Honda Jazz Hybrid - How should it work

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Tue 9 Oct 2012 10:57
Honda Jazz Hybrid - How should it work - tennand

I rarely see the battery driving the engine by itself, in particular if I brake the car gently in the garage the engine continues to use petrol. If I brake the car with sufficient force then the "Auto Stop" kicks in and the engine stops until I take my foot off the brake, then it restarts but again using petrol ! The battery is always at least 3/4 charged so I would have thought under these circumstances if no other I should not be using petrol?

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Tue 9 Oct 2012 16:07
Honda Jazz Hybrid - How should it work - Peter D

Have you had the battery fully charged. Regards Peter

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Tue 9 Oct 2012 18:28
Honda Jazz Hybrid - How should it work - bathtub tom

How old is it, how long have you had it and is this a significant change from the way it used to behave?

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Tue 9 Oct 2012 18:50
Honda Jazz Hybrid - How should it work - puckdrop

I thought the Honda IMA hybrid system was series - in other words, the motor HELPS the engine, but doesn't provide motion on its own.

My Prius on the other hand, is a a parallel hybrid, so you can have either/or/both.

Both have thier +/- points, but I don't think you'll get a pure electric drive from a stop in the IMA system.

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Tue 9 Oct 2012 20:54
Honda Jazz Hybrid - How should it work - unthrottled

battery driving the engine by itself, in particular if I brake the car gently in the garage the engine continues to use petrol.

I don't think you understand how a hybrid works. The electric motor does NOT drive the engine because this set-up would be less efficient than a conventional engine.

The motor is used in lieu of the engine or to augment the engine under hard acceleration. The engine usually won't cut out when it is very cold. You can't really test the system in the garage. Take it for a run-the engine should happily switch on and off under the right conditions.

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Mon 15 Oct 2012 21:13
Honda Jazz Hybrid - How should it work - tennand

Thanks for all the info folks.

The car is 7 months old, ex demo and I have owned it for a month.

So the majority view is that I should not expect the electric motor to kick in under these circumstances.

The motor does work fine when the petrol engine is under pressure & the combined power from the two sources exceeds that of my 2007 1.4 Jazz.

Thanks again.

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Tue 16 Oct 2012 08:59
Honda Jazz Hybrid - How should it work - TeeCee

The motor is used in lieu of the engine or to augment the engine under hard acceleration.

No, "puckdrop" has it right, so only the latter part of that is true. The Honda system has the electric motor in line with the engine / transmission as a series hybrid and it cannot run without the engine also running. Thus you can have engine alone or engine and electric assistance, but not electric drive alone.

The clue is in the name, IMA - Intelligent Motor Assist.

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Tue 16 Oct 2012 10:38
Honda Jazz Hybrid - How should it work - madf

Toyota's hybrid works only on electric motor power.. Silently. The engine kicks in when the power demand is higher or the battery needs to be charged.

As TeeCee says, teh Honda engine works all the time.

Hence the far better fuel consumption for Toyota hybrids vs Honda ones.

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Tue 16 Oct 2012 13:06
Honda Jazz Hybrid - How should it work - unthrottled

The clue is in the name, IMA - Intelligent Motor Assist.

Seriously? There's nothing intelligent about that at all! It's a stupid idea. It's when the engine isn't doing very much that you want to substitute it for an electric motor. Otherwise it'll be less efficient than a conventional engine.

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Thu 18 Oct 2012 11:19
Honda Jazz Hybrid - How should it work - puckdrop

It all depends. I believe the IMA has stop/start shutdown technology, so that helps.

Also, remember that engine speed and fuel used are not always "in sync" - so the motor could be providing torque and power in a queue, supplimenting what the engine can do at "idle" in terms of RPM and fuel usage.

Different technology, but as an example, during warmup, my Prius will run at about 1100 rpm ALL the time until you get above a certain speed / acceleration, or warmup ends. During this time, the power available from the engine is either used for motion while being supplimented by the battery/motor (if needed) , or charging, . It's quite easy to run the battery down in warmup mode if you don't exceed 30mph or so (after which, the engine bursts into normal mode ).

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Thu 18 Oct 2012 12:09
Honda Jazz Hybrid - How should it work - unthrottled

Also, remember that engine speed and fuel used are not always "in sync" - so the motor could be providing torque and power in a queue, supplimenting what the engine can do at "idle" in terms of RPM and fuel usage.

I understand the idea of the motor bolstering the engine output (especially at low revs) but that just saves a downshift (not even that in an automatic). But electric motors are less efficient than the prime mover that drove the generator (in this case. the car's engine). So to realise an overall efficiency gain you have to switch off the engine in areas of operation where it is inefficient.

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Tue 6 Nov 2012 11:55
Honda Jazz Hybrid - How should it work - tennand

The Jazz effectivly freewheels down hills without using petrol but charging the battery thus when the motor is assisting the petrol engine it is not always using power derived inefficiently. I get the impression that on occasions like a downhill run the valves are locked open and the petrol is switched off. The transition back to normal running goes unnoticed without any jerking.

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Tue 6 Nov 2012 12:27
Honda Jazz Hybrid - How should it work - unthrottled

The Jazz effectivly freewheels down hills without using petrol but charging the battery thus when the motor is assisting the petrol engine it is not always using power derived inefficiently

That's a perpetual motion argument. The charging of the battery is not 'free'; it comes from the expense of momentum which then has to be regained. Of course, if you wanted to slow down anyway, then you're quids in, but if you didn't, then you're worse off.

Valves are invariably closed when cylinders are 'decativated'. Otherwise, the engine still functions as an air pump with the associated losses-and you cool the catalytic converter so it miay not immediately function when the engine commences firing again.

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Tue 6 Nov 2012 13:03
Honda Jazz Hybrid - How should it work - Oli rag

The Jazz effectivly freewheels down hills without using petrol but charging the battery thus when the motor is assisting the petrol engine it is not always using power derived inefficiently

That's a perpetual motion argument. The charging of the battery is not 'free'; it comes from the expense of momentum which then has to be regained. Of course, if you wanted to slow down anyway, then you're quids in, but if you didn't, then you're worse off.

Valves are invariably closed when cylinders are 'decativated'. Otherwise, the engine still functions as an air pump with the associated losses-and you cool the catalytic converter so it miay not immediately function when the engine commences firing again.

Would they not have the exhaust valves open to stop pumping losses, or am I missing something?

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Tue 6 Nov 2012 13:15
Honda Jazz Hybrid - How should it work - unthrottled

Would they not have the exhaust valves open to stop pumping losses, or am I missing something?

No-that just moves the pumping loss from inlet side to exhaust!

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Tue 6 Nov 2012 20:53
Honda Jazz Hybrid - How should it work - Oli rag

Unthrottled, my small brain still doesn't understand how a piston moving against closed valves can be more efficient than a piston moving in a cylinder with an open end, I just can't work it out.

Keep it simple please :)

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Tue 6 Nov 2012 21:37
Honda Jazz Hybrid - How should it work - unthrottled

It's not obvious, don't worry!

The problem with allowing the exhaust valves to keep opening and closing (they can't stay open all the time because they'd hit the pistons) is easiest to visualise with a syringe-which is basically a piston in a cylinder just like an engine.

If you take a syringe with the plunger fully pressed in and put your finger over the nozzle, and try to pull the plunger out, it takes a surprising amount of force to create the vacuum in the syringe.

If you let go of the plunger with your finger over the nozzle, atmospheric pressure pushes the plunger back to where it started. Ie we recover the work that we put in. This is a reversible process ie there is no net energy penalty.

But, if you take your finger off the nozzle before letting go of the plunger, the vacuum is destroyed and the plunger stays out. You can not recover the work that you expended pulling the plunger out. This is an irreversible process, ie there is an energy penalty. This is what a pumping loss is.

The finger over the nozzle is an exact anology of the exhaust valve. Exhaust valves open when the piston is near bottom dead centre and close near top dead centre. If the exhaust valve opens when there is a vacuum in the cylinder, there is a pumping loss.

To avoid pumping losses, the valves are kept closed so that there is no movement of gas in and out of the cylinder.

Now maybe you can reciprocate! I don't understand how mild hynrids work. Can you explain?

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Wed 7 Nov 2012 08:27
Honda Jazz Hybrid - How should it work - Oli rag

Many thanks for the explanation unthrottled, even a muppet like me can understand pumping losses now!

Sorry, I don't understand how the honda ima system works either.

Thanks again.

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Tue 6 Nov 2012 13:16
Honda Jazz Hybrid - How should it work - madf

The Honda Jazz hybrid effectively uses a standard Jazz engine without clever bells and whistles... The Yaris one uses a totally different cycle (Atkinson) designed to be efficient as possible at certain revs..

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