|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.)