5
C H A P T E R 2
Structural Description and
Work Principle of Full Hybrid
Vehicles
Figure 2.1 shows the configuration of the driveline of a power-split HEV with the CPGS,
consisting of an ICE, CPGS, torsional damper (D), reducer (R), electric motors (E1 and E2),
differential (
Diff
), drive shafts, and wheels. In addition, two brakes
B1
and
B2
are used to lock
the carrier and small sun gear S1, respectively. More specifically, the front view of the CPGS of
the four-shaft transmission with E1 and E2 is indicated in Fig. 2.2 as well [49].
Compound Planetary Gear Set
Damper
Battery
Wheel
Reducer
Oil Sump
ICE
E1
B1
B2S2
S1
c
r
E2
?
?
?
1
Differential
Figure 2.1: Configuration of the power-split hybrid powertrain.
6 2. STRUCTURAL DESCRIPTION AND WORK PRINCIPLE OF FULL HYBRID VEHICLES
As shown in Fig. 2.2, the CPGS acts as a power-split component in the hybrid powertrain.
It combines the power from the engine, E1, and E2, and drives wheels via the ring, reducer,
and differential. In addition, it also performs as an eCVT. e CPGS includes a ring (r), a
carrier (c), a small sun gear 1 (S1), a big sun gear 2 (S2), three short planets (p
s
), and three long
planets (p
l
). All planets are attached to (c) and the short planet and the corresponding long
planet engage with each other. S1 and S2 connects E1 and E2, respectively, and c is attached
to the engine via the torsional damper. Additionally, to realize the optimal control and have the
engine operate in high-efficiency regions, the powertrain utilizes two brakes to stop S1 and the
carrier, respectively.
Figure 2.2: Structure of the CPGS: (a) axial view and (b) geometry of the CPGS.
For the sake of analysis, the CPGS is split into two rows, where the first is composed of
S1, short planets, and the ring; while the second includes S2, short and long planets, and the
ring. e speed of the CPGS can be obtained with the tabular method as follows: first, bind
and rotate the CPGS with !
c
, the speed of carrier; second, lock the carrier, release others, and
then let the ring (or sun gear) rotate with
!
ring
!
c
. e speed of the CPGS in the third row
of Tables 2.1 and 2.2 can be obtained from the speed correlation between the first and second
row of the CPGS [50].
Table 2.1: e speed correlation of the first gear group in the CPGS
Carrier Ring Sun Gear 1
1
ω
c
ω
c
ω
c
2
0
ω
ring
–
ω
c
–(
ω
ring
– ω
c
) • α
1
3
ω
c
ω
ring
ω
c
(1 + α
1
) – ω
ring
• α
1
= ω
s1
2. STRUCTURAL DESCRIPTION AND WORK PRINCIPLE OF FULL HYBRID VEHICLES 7
Table 2.2: e speed correlation of the second gear group in the CPGS
Carrier Ring Sun Gear2
1
ω
c
ω
c
ω
c
2
0
ω
ring
–
ω
c
(
ω
ring
– ω
c
) • α
2
3
ω
c
ω
ring
ω
c
(1 – α
2
) + ω
ring
• α
2
= ω
s2
As shown in Tables 2.1 and 2.2, reformulate the speeds of the CPGS as follows:
!
S1
C ˛
1
!
ring
D
.
1 C ˛
1
/
!
c
˛
1
D
z
ring
z
S1
(2.1)
!
S2
˛
2
!
ring
D
.
1 ˛
2
/
!
c
˛
2
D
z
ring
z
S2
; (2.2)
where !
S1
and !
S2
denote the speed of S1 and S2, respectively; ˛
1
and ˛
2
refer to the stationary
gear ratios; !
ring
and !
c
are the speed of ring and carrier; z
ring
means the internal tooth number
of the ring; z
S1
and z
S2
are tooth numbers of S1 and S2, respectively. Based on the structure of
the CPGS, the speed of E1, E2, engine, and ring can be obtained:
!
E1
D
.
1 C ˛
1
/
!
c
˛
1
!
ring
(2.3)
!
E2
D
.
1 C ˛
2
/
!
c
C ˛
2
!
ring
(2.4)
!
engine
D
˛
1
!
S2
C ˛
2
!
S1
˛
1
C ˛
2
(2.5)
!
ring
D
.
˛
2
1
/
!
S1
.
˛
1
C 1
/
!
S2
˛
1
C ˛
2
: (2.6)
e equilibrium equation of CPGS power is rewritten as:
T
c
!
c
C T
ring
!
ring
C T
S1
!
S1
C T
S2
!
S2
D 0: (2.7)
Equation (2.5) shows the speed of engine does not rely on the vehicle speed. By manipu-
lating the torque and speed of E1 and E2, the engine is able to operate in high-efficiency regions
during the hybrid mode. In addition, continuous various speeds and a lower fuel consumption
are reached while the driving force is met. e working principle can be described clearly by lever
principle to draw a parallel. As depicted in Fig. 2.3, once the engine speed is set, the ring speed
is varying with speeds of electric motors. In other words, the ring speed can be continuously
varied via manipulating the motors.
8 2. STRUCTURAL DESCRIPTION AND WORK PRINCIPLE OF FULL HYBRID VEHICLES
S1 S2C Ring
E1 E2Engine Out
1
n
Engine
n
ring
n
E
1
n
E2
‒α
1
α
2
‒ 1
Figure 2.3: e lever principle for the CPGS.
e following equilibrium equations can be obtained:
T
S1
T
E1
C J
S1
˛
S1
D 0 (2.8)
T
S2
T
E2
C J
S2
˛
S2
D 0 (2.9)
T
engine
T
carrier
J
carrier
˛
carrier
D 0 (2.10)
T
ring
C T
L
C J
ring
˛
ring
D 0; (2.11)
where T
S1
; T
S2
; T
carrier
; T
ring
denote the torque applied on S1, S2, carrier, and ring, respectively.
T
E1
, T
E2
, T
engine
, and T
L
denote the driving torque of E1, E2 , ICE, and loading torque, re-
spectively. J
S1
, J
S2
, J
carrier
, and J
ring
refer to the moment of inertia of S1, S2, carrier, and ring,
respectively. ˛
S1
, ˛
S2
, ˛
carrier
, and ˛
ring
indicate the accelerations of S1, S2, carrier, and ring,
respectively.
e equilibrium equations of the torques of the whole system are:
T
carrier
C T
S1
C T
S2
C T
ring
D 0 (2.12)
T
ring
C T
S1
˛
1
C T
S2
˛
2
D 0 (2.13)
T
carrier
!
carrier
C T
ring
!
ring
C T
S1
!
S1
C T
S2
!
S2
D 0: (2.14)
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