An improved protection system for a battery pack mounted between the passenger cabin floor panel of an electric vehicle and the driving surface is provided, the system utilizing a ballistic shield mounted under the electric vehicle and interposed between the battery pack enclosure and the driving surface, where the ballistic shield is spaced apart from the enclosure bottom panel. A layer of a compressible material is interposed between the ballistic shield and the battery pack enclosure.
BACKGROUND OF THE INVENTION A large percentage of the world’s vehicles run on gasoline using an internal combustion engine. The use of such vehicles, more specifically the use of vehicles which rely on fossil fuels, e.g., gasoline, creates two problems. First, due to the finite size and limited regional availability of such fuels, major price fluctuations and a generally upward pricing trend in the cost of gasoline are common, both of which can have a dramatic impact at the consumer level. Second, fossil fuel combustion is one of the primary sources of carbon dioxide, a greenhouse gas, and thus one of the leading contributors to global warming. Accordingly, considerable effort has been spent on finding alternative drive systems for use in both personal and commercial vehicles.  Electric vehicles, due to their cleaner and more efficient drive systems, offer one of the most promising alternatives to vehicles that use internal combustion drive trains. To be successful, however, an electric vehicle must meet consumers’ expectations relative to performance, range, reliability, lifetime and cost. These expectations, in turn, place considerable importance on the design, configuration and implementation of the electric vehicle’s rechargeable batteries.  In a typical electric vehicle, either an all-electric or hybrid vehicle, the battery pack is mounted to the vehicle’s floor in a location intended to be as unobtrusive as possible. For example, in U.S. Pat. No. 7,427,093, issued 23 Sep. 2008, the battery pack is mounted to the vehicle floor panel, under the front seat. The disclosed system includes a protective member, for example attached to the battery pack itself, which is shaped and positioned to protect the battery pack and the wiring harness from possible damage by passengers in the rear seat.  U.S. Pat. No. 7,717,207, issued 18 May 2010, discloses an alternate battery pack mounting structure that is intended to minimize battery pack damage in the event of a vehicle collision. As disclosed, the battery pack is mounted to the rear portion of the vehicle frame, the frame including a deformable portion that deforms in an up-down direction when an impact load is applied in a longitudinal direction. The battery pack is fixed to the frame in such a way that it will move relative to the deformable portion when the deformable portion deforms under load, thus minimizing the transfer of load energy to the battery pack and allowing the shape of the pack to be maintained during a collision.  U.S. Pat. No. 8,037,960, issued 18 Oct. 2011, discloses an alternate battery mounting structure designed to minimize battery pack damage in the event of a vehicle collision. As disclosed, the battery pack structure is mounted to the rear side of the rear vehicle seats using bolts/screws that are designed to break and allow the battery pack to detach and move when the vehicle is in a collision.  Although the prior art teaches a variety of techniques for mounting large battery packs within an electric vehicle, what is needed is a battery mounting system that fully integrates the battery pack enclosure into the vehicle in such a way as to take advantage of the pack’s rigidity and strength, while still protecting the battery pack from accidental damage and minimizing the effects of the battery pack on vehicle occupant comfort and safety. The present invention provides such a system.
SUMMARY OF THE INVENTION The present invention provides a system for protecting a battery pack mounted to an electric vehicle, the system utilizing a battery pack enclosure that includes an enclosure top panel, an enclosure bottom panel, and a plurality of enclosure side members, where the battery pack enclosure is configured to hold a plurality of batteries, and where the battery pack is mounted between the passenger cabin floor panel and the driving surface. The system further includes a ballistic shield mounted under the electric vehicle and interposed between the battery pack enclosure and the driving surface, where the ballistic shield is spaced apart from the enclosure bottom panel by at least 5 millimeters; alternately, by at least 10 millimeters; alternately, by at least 15 millimeters; alternately, by at least 25 millimeters; alternately, by at least 35 millimeters; alternately, by at least 50 millimeters. The ballistic shield may be fabricated from aluminum, an aluminum alloy, steel, fiberglass, a carbon fiber/epoxy composite, and/or plastic. A layer of compressible material is interposed between the ballistic shield and the battery pack enclosure, where the compressible material may deform in an elastic manner, or in an inelastic manner, upon compression. The compressible material layer may be fabricated from foam or plastic. The compressible material layer may be shaped, for example with a plurality of projections and a plurality of dips (e.g., egg crate shaped).  The battery pack enclosure may be substantially airtight; may be fabricated from an aluminum, aluminum alloy or steel; may have the enclosure bottom panel welded, brazed, soldered or bonded to the plurality of enclosure side members; may have the enclosure top panel bolted to the plurality of enclosure side members; may be positioned between the front and rear vehicle suspension assemblies and mounted between, and mechanically coupled to, vehicle structural members (e.g., rocker panels) located on either side of the vehicle; and may include a plurality of cross-members that transverse the battery pack enclosure and segregate the batteries into groups of batteries.  A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.