Fuel saving hydraulic systems
Mobile diesel engined road equipment.
Typical refuse, green waste recycling truck fitted with single body, twin bin lifts, compactor and ejector plate.
Vehicle comes to a halt, neutral selected, Roadside bins fitted to bin lift, automatic lift to empty bin into hopper. Hopper emptied by compactor. Refuse pushed up into body against back plate. When cycle completed, vehicle moves forward. When power switch is activated (automatically by action of bin placement or manually), engine revs increase into the green and will stay there until the loading cycle is completed.
Why constant high revving?
Fixed displacement gear or vane pump runs up to maximum flow. Excess flow dumped back to tank. Only when compactor body becomes full, and therefore compactor really working does the system require high pressure. Hydraulic pumps only create flow:- the speed at which actuators work. Resistance to flow creates pressure:- the grunt behind the push. Therefore, until the machine starts filling to capacity, flow is the main requirement.
The power of the diesel engine in the vehicle is dictated by the traction load requirement. As far as the hydraulic system is concerned it is well over powered. Fixed displacement pumps coupled directly to the engine (via the gearbox p.t.o.) are working moving hydraulic fluid all the time, but when not required by the compacting system dumps the fluid back to tank, drawing power from the engine and creating excess heat, even when driving on the road.
By replacing gear or vane pumps with variable displacement piston pumps and fine load-sensing technology, only the flow required to operate the system will be generated, allowing the engine to operate from a lower speed and will only be required to develop higher power as the compactor starts to struggle. When a fill cycle is completed, the pump will shut down delivery, and while still being directly connected to the engine, will draw hardly any engine power, therefore releasing more power to be available for traction.
Of all the vehicles to benefit in fuel saving from these hydraulic technology upgrades, refuse vehicles come top of the list, with an average 1000 fuel guzzling stop-start cycles per day. In Europe equipment is built to a price, always to the bottom line, to make a vehicle competitively priced against the competition, often without consideration of operating costs. However, it is the operator who has to fund the running costs, but by replacing the original hydraulic components when they reach the end of their service life, it is possible to lower the operating costs in fuel saving by as much as 25%. The fuel saving cost of just one year should finance the installation of this efficient hydraulic power system, with years of savings still to come, let alone the reduction of greenhouse gas emissions. With many vehicles being rebuilt and refitted within several years of manufacture, this is an ideal time to upgrade hydraulic systems. With the additional operating and maintenance costs incurred on Euro 6 vehicles, we will probably see many more quite serviceable but older vehicles being rebuilt for a longer operational life in an attempt to keep costs down.
In earlier diesel engines, an injector pump working similarly to a hydraulic pump supplied cylinder fuel injectors, delivering the required amount of fuel to each injector. While with this type of system we can control engine speed, we cannot change the power characteristics of the engine, which will be set up for road use.More modern diesel engines use common rail injection systems, which, while still injecting directly into the engine cylinder, work in a similar way to petrol injection systems, having electronically controlled injectors and managed by an Engine Control Unit (ECU). These ECU’s can be “remapped” to change engine power characteristics, so it is possible to run two systems together. One, to satisfy traction road power requirements when the vehicle is placed in gear, and a second to change the engine torque characteristics when placed in neutral to power the hydraulic system.As the development of this type of twin system is in its infancy, it is yet unclear how great the financial saving would be, against the installation costs.
For further information please contact Edward Holt email email@example.com
Tele 44(0)1634 364832