Environmental Engineering Reference
In-Depth Information
Electric power from the S/A is then routed to the dc bus and consumed by the main
M/G for propulsion or sent to the battery. The M/G is the main traction motor used
for propulsion and for regenerative braking.
There are no driveline clutches in a power split propulsion system, only
indirect mechanical paths from the engine to the driven wheels. Figure 2.18 illus-
trates the basic functionality of power split architecture.
In Figure 2.18 it can be seen that the M/G has its rotor connected to the pla-
netary set ring gear and from there directly to the wheels via gearing and the final
drive. In the actual implementation there is a chain drive link between the ring gear
and the input to the fixed ratio gearbox. The electric fraction of power split is
determined by the peak power rating of ICE and M/G. The S/A is a torque reaction
source necessary to hold the ICE speed within a confined range, via its sun to
carrier gear ratio. The benefit of constraining engine speed to more restricted ran-
ges within fuel islands was described in Chapter 1.
In power split operation, engine torque is delivered to the wheels for propul-
sion by first splitting off a portion and converting it to electricity. This diverted
power is then recombined with engine mechanical power at the planetary set ring
gear. In the process of power splitting, the engine speed becomes decoupled from
vehicle speed through the action of MG1. This balancing act is best described using
stick diagrams as shown in Figure 2.19.
Engine
speed
Vehicle
speed
S/A
speed
S
R
C
Figure 2.19 Power split 'stick' diagram of speed constraints
Figure 2.19 is a static illustration of power split operation at a static operating
point. Before describing the dynamic operation we examine the kinematics of
the epicyclic gear set to illustrate the power splitting function. The epicyclic gear
set is illustrated in Figure 2.20 showing its respective components and speeds.
Torques at each gear are in proportion to the respective speeds and the power being
transmitted.
