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Integrating Analog Functionality for Automotive Applications: Tougher Than You’d Think

One area of new IC design where it is tough to get lots of functionality in a small space is industrial/automotive applications. The ambient temperature requirements make it difficult in general, especially for the automotive sector. Further, if you put 10 pounds of circuitry in a five-pound IC package, it will probably run pretty warm. Put that IC in a 125°C environment, and you'll find out pretty quickly just how good it really is.

Let's assume that the design team knows what it's doing and can create devices to work in this environment. What functionality do you need under the hood? I'm fond of control systems in general and controls for internal combustion engines in particular, so let's look at some of the pieces in typical setups.

The starting point (pun intended) is the ignition control. The simplest electronic ignition system would use a magnetic pickup to sense crankshaft position and a power transistor (FET or bipolar) to replace the points and drive the ignition coil primary. In between would be an amplifier stage, a low-pass filter (LPF) network, and a comparator. Put an adjustable reference voltage on the comparator, and you can tweak spark advance.

We can make that more sophisticated by adding a microcontroller unit (MCU) to tweak spark timing based on data from various sensors. The likely sensors needed measure engine temperature, ambient temperature, barometric pressure, air flow rate, water flow rate, and engine knock. We will need the circuitry to interface between the sensors and the MCU — amplifiers, LPFs, and ADCs.

If we need higher performance, we can beef up the spark by using a capacitive discharge topology. These charge up a capacitor and then dump it into the ignition coil primary with either an SCR or a large power FET.

There would still be a distributor in this setup functioning as a motorized high-voltage rotary switch. We can eliminate that by using multiple ignition coils. Some versions bring out both ends of the coil secondary and fire spark plugs in two cylinders simultaneously. In this scenario, one cylinder is approaching TDC for the power stroke, and one cylinder is in the exhaust stroke. This saves on the number of coils needed. The coil primaries are driven with multiple power transistors as above. The additional drive circuitry is trivial.

If the engine is fuel injected, we can drive the injector solenoids with more power transistors. Again, that MCU can control and adjust timing as needed. Regarding the handful of power transistors, these could be integral to the IC, but maybe that's not such a good idea.

The typical switching configuration here has the transistor as a low-side switch, so its drain or collector sees the battery voltage plus whatever load dump and ignition coil transients are present. In automotive systems, that's typically a lot. Surge specs range from 45V to 70V, depending on which section of which design standard you read.

If the transistors are integral to the IC, the IC needs to be built on a high-voltage process. That drives up the cost. It's cheaper to fab the chip on a 3.3V or 5V process and then add discrete power transistors.

You could put battery charging and status monitoring circuitry on the same device, but it's best to keep that separate. The functionality is different, and the voltage requirements are higher. As detailed above, put that on a separate IC.

Have you worked on any electronics for internal combustion engines? What problems did you encounter? How did you work around the problems?

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28 comments on “Integrating Analog Functionality for Automotive Applications: Tougher Than You’d Think

  1. eafpres
    August 13, 2013

    @Brad–I might have mentioned this here before but we and a tire pressure sensor antenna for the “base unit”; it was a low frequency (~ 400 MHz) coil in a plastic housing (had to be plastic to get the RF in).  They mounted it next to the exhaust pipe under the car.  It had to meet 125C max temp, then immersion (while hot) into 1 meter of cold water for something like 5 minutes wihtout leaking.  We had lots of trouble getting to seal, findng a plastic that would survive 125C, etc.  Automotive is full of fun surprises like this.

  2. eafpres
    August 13, 2013

    @Brad–in a previous company we made soft ferrite products for automotive including multi-hole plates that slid over all the pins in an ECU to reduce conducted EMI for these modules in the engine compartment.  Those pesky spark plugs you talk about, among other things, generate a lot of electrical noise under the hood.  You need a lot more EMI/ESD/EMC protection and mititgation in most of those designs.

  3. eafpres
    August 13, 2013

    @Brad–one more thought on automotive elecronics; the engine control module you describe might be simplified a little bit by using Piezoelectric fuel injectors which substitute a PZ material to actuate the injector valve instead of a solenoid/magnet setup.  There are several of the fuel system Tier1s making such systems now.

  4. Davidled
    August 13, 2013

    It is not easy to minimize the background sound on a certain DB value coming from engine compartment in dynamic mode. To do that, all engine compartment and bracket location is redesigned based on cabin acoustic engineer and Noise Vibration and Hardness (NVH) Engineer criteria.

  5. Brad_Albing
    August 13, 2013

    Yep – I experienced a little of that when I was an FAE – working some accounts around Detroit MI.

  6. Brad_Albing
    August 13, 2013

    Interesting – that's the opposite end of the spectrum with respect to energy harvesting that I wrote about a few weeks ago, using a PZ bender as an energy transducer.

  7. Brad_Albing
    August 13, 2013

    True enough. In a further back former job (15 or 20 years ago) I worked at a company that produced electronic ignition systems for gas-fired appliances. Just a wee bit of EMI with those.

  8. samicksha
    August 14, 2013

    You are right eafpres, and one the major advantage of using is is their speed of operation and the repeatability of the movement of the valve which further makes it more precise proportioning of the injected fuel and a greater number of injections per cycle.

    A pic from densomediacenter.com..

  9. BillWM
    August 14, 2013

    Gas Turbine engines present their own unique challenges —  (Believe it or not UP Railroad even experimented with coal fired gas turbine rail engines for use going over the continental divide in the 1950's)

  10. Brad_Albing
    August 14, 2013

    Seems like I recall those – gasification of coal, maybe? Guess they had big piles of coal still available, so they were looking for ways to use it as they were moving towards complete dieselization.

  11. BillWM
    August 14, 2013

    Back then the Diesels were about 50% -75% less powerful in the same package as a modern Diesel — they just had trouble pulling the mountain grades with a full load of cars.

  12. Brad_Albing
    August 14, 2013

    @Will Murray – hence the pursuit of the turbine. Now (like you said) more powerful diesel engines – combined with AC traction motors and traction control to detect slip.

    Just a wee bit more sophisticated.

  13. BillWM
    August 14, 2013

    Here in the photo one can see the locomotive, and tender — about the size of 3 diesels — and had something like 12,000 to 15,000 shp.  The tender carried a large sand bunker which automatically delived sand to the traction wheels – a requirement at that time.

    Back then they even experimented with Turbine powered cars — with one even nearly winning the Indy 500 once — prior to the race being limited to piston engines

     

    During my time doing helicopter portable petroleum exploration, the crew relied on a Bell-47 with the Soloy gas turbine conversion — this about doubled the power to weight ratio for the Helicopter, and the Turbine had very little power derating for altitude, so this was the Helicopter of choice when working at 10Kft.  The only other game in town for high altitude small helicopters was the Lama which was a bit larger, and therefore harder to tow behind a 4×4 support truck if needed.

     

     

  14. Davidled
    August 14, 2013

    I remembered that air compressor had been developed a long time ago in the train.  A huge air tank is connected to cabin. Air compressor is better than Coal in the eco environment. I knew that big OEM used air compressor in the engine compartment. Air compressor is a green technology.

  15. BillWM
    August 15, 2013

    — Compressed air engines — were developed for use inside coal mines and other short-haul lines where flamibility / exhaust were a concern  — There is not the power/weight ratio of modern electric/battery systems — Also most rail brakes are compressed air — modern ones use electric control of compressed air for better brakeing.

     

  16. Davidled
    August 15, 2013

    Air /Hydraulic Engine

    The most creative engineers who had passion for innovation during their life time equipped air compressor with a lot of hose and pipe line with computer module in the powertrain of this vehicle. What engine  truly means is the driving force. So, elements of the driving force could be oil, coil, air, wind, and battery.  

  17. BillWM
    August 15, 2013

    A run-down of compressed air — from one point of view

    http://www.aqpl43.dsl.pipex.com/MUSEUM/TRANSPORT/comprair/comprair.htm

     

    Presently there are some large underground compressed air energy storage systems that can be used to release energy when needed.  Some use salt caverns, others use limestone formations

  18. Netcrawl
    August 16, 2013

    @Brad coal gasification could be a good idea, turning those tons of coal into something useful. I think it will take more time to do that, right now the main focus is on diesel and electric motors

  19. Netcrawl
    August 16, 2013

    The best engineer is one that could completely changed the entire automotive landscape and goes beyond, I think the next phase here could be a new breed of microcontroller, something that can significantly improve power supply system stability.    

     

     

     

  20. Netcrawl
    August 16, 2013

    Thanks for the link @Will, I think one of the big disdavantages for compressed air driven engine is the continued used of the conventional valve assembly, its a complex things and highly susceptible to machine or material failure.  

    Yes its a great stuff, compressed air driven engine is a big attempt to provide a better mean of transporation that's is pollution free.

  21. Brad_Albing
    August 16, 2013

    @Netcrawl – well, sort of pollution free. You still need a way to compress the air. Some sort of motor or engine spinning an air compressor. You need an energy source for that motor or engine – maybe burning coal, oil, natural gas, gasoline. Now if you used wind turbines, ocean wave motion, solar heat gatherers, or photovoltaic, that would be pollution free, mostly.

  22. Brad_Albing
    August 16, 2013

    @Netcrawl – I'm looking forward to a blog from you that gives more details of a possible new breed of microcontroller.

  23. Brad_Albing
    August 16, 2013

    @Netcrawl – It's certainly possible to do that and mildly practical. But you end up with sulfur as a byproduct from some of the cheaper grades of coal. The better quality, low sulfer coal will be used for metalurgical applications.

    With more deposits of natural gas being developed (via hydralic fracturing), I expect to see hardly any effort put into coal gasification.

  24. Netcrawl
    August 16, 2013

    @Brad that would be great, There's a lot development going on in this area like Fujitsu Semiconductor's new microcontroller for automotive applications, Fujitsu managed to incorporate digital power supply system control onto single microcontroller chip. It target power transmission circuitry in hybrid electric vehicles. 

    http://www.japanportal.jp/article/413541.html

     

     

  25. Netcrawl
    August 16, 2013

    @Brad I can't wait to see that, Currently, there's a growing demand for enhanced safety features, entertainment systems and emissions control. Many of these new controllers will have more “silicon muscles” devoted to communication capabilities than a computer's CPU. There's a lot of devlelopment going on here, I think in the next few years, system such GPS-based Navigation system, Steering system, Collision Warning System and Voice Recognition will start to be introduced, and more are coming. 

     

     

     

     

  26. Davidled
    August 16, 2013

     think that they use 32 bit microcontroller. If you say, “single microcontroller,” I think that one powerful microcontroller can control tasks that two microcontroller handles. They might have a dual core processor. New microcontroller is better performance than old and the effect is the efficiency of energy.

  27. Netcrawl
    August 17, 2013

    @Daej you're right they use 32-bit microcontroller, Daej its single microcontroller chip. The new Fujitsu's 32-bit microcontroller MB91F552 incorporates a host of optimal function for digital power supply control and other network control functions all on a single microcontroller chip, 

     

     

  28. SunitaT
    August 20, 2013

    Combustion occurs interchangeably at each end of the piston and a contemporary two-stroke series scavenging procedure is used. The alternator element controls the piston's gesture, and thus the range of cylinder gas compression, by proficiently managing the piston's dynamic energy through each stroke. Compression of the fuel mixture is achieved inertially and as an outcome, a mechanically simple, adjustable compression ratio strategy is possible with refined electronic control.

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