State of the Art In vehicles which can be fuelled by gas, the compressed gas is loaded into at least one cylinder placed on board the vehicle. The cylinders or containers for the compressed gas are made of either steel, aluminium, composite materials or other synthetic materials, and are usually equipped with a valve unit to enable loading of the gas under pressure and to control the flow of said gas towards the engine of the vehicle.

According to safety regulations in force in the field, each cylinder should be equipped directly or indirectly with a discharge unit suitable for automatically opening a release passage and exit for the gas into the atmosphere so as to avoid the cylinder exploding in the presence of a fire or however if the temperature around it tends to exceed, for some reason, a set temperature threshold.

In fact, according to the state of the technique, thermal safety devices have already been provided which associate with a cylinder as an automatic gas release, at least one, solid or non solid, heat sensitive element, which maintains its state up to a required safety temperature, e. g. about 90 to 120°.

The heat sensitive element can be housed in the valve unit of the cylinder or form a group of its own, positioned in one or more parts of the cylinder, in communication with the inside of the latter. At all events, the heat- sensitive element is positioned and enclosed in a chamber to close a discharge hole or conduit in communication with the inside of the gas cylinder, and modifies its state on reaching the preset safety temperature threshold, thus opening the gas discharge to empty the cylinder.

These thermal safety devices are certainly efficient when the heat source causing an anomalous rise in temperature, usually a fire onboard the vehicle, is either in direct contact with the unit enclosing the heat sensitive element or the gas cylinder. But there is also the possibility of the fire developing in zones which are distant from the cylinder or a wind or a physical obstacle prevents the heat from spreading to the cylinder. In this case the thermal safety device, that is the heat sensitive element, may not be reached or is actuated in delay, thus failing to remove potentially dangerous conditions quickly.

Moreover, there could be more than one compressed gas cylinder assembled on a vehicle, in which case, the fire will not necessarily come into direct contact with each of the cylinders, actuating the safety devices at the same time.

In this case, at least one of the cylinders could remain in the danger of explosion condition. In the attempt to avoid this situation, at present, walls separating the cylinders are used but without eliminating the possible danger.

Obiecs and Summary of the Invention The primary objective of this invention is to create the conditions for a timely intervention of the thermal safety device associated with compressed gas cylinders for fuelling vehicles as soon as any irreversible cause develops leading to an anomalous rise in temperature in any part of a vehicle equipped with gas equipment.

Another objective of the invention is to provide a thermal safety system for compressed gas cylinders or containers for fuelling vehicles, which can be actuated and therefore automatically come into operation even in the presence of anomalous sources of heat at a distance from the cylinders and reasons which tend to avoid the fire directly reaching the cylinders themselves.

These objectives and the implicit advantages deriving from them are achieved, according to the invention, by a safety device which includes, in combination with each compressed gas cylinder on a vehicle with an engine fuelled by gas, at least one gas discharge unit incorporating a heat sensitive element designed to change its state at a preset safety temperature to open a gas discharge conduit from the cylinder towards the external of the latter, and which has - at least one electric heating element associated with said heat sensitive element and connected with a normally open electric circuit, and - heat sensors positioned in different zones of the vehicle, each one supplying a read out of the temperature present in that part of the vehicle and commanding the closing of the electric circuit on said heating means to actuate it and cause the change in state of the heat sensitive element

so as to open the discharge conduit of the gas from the cylinder when, in at least one of said zones of the vehicle, the temperature reaches a preset safety limit threshold.

Advantageously, the assembly may also include a means for receiving and managing the signals arriving from the temperature sensors placed in various zones and close the circuit on the electric heating means if the read- out temperature of one of said sensors is above threshold.

Brief Description of Drawings Further details of the invention will become more evident in the continuation of this description made in reference to the enclosed, indicative and non-limiting drawings, in which: Fig. 1 shows a diagram of the safety device with two compressed gas cylinders; Fig. 2 shows one gas cylinder with two safety devices; Fig. 3 shows an example of a valve housing a plug fuse associated with an electric heating element.

Detailed Description of the Invention The diagram in Fig. 1 shows two compressed gas cylinders 11 which can be assembled on the same vehicle with a gas fuelled engine. Each cylinder 11 is equipped with a valve 12 housing a thermal safety device indicated generically by 13 and forming an automatic discharge unit of the gas from the cylinder.

The diagram in Fig. 2 shows a gas cylinder 11'which also has a valve 12 housing an automatic gas discharge unit and in addition another thermal

safety device 13'placed in a conduit 13"connected to the inside of the cylinder in a different part in respect to the deployment of valve 12.

Valve 12 is well known and does not require describing. When it houses the safety device 13, a condiut 14 is formed in the body of said valve, as can be seen in Fig. 3, so as to connect the inside of the cylinder 11 with a discharge passage 15. The safety device 13 is associated with this discharge passage 15 and includes, in the known way, a heat sensitive element 16 which will modify physically at a preset safety temperature, for example between about 90 to 120°C. The heat sensitive element 16 can be either a material in a solid state, but which fuses on reaching a safety temperature or a liquid or paste material in a capsule which breaks on reaching the safety temperature. As long as the heat sensitive element 16 remains in its initial state, it will act as a stop and obstruct the discharge passage 15 preventing the gas from discharging. When on the other hand it changes its state on reaching the preset safety temperature, it frees the discharge passage 15, permitting the release of the gas from the cylinder with the possible additional help of a small piston 17 in expelling the material making up the heat sensitive element.

When the thermal safety device 13'is associated with a conduit 13" connected to the cylinder, the heat sensitive element 16 is placed in a body or capsule so as to block the passage formed by the conduit itself.

In both cases, the heat sensitive element 16 is associated with an electric heating means 18 placed in an electric circuit 19 which is normally open and connected to a powering battery 20. The heating means 18 can be made up an electric heater or some other suitable means placed around or

however adjacent to the heat sensitive element and chosen on the basis of the mass of the latter. It must be powered continuously even when the vehicle is switched off, consequently the battery 20 to power it can be the one usually on board the vehicle or an auxiliary dedicated battery.

In addition, at least in some zones of the vehicle and possibly close to each cylinder 11 there are temperature sensors 21 which can be made up of heat probes or any heat sensitive electronic device each capable of sending a signal indicating the temperature in their respective part of the vehicle. The quantity and position of the heat sensors 21 can be chosen according to the type of vehicle, the location of the gas cylinders in the vehicle etc.

Each heat sensor 21 will be set up to provoke the closing of the electric power circuit 19 powering the heat sensitive element 16 of the heating means 18, when the temperature in the zone it controls, reaches a preset threshold as indicated above. But preferably, the heat sensors 21 can be connected and governed by an electronic controller 22-Fig. 1-able to elaborate the signals coming from each sensor and enable closing of the electric circuit 19 on the heating means 18 when at least one of said sensors signals an increase in temperature above the preset safety threshold.

The heat sensitive element 16 will then be heated so as to change its state and allow the gas to be discharged from the cylinder through the discharge passage 15, or the discharge conduit 13", not only when the cylinder is directly involved by an unwelcome increase in temperature, but also if and when a fault and irreversible increase in temperature is found which involves zones of the vehicle distant from the cylinder or cylinders positioned on the vehicle.

In the second case in fact, the electrically powered heating means 18 is actuated and causes a change in the state of the heat sensitive element 16 which leads to a discharge of gas from the cylinder as soon as one of the heat sensors 21 finds a temperature above the preset safety threshold.