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Conceptual design of hybrid scooter transmissions with planetary gear-trains
APPLIED ENERGY
Applied Energy 84 (2007) 526–541
www.elsevier.com/locate/apenergy
Conceptual design of hybrid scooter transmissions with planetary gear-trains Kuen-Bao Sheu
*
Department of Vehicle Engineering, National Formosa University, 64 Wunhua Road, Huwei, Yuenlin 63208, Taiwan, ROC Received 11 November 2005; received in revised form 4 February 2006; accepted 25 February 2006 Available online 15 December 2006
Abstract This paper presents an approach for designing hybrid scooter transmissions with planetary gear trains. The basic concept is to combine two planetary gear trains into a split-power system; so, by incorporating clutches and brakes when engaged, the system becomes a hybrid scooter transmission. The transmissions combine the power from two power sources, a gasoline engine and an electric motor. The systems use four different modes in order to maximize the performance and reduce emissions: electric-motor mode; engine-mode and engine/charging mode; power-mode; and regenerativebraking mode. Kinematic and power flow analyses are performed. According to the analysis results, formulae for the speed ratio of the transmission are derived and a procedure for identifying the arrangements with no internal recirculation of the split power system is developed. Sixteen possible configurations of hybrid scooter transmission satisfying the design requirements are presented. A design example is used to illustrate the design procedure and operation principle of the transmission. 2006 Published by Elsevier Ltd. Keywords: Hybrid scooter; Transmission; Split-power system; Planetary gear-train
1. Introduction Due to geographic factors, the motor scooter is one of the most important transportation modes in many of Taiwan’s urban areas. To combat pollution from the scooters’ *
Tel.: +886 5 6315697; fax: +886 5 6321571. E-mail address: [email protected].
0306-2619/$ - see front matter 2006 Published by Elsevier Ltd. doi:10.1016/j.apenergy.2006.02.006
K.-B. Sheu / Applied Energy 84 (2007) 526–541
527
Nomenclature a, c, s B Ci, Ct E F
ring gear, carrier and sun gear of planetary gear train brake adjacent to axis of split-power system idling clutch of gasoline engine and shifting clutch of split-power system input member adjacent to gasoline engine of split power system one-degree-of-freedom (F = 1) and two-degrees-of-freedom (F = 2) of planetary gear-train i, j, k input member, output member and remaining member adjacent to twodegrees-of-freedom of planetary gear-train M/G input member adjacent to electric motor/generator of split-power system PF1 power carried by one-degree-of-freedom of planetary gear-train (kW) Pi, Pj, Pk powers adjacent to the input member, output member and remaining member of the two-degrees-of-freedom of planetary gear-train (kW) Pin input power of transmission (kW) RF1 speed ratio of one-degree-of-freedom of planetary gear-train RF2 speed ratio of two-degrees-of-freedom of planetary gear-train rE speed ratio of engine mode and engine/charging mode rG speed ratio of generator to engine as operating in engine/charging mode ric speed ratio of input-coupled system rM speed ratio of electric motor mode roc speed ratio of output-coupled system rP1 speed ratio of power mode 1 rRe g speed ratio of regenerative-braking mode TE torque of input member adjacent to gasoline engine of split-power system (N m) Ti, Tj, Tk torques adjacent to input member, output member and remaining member of two-degrees-of-freedom of planetary gear-train (N m) TM/G torque of input member adjacent to electric motor/generator of split-power system (N m) TW torque of output member adjacent to real wheel of split-power system (N m) W output member adjacent to real wheel of split-power system Za, Zb, Zc numbers teeth of ring gear, planet gear and sun gear of simple planetary gear train xE angular velocity of input member adjacent to gasoline engine of split power system (rpm) xM/G angular velocity of input member adjacent to electric-motor/generator of split power system (rpm) xW angular velocity of output member adjacent to real wheel of split-power system (rpm) xi, xj, xk angular velocity of input member, output member and remaining member adjacent to two-degrees-of-freedom of planetary gear-train (rpm)
gasoline engines, many efforts had been taken by the government and motorcycle industries to research and develop battery/fuel-cell powered electric scooters [1–5]. However, the battery-powered electric scooters have not yet successfully captured significant
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K.-B. Sheu / Applied Energy 84 (2007) 526–541
market share because of the poor performance of batteries together with the lack of recharge stations. Although using fuel cells in automobiles could significantly reduce emissions to almost zero, its application for scooters is limited by cost and weight. It is obvious that the fuel-cell powered scooters are not likely to displace gasoline scooters in the near future. Hybrid electric-vehicles are being developed in an attempt to overcome the limited range problems of battery-powered electric vehicles, while significantly reducing the emissions. Over the past few years, hybrid electric vehicles, primarily automobiles, have been actively developed and marketed [6–10]. In 1997, Honda Motors released a hybrid 2-wheeler concept in the 1997 Tokyo Motor show with the key goals of a 60% reduction in CO2 emissions and a 2.5 times better fuel-efficiency. In this system, a water-cooled 49 cc gasoline engine is backed by a DC brushless electric-motor, together driving the rear wheel. The gasoline engine delivers sufficient power for highspeed performance and for hill climbing, while the electric motor is engaged for lowspeed cruising. In 1999, AVL Company proposed a hybrid system that used a 50 cc carburetted lean-burn 2-stroke engine with a 0.75 kW electric motor mounted on the engine crankshaft mainly to provide increased torque during acceleration [11]. Matsuto and Wachigai proposed a motorcycle hybrid-drive system, consisting an engine and an electric motor as power sources, a traction drive continuously variable transmission (CVT), a final reduction drive and three clutches [12–14]. The system’s transmission shaft and electric-motor shaft are coaxially in series in the longitudinal direction of the vehicular body and in parallel to the crankshaft of the engine. Sheu and Hsu also presented a parallel hybrid motorcycle transmission [15]. This system incorporates a mechanical type rubber V-belt CVT and chain drives to combine power of the two power-sources, namely a gasoline engine and an electric motor. Advantages of this transmission include the use of only one electric motor/generator and the shift of the operating mode accomplished by the mechanical type clutch for easy control and low cost. A transmission used in gasoline motorcycles typically utilizes the discrete speed ratio transmission that works by alternating the gear pairs, and the CVT that transmits power by using the rubber V-belt drive. Advantages of the CVT include smoother speedcharacteristics, adequate speed ratio, a simpler mechanism, low cost, etc. The benefits claimed for conventional fixed-speed gear transmissions in comparison to CVT include reliability, higher mechanical efficiency and mature manufacturing technology. Planetary gear trains (PGTs) offer the possibility of achieving a given speed-ratio with a smaller weight and size than could be acheived with an ordinary gear-train. The coaxial design of the PGT provides an advantage in that a different speed-ratio can be achieved using the same planetary gear set by simply changing the input, output or reaction member. Hence, we consider the design of hybrid scooter transmission using the PGTs in this paper. This paper presents a procedure for designing the hybrid scooter transmissions with PGTs. We first propose two design concepts utilizing the split-power system. Then, we perform the kinematic and power flow analyses. Finally, according to the design requirements suitable for the hybrid scooter, we recognize the new designs. A design example is also used to illustrate the design procedure and operation principle of the transmission. 2. Design concepts As shown in Fig. 1, the hybrid scooter system proposed here utilizes a gasoline engine and an electric motor to provide the traction force to the rear wheel. The electric motor
K.-B. Sheu / Applied Energy 84 (2007) 526–541
529
Feed-back signals
Operator commands
Controller Transmission gear box
Motor/ Generator Inverter
Engine
Wheel
Battery Fig. 1. Schematic diagram of hybrid scooter.
can function as a motor or a generator, according to the driving condition and battery power levels. The electronic controller receives commands from a driver and receives feedback signals from sensors to select the operating mode and to decide how much power is needed to drive the scooter and how much to charge the battery. Traditionally, the top speed of a 50cc gasoline engine scooter is about 70–75 km/h, and a two-speed transmission can satisfy this requirement for the hybrid scooter. One of the strategies applied in this hybrid system is to run the electric motor only for the lower speeds so that the emission in urban areas is limited to the minimum. For the maximum performance and climbing hills, both the electric motor and the engine drive the scooter simultaneously. On cruising, the engine drives the scooter and simultaneously charges the batteries by switching the electric motor into a generator. The engine will be controlled to operate at the optimal specific fuel consumption regions where the emissions are also lower. The synthesis of the PGTs has been studied extensively [16–20], and various PGTs have been developed as a hybrid transmission. The design concepts proposed here are referred to as a split-power system that consists of a one-degree-of-freedom (dof) PGT (F = 1) and a two-dof PGT (F = 2) as shown in Fig. 2. This split-power system can be classified as an input-coupled system or an output-coupled system. One shaft of the gear train is linked to the power input side of an input-coupled system, as shown in Fig. 2(a); while the other shaft of the gear train is linked to the power output side for an output-coupled system, Fig. 2(b). One of the two-dof PGT members and the two coupled rotating members can be linked to the two power sources of the gasoline engine (E) and electric motor/generator (M/G), and one output member to the rear wheel (W) of the hybrid scooter.
PGT F=1 i E
k PGT F=2
(a) Input-coupled system
M/G
M/G
j
i W
E
PGT F=1 k PGT F=2
j W
(b) Output-coupled system
Fig. 2. Design concepts of a hybrid scooter transmission with the split-power system.
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K.-B. Sheu / Applied Energy 84 (2007) 526–541
When such concepts are used for designing the hybrid scooter transmissions, using an engine idling clutch Ci, a shifting clutch Ct and a brake B, the block diagram can be rearranged as shown in Fig. 3. Five operation modes of this new design can be achieved as listed in Table 1, where ‘·’ denotes that the corresponding clutches and brakes are engaged: (1) Electric-motor mode: When in the start-up or low speed situation, by engaging brake B and disengaging both clutch Ci and Ct, the two-dof PGT functions as a one-dof gear set. The electric motor alone transmits power to the scooter operating in the electric-motor mode. (2) Engine mode and engine/charging mode: During moderate and high speeds, both clutch Ci and clutch Ct are engaged and brake B is disengaged. Here, the engine alone drives the scooter via the coupled arrangement operating in the engine mode. If the battery power is low, the electric motor is switched into a generator to charge the batteries, and the transmission is operated in an engine/charging mode. (3) CVT/charging mode: During moderate and high speeds, clutch Ci is engaged and both clutch Ct and brake B are disengaged. The two-dof PGT functions as a single-input and dual-output device. Part of the engine power is transmitted to the wheel and the other part to the electric motor that is switched into a generator for charging the batteries. By regulating the speed and the load of the electric motor, the transmission functions as a CVT. (4) Power mode: When maximum acceleration is needed or during hill climbing, the scooter is operated in a power mode. With both clutch Ci and Ct engaged and brake B disengaged, the electric-motor’s power and the engine’s power are coupled together simultaneously to drive the scooter operating in the power mode 1. In addition, for the power mode 2, clutch Ci is engaged and the other clutches are disengaged. The electric motor and the engine together drive the scooter via the two-dof PGT.
PGT F=1 Ci E
B
Ct
Ct M/G PGT F=2
(a) Input-coupled system
M/G
Ci B W
E
PGT F=1
PGT F=2
W
(b) Output-coupled system
Fig. 3. Transmission configurations using an engine idling clutch Ci, a shifting clutch Ct and a brake B.
Table 1 Clutches conditions Operating mode
1 2 3 4 5
Clutches engaged
Electric-motor mode Engine mode Engine/charging mode CVT/charging mode Power mode 1 Power mode 2 Regenerative-braking mode
Ci
Ct
· · · · ·
· ·
B ·
· ·
K.-B. Sheu / Applied Energy 84 (2007) 526–541
PGT F=1 Ci E
M/G PGT F=2
(a) Input-coupled system
W
PGT F=1
M/G
Ci E
531
PGT F=2
W
(b) Output-coupled system
Fig. 4. Transmission configurations using an engine-idling clutch Ci.
(5) Regenerative-braking mode: During braking periods, with brake B engaged and both clutches Ci and Ct disengaged, the kinetic energy of the scooter is transmitted through the two-dof PGT to the generator to charge the batteries. Another rearrangement is shown in Fig. 4, where only an engine-idling clutch Ci, is used in the hybrid scooter transmissions. However, only four operating modes can be achieved: (1) electric-motor mode; (2) engine mode and engine/charging mode; (3) power mode; (4) regenerative-braking mode. Due to its benefits in terms of cost, efficiency and axial width, a simple PGT consisting of a ring gear, a carrier and planets and a sun gear is selected here. Two simple PGTs linked as a split-power system include one grounded member and two gear-trains of coupled rotating members. Theoretically, 36 connection arrangements for the input-coupled and output-coupled system are possible, since the all three members of the two simple PGTs can change positions. 3. Kinematic analysis The speed ratio of a PGT is defined as the ratio of the output speed to the input speed with the remaining members of the PGT being relatively fixed. Letting RF2 be the speed ratio of the two-dof PGT as the input member i, the output member j and the remaining member k, we have xj xk RF 2 ¼ ð1Þ xi xk For the input-coupled system as shown in Fig. 2(a), dividing Eq. (1) by xk and letting RF1 = xk/xi and ric = xj/xi be the speed ratio of the one-dof PGT and the speed ratio of the input-coupled system, we obtain ric ¼ RF 1 þ RF 2 ð1 RF 1 Þ
ð2Þ
In the same manner, the speed ratio of the output-coupled system roc as shown in Fig. 2(b) can be expressed as roc ¼
R F 1 RF 2 R F 1 þ RF 2 1
ð3Þ
Below, we derive the speed ratio of the transmission with the configurations of the inputcoupled system for each of the five operating modes. (1) Electric-motor mode: The speed ratio of a transmission is defined as the ratio of the output speed to the input speed. For the hybrid scooter transmissions, with the inputcoupled system as shown in Fig. 3(a), the speed ratio of the electric-motor mode
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rM = xj/xk can be achieved by the two-dof PGT with one member serving as a reaction member. Substituting xi = 0 into Eq. (1), we have r M ¼ 1 RF 2
ð4Þ
(2) Engine mode and engine/charging mode: The speed ratios of the engine mode and the engine/charging mode rE = xj/xi can be obtained by the input-coupled system – see Eq. (2). In addition, we let rG = xk/xi be the speed ratio of the generator to the engine as operating in the engine/charging mode. We then have rE ¼ RF 1 þ RF 2 ð1 RF 1 Þ r G ¼ RF 1
ð5Þ ð6Þ
(3) CVT/charging mode: From Eq. (1), the speed ratio of the CVT/charging mode can be achieved as xW ð1 RF 2 ÞxM=G ¼ RF 2 xW
ð7Þ
where xE, xM/G and xW are the angular speeds of the engine, the electric motor/generator and the wheel, respectively. (4) Power mode: For power mode 1, since the speeds of the engine and the electric motor are related by the kinematics of the gear trains, the transmission output speeds depend on the speeds of either the engine or electric motor, but not both. The speed ratio of the power mode 1 can be obtained from Eqs. (4) and (5) as rP1 ¼ RF 1 þ RF 2 ð1 RF 1 Þ
or
rP1 ¼ 1 RF 2
ð8Þ
In addition, from Eq. (1), the speed ratio of the power mode 2 can be achieved as xW ¼ RF 2 xE þ ð1 RF 2 ÞxM=G
ð9Þ
(5) Regenerative-braking mode: The speed ratio of the regenerative-braking mode rRe g = xk/xj can be achieved by the two-dof PGT with one member serving as a reaction member. Substituting xi = 0 into Eq. (1), we have rRe g ¼
1 1 RF 2
ð10Þ
In the same manner, for the arrangements of the output-coupled system shown in Fig. 3(b), the speed ratio of the five operating modes of the transmission can be expressed in the following equations: r M ¼ 1 RF 2 RF 1 R F 2 rE ¼ RF 1 þ R F 2 1 RF 2 rG ¼ RF 1 þ RF 2 1 RF 1 R F 2 rP1 ¼ or rP1 ¼ 1 RF 2 RF 1 þ R F 2 1 xW ¼ RF 2 xE þ ð1 RF 2 ÞxM=G 1 rRe g ¼ 1 RF 2
ð11Þ ð12Þ ð13Þ ð14Þ ð15Þ ð16Þ
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Table 2 Equations of the speed ratio of the four operating modes Operating mode
Configurations as shown in Fig. 4 Input-coupled system
Electric-motor mode Engine/charging mode
Power mode Regenerative-braking mode
rM = 1 + RF2(1/RF1 1) rE = RF1 + RF2(1 RF1)
Output-coupled system rM = RF1 F 1 RF 2 rE ¼ RFR1 þR F 2 1
rG = RF1
RF 2 rG ¼ RF 1 þR F 2 1
rP1 = RF1 + RF2(1 RF1) or rP1 = 1 RF2
F 1 RF 2 rP1 ¼ RFR1 þR or rP1 = 1 RF2 F 2 1
rRe g ¼
RF 1 RF 1 þRF 2 ð1RF 1 Þ
rRe g ¼ R1F 1
Moreover, for the design concepts using only an engine-idling clutch in the split-power system to achieve a hybrid scooter transmission, as shown in Fig. 4, the speed ratios of the four operating modes of the transmission are listed in Table 2. 4. Power-flow analysis There have been many power flow analyses of split-power transmissions [21–25]. Here Pi(Pj, Pk), Ti(Tj, Tk), and xi(xj, xk) represent the power, the torque, and the angular velocity adjacent to the input member (output member, remaining member) of the two-dof PGT, respectively. With no energy losses and under steady-state operation, the relation between the external torques and powers acting on the two-dof PGT can be expressed as Ti þ Tj þ Tk ¼ 0 T i xi þ T j xj þ T k xk ¼ 0
ð17Þ ð18Þ
From Eqs. (17) and (18) and kinematic analysis results, the torque and power relationships of the five operating modes can be obtained. Moreover, there are three types of power flow within a split-power transmission: the true split system, the negative recirculation system and the positive recirculation. The direction of power flow varies according to the speed ratio of the two-dof PGT and transmission. From Eqs. (2), (17), and (18), the ratio of the power carried by the one-dof PGT PF1 to the input power of the transmission Pin for the input-coupled system can be obtained as PF1 RF 2 ¼1 P in ric
ð19Þ
Similarly, for the output-coupled system, we have PF1 roc ¼1 P in RF 2
ð20Þ
The simple PGT can serve different functions under proper operating conditions. These functions include two gear-reduction ratios (0 < RF2 < 0.5 and 0.5 < RF2 < 1) by using the planet carrier as the output member, two overdrive ratios (1 < RF2 < 2 and RF2 > 2) by using the planet carrier as the input member and two reverse ratios (1 < RF2 < 0 and RF2 < 1) by using the planet carrier as the reaction member. Hence, according to Eqs. (19) and (20), the three types of transmission power flow can be identified as listed
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Table 3 Types of power flow of split-power transmissions Range of relative speed ratio
Type of power flow (ric > 0, roc > 0) 0 < RF2 < 1
RF2 > 1
RF2 < 0
Input-coupled
RF2 < ric RF2 > ric
0 < PF1/Pin < 1 PF1/Pin < 0
0 < PF1/Pin < 1 PF1/Pin < 0
PF1/Pin > 1
Output-coupled
RF2 < roc RF2 > roc
PF1/Pin < 0 0 < PF1/Pin < 1
PF1/Pin < 0 0 < PF1/Pin < 1
PF1/Pin > 1
in Table 3: the true split power system (0 < PF1/Pin < 1), the negative recirculation-system (PF1/Pin < 0) and the positive recirculation-system (PF1/Pin > 1). Substituting Eq. (2) into Eq. (19), the ratio of the power carried by the one-dof PGT to the input power of the transmission for the input-coupled system can be rewritten as PF1 1 ¼ P in 1 þ RF 2 =ð1 RF 2 ÞRF 1
ð21Þ
For the output-coupled system, substituting Eq. (3) into Eq. (20), we have PF1 1 ¼ P in 1 þ RF 1 =ðRF 2 1Þ
ð22Þ
From Eqs. (21) and (22), no recirculation of power of the transmission corresponds to RF2/(1 RF2)RF1 > 0 and RF1/(RF2 1) > 0 for the input-coupled and output-coupled system, respectively. Therefore, by selecting the speed ratios of the one-dof PGT RF1 and the two-dof PGT RF2, the ranges of the speed ratio for the true split-power systems can be identified and are listed in Table 4. 5. Acceptable design-concepts for hybrid scooter-transmissions To design new transmissions suitable for these hybrid scooters, the design requirements include: Because a scooter does not have a reverse gear, the speed ratio of the transmission is greater than zero; i.e. rM > 0, rE > 0. When the electric motor is serving as a generator, the rotation direction is the same as serving the electric motor; i.e. rG > 0. Because the electric motor runs at start-up to reduce emissions, the speed ratio of the transmission operating in the electric motor mode is less than in the engine mode; i.e. rM < rE.
Table 4 Range of speed ratios for the true split-power systems
Input-coupled Output-coupled
0 < RF2 < 1
RF2 > 1
RF2 < 0
RF1 > 0 RF1 < 0
RF1 < 0 RF1 > 0
RF1 < 0 RF1 < 0
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535
Since recirculation of power around an internal loop of a split-power transmission increases tooth and bearing losses and results in a lower efficiency, only the true split-power transmissions are adopted here; i.e. 0 < PPFin1 < 1. For the input-coupled system as shown in Fig. 3(a), from Eqs. (4) and (5), the relationship of the speed ratio between the one-dof PGT and two-dof PGT as Eq. (23) satisfied design requirement (1). Hence RF 1 < RF 2 < 1 RF 1 1
ð23Þ
For design requirement (2), from Eq. (6), we obtain the ranges of the speed ratio of the one-dof PGT as ð24Þ
RF 1 > 0
For design requirement (3), from Eqs. (4) and (5), the relationship of the speed ratio between the one-dof PGT and two-dof PGT as RF 2 >
1 2RF 1 1 RF 1
ð25Þ
For design requirement (4), the true split-power systems, as shown in Tables 3 and 4, correspond to the ranges of speed ratio of the one-dof PGT and two-dof PGT as the following equations: RF 1 > 0 0 < RF 2 < 1
and
RF 2 < r E
ð26Þ
According to Eqs. (23)–(26), the acceptable design concepts of hybrid scooter transmissions with the input-coupled configuration proposed here can be identified; that is, the ranges of speed ratio of the PGTs using this new transmission are defined by RF 1 > 0 0 < RF 2 < 1
and
RF 2 < r E
ð27Þ
Eq. (27) indicates that a total of eight different arrangements can be used in the hybrid scooters as shown in Fig. 5. However, from Eq. (27), we observe that the CVT/charging mode of this new transmission cannot be achieved. In Fig. 5, the ring gear, carrier and sun gear of the PGT are denoted by a, c and s, respectively, while the speed ratios for each connection are shown in terms of ring/sun teeth Za/Zs on each gear-train block. In addition, according to Eqs. (11)–(13) as well as Tables 3 and 4, no arrangement of the output-coupled system, Fig. 3(b), satisfies the design requirements be utilized in hybrid scooters. In the same manner, for the arrangements of the hybrid scooter transmissions shown in Fig. 4, the ranges of speed ratio of the PGTs used in the transmissions are defined as in Eqs. (28) and (29) for the input-coupled and output-coupled system, respectively. RF 1 > 1 and 0 < RF 1 < 1
0 < RF 2 < 1 and
RF 2 > 1
ð28Þ ð29Þ
K.-B. Sheu / Applied Energy 84 (2007) 526–541 a
a
a
B
Zs Za + Zs
s
E
Ct
B Ci
M/G
W
Ct
>
>
0.5, 0
RF 2
RF 1
0.5, 0.5
a
M/G a Zs Za + Zs
s
>
Ct
RF 2
>
>
>
1, 0
Zs
a
Ct
0.5
R F1
c
M/G a Zs
s
>
Za
E
Ct
1, 0.5
Za
a
Zs
Ci
c Zs
RF 2
Ct
E
1
M/G
RF 2
Ct E
c W
Za Zs
B
M/G
Ci E
(f) Speed ratio of PGTs:
1 R F1
0.5
2, 0.5
a Zs
a Za
W
(e) Speed ratio of PGTs:
2, 0
s
B
E
W
B Ci
M/G
W
RF 2
1
a Za
s
Ct
c
M/G
B
a Zs
s Za
E
Ct
M/G
W
Zs
Za
s
Ct
M/G
Zs
Zs
Ci
B Ci
M/G
Za
B
c
c W
Za Za + Zs
(d) Speed ratio of PGTs:
0.5
Za
1 R F1
M/G
s
Za
Ci
a
Ct
s c
1
s
B
W
E
(c) Speed ratio of PGTs:
R F1
Ct
E
W
B Ci
M/G
W
Ci
c
>
B
c
Za Za + Zs
>
c
Ct
E
0.5
E
s
Za Za + Zs
Ci
B Ci
RF 2
>
>
s a
c W
(b) Speed ratio of PGTs:
0
0.5
>
R F1
Za Za + Zs
M/G
W
(a) Speed ratio of PGTs:
0
a
E
E
M/G s
B
Ci
c W
Ct
c
Zs Za + Zs
>
Ci
s
M/G
>
c
Zs Za + Zs
>
s
Ct
>
536
Zs
B Ci
B
Ci
c W
Za Za
E
Ct E
s a
Zs
B Ci
M/G
W
(g) Speed ratio of PGTs:
(h) Speed ratio of PGTs:
R F1
R F1
2, 0
RF 2
0.5
2, 0.5
RF 2
c W
E
1
Fig. 5. Acceptable designs of the hybrid scooter-transmission corresponding to Fig. 3(a).
K.-B. Sheu / Applied Energy 84 (2007) 526–541
s
s c
Za
Zs
M/G
a
c
Za
a
Ci
Zs
s Za
E
Zs
2, 0
a
Ci E
RF 2
c W
Za Za
E
W
Zs
Ci
M/G
W
E
(b) Speed ratio of PGTs:
(a) Speed ratio of PGTs:
1 R F1
0.5
2, 0.5
a Zs
M/G s
Ci
c
M/G
W
c
a
Zs Za
Za
1 R F1
537
RF 2
1
a Za
c
M/G
s
Zs
Zs
s Za
E
Zs
M/G
s
c W
s
Ci
a
E
Za Za
E
Ci
M/G
W
Za Zs
a
Ci
Zs
Zs
c W
Ci
M/G
W
E
(c) Speed ratio of PGTs:
(d) Speed ratio of PGTs:
R F1
R F1
2, 0
RF 2
0.5
2, 0.5
RF 2
1
Fig. 6. Acceptable designs of the hybrid scooter-transmission corresponding to Fig. 4(a).
Eqs. (28) and (29) show a total of four different arrangements that can be used in the hybrid scooters for the input-coupled and output-coupled system, respectively, as shown in Figs. 6 and 7. 6. Design example In this section, we demonstrate the feasibility of the hybrid scooter transmission proposed in this paper by a numerical example. Assume that the top speed of the hybrid scooter of 75 km/h corresponding to an engine speed of 8500 rpm is desired. The top speed of the hybrid scooter occurs when the hybrid scooter is operating in the engine mode. With the drive wheel tyre diameter of 0.425 m and the final reduction ratio of 13, the speed ratio of the engine mode can be obtained as rE ¼ 0:716
ð30Þ
Selecting the ratio between the two speed stage of the electric-motor mode and the engine mode rE/rM = 1.8, then the speed ratio of the electric mode is rM ¼ 0:4
ð31Þ
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K.-B. Sheu / Applied Energy 84 (2007) 526–541
a
a Zs
M/G Za
Ci
c
Za
M/G
W
W
E
E
W
0
RF 1
0.5, 1 RF 2
c
Za
s
Zs Zs
W
Ci
(a) Speed ratio of PGTs:
a
Ci
c
Za
Zs
(b) Speed ratio of PGTs:
2
0
RF 1
0.5, RF 2
c
M/G
Za
Ci
a W
M/G
W
2
E
RF 1 1, 1 RF 2
2
c Zs
a c
Za
Zs
s
Zs
E
Ci
(c) Speed ratio of PGTs:
0.5
Za
a
Zs
Za
E
E
s
Za Za
Ci
M/G
s M/G
c Zs
a
Ci
Za
E
Zs Za
a
Zs
s
M/G
c Zs
W
M/G
W
Ci E
(d) Speed ratio of PGTs:
0.5
RF 1 1, RF 2
2
Fig. 7. Acceptable designs of the hybrid scooter-transmission corresponding to Fig. 4(b).
Substituting Eq. (31) into Eq. (4), we obtain the speed ratio of the two-dof PGT as RF 2 ¼ 0:6
ð32Þ
Substituting Eqs. (30) and (32) into Eq. (5), the speed ratio of the one-dof PGT can be obtained as RF 1 ¼ 0:29
ð33Þ
For this design example of RF1 = 0.29 and RF2 = 0.6, the configuration shown in Fig. 5(b) can be satisfied. Moreover, with the speed ratio of RF2 = 0.6, the teeth of the ring gear, planets and sun gear of the two-dof PGT can be selected as Za = 72, Zp = 12 and Zs = 48, respectively. Similarly, for the one-dof PGT, the teeth of the ring gear, planets and sun gear, respectively, Za = 21, Zp = 15 and Zs = 51 can be selected. Fig. 8 shows a preferred example of this new transmission. This transmission is made up of two simple PGTs, a final reduction assembly consisting of a simple PGT and a chain drive, a one-way clutch as the brake B, a shoe type centrifugal clutch as the engine-idling
K.-B. Sheu / Applied Energy 84 (2007) 526–541
72 12
51 15 Ct
48
21
M/G
539
B Ci E
W
Two-dof PGT
One-dof PGT
Final reduction ratio of 13 Output shaft Fig. 8. Design example of the hybrid scooter-transmission. Table 5 Numerical example for the design of RF1 = 0.29 and RF2 = 0.6 Operating mode
Equation of the speed ratios and torque ratios
Numerical relations
Electric-motor mode
rM = 1 RF2 TW = (1/rM)TM
xW = 0.4xM TW = 2.5TM
Engine mode and Engine/charging mode
rE = RF1 + RF2(1 RF1) TW = (1/rE)/TE rG = RF1
xW = 0.716xE TW = 1.4TE xG = 0.29xE
Power mode 1
rP1E = RF1 + RF2(1 RF1) or rP1M = 1 RF2 TW = (1/rP1E · TE + 1/rP1M · TM)
xW = 0.716xE or xW = 0.4xM TW = (1.4TE + 2.5TM)
Power mode 2
xW = RF2xE + (1 RF2)xM TW = (TE/rE + RF1/rE · TM)
xW = 0.6xE + 0.4xM TW = (1.4TE + 0.4TM)
clutch Ci and an electromagnetic clutch as the shifting clutch Ct. The electric motor is connected to the sun gear of the two-dof PGT and to the carrier of the one-dof PGT by the clutch Ct. The sun gear of the one-dof PGT and the ring gear of the two-dof PGT are connected together by a common shaft. The common shaft is connected to the one-way clutch B while to the engine by the clutch Ci. The carrier of the two-dof PGT is linked to the final reduction assembly. Three operation modes of this transmission can be achieved based on the clutching conditions as listed in Table 1: (1) electric-motor mode; (2) engine mode and engine/charging mode; (3) power mode 1 and power mode 2. The regenerative braking mode is ignored since the one-way clutch is used as the brake B. The speed and torque ratios of the three operating modes can be obtained as summarized in Table 5. 7. Conclusions Although different types of clean-energy scooters have been introduced, they are unlikely to replace conventional gasoline-powered scooters. The hybrid concept is emerging to fill the gap between zero emissions and the currently well-established gasoline-engine technology.
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In this work, a method for designing the hybrid scooter transmissions is presented by utilizing the concepts of the split-power system. The split-power system, consisting of a one-dof PGT and a two-dof PGT, is classified as an input-coupled and output-coupled system. Two kinds of the split-power transmission concepts, utilizing the clutches and brakes engaged, used in the hybrid scooter are proposed in this paper. The new transmissions provides four modes of operation that can be used in the hybrid scooter: (1) electricmotor mode, (2) engine mode and engine/charging mode, (3) power mode, and (4) regenerative braking mode. Kinematic and power flow analyses have been performed, and a method for identifying the arrangements with no internal recirculation of the split-power system has been developed. With four design requirements adopted in this paper, the ranges of speed ratio of the PGTs using in the hybrid scooter transmissions have been defined. According to the two kinds of new design concepts, there are 16 configurations of the hybrid scooter transmission satisfying the design requirements. Lastly, a design example is used to illustrate the design procedure and operation principle of the transmission. Acknowledgment The author is grateful to the National Science Council of Republic of China for the support of this research through Grant NSC 93-2212-E-150-010 and to the National Formosa University. References [1] Chiu YC, Tzeng GH. The market acceptance of electric motorcycles in Taiwan experience obtained through a stated-preference analysis. Transport Res D 1999;4:127–46. [2] Wang JH, Chiang W-L, Shu Jet PH. The prospects of the fuel-cell motorcycle in Taiwan. J Power Sources 2000;86:151–7. [3] Lin B. Conceptual design and modeling of a fuel-cell scooter for urban Asia. J Power Sources 2000;86:202–13. [4] Colella WG. Market prospects, design features, and performance of a fuel-cell powered scooter. J Power Sources 2000;86:255–60. [5] Asia Pacific Fuel-Cell Technology Ltd. (APFCT). Available from: http://www.apfct.com/. [6] Yamaguchi K, Miyaishi Y. Hybrid vehicle power train, US Patent 5643119; 1997. [7] Yamamoto Y, Chubachi K. Power transmitting apparatus for a hybrid vehicle, US Patent 5755303; 1998. [8] Brown LT, Ortmann WJ, Kraska MP. Hybrid vehicle power train and control thereof. US Patent 6176808; 2001. [9] Tsai LW, Schultz G, Higuchi N. A novel parallel hybrid transmission. Trans ASME J Mech Design 2001;123:161–7. [10] Bitsche O, Gutmann G. Review – systems for hybrid cars. J Power Sources 2004;127:8–15. [11] Laimbock FJ et al. HYC – a hybrid concept with small lean-burn engine, electrically-heated catalyst and asynchronous motor for enhanced performance and ULEV level emissions. SAE Paper 991330; 1999. [12] Matsuto T, Wachigai K. Power unit for motorcycle. US Patent 6109383; 2000. [13] Matsuto T, Wachigai K. Motorcycle with hybrid-drive system. US Patent 6158543; 2000. [14] Matsuto T, Wachigai K. Power unit arrangement structure for motorcycle. US Patent 6276481; 2001. [15] Sheu K-B, Hsu T-H. Design and implementation of a novel hybrid electric motorcycle transmission. Appl Energy 2005 [accepted for publication]. [16] Freudenstein F. An application of Boolean algebra to the motion of epicyclic drives. ASME J Eng Ind 1971;93:176–82. [17] Tsai LW, Lin CC. The creation of non-fractionated, two-degrees-of-freedom epicyclic gear trains. ASME J Mech Trans Automat Design 1989;111:524–9.
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[18] Olson DG, Erdman AG, Riley DR. Topological analysis of single-degree-of-freedom PGTs. Trans ASME 1991;113:10–6. [19] Hsu CH, Wu YC. Automatic detection of embedded structure in PGTs. ASME J Mech Design 1997;119:315–8. [20] White G. Derivation of high efficiency two-stage epicyclic gears. Mech Mach Theory 2003;38:149–59. [21] White G. Properties of differential transmissions. The Engineer, Technical Contributors Section; 1967. p. 105–11. [22] White G. Multiple-stage, split-power transmissions. J Mechanisms 1970;5:505–20. [23] Sanger DJ. The determination of power flow in multiple-path transmission systems. Mech Mach Theory 1972;7:103–9. [24] White G. Compounded two-path variable-ratio transmissions with coaxial gear-trains. Mech Mach Theory 1976;11:227–40. [25] Pennestri E, Freudenstein F. A systematic approach to power-flow and static-force analysis in epicyclic spurgear trains. ASME J Mech Design 1993;115:639–44.
Applied Energy 84 (2007) 526–541
www.elsevier.com/locate/apenergy
Conceptual design of hybrid scooter transmissions with planetary gear-trains Kuen-Bao Sheu
*
Department of Vehicle Engineering, National Formosa University, 64 Wunhua Road, Huwei, Yuenlin 63208, Taiwan, ROC Received 11 November 2005; received in revised form 4 February 2006; accepted 25 February 2006 Available online 15 December 2006
Abstract This paper presents an approach for designing hybrid scooter transmissions with planetary gear trains. The basic concept is to combine two planetary gear trains into a split-power system; so, by incorporating clutches and brakes when engaged, the system becomes a hybrid scooter transmission. The transmissions combine the power from two power sources, a gasoline engine and an electric motor. The systems use four different modes in order to maximize the performance and reduce emissions: electric-motor mode; engine-mode and engine/charging mode; power-mode; and regenerativebraking mode. Kinematic and power flow analyses are performed. According to the analysis results, formulae for the speed ratio of the transmission are derived and a procedure for identifying the arrangements with no internal recirculation of the split power system is developed. Sixteen possible configurations of hybrid scooter transmission satisfying the design requirements are presented. A design example is used to illustrate the design procedure and operation principle of the transmission. 2006 Published by Elsevier Ltd. Keywords: Hybrid scooter; Transmission; Split-power system; Planetary gear-train
1. Introduction Due to geographic factors, the motor scooter is one of the most important transportation modes in many of Taiwan’s urban areas. To combat pollution from the scooters’ *
Tel.: +886 5 6315697; fax: +886 5 6321571. E-mail address: [email protected].
0306-2619/$ - see front matter 2006 Published by Elsevier Ltd. doi:10.1016/j.apenergy.2006.02.006
K.-B. Sheu / Applied Energy 84 (2007) 526–541
527
Nomenclature a, c, s B Ci, Ct E F
ring gear, carrier and sun gear of planetary gear train brake adjacent to axis of split-power system idling clutch of gasoline engine and shifting clutch of split-power system input member adjacent to gasoline engine of split power system one-degree-of-freedom (F = 1) and two-degrees-of-freedom (F = 2) of planetary gear-train i, j, k input member, output member and remaining member adjacent to twodegrees-of-freedom of planetary gear-train M/G input member adjacent to electric motor/generator of split-power system PF1 power carried by one-degree-of-freedom of planetary gear-train (kW) Pi, Pj, Pk powers adjacent to the input member, output member and remaining member of the two-degrees-of-freedom of planetary gear-train (kW) Pin input power of transmission (kW) RF1 speed ratio of one-degree-of-freedom of planetary gear-train RF2 speed ratio of two-degrees-of-freedom of planetary gear-train rE speed ratio of engine mode and engine/charging mode rG speed ratio of generator to engine as operating in engine/charging mode ric speed ratio of input-coupled system rM speed ratio of electric motor mode roc speed ratio of output-coupled system rP1 speed ratio of power mode 1 rRe g speed ratio of regenerative-braking mode TE torque of input member adjacent to gasoline engine of split-power system (N m) Ti, Tj, Tk torques adjacent to input member, output member and remaining member of two-degrees-of-freedom of planetary gear-train (N m) TM/G torque of input member adjacent to electric motor/generator of split-power system (N m) TW torque of output member adjacent to real wheel of split-power system (N m) W output member adjacent to real wheel of split-power system Za, Zb, Zc numbers teeth of ring gear, planet gear and sun gear of simple planetary gear train xE angular velocity of input member adjacent to gasoline engine of split power system (rpm) xM/G angular velocity of input member adjacent to electric-motor/generator of split power system (rpm) xW angular velocity of output member adjacent to real wheel of split-power system (rpm) xi, xj, xk angular velocity of input member, output member and remaining member adjacent to two-degrees-of-freedom of planetary gear-train (rpm)
gasoline engines, many efforts had been taken by the government and motorcycle industries to research and develop battery/fuel-cell powered electric scooters [1–5]. However, the battery-powered electric scooters have not yet successfully captured significant
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market share because of the poor performance of batteries together with the lack of recharge stations. Although using fuel cells in automobiles could significantly reduce emissions to almost zero, its application for scooters is limited by cost and weight. It is obvious that the fuel-cell powered scooters are not likely to displace gasoline scooters in the near future. Hybrid electric-vehicles are being developed in an attempt to overcome the limited range problems of battery-powered electric vehicles, while significantly reducing the emissions. Over the past few years, hybrid electric vehicles, primarily automobiles, have been actively developed and marketed [6–10]. In 1997, Honda Motors released a hybrid 2-wheeler concept in the 1997 Tokyo Motor show with the key goals of a 60% reduction in CO2 emissions and a 2.5 times better fuel-efficiency. In this system, a water-cooled 49 cc gasoline engine is backed by a DC brushless electric-motor, together driving the rear wheel. The gasoline engine delivers sufficient power for highspeed performance and for hill climbing, while the electric motor is engaged for lowspeed cruising. In 1999, AVL Company proposed a hybrid system that used a 50 cc carburetted lean-burn 2-stroke engine with a 0.75 kW electric motor mounted on the engine crankshaft mainly to provide increased torque during acceleration [11]. Matsuto and Wachigai proposed a motorcycle hybrid-drive system, consisting an engine and an electric motor as power sources, a traction drive continuously variable transmission (CVT), a final reduction drive and three clutches [12–14]. The system’s transmission shaft and electric-motor shaft are coaxially in series in the longitudinal direction of the vehicular body and in parallel to the crankshaft of the engine. Sheu and Hsu also presented a parallel hybrid motorcycle transmission [15]. This system incorporates a mechanical type rubber V-belt CVT and chain drives to combine power of the two power-sources, namely a gasoline engine and an electric motor. Advantages of this transmission include the use of only one electric motor/generator and the shift of the operating mode accomplished by the mechanical type clutch for easy control and low cost. A transmission used in gasoline motorcycles typically utilizes the discrete speed ratio transmission that works by alternating the gear pairs, and the CVT that transmits power by using the rubber V-belt drive. Advantages of the CVT include smoother speedcharacteristics, adequate speed ratio, a simpler mechanism, low cost, etc. The benefits claimed for conventional fixed-speed gear transmissions in comparison to CVT include reliability, higher mechanical efficiency and mature manufacturing technology. Planetary gear trains (PGTs) offer the possibility of achieving a given speed-ratio with a smaller weight and size than could be acheived with an ordinary gear-train. The coaxial design of the PGT provides an advantage in that a different speed-ratio can be achieved using the same planetary gear set by simply changing the input, output or reaction member. Hence, we consider the design of hybrid scooter transmission using the PGTs in this paper. This paper presents a procedure for designing the hybrid scooter transmissions with PGTs. We first propose two design concepts utilizing the split-power system. Then, we perform the kinematic and power flow analyses. Finally, according to the design requirements suitable for the hybrid scooter, we recognize the new designs. A design example is also used to illustrate the design procedure and operation principle of the transmission. 2. Design concepts As shown in Fig. 1, the hybrid scooter system proposed here utilizes a gasoline engine and an electric motor to provide the traction force to the rear wheel. The electric motor
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529
Feed-back signals
Operator commands
Controller Transmission gear box
Motor/ Generator Inverter
Engine
Wheel
Battery Fig. 1. Schematic diagram of hybrid scooter.
can function as a motor or a generator, according to the driving condition and battery power levels. The electronic controller receives commands from a driver and receives feedback signals from sensors to select the operating mode and to decide how much power is needed to drive the scooter and how much to charge the battery. Traditionally, the top speed of a 50cc gasoline engine scooter is about 70–75 km/h, and a two-speed transmission can satisfy this requirement for the hybrid scooter. One of the strategies applied in this hybrid system is to run the electric motor only for the lower speeds so that the emission in urban areas is limited to the minimum. For the maximum performance and climbing hills, both the electric motor and the engine drive the scooter simultaneously. On cruising, the engine drives the scooter and simultaneously charges the batteries by switching the electric motor into a generator. The engine will be controlled to operate at the optimal specific fuel consumption regions where the emissions are also lower. The synthesis of the PGTs has been studied extensively [16–20], and various PGTs have been developed as a hybrid transmission. The design concepts proposed here are referred to as a split-power system that consists of a one-degree-of-freedom (dof) PGT (F = 1) and a two-dof PGT (F = 2) as shown in Fig. 2. This split-power system can be classified as an input-coupled system or an output-coupled system. One shaft of the gear train is linked to the power input side of an input-coupled system, as shown in Fig. 2(a); while the other shaft of the gear train is linked to the power output side for an output-coupled system, Fig. 2(b). One of the two-dof PGT members and the two coupled rotating members can be linked to the two power sources of the gasoline engine (E) and electric motor/generator (M/G), and one output member to the rear wheel (W) of the hybrid scooter.
PGT F=1 i E
k PGT F=2
(a) Input-coupled system
M/G
M/G
j
i W
E
PGT F=1 k PGT F=2
j W
(b) Output-coupled system
Fig. 2. Design concepts of a hybrid scooter transmission with the split-power system.
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K.-B. Sheu / Applied Energy 84 (2007) 526–541
When such concepts are used for designing the hybrid scooter transmissions, using an engine idling clutch Ci, a shifting clutch Ct and a brake B, the block diagram can be rearranged as shown in Fig. 3. Five operation modes of this new design can be achieved as listed in Table 1, where ‘·’ denotes that the corresponding clutches and brakes are engaged: (1) Electric-motor mode: When in the start-up or low speed situation, by engaging brake B and disengaging both clutch Ci and Ct, the two-dof PGT functions as a one-dof gear set. The electric motor alone transmits power to the scooter operating in the electric-motor mode. (2) Engine mode and engine/charging mode: During moderate and high speeds, both clutch Ci and clutch Ct are engaged and brake B is disengaged. Here, the engine alone drives the scooter via the coupled arrangement operating in the engine mode. If the battery power is low, the electric motor is switched into a generator to charge the batteries, and the transmission is operated in an engine/charging mode. (3) CVT/charging mode: During moderate and high speeds, clutch Ci is engaged and both clutch Ct and brake B are disengaged. The two-dof PGT functions as a single-input and dual-output device. Part of the engine power is transmitted to the wheel and the other part to the electric motor that is switched into a generator for charging the batteries. By regulating the speed and the load of the electric motor, the transmission functions as a CVT. (4) Power mode: When maximum acceleration is needed or during hill climbing, the scooter is operated in a power mode. With both clutch Ci and Ct engaged and brake B disengaged, the electric-motor’s power and the engine’s power are coupled together simultaneously to drive the scooter operating in the power mode 1. In addition, for the power mode 2, clutch Ci is engaged and the other clutches are disengaged. The electric motor and the engine together drive the scooter via the two-dof PGT.
PGT F=1 Ci E
B
Ct
Ct M/G PGT F=2
(a) Input-coupled system
M/G
Ci B W
E
PGT F=1
PGT F=2
W
(b) Output-coupled system
Fig. 3. Transmission configurations using an engine idling clutch Ci, a shifting clutch Ct and a brake B.
Table 1 Clutches conditions Operating mode
1 2 3 4 5
Clutches engaged
Electric-motor mode Engine mode Engine/charging mode CVT/charging mode Power mode 1 Power mode 2 Regenerative-braking mode
Ci
Ct
· · · · ·
· ·
B ·
· ·
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PGT F=1 Ci E
M/G PGT F=2
(a) Input-coupled system
W
PGT F=1
M/G
Ci E
531
PGT F=2
W
(b) Output-coupled system
Fig. 4. Transmission configurations using an engine-idling clutch Ci.
(5) Regenerative-braking mode: During braking periods, with brake B engaged and both clutches Ci and Ct disengaged, the kinetic energy of the scooter is transmitted through the two-dof PGT to the generator to charge the batteries. Another rearrangement is shown in Fig. 4, where only an engine-idling clutch Ci, is used in the hybrid scooter transmissions. However, only four operating modes can be achieved: (1) electric-motor mode; (2) engine mode and engine/charging mode; (3) power mode; (4) regenerative-braking mode. Due to its benefits in terms of cost, efficiency and axial width, a simple PGT consisting of a ring gear, a carrier and planets and a sun gear is selected here. Two simple PGTs linked as a split-power system include one grounded member and two gear-trains of coupled rotating members. Theoretically, 36 connection arrangements for the input-coupled and output-coupled system are possible, since the all three members of the two simple PGTs can change positions. 3. Kinematic analysis The speed ratio of a PGT is defined as the ratio of the output speed to the input speed with the remaining members of the PGT being relatively fixed. Letting RF2 be the speed ratio of the two-dof PGT as the input member i, the output member j and the remaining member k, we have xj xk RF 2 ¼ ð1Þ xi xk For the input-coupled system as shown in Fig. 2(a), dividing Eq. (1) by xk and letting RF1 = xk/xi and ric = xj/xi be the speed ratio of the one-dof PGT and the speed ratio of the input-coupled system, we obtain ric ¼ RF 1 þ RF 2 ð1 RF 1 Þ
ð2Þ
In the same manner, the speed ratio of the output-coupled system roc as shown in Fig. 2(b) can be expressed as roc ¼
R F 1 RF 2 R F 1 þ RF 2 1
ð3Þ
Below, we derive the speed ratio of the transmission with the configurations of the inputcoupled system for each of the five operating modes. (1) Electric-motor mode: The speed ratio of a transmission is defined as the ratio of the output speed to the input speed. For the hybrid scooter transmissions, with the inputcoupled system as shown in Fig. 3(a), the speed ratio of the electric-motor mode
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rM = xj/xk can be achieved by the two-dof PGT with one member serving as a reaction member. Substituting xi = 0 into Eq. (1), we have r M ¼ 1 RF 2
ð4Þ
(2) Engine mode and engine/charging mode: The speed ratios of the engine mode and the engine/charging mode rE = xj/xi can be obtained by the input-coupled system – see Eq. (2). In addition, we let rG = xk/xi be the speed ratio of the generator to the engine as operating in the engine/charging mode. We then have rE ¼ RF 1 þ RF 2 ð1 RF 1 Þ r G ¼ RF 1
ð5Þ ð6Þ
(3) CVT/charging mode: From Eq. (1), the speed ratio of the CVT/charging mode can be achieved as xW ð1 RF 2 ÞxM=G ¼ RF 2 xW
ð7Þ
where xE, xM/G and xW are the angular speeds of the engine, the electric motor/generator and the wheel, respectively. (4) Power mode: For power mode 1, since the speeds of the engine and the electric motor are related by the kinematics of the gear trains, the transmission output speeds depend on the speeds of either the engine or electric motor, but not both. The speed ratio of the power mode 1 can be obtained from Eqs. (4) and (5) as rP1 ¼ RF 1 þ RF 2 ð1 RF 1 Þ
or
rP1 ¼ 1 RF 2
ð8Þ
In addition, from Eq. (1), the speed ratio of the power mode 2 can be achieved as xW ¼ RF 2 xE þ ð1 RF 2 ÞxM=G
ð9Þ
(5) Regenerative-braking mode: The speed ratio of the regenerative-braking mode rRe g = xk/xj can be achieved by the two-dof PGT with one member serving as a reaction member. Substituting xi = 0 into Eq. (1), we have rRe g ¼
1 1 RF 2
ð10Þ
In the same manner, for the arrangements of the output-coupled system shown in Fig. 3(b), the speed ratio of the five operating modes of the transmission can be expressed in the following equations: r M ¼ 1 RF 2 RF 1 R F 2 rE ¼ RF 1 þ R F 2 1 RF 2 rG ¼ RF 1 þ RF 2 1 RF 1 R F 2 rP1 ¼ or rP1 ¼ 1 RF 2 RF 1 þ R F 2 1 xW ¼ RF 2 xE þ ð1 RF 2 ÞxM=G 1 rRe g ¼ 1 RF 2
ð11Þ ð12Þ ð13Þ ð14Þ ð15Þ ð16Þ
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Table 2 Equations of the speed ratio of the four operating modes Operating mode
Configurations as shown in Fig. 4 Input-coupled system
Electric-motor mode Engine/charging mode
Power mode Regenerative-braking mode
rM = 1 + RF2(1/RF1 1) rE = RF1 + RF2(1 RF1)
Output-coupled system rM = RF1 F 1 RF 2 rE ¼ RFR1 þR F 2 1
rG = RF1
RF 2 rG ¼ RF 1 þR F 2 1
rP1 = RF1 + RF2(1 RF1) or rP1 = 1 RF2
F 1 RF 2 rP1 ¼ RFR1 þR or rP1 = 1 RF2 F 2 1
rRe g ¼
RF 1 RF 1 þRF 2 ð1RF 1 Þ
rRe g ¼ R1F 1
Moreover, for the design concepts using only an engine-idling clutch in the split-power system to achieve a hybrid scooter transmission, as shown in Fig. 4, the speed ratios of the four operating modes of the transmission are listed in Table 2. 4. Power-flow analysis There have been many power flow analyses of split-power transmissions [21–25]. Here Pi(Pj, Pk), Ti(Tj, Tk), and xi(xj, xk) represent the power, the torque, and the angular velocity adjacent to the input member (output member, remaining member) of the two-dof PGT, respectively. With no energy losses and under steady-state operation, the relation between the external torques and powers acting on the two-dof PGT can be expressed as Ti þ Tj þ Tk ¼ 0 T i xi þ T j xj þ T k xk ¼ 0
ð17Þ ð18Þ
From Eqs. (17) and (18) and kinematic analysis results, the torque and power relationships of the five operating modes can be obtained. Moreover, there are three types of power flow within a split-power transmission: the true split system, the negative recirculation system and the positive recirculation. The direction of power flow varies according to the speed ratio of the two-dof PGT and transmission. From Eqs. (2), (17), and (18), the ratio of the power carried by the one-dof PGT PF1 to the input power of the transmission Pin for the input-coupled system can be obtained as PF1 RF 2 ¼1 P in ric
ð19Þ
Similarly, for the output-coupled system, we have PF1 roc ¼1 P in RF 2
ð20Þ
The simple PGT can serve different functions under proper operating conditions. These functions include two gear-reduction ratios (0 < RF2 < 0.5 and 0.5 < RF2 < 1) by using the planet carrier as the output member, two overdrive ratios (1 < RF2 < 2 and RF2 > 2) by using the planet carrier as the input member and two reverse ratios (1 < RF2 < 0 and RF2 < 1) by using the planet carrier as the reaction member. Hence, according to Eqs. (19) and (20), the three types of transmission power flow can be identified as listed
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Table 3 Types of power flow of split-power transmissions Range of relative speed ratio
Type of power flow (ric > 0, roc > 0) 0 < RF2 < 1
RF2 > 1
RF2 < 0
Input-coupled
RF2 < ric RF2 > ric
0 < PF1/Pin < 1 PF1/Pin < 0
0 < PF1/Pin < 1 PF1/Pin < 0
PF1/Pin > 1
Output-coupled
RF2 < roc RF2 > roc
PF1/Pin < 0 0 < PF1/Pin < 1
PF1/Pin < 0 0 < PF1/Pin < 1
PF1/Pin > 1
in Table 3: the true split power system (0 < PF1/Pin < 1), the negative recirculation-system (PF1/Pin < 0) and the positive recirculation-system (PF1/Pin > 1). Substituting Eq. (2) into Eq. (19), the ratio of the power carried by the one-dof PGT to the input power of the transmission for the input-coupled system can be rewritten as PF1 1 ¼ P in 1 þ RF 2 =ð1 RF 2 ÞRF 1
ð21Þ
For the output-coupled system, substituting Eq. (3) into Eq. (20), we have PF1 1 ¼ P in 1 þ RF 1 =ðRF 2 1Þ
ð22Þ
From Eqs. (21) and (22), no recirculation of power of the transmission corresponds to RF2/(1 RF2)RF1 > 0 and RF1/(RF2 1) > 0 for the input-coupled and output-coupled system, respectively. Therefore, by selecting the speed ratios of the one-dof PGT RF1 and the two-dof PGT RF2, the ranges of the speed ratio for the true split-power systems can be identified and are listed in Table 4. 5. Acceptable design-concepts for hybrid scooter-transmissions To design new transmissions suitable for these hybrid scooters, the design requirements include: Because a scooter does not have a reverse gear, the speed ratio of the transmission is greater than zero; i.e. rM > 0, rE > 0. When the electric motor is serving as a generator, the rotation direction is the same as serving the electric motor; i.e. rG > 0. Because the electric motor runs at start-up to reduce emissions, the speed ratio of the transmission operating in the electric motor mode is less than in the engine mode; i.e. rM < rE.
Table 4 Range of speed ratios for the true split-power systems
Input-coupled Output-coupled
0 < RF2 < 1
RF2 > 1
RF2 < 0
RF1 > 0 RF1 < 0
RF1 < 0 RF1 > 0
RF1 < 0 RF1 < 0
K.-B. Sheu / Applied Energy 84 (2007) 526–541
535
Since recirculation of power around an internal loop of a split-power transmission increases tooth and bearing losses and results in a lower efficiency, only the true split-power transmissions are adopted here; i.e. 0 < PPFin1 < 1. For the input-coupled system as shown in Fig. 3(a), from Eqs. (4) and (5), the relationship of the speed ratio between the one-dof PGT and two-dof PGT as Eq. (23) satisfied design requirement (1). Hence RF 1 < RF 2 < 1 RF 1 1
ð23Þ
For design requirement (2), from Eq. (6), we obtain the ranges of the speed ratio of the one-dof PGT as ð24Þ
RF 1 > 0
For design requirement (3), from Eqs. (4) and (5), the relationship of the speed ratio between the one-dof PGT and two-dof PGT as RF 2 >
1 2RF 1 1 RF 1
ð25Þ
For design requirement (4), the true split-power systems, as shown in Tables 3 and 4, correspond to the ranges of speed ratio of the one-dof PGT and two-dof PGT as the following equations: RF 1 > 0 0 < RF 2 < 1
and
RF 2 < r E
ð26Þ
According to Eqs. (23)–(26), the acceptable design concepts of hybrid scooter transmissions with the input-coupled configuration proposed here can be identified; that is, the ranges of speed ratio of the PGTs using this new transmission are defined by RF 1 > 0 0 < RF 2 < 1
and
RF 2 < r E
ð27Þ
Eq. (27) indicates that a total of eight different arrangements can be used in the hybrid scooters as shown in Fig. 5. However, from Eq. (27), we observe that the CVT/charging mode of this new transmission cannot be achieved. In Fig. 5, the ring gear, carrier and sun gear of the PGT are denoted by a, c and s, respectively, while the speed ratios for each connection are shown in terms of ring/sun teeth Za/Zs on each gear-train block. In addition, according to Eqs. (11)–(13) as well as Tables 3 and 4, no arrangement of the output-coupled system, Fig. 3(b), satisfies the design requirements be utilized in hybrid scooters. In the same manner, for the arrangements of the hybrid scooter transmissions shown in Fig. 4, the ranges of speed ratio of the PGTs used in the transmissions are defined as in Eqs. (28) and (29) for the input-coupled and output-coupled system, respectively. RF 1 > 1 and 0 < RF 1 < 1
0 < RF 2 < 1 and
RF 2 > 1
ð28Þ ð29Þ
K.-B. Sheu / Applied Energy 84 (2007) 526–541 a
a
a
B
Zs Za + Zs
s
E
Ct
B Ci
M/G
W
Ct
>
>
0.5, 0
RF 2
RF 1
0.5, 0.5
a
M/G a Zs Za + Zs
s
>
Ct
RF 2
>
>
>
1, 0
Zs
a
Ct
0.5
R F1
c
M/G a Zs
s
>
Za
E
Ct
1, 0.5
Za
a
Zs
Ci
c Zs
RF 2
Ct
E
1
M/G
RF 2
Ct E
c W
Za Zs
B
M/G
Ci E
(f) Speed ratio of PGTs:
1 R F1
0.5
2, 0.5
a Zs
a Za
W
(e) Speed ratio of PGTs:
2, 0
s
B
E
W
B Ci
M/G
W
RF 2
1
a Za
s
Ct
c
M/G
B
a Zs
s Za
E
Ct
M/G
W
Zs
Za
s
Ct
M/G
Zs
Zs
Ci
B Ci
M/G
Za
B
c
c W
Za Za + Zs
(d) Speed ratio of PGTs:
0.5
Za
1 R F1
M/G
s
Za
Ci
a
Ct
s c
1
s
B
W
E
(c) Speed ratio of PGTs:
R F1
Ct
E
W
B Ci
M/G
W
Ci
c
>
B
c
Za Za + Zs
>
c
Ct
E
0.5
E
s
Za Za + Zs
Ci
B Ci
RF 2
>
>
s a
c W
(b) Speed ratio of PGTs:
0
0.5
>
R F1
Za Za + Zs
M/G
W
(a) Speed ratio of PGTs:
0
a
E
E
M/G s
B
Ci
c W
Ct
c
Zs Za + Zs
>
Ci
s
M/G
>
c
Zs Za + Zs
>
s
Ct
>
536
Zs
B Ci
B
Ci
c W
Za Za
E
Ct E
s a
Zs
B Ci
M/G
W
(g) Speed ratio of PGTs:
(h) Speed ratio of PGTs:
R F1
R F1
2, 0
RF 2
0.5
2, 0.5
RF 2
c W
E
1
Fig. 5. Acceptable designs of the hybrid scooter-transmission corresponding to Fig. 3(a).
K.-B. Sheu / Applied Energy 84 (2007) 526–541
s
s c
Za
Zs
M/G
a
c
Za
a
Ci
Zs
s Za
E
Zs
2, 0
a
Ci E
RF 2
c W
Za Za
E
W
Zs
Ci
M/G
W
E
(b) Speed ratio of PGTs:
(a) Speed ratio of PGTs:
1 R F1
0.5
2, 0.5
a Zs
M/G s
Ci
c
M/G
W
c
a
Zs Za
Za
1 R F1
537
RF 2
1
a Za
c
M/G
s
Zs
Zs
s Za
E
Zs
M/G
s
c W
s
Ci
a
E
Za Za
E
Ci
M/G
W
Za Zs
a
Ci
Zs
Zs
c W
Ci
M/G
W
E
(c) Speed ratio of PGTs:
(d) Speed ratio of PGTs:
R F1
R F1
2, 0
RF 2
0.5
2, 0.5
RF 2
1
Fig. 6. Acceptable designs of the hybrid scooter-transmission corresponding to Fig. 4(a).
Eqs. (28) and (29) show a total of four different arrangements that can be used in the hybrid scooters for the input-coupled and output-coupled system, respectively, as shown in Figs. 6 and 7. 6. Design example In this section, we demonstrate the feasibility of the hybrid scooter transmission proposed in this paper by a numerical example. Assume that the top speed of the hybrid scooter of 75 km/h corresponding to an engine speed of 8500 rpm is desired. The top speed of the hybrid scooter occurs when the hybrid scooter is operating in the engine mode. With the drive wheel tyre diameter of 0.425 m and the final reduction ratio of 13, the speed ratio of the engine mode can be obtained as rE ¼ 0:716
ð30Þ
Selecting the ratio between the two speed stage of the electric-motor mode and the engine mode rE/rM = 1.8, then the speed ratio of the electric mode is rM ¼ 0:4
ð31Þ
538
K.-B. Sheu / Applied Energy 84 (2007) 526–541
a
a Zs
M/G Za
Ci
c
Za
M/G
W
W
E
E
W
0
RF 1
0.5, 1 RF 2
c
Za
s
Zs Zs
W
Ci
(a) Speed ratio of PGTs:
a
Ci
c
Za
Zs
(b) Speed ratio of PGTs:
2
0
RF 1
0.5, RF 2
c
M/G
Za
Ci
a W
M/G
W
2
E
RF 1 1, 1 RF 2
2
c Zs
a c
Za
Zs
s
Zs
E
Ci
(c) Speed ratio of PGTs:
0.5
Za
a
Zs
Za
E
E
s
Za Za
Ci
M/G
s M/G
c Zs
a
Ci
Za
E
Zs Za
a
Zs
s
M/G
c Zs
W
M/G
W
Ci E
(d) Speed ratio of PGTs:
0.5
RF 1 1, RF 2
2
Fig. 7. Acceptable designs of the hybrid scooter-transmission corresponding to Fig. 4(b).
Substituting Eq. (31) into Eq. (4), we obtain the speed ratio of the two-dof PGT as RF 2 ¼ 0:6
ð32Þ
Substituting Eqs. (30) and (32) into Eq. (5), the speed ratio of the one-dof PGT can be obtained as RF 1 ¼ 0:29
ð33Þ
For this design example of RF1 = 0.29 and RF2 = 0.6, the configuration shown in Fig. 5(b) can be satisfied. Moreover, with the speed ratio of RF2 = 0.6, the teeth of the ring gear, planets and sun gear of the two-dof PGT can be selected as Za = 72, Zp = 12 and Zs = 48, respectively. Similarly, for the one-dof PGT, the teeth of the ring gear, planets and sun gear, respectively, Za = 21, Zp = 15 and Zs = 51 can be selected. Fig. 8 shows a preferred example of this new transmission. This transmission is made up of two simple PGTs, a final reduction assembly consisting of a simple PGT and a chain drive, a one-way clutch as the brake B, a shoe type centrifugal clutch as the engine-idling
K.-B. Sheu / Applied Energy 84 (2007) 526–541
72 12
51 15 Ct
48
21
M/G
539
B Ci E
W
Two-dof PGT
One-dof PGT
Final reduction ratio of 13 Output shaft Fig. 8. Design example of the hybrid scooter-transmission. Table 5 Numerical example for the design of RF1 = 0.29 and RF2 = 0.6 Operating mode
Equation of the speed ratios and torque ratios
Numerical relations
Electric-motor mode
rM = 1 RF2 TW = (1/rM)TM
xW = 0.4xM TW = 2.5TM
Engine mode and Engine/charging mode
rE = RF1 + RF2(1 RF1) TW = (1/rE)/TE rG = RF1
xW = 0.716xE TW = 1.4TE xG = 0.29xE
Power mode 1
rP1E = RF1 + RF2(1 RF1) or rP1M = 1 RF2 TW = (1/rP1E · TE + 1/rP1M · TM)
xW = 0.716xE or xW = 0.4xM TW = (1.4TE + 2.5TM)
Power mode 2
xW = RF2xE + (1 RF2)xM TW = (TE/rE + RF1/rE · TM)
xW = 0.6xE + 0.4xM TW = (1.4TE + 0.4TM)
clutch Ci and an electromagnetic clutch as the shifting clutch Ct. The electric motor is connected to the sun gear of the two-dof PGT and to the carrier of the one-dof PGT by the clutch Ct. The sun gear of the one-dof PGT and the ring gear of the two-dof PGT are connected together by a common shaft. The common shaft is connected to the one-way clutch B while to the engine by the clutch Ci. The carrier of the two-dof PGT is linked to the final reduction assembly. Three operation modes of this transmission can be achieved based on the clutching conditions as listed in Table 1: (1) electric-motor mode; (2) engine mode and engine/charging mode; (3) power mode 1 and power mode 2. The regenerative braking mode is ignored since the one-way clutch is used as the brake B. The speed and torque ratios of the three operating modes can be obtained as summarized in Table 5. 7. Conclusions Although different types of clean-energy scooters have been introduced, they are unlikely to replace conventional gasoline-powered scooters. The hybrid concept is emerging to fill the gap between zero emissions and the currently well-established gasoline-engine technology.
540
K.-B. Sheu / Applied Energy 84 (2007) 526–541
In this work, a method for designing the hybrid scooter transmissions is presented by utilizing the concepts of the split-power system. The split-power system, consisting of a one-dof PGT and a two-dof PGT, is classified as an input-coupled and output-coupled system. Two kinds of the split-power transmission concepts, utilizing the clutches and brakes engaged, used in the hybrid scooter are proposed in this paper. The new transmissions provides four modes of operation that can be used in the hybrid scooter: (1) electricmotor mode, (2) engine mode and engine/charging mode, (3) power mode, and (4) regenerative braking mode. Kinematic and power flow analyses have been performed, and a method for identifying the arrangements with no internal recirculation of the split-power system has been developed. With four design requirements adopted in this paper, the ranges of speed ratio of the PGTs using in the hybrid scooter transmissions have been defined. According to the two kinds of new design concepts, there are 16 configurations of the hybrid scooter transmission satisfying the design requirements. Lastly, a design example is used to illustrate the design procedure and operation principle of the transmission. Acknowledgment The author is grateful to the National Science Council of Republic of China for the support of this research through Grant NSC 93-2212-E-150-010 and to the National Formosa University. References [1] Chiu YC, Tzeng GH. The market acceptance of electric motorcycles in Taiwan experience obtained through a stated-preference analysis. Transport Res D 1999;4:127–46. [2] Wang JH, Chiang W-L, Shu Jet PH. The prospects of the fuel-cell motorcycle in Taiwan. J Power Sources 2000;86:151–7. [3] Lin B. Conceptual design and modeling of a fuel-cell scooter for urban Asia. J Power Sources 2000;86:202–13. [4] Colella WG. Market prospects, design features, and performance of a fuel-cell powered scooter. J Power Sources 2000;86:255–60. [5] Asia Pacific Fuel-Cell Technology Ltd. (APFCT). Available from: http://www.apfct.com/. [6] Yamaguchi K, Miyaishi Y. Hybrid vehicle power train, US Patent 5643119; 1997. [7] Yamamoto Y, Chubachi K. Power transmitting apparatus for a hybrid vehicle, US Patent 5755303; 1998. [8] Brown LT, Ortmann WJ, Kraska MP. Hybrid vehicle power train and control thereof. US Patent 6176808; 2001. [9] Tsai LW, Schultz G, Higuchi N. A novel parallel hybrid transmission. Trans ASME J Mech Design 2001;123:161–7. [10] Bitsche O, Gutmann G. Review – systems for hybrid cars. J Power Sources 2004;127:8–15. [11] Laimbock FJ et al. HYC – a hybrid concept with small lean-burn engine, electrically-heated catalyst and asynchronous motor for enhanced performance and ULEV level emissions. SAE Paper 991330; 1999. [12] Matsuto T, Wachigai K. Power unit for motorcycle. US Patent 6109383; 2000. [13] Matsuto T, Wachigai K. Motorcycle with hybrid-drive system. US Patent 6158543; 2000. [14] Matsuto T, Wachigai K. Power unit arrangement structure for motorcycle. US Patent 6276481; 2001. [15] Sheu K-B, Hsu T-H. Design and implementation of a novel hybrid electric motorcycle transmission. Appl Energy 2005 [accepted for publication]. [16] Freudenstein F. An application of Boolean algebra to the motion of epicyclic drives. ASME J Eng Ind 1971;93:176–82. [17] Tsai LW, Lin CC. The creation of non-fractionated, two-degrees-of-freedom epicyclic gear trains. ASME J Mech Trans Automat Design 1989;111:524–9.
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