Mobility Solutions

Bosch hydraulic hybrid Practical and fun to drive An alternative powertrain that offers an efficient way to recover braking energy

  • Can reduce urban fuel consumption by up to 45 percent
  • Low-cost, robust, and easy-to-service hybrid drive
  • The world’s first hydraulic hybrid with a pneumatic pressure accumulator
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  • March 05, 2013
  • Mobility Solutions
  • Press releases

press release

Bosch’s new, hydraulic full-hybrid powertrain shows that frugality can be fun. The technology, which Bosch is developing in collaboration with PSA Peugeot Citroën, is clear in its aims: to supply a hydraulic hybrid powertrain that will significantly reduce fuel consumption and CO2 emissions in compact cars. The system is also compatible with passenger cars from other vehicle segments, as well as light delivery trucks operating in urban environments.

The hydraulic hybrid is designed to enable a boost effect that would normally be offered only by complex electric drives. Here, a conventional internal-combustion engine combines with hydraulic units and an accompanying nitrogen pressure accumulator to provide a brief boost to acceleration. The hybrid system is able to support gasoline and diesel engines in ranges where they do not work at optimum efficiency.

The power-split concept permits various drive options. For short journeys, stored energy can be used to run exclusively on hydraulically generated power, with the internal-combustion engine remaining inactive and the vehicle producing zero emissions. For longer journeys, or when driving at higher speeds, accelerative force is provided by the internal-combustion engine. Alternatively, the two types of powertrain can also be combined. In this case, the energy stored in the hydraulic system and the fuel burned in the internal-combustion engine work together to drive the vehicle, which also provides a brief boost effect.

Bosch and PSA Peugeot Citroën see great potential in this technology. In the new European driving cycle, it has the capacity to reduce fuel consumption by up to 30 percent when compared to a conventional internal-combustion engine. For purely urban driving, this rises to as much as 45 percent. As a result, the range of a compact car can be greatly increased using this alternative powertrain. The improved efficiency is due to the careful configuration of the two powertrain components.

What’s more, the hybrid system makes use of energy that would normally go to waste. Braking, for instance, quickly fills up the hydraulic accumulator: the kinetic energy captured during braking is converted into hydraulic energy and stored in the pressure accumulator. Normally, this energy would go to waste, turning into heat in the friction linings of the brakes. The advantages of a hybrid powertrain are equally evident when the vehicle is travelling at a constant speed. Here, the engine can be run within an efficient range while also filling the hydraulic energy accumulator.

This hydraulic-mechanical system makes for a low-cost, robust, and easy-to-service hybrid powertrain. Since it needs no specialized infrastructure, it can be used around the world.

Detailed technical description of operation
In addition to a conventional internal-combustion engine, a hydraulic hybrid powertrain also includes a pressure accumulator and a reservoir. Hydraulic units compress a gas cushion using hydraulic fluid. Fluid and gas are kept separate from one another. The gas cushion stores energy by the gas being compressed rather like a coiled spring. At this point, the pressure in the system is over 300 bar. The amount of energy that can be stored in the pressure accumulator depends on the size of the system. As soon as the pressure within the accumulator is relieved, the system works in reverse. The gas expands once more, providing a compressive force on the hydraulic fluid and driving a hydraulic motor. This motor takes the stored energy and delivers it back to the vehicle via the transmission.

It is true that the pressure accumulator has a more limited capacity and range than the lithium-ion batteries found in electric cars. Nonetheless, it is much quicker to recharge and can use the extra energy provided by the internal-combustion engine more efficiently.

About the collaboration between Bosch and PSA
The close collaboration between Bosch and PSA Peugeot Citroën dates back to an engineering alliance set up in 2008. In 2011, this strategic partnership saw Peugeot launch the 3008 HYbrid4, the world’s first series-produced diesel hybrid passenger car with axle-split drive. PSA Peugeot Citroën developed the electrical components (electric motor, power electronics, and high-voltage generator) in close collaboration with Bosch, a collaboration which extended to developing the special technical setup needed to use the ESP® electronic stability program in hybrid vehicles. The hybrid powertrain concept now also features in PSA’s Peugeot 508 (both the RXH station wagon and the HYbrid4 sedan) and Citroën DS5 HYbrid4 models, for which Bosch supplies the electrical powertrain components.

Contact persons for press inquiries:
Udo Rügheimer, phone: +49 711 811-6283
Florian Flaig, phone +49 711 811-6282

Click here to find further information.

Mobility Solutions is the largest Bosch Group business sector. In 2014, its sales came to 33.3 billion euros, or 68 percent of total group sales. This makes the Bosch Group one of the leading automotive suppliers. The Mobility Solutions business sector combines the group's expertise in three mobility domains - automation, electrification, and connectivity - and offers its customers integrated mobility solutions. Its main areas of activity are injection technology and powertrain peripherals for internal-combustion engines, diverse solutions for powertrain electrification, vehicle safety systems, driver-assistance and automated functions, technology for user-friendly infotainment as well as vehicle-to-vehicle and vehicle-to-infrastructure communication, repair-shop concepts, and technology and services for the automotive aftermarket. Bosch is synonymous with important automotive innovations, such as electronic engine management, the ESP anti-skid system, and common-rail diesel technology.

The Bosch Group is a leading global supplier of technology and services. It employs roughly 360,000 associates worldwide (as per April 1, 2015). The company generated sales of 49 billion euros in 2014.* Its operations are divided into four business sectors: Mobility Solutions, Industrial Technology, Consumer Goods, and Energy and Building Technology. The Bosch Group comprises Robert Bosch GmbH and its roughly 440 subsidiary and regional companies in some 60 countries. Including its sales and service partners, Bosch is represented in roughly 150 countries. This worldwide development, manufacturing, and sales network is the foundation for further growth. In 2014, Bosch applied for some 4,600 patents worldwide. The Bosch Group’s strategic objective is to create solutions for a connected life. Bosch improves quality of life worldwide with products and services that are innovative and spark enthusiasm. In short, Bosch creates technology that is “Invented for life.”

Further information is available online at and,

*The sales figure disclosed for 2014 does not include the former joint ventures BSH Bosch und Siemens Hausgeräte GmbH (now BSH Hausgeräte GmbH) and ZF Lenksysteme GmbH (now Robert Bosch Automotive Steering GmbH), which have since been taken over completely.

PI8066 - March 05, 2013

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