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VT-HYDRAULIC BATTERY
In order to make hydraulics more attractive for hybrid vehicles, especially for the electrohydraulic concepts, installation of the hydraulic components, has to be simplified as much as possible.
Standard solutions relies on high and low pressure hydraulic accumulators as separate devices, of the similar design.
This new device 'Hydraulic battery' will provide only one device for same
task, and this will considerably simplify installation. Basically, it is standard high pressure accumulator wrapped in additional, external, bladder that serves as low pressure reservoir, Figure 1.
Figure 1. Hydraulic battery concept based on bladder accumulator
Limit of the existing systems and advantage that can be obtained with new system ‘Hydraulic battery’,regarding instalation simplification, e.i. reduced packaging volume, is explained by Figure 2. Note: packaging volume can be defined as a cubic space needed to install certain equipment e.i. packaging area x packaging cross-section.
Figure 2, case a), present’s standard solution as combination of two separate oil containers, one for high pressure oil and second for low pressure oil. Said containers are cylindrical hydraulic accumulators. Hydraulic accumulators have cylindrical shape in order to reduce stress produced by internal pressure. As it can be seen on Figure 1 this isn’t optimal shape regarding packaging volume.
In hydraulic battery concept, case b) on Figure 1, high pressure container is placed inside low pressure container. High pressure container will be same as for standard solution e.i. cylindrical hydraulic accumulator. But, as low pressure container is exposed to roughly hundred times lower stress, it can be created from rubber bladder wrapped around hydraulic accumulator. In addition, as rubber bladder now is also a flexible output wall, hydraulic battery can bi placed in cubic space, so that packaging volume for given total volume of low and high pressure container will bi minimal. There are two ways to define cubic space. First, placing hydraulic battery in cubic shell and second, placing hydraulic battery in cubic space created by design of the vehicle.
Comparing case a) and case b), presented by Figure 2, it can be easily observed that packaging volume is significantly reduced by hydraulic battery concept.
MODEL
Simple models were constructed in order to get first insight into the possibility to reduce packaging area with hydraulic battery concept. Standard hydraulic accumulator are presented with model based on bottle of 0.5 l volume, where red one indicates high pressure and blue one indicates low pressure container.
Figure 3 presents hydraulic battery model as model of high pressure accumulator wrapped in blue balloon. Blow balloon presents model of bladder used to store oil under low pressure.
Figure 3. Hydraulic battery model
Figure 4 presents hydraulic battery model placed in model of cubic shell. Cubic bottle of 1 l volume is used as model of cubic shell. So hydraulic battery limited by cubic shell of l l will have same total volume of two separate hydraulic accumulators of 0.5 l.
Figure 4. Hydraulic battery model in cubic shell model. High energy state-rubber bladder empty a) and Low energy state – rubber bladder full b).
COMPARISON
In order to allow estimation of packaging volume reduction, by introduction of the hydraulic battery concept, simplified models were used. Figure 5 presents comparison between hydraulic battery concept and concept with two hydraulic accumulators (standard solution) placed in parallel.
Figure 5. Comparison between packaging space (doted lines) needed for standard solution with two parallel hydraulic accumulators and new solution with hydraulic battery.
This figure also confirms note from Fig. 3 that further packaging volume reduction can be obtained if external bleader is constrained with cubic shape envelope.
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On of the driving ides, in development of the VT concepts is to be modular as possible. One example of the Hydraulic Battery, as it is shown below, is possibility to integrate with existing technologies in order to make systems that are even more compact. Namely as Hydraulic Battery has input and output close one to another it can be attached directly to piston hydrostatic machine, omitting tubing that will additionally save the space. Piston machine is of the MAC design that is also analyzed in scope of the this VT project.
