Environmental Engineering Reference
In-Depth Information
grade, no wind and at sea level is surprisingly small. Of course, for grade climbing,
running into a headwind and for denser air, the cruise power is higher. Q1 at the end
of this chapter requires a short calculation to show that a typical vehicle power
plant requires a peak/cruise power greater than 10:1.
Passenger car propulsion power plants require peak power to vehicle mass
ratios of 10 kW/125 kg for acceptable acceleration performance. Sports and luxury
cars tend to raise this metric to over 13 kW/125 kg, whereas compact and sub-
compact vehicles tend to ratios somewhat less than 10 kW/125 kg. Example 1 and
the result of Q1 show that for this mid-sized vehicle the peak power to mass ratio is
10.4 kW/125 kg.
In this chapter essential guidelines to propulsion power plant sizing are dis-
cussed, including the major hybrid components of M/G, power electronics and
energy storage system (ESS).
4.1 Matching the electric drive and ice
One of the most common matching elements used in hybrid electric passenger
vehicles is the epicyclic, or planetary, gear set. Continuously variable transmissions
of the compression belt and toroidal variator variety are gaining popularity in
compact vehicles and passenger vans because of seamless transitions in ratio. For
larger CVTs the issues of torque rating and efficiency at high ratio continue to be
developmental areas.
Figure 4.1 shows the epicyclic gear in schematic form. This is a three port
mechanical component used as a speed summing device. Most designs rely on dual
input and single output where one input source is the ICE and the second input
comes from an electric M/G. Epicyclic gear ports may be defined as input or
output according to the convection illustrated in Table 4.2. The epicyclic basic ratio
k
=
R
ring
/
R
sun
=
N
r
/
N
s
, where
R
x
(
N
x
) is the radius of ring and sun gears (can also be
defined as noted in terms of number of gear teeth,
N
x
).
R
C
S
w
s
w
r
w
c
Figure 4.1 Schematic of epicyclic gear set
