Gear Ratios Strategy of PROTON Waja CNG-DI Vehicle for Improved Performance

  •  B. B. Sahari    
  •  Hamzah Adlan    
  •  S. V. Wong    
  •  A. M. Hamouda    


A 1597cc gasoline CamPro engine was modified to adapt a Direct Injection (DI) technology that uses Compressed Natural Gas (CNG) as a fuel to form Compressed Natural Gas Direct Injection (CNGDI) engine. The modification includes increasing the compression ratio, redesigning the piston crown and cylinder head and a new engine control systems. These changes resulted in engine performance characteristics which is very different from its gasoline origin. This CNGDI engine is to be used with PROTON Waja vehicle body. Due to this change in the characteristics, the transmission systems utilizing an existing gear ratio combination, appears to be unsuitable, particularly for use in automatic transmission. Therefore, new gearbox with appropriate transmission matching needs to be developed. A computer based algorithm was developed for the purpose of predicting the PROTON Waja’s vehicle dynamic performance when CNGDI engine is used. The parameters being considered are maximum speed, acceleration, and elapsed time and these were optimized depending on the engine characteristics such as power, torque, gear ratios, and vehicle design parameters. The results recommended that the gear ratios of 3.58, 1.95, 1.34, 0.98, 0.8 and 4.33 for first, second, third, fourth, fifth and Final Drive (FD) respectively were the most suitable.

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