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Model-based design of multi-physics car systems

Posted: 18 Feb 2014     Print Version  Bookmark and Share

Keywords:multi-physics systems  sensors  simulation  RTOS  vehicle network 

Vehicles nowadays exemplify the concept of multi-physics systems. Design teams are bringing together software and electronics, along with airflow and environmental sensors, mechatronic, hydraulic and pneumatic sub-systems, to create increasingly sophisticated automotive systems.

Traditionally, the automotive industry has made extensive use of "downstream" engineering. Design teams have followed the traditional "V-cycle", which splits the engineering process into two phases—design and implementation followed by validation.

While design teams can benefit significantly from earlier validation of their concepts, the industry has historically favoured physical prototyping as a means of validating the design, which requires a commitment to build a hardware prototype early in the project lifecycle.

This is often followed by a sequence of reworking, patching and more prototyping. Design teams pursue this cycle until the design appears to be bug-free. Unfortunately, such a downstream approach to engineering can lead to periods of prolonged patch fixing while engineers chase their tails and lose production cycles. If we cannot fix the design by patching, it may require a complete re-design. In the worst case, we may not discover the problem until the vehicle is in production, which can lead to disastrous product recalls.

Upfront engineering
While simulation doesn't remove the need for physical prototyping, it does considerably reduce the number of prototyping cycles that we need to go through during a project. By spending more time upfront with the design, we avoid many of the downstream problems.

Simulation enables us to learn more about the system and understand how it works. Because simulation models give us better visibility into the way our designs work conceptually, we can get rid of bugs—hopefully before we build them into the prototype. An additional benefit is the ability for new team members to get up to speed with the design by experimenting with the simulation, which doesn't risk causing damage to (expensive) physical prototypes.

Cyber-physical systems
A model-based cyber-physical systems (CPSs) (figure 1) development approach enables design teams to integrate physical processes with computational systems during simulation. These virtual CPSs support abstractions appropriate for modelling and design, and analysis techniques suitable for integrated systems.

Figure 1: Simplified block diagram of cyber-physical system showing close integration between physical systems (plant) and computational systems (ECU).

The mechatronic control systems that are implemented in automotive applications include those used for engine control, transmission control, throttle control and braking. These typically involve multiple complex physical systems with dedicated embedded controllers that communicate with each other via a vehicle network, such as Controller Area Network (CAN) or FlexRay.

We have adopted model-based design for CPSs to improve the efficiency of the design process for these complex systems. During the system design stage we integrate models of physical system behaviour (also called "plant models") with controller models to produce an abstracted system implementation.

Accelerating project schedules
Simulation enables us to fix bugs before they manifest themselves as problems. That can sometimes make it difficult to put a value on our use of simulation in terms of the engineering time saved or improved design quality.

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