Unintended acceleration in 2024 MG4 Trophy LR

[ReintjeWA]

Huh, that works? How often and at what speeds do you do that?

The only trick I heard until now was switching to Neutral and braking.

The car also uses friction brakes when in reverse, fyi. I scrub every now and then by switching to neutral on an empty road.

 

[gary333]

I researched this a bit more and this seems like a terrible idea. It can quickly overheat the discs or even damage components (they are not made to accelerate while fighting against the brakes).

So I guess I'll stick to braking hard a few times or switching to Neutral

Give it up, think about what you have typed here

 

[decrep]

He did say "light pressure"

 

[siteguru]

Is the theory that pressing the accelerator overrides the car's intent to increase the regen %age when pressing the brake pedal, so the physical brakes are used instead?

 

[Vlyn]

Is the theory that pressing the accelerator overrides the car's intent to increase the regen %age when pressing the brake pedal, so the physical brakes are used instead?

You can just put it into Neutral for that, then it's 100% friction brakes on the MG4. What they are proposing is braking while having the motor trying to accelerate at the same time. Which I guess can work, but when I read about it it seems risky and very taxing for the components

I'm surprised the car would let that happen at all as usually braking would switch off the accelerator.

 

[gary333]

Is the theory that pressing the accelerator overrides the car's intent to increase the regen %age when pressing the brake pedal, so the physical brakes are used instead?

Correct. The car won't try to regen whilst the accelerator is pressed lightly at slow speeds, although as we are talking about 5-10mph the level of regen would be tiny either way..

The person is confused if he thinks lightly pressing the accelerator and brake at the same time at c.5-10mph is in some how more taxing on the car than it would be accelerating fast or braking from speed. Clearly has been researching driving an ICE car and what happens if you put full brake pressure on and full accelerator in an older manual car.

We're talking about lightly scrubbing the brakes here, we're not talking about trying to pull tree stumps up.

 

[gary333]

You can just put it into Neutral for that, then it's 100% friction brakes on the MG4. What they are proposing is braking while having the motor trying to accelerate at the same time. Which I guess can work, but when I read about it it seems risky and very taxing for the components

I'm surprised the car would let that happen at all as usually braking would switch off the accelerator.

Yet you're happy to cause strain on the reduction gear placing it from Neutral back in to Drive......

 

[Vlyn]

Yet you're happy to cause strain on the reduction gear placing it from Neutral back in to Drive......

That's where you're wrong, fast acceleration or braking with recuperation puts much more stress on the reduction gear. Coasting in neutral just disconnects the motor / lowers the resistance, but the only force on the reduction gear is its own inertia when you then brake with the friction brakes.

As for going Neutral to Drive, the MG4 has a VCU that first syncs things up and gradually applies torque. Without that you're right, the sudden jolt would damage things.

 

[gary333]

That's where you're wrong, fast acceleration or braking with recuperation puts much more stress on the reduction gear. Coasting in neutral just disconnects the motor / lowers the resistance, but the only force on the reduction gear is its own inertia when you then brake with the friction brakes.

Re-read what i said, i said when "you put the car back in drive"! Obviously when you put the car back in drive from neutral it places minute strain on the reduction gearbox, the same level of minute wear and tear the motor and reduction box would be under by lightly pressing both pedals.

 

[Vlyn]

Re-read what i said, i said when "you put the car back in drive"! Obviously when you put the car back in drive from neutral it places minute strain on the reduction gearbox, the same level of minute wear and tear the motor and reduction box would be under by lightly pressing both pedals.

Sorry, I edited my reply, read the second paragraph. The VCU is prepared to handle this and avoid the strain. While we have no clue what happens if you apply brake and throttle at the same time, it's not built for it.

 

[gary333]

Sorry, I edited my reply, read the second paragraph. The VCU is prepared to handle this and avoid the strain. While we have no clue what happens if you apply brake and throttle at the same time, it's not built for it.

The car can do it, it's not built for it. Just like the car can have the accelerator pressed lightly and brake pedal pressed lightly. They are exactly the same type of scenarios which the car could, if it wanted to either allow, or disallow. The fact other cars allow this to happen shows it's intentional design.

If you take one second away from your AI searching you would see that very slow speed and small levels of brake pressure are NOT going to cause any excess wear and tear compared to driving the car normally.

And finally, if it wasn't obvious, what i said about the reduction gear was said as tongue in cheek to show the ridiculousness of the argument you put forward (that wear and tear would be caused by the action of apply slight amount of braking force whilst driving forward). The car attempts to mitigate the action of returning to drive but still an amount of minute wear and tear will be encountered (moving from neutral to drive whilst still moving), however either way have so little perceptible risk that the car permits this to happen.

And for the record I perform both scrubbing at slow speed, and from high speed using neutral, and have done for at least the last 10 years of owning electric cars.