Thermal Management
Thermal Management
The DME control unit also controls thermal management.
Tasks of the cooling system with thermal management
- Bringing the engine to the optimum operating temperature and controlling this temperature.
- Controlling the cooling and heat distribution between:
- Combustion engine with high-temperature circuit and low-temperature circuit
- Transmission
- Passenger compartment
- Charge-air cooler, bank 1 and 2
- E-machine
- Power electronics
All Cayenne engines meet the high demands placed on a Porsche engine under all operating conditions and therefore also meet the special requirements that apply to hot countries. The Cayenne S Hybrid is designed to meet all performance requirements whether on-road, off-road or in traction mode. The main areas of the thermal management system in the Cayenne S Hybrid are heat distribution between the combustion engine, transmission and passenger compartment.
The basic goal is to ensure that all components reach their optimum operating temperature as quickly as possible and to also meet the comfort demands of passengers by heating up the cabin quickly. At low temperatures and for cold engine starts in particular, it is important to manage the low amount of available heat in the best possible way. Efficient use of the available heat helps to save fuel, reduced CO2 emissions and comply with strict emission regulations.
High-temperature circuit (for engine cooling)
Effect of thermal management
- Reduced cooling performance during the engine operation phase
- This results in faster heating of the transmission and engine oil
- Less internal friction in the engine and transmission components
Result
- Reduced fuel consumption
- Faster heating of the passenger compartment (with priority over engine oil heating)
- Increase in fuel economy of up to 1.5% approx.
The cooling system is part of the thermal management system and has two circuits which can be regulated depending on the coolant temperature. In the Cayenne S Hybrid, this is done by an electrically operated, map-controlled and deactivatable thermostat.
NOTE: Further information on thermal management with high-temperature circuit and low-temperature circuit is provided in the brochure "Cayenne S Hybrid Training Information", section 1 "Combustion engine".
Cold engine
When the bowl on the main water pump is closed in a cold engine, the water remains in the cylinder head and crankcase to heat the engine more quickly (stationary water).
Warm-up
Depending on the increase in engine temperature, the coolant flow through the engine (small circuit) is activated during warming up.
Engine at operating temperature
After this, the coolant radiator is activated (large circuit) depending on the engine operating point and based on a map stored in the engine control. The map control of the thermostat then regulates the coolant temperature between 201° F. (94° C.) and 221° F. (105° C.) depending on load and thus ensures optimum friction conditions in the engine that are adapted to the load point.
When the heating shut-off valve is opened and the auxiliary water pump is connected automatically, warm water is supplied to the heating system.
Low-temperature circuit (for power electronics and charge-air cooling)
The low-temperature circuit is responsible for temperature control of the charge-air coolers and power electronics.
Charge-air cooling, low-temperature circuit
Electric water pump for charge-air cooling
A PWM signal from the DME control unit controls the pump based on a program map.
In the event of an interruption in the signal, the DME control unit switches to 100% pump capacity.
The pump is activated according to the temperature taken from a map in the engine control unit downstream of the charge-air coolers and the pressure downstream of the charge-air coolers. It always runs from 1,300 mbar or from a coolant temperature of 122° F. (50° C.). The pump is controlled by the engine control unit via a PWM signal. The pump electronics use this signal to calculate the required pump speed and control the electric motor. If the pump is working correctly, the pump electronics send the current pump speed back to the DME control unit via the bidirectional signal line. This process runs cyclically throughout pump operation.
Effects in the event of faults
If the pump electronics detect an error, the PWM signal changes, i.e. either the pump speed is reduced or the pump is switched off. The changed signal is evaluated by the engine control unit. As the reduced power is only noticeable at full throttle and exhaust gas is not affected in the event of failure, the Check Engine light (MIL) is not activated. No direct reaction is triggered in the engine control unit in the event of pump failure. However, the charge air temperature is monitored. If this is found to be too high, the engine power is reduced.
If the signal line to the pump is interrupted or there is a short circuit to B+ on the signal line, the pump switches to emergency mode, in which it delivers 100% output. The pump stops in the event of a short circuit to ground on the signal line.