Abstract:
An electronic fuel injection augmentation system and method for a turbocharged diesel engine compression braking system injects a predetermined volume of fuel into cylinders of an engine at a predetermined timing prior to the piston of the cylinder reaching a top dead center position. Combustion of such injected fuel increases cylinder pressure and engine braking. The increased pressure is transferred to the turbocharger of the engine thereby increasing intake air flow and engine braking as a result thereof.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to internal combustion engines, especially turbocharged diesel engines, and more particularly, to a system for electronic fuel injection augmentation of an engine compression brake and method for performing the operation wherein a small quantity of fuel is injected into the cylinders of an engine equipped with an electronically-controlled fuel injection system during the compression stroke but well in advance of top dead center, thereby raising cylinder pressure during compression and also increasing energy to the turbocharger, inherently increasing boost pressure. Upon increasing of boost pressure, braking power would increase a corresponding amount. 
     THE PRIOR ART 
     The Cummins U.S. Pat. No. 3,220,392 discloses a vehicle engine compression brake, including a fuel control system wherein fuel supplied to the engine cylinders is automatically shut off when braking or coasting, converting the engine into an air compressor. 
     Also, the Pitzi U.S. Pat. No. 5,012,778 discloses an externally driven compression release retarder for use on an engine equipped with an electronically-controlled hydraulic unit injector system. In this system, when the retarder is in operation, fuel supplied to the cylinder is shut off. 
     As will be described in greater detail, the system of the present invention differs from those previously proposed by adding, rather than restricting, fuel to greatly increased the braking potential. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a primary object of the invention to provide an internal combustion engine equipped with a compression brake with increased engine braking potential. 
     It is a further object of the invention to provide an improved compression braking system for use in an electronically-controlled fuel injection system which increases engine braking power. 
     These and other objects are specifically met by the compression braking system of the present invention wherein the electronically-controlled fuel injection system of a diesel engine operates to inject a small quantity of fuel into the cylinders of the engine well in advance of top dead center on the compression stroke, raising cylinder pressure during compression and increasing energy to the turbocharger, inherently increasing boost pressure and braking power. A conventional engine braking device opens the exhaust valve of the cylinder at about top dead center to relieve the compression in the cylinder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become more apparent upon perusal of the detailed description thereof and upon inspection of the drawings in which: 
     FIG. 1 is a schematic diagram of a turbocharged diesel engine equipped with a compression brake and the electronically controlled fuel injection system and illustrates an engine cylinder with the piston approaching a top dead center position and a shot of fuel being injected into the combustion chamber according to the teachings of the present invention; 
     FIG. 2 illustrates the system of FIG. 1 with the piston at the top dead center position; and 
     FIG. 3 is a graph comparing useable engine braking cylinder pressure with and without the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1 and 2 in greater detail, there is illustrated therein one of a plurality of cylinders 26 of an internal combustion engine, preferably a turbocharged diesel engine 10, equipped with an improved engine compression brake system in accordance with the invention. Each cylinder 26 has a reciprocating piston 28 therein which has at least a compression stroke wherein the piston is travelling upward in the cylinder 26 toward a cylinder head 29, a top dead center position wherein the piston is no longer travelling upward, and a power stroke wherein the piston is travelling downward in the cylinder. 
     The engine 10 is equipped with an electronic control module 16 which is a microprocessor programmed to control the operation of the engine fuel injection system in response to a plurality of sensors. More particularly, the engine 10 is provided with a hydraulically-operated, electronically-controlled unit injector fuel system of the type illustrated in U.S. Pat. No. 5,245,970, although any electronically-controlled fuel injection system could be used, and a conventional engine compression brake system, for example, the compression brake shown in Pitzi U.S. Pat. No. 5,012,778, both of these patents being incorporated herein by reference. 
     An accelerator pedal sensor switch 12 and a dashboard mounted compression brake enabling switch 14 are electrically connected to the electronic control module 16 as are a coolant temperature sensor 18, a pressure sensor 20 which senses the pressure in the intake manifold 19, and an engine speed sensor 22, which senses the speed of the crankshaft 21 and its rotational position. The electronic control module 16 is connected to a fuel injector 25 for the engine cylinder 26 and controls, in accordance with its programming, the timing and amount of fuel injected into the combustion chamber 24 defined between the reciprocating piston 28 and the cylinder head 29. 
     As is known in the compression brake art, a compression relief device 32, which may be a hydraulically-actuated piston whose operation is also controlled by the electronic control unit 14 through a hydraulic valve (not shown) as shown in the aforementioned Pitzi patent, is disposed to contact and open an exhaust valve 30 of the cylinder at or about the point when the piston 28 reaches its top dead center position at the beginning of the power stroke, provided that the accelerator pedal switch 12 senses an idle condition and the compression brake switch 14 is turned on. Activation of the compression relief device 32 may be also be accomplished through any one of several known methods. 
     As indicated above, the engine 10 is turbocharged in a conventional manner with a turbine end of turbocharger 34 being fluidly connected through exhaust valve 30 to the combustion chamber 24 and a compressor end of the turbocharger 34 being connected to the intake manifold 19. 
     In accordance with the invention, the electronic control unit 16 is further programmed to increase the braking power of the compression brake system. With the switch 14 activated and the accelerator pedal switch 12 sensing an idle condition of said engine (before the switch 14 is activated) so that no significant amount of fuel is injected into the cylinder during the power stroke, and the temperature of the engine coolant above a predetermined level, to prevent misfiring, the electronic control module 16 senses the pressure in intake manifold 19 and the engine crankshaft 21 speed and position and accesses empirically determined lookup tables stored in the memory of the electronic control module to establish the specific amount of fuel to be injected by the fuel injector 25 and the particular time for this injection event to occur. More specifically, the electronic control module commands the fuel injector to inject a small predefined quantity of fuel, based on the intake manifold pressure and engine speed, at a predetermined timing in advance of top dead center based on the engine speed such that combustion of the injected fuel occurs before the cylinder piston 28 reaches its top dead center position, as shown in FIG. 2, while the timing is not so early that the engine misfires. The increase in pressure within the combustion chamber 24 of the cylinder 26 created by combustion of the small amount of fuel before top dead center increases the braking power required to compress the excess combustion pressure created. 
     At or about the point when the piston 28 reaches its top dead center position, the exhaust valve 30 is opened by the conventional compression relief device 32 and the energy of the compressed air plus the additional energy created by the pre-top dead center combustion is routed to the turbocharger 34 which in turn further compresses the intake air. 
     FIG. 3 shows the methodology of the system 10 in graph form, and shows a significant increase in cylinder compression brake pressure which may be produced by the addition of the pre-top-dead-center combustion of the present invention. The addition of the small quantity of fuel as described above should not only increase the cylinder pressure due to its combustion but also increase the engine&#39;s air flow by transferring the energy of combustion to the turbocharger 34. This increased air flow will result in an increase in compression work, increasing braking power. 
     As described above, the invention provides a number of advantages, some of which have been described above and others of which are inherent in the invention. It will be evident to those of ordinary skill of the art in view of the foregoing description that various modifications may be proposed to the embodiment described without departing from the inventive teaching herein. Accordingly the scope of the invention should only be limited as necessitated by the accompanying claims.