Innovative Thermal Management: Design and Function

Introduction

Cooling System Basics

The thermal behaviour of combustion engines has been an issue since the invention of the motor vehicle. On the one hand, the engine together with its fluids needs to be brought up to operating temperature quickly and, on the other, it needs to be cooled once it reaches high operating temperatures. In addition to this, the vehicle occupants require heat. Vehicles need clever thermal management systems to meet these thermal requirements.

Diagram showing energy distribution from fuel: 36% Exhaust gas, 24% Useful engine work, 33% Heat absorbed by cooling system (7% Radiation, rest dissipated).

The efficiency of an internal combustion engine is limited by mechanical friction and gearbox losses. Engine and gearbox oil provide optimum viscosity when heated. Materials like cast iron and aluminium also require specific temperatures. Therefore, a cold engine and gearbox consume more fuel for the same output. The cooling system has three primary tasks: to absorb and dissipate combustion heat, to aid engine warm-up, and to heat the interior.

Cooling the Engine - Basics

Temperatures up to 2,000°C produced during combustion are harmful. The engine is cooled to an "operating temperature". Air cooling dissipates heat directly to the surrounding air via cylinders and cylinder heads, often with cooling fins. Thermosyphon cooling, used historically (from 1910), relied on the density difference of hot and cold water to circulate coolant. Its weaknesses included long warm-up times, low engine temperatures in cold seasons, and higher CO2 emissions. Modern cooling systems are closed systems comprising components like a coolant pump (1), temperature sender (2), coolant expansion tank (3), thermostat (4), radiator (5), heat exchanger for heater (6), and engine oil cooler (7).

Innovative Thermal Management (ITM)

General Information

Thermal management involves controlling heat flow in the vehicle, with coolant playing a key role. It's used for both cooling (absorbing heat) and heating (dissipating heat) via heat exchangers.

ITM Tasks:

• Controlling heat flow during engine warm-up.
• Cooling the engine once operating temperature is reached.

The ITM is crucial for short journeys, improving cold start performance. It balances the heat requirements of engine components, gearbox, and interior heating, especially at low outside temperatures.

The ITM System

Networking

The ITM is a software application within the engine control unit (also called the ITM thermal manager). It networks with engine, gearbox, and air-conditioning control units, sensors, and actuators to optimize engine heat distribution based on interior, engine, and gearbox needs. Control units signal heating requirements to the ITM, which weighs these with other inputs (like coolant temperature) to command actuators. Pumps are activated directly by the engine control unit.

Diagram illustrating the ITM system network, connecting the Gearbox control unit, Engine control unit (ITM), and Air-conditioning control unit, showing control signal flow.

Cooling Circuit

Design

The coolant circuit for the 3.6l V6 FSI engine is detailed in a schematic diagram and component location overview. The schematic shows numbered components like the on-demand coolant pump (1), thermostat (2), various senders (3, 4), radiators (5, 9), coolers (6, 11), pumps (7), valves (8, 10, 12, 13, 20), control units (15, 16, 17), and engine parts (18, 19).

Schematic diagram of the coolant circuit for the 3.6l V6 FSI engine, detailing components numbered 1 through 20.

Diagrams showing the physical locations of coolant circuit components on the engine and gearbox.

Key Components:

• On-demand coolant pump (1): Driven by the belt, pumps coolant. Switched off by a shutter for faster engine warm-up. Can be switched on below -15°C or above 75°C, or pulsed.
• Coolant circulation pump 2 V178 (7): Electronically regulated via PWM. Operates independently to supply coolant to the heater exchanger or gearbox oil heat exchanger when the main circuit is deactivated or during specific conditions.
• Valves:
  • Shut-off valve for gearbox oil heat exchanger and cooling oil valve N471 (10): Controls vacuum to a pneumatic shut-off valve, interrupting or allowing coolant flow to the gearbox oil heat exchanger.
  • Shut-off valve for cylinder block and coolant valve for cylinder block N545 (13): Interrupts coolant flow to the cylinder block during warm-up.
  • Coolant shut-off valve N82: Operated by an electric motor, allows or interrupts coolant flow through the heat exchanger for the heater.
• Non-return valves:
  • Cylinder head circuit non-return valve (12): Prevents direct flow from the cylinder head to the pump, ensuring flow through the cylinder head circuit.
  • Coolant return non-return valve: Prevents air intake from the expansion tank.
• Sensors:
  • Coolant temperature sender G62 (3): Measures coolant temperature at the engine outlet.
  • Temperature sender for engine temperature regulation G694 (4): Measures coolant temperature in the cylinder head, used for heating phase control and preventing boiling.

Function

The ITM system is divided into four sub-functions:

• Sub-function 1 - Stationary coolant: Warms up the engine quickly by preventing coolant circulation through the entire engine.
• Sub-function 2 - Autarkic heating: Quickly heats the vehicle interior using heat from the cylinder head for the heat exchanger.
• Sub-function 3 - Gearbox oil heating: Warms up the gearbox by activating the gearbox oil heat exchanger with hotter coolant.
• Sub-function 4 - Separation of interior heating circuit: Reduces engine warm-up phase by disconnecting the heat exchanger for the heater when no heating is required.

These sub-functions can operate independently or in conjunction, depending on the engine and operating conditions.

Warm-up Strategy (Winter Operation):

• Phase 1: Stationary coolant sub-function warms the cylinder block.
• Phase 2: Autarkic heating activates if interior heating is requested, using cylinder head heat. Coolant flow to the cylinder block is switched off.
• Phase 3: Coolant pump (1) activates at ~75°C, pulsing to balance temperatures between block and head.
• Phase 4: Gearbox oil is heated via the gearbox oil heat exchanger (11).
• Phase 5: Shut-off valve for cylinder block (13) opens at ~87°C; warm-up is completed. Pump output is usually sufficient.
• Phase 6: Thermostat (2) opens the main radiator circuit at 89°C. Gearbox oil heating ends if no heating is required.

Diagrams illustrating coolant flow during Phases 1-3 of the winter warm-up strategy.

Diagrams illustrating coolant flow during Phases 4-6 of the winter warm-up strategy.

Graph showing coolant and gearbox oil temperatures over time during winter warm-up, comparing ITM vs. non-ITM systems.

Warm-up Strategy (Summer Operation):

• Phase 1: Stationary coolant warms the cylinder block.
• Phase 2: Autarkic heating is not active as there is no heating requirement.
• Phase 3: Coolant pump (1) activates at ~75°C, pulsing.
• Phase 4: Gearbox oil is heated.
• Phase 5: Shut-off valve for cylinder block (13) opens at ~87°C; warm-up is completed.
• Phase 6: Thermostat (2) opens the main radiator circuit at 89°C.

System Overview

Sensors: The system utilizes various sensors, including Coolant temperature sender G62, Temperature sender for engine temperature regulation G694, Engine speed sender G28, Air mass meter G70 with intake air temperature sender G42, and Gearbox oil temperature sender G93. These sensors provide data to the Engine control unit J623 and Automatic gearbox control unit J217.

Actuators: The system controls actuators such as Coolant valve for cylinder block N545, Coolant regulating valve N515, Coolant circulation pump 2 V178, Coolant shut-off valve N82, and Cooling oil valve N471. These are managed by the Engine control unit J623 and Climatronic control unit J255.

Block diagram showing sensors and their connections to engine and gearbox control units.

Block diagram showing actuators and their connections to engine and climate control units.

Function Matrix

The implementation of ITM sub-functions varies across different Volkswagen engines. The table below summarizes which sub-functions (Stationary coolant, Autarkic heating, Gearbox oil heating, Separation of interior heating circuit) are active for specific engine models, including the 1.2l 77kW TSI, 3.6l 206kW V6 FSI, 4.2l 265kW V8 FSI, 3.0l 176kW V6 TDI, 4.2l 250kW V8 TDI, 3.0l 245kW V6 TSI (hybrid), and 3.0l 180kW V6 TDI (W36 - generation 2).

Note: Country-specific ITM systems may exist.

Test Yourself

Questions:

1. What do you understand by innovative thermal management (ITM)?
   • a) The airstream is directed at hot engine components.
   • b) The specific control of the flow of heat in the vehicle.
   • c) The ITM is a thermal management system similar to an auxiliary heater.
2. Where is the ITM thermal manager fitted?
   • a) The ITM thermal manager is a separate control unit that is networked with the engine control unit on the CAN data bus.
   • b) The ITM thermal manager is a software application that is installed in the gearbox, air-conditioning and engine control unit.
   • c) The ITM thermal manager is a software application in the engine control unit.
3. Which phase of the warm-up strategy in winter operation is identical to an ITM sub-function?
   • a) Sub-function 1 - Stationary coolant is identical to phase 1 of the warm-up strategy.
   • b) Sub-function 1 - Stationary coolant is identical to phase 2 of the warm-up strategy.
   • c) Sub-function 3 - Gearbox oil heating is identical to phase 5 of the warm-up strategy.
   • d) Phase 2 of the warm-up strategy is identical to sub-function 2 - Autarkic heating.
4. Name the components. (Refer to schematic diagram)
5. What function do the four sub-functions of the ITM have in winter operation?
   • a) The four sub-functions are used to warm up the engine, the interior and the gearbox more quickly.
   • b) The four sub-functions are identical to the 4 stages of the interior heating requirement.
   • c) The sub-functions can only ever be active together and not independently.
6. Why is the coolant pump pulsed when switched on?
   • a) So that the components are not subjected to any high temperature fluctuations (protection of engine components).
   • b) The pump is protected from freezing.
   • c) It is a function check for the pump and its components.