New technology in buses
New technology in buses
On a conventional hydraulically driven fan system, air is sucked from the outside of the bus through a charge air cooler with a hydraulic oil cooler alongside and then through a jacketed water filled radiator by a large fan driven by a hydraulic motor and controlled by a hydraulic control valve. AVID say this method traps debris within the system making it less effective. The debris becomes difficult to remove and the radiators are easy to damage. The system is also prone to hydraulic leaks.
With the AVID eFan micro hybrid system, air flows through a bank of high performance brushless DC electric fans, cooling a charge air cooler and a water radiator. There are usually six fans, four cooling the water system and two the charge air. Cooling the charge air cooler and the water radiator independently enables their temperatures to be more accurately controlled. The electric fans used are units specially designed for vehicle applications delivering 50% more airflow than the most efficient similarly sized units available commercially. They can be run in reverse, effectively as powerful blowers, to remove accumulated debris and keep the system running cleanly and efficiently. There is no hydraulic system so it can’t leak and doesn’t need cooling.
The system is controlled by an electronic controller connected to the vehicle’s CANbus system. It monitors the water temperature through a sensor in the radiator inlet and the charge air temperature through a sensor in the charge air cooler outlet. There are three functions available to the maintenance team on each system, a reversing switch that enables the fans to be run as blowers, a diagnostic connector port and a diagnostic lamp button.
A major difference between the hydraulic and electric systems is the energy required. When operating at full capacity, the eFan uses 3kW compared with a figure of around 20kW for a hydraulic system. On top of this, it only runs when needed and switches itself off when it isn’t. This ensures that engines operate at their optimum running temperature and also, because the fans do not operate when they are not needed in the early stages of a vehicle’s duty cycle, reduces the warm up time.
The absence of hydraulic fluid is a significant safety factor because, they claim, it is often a hydraulic problem that will start an engine bay fire or exacerbate one started in another way.
Another benefit from fitting an eFan is a reduction in problems with diesel particulate filters (DPFs). This is because additional soot is created when engines are not running sufficiently hot to optimise combustion. This soot collects in the DPF and the exhaust temperature is often not high enough to burn it off. As the eFan helps keep the engine running at its best temperature, less soot is created.
In more extreme cases of overcooling, it can be that overcooled coolant is released into the engine by the thermostat creating thermal shock which damages the power unit. Only running the fan when it is needed makes overcooling less likely and reduces instances of thermal shock.
Elucidating on the benefits of the eFan, typically, a bus radiator is designed to last a couple of years at most but the eFan is designed to last at least ten years and was essentially a fit and forget type system. A robust technology called bar and plate was used because, while the traditional tube and fin construction method was OK on trucks, it was less durable in bus applications. The eFan is designed to be robust for bus applications, which was hard. Although the eFan is more durable it is not heavier. The complete pack weighs 60-70Kg which is comparable to a conventional hydraulic pack. ‘We don’t have a heavy hydraulic fan and supporting framework,’ said Chris, adding, ‘because of this there is less vibration and less noise.’
Noise is increasingly important and here there are advantages to the eFan in two more respects. Firstly, there is a kerbside quiet feature that has been developed whereby at below 5kmh, the noise output is reduced through an algorithm that prevents overcooling. Secondly, and of local benefit to operators with residential neighbours, is the low start up noise characteristic that it gives a bus because the eFan does not activate as soon as it is turned on, only when the engine reaches a temperature at which it needs cooling. It is also quieter because it runs for less of the time.
An advantage that becomes increasingly important as space becomes ever more at a premium within the bus envelope, is the eFan’s packaging attributes. ‘We can split the charge air from the water and have the relevant components in different locations, which is far more difficult to do with a belt or hydraulic driven system. Also, with one big fan you have to have a big square heat exchanger but with our smaller multiple eFans you can have virtually any shape of heat exchanger.’
For those interested in what the eFan Micro Hybrid System involves, it simply replaces the hydraulically-driven cooling fan (and the combined water/air intake charge cooler) with electrically-powered cooling fans working on separate air-charge cooler and water radiator.
In simple terms, it replaces the drag required to constantly power the hydraulic fan from 20 kW to 3 kW with electric fans that can be switched on and off as required. This will reduce the fuel consumption.
On a conventional hydraulically driven fan system, air is sucked from the outside of the bus through a charge air cooler with a hydraulic oil cooler alongside and then through a jacketed water filled radiator by a large fan driven by a hydraulic motor and controlled by a hydraulic control valve. AVID say this method traps debris within the system making it less effective. The debris becomes difficult to remove and the radiators are easy to damage. The system is also prone to hydraulic leaks.
With the AVID eFan micro hybrid system, air flows through a bank of high performance brushless DC electric fans, cooling a charge air cooler and a water radiator. There are usually six fans, four cooling the water system and two the charge air. Cooling the charge air cooler and the water radiator independently enables their temperatures to be more accurately controlled. The electric fans used are units specially designed for vehicle applications delivering 50% more airflow than the most efficient similarly sized units available commercially. They can be run in reverse, effectively as powerful blowers, to remove accumulated debris and keep the system running cleanly and efficiently. There is no hydraulic system so it can’t leak and doesn’t need cooling.
The system is controlled by an electronic controller connected to the vehicle’s CANbus system. It monitors the water temperature through a sensor in the radiator inlet and the charge air temperature through a sensor in the charge air cooler outlet. There are three functions available to the maintenance team on each system, a reversing switch that enables the fans to be run as blowers, a diagnostic connector port and a diagnostic lamp button.
A major difference between the hydraulic and electric systems is the energy required. When operating at full capacity, the eFan uses 3kW compared with a figure of around 20kW for a hydraulic system. On top of this, it only runs when needed and switches itself off when it isn’t. This ensures that engines operate at their optimum running temperature and also, because the fans do not operate when they are not needed in the early stages of a vehicle’s duty cycle, reduces the warm up time.
The absence of hydraulic fluid is a significant safety factor because, they claim, it is often a hydraulic problem that will start an engine bay fire or exacerbate one started in another way.
Another benefit from fitting an eFan is a reduction in problems with diesel particulate filters (DPFs). This is because additional soot is created when engines are not running sufficiently hot to optimise combustion. This soot collects in the DPF and the exhaust temperature is often not high enough to burn it off. As the eFan helps keep the engine running at its best temperature, less soot is created.
In more extreme cases of overcooling, it can be that overcooled coolant is released into the engine by the thermostat creating thermal shock which damages the power unit. Only running the fan when it is needed makes overcooling less likely and reduces instances of thermal shock.
Elucidating on the benefits of the eFan, typically, a bus radiator is designed to last a couple of years at most but the eFan is designed to last at least ten years and was essentially a fit and forget type system. A robust technology called bar and plate was used because, while the traditional tube and fin construction method was OK on trucks, it was less durable in bus applications. The eFan is designed to be robust for bus applications, which was hard. Although the eFan is more durable it is not heavier. The complete pack weighs 60-70Kg which is comparable to a conventional hydraulic pack. ‘We don’t have a heavy hydraulic fan and supporting framework,’ said Chris, adding, ‘because of this there is less vibration and less noise.’
Noise is increasingly important and here there are advantages to the eFan in two more respects. Firstly, there is a kerbside quiet feature that has been developed whereby at below 5kmh, the noise output is reduced through an algorithm that prevents overcooling. Secondly, and of local benefit to operators with residential neighbours, is the low start up noise characteristic that it gives a bus because the eFan does not activate as soon as it is turned on, only when the engine reaches a temperature at which it needs cooling. It is also quieter because it runs for less of the time.
An advantage that becomes increasingly important as space becomes ever more at a premium within the bus envelope, is the eFan’s packaging attributes. ‘We can split the charge air from the water and have the relevant components in different locations, which is far more difficult to do with a belt or hydraulic driven system. Also, with one big fan you have to have a big square heat exchanger but with our smaller multiple eFans you can have virtually any shape of heat exchanger.’
