1
C H A P T E R 1
Introduction
Since the beginning of the 21st century, resource depletion and environmental pollution have
become the two major issues of human survival and development. Resource conservation and
environmental protection have become a global consensus [1–8]. Automobiles have changed
people’s lifestyle and brought development and progress to mankind. However, automobiles
also consume a lot of oil resources and cause noise and environmental pollutions. Carbon diox-
ide emissions from automobile, industrial enterprise, and fossil fuel combustion are the main
causes of global warming. For instance, carbon dioxide emissions from vehicles account for more
than 60% of all carbon dioxide emissions. In order to achieve sustainable development and re-
duce carbon dioxide emissions, it is necessary to control the energy consumptions and reduce
the dependence on petroleum [9–14]. Accordingly, the universities, carmakers, and research in-
stitutes put their emphasis on developing hybrid vehicles with a higher fuel economy and lower
emission to replace traditional vehicles [15–21].
Hybrid electric vehicles (HEVs) driven by an internal combustion engine (ICE) and one
or more electric motors have been well known for a long time. With the advantages of fuel
economy, emissions, and environmental protection, an HEV is taken as one of the most popular
traffic tools. In addition, lots of vehicle manufacturers, research departments, and universities
worldwide have devoted their efforts to developing HEVs [22–31].
e compound planetary gear set (CPGS) of an HEV is able to combine the power from
the ICE, MG1, and MG2, and then provide the power via the ring to achieve power-split. In
addition, it can also act as an electronic continuously variable transmission (eCVT) [32–36].
Compared to the traditional Ravingneaux gear set, the proposed system can improve the lever
efficiency to reduce the required power of MG2 and save costs. By manipulating the torque and
speed of the electric motors, the engine is able to work in the high-efficiency region in the hybrid
mode [37–42]. Figure 1.1 shows the schematic of the dual motors HEV.
To identify abnormal noise sources for the HEV with the power-split transmission in
different modes, acoustic levels and TVs are measured in a powertrain test bench. e Leuven
Measurement & System (LMS) data acquisition instrument and corresponding software are
adopted to acquire acoustic and vibration information of the hybrid powertrain. Pressure sen-
sors, acceleration sensors, and photoelectric sensors are also located to acquire the acoustic and
vibration information in both the pure and hybrid driving mode. By means of spectral analysis
and order tracking, the main noise sources are found and presented.
2 1. INTRODUCTION
Power Converging
Device
MG1
Damper
Transmission
Ring
Small Sun Gear Short Planet
Big Sun Gear Long Planet
Engine
MG2
Figure 1.1: Schematic of the dual motors hybrid electric vehicle [20].
e gear meshing of the CPGS is the main noise source in a deep HEV during the pure
electric driving mode. Based on the theory of gear meshing noise, meshing noises of gear pairs
in the CPGS and hybrid driveline are computed. e meshing noise responses of different pitch
error, tooth error, gear speed, and meshing stiffness are analyzed. e results show that the errors
of the short planet and the long planet in the CPGS can lead to a higher noise. erefore, the
pitch error and tooth error of the short planet and the long planet should be reduced in producing
the compound planetary gear set. is study can provide a theoretical basis for reducing gear
meshing noise.
Based on the configuration, dynamic equations of the CPGS are derived by the La-
grangian method. Moreover, the dynamic equations of hybrid driveline including engine, re-
ducer, differential, half shafts, wheels, and vehicle are also derived. Combining those dynamic
equations, the mathematical model of the HEV is established. e theoretical predictions of
natural frequencies and corresponding vibration modals of the proposed hybrid powertrain un-
der different driving modes are presented.
A torsional model is also built in ADAMS, a commercial software, to acquire the TV
characteristics of the studied HEV. e vibration modals and natural frequencies obtained from
ADAMS and mathematical model show a remarkable agreement. erefore, two models are
good enough in representing torsional characteristics of the hybrid powertrain. Moreover, the
1. INTRODUCTION 3
main factors affecting the TV under different excitations are studied by the forced vibration
analysis. Optimal parameters are also provided, where the amplitude of TV of the powertrain is
minimized.
A dual mass flywheel torsional damper is introduced to the powertrain to analyze TV
characteristics. Comparing to simulation results, it is found that the dual mass flywheel torsional
damper can effectively reduce TVs of the hybrid powertrain. In addition, the different rotational
inertia of the first and second flywheel, torsional stiffness (TS), and damping are also considered
in this research and at last, their optimal values are obtained and presented.
is study can definitely be used as a valuable reference when developing an HEV.
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