Sensing Design Challenge Solutions for Automotive Electronics

Sensing Design Challenge Solutions for Automotive Electronics

Consumer car buying habits are changing, which is also driving the growth of the automotive electronics industry. Automakers are adding more new or enhanced Electronic components to passenger vehicles each year, with body electronics currently growing at four times the rate of vehicle production.

Consumer car buying habits are changing, which is also driving the growth of the automotive electronics industry. Automakers are adding more new or enhanced electronic components to passenger vehicles each year, with body electronics currently growing at four times the rate of vehicle production.

Some of the current trends in new or enhanced functions are the addition of more complex electronic components in order to improve brand reputation and competitive differentiation, while making consumers safer and more comfortable. For example a hybrid electric car is like putting an iPod? Connecting to car entertainment systems has now become a fashion. Consumers also see Bluetooth connectivity between cell phones and integrated speakerphone devices as standard.

Complications

These features are just the tip of the iceberg. Other well-designed complex features that are not seen or touched by passengers, but affect their driving experience, are gradually being introduced into car design. Sensing lighting systems, multi-axis adjustable seats, intelligent weather control systems, collision avoidance systems and power cruise control have become extremely important in the 21st century automotive market. Consumers even expect high-quality dashboard features from automakers. Bringing these advanced capabilities into automotive systems often comes at a price.

One of the challenges for automotive electronics designers is to rapidly introduce new electronic components that improve passenger comfort, safety protection and other enhancements. Designers must reduce overall design and certification time and enhance existing system functionality without compromising increasingly stringent quality and reliability requirements and cost goals. To overcome these challenges, automotive electronics designers need more integrated solutions to increase the functional density of the system. High-function integration of mixed-signal components is an attractive alternative.

Capture, compute and communicate

new design challenges

Fuel tank sensing is a good example of the challenges faced by automotive electronics designers. Only a few years ago, fuel level sensors were a fairly straightforward design issue. It consists of a simple float device with scanning carbon brushes contacting a resistive surface, which causes the analog output Voltage to be proportional to the amount of oil remaining in the tank. But with today’s cars, tank design typically has to wait until near the end of the platform design, and most likely uses any unused space. This can result in an oddly shaped tank and a capacity no longer proportional to the liquid level, which complicates the design of the pontoon system. More importantly, the advent of alternative fuels and fuel derivatives has made the fuel composition of the tank important. For example, the ratio of gasoline to ethanol fuel affects engine dynamics such as ignition, burn time and exhaust emissions. Manufacturers now believe that a new generation of fuel tank sensors must be able to determine fuel composition, while providing this information to the car’s other electronic control systems. This has turned what was once considered a simple sensing design into a complex analytical control challenge.

It is worth noting that almost all systems in the car are being expanded. Active dew-point controllers are replacing windshield defogging, which avoids or eliminates the conditions needed for water droplets to condense. The rain-sensing wiper system integrates motor control and rain-sensing functions into one system. The closing of next-generation anti-pinch windows and sunroofs is another representative application where the microelectronic components of these safety systems need to be integrated.

The first generation of anti-pinch technology

The first generation of anti-pinch designs typically consisted of a mechanical drive system powered by an electric motor. The motor current is monitored by a controller and then compared to a fixed threshold representing a stall condition (where the motor is blocked from turning); as soon as this threshold is reached, the direction of the window is reversed from up to down. This system is shown in Figure 1.

  Sensing Design Challenge Solutions for Automotive Electronics

Figure 1: Control diagram of the first-generation anti-pinch window lift system

The first-generation design had several shortcomings. The first is to develop a method to distinguish the motor stall current when the motor is started and when the window is blocked (Figures 2 and 3). To meet this requirement, a fixed delay is added to the comparator circuit to ensure that it only starts comparing the stall current threshold after the motor has turned, although this sometimes fails to provide anti-pinch protection for a half-open window. For example, if the starting position of the window is only 10mm from the top, then the window is likely to hit the hard-stop before the critical timer expires.

Sensing Design Challenge Solutions for Automotive Electronics

Figure 2: Current Variation with Closed Window

Sensing Design Challenge Solutions for Automotive Electronics

Figure 3: Current Variation When Closing the Windows Meets Obstruction

The second disadvantage is that the parameters of the mechanical system can change over time, which can affect the working load of the motor, making the anti-pinch threshold larger or smaller.

Finally, these systems cannot adapt to changes in the driving environment due to the use of fixed thresholds. Thermal expansion effects of window weatherstrips can have a large effect on workload due to temperature changes. The force required to close the sunroof when the car is stationary is very different from that of a moving vehicle, and the force required to raise the window on a smooth road is also different from when the vehicle is driving on a rocky road. In both cases, the inability to compensate for these changes can affect safety or cause the windows to not operate properly.

Designers have tackled these three important challenges in different ways in the past. In some cases, they will add more sensors or use more precise control materials and components to alleviate these problems, but these approaches increase the cost and complexity of the design. This makes them increasingly need a low-cost anti-pinch function design to overcome these shortcomings.

new design solutions

As shown in Figure 4, a mixed-signal microcontroller containing a high-speed central processing unit (CPU) and a high-performance analog-to-digital converter (ie, bandwidth greater than 180 MSPS and resolution greater than 12 bits) is the best solution to this problem .

Sensing Design Challenge Solutions for Automotive Electronics

Figure 4: Anti-pinch system using a mixed-signal microcontroller

This approach allows designers to use a microcontroller to perform both the communication functions of the motor and the monitoring of the motor current. Communication noise can be detected directly by the on-chip analog-to-digital converter on the current sensor (ie, the shunt resistor) in the motor power circuit. This method can more accurately distinguish whether the motor is running or stalled, not only does the comparator circuit not need to add a fixed delay time, but also provides a complete anti-pinch function even when the window is half-open.

As shown in Figure 5, the system sets a variable motor current threshold based on historical data and parameter calculations to dynamically respond to motor load changes and limit system torque to an appropriate range, while limiting long-term factors such as motor wear and seals material aging) and short-term factors such as environment, humidity, temperature and vibration are taken into account. In addition, the system can exchange information with other electronic control units (ECUs), and use information such as outside temperature and vehicle speed as weighted inputs to determine appropriate thresholds (see Figure 6). Utilizing other systems not only improves overall system performance, but also avoids the additional cost of duplicating sensors on the vehicle.

Sensing Design Challenge Solutions for Automotive Electronics

Figure 5: Current variation during window closing with variable thresholds

Sensing Design Challenge Solutions for Automotive Electronics

Figure 6: Environmental parameters and historical data stored in in-memory tables that can be used to determine critical values

growth market

Automotive applications account for one-third of 8-bit microcontroller sales, and not only has the market size exceeded $3 billion, but it is also growing at a rate of nearly 10% per year. Automotive embedded system designers must develop more reliable, lower cost and more integrated solutions, so they need the most advanced microelectronic building blocks at their disposal. Mixed-signal microcontrollers with powerful analog and digital performance are the most cost-effective solution for these next-generation automotive electronics applications.

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