363
Hybrid Vehicles
interim solution before the full implementation of pure EVs when there is a
breakthrough in energy sources (Wakefield 1998). The definite advantages of
the HEV are to greatly extend the original BEV driving range by two to four
times, and to offer rapid refueling of liquid gasoline or diesel. An important
plus is that it requires only little changes in the energy supply infrastructure.
The key drawbacks of the HEV are the loss of zero-emission vehicle (ZEV)
concept and the increased complexity. Nevertheless, the HEV is vastly less
polluting and has less fuel consumption than the ICEV while having the
same range. These merits are due to the fact that the engine of the HEV can
always operate in its most efficient mode, yielding low emissions and low
fuel consumption. Also, the HEV may be purposely operated as a BEV in the
zero-emission zone. It is becoming a consensus that the HEV is not only an
interim solution for implementation of ZEVs, but also a practical solution for
commercialization of super, ultra-low emission vehicles (SULEVs).
The concept of HEVs is nothing new. A patent in 1905 delineated that a
battery-powered electric motor was used to boost the acceleration of an ICEV
(Wouk 1995). However, over the years, the development of HEVs had been
discouraging. One possible reason was due to their complexity, especially on
how to coordinate and combine the mechanical driving forces from both the
engine and electric motor. The turning point of HEV development was the
advent of the Toyota Prius in 1997 (Hermance and Sasaki 1998). Subsequently,
the development of HEVs has taken on an accelerated pace.
12.2 Hybrid Vehicle Configurations
Based on the flows of electrical and mechanical powers, HEVs used to have
two basic configurations—the series hybrid and parallel hybrid. With the
introduction of some HEVs having the features of both the series hybrid
and parallel hybrid, the basic configurations have been extended to three
kinds—series, parallel, and series-parallel. Additionally, some HEVs with
both front-axle and rear-axle drives cannot be represented by these three
kinds. Thus, they are further extended to four kinds (Chau and Wong 2002;
Ehsani et al. 2005): series hybrid, parallel hybrid, series-parallel hybrid, and
complex hybrid.
Figure 12.2 shows the corresponding functional block diagrams, in which
the electrical link is bidirectional, the hydraulic link is unidirectional, and
the mechanical link (including shafts, brakes, clutches, and gears) is also
bidirectional. It can be found that the key feature of the series hybrid is to
couple the engine with the generator to produce electricity for pure electric
propulsion, whereas the key feature of the parallel hybrid is to couple both
the engine and electric motor with the transmission via the same driveline
to propel the wheels. The series–parallel hybrid is a combination of both the
Hybrid Vehicles
interim solution before the full implementation of pure EVs when there is a
breakthrough in energy sources (Wakefield 1998). The definite advantages of
the HEV are to greatly extend the original BEV driving range by two to four
times, and to offer rapid refueling of liquid gasoline or diesel. An important
plus is that it requires only little changes in the energy supply infrastructure.
The key drawbacks of the HEV are the loss of zero-emission vehicle (ZEV)
concept and the increased complexity. Nevertheless, the HEV is vastly less
polluting and has less fuel consumption than the ICEV while having the
same range. These merits are due to the fact that the engine of the HEV can
always operate in its most efficient mode, yielding low emissions and low
fuel consumption. Also, the HEV may be purposely operated as a BEV in the
zero-emission zone. It is becoming a consensus that the HEV is not only an
interim solution for implementation of ZEVs, but also a practical solution for
commercialization of super, ultra-low emission vehicles (SULEVs).
The concept of HEVs is nothing new. A patent in 1905 delineated that a
battery-powered electric motor was used to boost the acceleration of an ICEV
(Wouk 1995). However, over the years, the development of HEVs had been
discouraging. One possible reason was due to their complexity, especially on
how to coordinate and combine the mechanical driving forces from both the
engine and electric motor. The turning point of HEV development was the
advent of the Toyota Prius in 1997 (Hermance and Sasaki 1998). Subsequently,
the development of HEVs has taken on an accelerated pace.
12.2 Hybrid Vehicle Configurations
Based on the flows of electrical and mechanical powers, HEVs used to have
two basic configurations—the series hybrid and parallel hybrid. With the
introduction of some HEVs having the features of both the series hybrid
and parallel hybrid, the basic configurations have been extended to three
kinds—series, parallel, and series-parallel. Additionally, some HEVs with
both front-axle and rear-axle drives cannot be represented by these three
kinds. Thus, they are further extended to four kinds (Chau and Wong 2002;
Ehsani et al. 2005): series hybrid, parallel hybrid, series-parallel hybrid, and
complex hybrid.
Figure 12.2 shows the corresponding functional block diagrams, in which
the electrical link is bidirectional, the hydraulic link is unidirectional, and
the mechanical link (including shafts, brakes, clutches, and gears) is also
bidirectional. It can be found that the key feature of the series hybrid is to
couple the engine with the generator to produce electricity for pure electric
propulsion, whereas the key feature of the parallel hybrid is to couple both
the engine and electric motor with the transmission via the same driveline
to propel the wheels. The series–parallel hybrid is a combination of both the