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Mick F

Reversing with a hybrid Yaris

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As there's no gearbox, reversing is always done on electric drive.

I know that when the Battery is getting low, the engine kicks in to recharge it.  However, I expect that you can use the electric faster than the engine can replenish it.

Theoretically, how far can you reverse?

Mick.

 

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There's a few steep lanes round here, in fact we live on one.  Often two cars meet halfway and one has to reverse to a wider bit so they can pass.  Sometimes big vans use the lane, so it could require a long reverse up the hill.

Just under half a mile of single-track lane at 25% incline.  I wonder if I can reverse all the way up?

Mick.

 

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Posted (edited)

Hi, why don't you try it.?? You could have someone drive normally before you.and would be able to drive into the passing places. I would imagine that you'd get similar mile as going forward as the gearing is the same.

Edited by Bomber209
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On 6/2/2019 at 10:18 AM, Mick F said:

As there's no gearbox, reversing is always done on electric drive.

I know that when the battery is getting low, the engine kicks in to recharge it.  However, I expect that you can use the electric faster than the engine can replenish it.

Theoretically, how far can you reverse?

Mick.

 

You can probably drive in reverse as far as the fuel tank will allow! You really need to look at the power available. I noticed that the maximum regeneration is around 17kW and this is about 22bhp - I suggest this is the safe limit for the inverter hardware. 22bhp in reverse should be enough for any hill.

What is really interesting is "what is the maximum speed attainable in reverse"! Note that old DAF variomatics have raced, but in reverse 'gear'. Will the unwanted Toyota hybrids race this way in 20 years time ….

DAF CVT racing

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22bhp for a 25% hill?  Dunno at all about that.

I was considering trying it to see what happens.  Going forwards gently with 7 or 8 bars green with the system warm, I can get up some of the hill, but the engine starts up within 200yds or so.  No doubt the Battery is getting too hot and the engine takes over.

The way I see it, in reverse, the engine cannot take over, and the Battery alone has to get you up the hill.  Can the engine provide enough power to replace the energy consumed from the Battery?

Is 22bhp enough for a 25% hill?  What happens if you have five adults in the car?  I reckon 22bhp won't do it and the Battery will stop producing power and the car will stop with the engine racing to try and top it up enough to carry on.

I'll have to give it a go. 😀

Mick.

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I once had a Fiat Panda (750cc) with all of 30-odd BHP. Never any problem. It all depends on gearing.

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6 hours ago, bathtub tom said:

I once had a Fiat Panda (750cc) with all of 30-odd BHP. Never any problem. It all depends on gearing.

That's another issue.

What equivalent gearing does a hybrid use?

There's so much torque with an electric motor, the "bottom" gear doesn't have to be that low.  No doubt reverse is the same as forward.

Mick.

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Mick Hi, your 4 pax could get out (and push??) The gear ratio is the same going Fwd or Rev, as it's an Epicyclic system. In theory on a flat surface you could do about 25mph fwd or rev.

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Yes, you're correct of course, but I'm not sure about three people pushing a Yaris up a 25% hill! 🤣

I had a small experiment earlier today.  We have a steep drive, easily 25% maybe 30% and it's just under 100yds long gate to house.  Because of the shape of the drive as it enters the lane, it's necessary to reverse up if you come from one way, and forwards if you come from the other way ........... if you see what I mean.

Anyway, I reversed up and came up as fast as I could.  Just as I selected reverse, the reversing camera came on of course, but I switched the screen over to to show the Battery state etc. before setting off up. It was full to start, as it often is as we come home due to living in a long steep valley, but after thrashing the car in reverse up the steep drive, I ended up with only six bars showing.  The engine didn't start up as I reversed.

This means, that within 100yds in reverse up a steep hill driving quickly, it consumes two bars of the Battery. Taking this argument to extreme, 200yds it would be down to half Battery, and 400yds it would be empty.

What I could do, is to repeat the test one after the other, but select neutral and coast back down before reversing hard back up again.  Would that be a valid experiment?

Can the engine replenish the Battery enough to carry on ad infinitum?

Mick.

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On 6/4/2019 at 3:17 PM, Mick F said:

What I could do, is to repeat the test one after the other, but select neutral and coast back down before reversing hard back up again.  Would that be a valid experiment?

Can the engine replenish the battery enough to carry on ad infinitum?

Experiment complete.

Came home, all eight bars green, and came up the drive in reverse.  By the time I was at the top, only six bars green.  Neutral and coasted back to the gate.

Neutral doesn't charge the Battery, so at the gate, I selected reverse again and drove hard back up.  Four bars green, and then repeated, then two bars green.

Next time up, the engine revved high and at the top, I still had two bars green.  Repeated another four times, and each time the engine revved and it stayed at two bars green.

After the next one, I was a bit bored so didn't do any more, but it seems that two bars green was the minimum.  The car wasn't as eager on the latter runs than on the first few, but it still did well.

There you have it.  Probably no limit to how far you can reverse.

Mick.

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So, the computer recognised what was required, kicked in at 2 bars and put enough into the Battery to keep you going. Computer programmers at Toyota must of been thinking of you, Mick, when they did the design.

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Yes, thinking of little old me! 😀

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Very interesting experiment and it validates what I have always thought about Toyota/Lexus hybrids, just bung it in D or R and let the computers do the rest.

 

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Just another little fact about my experimentation.

The power meter - Charge/Eco/Power meter - doesn't show anything in reverse.  The needle sits in the middle as if switched off.

Mick.

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Mick Hi,  Probably because there's no Kinetic energy recovery (KERS) for Reverse.

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2 comments:

  1. the Hybrid system is less efficient in reverse than going forward because while reversing the MG alone has to propel the car and work against the engine while it is generating electricity due to the way the planetary gear system works, therefore it will take more electric energy to do the same distance in reverse than forwards.  It obviously makes sense for this to be most efficient while going forwards.
     
  2. the 8th bar was possibly nowhere near full when you started your first test - the very few times I've seen the 8th bar lit, it's gone out very quickly too.  The only times I've experienced a truly 'maxed out' HV Battery (i.e. 8th bar 'full') was on very long, steep hills in Scotland and Devon, and it took quite a while after the last bar lit up before the noticeable effects of the Hybrid System refusing any further regenerated power.  The chart in the link below (for an older Prius version) gives an idea of how the graph display works:

 

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We have a hill near here.  Top of Kit Hill all the way down to Lucket.  

1000ft downhill or thereabouts, for just over two miles.  I'm a cyclist, and it's a pig of a long climb back up! 😀

If I get time, I'll see what it feels like to get all eight bars (more than) full.  I could try reversing back up as it's a quiet road if you pick the right time of day.

Mick.

 

Screen Shot 2019-09-16 at 19.32.55.png

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If I've done my sums right (and I'm by no means certain!), that about 8½% average gradient.

I can't speak for the Yaris, and it depends also how many bars are lit when you start the descent, but on a Gen 1* or 2 Prius (the only cars I've experience a 'max out' on), it took between 4 and 5 miles on a 20% gradient (according to the road signs) in Scotland to max out.  To be fair, we'd have started with less than 4 bars because of the climb to get up there in the first place.

The HV batteries have got slightly lower in capacity over the generations, plus I believe the Yaris Battery is fairly small compared to larger Hybrids (again, might be wrong on that) and you may start with 5, 6 or 7 bars, in which case it may be feasible to reach true 'max' capacity.  It should be fairly obvious, you should hear the engine revving even without using B mode, and when you level out it should behave like an EV without using the EV Mode button as the software tries to make some room for any further regeneration.

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Ours behaves like an EV quite regularly.  We can get into the village half a mile way without the engine kicking in at all unless the ACC is set for warm.  Fairly flat road.  Also, in town the engine rarely fires up until the Battery gets down to two bars.

The EV button seems a pointless facility.

Yaris batteries are much smaller than Prius batteries I understand.  Hence the poorer economy overall.

Mick.

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