382
Alternative Fuels for Transportation
Sadarangani 2002). Different topologies have different space and thermal
requirements.
Although the above integrated double-rotor machines can perform ECVT
operations without using a planetary gear, they still need carbon brushes
and slip rings to withdraw power from the primary rotor. With no doubt,
this will deteriorate the reliability of the whole system.
Recently, a high-performance coaxial magnetic gear has been proposed
(Atallah and Howe 2001; Jian and Chau 2009). It can provide noncontact
torque transmission and speed variation using the modulation effect of
PM fields. Hence, the drawbacks of low-transmission efficiency, significant
mechanical friction, and annoying audible noise brought by the mechanical planetary gear can be avoided. Figure 12.19 shows the configuration of
the coaxial magnetic gear. It employs high-energy rare-earth PMs on both
the inner rotor and outer rotor, and has the modulating ring sandwiched
between the two rotors. The modulating ring takes charge of modulating
the magnetic fields in the two air-gaps that interface with the inner rotor and
the outer rotor. In order to provide magnetic paths with high permeability
as well as to reduce eddy current loss, the modulating ring is built of thin
sheets of laminated ferromagnetic material. Also, epoxy is filled in its slots to
reinforce structural strength for high-torque transmission. The coaxial magnetic gear can achieve stable torque transmission if it satisfies the following
relationship:
n = p p
s
1 + 2 ,
where p 1 and p 2 are the pole-pair numbers of the inner rotor and outer
rotor respectively, and n s is the number of ferromagnetic segments on the
Inner rotor
Outer rotor
Modulating ring
PMs
Air-gaps
ω 1
ω 2
ω 3
Figure 12.19
Coaxial magnetic gear.
Alternative Fuels for Transportation
Sadarangani 2002). Different topologies have different space and thermal
requirements.
Although the above integrated double-rotor machines can perform ECVT
operations without using a planetary gear, they still need carbon brushes
and slip rings to withdraw power from the primary rotor. With no doubt,
this will deteriorate the reliability of the whole system.
Recently, a high-performance coaxial magnetic gear has been proposed
(Atallah and Howe 2001; Jian and Chau 2009). It can provide noncontact
torque transmission and speed variation using the modulation effect of
PM fields. Hence, the drawbacks of low-transmission efficiency, significant
mechanical friction, and annoying audible noise brought by the mechanical planetary gear can be avoided. Figure 12.19 shows the configuration of
the coaxial magnetic gear. It employs high-energy rare-earth PMs on both
the inner rotor and outer rotor, and has the modulating ring sandwiched
between the two rotors. The modulating ring takes charge of modulating
the magnetic fields in the two air-gaps that interface with the inner rotor and
the outer rotor. In order to provide magnetic paths with high permeability
as well as to reduce eddy current loss, the modulating ring is built of thin
sheets of laminated ferromagnetic material. Also, epoxy is filled in its slots to
reinforce structural strength for high-torque transmission. The coaxial magnetic gear can achieve stable torque transmission if it satisfies the following
relationship:
n = p p
s
1 + 2 ,
where p 1 and p 2 are the pole-pair numbers of the inner rotor and outer
rotor respectively, and n s is the number of ferromagnetic segments on the
Inner rotor
Outer rotor
Modulating ring
PMs
Air-gaps
ω 1
ω 2
ω 3
Figure 12.19
Coaxial magnetic gear.