Conveyor having self-propelled carriers with a first motor for high speed driving and a second motor for low speed driving

A conveyor comprising a plurality of self-propelled carriers adapted to run along a rail,

• the rail having horizontal portions and a gradient portion therebetween, at least one horizontal portion having a high-speed running portion wherein the carrier is adapted to run at a high speed and a low-speed running portion wherein the carrier is adapted to run at a low speed, a first drive bearing surface facing upward provided at the rail, a rack having a plurality of teeth facing downward provided at the gradient portion of the rail, and a friction roller bearing surface facing downward provided at the low-speed running portion;
• each carrier having a first electric motor, a first drive wheel driven by the first electric motor and rolling on the first drive bearing surface, a second electric motor, a gear driven by the second electric motor for engagement with the teeth of the rack of the rail, and a friction roller driven by the second electric motor together with the gear for pressing contact with the friction roller bearing surface of the rail;
• the first drive wheel driven by the first electric motor and rolling on the first drive bearing surface driving the carrier at a high speed at the high-speed running portion of the rail, the friction roller driven by the second electric motor and in pressing contact with the friction roller bearing surface driving the carrier at a low speed at the low-speed running portion of the rail, and the gear driven by the second electric motor and engaged with the teeth of the rack driving the carrier at a low speed at the gradient portion of the rail.