circuit and capacitor (C1) through resistor (R1)
discharging said capacitor (C1); and
connecting a turn OFF threshold circuit (111) to a delay circuit to provide a desired voltage when a voltage across said capacitor (C1) is less than a threshold voltage.
, Description:TECHNICAL FIELD
[0001] The present subject matter relates to a time delay switch for a vehicle. More particularly, internal circuit for a convenience light for a utility box in a vehicle is disclosed.

BACKGROUND
[0002] Existing vehicles has convenience light for illuminating the utility box or a storage compartment which is provided at the rear portion of the vehicles. The above mentioned light is switched on using reed switch which is actuated by a magnet. The magnet is placed underneath the rear side of the seat that is lifted to open utility box. The reed switch is placed on top rear portion of utility box in such a way that it is able to sense magnet when seat is closed. The light is activated when seat is open and deactivated when the same is closed.
[0003] The usage of reed switch and magnet which is additionally provided with a separate housing structure results in increase of cost of overall system. As reed switch is a separate part, it has separate coupler, wiring and mounting requirements. Magnet has to be placed underneath the seat which adds additional step in manufacturing.
[0004] To overcome the above mentioned problem and to reduce the cost of this system, reed switch and magnet sensing mechanism can be changed to toggle switch. However, there arises a possibility that the user might forget to turn OFF the light and this results in discharge of battery. Discharge of battery due to this unintended operation may lead to failure of electrical cranking of vehicle due to which the vehicle may fail to start.

BRIEF DESCRIPTION OF DRAWINGS
[0005] The detailed description is described with reference to a saddle type scooter along with the accompanying figures. The same numbers are used throughout the drawings to reference like features and components.

[0006] Fig. 1 exemplarily illustrates a light emitting device in utility box or a storage compartment of a vehicle;
[0007] Fig. 2 exemplarily illustrates mechanical mounting of manual push button on UB (utility box) light and USB charger;
[0008] Fig. 3 exemplarily illustrates the block diagram to provide time delay switch and its interfacing circuits;
[0009] Fig. 4a exemplarily illustrates complete circuit diagram with all features disclosed in subject matter such as delay circuit, turn OFF threshold circuit and ignition switch sense circuit;
[00010] Fig. 4b exemplarily illustrates circuit diagram with delay feature. This circuit only provides turn OFF delay after Push button is released;
[00011] Fig. 4c exemplarily illustrates circuit diagram with delay and ignition key sense feature. This circuit provides turn OFF delay after Push button is released and when ignition switch input falls from high to low;
[00012] Fig. 4d exemplarily illustrates circuit diagram with delay and turn OFF threshold feature. This circuit provides turn OFF delay after Push button is released and also switches OFF when capacitor voltage goes below predetermined value. This prevents MOSFET from operating in linear region.

DETAILED DESCRIPTION OF THE INVENTION
[00013] In the existing vehicles, usage of reed switch is prevalent which increases the cost of overall vehicle. Sometimes, when a sizeable luggage or object is kept in the utility box or storage compartment then it may be possible that the utility box or storage compartment is not closed properly. In that scenario, the necessary reed switch and magnet coupling will not occur and the light will always be in ON state resulting in drainage of battery of the vehicle. Discharge of battery may lead to failure of electrical cranking of vehicle due to which the vehicle may fail to start.
[00014] Further, in some vehicles additional switches are provided on handlebar to turn ON the utility box or storage compartment light which requires restructuring and redesigning the entire handle bar assembly thus increasing wiring harness and overall cost of the vehicle.
[00015] To avoid this, conventional vehicles have time delay switches which delays the switching operation of a light emitting device. However, these time delay switches involve a complex circuitry where relay circuits with high inductive and capacitive loads are used.
[00016] Therefore, to eliminate the above-mentioned problem, manual push button can be used. The convenience light can be activated once push button is pressed and then deactivated after some time from the instant of release of the push button. To achieve delay turn-off functionality, delay circuit as per the present invention discloses a simple R-C circuit which is cheap to implement and overcome all problems disclosed as well as other problems of the known art. Further, the present invention can be used in conditions where delay is required in switching of load or in providing signal in the circuit.
[00017] With the above concerns in view, the main objective of present invention is to provide OFF delay for convenience light for utility box or storage compartment from the instance of operation of a push button positioned on utility box or storage compartment light housing and also to actuate operation of utility box or storage compartment light when ignition switch transition from ON to OFF state occurs. Whenever user wants to use utility box or storage compartment light, the utility box or storage compartment light can be actuated using a mechanical push button positioned on utility box or storage compartment light housing. The utility box or storage compartment light will be actuated and remain lit for a predetermined duration. Then, the utility box or storage compartment light will be automatically deactivated. The utility box or storage compartment light is also activated whenever there is a transition from ON state to OFF state of ignition key. Turn OFF threshold feature can be used whenever the switching device used in delay circuitry is used for switching high power application. This ensures that the switching device in delay circuitry does not operate in active mode.
[00018] In an embodiment, delay circuit is provided for delaying turn OFF time of utility box or storage compartment light from the instance of release of mechanical push button. Delay circuit consists of MOSFET that switches the load (in this case utility box or storage compartment light), three resistors, a capacitor and zener network for providing delay time and to compensate delay time variation due to supply voltage fluctuation. The first resistor along with capacitor forms RC network. The one end of the first resistor is connected to one end of the manual push button. The other end of the manual push button is connected to supply voltage. The other end of first resistor is connected to one end of capacitor. The other end of capacitor is connected to ground. The first resistor and capacitor junction is connected to one end of second resistor and third resistor. The other end of second resistor is connected to ground. The other end of third resistor is connected to gate of said MOSFET and cathode of said Zener diode. The anode of Zener diode is connected to ground.
[00019] Whenever the manual push button is pressed supply voltage is applied across first resistor and capacitor and capacitor begins to charge. The value of first resistor is very low such that within few milliseconds the capacitor gets charged. The gate source voltage of the MOSFET is configured to be higher than gate threshold voltage of MOSFET and hence MOSFET switches ON.
[00020] When the manual push button is released, the capacitor begins to discharge through second resistor. The discharge also happens through third resistor and said Zener diode in series if the voltage across capacitor is above the breakdown voltage of Zener diode. This provides different discharge rate if supply voltage is higher, thus, helping in reducing variation in delay time due to supply voltage variation. As long as capacitor voltage is higher than gate threshold voltage of the MOSFET, the MOSFET switch will be turned ON, thus, creating a delay time. Unlike transistor, MOSFET does not require continuous current in gate to keep the MOSFET ON. Thus, it allows to achieve higher delay time using low capacitance value of capacitor.
[00021] In another embodiment, a Turn OFF threshold circuit is disclosed. Turn OFF threshold circuit turns OFF utility box or storage compartment light by shorting capacitor of delay circuit when the potential across the same goes below predetermined value. This circuit is used to prevent operation of MOSFET in active region.
[00022] Turn OFF threshold circuit has first switching device that supplies voltage to threshold circuit and is controlled by MOSFET of Delay circuit to eliminate current consumption during deactivated state. A first resistor and first Zener diode network is configured to provide reference voltage, second and third resistor for biasing first switching device and second and third switching device in which second switching device is used for controlling third switching device based on potential difference between the reference voltage provided by said first resistor and first Zener diode network and the capacitor in delay circuit, then fourth and fifth resistor for biasing second and third switching device. Third switching device is used for discharging capacitor in delay circuit at higher rate if voltage at capacitor is below predetermined threshold value set by first resistor and first Zener diode network. The first and second switching device are configured for high side operation and third switching device is configured for low side operation. This circuit may not be required if the switching operation is done through enable pin of driver rather than directly controlling power circuitry.
[00023] In another embodiment, Ignition switch sense circuit is disclosed which senses high to low signal from ignition switch and activates delay circuit by bypassing the manual push button. Ignition switch sense circuit consists of switching device to bypass the manual push button, first and second resistor for biasing said switching device, third and fourth resistor connected in resistor divider fashion with input connected to ignition switch output and output connected to one end of capacitor. The other end of capacitor is connected to base of switching circuit through second resistor. The anode of diode is connected to one end of capacitor and switching device biasing junction. The cathode of diode is connected to input supply. This diode provides path to discharge capacitor whenever the potential at capacitor end exceeds input supply voltage.
[00024] Therefore, it is an aspect of present invention to provide a circuit where Turn OFF delay time was achieved for switching OFF utility box or storage compartment light after predetermined delay time is achieved using RC circuit as it has cost benefit over other models.
[00025] In yet another aspect, the shortcoming in RC delay circuit is overcome using minimal number of components. This result in achievement of satisfactory result with less cost.
[00026] However, the convenience of the user is degraded as existing system does not require user to press switch to operate utility box or storage compartment light. This inconvenience was overcome to certain extent by ignition switch sense circuit that operate utility box or storage compartment light for said predetermined delay set by delay circuit whenever, ignition switch transition from ON to OFF is detected. This is helping in improving convenience of the user as it is intuitive that the user wants to take away his/her belongings after switching OFF the vehicle.
[00027] Fig.1 exemplarily illustrates the utility box or storage compartment 105 inside a vehicle body 100. A light emitting device 102 with USB connector 104 and push button 103 is provided. The user has to press the manual press button 103 to switch the light emitting device 102. The push button 103 as per an embodiment has a coating of radium over it so that the user can easily identify it during the night time or when no ambient light is there.
[00028] Fig. 2 exemplarily illustrates the housing of light emitting device 102 provided with a USB connector 104 and a push button 103. The push button 103 has a coating of radium over it so that the user can easily identify it during the night time or when no ambient light is there.
[00029] Fig. 3 exemplarily illustrates the block diagram of various interfacing circuits to provide a delay during turn OFF of light emitting device 102 in utility box or storage compartment 105 of a vehicle. Whenever user wants to use utility box or storage compartment light, the light emitting device 102 can be actuated using a mechanical push button 103 positioned on utility box or storage compartment light housing. The utility box or storage compartment light will be actuated and remain lit for a predetermined duration. Then, the utility box or storage compartment light will be automatically deactivated. The utility box or storage compartment light is also activated whenever there is a transition from ON state to OFF state of ignition switch sense circuit 108 and the storage unit is being accessed. Turn OFF threshold circuit 111 feature can be used whenever the switching device used in delay circuit 107 is used for switching high power application. This ensures that the switching device in delay circuitry does not operate in active mode.
[00030] Fig. 4a exemplarily illustrates key elements of the block diagram shown in Fig. 3 i.e. LED regulation circuit 106, Delay circuit 107, Ignition switch sense circuit 108, Turn OFF threshold circuit 111, Manual push button 110, Ignition key 109.
[00031] LED regulation circuit 106 regulates supply voltage and provides constant current output to LED. The regulation circuit 106 can be either monolithic driver IC or collection of active components or switching regulator. The regulation circuit can be connected to either high side or low side or both side of LED. In Fig. 4a, a monolithic driver IC is used in high side of LED for current regulation. The node (vs), which is connected to supply voltage, is connected to input of driver IC. The output of driver IC is connected to anode of LED. The cathode of LED is connected to node (vd) whose potential is controlled by switching device MOSFET (M1) in delay circuit.
[00032] Delay circuit 107 senses mechanical push button and provides turn OFF delay. The mechanical push button 110 is connected to delay circuit in node (utility box or storage compartment light switch). On pressing mechanical push button 110, capacitor C1 charges though said button and resistor R1. The capacitor C1 charges within few milliseconds as value of R1 is less. Based on potential at node (cap), the MOSFET M1 is switched. If the potential at node (cap) is above gate threshold voltage of M1, then MOSFET M1 switches ON connecting node (vd) to ground. This enables operation of LED in LED regulation circuit 106. Once mechanical push button is released, capacitor C1 begins to discharge through resistor R3 and resistor R2 in series with Zener diode D4 if capacitor voltage is greater than breakdown voltage of Zener diode D4. This creates delay in discharge of capacitor which in turn introduces turn OFF delay. MOSFET M1 remains ON until voltage across capacitor is above gate threshold voltage of MOSFET M1. It is possible that MOSFET is operating in active region when potential across capacitor is above gate threshold voltage of MOSFET M1 but below required voltage by MOSFET M1 for passing load current.
[00033] Ignition switch sense circuit 108 senses high to low signal from ignition switch 109, that is, whenever ignition switch 109 is turned OFF. Upon sensing turn OFF condition of ignition switch 109, this circuit 108 bypasses mechanical pushbutton 110 and charges capacitor C1 of delay circuit 107 through switching device Q4. The sensing operation was enabled using resistor and capacitor network. Switching device Q4 is controlled by voltage at base of the switching device Q4. Resistor R10 and R13 is used for biasing the switching device Q4. Resistor R12 provides pull down to first end of capacitor C2. This provides ground to first end of capacitor when ignition switch 109 is open. Resistor R7 limits current through ignition switch 109. Ignition switch 109 is connected to node (IGSwitch). Diode D3 discharges capacitor C2 to supply voltage when potential at second end of capacitor C2 is more than supply voltage. The ignition key switch off sensing operation takes place as follows: In first state, ignition switch 109 is closed. When ignition switch 109 is closed, voltage potential at first end and second end of the capacitor is almost same. Hence no current flows through base of switching device Q4 resulting in open condition of Q4. When ignition switch is opened, first end of capacitor C1 connected to ground through resistor R12. This provides path to charge capacitor C2. Capacitor C2 charges through base of switching device Q4 which in turn results in closing of switching device Q4. The switching device Q4 remains closed as long as capacitor C2 is charging. During this period capacitor C1 of delay circuit 107 is charged through switching device Q4.
[00034] Turn OFF threshold circuit 111 senses voltage across capacitor C1 and if the voltage falls below predetermined threshold set by Zener diode D1 then it discharges capacitor C1 within time limit through resistor R6 and transistor Q2, where time limit is set by switch OFF time of MOSFET M1 for which power dissipation at MOSFET M1 is within safe operating region of the MOSFET M1. This circuit 111 is useful only when there is possibility of high power dissipation in MOSFET M1 due to operation in active region. A single MOSFET M1 is capable enough to maintain the delay time without fluctuation when the turn OFF threshold circuit 111 is providing a minimum threshold voltage to the capacitor C1 of the delay circuit 107 at the time of discharging. The threshold voltage keeps the MOSFET M1 (switching device) operating in an active region. Hence, a single MOSFET M1 helps in maintaining the delay time. The PNP type transistor Q1 emitter is connected to the voltage reference set by Zener diode D1. The base of transistor Q1 is connected to capacitor C1 of delay circuit through resistor R11. The collector of transistor Q1 is connected to base of transistor Q2. When the voltage across capacitor C1 of delay circuit is greater than the voltage across Zener diode D1 than there will be no current flow through base of transistor Q1 and transistor Q1 remains open. Thus, transistor Q2 also remains open. When the voltage across capacitor C1 of delay circuit 107 is less than the voltage across Zener diode D1 than there will be current flow through base of transistor Q1 and transistor Q1 will be closed. This will turn ON transistor Q2 which is connected across capacitor C1 of delay circuit 107 through R6. Thus, capacitor C1 starts to discharge also through resistor R6 and transistor Q2. The value of resistor R6 is low such that the capacitor C1 will be discharged within short period of time but also value of resistor R6 is high enough that the power dissipation on transistor Q2 is within limit when capacitor C1 is discharging through the same.
[00035] In Manual push button circuit 110, one end of the manual push button is connected to supply voltage and other end is connected to Capacitor C1 of delay circuit 107 through resistor R1. This is normally open and closed when pressed mechanically.
[00036] In Ignition switch circuit 109, Ignition switch used to turn ON and OFF the vehicle. Unlike push button 110, the switch will be either in ON state or OFF state. The input of ignition switch is connected to supply voltage. The output of ignition switch is connected to ignition switch sense circuit that senses the transition from ON to OFF state of ignition switch.
[00037] In Fig. 4b, another embodiment is shown where LED regulation circuit 106, delay circuit 107 and manual push button circuit 110 are provided to illuminate the light emitting device 102.
The utility box or storage compartment light can be activated in two ways: by actuation of mechanical push button 110 or by transition from ON state to OFF state of ignition key 109. The utility box or storage compartment light remain lit for a predetermined time set by delay circuitry from the instance of activation of utility box or storage compartment light.
When mechanical push button is pressed, and released, supply voltage is connected to capacitor C1 of delay circuit through resistor R1. The value of resistor R1 is such that the capacitor C1 will be charged within milliseconds. This time is well below operation time of the switch and thus capacitor C1 will be fully charged. Now, the voltage across the capacitor C1 will be almost equal to supply voltage. Now, Capacitor C1 starts to discharge. The discharge path of capacitor C1 will be through resistor R3 and through resistor R2 and Zener diode D4 in series if the voltage of the capacitor C1 is above breakdown voltage of Zener diode D4. There is no continuous flow of current through Gate of switching device MOSFET M1 and hence capacitor will not discharge through this path. This reduces requirement of capacitance for achieving certain delay time as it is not loaded additionally by switching device. The voltage across capacitor C1 will be applied across Gate-Source of switching device MOSFET M1 through resistor R2. MOSFET M1 will be completely switched ON as long as the Gate-Source voltage of switching device MOSFET M1 is greater than the required threshold specific to MOSFET M1 for conducting load current. Utility box or storage compartment light is controlled by MOSFET M1. If MOSFET M1 is ON, then utility box or storage compartment light will be activated. If MOSFET M1 is turned OFF, utility box or storage compartment light will be deactivated. By selecting appropriate value for resistor R3 nominal delay time is achieved for nominal supply voltage. But whenever, supply voltage fluctuates it affects delay time drastically. To reduce this effect, resistor R2 and Zener diode D4 can be selected so that the discharge rate shall be adjusted depending on supply voltage. By adjusting discharge rate to higher value for higher supply voltage and lower for lower supply voltage it enables to attain minimal variation in delay time across fluctuation of supply voltage.
[00038] In Fig. 4c, as per an alternate embodiment, when ignition switch 109 is turned ON, supply voltage is connected to node (IGSwitch) that supplies voltage to first end of capacitor C2 through voltage divider formed by resistor R7 and R12. The purpose of R12 is to provide ground path to capacitor C2 for OFF state of ignition switch as first end of capacitor will be floating without resistor R12. Initially, capacitor will be charged through base of transistor Q4 and resistor R13. Thus, voltage at second end of capacitor C2 is almost equal to supply voltage. When ignition switch 109 is turned ON, supply voltage will be applied to first end of capacitor C1 after reduction by voltage divide formed by R7 and R12. Because of this the potential at second end of capacitor C2 will be shifted to almost double the value of supply voltage. The capacitor now starts to discharge through diode D3 into supply voltage. After complete discharge of capacitor C2, voltage across capacitor C2 is almost zero. When ignition switch is turned ON, transistor Q4 will be in OFF state. When ignition switch is turned OFF, application of supply voltage at node (IGSwitch) will be removed. Now, first end of the capacitor C2 will be connected to ground through resistor R12. The voltage at second end of capacitor C2 will be almost zero. This results in potential difference that cause flow of current through base of transistor Q4 that charges capacitor C2 through resistor R13 and R12. During this period, since there is flow of current through base of transistor Q4, transistor Q4 will be turned ON. Transistor Q4 will be turned ON until the voltage at second end of capacitor C4 charges to supply voltage. After capacitor C4 completely charges, the potential difference vanishes, resulting in pause of flow of current in base of transistor Q4. This turns OFF transistor Q4. Thus, whenever ignition switch turns from ON state to OFF state, switching device transistor Q4 turns ON for some time. This time is determined by capacitor C2 and resistor R10 and R12. This time is set so that the capacitor C1 of delay circuit 107 could be charged completely. Thus, whenever transition from ON state to OFF state occurs in ignition switch 109, utility box or storage compartment light 102 is activated for predetermined time delay.
[00039] In Fig. 4d, as per an alternate embodiment, when Gate-Source voltage of switching device MOSFET M1 of delay circuit 107 falls less than the required threshold specific to MOSFET M1 for conducting load current then MOSFET M1 enters active mode of operation. This results in high power dissipation in MOSFET M1 if load current is high. To avoid operation of MOSFET M1 in active region, a threshold voltage can be set using Zener diode D1 in turn OFF threshold circuit 111, below which capacitor can be instantly discharged. The said threshold voltage can be set based on characteristics of MOSFET M1. When capacitor voltage falls below the said threshold voltage set by Zener diode D1, current flows through base of transistor Q1 that turns Q1 ON resulting in flow of current to base of transistor Q2. As a result, Q2 turns ON discharging capacitor C1 of delay circuit 107 through resistor R6 and thus instantaneously discharging capacitor C1. Transistor Q3 is activated only when MOSFET M1 is ON. This arrangement eliminates current requirement for voltage threshold setting circuit comprising of Zener diode D1 in series with resistor R8 during inactive condition of turn OFF threshold circuit.
[00040] Fig. 5 illustrates a method to operate a time delay switching device. In step 501, the ignition key is switched ON in order to supply a constant voltage to a capacitor (C2) then in step 502, switching OFF the ignition key to enable discharging of capacitor (C2) through a resistor (R12). In step 503, supplying a voltage (Vs) to a light switch in a delay circuit and capacitor (C1) through resistor (R1) discharging said capacitor (C1). In step 504, connecting a turn OFF threshold circuit (111) to a delay circuit to provide a desired voltage when a voltage across said capacitor (C1) is less than a threshold voltage. The threshold voltage is a voltage at which the MOSFET (M1) is functioning at an active region and below the threshold voltage the MOSFET (M1) functions as resistor which leads to generation of heat.
[00041] Improvements and modifications may be incorporated herein without deviating from the scope of the invention.

LIST OF REFERENCE NUMERALS

100 – vehicle body
101 – seat lock
102 – light emitting device
103 – push button
104 – USB connector
105 – utility box/ storage compartment
106 – LED regulation circuit
107 – delay circuit
108 – ignition switch sense circuit
109 – ignition key circuit
110 – manual push button circuit
111 – turn off threshold circuit