Electronic differential in electric vehicle

Abstract

Electronic differential is advancement in electric vehicles technology along with the more traction control. The electronic differential provides the required torque for each driving wheel and allows different wheel speeds electronically. It is used in place of the mechanical differential in multi-drive systems. When cornering the inner and outer wheels rotate at different speeds, because the inner wheels describe a smaller turning radius. The electronic differential uses the steering wheel command signal, throttle position signals and the motor speed signals to control the power to each wheel so that all wheels are supplied with the torque they need. The proposed control structure is based on the PID control for each wheel motor. PID Control system is then evaluated in the Matlab/Simulink environment. Electronic differential have the advantages of replacing loosely, heavy and inefficient mechanical transmission and mechanical differential with a more efficient, light and small electric motors directly coupled to the wheels using a single gear reduction or an in-wheel motor.

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Electronic differential in electric vehicles
Akshay aggarwal
Abstract - Electronic differential is advancement in electric vehicles technology along with the more traction control. The
electronic differential provides the required torque for each driving wheel and allows different wheel speeds
electronically. It is used in place of the mechanical differential in multi-drive systems. When cornering the inner and outer
wheels rotate at different speeds, because the inner wheels describe a smaller turning radius. The electronic differential
uses the steering wheel command signal, throttle position signals and the motor speed signals to control the power to
each wheel so that all wheels are supplied with the torque they need. The proposed control structure is based on the PID
control for each wheel motor. PID Control system is then evaluated in the Matlab/Simulink environment. Electronic
differential have the advantages of replacing loosely, heavy and inefficient mechanical transmission and mechanical
differential with a more efficient, light and small electric motors directly coupled to the wheels using a single gear
reduction or an in-wheel motor.
Index terms PID controller, electric vehicle, controller area network, electronic control unit, electronic differential
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1 Introduction
The heavy body including the structure and materials
used in Electric Vehicle has always been a field of
interest to designers. Their continuous research work to
reduce the weight of the body has interested many
people worldwide. The main attraction has always been
reduction of body mass, including structure and form
optimization or by adopting aluminum materials.
Vehicles have seen an improvement on both motor
design and control technology. Modern configurations
include motorized wheels, where motors are fitted in the
wheels of EVs and thus improve air quality, reducing
the reliance on fossil fuels of power vehicles.
Here we ponder upon the use of Electronic Differential
(ED), replacing the conventional gearbox and the usual
configuration of EVs with only one traction-motor
driving two wheels. It reduces the overall mass of an EV
by replacing the conventional mechanical differential.
Now the speed reference computation in the double-
driven EV can be controlled by ED through the
torque/rotation-speed curve of an electric motor which is
almost perfectly adapted to the resistance-torque/speed
curve of an electric vehicle. In case of curvilinear
trajectory or a lane change each wheel is controlled
through an ED in order to satisfy the motion
requirements.
3 Electric Vehicle Mechanical Load
The vehicle mechanical load is characterized by many
torqueses, which are considered resistive. The different
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torques include: – The vehicle inertial torque defined by
the following relationship:
Fres = froll + faero + fslo pe
Froll = µ.mg
Faero = 1/2pCxSv2
Fslope =Mg.sinα
3 Electronic Differential
The main purpose of the electronic differential (ED) is to
substitute the mechanical differential in multi-drive
systems, providing the required torque for each driving
wheel and allowing different wheel speeds.
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2
=
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 =  
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< 0  
4 PID control system
A proportional-integral-derivative controller (PID
controller) is a family of controllers. They are the
solution of choice when a controller is needed to close
the loop and gives the designer a larger number of
options and those options mean that there are more
possibilities for changing the dynamics of the system in
a way that helps the designer. A PID controller
calculates an "error" value as the difference between a
measured process variable and a desired set point. The
controller attempts to minimize the error by adjusting
the process control inputs.it takes the in wheel encoder
values as feedback and will check it again and again in
closed loop to reduce the error.
PID controllers can be viewed as three terms - a
proportional term which provides an overall control
action proportional to the error signal through the all
pass gain factor, and integral term, reducing steady state
errors through low frequency compensation by an
integrator and a derivative term, improving transient
response through high-frequency compensation by a
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differentiator - added together. PID controllers are also
known as three-term controllers and three-mode
controllers.
5 Electronic control units
Two DC hub motors are used in this case. The Electronic
control unit carries out the following basic tasks:
1. Reads the calibrated steering angle potentiometer
voltage and based on this it then calculates the steering
angle and also determines whether the vehicle is moving
straight, turning left or right.
2 .Reads the throttle potentiometer voltage so that the
desired vehicle speed is known.
3. Based on the above information, the ratio of the two
speeds VL/VR is calculated using the appropriate
equation such as Equation shown earlier
4. A separate Pulse Width Modulated (PWM) signal is
then applied to each of the two motors in accordance
with the required speed ratio.
The above sequence is repeated at an extremely fast rate
so that the ECU continues to make adjustments on a
continuous basis
6 Vehicle communication can bus
The CAN bus (controller area network) is a vehicle bus
standard. It communicates with the microcontrollers and
devices within a vehicle without a host computer. CAN
bus is a message-based protocol, designed specifically
for automotive applications. CAN is a multi-master
broadcast serial bus standard for connecting electronic
control units (ECUs).
Here we are using embedded Atmel controllers family
with embedded can. CAN controller will help us to
communicate within the vehicle up to a speed of 1 mbps
without any host computer, to get the data from sensors
at very high speed in serial communication. The can
controller is designed in matlab.
7. Results
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Initially when the throttle input is 1.7 volt.
When steering wheel is turned left
When the steering wheel turned right
8. Conclusion
In this paper, a PID controller has been used for an
electronic differential to control two-independent-wheel
drive electric vehicle. The electronic differential has been
discussed over mechanical differential, proving it to be a
better device with better features implemented in it. The
results of the electronic differential system operated
satisfactorily and that a two-wheel-individual drive
electric vehicle can operate smoothly on both a straight
or curved path using a PID closed loop control system.
References
1. Kada HARTANI, Mohamed BOURAHLA ,Yahia
MILOUD, Mohamed SEKOUR ”Electronic Differential
with Direct Torque Fuzzy Control for Vehicle
Propulsion System” Vol.17, No.1, 2009©TUBITAK
doi:10.3906/elk-0801-
2. P. Presage, R. Krishnan. “Modelling, Simulation, and
Analysis of Permanent Magnets Motor Drives, Part I:
The Permanent Magnets Synchronous Motor
Drive,”IEEE Transactions on Industry Applications
Vol.25, no.2, 265-273, 1989.
3.K.H. Nag, G. Chang, Y. L: PID Control System
Analysis, Design and Technology, IEEE Transaction on
Control System Technology, Vol. 13, No. 4, July 2005,
pp. 559 – 576
4. Milliken, F.W.; Milliken, D.L.: ‘Rave Car Vehicle
Dynamics’, SAE International, 1995.
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5. R.E. Colyer et al., “Comparison of steering
geometries for multiwheeled vehicles by
modelling and simulation,” in Proceedings of
IEEE CDC'98, vol. 3, pp. 3131-3133, December
1998.
6. A. Ece Hartavi et al., “Signal interfacing for
hybrid electric vehicular electronics and an
implementation study,” in Proceedings of the
IEEE ICVES’08, Columbus, OH (USA), pp. 151-
156, September 2008.
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