Abstract:
Autorickshaws, known as Keke Marwa in Nigeria, were designed such that clutch and gear change levers were mounted on the same steering handle, making gear change strenuous for the drivers. Research efforts on autorickshaws have centred on alternative fuel sources and exhaust characteristics with little consideration for the transmission system which eliminates the strenuous driving condition. This study was therefore designed to investigate the performance of a Continuously Variable Transmission (CVT) system for an autorickshaw engine to eliminate the stress in gear change.
An autorickshaw engine with cubic capacity of 145.55 cm3, speed and power rating of 6000 rpm at 8.5 kW equipped with a manual transmission (MT), and a 250 cm3 retrofitted CVT unit was selected. A test rig equipped with tachometer and dynamometer was used to measure the performance of the MT and CVT fitted engines under varying load conditions: No Load (L0), Low Load, 120 Watt (L1), Medium Load, 800 Watt (L2), High Load, 920 Watt (L3) and Overload, 1600 Watt (L4). Output speed, output power, output torque and the fuel consumed for the drive cycles were determined using standard procedures. The drive cycle was defined as running the engine through all the gear ratios. Data were analysed using descriptive statistics and ANOVA at α0.05.
The output speeds of MT at L0, L1, L2, L3 and L4 were 54.96±23.04, 53.74±23.19, 53.09±22.89, 51.09±23.32, 40.74±16.40 ms-1, respectively. The output speed of CVT at L0, L1, L2, L3 and L4 were 177.15±86.16, 169.22±72.52, 164.97±79.08, 162.75±74.34 and 158.28±63.87 ms-1, respectively. Speed variation was low for MT showing that the CVT responded better to high loads. Output power for MT at L0, L1, L2, L3 and L4 were 33.38±22.94, 30.09±22.27, 28.54±21.21, 26.20±18.56 and 24.26±13.96 Watt, respectively while the output power for CVT at L0, L1, L2, L3 and L4 were 54.40±17.97, 51.37±17.49, 47.84±14.80, 44.30±15.99 and 34.95±18.59 Watt, respectively. The CVT had a wider power range compared to MT, implying that it has higher capacity to withstand load. The output torque for MT at L0, L1, L2, L3 and L4 were 5.61±1.79, 5.51±1.77, 5.80±1.80, 5.79±1.42 and 7.37±1.41 Nm, respectively while the output torque for CVT at L0, L1, L2, L3 and L4 were 3.51±1.04, 3.21±0.56, 3.37±1.17, 3.07±0.86 and 1.87±0.81 Nm, respectively. The CVT required lower torque throughout its drive cycle than MT, allowing the engine do less work in overcoming load. Fuel consumed for the MT and CVT drive cycles was 0.17 and 0.032 litres/m, respectively. The CVT attained maximum speed of 242± 14.35 ms-1 in 6 seconds while the MT attained maximum speed of 79±14.33 ms-1 in 18 seconds for the various loading conditions. The MT and CVT retrofitted autorickshaw engine showed significant difference in output speed, output power and output torque.
The continuously variable transmission retrofitted engine showed significant improvement over the manual transmission in terms of fuel consumption, power range and also eliminated the stress associated with manual gear change.
Keywords: Autorickshaw, Power transmission, Engine performance
