Over the last few years there has been a significant increase in the popularity of electric cars. These vehicles are efficient, silent and do not pollute the air (at least where they are driven). In looking at the function of an electric car, there are several keys to the success of the electric technology. First and foremost, is the fact that the battery, inverter and electric motor have reached a level of efficiency and power density that allows a car to be driven several hundred miles between charges. Even with the weight of a battery, the weight of an electric car is about the same as a combustion engine car. The added battery mass is offset by weight savings in the engine and by simplifying the driveline. And finally, an electric car efficiently utilizes energy recovery with its brakes. All these factors put passenger cars in a “sweet spot” for electrification today.
Vehicles that are based on a truck chassis demand more from electrification than passenger cars. For these vehicles, the primary energy source must not only power the driving but also power the transportation of loads and the hydraulic functions, which can be significant throughout the day. This is the situation for automated side loader (ASL) refuse collection vehicles. A side loader can carry approximately 15,000 pounds of garbage and uses a hydraulic system to pick individual trash cans while compacting the load. The work of hydraulics becomes very significant considering that a truck normally collects between 1,000 and 1,500 trash can loads per day. In order for a fully electric vehicle to complete this amount of work, it must be powered by a very large battery. Besides being a significant cost adder, a large battery leads to a decrease in payload, which is the most important factor when it comes to material collection and transportation. Various fully electric automated side loaders have been built and tested as vehicle demonstrators. However, as of today, the electrification technology that is driving the success of electric passenger cars has not found commercial applications for this class of vehicles.
The electric hybrid solution is particularly attractive in machines that work with repetitive cycles and require a significant amount of power to move hydraulic functions. In traditional ASLs, the operator drives the machine and between stops collects the garbage cans by operating a hydraulic arm. While performing these functions, the packer continuously runs to compact the load inside the body. The collection of the trash cans happens while the truck is at idle and the pumps rotate at low speed. This operating condition is the opposite of ideal because the pumps and the engine produce the work at a very inefficient operating condition. Furthermore, the engine is loaded at idle and, in order not to stall it produces the traditional muffled noise, which also accompanies higher emissions.
A significant but simple improvement to this situation can be achieved by implementing an electric hybrid system for implement control. Here, the hydraulic pump(s) use a thru-drive configuration and are piggy-backed to a permanent magnet electric motor. This sub-assembly is mounted on the truck transmission using a traditional clutch-shift PTO. The electric motor is controlled via an inverter which derives power from a compact battery pack.
If you would like to learn more about Parker's Electric Hybrid System and the performance results when used on the ASL in a dense route, download the white paper "An Electric Hybrid System for Refuse Vehicle Applications." The white paper presents an in-depth description of the system and an energy mapping analysis applied to the specific case of an automated sided loader in a typical duty cycle.
Article contributed by Germano Franzoni, Ph.D., senior systems engineer, Parker Hannifin, Global Mobile Systems.