| Author | Message | ||
| Mark R. Obtinario (Cowlitzcoach)
Rating: |
I really don't want to pour fuel on the fire of this discussion but in the latest issue of Bus Ride magazine it was reported Tri-Met (the transit agency in Portland, OR) is experimenting with electric cooling fans. In the picture the rear side mounted radiator has four large and two small electric fans mounted on the outside surface of the radiator. The fans basically cover the surface of the radiator. The six variable speed fans are going to be working in conjunction with an electrical variable speed water pump and an electric mixing valve that are going to be computer controlled to deliver optimum heating or cooling. Now while I admit a transit bus operating in the Pacific Northwest will rarely experience the kind of severe service a fully loaded motorcoach will experience when crossing a high mountain pass at extreme ambient temperatures, we do get some warm days and we do have a lot of hills. The operative word from Tri-Met for the reason for the test is to see if it will result in increases in fuel economy. Since they plan on running the test bus at least 40K miles it should turn in some reliable data. It will be interesting to see the results. Mark O. | ||
| niles steckbauer (Niles500)
Rating: N/A |
Thanks for the info - I think the reason this is such a contested issue is there are no (except for Tim, who appears to be a genius with a lot of time on his hands) long term verifiable successful experiences with Electric Fan cooling - It would make me feel better if it wasn't taxpayer money they were using, but so be it - Please keep us informed - | ||
| Stan Rating: N/A |
The horsepower to cool the engine has to come from the prime mover. I would think a variable, mechanical driven fan and adjustable coolant flow valve would give the same end result with less input horsepower. V drive buses can have the fan coupled directly to the engine (with a torus) so there is no loss in belts, countershafts or coverting to electricity and back again to mechanical. The same thing applies to the water pump so total input energy should be less. There are various reasons for converting to electric fans but saving fuel is not one of them. As Niles points out, public transit agencies are quick to try every gimmick that is brought to their attention and they do it with your money. They usually tell you that it is not your money, that they got a grant from the state or feds. This means that the total cost is double because of the bureaucracy involved. | ||
| Brian Elfert
Rating: N/A |
Transit agencies are spending our money on fuel too, so it is in our interest that they save on fuel. (I don't think any public transit is not subsidized except maybe NYC.) The electric power to run an electric fan isn't free so I don't know electric fans are any better. Brian Elfert | ||
| motorcoach1 Rating: N/A |
if they ever get a Flynn parallel path motor built it just might work but until then we got what we got and for transit budgets thats a big laugh. | ||
| herman Rating: N/A |
Mark, can you give us a link to the article? The one below, to the index of the May issue, doesn't seem to describe anything similar to what you speak of. http://www.busride.com/2006/05/Default.asp | ||
| t gojenola
Rating: N/A |
Here's the tri-met blurb: http://www.trimet.org/news/releases/mar21cooling.htm tg | ||
| Gary Stadler (Boogiethecat)
Rating: N/A |
The key phrase here is "variable speed computer controlled" Yes adding electric fans will actually eat more raw engine power than just mechanically driving them, due to the efficiency losses in converting mechanical->electrical energy. BUT if you precicely manage how fast the fans and water pump are spinning (thus their energy consumption), exactly matching cooling system needs as the vehicle encounters various loading situations, I'm sure that even with the conversion inefficiency that you could get better fuel mileage in many if not all circumstances. Take my Crown for example, with my 2 speed eddy current fan clutch. I'd say my fan stays on "slow" during 80% of my driving. In a lot of situations I't'd probably do well going even slower if it could, but it can't. I only have slow and fast as choices. With microprocessor control of both the fan and the water pump, both would always be going as slow as they could to keep the engine happy... I'm certain that'd save fuel over a standard system. Stan, you're right, doing all the above mechanically would probably work even better from an efficiency standpoint. But doing that mechanically vs electronically is hasselsome. With the efficiency of the neodymium based motors (and generators) these days, electrical is getting pretty darned decent, and it's one heck of a lot easier to physically implement.... (Message edited by boogiethecat on June 10, 2006) | ||
| Tim Strommen (Tim_strommen)
Rating: N/A |
Well, I figure I could chime in a little on some arguments regarding the pros/cons of Mechanical (direct), Belt Driven, Hydraulic, and Electric. I'll address them in the order listed in this post. Mechanical. This system is ideal in situations where the fan can be directly coupled to a hard drive shaft protruding from the actual engine block of the prime mover. Many COTS RV Manufacturers use this configuration when using T-drive Bus frames. With this configuration, all of the power output from the shaft is delivered to the fan's hub - leaving the overall efficiency up to the design of the airflow inside the engine, the proximity of the fan to the engine block and/or radiator, any ducting or shrouding, the air density, any mechanical devices (like clutches and bearing blocks), and finally the design of the fan itself. Pros: Least amount of conversion or mechanical loss due to changes in shaft angle or energy medium, also least points of failure. Fan is almost guaranteed to work so long as the engine is running. Cons: Fan placement on the engine block is usually determined by the engine manufacturer (and is typically rather high on the block) which limits its use to T-Drive (truck-like) drive trains with either front or rear mounted radiators. It is complicated to change the rotation of a fan hub, so the fan design has limitations. The speed of the fan is determined by the engine RPMs so this system must be designed to facilitate the highest load (plus some safety margin percentage) at the lowest expected RPMs (idle). Any engine movement must be accommodated otherwise the fan tips may impact the shroud or housing. Other than the engine temperature rising there is no easy way to tell if there is a fan failure – which could destroy an engine. Geared angle and rotation boxes require oil and maintenance and can fail catastrophically causing mechanical damage to the engine itself. Belt Driven. This system is ideal in situations where the power of the engine must be transferred to a fan that is not perfectly in line with an existing PTO engine shaft and/or must either be relocated too close to a wall surface. MCI has successfully used this design for years by routing a belt above a T-Drive and folding the cooling system back and on top of the engine (combined with a geared 90 degree gear box for the fans). This system gives designers a great deal of flexibility in component placement, while maintaining overall simplicity in the fan’s drive train. The efficiency of this system is usually very high. Pros: Great flexibility in component placement while adding some immunity to engine movement. Fan speed can be simply increased or decreased by selecting different pulleys (or controlled in real time by using a variable diameter pulley and a tensioner idler pulley). This type of system is easily used in conjunction with an angle gear box for final output to a fan or to make abrupt right angles or rotation changes. Belts can be stacked to add to the horsepower capability of the drive. Belts absorb some of the shock load of a clutch engaging, which is easier on the engine’s mechanicals. Cons: Simply put, belts. Belts are a continuous service item, and need to be utilized in a drive system correctly to ensure that the belt is not overloaded or will wear prematurely. Also the compound that belts are made of is affected by the environment of an engine compartment. Attention must be paid to the shock loads of fan clutches grabbing the fan, overall horsepower transmitted, the radius of the smallest pulley, the tension of the belts, and the alignment of the pulleys. Frequently in multi belt systems, when one belt breaks it fragments and can get ingested by the other belts either derailing them or causing them to fail as well. Also belts are an additional hazard in an engine compartment – a finger, hand or clothing item getting grabbed and/or tangled in a pulley can dislocate, break, de-glove (ouch), tear off (really ouch), or at worst kill a person. There is again no easy way to determine if the fan drive has failed other than a temperature rise in the engine – however a simple belt presence detector (photo interrupter) can tell if the belts are at least in place. Hydraulic. This system is best suited when the accessory drive pulleys of an engine are used by other hardware (A/C, second or very large alternator, etc.) and an existing power steering pump is installed. This type of fan drive is very common on transit busses (especially more recent models). Pros: Almost unlimited flexibility in fan placement and control. The efficiency of the drive can be tuned by using different sized motors, multiple fans from the same hydraulic source line, etc. Hoses can be routed right next to each other, and fan direction can be controlled with common simple valves. Multiple power sources can be used to provide hydraulic pressure to the system as a back-up (for power steering too), and the fan can be run slowly to remove some hot air from the ambient air after the prime mover has been shut down by using an accumulator (or second power source). Hydraulic system failure can be easily monitored by using a pressure gauge at the fan motor (or a pressure sender) – but typically the power steering fails with the fan as pressure is lost so the failure could be observed through reduced steering assistance. Cons: The hydraulic lines to a fan can fail causing the vehicle to lose steering assistance (and potentially control of the vehicle). Control valving can be complicated and prone to service problems. Small leaks in hydraulic lines are typically difficult to find and road grime soaks with fluid requiring full pressure washing and system energizing to detect pin-holes. Large hose failures could spew flammable hydraulic fluid onto red-hot exhaust manifolds causing a major fire and potentially the loss of the rig. Line length, curves, valves, and couplings add resistance to the hydraulic circuit reducing overall efficiency. Electric. These systems offer the most in flexibility of placement as electricity is one of the most commonly stored and controlled forms of energy in a vehicle (after fuel). Newer Hybrid and Fuel Cell Vehicles are beginning to have these systems more frequently due to the surplus of energy available (and may be the only option in a purely electrical fuel cell plant). Pros: Fan placement and quantity can be almost unlimited. Motors can be run well after the prime mover is shut off to assist in cool-down, and can be off-loaded from the prime mover by switching the power source to an auxiliary power plant. Motors can be controlled with high speed switching solid state controllers to drive the speed to exactly what is needed to undertake a measured ammount of cooling. Due to relatively simple control, several different fans in strategic locations can play a synchronized part in an overall cooling scheme. Cons: Size, Weight, Availability of Energy, Maintenance, and Cost. In order to spin a large radiator fan in a Class 8/Class A chassis, about 12-25 HP is required. Typically the size of a standard wound DC motor prohibits the use of an electric system simply due to space constraints. When it is feasible motors add around 100lbs for the motor and usually require the addition of a larger engine driven alternator – or secondary power supply which can be between 60-1,500lbs. In order to get more horsepower out of standard wound DC motors, most manufacturers have specified motors above 48 volts. This puts most of the 10+HP (continuous) motors out of bounds for the typical 12/24 volt systems found in today’s street vehicles. The harder a DC brushed motor runs (and the hotter due to the high engine temps and due to being on the hot side of the radiator) the faster the brushes wear out. Brushes can be between $20 and $350 depending on the type of motor – and may need to be replaced within 500-1000 hours (about as often as Halogen bulbs get replaced). Wires that are exposed to high continuous currents and temperatures need to be replaced more often and since the system is high energy, has a greater potential to become an ignition source. There are many possible weak points in an electric system, so careful ENGINEERED design is critical in order for the system to behave correctly and safely. As the electric fans can be powered from a source that is active while the prime mover is inert, careful safety procedures must be followed to ensure that a person is not injured in the process of servicing the vehicle. Finally, motors alone can exceed $1000, with maintenance parts quickly exceeding $250 at the first service interval (between 500-1000 hours) and this figure will only go up over time. Total system cost including controllers, wire motor and additional power generation can push an electric system in a standard Internal combustion engine install over $4,000 (wouldn't you rather do an in-frame rebuild in ten years and let that money sit in a savings account gaining interest?). For home-brew systems featuring electric primary cooling, most people are not equipped to test the system before it is applied to the real world, which puts the rig and every one on the road at risk. I've done a bit of work on this and what I'm coming up with is that the hydraulic system is best for vehicles that already have power steering and can support accesories, while the belt driven systems are best for those that don't have power steering systems. However, hydraulic systems require some additional design considerations for safety, but are relatively easy to work with (and power isn't hard to come by). For those who see some benefit to some of the details of each of these - you can always mix the systems (I personally have hydraulic/electric in my rig). Digital control can be added to many of these systems making the overall control more resolved than an on/off (1-bit) control. I have built a 1-of variable flow rate control servo that has 8-bit accuracy from 0-psi to system pressure. In a hydraulic system, since the available power in the lines varies with the RPMs, the cooling controller looks at speeds and RPMs and determines how much pressure is required at the fan motor to get out the correct RPMs. Therefore, I'd typically advise people to fix what they have if it breaks - but think about how to make it smarter and more efficient. Many of these busses we drive were built before this type of control was feasable and cheap. Cheers! -Tim Strommen [Edit] Final comments added -Tim (Message edited by Tim Strommen on June 13, 2006) | ||
| herman Rating: N/A |
Indeed, hydraulic systems have long been touted as being more dense than mechanical (e.g. transmissions) and electric alternatives as regards both weight and volume per unit power. I'd be curious as to your view of recent electric motor technology, e.g. BLDC, liquid cooling, PM-field hybrids, low gap designs, flywheel mounted alternators, variable reluctance PM designs, etc. |
