System for the storage of electrical energy for a vehicle with electric propulsion

A system for the storage of electrical energy for a vehicle with electric propulsion; the storage system presents: at least one group of chemical batteries, which are arranged aligned with one another and each of which presents an upper wall, which is provided with a pair of electrical terminals and with a safety valve, and a lower wall, which is parallel and opposite to the upper wall; a container, which houses the group of chemical batteries; a relief duct, which rests against the upper walls of the chemical batteries and presents, for each safety valve, a corresponding opening, which is coupled to the safety valve; and a cooling element, which is parallel and opposite to the relief duct and rests against the lower walls of the chemical batteries.

RELATED APPLICATION

This application claims the benefit of priority, under 35 U.S.C. §119 to Italian Patent Application Serial No. BO2012A 000466, filed on Sep. 4, 2012, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a system for the storage of electrical energy for a vehicle with electric propulsion.

PRIOR ART

Currently, a system for the storage of electrical energy for a vehicle with electric propulsion comprises a plurality of chemical batteries which are arranged beside each other to form a pack, and are generally electrically connected to each other in parallel.

Each chemical battery comprises at least one electrochemical cell and an outer shell, which houses the electrochemical cell by keeping the electrochemical cell compressed, and is made of a material with a high mechanical strength (typically a metal material such as steel or reinforced aluminium). The use was recently proposed of Li-Ion electrochemical cells which have one of the best power-weight ratios, no memory effect, and a slow loss of charge when not in use. However, a Li-Ion electrochemical cell is subject to a destructive phenomenon called thermal shift which is started by a short circuit caused by the decomposition of the individual components of the electrochemical cell (typically following production defects), and stands out for highly exothermic reactions which cause a sudden and high increase in temperature and pressure (in the case of thermal shift the temperature in the outer shell may quickly reach several hundreds of degrees). Hence, to prevent a violent explosion in the case of the thermal shift of a chemical battery, there is a need to relieve the pressure/temperature through a safety valve which is obtained in the outer shell of the chemical battery and opens autonomously; once the safety valve has opened autonomously due to the effect of the thrust of the pressure inside the outer shell, so-called venting consisting of flames, high-temperature gas and melted lithium leaks out of the safety valve. Obviously, there is a need for the storage system to be provided with relief ducts, which connect all the safety valves of the chemical batteries to (at least) one exhaust opening which opens outside the vehicle: thereby, the relief ducts collect the venting and channel the venting outside the vehicle to bring the venting far from the other chemical batteries which are therefore protected (it is indeed imperative to prevent a chain reaction in which the thermal shift of one chemical battery extends to the other adjacent chemical batteries which are struck by venting).

Furthermore, the functioning (both when charging and discharging) of the chemical batteries is exothermic, i.e. determines the generation of heat which is to be adequately expelled to prevent overheating of the chemical batteries. Hence, there is a need for the storage system to be provided with a cooling system which may constantly remove part of the heat generated in the chemical batteries. For example, the cooling system could comprise a cooling plate, which is kept pressed against a wall of the chemical batteries and is thermally connected to a cooling system to expel the heat generated by the chemical batteries.

As it is to comprise both the relief ducts and the cooling system (naturally, in addition to the electrical connections), the storage system is relatively cumbersome and heavy and therefore housing it is more complex inside a vehicle with reduced spaces available for the storage system (particularly in a highly performing road vehicle in which an attempt is made to contain the dimensions to minimize aerodynamic resistance).

Patent Application US20110293974A1 and Patent Application US20120021260A1 describe respective systems for the storage of electrical energy for a vehicle with electric propulsion. Each of these systems for the storage of electrical energy comprises:

a group of chemical batteries, which are arranged aligned with one another and each of which presents an upper wall, which is provided with electrical terminals and with a safety valve, and a lower wall, which is parallel and opposite to the upper wall;

a container, which houses the group of chemical batteries;

a rigid element, which rests against the upper walls of the chemical batteries at the safety valves and presents, for each safety valve, a corresponding opening, which is coupled to the safety valve; and

a cooling element, which is parallel and opposite to the rigid element and rests against the lower walls of the chemical batteries, so as to be thermally coupled to the chemical batteries.

However, in the systems for the storage of electrical energy described in Patent Applications US20110293974A1 and US20120021260A1, a relatively frequent premature death (i.e. a breakdown which occurs well in advance of reaching rated life) can occur of certain chemical batteries.

DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a system for the storage of electrical energy for a vehicle with electric propulsion, which is free from the above-described drawbacks and at the same time is easy and affordable to embody.

According to the present invention, a system is provided for the storage of electrical energy for a vehicle with electric propulsion, according to what claimed by the accompanying claims.

PREFERRED EMBODIMENTS OF THE INVENTION

Numeral1inFIG. 1is a system1for the storage of electrical energy for a vehicle with electric propulsion.

The storage system1comprises a tubular parallelepiped container2having two larger lateral walls3(only one of which is shown inFIG. 1), two smaller lateral walls4(only one of which is shown inFIG. 1), and two open ends (upper and lower, respectively). By way of example, container2could be made of a thermally conductive and electrically insulating plastic material. Two groups5(only one of which is seen inFIG. 1) of chemical batteries6are housed inside container2, each of which consists of a plurality of chemical batteries6arranged in a row. As shown inFIG. 4, the two groups5of chemical batteries6are arranged one above the other, that is they are overlapping; furthermore, the two groups of chemical batteries6present an inverted orientation (opposite), i.e. the upper group5of chemical batteries6presents an upwards orientation and the lower group5of chemical batteries6presents a downwards orientation.

Each chemical battery6comprises at least one electrochemical cell, preferably Li-Ion, and an outer shell, which houses the electrochemical cell by keeping it compressed, and is made of a material with a high mechanical strength (typically a metal material such as steel or reinforced aluminium, but the use is not excluded of composite materials such as carbon fibre). According to what shown inFIG. 2, each chemical battery6is substantially parallelepiped in shape and presents an upper wall7and a lower wall8(not seen inFIG. 2) which are parallel and opposite to each other, a pair of larger lateral walls9(only one of which is seen inFIG. 2) which are parallel and opposite to each other, and a pair of smaller lateral walls10(only one of which is seen inFIG. 2) which are parallel and opposite to each other.

According to what shown inFIG. 4, the upper walls7of the chemical batteries6in each group5of chemical batteries6are arranged at the open ends of container2so as to be seen. The larger lateral walls9of the chemical batteries6are parallel to the smaller lateral walls4of container2, while the smaller lateral walls10of the chemical batteries6are parallel to the larger lateral walls3of container2. Following the opposite orientation of the two groups5, the lower walls8of the chemical batteries6of the upper group5of chemical batteries6are arranged close to the lower walls8of the chemical batteries6of the lower group5of chemical batteries6.

Each chemical battery6presents a pair of electrical terminals11which project from the upper wall7. Furthermore, each chemical battery6presents a safety valve12(i.e. a release or overpressure valve) which is arranged on the upper wall7between the two electrical terminals11. Each safety valve12is calibrated to open when the pressure in the chemical battery6exceeds a predetermined safety pressure; in other words, each safety valve12is a mechanical maximum pressure valve which opens when the pressure in the chemical battery6is too high to prevent a violent explosion of the chemical battery6. A Li-Ion electrochemical cell subject to a destructive phenomenon called thermal shift which is started by a short circuit caused by the decomposition of the individual components of the electrochemical cell (typically following production defects) and stands out for highly exothermic reactions which cause a sudden and high increase in temperature and pressure (in the case of thermal shift the temperature in the chemical battery6may quickly reach several hundreds of degrees). Hence, in the case of the thermal shift of the chemical battery6, there is a need to relieve the pressure/temperature by means of the safety valve12which opens autonomously, to prevent a violent explosion; once a safety valve12has opened autonomously due to the effect of the thrust of the pressure inside the chemical battery6, so-called venting consisting of flames, high-temperature gas and melted lithium leaks out of the safety valve12.

According to what shown inFIGS. 1 and 3 to 5, the storage system1comprises a pair of relief ducts13which are coupled to the corresponding groups5of chemical batteries6. Each relief duct13rests against the upper walls7of the chemical batteries6of the corresponding group5and for each safety valve12presents a corresponding opening14(clearly seen inFIG. 5) coupled to the safety valve12. Preferably, arranged around each opening14of the relief duct13is an annular gasket15(clearly seen inFIG. 5) which rests, in a sealing manner, against the upper wall7of the corresponding chemical battery6and around the safety valve12; the function of the annular gasket15is to seal the safety valve12to prevent blow-bys of the venting which leaks from the safety valve12. According to what shown inFIG. 1, each relief duct13is made of a rectilinear metal tube (or of another material with a high mechanical strength) which presents a closed end (blind) and an opposite open end which flows into a collecting chamber CC (common to both relief ducts13) through a coupling tube16(the relief duct13presents a constant cross section and is typically made by means of extrusion). When the storage system1is mounted in a vehicle, the common collecting chamber CC is connected to an exhaust opening which communicates with the outside environment (typically through the bottom of the vehicle) to expel any venting into the outside environment.

The function of each relief duct13is to collect and channel the venting to bring the venting far from the other chemical batteries6which are therefore protected (it is indeed imperative to prevent a chain reaction in which the thermal shift of one chemical battery6extends to the other adjacent chemical batteries6). Indeed, the venting generated by a chemical battery6which has gone into thermal shift is collected and conveyed by the relief duct13to be expelled outside the vehicle (and directly onto the surface of the road); thereby, the venting generated by a chemical battery6that has gone into thermal shift in no manner at all involves the adjacent chemical batteries6.

According to what shown inFIG. 1, each relief duct13is rigidly connected (restrained) to container2and in particular, is fixed to the upper edges of the smaller lateral walls4of container2. Preferably, each relief duct13is screwed to the smaller lateral walls4of container2by means of the screws17.

According to what shown inFIG. 4, storage system1comprises a parallelepiped cooling element18which is common to both groups5of chemical batteries6and is interposed between the groups5. In other words, the cooling element18is interposed between the two groups5of chemical batteries6so as to be resting on one side against the lower walls8of the chemical batteries6of the upper group5, and on the opposite side against the lower walls8of the chemical batteries6of the lower group5. Accordingly, the cooling element18is parallel and opposite to each relief duct13and rests against the lower walls8of the chemical batteries6, so as to be thermally coupled to the chemical batteries6. The cooling element18is thermally connected to an external cooling system to expel the heat generated by the chemical batteries6; according to what shown inFIG. 1, the cooling element18comprises a pair of pipes19which come out of a smaller lateral wall4of container2and are used to circulate a coolant inside the cooling element18.

Each relief duct13rests against the upper walls7of the chemical batteries6of the corresponding group5, is rigidly connected to container2and is shaped so as to press against the upper walls7of the chemical batteries6of the corresponding group5in order to apply a thrust to the chemical batteries6, which is perpendicular to the upper walls7and keeps the chemical batteries6pressed against the cooling element18. In other words, the two relief ducts13push the chemical batteries6of the corresponding groups5against the cooling element18so as to maximize the contact surface and therefore the heat exchange between the cooling element18and the lower walls8of the chemical batteries6.

The relief duct13comprises a plurality of pressing elements20, each of which is elastically deformable in a vertical direction which is perpendicular to the upper walls7of the chemical batteries6and transmits the thrust from the relief duct13to the upper walls7of the chemical batteries6. In the embodiment shown in the accompanying figures, the pressing elements20are arranged on opposite sides of the relief duct13(in essence, the pressing elements20are shaped like lateral “legs” of the relief duct13). Furthermore, in the embodiment shown in the accompanying figures, each pressing element20presses against the upper wall7of a single corresponding chemical battery6. According to what shown inFIGS. 3 and 5, each pressing element20projects from a lateral wall21of the relief duct13, which is perpendicular to the upper walls7of the chemical batteries6.

Each pressing element20comprises an outer body22, which is parallel and rests against the upper walls7of the chemical batteries6, and a connecting body23, which is inclined both with respect to the outer body22, and with respect to the lateral wall21of the relief duct13, and connects the outer body22to the lateral wall21of the relief duct13. By projecting from a lateral wall21of the relief duct13, each pressing element20has a given vertically direct elasticity (i.e. perpendicular to the upper walls7of the chemical batteries6) so as to elastically press (i.e. with a given “auto-adaptation” capacity) against the upper walls7of the chemical batteries6. The vertical elasticity (i.e. perpendicular to the upper walls7of the chemical batteries6) of the pressing elements20is important to uniformly distribute the thrust on all the corresponding chemical batteries6thus compensating for inevitable construction tolerances.

According to a preferred embodiment shown inFIG. 5, an insulating layer24, which is made of an electrically insulating material (preferably in TEFLON—polytetrafluoroethylene), is interposed between the pressing elements20and the upper walls7of the chemical batteries6(i.e. between the outer bodies22of the pressing elements20and the upper walls7of the chemical batteries6).

According to a preferred embodiment shown inFIG. 4, an insulating layer25, which is made of an electrically insulating and thermally conductive material, is interposed between the cooling element18and the lower walls8of the chemical batteries6of each group5.

System1for the storage of electrical energy described above has several advantages.

Firstly, system1for the storage of electrical energy described above is particularly lightweight and compact. Such a result is obtained due to the fact that one same component (i.e. the relief duct13) carries out two functions (therefore with apparent savings): its main function of connecting the safety valves12to the collecting chamber CC and further function of pushing against the upper walls7of the chemical batteries6of the corresponding group5to keep the chemical batteries6pressed against the cooling element18.

Furthermore, due to the presence of the pressing elements20, the thrust which is transmitted from the relief duct13to the upper walls7of the chemical batteries6is uniform (i.e. is equal for all the chemical batteries6); thereby, all the chemical batteries6present the same heat exchange with the cooling element18and hence are all cooled in the same manner. In other words, the cooling of the chemical batteries6is uniform due to the presence of the pressing elements20and therefore certain chemical batteries6are prevented from cooling worse than others, thus determining a thermal overload which can also cause a premature death (i.e. a breakdown which occurs well in advance of reaching rated life) of the chemical batteries6.

Finally, above-described system1for the storage of electrical energy is simple and affordable to make, because the relief duct13is easy to make by means of extrusion and is easy to fasten to container2by means of the screws17.