Transcript
Camshaft revamp brings savings and clean air Cleaner, more powerful and economical diesel engines may soon be available with the introduction of camless engine technology. Kondinin Group research engineer Josh Giumelli reviews the new hydraulic valve actuator design. eplacing the traditional engine camshaft design with electronically controlled hydraulic valve actuators is improving engine performance, resulting in cost savings and cleaner air. A camshaft is an essential part of any four-stroke petrol or diesel engine, opening and closing the inlet and exhaust valves at specific times. But the new 530E diesel engine recently unveiled by the International Truck and Engine Company features electronically controlled hydraulic valve actuators (see Figure 1). This development provides unlimited control over valve timing and allows designers to optimise running characteristics to improve power, economy and emissions. The manufacturer claims a torque improvement of up to 40 per cent at clutch engagement and reduced emissions of about 50% compared with the cleanest engines currently produced. The camshaft in a four-stroke engine is driven at half the speed of the crankshaft by either gears, chain or belt drive. This ensures the valves open and close every two cycles of the piston. Lumps on the camshaft (called lobes) drive followers up and down, which in turn open and close the valves through a series of linkages. With the trend toward multi-valve engines (more than two valves per cylinder) the complexity of the valve train is increasing, along with the drive power required. Overhead camshaft engines reduce valve train power losses and associated noise but do not provide the flexibility of the camless design.
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Variation on a theme The camless design is similar in operation to the common rail fuel system (see Farming Ahead, No 99, pages 28–29), which is also fitted to the new engine. The rail fuel system uses electronic solenoid valves to direct fuel to individual injectors from the common rail, which acts as an accumulator of high-pressure fuel. It has the advantage over conventional injection systems in that injection timing is electronically controlled and can be mapped over the engine’s speed range to optimise power and economy and reduce emissions. The camless engine is an extension of the rail fuel technology, offering the same benefits of variable, electronically controlled timing in the valve train. Solenoids above each valve direct high-pressure oil to valves to small hydraulic cylinders. When the solenoid opens, FARMING AHEAD No. 117 - September 2001
FIGURE 1 The camless engine Conventional diesel engine Rocker
Camless diesel engine Inlet–outlet High valve pressure oil in
Valve
Injector
Pushrod
Camshaft
Source: International Truck and Engine Company.
high-pressure oil fills the cylinder and opens the valve. To close the valve, the oil is simply drained away from the cylinder. Camshaft, pushrods, rockers, timing belts or gears are not required, which can significantly reduce the weight and size of an engine. Electro-hydraulic valve actuation offers engine designers total control over valve timing as valve opening and closing can be varied over the engine’s entire speed range, instead of only achieving optimum performance at one particular speed as has been the case.
Driving benefits The manufacturer claims camless technology will improve the ‘driveability’ of diesel engine vehicles, providing smoother and higher acceleration. Engine compression braking is also improved. When decelerating in a truck, the common rail fuel system can stop fuel to the cylinders and the engine will act as an air compressor. The inlet valve is opened to allow a fresh charge of compressed air, slowing the vehicle. At the end of each stroke the exhaust valve is opened to expel the compressed air. As this can occur in each cycle (instead of every second cycle), engine braking is twice as effective and brake shoe wear is reduced.
Cylinders also can be stopped (‘idled’) without any power-robbing compression strokes occurring, as the valve train can hold the valves open in unused cylinders. This feature would save fuel in trucks returning without a load. It also would be ideal in larger tractors, where cylinders could be switched off for light work, saving fuel and exhaust emissions and reducing cylinder glazing caused by prolonged running at light loads.
Reliability Improving the reliability of the valve train is not an issue when these components in a conventional engine outlast bearings and piston rings by several times. But gradual wear over a long period will affect engine performance and could go unnoticed. The electro-hydraulic control enables the valves to be ‘cushioned’ as they are turned off, avoiding the harder shutting of conventional valves and prolonging the life of valves and valve seats. Noise is also significantly reduced.
About the author Josh Giumelli is an engineer with the Kondinin Group's research team, based at Perth, Western Australia. Contact him on
[email protected] or phone (08) 9478 8313. 19
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