SAE World Congress: UPS delivery truck with FEV hydraulic series hybrid drivetrain
At the SAE World Congress, FEV is displaying a number of vehicles that they have contributed to recently including a diesel powered version of the new Chrysler Sebring and the Lincoln MKR concept. Perhaps the most interesting vehicle is a large brown UPS delivery van. This is no ordinary UPS truck though. This one has a series hybrid drivetrain, but even that is different. Unlike the Chevy Volt or the Ford Airstream/HySeries Edge, this van has no batteries for energy storage or electric motors. Instead this one has a hydraulic hybrid system.
Continue reading after the jump.
A conventional UPS van is powered by a diesel engine driving through a transmission and drive-shaft and rear axle. In the hydraulic hybrid version everything behind the engine is replaced. The diesel engine drives a hydraulic pump which draws fluid from a reservoir and pressurizes a high pressure accumulator. The accumulator acts as a power buffer, in a similar manner to a battery in an electric hybrid. The pressure from the accumulator is used to drive a hydraulic motor attached to the rear axle.
The hydraulic motor actually provides power to the rear axle to propel the vehicle. The fluid coming out the motor is fed back to the reservoir. Regenerative braking is achieved by having another hydraulic pump attached to the rear axle. When the driver lifts off the accelerator the rear axle drives the second pump which also pressurizes the accumulator. The resistance working back against the pump provides simulated engine braking. When the accumulator pressure is above a threshold the diesel engine can be shut off just as it would be with an electric hybrid.
The advantage a hydraulic hybrid system has over an battery electric system is the rate at which it can capture regenerative braking energy. Because a battery cannot absorb energy that quickly it can generally only capture about thirty percent of the energy from braking. A hydraulic system like this one can capture up to seventy percent of the braking energy. On the negative side, the hydraulic system has a limited energy capacity can only propel the vehicle short distances. The performance of the hydraulic hybrid system is actually more akin to a ultracapacitor, with the quick charge and discharge and limited capacity. Unlike the capacitors, the system is bulky and wouldn't be well suited to a smaller vehicle but is relatively simple and inexpensive for a system of it's size..
The system works very well on large 20,000 pound urban delivery trucks like this one. The continuous charging and discharging of the high pressure accumulator in this usage scenario takes maximum advantage of the system. FEV built two demonstration vehicles for UPS to test and they have been running since last fall. They have been testing several setups , including the engine running all the time, engine off when the vehicle is stopped and engine off when the vehicle is stopped or decelerating. Fuel consumption savings of 39-44 percent, 52-59 percent and 70-74 percent were found in the three scenarios. They also estimate a reduction in greenhouse gas emissions of forty percent.
Some of the hydraulic components used in the hybrid system
FEV estimates fuel savings of 1,000 gallons per year per vehicle and payback time for the hybrid system of only 2-3 years and $50,000 in lifetime savings per vehicle. FEV isn't a parts supplier, rather they are an engineering and design consultant. They do systems integration work and build prototypes for manufacturers. In this case FEV worked with UPS, EPA, Eaton, and International Truck to design and build these vehicles. Hopefully UPS and other delivery companies will take note of this and expand the use of such systems to all of their vehicles soon.
Reader Comments (Page 1 of 1)
Owen 9:39AM (4/20/2007)
I'm sure I'm biased because I'm a mechanical engineer, but this technology makes so much sense. Environmentally, the lack of batteries has to have a HUGE impact. I don't understand why this application can't be used more widely for smaller vehicles as well. Hydraulic motors are very efficient and are extremely compact. Plus it has to be cheaper to have 4 in wheel hydraulic motors, with a single electric motor (or whatever kind of motor you want) powering the pump vs. 4 in wheel electric motors. Not to mention reliability is much higher on hydraulic motors than electric ones. Control is one thing I see as being an issue, and also accumulators for hydraulic purposes can't store as much energy as batteries. Either way, it's something that at the very least needs to be implemented on larger vehicles, eventually it may trickle down into smaller vehicles, or at least the land-yacht soccer-mom machines.
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Tim 10:42AM (4/20/2007)
Fluids (liquids/air/gasses) MAY be an efficient way to capture, store and release energy, however the wasted heat energy may greatly reduce overall efficiency. By the time you add the weight of fluid, storage and motors, the system weight of batteries vs hydraulics may not be that far apart. Then there is the price and abilities of the batteries vs the choice of fluid…
This may be application driven. The greater mass of trucks may be better suited for hydraulics whereas the opposite may be true for smaller application such as passenger cars. Can anyone speak to this?
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Sam Abuelsamid 10:50AM (4/20/2007)
Tim, I think you are exactly right, the appropriate system will be application driven. The performance characteristics, weight and packaging size of the hydraulic system lends itself to larger vehicles like this. The elevated load floor of these vehicles provides for plenty of space for the reservoir and accumulator. A passenger car is more suited to batteries. There is no silver bullet. As always we need to use the correct tool for each job.
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Henry 11:35AM (4/20/2007)
Very interesting article Sam. It seems useful and cheap for a vehicle which constantly stops and mainly travels in the city but not so much for a large long-haul semi.
I have to agree with Tim that the Series Hybrid setup is the most effective and economical for longhaul trucks, trains, suvs and cars. That is only electric engine/s running the vehicle with a plug-in capable nanosafe batteries charged by an ICE engine.
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Tim 11:46AM (4/20/2007)
Sam- I'm certain that these 2 technologies and many others that we have not even yet dreamed of will be combined in interesting and innovative ways over time.
The market is calling for full energy cycle efficiency (sans the “well’) and the reduction of both acquisition & operating costs of the rolling stock.
Whereas the past transportation energy was primarily a monopoly, the future will be varied and widely distributed even to the point of the individual consumer such as home wind & solar.
While gov’t can help by investing OUR TAX MONEY (important paradigm) wisely to further research and development, we must also beware of these politicians pandering to their “friends” (think corn ethanol and hydrogen) and creating new energy monopolies therefore squelching innovation.
This blog and others like it are invaluable in disseminating information which will help to keep innovation alive and the politicians in their place. This sharing of ideas presents the consumer with the best possibilities in the future.
For this we thank you.
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Bob 3:19PM (4/20/2007)
To Owen...
Simply put-any "motor" mounted in the knuckle area to drive the wheel has an immediate and unsatisfactory effect on the unsprung weight of the assembly in a passenger car. Even 5 lbs will create so much of a suspension damping and NVH issue, test vehicles cannot meet current industry (let alone the increasing customer) requirements for NVH control and smooth ride under all conditions.
The idea is nothing new-hydrostatic drive systems have been used in industrial and offroad equipment for years, even the automotive industry (GM was playing with it back in the mid 1970's). While interesting, the modifications to the idea presented by FEV are nothing extraordinary and are a simple adaptation of existing technology.
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Neil 10:43PM (4/22/2007)
I drove FedEx Ground trucks through college so I got a pretty good idea of how much fuel those guys are burning. A primarily city truck would burn through about 90-120$ in fuel a week. A primarily rural truck would burn through over 300$ a week. The thousand cubic foot step vans with automatic transmissions could only get about 6-8 mpg. A stick would do a couple mpg better. The typical contractor seemed to use a truck for 7-8 years so a system like the one described above could save contractors and companies tens of thousands of dollars per truck easily.
I am not a mechanical engineer so I was wondering if this hydraulic system could be adapted to an electric motor?
The reason I ask is that delivery vehicles are only driven 100-350 miles per day and parked in the same place each night so they can be reloaded in the morning and have plenty of electricity available. Most of them are already plugged in each night because they have electric engine block warmers so they start in the morning. It seems like the perfect match.
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Neil 10:48PM (4/22/2007)
Tim, I fully agree with what you said about government investing our tax money in these technologies. Obviously the easiest way they could do that is by simply insisting vehicles they buy are equipped with fuel saving technologies. They are such a huge customer they would assure new technologies the threshold numbers needed to guarantee the business to set up mass production facilities. I've seen local governments buy Toyota Prius hybrid gas/electrics for parking cops, but the potential is so much greater. If the USPS insisted every new postal vehicle were a hybrid or got so many mpg, there would be an instant demand created for such vehicles. I'd rather see my tax dollars go to that rather than pie in the sky corporate subsidies for hydrogen economies that always remain 20 years off.
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Jim 9:22PM (12/03/2007)
I personally feel that the hydraulic system has a much brighter future then electric in terms of overall economy, ease and cost of production, reliability. Check the concepts presented at the link provided here: http://www.valentintechnologies.com/default.asp
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tim mcleod 12:41PM (12/10/2007)
can anyone speak more to the issue of unsprung weight? why do we stick with the habit of considering the "spring point" to be the junction between the wheel supports and the chassis? is there a way to allow all these "in-wheel" concepts to move forward by moving our definition of the spring point to the junction of the wheel/tire or the tire/road interface? literally re-invent the wheel to more like moon rover wheels, perhaps coated with rubber for traction/wear, but not inflated? or would the friction losses or control issues become too great?
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