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EPA Series Hydraulic Hybrid Yard Hostler To Be Put Into Service for First Time

Parker Hannifin Commercializing Series Hydraulic Hybrid System for Delivery Vehicles; Initial 20 Unit Order from Freightliner Custom Chassis

The FCCC hydraulic hybrid chassis. Source: FCCC.Click to enlarge.

Freightliner Custom Chassis Corporation (FCCC), a subsidiary of Daimler Trucks North America, has made an initial 20 unit commercial commitment for a series hydraulic drive system from Parker Hannifin. (Earlier post, earlier post.) The commitment came as part of a grant under the United States Department of Energy’s Clean Cities program and was funded through the American Recovery and Reinvestment Act.

Daimler Trucks North America LLC (DTNA) spearheaded the submittal of these winning applications which will support the purchase of 638 hybrid and alternative fuel vehicles. Parker is the only supplier of the hydraulic hybrid systems for the vehicles. The series hydraulic hybrid systems will be incorporated into delivery vehicle models, based on the FCCC MT-55 chassis, intended for use by United Parcel Service (UPS).

Hydraulic hybrid system in the FCCC chassis. Source: FCCC. Click to enlarge.

A hydraulic hybrid drivetrain uses hydraulic accumulators to store energy. As hydraulic fluid enters either accumulator, the nitrogen that accumulator compresses and its pressure rises. Like other hybrid systems, energy saved when applying the brakes is reused to help accelerate the vehicle. Compared to batteries as an energy storage device for hybrids, the hydraulic accumulators offer a higher power density, but a lower energy density. The accumulators support a higher energy flow, not limited by overheating, and are more efficient at charging/discharging.

Field testing of the system during the past year has indicated that the hydraulic system is capable of generating as much as a 50 to 70% increase in fuel economy in stop-and-go applications when compared with traditional diesel powered vehicles that have automatic transmissions. The hydraulic hybrid improves fuel economy in three ways: recovered braking energy; improved engine efficiency; and its engine-off feature.

  • Brake Energy Recovery. The hydraulic hybrid is able to recover and reuse about 70% of the energy that otherwise would have been wasted during the braking process. Typical electric hybrids can only recapture about 20-25% of the brake energy, according to Parker.

  • Optimized Engine Control. WIth the engine decoupled from the drive axle (it drives the hydraulic pump when needed), the engine can operate in “the sweet spot” to optimize fuel consumption. There are also no torque converter spin losses.

  • Engine “Off” Strategy. The engine is off during vehicle operation until needed to drive the hydraulic motor.

Engine operating points (torque vs. rpm). (Left) Baseline engine. (Right) Series hydraulic hybrid. Source: FCC. Click to enlarge.

Prior to field testing, the system was validated for fuel efficiency by the United States Environmental Protection Agency at its National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan.

We believe the series hydraulic hybrid technology has application not only in delivery vehicles, but also for yard hostlers and city buses. Additionally, our advanced series hydraulic hybrid system, called RunWise, is currently being field tested in more demanding applications such as with refuse vehicles. This is a technology that holds great promise as a contributor to reduced environmental impact and increased fuel efficiency.

—Dr. Joe Kovach, Group Vice President of Technology and Innovation for Parker's Hydraulics Group

The RunWise advanced series hydraulic hybrid system. Click to enlarge.

In June, Parker introduced its latest version of its advanced series hydraulic hybrid system (RunWise) (earlier post), targeted at Class 8 refuse vehicles.

Unveiled at Waste Expo 2009, RunWise – Modular Gen I features a patent-pending cradle design for packaging mechanical, hydraulic, and electrical components. Because the cradle houses all major hydraulic subsystems, it facilitates manufacturing, installation, testing, and servicing. Cradle design flexibility accommodates multiple chassis configurations and simplifies OEM truck assembly with minimal electrical, driveshaft, and cooling system hookups. If major service is required, the cradle can be removed and a new cradle reinstalled quickly, eliminating vehicle downtime.

A Parker hydraulic hybrid system is also incorporated in the series hydraulic hybrid yard hostler developed by EPA and FEV that will be going into service in New York. (Post.)




Wouldn't this type of htbrid technology be suited for garbage trucks?


NR Train (Japan) has developed an electric suburb train car that can run on lithium batteries for 50 Km at up to 100 Km/h or on overhead power lines (where available).

The idea is to install overhead charge lines (points) at selected stops only to top off the on-board batteries and avoid many Km of expensive overhead power lines. The same could be done with e-city buses and garbage trucks. Those two could share the same quick charge points.



This idea is generally known as a 'short wire system.' I remember hearing of another streetcar that used banks of supercapacitors instead of batteries because they charge faster and a streetcar does not want to stay at a stop too long.


So, we have Parker Hannifin and Lightning Hybrids both working on series hydraulic hybrids, which use relatively old off the shelf technology to get regenerative braking, stop-start engines, and run ICE engines at their sweet spots for better thermodynamic efficiency. It also provides instant torque to allow undersizing the ICE engine. The upshot should be midsized cars that get 50+ mpg.

The benefits: Lower cost than batteries, no rare earth metals needed, technology appears close enough now.

So...when do we get the Chevy Compressor convertible?

Nick Lyons


I think the duty cycle of refuse trucks, urban delivery vehicles, etc. is the perfect application for these types of hybrids. Highway cruising is another story--I expect the mechanical efficiency of the hydraulic drive would be significantly less than a conventional drivetrain, so don't expect to see a hydraulic Chevy Compressor any time soon. ME types with a more expert take on this topic please chime in.



On a smaller passenger vehicle you could put a small ICE driving a hydraulic compressor near the rear axle, with a clutch to allow it to drive the axle directly at highway speeds. That way the main hydraulic motor could be on the front axle for maximum brake energy recovery.

Basically a reverse of the layout shown above. Also that way the hydraulic could provide a boost of pwoer for over taking.



That would work; a smaller passenger vehicle needs very little hp to cruise at highway speeds.


From a 'practical' / ME perspective,
As soon you mention hydraulic motor/pump, I see a 30% drop in efficiency.
parasitic , thermal, frictional losses.Times two if a conventional pump and motor are used. The 'usual' pump and at the other end the motor.

The different systems we are seeing developed are not necessarily using the traditional approach.

Scotch yoke drive, drive line (brake energy)energy recuperator with accumulator storage and returning tourque to the drive shaft intermittently.
The application there is very efficient. Taking otherwise wasted braking energy, store and return.
Any penalty then is from the xtra system weight.
That would be a parallel application.

These Serial applications require larger storage volume and accumulators and do all the work . They work constantly.
They derive most of their energy from the engine and in constant driving will always be very inefficient.

The benifit is from sweet spot motor tuning,downsizing and engine off and idle stop.

The garbage compacter, which would share the hydraulics suited to idle off, downsizing,torque boost is an example of economical efficiency improvements.

When battery storage and electrical circuits and techs are so common and give equivalent function, I see limited application except where

1 Electric systems don't suit ie no external electric power available. No E service available.

2 Where the plant requires a large hydraulic system ie garbage earthmoving others.(system rationalising.)

3 Where emissions are the overriding priority the engine being intermittent in power requirement including much idle/ low speed and power averaging is desirable.yard holsters, high density city use incl garbage.

Nick Lyons


Sounds right to me.

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