Author Topic: I-MMD v eCVT  (Read 3678 times)

Paulwhitt20

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I-MMD v eCVT
« on: December 13, 2019, 05:08:09 PM »
I am familiar with the Toyota/Lexus eCVT system. What are the differences with the Honda I-MMD system?

Particularly when in engine drive mode where the engine is connected directly to the wheels by the clutch.  Is it like being in a fixed gear say fourth in a manual. So road speed follows engine speed. Is engine drive mode only used for cruising,  what happens when accelerating or slowing down. Also it seems to suggest that in hybrid mode the engine is used to generate electricity to make the motor turn the wheels and so the engine is not connected directly to the wheels (clutch disengaged) is this correct?

Is there a link to how this works for those interested in these things.
Thanks
Paul


Thanks
Paul

Jocko

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Re: I-MMD v eCVT
« Reply #1 on: December 13, 2019, 05:21:02 PM »

John Ratsey

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Re: I-MMD v eCVT
« Reply #2 on: December 13, 2019, 06:21:41 PM »
My understanding is that the engine drive is a fixed gear (to minimise the transmission losses, as well as saving a little cost). From that link:

"The i-MMD (intelligent Multi Mode Drive) system determines how to use fuel and electrical energy in the most efficient way, which means there’s no requirement for the driver to adjust between the three driving modes; Electric Drive, Hybrid Drive and Engine Drive.

How Hybrid works in Electric Drive

In Electric Drive, the propulsion motor draws its power solely from the batteries, delivering super-quiet and low-emissions driving.

How Hybrid Drive works

In Hybrid Drive, the petrol engine supplies power to the electric generator motor, which in turn delivers power to the electric propulsion motor, so that any excess power from the petrol engine is diverted back through the generator motor to recharge the batteries.

How Hybrid works in Engine Drive
In Engine Drive, the wheels driven by the petrol engine, with an ‘on-demand’ peak-power ‘boost’ available from the electric motor when you need to make a quick overtaking manoeuvre."

It will be interesting to see what driving conditions trigger the engine drive mode as the engine will be Atkinson cycle and therefore relatively low torque at lower speeds (but the motor is available at any time to provide a torque boost). Perhaps cruising at 35 mph with the engine at a bit over 1000 rpm? This would mean the engine running at around 2000 rpm at 60 mph which is similar to the current CVT gearing.
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jazzaro

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Re: I-MMD v eCVT
« Reply #3 on: December 31, 2019, 09:57:45 AM »
It will be interesting to see what driving conditions trigger the engine drive mode as the engine will be Atkinson cycle and therefore relatively low torque at lower speeds (but the motor is available at any time to provide a torque boost). Perhaps cruising at 35 mph with the engine at a bit over 1000 rpm? This would mean the engine running at around 2000 rpm at 60 mph which is similar to the current CVT gearing.
To be technically precise, we have to call I-MMD the Honda system and HSD the Toyota system, and they both are E-CVT.
There will be many parameters for triggering; vehicle speed,  rpm, state of charge, gas pedal pressure, air conditioning request (cooling or heating), slope, cooling temperatures (petrol engine, battery, inverter and electric motorgenerators), and maybe the ECU could have an adaptive software, so triggering points could change for each driver.
As for Toyotas, the aim for this kind of hybrids is the highest efficiency, this means keeping the petrol engine in the best working conditions. We know that traditional engines, coupled with standard transmissions (manual, cvt, converter) are set to have a medium efficiency in all working conditions, from idle to max revs, for each gas pressure, this to ensure a good driveability and low emissions both for low speed and for high torque requests; engineers work to rise the medium efficiency, because they cannot sell an engine with a 6 gear transmission that works very well at 2000rpm with 1/5 of gas and rattles at 2200 rpm with a 2/3 of gas pressure. But they can sell an engine that works very well in some conditions and very bad in others with a system that keeps the engine only in the best and avoids it running badly, for instance avoiding to run with the throttle valve at less than 50% opening: under that value, the engine is switched off, because of pumping losses. For instance, avoiding frequent rpm and torque variations, so the system will keep the engine as stable as possible, and will regulate the power request to wheels   using the electric side: if the petrol engine gives 30hp but the driver needs 40, the other 10 will arrive from the battery, and if the driver wants 25hp five seconds after, the surplus 5hp will be sent to the battery.
At cruising speed the I-MMD prefers to close the clutch because the whole system efficiency (petrol engine plus transmission) is higher; the petrol engine runs in medium rpm, throttle valve well opened (surely the i-vtec will set an high livc, late intake valve closing, and this will regulate the power limiting pump losses), and in this conditions it's better to feed the wheels using a direct shaft than a double energy conversion (mechanical to electric, regulation, electric to mechanical), leaving this at lower speeds and when power request changes frequently.
Toyota use another system with the petrol engine always connected to wheels using a sort of differential called PSD, power split device; this pattern was patented in 1972 in the USA, power from petrol engine is sent to this asymmetrical differential, about 70% goes to wheels, 30% goes to another electric motor-generator used to regulate the whole system, because this electric machine can be used as generator or a motor to raise or reduce ICE rpms.
http://eahart.com/prius/psd/
Toyota used this pattern to have smaller and lighter electric motors, best for system efficiency but worst for power response, I-mmd is definetly more powerful and fast responsive.
https://www.caranddriver.com/reviews/comparison-test/a28316198/2019-honda-insight-vs-2020-toyota-corolla-hybrid/

John Ratsey

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Re: I-MMD v eCVT
« Reply #4 on: January 01, 2020, 05:13:37 PM »
Thanks for this and, in particular, the link to the Insight vs hybrid Corolla comparative review.

I drove a rental (non-hybrid) Corolla when visiting New Zealand in 2019 and was surprised by the small size of the boot (it did have a spare wheel under the floor) and half our baggage had to travel on the back seat. Aside from this important detail of lack of baggage capacity the vehicle was very pleasant to drive.

Anyway, the significant observation from the review was that the real life mpg fell well short of the manufacturer's claims. It's something that Honda need to address in the MK. 4 Jazz if they want it to be a success. In contrast, the hybrid CR-V has a 1kWh battery and Honest John found it capable of exceeding the WLTP mpg https://www.honestjohn.co.uk/road-tests/honda/honda-cr-v-hybrid-2019-road-test/ . The easy way to improve the mpg is to add more battery - an extra 1kWh would only add about 10kg weight but a lot may depend on software optimisation and the driver treating the vehicle in a sympathetic manner.
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Downsizer

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Re: I-MMD v eCVT
« Reply #5 on: January 02, 2020, 03:10:35 PM »
Anyway, the significant observation from the review was that the real life mpg fell well short of the manufacturer's claims. It's something that Honda need to address in the MK. 4 Jazz if they want it to be a success. In contrast, the hybrid CR-V has a 1kWh battery and Honest John found it capable of exceeding the WLTP mpg https://www.honestjohn.co.uk/road-tests/honda/honda-cr-v-hybrid-2019-road-test/ . The easy way to improve the mpg is to add more battery - an extra 1kWh would only add about 10kg weight but a lot may depend on software optimisation and the driver treating the vehicle in a sympathetic manner.
I'm puzzled by the consumption figures quoted by Honest John.  The CR-V brochure shows WLTP combined consumption figures for the I-MMD hybrid in the range 38.7 - 40.9 mpg for the various models (2WD, AWD, S,SE, SR and EX) whereas he is quoting figures of over 50 mpg.
https://carfueldata.vehicle-certification-agency.gov.uk/search-new-or-used-cars.aspx
Also, I don't understand how a larger battery would increase the fuel efficiency; all the energy comes from the fuel, so the battery is in effect serving as an energy buffer between the generator (engine) and the electric motor.
« Last Edit: January 02, 2020, 03:39:53 PM by Downsizer »

Jocko

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Re: I-MMD v eCVT
« Reply #6 on: January 02, 2020, 05:07:58 PM »
Honest John's figures come from ordinary punters so the figures are only as good as their data. If they go by the fibometer then Honest John figures will be vastly inflated.

John Ratsey

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Re: I-MMD v eCVT
« Reply #7 on: January 02, 2020, 07:06:00 PM »
Also, I don't understand how a larger battery would increase the fuel efficiency; all the energy comes from the fuel, so the battery is in effect serving as an energy buffer between the generator (engine) and the electric motor.
A larger battery would help the vehicle better handle sustained conditions needing some charge or discharge and reduce the occurrence of battery full or battery empty. One of my frustrations with the hybrid Mk 2 Jazz I drove for several years was that there would be some boost from the battery for hill climbing but sometimes this boost would stop before reaching the top. The loss of power was noticeable. Spreading the workload over more cells should also improve longevity.

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culzean

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Re: I-MMD v eCVT
« Reply #8 on: January 02, 2020, 08:54:15 PM »
Also, I don't understand how a larger battery would increase the fuel efficiency; all the energy comes from the fuel, so the battery is in effect serving as an energy buffer between the generator (engine) and the electric motor.
A larger battery would help the vehicle better handle sustained conditions needing some charge or discharge and reduce the occurrence of battery full or battery empty. One of my frustrations with the hybrid Mk 2 Jazz I drove for several years was that there would be some boost from the battery for hill climbing but sometimes this boost would stop before reaching the top. The loss of power was noticeable. Spreading the workload over more cells should also improve longevity.



The battery has most affect on economy during start / stop driving where ICE is not too efficient, so the bigger the battery the more it can help the ICE in traffic.
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

ColinS

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Re: I-MMD v eCVT
« Reply #9 on: January 02, 2020, 10:24:54 PM »
Downsizer point, I believe, was based around Newton's law of conservation of energy.  So better economy can only be achieved by better efficiency of the overall system.

Downsizer

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Re: I-MMD v eCVT
« Reply #10 on: January 03, 2020, 10:55:55 AM »
Downsizer point, I believe, was based around Newton's law of conservation of energy.  So better economy can only be achieved by better efficiency of the overall system.
Thanks, yes, though I can see how a larger battery buffer could be helpful on occasions, for example by being able to store more energy from regenerative braking, or delaying the point at which the engine has to cut in to deliver the required power.  As with all engineering design, a balance has to be struck somewhere between cost and efficiency.

Paulwhitt20

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Re: I-MMD v eCVT
« Reply #11 on: January 03, 2020, 12:42:20 PM »
You also have to factor in the weight of the battery.

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