Operational
Forward / Reverse Switch
What physically happens if the vehicle is in operation at 30km/h (speed limit in underground mines) with steady pressure on the accelerator and the switch is immediately switched to reverse?
The vehicle comes to a controlled stop exactly the same as if the accelerator has been released, and then begins to move in reverse.
What physically happens if the vehicle is in operation but in the process of slowing down and the switch is immediately switched to reverse?
As above, if the vehicle is slowing because the accelerator has been released, it continues a controlled brake, and then stops completely before engaging reverse.
Obviously an electric motor (if not attached to a driveline) can slow down and spin in reverse very quickly. However, being attached to a LandCruiser driveline, do we assume it would slow down and start reversing at the same velocity and rate as the regenerative braking?
Yes – except that the motor is “tuned” differently for forward and reverse, and has different limits imposed on it so that the maximum speed in reverse is less than the maximum possible speed in drive.
Is this rate adjusted through software tuning? If you adjust the rate of the regenerative braking, would this directly affect the rate of deceleration in the previous scenario?
Correct – this is adjusted via the ‘proportional integral derivative’ (PID) tuning of the motor. In general, the regenerative braking effect reduces as the vehicle speed approaches zero. If the opposite direction of travel is selected, then the braking action is sustained.
Is it possible to electronically stop the reverse function from working until vehicle comes to a standstill?
There is no need. Especially with low speed maneuvering, it is a desirable feature to be able to switch direction of travel at any time.
Even though there may be no need for this, if the company or mine site requires this function, can Voltra provide it?
Yes, Voltra could provide this, but it would not dramatically change the actual behaviour of the vehicle. It would still come to a controlled stop and then go into reverse (because reverse is selected). The only difference is that if the vehicle is in reverse, the regenerative braking is higher as the vehicle speed approaches zero.
Regenerative braking
What is the science of regenerative braking and how does it provides charge back to the motor? How is it controlled and adjusted?
The electric motor is a motor/generator. It has the same power characteristics whether operating as a motor or as a generator and is direction of rotation agnostic. The control of the motor is via dynamic adjustment of the torque, which can be either a positive (driving) or negative (generating) value. The torque control is via a feedback loop being a ‘proportional integral derivative’ (PID) control algorithm. The motor/generator torque values are recalculated every 2 – 10 milliseconds.
Currently, diesel LandCruiser operators mostly use 3rd gear (low range) to ‘coast’ down the decline – could the regenerative braking on the Voltra be controlled to mirror and replicate that level or rate of braking?
Yes – that’s what it does now, no change required. The vehicle speed, whether driving or regenerating, is set by the throttle position. A variation in the speed relative to the throttle position when going uphill versus downhill will be present, as this is the value of the positive or negative value in the PID error. This difference in speed will not be detectable by any human operator.
Software
Apart from diagnostics, what other information can we get from the software?
Data available includes: Position (GPS dependent), vehicle speed, condition of all electrical subsystems, temperatures of all cell groups, voltage of all cells, motor torque, motor RPM, battery capacity, odometer value, energy use driving, energy from charger, energy used for the A/C, park brake status, throttle position, drive selection, charger status, charger charge current and voltage, Diagnostic Trouble Codes (DTC)
What are other inherent features available with the software?
Other software features include: speed/power/torque limiting, charging status, location, ability to remotely disable, ability to update most vehicle software remotely, ability to link to fleet management systems, and vehicle operating history.
