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 Post subject: ETC - Electronic throttle Control (DBW)
PostPosted: Sat Oct 31, 2015 7:11 am 
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This is now pretty high on my to do list but I'm missing almost all knowledge here.... :(

I know I want redundant TPS and pedal signals
I know I want to compare those signal and kick out if they mismatch by too much.
I know the drive signal comes out of something called a 1/2 bridge

That is the full extent of my knowledge......can any one here school me a bit?


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Sat Oct 31, 2015 1:59 pm 
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We've talked about this a bit so you know my position is somewhat sceptic, if I put it gently. The software needs to be written to be robust in the face of single bit errors in the data and also the code. If the code is publicly available, what if someone changes something else unrelated in the code and it becomes susceptible is some obtuse way?

I would encourage discussion of this because I think it's an interesting problem. High reliability, high availability and multi processing stuff has been at the forefront of difficulty and interest in computers for decades. I will also say as another caution that the people who wrote the code for Toyota got this wrong and it cost Toyota well over a billion dollars in settlements. You can read a bunch of interesting details about this on the "embedded gurus" website. As a starter I would recommend not doing any of the bad things those folks did! :rofl:

It seems like it would take more than 100 hours of effort to do this, and the tradeoff would be investing that much time in designing a good mechanical system.

Advantages of the DBW would include:
- no cable with friction and or associated bell cranks and stuff
- the digital system can be filtered to limit response times
- digital system can be connected with wheel spin sensors

The down side of some of that is that the auto controls take away the fun from the driver. There is a spectrum with the driver and simple mechanical systems at one end and the driver sitting in the pits watching his automatic car driving around at the other end. When I started driving my Formula Ford, I had no idea how good a driver could actually be. Developing that connection with the car where my spinal cord basically drove the car was my greatest pleasure. It was never possible to drive that car consciously at anything like a competitive level.

Once you get the car to the point it has traction control, you're just a spectator in your own vehicle. I think that is a bad situation when you are in a high performance vehicle. I know it's accepted in top level racing now, but why go there? This is for your pleasure and you don't have to compete against computers...


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Sun Nov 01, 2015 6:02 am 
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There's reason to be concerned but even if the throttle bangs wide open without any driver input the brakes, clutch, gear selector, and ignition switch are all perfectly capable of preventing anything bad from happening. OEMs can't expect competent drivers and need to be certain the system doesn't do anything unexpected they might be blaimed for, but dealing with the unexpected is to be expected on a race track....I've had throttle stick dozens of times over the years.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Sun Nov 01, 2015 5:42 pm 
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Automobile manufacturers have a reasonable "right" to assume "qualified" people will be permitted to drive vehicles. That's why there are "license" requirements, correct?


Unless you have a compelling reason to support throttle by wire, I suggest you don't.

Maybe, provide some stub in the code, but do not implement things- let those willing to assume responsibility develop it.

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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Sun Nov 01, 2015 8:49 pm 
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OK, that's fine, I guess I just needed a minor tirade. It's only happened to me twice, but it felt like a big deal in a Formula Ford. The braking zone is late, on the track I can pass a very fast bike after he hits the brakes and still upshift before I hit my zone. I think almost the only choice is the off switch. I was grateful for a very simple dash that day. I don't think you can shift out of gear under full throttle and under brakes. The clutch would work though.

Let's cover any differences in the sensors like the TPS first so that I can make sure it's easy to use the proto boards for this. I'm planning on submitting the board to fab this week. If we can find some schematics we can figure out how they are using half bridges. Usually it's a way to work with sensors where the transducer is in a circuit with precision resistors in the other legs and the out puts are compared.

Do DBW systems typically have a backup actuator of some type or do they just depend on a single stepper motor? A voice coil type actuator would let you have a return spring and you could also have a watchdog that could kill the drive voltage.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Mon Nov 02, 2015 1:32 am 
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Horizenjob wrote:
...I don't think you can shift out of gear under full throttle and under brakes. The clutch would work though....

You've pretty much just explained, in short form, how to get around a corner with a turbo'd bike without loss of power. One has to keep the engine up and loaded, and bang through gears. Little mistake made though, and the bike is laying down.

Not much difference, I guess, with a peaky, turbo'd car either, though.

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My O5E candidate: 1982 Honda CX500TC motorcycle.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Mon Nov 02, 2015 1:45 am 
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My opinion is the ECU itself has no direct control over the throttle. Rather, it commands a separate MCU to control the throttle and monitors its operation. And it monitors via separate sensors what the external MCU is doing.

If the MCU cannot maintain proper throttle control, the ECU stops the engine in a safe manner so that the driver can at least navigate to the side of the road, with the engine running as well as possible using rev limiting techniques including things like dry-firing cylinders (no fuel) to keep RPMs manageable, so that power steering and power braking are not adversely affected.

Hmm... more sensors.

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/me goes off to the corner feeling like Jerry Springer with a mullet.

My O5E candidate: 1982 Honda CX500TC motorcycle.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Mon Nov 02, 2015 3:21 am 
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I don't think breaking the job up into different chips is a better solution. it sort of lands up being the same really. The chips now have multiple CPUs on one die, so that gives you similar solutions in one package if that's what you want. Those newer chips have more safety features too like better ECC etc.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Mon Nov 02, 2015 9:31 am 
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abecedarian wrote:
Automobile manufacturers have a reasonable "right" to assume "qualified" people will be permitted to drive vehicles. That's why there are "license" requirements, correct?


You'd be surprised.

My day job is medical....where it's specifically illegal for me to assume the Doctor will read the instructions before using the device.

I can count on about 1 finger the number of people I know who have ever read a car's owner's manual.

Way back when Ford had tired exploding and people where dying in the resulting rollover crashes one of the car magazines setup a test to see it happen. They drove at 55 or 60 across a spike that punctured a tire....and nothing happened. They assumed it was because the trained drivers were making corrections so they did it again with the driver's hand off the steering wheel....and nothing happened. The conclusion was that when a tire punctures it the steering wheel no longer sits straight and what much have been happening is the drivers where watching the steering wheel not the road and forcing the steering wheel back to center, throwing the car into a hard turn onto the flat tire causing the roll over.....completely operator error.

So no, automobile manufactures do not have a right to assume only qualified people will use their products and that is why all the concern over the car doing ANYTHING unexpected.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Mon Nov 02, 2015 9:43 am 
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Horizenjob wrote:

Let's cover any differences in the sensors like the TPS first so that I can make sure it's easy to use the proto boards for this. I'm planning on submitting the board to fab this week. If we can find some schematics we can figure out how they are using half bridges. Usually it's a way to work with sensors where the transducer is in a circuit with precision resistors in the other legs and the out puts are compared.

Do DBW systems typically have a backup actuator of some type or do they just depend on a single stepper motor? A voice coil type actuator would let you have a return spring and you could also have a watchdog that could kill the drive voltage.


first, don't let anything I'm doing for my car derail you. I have hardware to do this for me and I can continue to use the hw I have along side o5e.

What I 've learned is the system is pretty simple. Its a single motor with a return spring. You sent a + and - signal to the control motor which is just a DC motor so varying the current varies the torque and the throttle moves until the motor torque matches the spring force. That's all that's needs but there is normally a PID control to match throttle position to pedal position.

Basic safety comes from redundant TPS and pedal sensors, any mis-match and the system shuts down.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Mon Nov 02, 2015 1:35 pm 
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I won't get derailed, I'm just sort of going thru the laundry and check lists now.

There are two ways to provide that control for the throttle motor. One is a PWM signal that is then filtered to provide an analog voltage. That is most likely and could be provided by the existing CPU board and what is currently on the driver board. You could also provide a digital to analog converter chip and then put an amplifier after it. That would consume more power though, which means more heat in the box.

Both of the above methods would use SPI to set the levels and would also have an independent enable signal.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Tue Nov 03, 2015 1:57 am 
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Horizenjob wrote:
I don't think breaking the job up into different chips is a better solution. it sort of lands up being the same really. The chips now have multiple CPUs on one die, so that gives you similar solutions in one package if that's what you want. Those newer chips have more safety features too like better ECC etc.

So you say that breaking up is not good, then say new chips that do that have better features?

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My O5E candidate: 1982 Honda CX500TC motorcycle.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Tue Nov 03, 2015 1:58 am 
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Horizenjob wrote:
I won't get derailed, I'm just sort of going thru the laundry and check lists now.

There are two ways to provide that control for the throttle motor. One is a PWM signal that is then filtered to provide an analog voltage. That is most likely and could be provided by the existing CPU board and what is currently on the driver board. You could also provide a digital to analog converter chip and then put an amplifier after it. That would consume more power though, which means more heat in the box.

Both of the above methods would use SPI to set the levels and would also have an independent enable signal.

And you've done nothing here to address safety.

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/me goes off to the corner feeling like Jerry Springer with a mullet.

My O5E candidate: 1982 Honda CX500TC motorcycle.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Tue Nov 03, 2015 5:33 am 
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Quote:
So you say that breaking up is not good, then say new chips that do that have better features?


Quote:
And you've done nothing here to address safety.


I feel like we're talking past each other. Maybe you need to make longer than one sentence comments for me to understand you. :)

I can address the first comment but it would take a little more than I want to write at this moment, just because it's late. In the second comment I was just talking about how you drive the signal for the throttle motor, nothing more.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Tue Nov 03, 2015 7:27 am 
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abecedarian wrote:
And you've done nothing here to address safety.


racing 101 - when you're out of control clutch and brake to the floor.

cables fry and jam
linkages bind
springs break

all leading to throttles doing unexpected and undesired things and I've experience all of them over the years. Mechanical throttles are gone from production vehicles now for a reason.

There is nothing inherently safer about mechanical systems over electric/electronic systems, they just have different failure mode. I used to be worried more about this and it probable won't be part of the "released" o5e code, but my car is getting ETC.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Tue Nov 03, 2015 1:45 pm 
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It seems to make sense that the ETC code will be some type of add on patch to the code base. Something that would take an extra step or two to apply.

I think it makes sense to write the code for our current ECU chip and environment. If we choose another chip to perform this function then we might also choose a different processor and my plate is too full to get involved in another toolchain. I'm open to other approaches by other folks, I won't discourage them but contributing to this code base is my own goal. A middle ground would be if the hardware on one of Freescale's $25 demo boards would work.

We can start with just the simple code to read and validate the throttle position and then produce and validate an output. Mark have you chosen hardware for this? Once you do that we can measure or learn how the sensors work and it can be breadboarded at my end.

The sensors are dual with complementing signals, if I remember right. I've seen this stuff just haven't needed to remember it all. So validating the input involves comparing the signals to each other - the positive and minus versions of the the throttle position and pedal position.

The throttle and pedal also need to be compared to each other to make sure the the throttle is tracking. Failure to compare is a reset and/or shutdown.

During movement the throttle may lag the pedal signal. We'll have to measure that and then potentially apply a filter to the pedal position when we compare it to the throttle position. If the throttle position does not match the pedal position after being modeled by the filter, that's a reset and/or shutdown.

We need to verify that the data for the throttle and pedal is being updated. Maybe observing noise in the readings will be enough to do that. Failure to acquire data at the specified rate would be a reset and/or shutdown.

I think the watchdog provides a facility to break up the magic value into multiple bit fields which all need to be feed to the dog. These bit fields can be scattered in the code to make sure that multiple components of the system are running at the required rate. It's important to make sure the processor doesn't get hung up in a small piece of critical code which also includes the watchdog update. Once you start thinking about what is going on in the processor if one of the instructions has a single bit error, things get tougher...

The driver chips on the driver board have a PWM feature that allows setting the period from %0 to %100 in one percent intervals. I think that's adequate for this job but probably needs a logarithmic function to make it more sensitive at the bottom of the scale.

All of this work would easily apply and scale to one of the new 176 pin processors. That includes the board design and layout. We are having some skepticism about needing to use the new ECC processors. If nothing else I think the perceived safety is a worthwhile marketing feature for us. Sometime in the very near future it will be the same cost, so why not?


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Tue Nov 03, 2015 2:01 pm 
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I have the HW, a Porsche pedal and BMW actuator.

I'm writing engine control logic in enginelab at the moment and just starting the ETC stuff. This is just much easier for me to work with as my C is limited. Once I have something working that I like I'll focus on moving everything into o5e.

One of the outputs I can get is a flow chart, attached is the one for the NBO2 stuff I just did. I've got a ton of stuff written and tested in the simulator and moving to stuff like ETC and closed loop.....and with luck I'll be testing on my engine around Christmas time.

I found this site with all the back info
https://www.picoauto.com/library/traini ... ly-by-wire


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NBO2.JPG [ 105.08 KiB | Viewed 7853 times ]
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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Tue Nov 03, 2015 3:43 pm 
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I'm starting to lay this out now. I'm thinking rather than compare the sensor readings I'll calculate the error and desired output using the data from the 2 sets of sensors and compare the results...that will test as much of the the code as possible as well as the sensors I think.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Tue Nov 03, 2015 10:48 pm 
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Freescale has a nice special purpose chip for driving a throttle motor, the MC33931. It may be the way to go.The special dedicated chip uses the least board space which makes it more reliable and it has a lot of safety features.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Wed Nov 04, 2015 5:57 am 
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Horizenjob wrote:
Freescale has a nice special purpose chip for driving a throttle motor, the MC33931. It may be the way to go.The special dedicated chip uses the least board space which makes it more reliable and it has a lot of safety features.


I think that is what's in the AEM HW.... I know for sure its a 5A freescale chip that shuts itself down it overloaded.

The throttle actuator I have did not come with a TPS so I never noticed it's only got 3 wires which means no redundancy. I have a single channel TPS on the one of the TBs which I would think is a better location than the actuator......

another thing I noticed is a GM TB I had was spring loaded to ...10-15% throttle but the BMW is spring loaded closed. I think this probably means that GM never allows the TB to be commanded opened more than the pedal position, they control how much they command it to match below that 15% point. BMW on the other hand is commanding the throttle open more than the pedal is asking for.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Thu Nov 05, 2015 3:34 am 
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Freescale also has the MC33926 for throttle control. These chips have 30 page data sheets with a lot of identical text in them. I'm not completely sure what the difference is yet... This chip has a cheap board available and also an eval module, so maybe it's been around a bit longer.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Thu Nov 05, 2015 7:42 am 
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Horizenjob wrote:
Freescale also has the MC33926 for throttle control. These chips have 30 page data sheets with a lot of identical text in them. I'm not completely sure what the difference is yet... This chip has a cheap board available and also an eval module, so maybe it's been around a bit longer.


I learned yesterday this is the chip in the AEM HW.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Thu Nov 05, 2015 2:30 pm 
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There's a couple ways forward with that chip with boards available from Digikey. There is a bare bones board with 2 of these driver chips for $25. It appears to be intended for hobby robot applications. There is also a $75 version from Freescale that also includes the chip we are using for the fuel injector and coil driving. This board uses the coil drivers alternate function to provide a PWM signal as input to the motor driver chip.

Using the coil driver's PWM function is what I mentioned above in an earlier post. I think going this route makes sense because it would also let us get a leg up on programming the fuel injector/coil driver chip (MC33810).

I need to read the manual for this little Freescale board, but I imagine it has an SPI connection we could attach to the devel boards we are already using. That needs to be checked.

http://www.digikey.com/product-detail/en/KIT33926PNBEVBE/KIT33926PNBEVBE-ND/2185294

edit: I looked a little more carefully and it is run off an USB to SPI converter. So we don't get to directly work on the DEV board with SPI, at least to start. It might be possible to learn what's needed though and then maybe hack the board to talk SPI to the DEV board.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Thu Nov 05, 2015 4:32 pm 
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Horizenjob wrote:
Using the coil driver's PWM function is what I mentioned above in an earlier post. I think going this route makes sense because it would also let us get a leg up on programming the fuel injector/coil driver chip (MC33810).

I need to read the manual for this little Freescale board, but I imagine it has an SPI connection we could attach to the devel boards we are already using. That needs to be checked.

http://www.digikey.com/product-detail/en/KIT33926PNBEVBE/KIT33926PNBEVBE-ND/2185294

edit: I looked a little more carefully and it is run off an USB to SPI converter. So we don't get to directly work on the DEV board with SPI, at least to start. It might be possible to learn what's needed though and then maybe hack the board to talk SPI to the DEV board.
What is brought over to the 16 pin header are the 8 parallel control lines to the MC33810, 3 parallel control signal to the MC33926, SPI signals to/from 33810, GND and a DC reference used to set the logic voltage levels used by SPI and parallel I/O: both chips are compatible with 3v3 and 5v0 logic.

The screw terminals provide for the 4 low-side outputs from the 33810; there's a separate screw terminal header for H-bridge out and DC in.

The USB>SPI converter is optional for the board but it and the SPIGEN software help get started. Some of the SPI control data is a little tough to get through. So theoretically you could work with this board out of the box.

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My O5E candidate: 1982 Honda CX500TC motorcycle.


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 Post subject: Re: ETC - Electronic throttle Control (DBW)
PostPosted: Thu Nov 05, 2015 6:01 pm 
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Thanks, that sounds good, so all the options are on the table. Did you just get a manual from Freescale or were you already familiar with this board?


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