RAV4 Hybrid - Driving Auto in Semi-Auto

[Scottydog007]

I have driven auto gearboxes many times but the Rav4 was my first auto I owned. One down side I found for the 2018 model was that when stationary when the car was in drive, the car would creep forward unless the brakes were applied. Now this also meant that coming up to a junction and wanting to slow down that car would want to drive on. I am so used to using a manual gear box torque to slow down at junctions. So the habit slowing down meant applying the breaks with the Rav4 auto.
Now a tip that was given to me when I was on a speed awareness course (the only good thing that came out of the £95 course), was to go to semi-auto, so use the step-down and this now gives the torque to slow the car down and reduce using the brake or even stop using the brake. When through the junction I would flip back to full auto. All this adds for a nice smooth drive.

[roadster-rav]

The latest car does a reasonable job of slowing down and transferring energy to the traction Battery in normal mode. But it does depend on what you're used to. My previous car with a 9 speed ZF automatic box would sail on regardless on a closed throttle so I have a slightly different expectation. I also like the fact that if you brake gently the disks and pads are not brought into play and you just get more regenerative braking. As with any automatic I always use left foot braking so I don't find it difficult to moderate speed as needed. Regarding the issue of creeping forward I find that the HOLD button is usually effective in automatically applying the parking brake when the vehicle comes to a complete halt with brakes applied. I haven't had mine long enough to give the manual shift positions a real work out. I'll have to wait until I find a challenging twisty hill for that.

[IanML]

I don't have a hybrid, but I have auto and manual transmission cars.  For that reason, I always use the right foot on the brake - that way I don't foul-up when swapping over.  I think it's a good discipline.  I do agree that the reduced engine braking is a nuisance - using the lower gears helps, but regen braking with a hybrid sounds good, so I'm tempted when the prices come down with age.

I don't have a problem with the auto creeping when stopped - I just keep the brake pedal pressed.  However, driving instructors and examiners seem to think its ok to do this when waiting for a long period, i.e. at the lights.  I disagree with that, and use N and the handbrake.  If someone shunts you at the back, and your foot slips off the pedal.....

[_dct_]

1 hour ago, Scottydog007 said:

was to go to semi-auto, so use the step-down and this now gives the torque to slow the car down and reduce using the brake or even stop using the brake.

I believe this is the same as lightly applying the brake pedal to trigger regenerative braking. Under the right conditions the engine completely cuts off and inertia is turned into electricity slowing the car down. One thing I'm not quite sure about is whether the brake lights would come on at this point, otherwise it behaves rather similarly to engine braking on non-hybrid cars.

[Scottydog007]

27 minutes ago, IanML said:

..................I don't have a problem with the auto creeping when stopped - I just keep the brake pedal pressed.  However, driving instructors and examiners seem to think its ok to do this when waiting for a long period, i.e. at the lights.  I disagree with that, and use N and the handbrake.  If someone shunts you at the back, and your foot slips off the pedal.....

I will say I'm a mechanical design engineer for my sins, I know keeping a car in gear and holding the clutch adds to wear & tear so I always put handbrake on.

Incidentally you are correct the 2019 Rav4 seems better at slowing down just using auto mode than my previous 2018 Rav4.

[roadster-rav]

22 hours ago, Scottydog007 said:

I will say I'm a mechanical design engineer for my sins, I know keeping a car in gear and holding the clutch adds to wear & tear so I always put handbrake on.

Incidentally you are correct the 2019 Rav4 seems better at slowing down just using auto mode than my previous 2018 Rav4.

This is where the hybrid is a bit different because once stopped the transmission is inherently not engaged and in fact usually the engine won't be running. If the parking brake is applied, either automatically if hold is engaged or manually otherwise, the car will not creep although if you were to accidentally press the throttle pedal then it would begin to move after the parking brake automatically releases. For longer stops moving the selector to park is probably better. The real puzzle is why there is a neutral position on the selector. The manual says:-

Quote

If the shift lever is in N, the hybrid battery  (traction  battery) will not be charging,
even when the engine is running. Therefore, if the vehicle is left with the shift lever in N for a long period of time,
the hybrid battery (traction battery) will discharge, and this may result in the vehicle not being able to start.

So it seems inadvisable to use the neutral position in any normal driving and its only there for workshop or recovery situations. I don't know if you can be sure the engine will never start if in neutral though or even how you force the engine to run if required in that position.

[IanML]

It seems that neutral isolates the engine from the motor-generator which charges the traction Battery.  If the driver has ventilation and aircon running, I suppose that would run the Battery down.  That does not explain why the engine might be unable to start.  One assumes there is a separate starting Battery, so one can only assume that the control electronics are powered by the traction battery - if so, it seems like a design error.

[PeteB]

On 9/11/2019 at 9:56 AM, IanML said:

...I don't have a problem with the auto creeping when stopped - I just keep the brake pedal pressed...

I don't have a problem either, but love the "Hold" feature of the current RAV4 that keeps the service brakes (and lights) on when the foot is removed and releases it seamlessly when the accelerator is pressed.  If the wait becomes protracted I select P which also applies the parkign brake, to get the brakes lights out of the following driver's face.

To keep my membership of RoSPA's driving section I have to take a demanding test every three years, and left foot on the brake would almost certainly be a fail.

[PeteB]

On 9/11/2019 at 9:42 AM, roadster-rav said:

...I also like the fact that if you brake gently the disks and pads are not brought into play and you just get more regenerative braking...

Plus on the AWD, you get extra regen from the rear Motor/Generator.  I can't remember enough about my 2WD test drive to say whether it actually gives slightly more engine braking, I'd need to do a back to back test for that.

[PeteB]

1 hour ago, IanML said:

It seems that neutral isolates the engine from the motor-generator which charges the traction battery.  If the driver has ventilation and aircon running, I suppose that would run the battery down.  That does not explain why the engine might be unable to start.  One assumes there is a separate starting battery, so one can only assume that the control electronics are powered by the traction battery - if so, it seems like a design error.

The engine is started from the Hight Voltage (Traction) Battery only.  If it becomes too deleted, a special charger is needed.  In the noughties, there was only one charge in all of Europe (might be more now,. but I wouldn't bank on it), and it could take over a month for a dealer to get hold of it depending on the queue at the time.  At least one HV Battery died irretrievably by the time the charger was available.  The 12V Battery runs some pumps for the brakes (the noise you hear when unlocking the car) accessories and the computers.  When you press Start, it also operates a couple of solenoids that connect the HV battery to the Hybrid system and enable the car top start.

This is one reason the Hybrids have relativity low capacity (and lighter) 12V batteries, as the process described above is less demanding than operating a starter motor, but does mean it's easier to flatten the 12V if you're not careful.

[IanML]

Thanks for the details, PeteB.  My impression is that the design is too compromised in the interest of weight-saving to appeal to me.  I do not like starting from the traction Battery.  Perhaps a PHEV would improve matters - assuming the charging arrangements would be adequate to rescue a depleted traction Battery.

[PeteB]

You've got to be pretty determined to discharge an HV Battery to that extent. 

The only 2 ways I've heard of, is leaving it far too long in "N" or putting diesel fuel in and repeatedly trying to start SO many times it flattens it.  I've heard of this once on a Gen 1 Prius, and once on a Gen 2 on a fleet I later managed.

I'm told Gen 3 HSD (2009 onwards) warn if N is used too long and one or two people have suggested the car then enters a charge mode, but I've not experienced this so don't know how true it is.

I certainly have no worries about depleting the HV Battery (on a Toyota at least) because I've seen so many ways every part of the Hybrid System protects every other part in the 17 years and 320,000 miles I've been driving them.

[PeteB]

4 hours ago, IanML said:

...If the driver has ventilation and aircon running, I suppose that would run the battery down...

Come to think of it, if it's dusk or darker, the auto headlights that I hate so much will come on too.

If you're in READY mode and N, it will put even more demand on the HV Battery.  If in IGNITION ON mode (not READY) it will help flatten the 12V battery more quickly. 

[IanML]

Hmm, the more I hear, the more I like the idea of hydrogen fuel cell propulsion, but it doesn't seem like that is going to happen.

[PeteB]

I wouldn't like to put money on whether EVs or Hydrogen Fuel Cells (or something else) will win the day eventually, but a significant number of "experts" are forecasting Fuel Cells will become prevalent. 

[IanML]

Sounds good.  My personal wish is for a fuel cell PHEV, so regen braking and home charging can supplement the hydrogen-derived power.  Best of all worlds.  If I tell enough people ……..😉