[RahulNagaraj]

According to media reports, Harley-Davidson's EV brand, LiveWire, has applied for a patent called "Virtual Brakes". As per this, the company is looking at ways in which LiveWire can entirely remove the mechanical, frictional brakes from at least one wheel of the motorcycle. This, according to the brand, will help reduce both the cost and weight of the motorcycle.



The patent states, "Mechanical, frictional brakes, such as hydraulic brakes, add cost and weight, which can impact the performance of a vehicle, especially electric vehicles, such as electric motorcycles. Furthermore, mechanical, frictional brakes dissipate kinetic energy, which otherwise could be used to charge an electric power store included in the vehicle, which may otherwise limit the range and operation of an electric vehicle."

The patent further mentions how these mechanical brakes can be replaced by its "virtual brakes", which use regenerative braking as the sole mechanism to brake at least one wheel. It also mentions how replacing the hydraulic brakes with regenerative braking could reduce a vehicle's weight, cost and complexity.

The official statement reads, "Accordingly, embodiments described herein provide methods and systems for regeneratively braking at least one wheel of a vehicle, such as, for example, an electric motorcycle. In some embodiments, regenerative braking is used as the sole mechanism to brake a wheel of the vehicle, such as the rear wheel of a motorcycle. Replacing a rear hydraulic brake with regenerative braking reduces the cost, weight, and complexity of the vehicle, which, as noted above, impacts the performance of the vehicle."

Source: RideApart

Link to Team-BHP news

[ruskyhead]

As it is bigger bikes barely have rear braking power. I think it is ok for bigger bikes to have just the front dosc and a regenerative braking option as the "rear brake".

Could be done on smaller scoots too. But should come with mandatory front ABS.

[PreludeSH]

What happens when the battery is full ? Do they dissipate through resistor loads or always maintain some buffer in battery charge ?
Even if they default to friction braking on other wheel, will it be seamlessly handled ?

[ashivas89]

Originally Posted by PreludeSH

What happens when the battery is full ? Do they dissipate through resistor loads or always maintain some buffer in battery charge ?
Even if they default to friction braking on other wheel, will it be seamlessly handled ?

Purely theoretically:

Some energy is always needed to get to a certain speed anyway. That amount of energy (expended to accelerate and maintain speed) is greater than the energy that regen puts back in the battery.

No vehicle can accelerate to say 100 km/h and still be at 100% SoC.

Practically, other considerations like battery readiness (especially in terms of temperature) to accept being charged at rates (wattage) typical to braking power come into the picture and need to be engineered into the system.

[rkv_2401]

Originally Posted by PreludeSH

What happens when the battery is full ? Do they dissipate through resistor loads or always maintain some buffer in battery charge ?
Even if they default to friction braking on other wheel, will it be seamlessly handled ?

Regenerative braking isn't strong enough to be greater than the energy required to accelerate the vehicle to a certain speed. There is friction at the wheel during acceleration and steady state operation (cruising), electrical losses incurred at the motor, drag becomes a factor at low-to-moderate speeds. Regen braking isn't 100% efficient too, some of the heat generated under braking will always be lost.

Case in point - The MGU-K in Formula 1 cars is probably one of the most advanced and efficient regenerative braking systems we can imagine. The drivers always brake at 90-95%+ of the car's peak stopping potential, unlike road driving where that's almost never going to happen. You know beforehand exactly when the car is going to brake and also for how long, and can even switch between various mappings that are all suitable for the same circuit. There are tremendous benefits to having it be even 1% more efficient. But even this can only, at most, provide around 15 seconds of ~100hp (MGU-H and MGU-K together are limited to 160hp) on a lap-by-lap basis. And this is in a car where the engine produces ~840hp for the rest of the lap!

[srini1785]

I would say, its another catchy marketing phrase. The block diagram in the source is too technical and sketchy for me. I can only comment that the energy obtained by braking would not be sufficient to effectively brake a 300Kg or so machine. From what I know, regen energy is a function of mass and speed (instant) and that Regen starts the moment you lift your leg from the pedal or grip. From that we need to infer that Regen energy starts dwindling down with time. Mr. Newton would be a very disappointed man if regen alone can produce enough energy solely to stop a vehicle.

[abhikb2005]

Honest question - what happens if I have to brake suddenly because a dog ran across in front of me? Will that single brake have enough bite? Regen is surely not instantaneous.

I haven't read the source article, (so I apologize in advance if it is answered there) but this is a reflexive question that popped up as soon as I read the headline.

[DIY410]

To stop a motor or come to a complete motor stop, all you have to do is short the cables of the pmsm or bldc motor, which will complete the circuit inside the stator, this causes lot of heat to be generated. But a motor controller will use mosfets to switch On and Off (pwm) to get variable regen and also pass the electricity produced to charge the battery.

But to just stop the vehicle all one needs to do is short the cables of the motor and this can be done only if the motor is liquid cooled.

[viggienomad]

Originally Posted by DIY410

...
But to just stop the vehicle all one needs to do is short the cables of the motor and this can be done only if the motor is liquid cooled.

So this is independent of wheels? And there will no free wheeling?!! Sorry for a noob question.

[roy_libran]

This might actually be a good idea to provide a brake assist, based on my EV regen experience.

From what I observed this patent was only for the rear wheel which has a much lesser share of braking duty on a motorcyle, and as long as the Front wheel's braking is handled in a traditional manner which does the bulk of the braking, this could potentially be a better setup.

[DIY410]

Originally Posted by viggienomad

So this is independent of wheels? And there will no free wheeling?!! Sorry for a noob question.

The back wheel needs to be connected mechanicaly by chain or belt to the drive motor. If you do not close the stator circuit in the motor it will be free wheeling. But once you do, it will start resisting to 100% but with a motor controller you can control the regen due to pwm. Which is basically doing a pwm of the back emf produced by the motor.