1. Field of the Invention
This is a National Stage entry of International Application PCT/1B03/03408, with an international filing date of Jul. 30, 2003, which was published under PCT Article 2 1(2) as WO 2004-0 15839 Al, and the complete disclosure of which is incorporated into this application by reference.
The present invention refers to a system for protecting the battery of a vehicle.
2. Description of the Related Art
Some vehicles are equipped with at least a battery, in order to allow for the ignition of a respective motor, as well the supply, also with the motor off, of certain electric equipments of the vehicle (such as position lights, courtesy lights, emergency lights, a door-lock system, an anti-theft system, etcetera); the vehicle is usually equipped with an alternator, actuated by the motor and operative for supplying an electric current for recharging the battery.
It may happen into practice that, with the motor off, a given electric load of the vehicle remains supplied for a given time, being sufficient for lowering the level of electric energy of the battery below the minimum threshold necessary for carrying out the ignition of the vehicle's motor; such a circumstance may happen, for instance, when the vehicle's lamps are unintentionally left switched on for a long period of time.
In order to avoid such a disadvantage, and therefore allow the battery to keep a minimum charge threshold being sufficient for allowing motor ignition, there have been proposed proper devices operating for disconnecting in an automatic way the battery from one or more associated electric loads, should the charge state of the battery tend to fall below a predefined safety level.
A device of the indicated type is described, for example, in U.S. Pat. No. 4,902,956, which comprises a control circuit capable of detecting the state of charge of the battery and consequently control a solenoid, the latter being operative for causing commutation to the open position of an electric contact, in order to isolate the battery from the electric loads of the vehicle. In such a solution, the commutation of the contact in the closed position has to be done manually, by means of a respective mechanical push-button. Such a solution is scarcely efficient and uncomfortable for a user which, following the safety intervention of the device, will be forced to open the bonnet of the motor vehicle in order to reach the aforesaid manual actuation device.
Document U.S. Pat. No. 5,089,762 describes a similar safety device wherein the disconnection contact of the battery is actuated towards the open position by means of a small electrical drive. The detecting and control circuit of the device also comprises means for detecting an attempt by the user to start the vehicle; in the case in which, following the safety intervention, such a start attempt is detected, the control circuit actuates the small drive in a sense being opposite to the previous one, so as to bring back the contact in the respective closed position, wherein the battery is connected to the electric loads of the vehicle. Such a solution, besides being complicated and critical, implies the provision of control means of the small electric drive actuating the contact, with the relevant additional costs; the small drive producing the device's intervention also causes a certain absorption of electric current and increases the overall dimensions of the device.
In the case of U.S. Pat. No. 6,249,106 the safety device comprises instead a plurality of electronic switches, which are configured for passing from a respective open condition to a respective closed condition, in the former the electric load being connected to the battery, whereas in the latter the electric load is disconnected from the battery. The electronic switches are controlled by a gate circuit, upon receiving a signal from a microprocessor which is part of the control and detecting circuit. The use of solid state switches, as in U.S. Pat. No. 6,249,106, is decidedly expensive and is a source of possible criticalities in the operation of the device, due to their intrinsic “fragility” and the high sensitivity to voltage peaks or short circuits, unless suitable expedients are foreseen, that however further increase the manufacturing cost.
The devices of the indicated type are also occasionally subjected to severe environmental conditions, and typically undergo high temperatures being present in the motor space and conditions of cold or of elevated humidity, for instance during winter, rain periods, etcetera.
The repeated thermal cycles or also the long exposure to a high level of heat can determine significant increases of pressure within the casing of the device, that it is usually hermetically sealed, with consequent mechanical stresses on the same and likely deformations or breakages; even if the casing it is theoretically hermetically sealed, humidity infiltrations may occur, above all in correspondence of the points in which the terminals for the electric connection of the device protrude out of the casing.
It must then be considered that, in the case of dead battery, vehicle's ignition must be carried out through an auxiliary battery which must be surely charged, or through a workshop starter; under such circumstances, the auxiliary battery or the starter must be connected in parallel to the discharged battery of the vehicle, by means of power cables usually having clamp terminals. Such an operation is often uncomfortable, above all because of the difficulty of connecting one of said power cables to the positive polarity of the discharged battery.