Environmental Engineering Reference
In-Depth Information
commanded and is fully compatible with all vehicle stability programmes. Vehicle
stability programmes are discussed in Chapter 3, Section 3.3.4.
4.7.3 Cabin climate control
Actively controlled air conditioning is a necessity in hybrid vehicles. Cabin climate
control ranges from cold storage boxes such as the cold storage unit used in the
prototype ES
3
environmental vehicle build by Toyota, to hybrid drive air con-
ditioning compressors. A hybrid drive air conditioning compressor unit consists of
the conventional A/C belt driven compressor plus a clutch mechanism and linkage
to a separate electric motor and controller that is used to drive the pump when the
engine is off. In such a system a brushless dc motor rated 1.5-2.0 kW at 42 V is
used to maintain cabin cooling during idle-OFF intervals.
A/C compressors used in hybrid vehicle climate control systems are of the two
stage, rotary vane, variable displacement type. When the A/C compressor is engine
driven, the displacement is highest to provide sufficient coolant flow to the pas-
senger cabin evaporator assembly during cabin temperature pull-down. When the
A/C compressor is brushless dc motor driven, the displacement is lower since only
1.0-1.5 kW of drive power is needed to maintain cabin temperature within the
comfort zone.
4.7.4 Thermal management
Managing the thermal environment within the complexity of a hybrid powertrain
requires close attention to package locations, airflow patterns and vibration modes.
Bolting modules directly to the engine or transmission has historically been a very
challenging if not a daunting task [44,45]. The vibration levels alone on the power-
train can reach magnitudes of 20 g peak over a broad frequency spectrum. Tem-
perature extremes on the high end can reach 115
C on the transmission to 150
Con
the engine (exclusive of exhaust bridge and manifold areas) with a potential to reach
175
C for under-hood packaging that restricts airflow or creates air dams. It is this
simultaneous temperature plus vibration regime that dictates the durability of elec-
tronic modules in the automobile. Given a service life requirement of 6,000 h, it is no
wonder that few modules are packaged directly on the powertrain. Figure 4.54
illustrates schematically the various regions of temperature and vibration extremes.
The temperature and vibration extremes illustrated in Figure 4.54 are sufficient
to shake conventional electronic assemblies to pieces. Today's electronic modules
are fabricated with very low mass, surface mounted devices (SMD) plus chip and
wire on ceramic substrates, to tolerate such conditions. Vibration transmitted along
the vehicle powertrain originates from the engine itself due to misfire (now very
infrequent) to pre-detonation due to improper timing and/or improper fuel blends,
to engine hop due to its moving components. Resonance can also play a role, but
these tend to be at low frequencies in the range of powertrain bending and engine
hop. Higher frequencies are generated by crankshaft whirl due to imbalance and
journal bearing wear out. Figure 4.55 summarizes the automotive temperature and
vibration environment by zone.
