Plures Intelligens Modicum Machinatorem
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Dr. Glen Stevick, P.E. ext. 101 | Dr. Dave Rondinone, P.E. ext. 102 | Derek King, P.E. ext. 103 | Mingxi Zheng, P.E. ext. 106
Vehicle Engineering and Transformation
Vehicles of all sizes are built to move, and they are machines. We have experience on all kinds.
Understanding the science of complex machines moving in the real world can be a challenge, but Berkeley Engineering and Research provides engineering answers from the perspective of multiple disciplines. We can analyze the internal mechanisms of the system – and how those systems interact in a non-laboratory environment.
While most of our work with vehicles is related to finding the causality of accidents and collisions, we can also provide the redesign of components and the analysis on safety improvements.
Dr. David Rondinone, an engineer who has been with BEAR for over three decades, recently converted a 1967 Volkswagen Beetle to electric drive. The conversion included an SME AC-X1 motor controller, used to provide power to and draw regen power from the drive motor, a Hyper 9 by Netgain.
The SME controller is designed to use analog inputs from various sources to dictate how much power is either sent to or generated from the motor. One analog input determines the power sent to the motor, and a separate analog input determines the power regenerated by the motor. These inputs are both assumed to be monotonically increasing voltages, such that the higher the input voltage, the higher the power provided to or generated from the motor.
The conversion uses an electronic throttle pedal taken from a Toyota Prius. The pedal requires a constant 5V supply, and provides a variable voltage output based upon throttle position. The pedal provides a monotonically increasing voltage, with greater throttle input resulting in greater voltage output. This voltage can be used directly by the SME controller to determine the desired level of drive power sent to the motor.
One feature desired was for the VW conversion to be able to use single pedal driving, where the throttle pedal provides both the motor drive signal and the motor regen signal (similar to the setup used in Tesla and other modern electric vehicles). Unfortunately, the pedal only provides a monotonically increasing signal that increases with pedal depression, and the controller requires two monotonically increasing signals, one for drive and the other for regen. In order for a single pedal output to be used for both, the pedal output signal needs to be split into two separate signals, one that monotonically increases with pedal depression, and one that monotonically decreases with pedal depression.
One method that can accomplish this is the differential amplifier, which uses a circuit that incorporates an op-amp and several resistors.
The circuit uses two input voltages to the op-amp, one (VI1) is the 5V supply, the other (VI2) is the output of the pedal. If all of the resistors are equal, then the circuit provides an unamplified output that monotonically decreases as the pedal output increases.
By incorporating this circuit, a single pedal output can be used to provide both signals to the controller. Once the inputs are established, the software of the controller is set up such that pedal positions between greater than 20% depression are used to provide a drive signal (with higher pedal depression leading to higher drive power), and pedal positions below 20% are used to provide a regen signal (with lower pedal positions leading to higher regen power). An additional advantage of this approach is that the controller will smoothly transition from full regen - light regen - no regen or drive - light drive - full drive.