A Preliminary Study of Energy Recovery in Vehicles by Using Regenerative Magnetic Shock Absorbers R. B. Goldner and P. Zerigian Tufts Univ., Dept of EECS J. R. Hull Argonne National Laboratory obtaining significant energy savings by using optimized regenerative magnetic shock absorber in vehicles the average vehicle on the average road driving at 45 mph might be able to recover up to 70% of the power that is needed for such a vehicle to travel on a smooth road at 45 mph DISCUSSION OF RESULTS OF ELECTRICAL GENERATOR EXPERIMENT – As seen in Figure 5, the peak voltage was approximately 1.3 volts when the vertical velocity, vz, was approximately 1.1 m/s. This corresponds to a tangential velocity of 2f R = 10 m/s -for a rotation frequency f = 20 Hz, and a wheel radius, R = 80 mm (3.187"), and a "bump" height = 2 mm and width =15 mm. For these dimensions and the geometry of the test setup the "short" bump model best applies (cf. below for a discussion of the short and long bump models). Using equation (2) for the generated voltage,and replacing (Nwdc) by the length of the coil, L = 5.2 m,one predicts that the average radial magnetic flux density,
= Bo, over the volume of the coil should have been approximately 2.3 kG (0.23 T). This is in good agreement with the field map of Figure 3, where one can observe that for the radial distance from the magnet outer surface r 0.5 mm and for the region 1.5 mm on either side of the magnet edge (where Br peaks) the average for Br is between 2 and 2.5 kG. Thus, we argue,these results also validate the eddy current damping model. It should be noted that because the "bump" was actually rounded, rather than having a sharp apex, one expects a relatively rapid (in time), but quite finite, initial rise (and final fall) in the voltage. Such was the case, as seen in Figure 5. In the next section, (where we discuss a road model), the case of a sharp (i.e., triangular) bump is discussed and a very rapid rise (and return) in the voltage is predicted. It is clear that the missing link in our analysis is an accurate road model, which we anticipate rectifying soon with test model regenerative magnetic shock absorbers mounted on an instrumented test vehicle as well as shaker table testing an isolated test model regenerative magnetic shock absorber. However, using road profile data, together with two models [(i) a validated eddy current damping model (Appendix A), and (ii) a (yet to be validated) road model (Appendix B)], we have been able to estimate that the range for the percentage of recoverable power/energy for a 2500 lb vehicle that employs four optimized design regenerative magnetic shock absorbers and whose average speed is 20 meters/s (45 mph) on a typical U.S. highway is likely to be between 20% and 70%. This result indicates that, with regenerative brakes and regenerative magnetic shock absorbers, electric vehicles might have significantly improved “charge-mileage”. Clearly, this would be a desirable result, especially if the shock absorbers could be manufactured economically.