Mitsubishi Heavy Industries Technical Review Vol. 46 No. 4 (December 2010)
19PTC Heater for Electric Vehicles and Plug-in Hybrid
Vehicles Using Water Heat Carrier

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Mitsubishi Heavy Industries, Ltd. (MHI) has begun commercial production of awater-based PTC (Positive Temperature Coefficient) semiconductor heater for the occupant’s
compartment of an electric vehicle (EV) or a plug-in hybrid vehicle (PHEV). A PTC heater
provides a heat source in an EV or a PHEV, where no engine exhaust heat is available, and isapplicable to each vehicle’s safety and packaging requirements.

|1. In-vehicle heating
Figure 1 shows the configurations of the vehicle-heating systems. EV and PHEV both use
hot water heated with a PTC heater instead of high-temperature coolant heated with engine waste
heat. The hot water is circulated with an electric water pump.
Compared with an air heater, the hot water heater offers the following advantages:(1) For safety’s sake, the high-voltage heating unit is located outside the occupant’s compartment.
(2) The heating, ventilation, and air conditioning (HVAC) module of the base vehicle can be used
to reduce the development cost.

Figure 1

Configuration of the vehicle heating systems (engine vehicle and EV)|2. Primary features(1) Safety assured by the self-regulating function of the heating element
This heater uses a PTC semiconductor as the heating element. A PTC semiconductor
increases drastically its electrical resistance at temperatures above a certain level and is able tomaintain a constant heating element temperature during load and supply voltage changes.
For this reason, the risk of the heating element’s overheating or catching fire is minimal,
even under unexpected boil-dry conditions due to the loss of hot water. Moreover, the heatgeneration capacity is nearly constant over a wide range of battery voltage fluctuations.

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 4 (December 2010)20(2) Easy packaging with small size
The plate-heating elements are placed between insulators with high heat conductivity, andthe heat is released to the upper and lower water passages (Figure 2). Thanks to its compactness
and high heat-release capability, the heater can be mounted in a limited space. In addition, theintegrated control board reduces the amount of wiring in the vehicle.

Figure 2

Construction of water-based PTC heater(3) Multi-stage on/off control with heating-element modules
Four heating-element modules are provided to achieve up to eight-step capacity control
utilizing various combinations of modules with differing capacities and on/off switching.
(4) Control board module
The control board is divided into three functions: (a) heat generator on/off, (b) capacity
calculation/control, and (c) communication. By combining these functions, the heater is applicableto varying customer requirements, such as those listed in the following section.

|3. Future development
Anticipating the electrification of future vehicles, we are proceeding with the development ofproducts to satisfy each automobile manufacturer’s requirements.
(1) Small size and light weightThe development will proceed in two stages (Figure 3).
(First stage) Miniaturization and weight trimming based on current design(Second stage) Further miniaturization and weigh trimming based on a new heat-exchanger
concept and adaptation of resin parts(2) High functionality(a) Autonomous temperature control
The present heater controls the heat-generator modules by turning the power on/off via
the external calculation unit (ECU) and its commands. Autonomous temperature control will beachieved by integrating the ECU and sensor.
(b) CAN/LIN interface
With the integration of the calculation unit in the heater, communication of command andself-diagnosis information as well as CAN/LIN communication to and from the vehicle will beavailable.

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 4 (December 2010)
21Figure 3

Future development of water-based PTC heater