| Idea of energy recovery in cars is
almost as old as car. Cars used in city conditions are constantly
accelerated and
braked prove significantly
higher fuel consumption than the ones used on
road. This is why interest in idea of irretrievable
braking energy is quite justifiable. There have been very many
conceptions for energy recovery. Some of them have been
attempted to realisation. All has gone to nothing because of complicated
mechanisms and gearboxes applied and their low efficiency. In
order to realise this it is enough to calculate, that braking a
car from speed 50 km/h to „0” is necessary to
apply mechanisms, which
have gear ratio about 60. Then the braking
route equaling 48metres (assuming braking taking place only on the front axle with acceleration of -2m/s2) will result in de-shaping of energy absorbing unit equaling 0.8 meters). |
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| This deformation seems to be a limiting one classic car, considering overall dimensions and design limits. Achieving so „gigantic” for automotive vehicle highly efficient gear ratio was unrealisable not long ago. New chances in this domain give contemporary feed-screw-and-nut gears. Application of precise ball nuts allows to achieve linear gear ratio about 10 at efficiency over 80%. The conclusion from facts mentioned above is, that for full gear ratio equal 60 in the case of applying a feed screw, there should be an additional gear ratio about 6. Gear ratio like this is achieved in classic car gearboxes. Feed-screw-and-nut gear may be applied directly (very effectively) in simplest pneumatic accumulator (energy magazine) of piston-cylinder kid. Abovementioned facts, it means application of feed-screw-and-nut gear and its direct use in pneumatic piston-cylinder assembly were fundamentals of design. | |
| Description of device
action The matter of desig,s
interest is a
classic car propeller combustion engine , which is place in rear.
The engine rear axle. Car front axle is free –
not driven axle, which is applied for recovery of braking
energy. Near shows the whole energy recovery system
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The basic elements of energy recovery system are: 1. Microprocessor – collects information referring positions of car control elements (gearbox lever, coupling, main brake pedal, accelerator pedal, lever switching the system on) and controls the energy recovery system acting on gearbox (2) and control brake (3).2. Gearbox – of classic kind containing differential gear and changing the direction of rotation enables energy recovery from front axle or drives the front axle. 3. Control brake – mechanically puts in motion or blacks the whole system. 4. Shaft – protrudes from gearbox (2) driving it or being driven. 5. Torsional pipe – through the control brake (3) drives a nut (6) or is driven by the nut (6). 6. Nut – rotating left or right displaces feed screw (7). 7. Feed screw - which is rigidly connected with a piston, makes it move or it is caused to be moved by the piston itself 8. Piston – displacing in a cylinder (9) compresses gas inside it or takes energy from decompressing gas. 9. Cylinder – main element of pneumatic accumulator (energy magazine). 10. Equalising tank – connected with the cylinder (9) enables choice of adequate dynamic and static characteristics of the system. Action of energy recovery system is best pictured by description of each element state depending on operation regime. This description was elaborated assuming that the system is switched on, it means that microprocessor (1) is on. I. Constant speed driving - brake (3) is on - gearbox (2) is off - Front axle wheels rotate on loose II. Braking - brake (3) is off - gearbox is on Rotation of shaft (4) causes through rotation of nut (6) displacement of feed screw (7) and piston (8) in cylinder (9). Gas pressure in cylinder (9) and tank (10) increases. Braking energy is accumulated in cylinder-tank system. III. Acceleration - brake (3) is off - gearbox (2) is on and simultaneously changes direction of rotation opposite to braking. Pressure in cylinder (9) causes displacement of feed screw (7) driving nut (6). Drive from nut (6) is transmitted through shaft (4) to gearbox driving wheels. Braking energy accumulated previously is returned now. Characteristic features of the solution Case for design realisation is presented below: 1.In cylinder-piston system energy accumulation and returning take place in one cycle thanks application of high gear ratios. This is why high thermodynamic efficiency is possible to be achieved (about 98-99%). In spite of thermal insulation of cylinder and equalising tank, which is performed according to idea described above, the two elements may be warmed with the use of fumes thermal energy. Meaningful forces acting in the system traction screw-nut are inner forces of the system itself , and they are relatively easy to transfer . This force are transferred into the car’s body. 2.In the whole system mechanic gearboxes are applied ( including feed-screw-and-nut gearbox), which are given to typical loads. It allows to apply part and assemblies available on market. 3.An 1000 kg weighing car braked and accelerated to 50 km/h was considered. The result of calculations conducted were the following technical parameters of the system: - piston stroke 800 mm - cylinder diameter 125 mm - maximum pressure 10 MPa - efficiency of recovery about 70% The above parameters show technological practicability of the enterprise. System,s size ( especially volume and mass) will be nearing gas installations used in many cars. |
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| System of regaining braking energy | |