COMMON PRESSURE RAIL
A New Hydraulic Architecture
Based on a Simple Grid
The Common Pressure Rail is a new driveline architecture. It can replace mechanical or hydraulic drive systems. However, most of the active components, such as cylinders , hydraulic motors, and the power source can stay the same. The architecture allows to use power components (pumps and motors) in their most efficient point of operation.
The architecture consists of a high pressure and a low pressure rail. Loads get their power from the high pressure line, and the used flow is then supplied to the low pressure line. The architecture is -in its design- similar to the electricity grid.
Hydraulic Transformers
Hydraulic transformers are the heart of the Common Pressure Rail. They convert and control the power from the high pressure rail to the hydraulic motors and cylinders. This conversion is reversible: energy from the loads can be recuperated and stored in the hydraulic accumulators. The transformers can also amplify pressures. This is an important security feature: the system can always deliver the maximum pressure i.e. the maximum force or torque, even when the pressure level in the accumulators is low. It also reduces the size of the hydraulic motors and cylinders and further improves the efficiency of the system.
Power Plant
The only task of the combustion engine, and connected pump is to maintain a preset minimum pressure level in the power line.
The engine is only started when the rail pressure drops under this level. When used, it is operated in or around the sweet spot in order to reach the best efficiency.
Accumulators
Hydraulic accumulators are connected the the common rail. They allow to store energy for peak shaving, and to recuperate energy. The hydraulic transformers allow the loads to restore energy to the high pressure rail, for example when lowering a load, or when braking a hydraulic motor. This further increases system efficiency.
SAVINGS
Wheel Loader Study
A joint study with Volvo CE concluded that energy savings up to 50% are feasible. In this study the so called Y-cycle was modelled for a 30 ton loader. On an annual basis, the savings represent many thousands litres of diesel per year. Click here for a presentation on the study.
Allocation of Savings
A joint study with Volvo CE concluded that energy savings up to 50% are feasible. In this study the so called Y-cycle was modelled for a 30 ton loader. On an annual basis, the savings represent many thousands litres of diesel per year. Click here for a presentation on the study.
Reduced Cooling
In the hydraulic circuit the throttle losses can be reduced with more than 80%. An attractive side effect is that the huge cooling capacity, needed for the transmission and hydraulics, can be reduced considerably.
AUTOMOTIVE
Existing hydraulic hybrids
Peugeot Citroën, Bosch, Ford, Chrysler and many others proved that hydraulics offer an attractive option for hybridization. They replaced the complete mechanical transmission of a car by a full hydrostatic transmission, allowing energy recuperation and an efficient operation. However, in order to be successful, extremely efficient hydrostatic pumps, motors and transformers are required. These components are now developed and available.
Key Components
The enabling technology for efficient, low cost hydraulic drivetrain is the Floating Cup. The Floating Cup pumps and motors have an extremely high efficiency, up to 97%. Power control is realized by the Floating Cup Transformer. The transformer allows to efficiently control vehicle speed and acceleration and to recuperate braking energy to an accumulator. The key components allow for automotive production technologies.
NVH
For automotive purposes, the characteristics of noise, vibrations (NVH) and harshness, are essential for technology acceptance. The multi-piston Floating Cup design creates a smooth, almost constant torque output which is necessary for excellent NVH characteristics. The sound output of the Floating Cup motors is comparable with electric motors.
CO2 & Fuel Consumption
Simulations performed by the German Institute for Fluid Power Drives and Controls (IFAS) at RWTH Aachen University proved that an average fuel consumption of 3.1 liter per 100 km (or 77 MPG) is possible for a mid-sized (1450 kg) passenger car. The Common Pressure Rail does what any efficient drive train should do: realise a high efficiency of the total drive train, independent of the vehicle speed. Prototypes of similar hydraulic hybrids, such as built by Peugeot Citroen have confirmed the potential of hydraulic Hybrids
No Compromises
The Common Pressure Rail does not require any compromises regarding performance of the vehicle. It has the same acceleration performance, the same trailer load capacity and the same maximum speed as the equivalent vehicle with a mechanical drivetrain. Contrary to electric vehicles, the total weight of the vehicle is not increased. The complete hydraulic drivetrain will have about the same weight as the mechanical transmission it replaces.
E-Integration
The Common Pressure Rail greatly enhance the use of electric battery systems. Electric batteries are excellent for storing large amounts of energy, but are less fit for handling the large power peaks that occur when accelerating or braking. Batteries need to be large, just to handle such power peaks. Hydraulic accumulators are the low-cost equivalent of ultracapacitors. When a hydraulic accumulator takes care of the intermittent power demands of a car, a 5 to 11 kW electric motor, combined with a small battery pack can power the common rail for most of the average driving cycles.
STATUS
Proven Technology
Common Rail systems already exist for many decades. Due to the absence of competitive transformers, their success was limited to niche markets. The new hydraulic transformers can change this fundamentally. The transformers developed by Innas have been tested in laboratory tests and in applications, such as lift trucks and off-road machinery.
IP & Know-How
The protection of IP of the Common Pressure Rail is based on protection of the system and its enabling key component, the transformer. The transformer is on its turn protected by basic patents and critical design improvements. The IP position is combined with know-how, both still exclusively owned by Innas.
Co-Development
Innas recently finished the development of a new transformer design, The FCT80. Now implementation projects become more important in contributing to the further development. Industrial parties can participate in these projects and the first projects have meanwhile started together with leading OEM’s. Please contact us to discuss the possibilities.
DOWNLOAD
Common Pressure Rail publications
Click on the zip icon or here to download a zip-file with all scientific papers which have been published on the Hydrid or common pressure rail system and the Hydraulic Transformer.
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