BACKGROUND

The inherent random variation of engine combustion from one engine cycle to another results in indicated mean effective pressure (IMEP) variations. These variations in IMEP cause a deviation in the normal motion of the engine about its axis, resulting in engine vibrations. This vibration is then transmitted to the vehicle body through the engine mounts, and ultimately felt as disturbances by the vehicle occupants. When the magnitude of the vibration is high, poor idle quality results.

With increasing quality demands by the customers, the idle quality issue is of major concern. It was necessary to find a solution that will improve idle quality by minimizing the effect of the noise factors in the field.

PROCESS

Instead of following the common one-factor-at-a time method, technically more efficient robust design methodology was used. Eight control factors were considered under customer usage conditions (engine mileage). Eighteen design configurations were tested for optimization. Fuel flow was the input signal and output response was pressure at the piston (IMEP).

BENEFITS

• Both objectives of the project, i.e., to apply the Taguchi/robust design methods to the idle quality problems and to improve the idle quality for the chosen application were accomplished.

• A 2.93-dB gain in S/N ratio was achieved, which was enough to produce a noticeable improvement in engine idle quality application.

• Improvement in the traditional quality indicator LNV (lowest normalized value) was 12%.

• A 14% increase in the efficiency was achieved, which resulted in an 8% increase in...