FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
and Patent Rules 2003
PROVISIONAL SPECIFICATION
(See section 10; rule 13)
1. Title
TIME BOUND PROTECTION AGAINST OVERHEATING OF
ELECTRICAL SYSTEM IN A VEHICLE.
2. Applicant
MAHINDRA & MAHINDRA LTD.
1, GATEWAY BUILDING, APOLLO BUNDER, MUMBAI - 400001, AN
INDIAN COMPANY.
The following specification describes the invention.
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Field of Invention
This invention generally relates to circuit protection device for various electrical circuits used for different applications such as heaters (glow plug), starter motor, solenoid, and other applications that carry similar load current that are used in automobile vehicles. More particularly, it relates to providing time bound protection against overheating of electrical system.
Background of the Invention (Prior-Art)
In cold climates, automobiles are provided with manifold heating systems (cold start) that enable quick starting of engines even at low atmospheric temperatures. Existing manifold heating systems typically consist of a battery (power source), a relay actuated by an electronic timer, a heater and an ignition switch as schematically shown in figure 1.
For the cold-start of an engine, during the start-up (ignition key ON) operation, the heater is turned ON for a period of about 42 seconds by means of a relay that is operated by an electronic timer. Electronic timers typically comprise a number of discrete components, failure of any one of which can cause continuous switching ON (or the actuation) of the relay. Under these circumstances, continuous high current (about 52 amps) flows through the heater circuit. This could result in overheating of wire harness which may weaken the insulation. If the overheating is sustained, it may raise the temperature of the wire harness to the flash point which may potentially cause fire. Moreover the continuous flow of current also causes complete drainage of the automobile battery. Additionally, such incidents potentially damage the automobile battery reducing its working life.
In order to address the above problems and drawbacks associated with the existing manifold heating systems, some automobile manufacturers suggested a
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manually controlled heating system for cold-start operations as shown in figure-3. The operator has to hold the ignition key in the 'ON' position for specific duration depending upon the atmospheric temperature. He / she has to repeat the operation till engine cranks.
There are several drawbacks to relying on a fully manual operation such as this above: To begin with, in case the relay is functioning properly, the operator may erroneously hold the key in the ON position for a longer-than-necessary duration. This will cause the continuous current to flow through the circuit for a longer-than-necessary duration. On the other hand, in case of malfunctioning of the relay, i.e. if the relay gets stuck during the manual cold-start operation (due to arcing or mechanical defects, etc,) the continuous current will flow through the heater circuit. The method is therefore prone to human error regarding the adequate / specific duration for any given atmospheric temperature.
Other associated problems remain, like drainage of battery because of possible longer than necessary durations of holding the ignition key in ON position and also due to the repeated operation. Furthermore, , in such systems there is no way to interrupt the continuous flow of current in the event of relay contact getting stuck.
Therefore, there is a need to provide a method of overriding the malfunctioning timers in order that the current will flow through the wire harness only for a desirable duration thereby preventing the temperature of the wire harness from reaching undesirable levels.
There is also a need to provide a method of restricting the duration of the continuous current flowing through the wire harness in case of manually operated systems, thereby preventing the temperature of the wire harness from reaching undesirable levels.
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Objects and Advantages of the Invention
Accordingly, one of the objects of the invention is to restrict duration of the continuous current flowing through electrical systems in automobiles in the event of malfunctioning of timer or relay contact by means of timer override protection.
A still further object of the present invention is to provide time bound protection in the electrical control system against continuous flow of high current in case of malfunctioning of timer and relay contact stuck-up, so that the resultant complete drainage of battery and also the damage to the battery itself are prevented.
Yet another object of the present invention is to provide a low cost device, which is re-settable with the device-life exceeding about 10000 trip cycles, thereby annulling the need for frequent fuse replacement as is the case in existing interrupting devices such as fuses.
Another objective of the present invention is to ensure safety of the automobiles employing devices such as manifold heating systems, and avoid hazards condition by means of controlling over-heating of the system circuitry.
Brief Description of Drawings
Figure 1 shows the conventional electrical circuit diagram for the heater application while cold starting of the vehicle.
Figure 2 shows the novel electric heater control circuit of the present invention. Figure 3 shows a typical manually operated heater circuit
Summary of the Invention :
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The present invention provides a novel tripping device connected in a circuit to prevent overheating of the circuit that may be caused by malfunctioning of timer devices used in circuits or on account of short circuiting.
List of Parts:
1. Relay
2. Electronic timer
3. Power source (Battery)
4. Heater element
5. Tripping device (set of Polymer PTC)
Detailed Description of the Invention :
The present invention describes a novel Electric Heater Control Circuit to restrict temperature of automobile wire harness from reaching hazardous level. The circuit comprises a relay (1) that is actuated by an electronic timer (2), a power source such as a 12 V battery (3) through an ignition switch, a heater element (4), and a novel tripping device (5), connected together as shown in Figure 2.
A polymer Positive Temperature Coefficient (PTC) element comprises a polymer matrix that is loaded with carbon black particles to make it conductive. Since it is conductive it will pass a given amount of current. If too much current is passed through the device, the element will begin to heat due to FR heating. As the element heats up it will expand. As it expands, the carbon particles will separate and the resistance (to electric current) of the device will increase. This will cause the element to heat faster and expand more, further raising the resistance. This increase in resistance is sufficient to substantially reduce the current in the circuit. When the power source is attached to the circuit, a small amount of current, referred to as residual current, will still flow through the element and is sufficient to maintain the temperature of the element and keep it at the high resistance level. When the power and fault are removed, the element will cool. As the device cools,
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it contracts to its original shape and returns to a low resistance level where it can hold / allow to pass the current as specified for the element.
The time it takes a PTC element to reset to the low-resistance state depends on a variety of factors including the type of the element; mounting; configuration; ambient temperature; and duration of the trip event.
In one preferred embodiment of the present invention, the tripping device (5) is used in a electric heater (4) control circuit along with an electronic timer (2). In cold temperatures, a heating element (4) is provided to raise the manifold temperature as a necessary condition to crank the engine. To do this, the ignition switch is turned ON. The electric timer (2) is actuated once the ignition switch is turned ON. The current flows through the heater (4) circuit. The timer has a pre-set cut off time after which it cuts off the circuit.
If the engine fails to crank within the pre-set cut off time, the operator will put the ignition switch to the OFF position and re-switch it to the ON position. Under this circumstance (ref. to Figure 1), the electronic timer (2) will again cut off the circuit after duration of the preset cut off time. These iterations can continue till the operator decides to stop. Every cycle of the cut-off time results in continued heating of the wire harness thereby continually raising the wire harness temperature. If unchecked, this may lead to raising the wire harness temperature to a flash point. It may also deplete the battery, reduce its working life or damage it.
In the circuits as shown in figure-2, that are equipped with the novel tripping device (5) of the present invention, the novel tripping device comes into play only when the temperature of the device exceeds a certain value, preferably 100°C -120°C, more preferably 103°C -107°C. During each attempt to crank the engine, the temperature of the manifold, that of the tripping device, and also that of the wire harness increases. If the engine doesn't crank in the first attempt the operator tries to crank it again. Therefore, in case of normal automobile vehicles operated in cold climates, these temperature conditions are caused by successive attempts to
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crank the engine, without appreciable gap between any two consecutive attempts, whereby there is a temperature build up of all parts of the heater circuit. If an appreciable gap is left between any two attempts, it will reduce the temperature of the parts of the circuit including that of the tripping device (5) accordingly.
When the temperature rises to a certain level, the resistance of the tripping device increases abruptly to a very high value. At this stage, the current flow through the tripping device reduces suddenly to a very low value (for example, of the order 600 mA). Thus a residual small current is maintained through the circuit to keep the device effectively in a tripped state. This in turn stops current flow through the circuit and in turn the heating of other components of the circuit, notably that of the wire harness. The manifold heater (4) doesn't get heated up under the residual current state.
The device (5) remains in the effectively tripped state, the residual current will maintain the temperature of the device with a tripping range such that the device remains tripped. When the supply of the residual current is cut off, for example when the ignition switch is turned off, the temperature of the tripping device will reduce gradually depending on the ambient temperature.
In absence of the novel tripping device (5) of the present invention, the temperature of the wire harness, after several consecutive attempts to start the engine, may reach a hazardous level. In such instances, any further attempts to crank the engine will only exacerbate the matters, however, the timer device will not intervene in any sense in such continued cranking attempts. In worst situations this may lead to fire and other damages as listed above. The presence of the novel tripping device in the heater circuit will effectively override the timer after certain temperature conditions. This is the major advantageous feature of the present invention.
The present invention has another major advantage. In some situations the tripped state may be maintained for an indefinite period. This may happen in case where
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the ignition switch is left in "ON" position indefinitely coupled by a stuck relay in a timer. Here a continuous load current flows through the circuit until the novel device trips. The tripped state is now maintained until the ignition switch is turned "OFF" or power (battery) connection removed.
In case of a short circuit in the heater circuit, a heavy inrush current trips the device instantly in case of both manually operated circuits and those with timers. The tripped state is maintained until the short circuit is rectified.
In both the cases, the absence of the novel device in the circuit would lead to various damages depending on the safety measures in place. For example, in case of another tripping device such as a fuse, the fuse will need replacement. In many situations where the fuses used in circuitry are non-standard or not in compliance with design, there is a serious risk that the wire harness may provide a channel for a much higher current, such as a few hundred amperes, in case of a short circuit. The presence of the novel tripping device will mean the circuit will open instantaneously thereby not permitting the current flow of such high value. This will advantageously ensure the safety of the system.
The circuit incorporating the device of the present invention was tested for tripping of the device at -30°C. For this purpose the device was kept in a cold chamber with the other parts of the circuit maintained at the ambient temperature of 27°C. A current of 52 A was passed through the circuit. The device tripped at 180 seconds from the start of current flow. A residual current of 600mA flows through the circuit immediately after tripping.

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