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The Concept to Measure the Overall Car Performance

  • Silpakorn University, Nakhon Pathom, Thailand

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The overall car performance investigating on-road experiments is necessary for research and development in automotive engineering. Car acceleration capability is a fi nal result depending on engine performance, transmission system design, suspension optimization, shape and dimension, aerodynamic, friction reduction technology, driving skill, and other factors. The purpose of this research is to present the concept to measure the overall car performance from acceleration capacity. We found that this concept is possible and convenient because we can collect digital input signals from an existing electronic control unit and transfer it to additional processor to analyze and display the fi nal result in every mobile display, such as laptop, tablet, and smart phone. The method is cheaper and easier for installation and usage.
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The Concept to Measure the Overall Car Performance
Jarut Kunanoppadol
Received: 25 January 2012 ; Accepted: 11 April 2012
The overall car performance investigating on-road experiments is necessary for research and development in automotive
engineering. Car acceleration capability is a nal result depending on engine performance, transmission system design,
suspension optimization, shape and dimension, aerodynamic, friction reduction technology, driving skill, and other
factors. The purpose of this research is to present the concept to measure the overall car performance from acceleration
capacity. We found that this concept is possible and convenient because we can collect digital input signals from
an existing electronic control unit and transfer it to additional processor to analyze and display the nal result in
every mobile display, such as laptop, tablet, and smart phone. The method is cheaper and easier for installation
and usage.
Keywords: car performance, acceleration, measurement
Silpakorn Automotive Research and Technology (SART), Department of Mechanical Engineering, Faculty of Engineering and Industrial
Technology, Silpakorn University, Nakhon Pathom 73000, Thailand. E-mail:,
The research and development in automotive engineering
have been done for long time and are still ongoing as
long as we need to take advantage from it. A number of
previous research studies have focused on various topics,
for example, conceptual development and shape design
(1, 2), aerodynamic analysis (3, 4), engine performance
improvement(5, 6), brake and suspensions optimization
(7-10), and car utility system development (11, 12). There
also have been a number of research studies on emis-
sions and alternative fuels (13-15), cost management
in product developing processes (16), and many others.
Car performance can be de ned by several criteria,
such as speed acceleration capacity, brake and control
capabilities, etc. For this research, we mainly focus on
speed acceleration capability only. There are various
implementations to increase the overall car performance,
such as engine performance improvement, transmission
and suspension system optimization, lubrication technol-
ogy development, aerodynamic design, or driver course
training, etc.
Engine performance developments involve increasing
the engine outputs; power and torque, and decreasing the
engine input; speci c fuel consumption (17). The engine
outputs depend on many operating parameters, such as
air-fuel ratio, compression ratio, intake air temperature
and pressure, load and engine speed, ignition timing (for
spark ignition engine), injection parameter and swirling
design (for compression ignition engine) (18). An engine
performance map is normally used to describe the effect
of operating parameters related to the engine outputs (19).
However, the simple way to present correlation between
engine power, torque and operating speed is normally
shown by engine performance curve (sometimes the
speci c fuel consumption is also shown) (20). Although it
is very useful, the engine performance curve is not usually
shown in car speci cation. Commercially, the engine
speci cation is detailed to consumers only the maximum
power, maximum torque, and engine speed at these
points. In automotive engineering analysis, there are two
ways to get this curve; rst, measured by dynamometer,
or second, simulated by calculation (21-23).
The Concept to Measure the Overall Car Performance
Vol 32, No1, January-February 2013
Car performance is a nal result depending on en-
gine outputs, transmission selection, tire size, aerodynamic
effect, rolling friction, and other factors. Twenty percentages
(20%) of indicated power from combustion is sent through
transmission and tire system to drive the car forward or
so-called driving force, while air resistance and rolling
resistance against car motion in the opposite direction
(24). So, the car is driven forward with one acceleration
value by the net force following the Newton’s second law
of motion. Currently, car performance is measured with
many types of dynamometer in a laboratory experiment,
and it is costly.
Our previous research studies have focused
on an engine performance development by using offset
piston to improve the engine power (5),and a combined
turbocharger set to increase a thermal ef ciency (6), and
now we are in the process of installing a dynamometer
for our experiment. We also have an idea to develop a
method for measuring the overall car performance for
on-road experiment (25-27).
The main objective of this research is to develop
and present a concept to measure the overall car perform-
ance for the on-road real-time experiment and describe
our conceptual framework for future implementation.
The remaining of the paper is organized as follows; rst,
we explain the information of a dynamometer; second,
we present the theoretical car performance calculation
method; third, the simulation results are shown; fourth,
we present the conceptual implementation framework;
and nally, this article concludes with the discussion.
The laboratory experimental tool to measure
the output performance of an engine or a vehicle is a
dynamometer. It can be classi ed into various types
depending on the criteria used for consideration. By instal-
lation, we separate dynamometers into two types; rst, the
engine dynamometer that directly connects an engine to
a dynamometer; and second, the chassis dynamometer
that can experiment by driving a car on the roller without
taking the engine off. Both of them are used to measure
and present the output power and torque of the engine
at an operating speed (20). Moreover, we can classify
dynamometers by a power transfer method and also split
it into two types; the absorption dynamometer, and the
transmission dynamometer (28). For the absorption type,
dynamometers measure and absorb the engine output
power to which they are coupled. The power absorbed
is usually dissipated as heat by some means, such as
prony brake, rope brake, mechanic or hydraulic friction,
eddy-current dynamometer. For the transmission type, the
power is transmitted to the load coupled to the engine
after it is indicated on some types of scale. These are
also called torque-meter. (28)
Inertia dynamometer is also included in the trans-
mission type. The rolling mass (called drum) is designed
to have enough inertia, directly connected to the engine,
and loaded of the engine. Then, the engine is run and
accelerated from low to maximum speed and measured
the angular acceleration and angular velocity of the drum.
Angular acceleration results are analyzed with the inertia
of drum to calculate the engine torque. Angular velocity
results are simply converted to the engine speed. Engine
power is calculated from these data and the engine
performance curve is presented. The inertia dynamometer
is applied to be the chassis dynamometer as well by using
the similar method. The concept of measuring the engine
torque by acceleration data is applied in this research
because it is convenient to install and measure it in a car.
However, in the measuring process, the car is driven in
maximum acceleration to let the engine work in full load.
Therefore, to avoid an accident, the experiment should be
done in the safety area such as test drive area, or raceway
only. For future application, we will apply this research to
design the equipment and install it in our race car called
Formula SAE and measure the overall car performance.
Car Performance
To perform the car performance curve, we have
to know the engine torque data at every operating speed.
These data are informed by the engine performance
curve. But if we do not have the engine curve, calculated
simulation is needed (21, 23). We can calculate the output
torque and power from the engine, and then simulate the
Jarut Kunanoppadol J Sci Technol MSU
engine performance curve from the details of car speci-
cation; maximum power, maximum torque, and engine
speed at these points as shown in equation 1. (22)
Then, we use the engine torque and engine
speed data to calculate with the transmission system
and tire data to nd the driving force and car velocity as
shown in equation 2. (22)
Driving forces at each speed have to be reduced
by resistances that is summarized from air resistance and
rolling resistance. Air resistance is related to car square
of velocity value, cross-section area, and drag coef cient
of the car. Rolling resistance depends on the weight and
rolling coef cient. The total resistance can be calculated
as shown in equation 3. (22)
After reducing the driving force by total resistance,
we have the net force data. Car acceleration performance
can be calculated from the net force and equivalence
mass that is depended on gear position. The car
acceleration can be calculated as shown in equation 4.
Finally, the overall car performance curve is
represented by accelerate capability curve that presented
correlation between accelerate performance related to the
engine speed or car velocity.
Simulation Results and Discussions
For a better understanding about the concept to
measure the overall car performance by the accelerate
capability, we presented a case study simulated from
speci cation data of Ford car; model Fiesta 5Dr 1.4L Style
AT as shown in table 1 (29).
Table 1 Car speci cation data (29)
Dimensions & Weight
Overall Width (mm.) 1,722
Overall Height (mm.) 1,496
Weight (kg.) 1,127
Maximum Power (kW/rpm) 70/5,750
Maximum Torque (Nm/rpm) 126/4,200
Gear Ratio 1st Gear 2.816
Gear Ratio 2nd Gear 1.498
Gear Ratio 3rd Gear 1.000
Gear Ratio 4th Gear 0.726
Final Gear Ratio 4.203
Tire Size 185/55 R15
Base on engine speci cation, we calculated output
torque at engine speed from 600 to 7,200 rpm and set
the speed range as 600 rpm. Transmission ef ciency was
assumed as 90% in calculating process. Simulated engine
performance curve was shown in Figure 1.
The Concept to Measure the Overall Car Performance
Vol 32, No1, January-February 2013
Figure 1 Simulated engine performance curve
For the engine speed lower than 4,200 rpm, the
engine output torque correlates with engine speed positively.
The maximum torque is equal to 126 Nm at 4,200 rpm
as shown in speci cation and decreases when the engine
speed is over 4,200 rpm. However, this engine performance
curve is not the exact data because it is calculated by
mathematical simulation. It is always better if we have the
information from the real performance curve.
Then, we used engine torque and operating
speed results, with the tire radius of 292.25 mm. to
calculate the driving force and car velocity. Total resistance
was also analyzed by using assumption parameter by
the following values (22); 0.80 for shape factor, 0.023
for air resistance coef cient, and 0.015 for rolling resist-
ance coef cient. After simulating, we performed the car
accelerate capability performance as contour plot between
car acceleration (m/s2) and engine speed (rpm) at each
gear position as shown in Figure 2. From the gure, the
areas under the curve line for each gear position were
acceleration that the car can move at each gear position
and not over the limit lines.
Figure 2 Simulated car performance curve
The overall car performance measured from
acceleration capability is a nal result from overall parameters,
such as engine output, transmission ratio, transmission
ef ciency, tire size, shape and car dimension, friction,
electronic control unit, and driver skill. The concept to
measure car performance from acceleration data is also
feasible for an on-road experiment. Since currently, most
cars have an electronic control unit (ECU), this concept
is convenient to track digital input signals such as engine
speed and car velocity to additional processor to analyze
and display the result. Moreover, we can transfer raw data
to process and display object on mobile equipment, such
as a notebook PC, tablet PC, or smart phone.
For future research, we will apply this concept to
design and develop an equipment to collect digital input
signals from existing ECU, to process the data, and to
display the result following the conceptual implementation
framework as shown in Figure 3.
Figure 3 Conceptual implementation framework
The overall car performance depends on various
operating factors, such as the engine performance,
transmission design, suspension optimization, car dimension
and shape design, aerodynamic, friction reduction technology,
and driver skill. An on-road experiment is necessary for
a designer, driver, tuner, developer, and researcher to
investigate the nal result (25-27). Overall, car accelerate
Jarut Kunanoppadol J Sci Technol MSU
performance speeds up a car within the considering time.
Thus, the concept to measure the overall car performance
from acceleration capability is possible and convenient
because we can collect digital input signals from an exist-
ing electronic control unit and transfer it to an additional
processor for analyzing and displaying the nal result in
every mobile display, such as laptop, tablet, and smart
phone. This concept is also cost effective and easier for
installation and usage.
We would like to thank the reviewer and the
editor of STISWB IV for their helpful comment on this
article. We also would like to thank the Department of
Mechanical Engineering, Faculty of Engineering and
Industrial Technology, Silpakorn University, Thailand for
providing research facilities.
Table A Calculation parameters
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... We are also working on a method for measuring the overall car performance during on-road experiments [12][13][14]. The main objective of this research is to develop and present a concept of improving the general vehicle performance, measuring the actual impact during an on-road real-time experiment, and to describe our conceptual framework for a future implementation [15]. There are many algorithms developed for engine control in the automotive industry, but the documentation is rarely disclosed to public. ...
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