NASA And Air Force To Establish Hypersonic Science Centers
Biobutanol Plans in Korea and India

Bosch Highlighting Hydraulic and Electric Hybrid Systems at IAA

Components of the hydraulic hybrid Hydrostatic Regenerative Braking System. Click to enlarge.

Bosch will highlight its hydraulic hybrid drivetrain at the IAA Commercial Vehicle Show in Hanover, Germany as one of its solutions to help reduce fuel consumption and lower emissions in the commercial vehicle sector. Bosch will also showcase its hybrid-electric, CNG, exhaust aftertreatment, and new higher-pressure common rail injection systems.

The Bosch-Rexroth Hydrostatic Regenerative Braking system (HRB) for heavy commercial vehicles reduces fuel consumption by up to 25%. The hydraulic hybrid drivetrain converts kinetic braking energy into hydraulic energy and stores it. The next time the vehicle accelerates, the stored energy is fed back into the powertrain, thereby reducing the load on the combustion engine.

The savings potential is significant in heavy vehicles that see frequent and strong braking cycles. The stronger the braking, the greater the possible reduction in fuel consumption offered by HRB.

Rexroth has developed parallel and series HRB systems for the various drive concepts in commercial vehicles and mobile equipment.

The parallel hybrid drive displayed at IAA is designed for vehicles with a conventional mechanical drive train and a combustion engine as the primary drive, such as refuse collection vehicles, school buses and city buses.

A gearbox links a hydraulic variable axial piston unit to the mechanical drive train to convert kinetic into hydraulic energy when braking. The axial variable piston unit acts here like a pump and converts the released braking energy into hydraulic energy by loading a hydraulic bladder accumulator with hydraulic fluid. This process is controlled by an electronic controller from Rexroth together with a hydraulic valve manifold.

During acceleration the entire process is reversed: The pressurized fluid is discharged in a controlled manner from the accumulator and flows back through the variable axial piston unit. The latter is driven by the fluid flow and, acting like a motor, gives up its energy to the mechanical drive train. A pressure relief valve in the system ensures a high level of safety for both processes.

The HRB also significantly reduces brake wear, with the production of fine dust from brake wear reduced accordingly.

Modular construction means the parallel HRB is be integrated into essentially any commonly available commercial vehicle frame. This also enables retrofitting of existing vehicle fleets.

The Berlin City Department of Sanitation has been testing an x2eco series refuse truck built by HALLER Umweltsysteme with a Rexroth parallel hybrid since July. The New York City Department of Sanitation is also preparing to test an HRB-equipped vehicle.

The x2eco series refuse truck from HALLER Umweltsysteme is based on a Mercedes-Benz Actros chassis (empty weight/permissible total weight approx. 15 / 26 t, diesel motor drive power 235 kW).

The parallel HRB system installed in the test vehicle weight approximately 500 kg (approximately 1,100 lbs), and delivers 250 kW (335 hp) of power with 2,500 Nm (1,844 lb-ft) of torque. Two bladder accumulators each hold 32 liters. Maximum accumulator pressure is 330 bar (4,800 psi); accumulator initial pressure is 210 bar (3,050 psi). Maximum accumulator capacity is 550 kilojoules (corresponding roughly to the kinetic energy of the fully loaded vehicle at 30 kph / 18.5 mph).

Hybrid-electric commercial vehicle systems. For light- and mid-sized commercial vehicles, Bosch is focusing on hybrid-electric systems. With the stop-and-go driving and frequent braking of urban commercial vehicle drive cycles, the ability to recapture braking energy, stop the engine at idle, and use electric drive for acceleration boosting or all-electric drive for short distances can reduce fuel consumption and emissions by up to 25% for gasoline hybrids and 20% for conventional diesel hybrids. If the share of stop-and-go driving is high during urban operation, the CO2 emissions of light trucks equipped with a diesel hybrid can be reduced by as much as 28%, Bosch says.

Bosch is focusing on parallel hybrid systems. Bosch electric motors are available up to an output of 50 kW (67 hp) and with torque of up to 350 Nm (258 lb-ft) for light and mid-sized trucks weighing up to 12 metric tons. In addition, Bosch is developing the associated power electronics, which delivers up to 350 volts.

Besides mild and strong hybrid concepts, Bosch is also developing simpler methods for start-stop technologies and the recovery of braking energy via the alternator, as these concepts also allow notable reductions in fuel consumption and CO2 emissions.

Bosch sees the greatest sales potential is in the light-truck segment, and expects a market volume of up to 280,000 vehicles by 2015 in this segment. The company already has its first orders for gasoline and diesel hybrids, in both the passenger-car and commercial-vehicle segments.

Bosch is partnering with transmission manufacturer Getrag for the development and marketing of parallel hybrid systems in conjunction with dual clutch transmissions and electric final-drive units. (Earlier post.) The company has also formed a joint venture with Samsung—SB LiMotive Co. Ltd.—to manufacture lithium-ion battery systems for automotive applications from 2011. (Earlier post.)



Why can't we have hydraulic hybrid systems for personal cars.

Less resources used, longer lifecycle, lower cost.

I guess it is just not sexy enough.

Healthy Breeze,

@ Abe,

Hydraulic systems have some drawbacks. They are very noisy. The large oil and nitrogen tanks which store the pressure can usually only hold 30 to 120 seconds of power, which makes them good for trash and delivery trucks that stop and start a lot...but not nearly as attractive for a commuter vehicle.

They may be able to allow a generator to run at it's most efficient RPMs to charge up the pressure for a vehicle with a hydraulic transmission. That may be, in effect a hydraulic Chevy Volt (albeit with a 2-mile "battery"). However, there are questions of wear and durability if you use hydraulics all the time. It's worth looking at to see if all of that can be overcome. Certainly, the hardware may be less dependent on expensive components than lithium.


There have been a few demonstration of the effectiveness of hydraulic/Hybrid powertrain by Eaton on others but still no commercial product, the beauty of the hydraulic hybrid train is that it can be retrofitted on existing truck or buses (a city bus which driving is essentially stop and go would save 50%)contrary to the electric/hybrid.


Wouldn't ultra-caps + integrated high power e-motors have the potential to supply equivalent short time power burst as hydraulic tanks without all the mechanical complications?

Ultra-caps + e-motors could last a very long time, be much quieter and would require a lot less go-going maintenace.

Hydraulics & steamers are not future looking solutions. Why not keep it simple and trouble free?

Roger Pham

To answer your question, let's look at the history of diesel train locomotives. Steam locomotives did not require transmission, but steam were not efficient. Diesel is far more efficient, but needs transmission. Mechanical transmission to all the wheels proved to be inadequate, with frequent failures. Then, hydraulic transmission were tried, but only with success in Germany where there are highly trained and meticulous maintenance personnel. Then, electric transmission was tried in diesel locomatives, and from then on, this proved to be the most reliable and durable. And Toyota researched and reached the same conclusion...and there, you have the rest of the story.

michael Bryant

we all know the draw back of hydraulics but all car companies give high performance with high cost. Many people are sick of expensive cars. hydraulics are cheaper. The people what efficient and cheap not expensive and efficient.I is time for companies to make the next generation of car for the average person or new company to be started that makes efficient cars that are. It is time to rethink the car. It time for new Henry ford to appear.

Roger Pham

@michael Bryant,

HEV's too expensive? Just wait for the next Honda dedicated Hybrid in April 2009, with MSRP of ~18,000 USD (?), which is thousands of dollars cheaper than current hybrids.

Meanwhile, the higher initial price of the Prius hybrid will save a lot in term of transmission work, brake work, starter/alternator repair...and the AC is hermetically sealed electric compressor meaning no more compressor burn out nor freon leak during the life of the car...

You pay a little more for a reliable car initially...or you'll pay a lot more to fix a cheaper car later...with all of the aggravation. Your choice.


Honda has the right idea with a hybrid under $20k. The IMA is simple, low cost and effective. Wait until the Chinese start selling HEVs under $15k in the next 5 years. You might just see a real shift in buying patterns then.

The advantage of this system is it is cheaper than electric for a huge torque and power for a short duration. If you stuck this system in a 3000lb car it would let you accelerate to (assuming no losses) 54 MPH REAL FAST. After that the accumulators are drained.

Or if you could scale it down ideally:

1.0 54
0.5 41
0.3 33
0.1 20

Seems like a 33 MPH 330lb system could give HEV some competition for a lower cost, and give you the same improved city MPG.


I forgot to mention that was all based on their data and a simple calc:

E = 1/2 x M x V^2

W=1,100 lbs
E=550 kJ


And hey with this system you can ditch the starter and downsize the battery.

Henry Gibson

There is always the posibility of the combination of hydraulics for short high power and electric for longer range. With the careful design of flow paths hydraulic transmissions can be highly efficient.

Steam locomotives can be made much more efficient with modern materials and design techniques. The Kitson-Still locomotive type should still be in use. The electronics of electric drives are not simple and are not robust and are very expensive and even weigh more than the motors some times. ..HG..

The comments to this entry are closed.