Throttle attenuator for an EV

[quince]

My car has an especially peppy throttle. If I stomp it at a stop light it'll easily break the tires from the pavement. Some cars like mine have a "chill mode" which cuts down the throttle substantially, but mine isn't in that price bracket.

An older car I owned had about half the kW rating of my current vehicle. I've been often thinking while driving about what it'd take to get the sedate throttle of my older car in my new one.

My solution is to cut the voltage increase (relative to zero throttle) by half as the throttle is applied. I've attached the OEM reference schematic, and a rough LTSpice simulation of my board.

Attenuation is achieved passively by dividing the difference between each throttle pin's actual voltage and a zero-throttle reference (generated via fixed resistor divider) by roughly two. This solution appears to output voltages within 1-5% of the correct value across the throttle resistance range; hopefully this is within the ECU's tolerances.

Results will be posted here in a few weeks when all the parts show up. Any feedback or suggestions would be appreciated! Feel free to re-use this design if it's useful to you.

[moffy]

Is the accelerator position proportional to speed or say motor current/power? I'm not sure how that works in an EV.

[SeanB]

There are throttle pedal adjusters, specific for a vehicle type, that act to change the law the sensor provides to the ECU. They read the 2 signals, and then use a small MCU to read the 2 pedal position voltages, one rising from 0V to Vref (typically 5V) as the pedal goes from released to flat to the floor, while the other is the exact opposite, so that the ECU can do sanity checking and prevent the runaway accelerator thing. They normally are going to do the opposite, providing a higher presented position according to some curve, but are quite capable of also limiting the max pedal position shown to the ECU instead, acting as power limiter.

[SteveThackery]

Is the accelerator position proportional to speed or say motor current/power? I'm not sure how that works in an EV.

Neither, almost certainly. It will just be one more input to the ECU, which will no doubt have sophisticated algorithms determining the motor current at that instance. I imagine all sorts of variables will be assessed: throttle pedal position, direction of movement and speed of movement; battery charge level; battery temperature; motor temperature; road speed; driving mode (sport, economy, etc); traction control setting; etc, etc.

[SteveThackery]

There's no chance that I would mess with such a safety critical sub-system. Also, it surely will invalidate your insurance.

[BrokenYugo]

Thinner sole shoes? Eco mode? An electronic throttle pedal is not something I'd mess with.

[langwadt]

Is the accelerator position proportional to speed or say motor current/power? I'm not sure how that works in an EV.

Neither, almost certainly. It will just be one more input to the ECU, which will no doubt have sophisticated algorithms determining the motor current at that instance. I imagine all sorts of variables will be assessed: throttle pedal position, direction of movement and speed of movement; battery charge level; battery temperature; motor temperature; road speed; driving mode (sport, economy, etc); traction control setting; etc, etc.

https://www.reddit.com/r/teslamotors/comments/inzuhz/model_3_factfinding_accelerator_pedal_position_vs/

[quince]

Here's the sim curve if anyone wanted it. Less power is genuinely safer unless you're trying to get away from someone who's about to rear-end you. From https://www.chevybolt.org/threads/how-are-you-handling-your-instant-torque.46186/:

Over on the EV6 boards, there has been a high report of crashed EV6s, and I can't help wonder if the instant torque is making people take chances that they normally would because of that instant torque

Thinner sole shoes? Eco mode? An electronic throttle pedal is not something I'd mess with.

I already wear thin soles. My car doesn't have an Eco mode. B mode makes the regen region deeper, but full pedal-to-the-medal is still full power. Sport Mode does the opposite of what I want and makes the low-end torque curve sharper.

I have much less confidence in mechanical solutions (nylon block glued to the back of the pedal, anyone?) than an electrical solution which I can switch on and off.

There's no chance that I would mess with such a safety critical sub-system. Also, it surely will invalidate your insurance.

This site says it's legal:

https://issautomotive.com/blogs/throttle-response-controller/are-throttle-controllers-safe-learn-more

In the United States, throttle controllers are allowed as long as they do not interfere with the manufacturer's original design and the vehicle remains safe to drive. In Europe, most countries allow throttle controllers as long as they meet EU safety requirements.

Also: I spent more than half my driving career behind the wheel of "slow ICE" and "slow EV" with glacial throttle response and almost zero low-end torque.

From my perspective, I'm not messing with the throttle of my EV. The OEM has been introducing a hazard to me in making all EVs, mine included, way quicker than is required because reviewers expect to have maximum torque and power available when stationary.

Nobody really talks about it, but EVs can be more expensive to insure partially because they're so overpowered.

[quince]

Is the accelerator position proportional to speed or say motor current/power? I'm not sure how that works in an EV.

Neither, almost certainly. It will just be one more input to the ECU, which will no doubt have sophisticated algorithms determining the motor current at that instance. I imagine all sorts of variables will be assessed: throttle pedal position, direction of movement and speed of movement; battery charge level; battery temperature; motor temperature; road speed; driving mode (sport, economy, etc); traction control setting; etc, etc.

This is technically true, but most of those variables are ignored beyond 20-30% throttle position. The throttle maps nearly linearly to torque with some smoothing near zero for reduced jerk. Below 20-30%, the computer does have to consider those variables to figure out what current to feed the battery in regeneration.

[quince]

There are throttle pedal adjusters, specific for a vehicle type, that act to change the law the sensor provides to the ECU.

There is even one for this particular EV, which strangely doesn't even have a display or monitor. My solution will show the driver an LED if the throttle attenuator is active and no light if not.

They read the 2 signals, and then use a small MCU to read the 2 pedal position voltages, one rising from 0V to Vref (typically 5V) as the pedal goes from released to flat to the floor, while the other is the exact opposite, so that the ECU can do sanity checking and prevent the runaway accelerator thing.

It's indeed odd that this car uses potentiometers going in the same direction, with more pedal always resulting in higher voltage. Maybe they allow this because each signal has a different range and they wired the connector symmetrically.

[SteveThackery]

Is the accelerator position proportional to speed or say motor current/power? I'm not sure how that works in an EV.

Neither, almost certainly. It will just be one more input to the ECU, which will no doubt have sophisticated algorithms determining the motor current at that instance. I imagine all sorts of variables will be assessed: throttle pedal position, direction of movement and speed of movement; battery charge level; battery temperature; motor temperature; road speed; driving mode (sport, economy, etc); traction control setting; etc, etc.

This is technically true, but most of those variables are ignored beyond 20-30% throttle position. The throttle maps nearly linearly to torque with some smoothing near zero for reduced jerk. Below 20-30%, the computer does have to consider those variables to figure out what current to feed the battery in regeneration.

Seriously? The ECU ignores battery temperature and charge level? And the driving mode?? It's beyond 20-30% throttle when these really start to matter, surely!

Do you have a good reference book or online source where I can learn more about it?  I hope you aren't offended by my scepticism - it's just that I cannot conceive of any electric vehicle that doesn't monitor, and manage, the temperature of its batteries. This is burn-like-a-bastard lithium we're talking about.

[SteveThackery]

This site says it's legal:
https://issautomotive.com/blogs/throttle-response-controller/are-throttle-controllers-safe-learn-more

Legal doesn't mean it won't invalidate your insurance! These are completely different issues. At the very least you WILL be required to tell the insurance company.  They are so uptight these days you basically have to tell them about everything.

[quince]

At the very least you WILL be required to tell the insurance company.  They are so uptight these days you basically have to tell them about everything.

They'll be notified, obviously!

[inse]

“I will slow down the acceleration of my car“ - maybe this gives you a bonus…

[SteveThackery]

At the very least you WILL be required to tell the insurance company.  They are so uptight these days you basically have to tell them about everything.

They'll be notified, obviously!

It isn't obvious, although I'm pleased we are of like mind. Time on various car and motorcycle forums has shown me that lots of people don't notify their insurance company when making modifications.

[mikeselectricstuff]

  I hope you aren't offended by my scepticism - it's just that I cannot conceive of any electric vehicle that doesn't monitor, and manage, the temperature of its batteries. This is burn-like-a-bastard lithium we're talking about.

It isn't that it doesn't monitor these and apply limits where needed, just that they are not factored in when determining throttle response in normal conditions. I'm sure that once you're in turtle mode at 1% SoC, some limits will be coming in  to play, but I'd expect these would just be limits applied at the end of he control chain.

[langwadt]

do you fly out the window every time you hit the brakes? if not then apply the same finesse to the throttle pedal

[SteveThackery]

It isn't that it doesn't monitor these and apply limits where needed, just that they are not factored in when determining throttle response in normal conditions. I'm sure that once you're in turtle mode at 1% SoC, some limits will be coming in  to play, but I'd expect these would just be limits applied at the end of he control chain.

Do you have a source for the above information? So far it's just an assertion. I want to learn more. 

Also, it is surely going to include the driving mode in its calculation, because that is the driver's primary control over the throttle response.

[Andy Chee]

My solution is to cut the voltage increase (relative to zero throttle) by half as the throttle is applied. I've attached the OEM reference schematic, and a rough LTSpice simulation of my board.

Surely there is an existing software setting for this? rather than relying on hardware sensor trickery.

[robert.rozee]

i doubt that a driver would be much aware of the position of a foot throttle, but instead be more sensitive to the increasing pressure required as the throttle is pressed further down.

as such, my first approach would be to add a simple pullup spring, so that far more force is required once the throttle gets closer to the floor. you could even go so far as multiple springs with linkages so that as you get closer to the full throttle additional springs come into play, although i doubt this will prove necessary.


cheers,
rob   :-)

[SteveThackery]

That is the best suggestion yet. Nice one.

[SteveThackery]

My solution is to cut the voltage increase (relative to zero throttle) by half as the throttle is applied. I've attached the OEM reference schematic, and a rough LTSpice simulation of my board.

Surely there is an existing software setting for this? rather than relying on hardware sensor trickery.

Exactly! On my motorcycles it's called the "riding mode" and it alters the mapping between the twistgrip position and the throttle butterfly opening. It also alters the maximum rate of change of the butterfly's opening.

Do EVs not have such a thing?

[Monkeh]

My car has an especially peppy throttle. If I stomp it at a stop light it'll easily break the tires from the pavement.

So will my car, and it's not an EV, it's just a small diesel.

Stop stomping. Precise control of both (.. all three, in my case) pedals is a basic requirement of driving.

[BrokenYugo]

i doubt that a driver would be much aware of the position of a foot throttle, but instead be more sensitive to the increasing pressure required as the throttle is pressed further down.

as such, my first approach would be to add a simple pullup spring, so that far more force is required once the throttle gets closer to the floor. you could even go so far as multiple springs with linkages so that as you get closer to the full throttle additional springs come into play, although i doubt this will prove necessary.


cheers,
rob   :-)

I considered that suggestion,but this not being the old steel lever style I worry about wear, binding, outright failure, etc. adding springs to a pedal assembly I assume is made of a minimal amount of nylon.