hybrid bicycle with electric CVT?

[NiHaoMike]

Has anyone thought about building a hybrid bicycle with an electric CVT? (Basically, it would work like a scaled down version of the CVT in the Prius, with the pedals instead of the engine.) One motor is directly coupled to a wheel, and the other motor has the shaft coupled to the rear wheel, the casing to the pedals, and slip rings used for the electrical connections. Two bidirectional DC/DC converters connect the motors to the batteries, with a microcontroller managing power flow.

[xcel]

Hi NiHaoMike:

___I am actually looking forward to what Honda comes up with in terms of their upcoming hybrid motorcycle in about 2.5 years. IMA on a bike should easily be able to propel from the pack and if the pack is large enough...

___Good Luck

___Wayne

[99HXCivic]

I think the worst thing with electric bicycles is the some state laws limit their speed to a slow 20 mph, - which is a road biker's unassisted cruising speed!

[NiHaoMike]

I actually started to think how the controls would work. To ensure it rides like a normal bicycle, the "gear shifting knob" will control the proportion of pedal speed to wheel speed. In other words, the microcontroller will measure the wheel speed and calculate a pedal speed based on the "gear ratio" selected by the knob.
* If the pedals are rotating faster than that, one DC/DC converter will pull power from the split motor to load down the pedals to slow them down to that speed while the other DC/DC converter will supply power to the wheel motor to (by default) net zero battery current.
* If the pedals are slower than the calculated speed, the motors will be inactive and the bike will "glide".
* If the pedals are going backwards, the bike will regen at a rate proportional to the speed of the pedals going backwards. (In other words, pedal backwards to regen!)
* Optionally, if the pedals are moving while the brake is engaged, use that to recharge the batteries.

To make use of electric boost, a twist handle will be used to control battery power used for boost just like a regular electric bike. (Optionally, the handle can twist backwards to engage regen, as an alternative to pedaling backwards. It can also allow for regen while pedaling forwards.)

The display panel will be based on a small video LCD, so the display layout and data will be defined by software. (A cheaper alternative can be a plain text LCD, although small video LCDs are cheap nowadays, often cheaper than some text LCDs! However, text LCDs are orders of magnitude easier to interface than video LCDs.) It can be programmed to look like a panel of meters (either digital or "analog"), a pictorial diagram, a combination, or whatever else you like! What I think would be interesting would be an animated diagram with icons of the wheel, batteries, and pedals arranged in a triangle. Arrows of varying sizes would show the flow of power when in operation (pedaling, boost, regen, and pedal recharge). For additional information, a few meter displays would be used. The diagram can also include the motors to be more accurate, but that would probably clutter it up too much.

The microcontroller would have to be advanced to accommodate the sophisticated system, so it would likely be something like the Parallax Propeller as it would be well suited for the many threads needed.

I don't think I'll actually build such a bike as bikes are of very limited use in my current neighborhood, but I will be happy to help with the development if someone else wants to build one.

[abcdpeterson]

Hope this helps.

When I looked around for an electric assist bike I found one that had the ability to do regen. I don’t know where and I can’t find it again.
But…
Everything I found on it basically said (just like I found with the Prius) You don’t really want to spend energy into charging the battery.
If you have the energy to pedal – pedal. That way you get 100% of your energy going to move the bike, without the losses in the charging system.
When costing down hill your better off keeping the speed and costing farther. You will cost farther than the power you generate would take you.
One web site said the regen would eat up a lot of your energy and at best you might get 5% charge back form it.

I might not recommend the regen side but I would spend time looking at the assets side.

There are a number of electric assist bikes that will allow you pedal or not while the electric motor is in use. You can have the motor help you or let the motor do all the work. If you help you go farther.

What would be nice is an electric assist that went through the same gearing as the peddles, or had it own changeable gearing. Most electric assist bikes do not have gearing that will change on the electric assist side. With out that gearing you end up with a choice, more high end speed or low end torque.
Most people go with torque, as hills are where the help is needed most.

That is where I think you could make the most improvement. On the assets side, giving torque when needed and higher top end to get longer distance when the torque is not needed.

IF you make a system that will allow for speed you need to be mind full of just what 99HXCivic said.

Originally Posted by 99HXCivic

I think the worst thing with electric bicycles is the some state laws limit their speed to a slow 20 mph, - which is a road biker's unassisted cruising speed!

If the electric is what gets you past 20mph you need to classify it as a scooter or motor cycle, in most all states. Then you no longer ride on sidewalks or trails only roads.
You can go over 20mph if it is You doing it and not motor.

In the end the biggest problem is the battery.
This is the choice for batteries: Heavy or expensive.


Sounds like your having fun with the idea. Keep working on it. maybe you come up with something marketable.

[NiHaoMike]

If the electric is what gets you past 20mph you need to classify it as a scooter or motor cycle, in most all states. Then you no longer ride on sidewalks or trails only roads.
You can go over 20mph if it is You doing it and not motor.

It can be designed so electric boost alone cannot accelerate it to more than 20MPH under normal conditions. That'll also reduce the battery requirements.

Everything I found on it basically said (just like I found with the Prius) You don’t really want to spend energy into charging the battery.
If you have the energy to pedal – pedal. That way you get 100% of your energy going to move the bike, without the losses in the charging system.
When costing down hill your better off keeping the speed and costing farther. You will cost farther than the power you generate would take you.
One web site said the regen would eat up a lot of your energy and at best you might get 5% charge back form it.

The bike will, by default, "glide" just like a normal bike when not pedaled. The twist handle or pedaling backwards can override that on demand. In other words, if you need to stop, you can manually engage regen. The implementation in the DC/DC converter would be simple as synchronous rectified (buck/boost) converters are bidirectional. And in a situation when the load is light, you can engage regen while pedaling to get a little more exercise while recharging the batteries. In the case of a bicycle, high efficiency is sometimes not a good thing. (Especially if you're trying to be as skinny as Shannon Liu or Jennie Chen!)

What would be nice is an electric assist that went through the same gearing as the peddles, or had it own changeable gearing. Most electric assist bikes do not have gearing that will change on the electric assist side. With out that gearing you end up with a choice, more high end speed or low end torque.
Most people go with torque, as hills are where the help is needed most.

What sets my idea for a hybrid bike apart is the use of an electric CVT - effectively a scaled-down version of the Prius transmission. Electric motors perform well both in terms of torque and in terms of speed. In fact, at low speeds, the torque might have to be electronically limited to avoid skidding the wheels. The fact that you can pedal at normal speeds even while the bike is stationary means that it should be able to accelerate quite well even without boost.

[Elixer]

When it comes to a bike you want to have direct drive. I have to say that a lot bikes these days have far more gears than I ever really use. It's very very rare that when on a well designed bike I feel like I don't have the gear that I need. 30 speeds is more than enough. A well oiled bike transfers the mechanical motion from the petals to the wheels with >95% efficiency.

However looking at going electric:

You're only looking at real efficiency of maximum 90% for the generator and the motor, and if you're really lucky 90% for the AC to DC/DC to DC conversion (depending on what type of generator you use).

.9*.9*.9 = .73 = 73%

Your battery is going to sink some current too so I think you'll get no more than 70% of your energy out that you put in, and only when your output power is the same as your input power. When they're not equal you have to take in the charge/discharge losses of the battery as well: ~80% effecient. Keep in mind the numbers I've used are close to what you'll see ideally, you're more likely to see even worse numbers in many cases.

Then you have to manage the whole system electrically: The "battery charger" has to connect and disconnect the generator appropriately.

Overall there's definite reason to think about building a regen system as that's a large amount of energy simply lost to the brakes that you can save. However there's absolutely no reason to go through the electrical system to drive the wheels from the petals. You're looking at huge losses, and a complicated system to do something that can be done cheaply and efficiently with a cheap bike chain.

Motors are generators (more or less) so it shouldn't be complicated to build a system which would allow regen-braking from the existing electrical motor. This is how current hybrids practice regenerative braking.

[NiHaoMike]

DC/DC converters easily exceed 90% efficiency. And it isn't a pure series hybrid. The torque applied to the split motor goes on to the wheel (just at a lower speed). Think of a smaller version of the Prius transmission. And if you're looking for efficiency, you try to minimize battery usage. Use it to get boost under high loads and use it to buffer excess energy under low loads.

I wonder how the electric CVT compares to implementing a mechanical CVT on a bike. Toyota chose an electric CVT for their Prius while Honda chose a mechanical CVT for their Civic, and they're both similarly efficient. I don't see why it would change when scaled down. The electric CVT would have the benefit of being more or less software-defined.

And I can think of some extras that can be thrown in for fun. One of which would be to use the ambient temperature sensor (used to compensate LCD drive voltages and possibly to improve accuracy of battery meter) to change the clothes on the figure of the person on the animated power flow diagram. (Possibly something like from a bikini in hot (above ~85F) weather to a winter coat in cold (below ~40F) weather.) Also add in some appropriate warnings (heat and ice) as well as change the behaviour of the drive system, such as more pedal recharge in cooler weather and less in hot weather.

[Xringer]

Originally Posted by 99HXCivic

I think the worst thing with electric bicycles is the some state laws limit their speed to a slow 20 mph, - which is a road biker's unassisted cruising speed!

We have a 25 MPH operating speed limit on Mopeds here in Mass.
http://www.mass.gov/rmv/forms/20017.pdf

With a maximum speed capability of 30 MPH..


So, 20 MPH max for an E-bicycle sounds about right to me..


Maybe 20 MPH is a road biker's unassisted cruising speed but the remaining 85%
of us bicyclists cruise at half that speed.. And 12 MPH when we are in a hurry.

And yes, I get very uncomfortable coasting down hills at anything over 22 MPH..
I know what my stopping distance is.
And I know that a tiny shard of glass in a tire at that speed can put me into a world of hurt.

[abcdpeterson]

well you did get me looking around at bikes again.
Need new battery for mine.

found this.... it may give you idea's
The Bionx (pronounced by-on-ex) electric bike motor conversion kits

GENERATION
Bionx offers four levels of power generation. Regenerative braking activates when the rear handbrake is used. It is possible to charge the Bionx battery pack by pedaling against motor resistance. Generation mode makes it harder to pedal so its often used when going downhill. Please note that the generative mode does not replace the existing brakes, but considerably increases braking quality, especially on extended downhill runs

Too spendy for me.