How Does The Cummins PT Injector and Drive Mechanism Work?

The Cummins PT fuel injection pump fuel supply system was first used in the development of Cummins diesel engines. As the regulating elements of the system are pressure and time, it is called the PT fuel injection pump fuel supply system. Its working characteristic is to adjust the fuel supply based on pressure and time changes to meet the requirements of various working conditions of the diesel engine. This article introduces the working principle of Cummins PT fuel injector and its driving mechanism from the perspective of PT fuel injector driving mechanism and the working process of PT fuel injector.

1. PT fuel injector drive mechanism. The PT injector drives cam 6 on the camshaft of the valve mechanism, and the liquid wheel on the follower arm 7 rolls on the contour of cam 6. The rotation of cam 6 causes the follower arm 7 to swing and push the push rod 4. Then, by adjusting screw 1, the rocker arm 3 is pushed, and the rocker arm presses down on the injector plunger 9 while compressing the spring 10; The cam rotates once to complete a working cycle, and the plunger moves back and forth once.

The cross-sectional profile of the PT injector drive cam consists of a large radius arc (called a base circle), a small radius arc, and two transition curves. When the roller of the follower arm contacts the small radius curved surface of the cam, the fuel injector plunger is located at the upper end of the working stroke; When the roller of the follower arm contacts the large radius curved surface of the cam, the injector plunger is located at the lower end of the working stroke.

2. The working process of PT fuel injectors. The working process of the fuel injector can be explained by the action of the fuel injector plunger and the corresponding diesel generator piston, as well as the position of the contact between the follower arm roller and the fuel injector drive cam. The working process of the fuel injector for the Cummins NH-220 diesel generator.

During the intake stroke of the diesel generator, as the boom roller gradually disengages from the large radius arc surface of the cam, it rolls towards the small radius arc surface and begins to swing downwards. The fuel injector plunger rises under the action of the spring, and when the piston reaches 44 ° below the top dead center, the metering hole of the fuel injector opens. Fuel flows into the metering chamber inside the conical seat of the fuel injector, and fuel metering begins.

As the cam rotates, the follower arm rolls over the transition surface of the cam and rolls on the small radius arc surface of the cam, reaching the lowest position. The fuel injector plunger stays at the highest position when it goes up, and the fuel continues to flow into the fuel injector metering chamber.

When the piston reaches 28 ° before the top dead center, the fuel injector plunger closes the metering hole, and the fuel no longer flows into the metering chamber, and the metering is completed. The fuel metering starts at 44 ° of the intake stroke and ends at 28 ° before the top dead center of the compression stroke, with a total crankshaft angle of 288 °. During the compression stroke, when the piston reaches the top dead center at 22.5 °, the fuel injector begins to inject fuel.

When the piston reaches the top dead center of compression at 18 °, the roller rises along the camshaft profile to the highest position, while the fuel injector plunger drops to the lowest position, at which point the fuel injection ends.

The fuel injection process continued with a 40.5 ° crankshaft angle. The contour of the cam is concave by 0.36mm and enters the large radius curved surface of the cam. The fuel injector plunger remains at this height after being slightly raised, until the crankshaft turns 44 ° after the top dead center of the intake stroke, starting the next working cycle. The working process of different types of PT injectors varies, but their basic principles are the same.

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