15-12-2012, 01:58 PM
The Solution of Hybrid Electric Vehicle Information System by Modbus Protocol
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Abstract
This paper introduces the hybrid electric vehicle
information system, which is realized by modbus protocol.
Using a remote terminal control unit (RTU) with EVEW
touch-screen, the system achieves the communication between
electronic control units (ECU) and the RTU by means of the
modbus protocol at the baud rate 38400kb/s, and it finishes the
task of human-machine exchange. Hybrid electric vehicle
control unit uses dual-core processors: the host processor and
the coprocessor XGATE. XGATE can reduce the load on the
host processor, which makes the host processor timely
response to a number of hybrid control tasks, and it improves
the requirements of real-time in hybrid control system. In
addition, because modbus protocol has opening
characteristics, most of serial communication controllers
support the protocol. Therefore, the system can be applied in
the serial communication with modbus protocol.
INTRODUCTION
With the development of automotive industry, Hybrid
electric vehicles need monitor and diagnose more and more
information. And requirements of data transmission rate are
increasing. The traditional meters can only show finite
parameters such as the speed of automotives and the quantity
of gasoline. Furthermore, the parameters’ correct are
intractability, it is helpless to the real time data, whose number
is often large. The hybrid electric vehicle information system
in the paper, which is based on the modbus protocol, shows a
new way to solve the problem. Furthermore, the system has
been applied in actual control of hybrid electric bus. With its
application and increasing products [1], Touch screen is the
most commonly used human-machine interface, and it is much
more intuitive at present. Widely used in the field of
automotive control, ECU can form a good condition for
human-machine interaction by combining with touch screen.
Touch-screen displays the running state and parameters of the
system. And the parameters can be corrected directly through
the touch-screen, which provides good human-machine
interaction.
HARDWARE PLATFORM OF THE SYSTEM
The Hardware platform of the system contains ECU, touchscreen,
RS-485 bus, 24-volt DC power supply. To display and
correct the running parameters, the system uses the touch
screen of Shenzhen Human-machine Electronics Co., Ltd as
the master. And the slave uses ECU of Zhenjiang Hents
Technologies Inc., whose main chip is MC9S12XD256 of
Freescale Semiconductor; MC9S12XD256 is used in the
dedicated control technology of automotive. Compared to the
other chips of 9S12, its cost is cheap, and it is a dual-core, 16-
bit Micro programmed Control Unit (MCU) .it has a main
processor and a coprocessor named XGATE. The coprocessor
is adapted to dispose communication so that it can reduce the
load of the main processor. The system adopts dual-line RS-
485 owing to its preferable stability [2]. Tow–line RS-485 is
used as the communication medium between touch screen and
ECU. There is also a 24-volt DC power supply in order to
supply power to the touch screen and ECU. Figure 1 shows
the connection of hardware platform.
Design of touch screen module
MT500 of EVEW touch screen has integrated modbus RTU
communication protocol; therefore, the design is mainly to add
several simulate elements and switch elements[5].
Building a window at first, setting the type and parameters
of the window in the menu of “system parameter”. Then,
adding “data display” elements to the window so as to realize
the statuses and parameters that the system needs to display.
such as the work current of importing controller, the voltage of
the battery, speed of the automotive, current status of drive,
current gear of the handle gear and current status of clutch.
In the properties of each element, “device address” and
“device type” should be set corresponding to the ECU. The
“device type” of the system contains ‘LW’ and ‘4x’. ‘LW’
indicates that the element reads the internal address of touch
screen. ‘4x’ indicates the registers’ address of the read-write
controller type. Both system diagnostics and parameter setting
should use “data input” elements that can produce a small
keyboard so as to realize entering and modifying data. It also
needs to set addresses corresponding to the ECU.
CONCLUSIONS
After the design of the hardware, we can see that the
hardware connection of the system is simple, easy to achieve.
The main chip of ECU uses MC9S12XD256, compared with
other chips of 9S12 series; it is a cheap dual-core processor.
And test proves the communication is still stable while baud
rate is set to 38400kb/s.this shows the system is fast
transmission rate, high communication reliability and low cost.
Besides, XGATE coprocessor can reduce the load of main
processor so that the main processor can better respond to some
tasks of hybrid control and meet the requirement of real-time
on the hybrid control system. It also achieves good monitoring
to the system and corrects its operating parameters. And it has
been used successfully in the Hybrid Electric Bus Control
System. It’s responsible for sampling and processing related
data information of the inspection of vehicle systems, faults
diagnosis and data collection. This information passes to touch
screen through RS-485 bus, then, we can set various working
conditions by the touch-screen interface.