Mentor Graphics, a leader in electronic design automation technology, recently released a research report titled "What is smoking? Automatic short-circuit test for automotive systems and harness designs."
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text:
The authors: Mike Stamper, Mentor Automotive
background:
Preventing catastrophic overload of automotive wiring harnesses is a key design criterion. Designers must ensure that the fuse strategy protects the line. This process typically involves manually calculating the maximum load per line and then comparing the results to an electronic watch created years ago.
The main points and outline of the full text are as follows:
a. Overview
b. Analysis and simulation
c. What should I do?
d. Choose the right tool and get started easily
e. You can do this
f. The problem is discovered early, save more money
g. No longer need a prototype
h. Fuse blow time vs. wire smoke characteristics
i. Summary
Overview
Preventing catastrophic overload of automotive wiring harnesses is a key design criterion. Designers must ensure that the fuse strategy protects the line. This process typically involves manually calculating the maximum load per line and then comparing the results to an electronic watch created years ago.
This process is highly error-prone due to its artificial nature. You may find the alarm and there is a situation, but the car and the plane are still driving and flying. The reasons are as follows:
The circuit is in an overprotected state. Due to the artificial nature of most design processes, designers tend to be too cautious; this means that the wires used are thicker than what is needed for the actual load.
Physical testing. Produce costly physical prototypes that are physically tested by test engineers to ensure circuits are protected. This is time consuming and expensive, and is often in the later stages of the design process, resulting in very high design changes due to this test.
Engineers and designers are smart. Many designs have indeed continued for many years. History tells them what works and what doesn't work – but we have to ask the question: Is this the most effective way to design?
Analysis and simulation
When it comes to circuit protection, we often hear the words "simulation" and "analysis". Although simulations are often hailed as saviors of harness protection design, they are rarely implemented, and if implemented, can cause huge bottlenecks in the process. First, a well-trained, highly skilled expert must be used to create complex models, run simulations, and then analyze the results. The results are then fed back to the wire harness engineering team, who must make decisions based on charts and results that are often complex and difficult to understand.
An important piece of information that is always missing when simulating in this way is the actual configuration of the car. Not all loads are present on all cars. Take an example of a car with an optional navigation system. Which simulation to perform, with or without navigation? Let's add the optional sunroof to the combination: Now you have 2 2 = 4 models to simulate. When more options are added, it can be seen that the number of analog combinations rises to 2 n , where n = the number of options.
For simulation and modeling experts specializing in motor model and line model creation, the complexity of billions of car combinations is beyond the scope of any simulation. Even if you can run so many simulations, there is not enough time to interpret all the resulting simulations to make meaningful design changes before the vehicle is put into production. Design-to-manufacturing time is shortened year after year; there is no time to simulate in this way, forcing designers to have to choose wire and fuse specifications based on spreadsheets or paper history questionnaires. If there are no human errors, the designer usually ends up with an over-protected design that results in increased cost and weight.
How to do?
The solution to this problem is to leverage the expertise of these simulation experts to enable each engineer to analyze their designs and provide quick and meaningful feedback. By grabbing the wire and fuse size specifications (this is your engineering intellectual property), we believe that your design tools will let your engineers know if there is a problem. Analytical tools should analyze the car, point out the problem directly to the engineer, and propose solutions to these problems based on your engineering know-how. A detailed look at the charts and graphs of the detailed simulation runs of the various options is a long process and the data remains to be explained.
Choose the right tool and get started easily
There is a cheaper, more accurate design. The correct step in the direction is to collect design data in an electronic format that can be analyzed by software. With the right design tools, engineers and designers can implement guidelines for implementing correct-by-construction design methods. You can find problems in the process very early before making physical prototypes - perhaps no longer need to make prototypes.
This correct construction of design analysis by software tools requires several parameters:
1. Accurate load information of equipment that draws current, such as:
2. Current through the electronic control unit (ECU):
a. We often hear that the interior of the ECU is proprietary and the modeling work is difficult. When you focus on the task at hand, to determine if the fuse can protect the line, then with the right engineering tools, ECU internal connection modeling becomes a piece of cake. Everything you need is shown in Figure 1 (hypothetical example).
Figure 1: A simple fuse blow model available for the ECU
3. Describe the location of the component and the relative temperature of each part of the car and the vehicle structure model of the harness connection point, as shown in Figure 2.
Figure 2: The position and temperature limits of the harness connection point must be modeled
4. Accurate models of batteries, fuses, wires, and basic discrete devices (lights, motors, switches, grounding devices, relays, etc.) on the car
You can do this
The example of Figure 3 shows the results that might be achieved with the right tools. Engineers can use the recommended wire size (Wire CSA (max) column) and actually apply it to the design to use this information to drive part selection.
Figure 3: Engineers can easily apply standardized wire sizes directly to the design with the right tools.
With this information, design decisions can be made early in the process before the actual part is manufactured. By leveraging the years of experience of your engineers, you can also provide this level of analysis and decision making to a wider range of clients.
The problem was discovered early, save more money
The graph of Figure 4 shows the relative cost of making design changes during the design cycle of the car. The later the problem is discovered, the higher the cost. Automakers have a one-year warranty and recall cost of billions of dollars, which seriously affects their profitability for companies that find problems until the car has been handed over to customers. You need to find problems early in the design process.
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