Fuel injection systems

Claim 1

A fuel injection system for supplying fuel to internal combustion engines, the system comprising an accumulator in which fuel is stored at a high pressure, pump means for charging the accumulator with fuel, a piston slidable within a cylinder, a fuel outlet from one end of the cylinder, said fuel outlet in use communicating with the inlet of an injection nozzle of the engine, valve means operable to place the other end of the cylinder in communication with said accumulator when it is desired to deliver fuel to the engine, said valve means when open allowing fuel to flow from the accumulator to said other end of the cylinder to cause displacement of said piston thereby to expel fuel from said one end of the cylinder, a stack of piezo electric crystals arranged when energised to generate a control pressure which is applied to a second piston forming part of said valve means to operate said valve means, an electrical control network for controlling the operation of said stack of crystals in timed relationship with the associated engine, said valve means comprising a second cylinder, said second piston being slidably located in said cylinder, a valve head connected to said second piston by a portion of reduced cross sectional area as compared with the piston, a valve seating for co-operation with said head, an outlet from said second cylinder intermediate the piston and the valve head, said outlet being connected to said other end of said first mentioned cylinder, said valve head being exposed to the pressure of fuel within the accumulator so that the valve head is forced onto the seating by the pressure of fuel within the accumulator, a third cylinder, a third piston slidable within said third cylinder, said third piston engaging said second piston, a fourth cylinder and a fourth piston within said fourth cylinder, said fourth piston engaging said third piston and at its end remote from said third piston being subjected to the fuel pressure within said accumulator, the area of said second and fourth pistons being substantially equal and also substantially equal to the seat area of the valve head, the area of said third piston being less than that of the fourth piston, said control pressure being applied to the presented faces of said second and third pistons and means for supplying a backing pressure to the presented faces of said third and fourth pistons, the control pressure when the stack of crystals is energised, being higher than said backing pressure but falling to a value less than the backing pressure when the crystals are de-energised, the arrangement being such that upon energisation of the crystals, the valve head will be moved away from the seating to permit flow of fuel from the accumulator to said first mentioned cylinder.