Brakes and regenerative braking.

Darklex · October 6, 2016

Hi All,

I have had my CT for about 3 months and drove it and done around 3K miles. I do like my car a lot and I am always thinking every time I press the brake is it the electric motor slowing the car down or is it actually the brake pads being used?. I heard on the internet that that the pad wear is not like other cars and will last longer between changes. But I do feel/sound when i do use the brakes it does seem like i use the brake pads all the time. Any thoughts?

Thanks..

Britprius · October 6, 2016

1 hour ago, Darklex said:

Hi All,

I have had my CT for about 3 months and drove it and done around 3K miles. I do like my car a lot and I am always thinking every time I press the brake is it the electric motor slowing the car down or is it actually the brake pads being used?. I heard on the internet that that the pad wear is not like other cars and will last longer between changes. But I do feel/sound when i do use the brakes it does seem like i use the brake pads all the time. Any thoughts?

Thanks..

The CT uses the same system as the Prius. The braking above 7 mph under normal circumstances is all regen. In an emergency situation or if an of the wheels slip on the road surface the brakes immediately return to the friction brakes.

The small downside to this is that the rear brakes often go rusty due to lack of use. To overcome this once or twice a month going down a hill select neutral and gently brake. Doing this forces the use of the friction brakes and keeps the rust at bay.

On the Prius it is not unusual for the brake pads to last 200,000 miles with good driving practice.

John.

floggit · October 7, 2016

Ive read this on the net, pads easily last over 100,000k and can easily last the lifetime of the vehicle. Nice benefit!

stormchaser · October 7, 2016

This is good to know. Thanks [emoji4]

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rayaans · October 10, 2016

Instead of doing the coasting in neutral down a hill I'd suggest some emergency braking instead when no one is behind you, its more controllable IMO. In neutral the car just seems to run away from you.

Granted I dont have a CT but my RX has done 42k miles and its got half its brakes left. Pretty good IMO considering the thing weighs 2 tonnes

RichyRich · October 10, 2016

How long do they last on the IS300H I wonder?

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-Rich- · October 11, 2016

Do the discs last just as long as the pads?

The first CT we looked at had 63k miles and the front discs had a large lip on them but I couldn't really see the pads so I wasn't sure how much meat they had left. I guess the wheel has to come off to see them properly. The car we bought had 59k miles but the lip on the disc was no where near as pronounced as the other car, so I can only assume they were heavy on the brakes.

stormchaser · October 11, 2016

I'm just about to hit 70K and mine are originals and about 50% worn pads and a tiny lip on the discs.

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rayaans · October 11, 2016

21 hours ago, RichyRich said:

How long do they last on the IS300H I wonder?

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Should be about 100k. Of course it does depend on driving. If you do steady motorway driving its likely you won't use them much as the car pretty much slows itself down on re-gen most of the time unless you're braking enthusiastically

RichyRich · October 11, 2016

So when tapping on the break at say 50mph to slow to say 40 in medium traffic it's unlikely to be using the pads at all? I do have a fair amount of break dust on my wheels so must be using some. 100k sounds more than enough though 😊

adnewton · January 20, 2017

Regen braking is when the motor/Generator is not in "Demand" mode. It will then either charge Battery or when braking reverse its direction of rotation to assist with braking - It is engine braking. The B position is just this but manually selected.

brake pads will last longer, however, if you drive like a F1 driver, they won't last long. Foundation brakes ( Pads & discs ) will be applied when the motor can't apply braking to level required ( foot pressure on brake ). So, to save brakes, drive moderately with soft braking action. Discs though will wear & corrode after 4/5 years on our salted roads.

Britprius · January 21, 2017

On 1/20/2017 at 10:20 AM, adnewton said:

Regen braking is when the motor/Generator is not in "Demand" mode. It will then either charge battery or when braking reverse its direction of rotation to assist with braking - It is engine braking. The B position is just this but manually selected.

Brake pads will last longer, however, if you drive like a F1 driver, they won't last long. Foundation brakes ( Pads & discs ) will be applied when the motor can't apply braking to level required ( foot pressure on brake ). So, to save brakes, drive moderately with soft braking action. Discs though will wear & corrode after 4/5 years on our salted roads.

There are two motor generators in the transmission, and it is MG2 the larger of the two units that is responsible for regen braking. This motor/generator cannot reverse when the car is going forwards as it is coupled to the wheels via the differential changing direction can only happen in reverse. If the wheels are going forwards so is MG2. If the wheels are stationary so is MG2. If the wheels are going backwards so is MG2 as it is driving the wheels. The engine is going the wrong way for reverse "there is no reverse gear".

MG1 can assist with braking, but only by forcing the engine to spin as in "B" mode. As such MG1 is limited in the amount of regen because of the physical limits of safe engine revs, and it's own current limit. MG1 can and does change direction when the car is accelerating as it is then being used as a generator it's output being supplied either to MG2 or the HV Battery. In this mode it controls the engine revs, and hence the "apparent" gear ratio

John.

adnewton · January 21, 2017

2 hours ago, Britprius said:

There are two motor generators in the transmission, and it is MG2 the larger of the two units that is responsible for regen braking. This motor/generator cannot reverse when the car is going forwards as it is coupled to the wheels via the differential changing direction can only happen in reverse. If the wheels are going forwards so is MG2. If the wheels are stationary so is MG2. If the wheels are going backwards so is MG2 as it is driving the wheels. The engine is going the wrong way for reverse "there is no reverse gear".

MG1 can assist with braking, but only by forcing the engine to spin as in "B" mode. As such MG1 is limited in the amount of regen because of the physical limits of safe engine revs, and it's own current limit. MG1 can and does change direction when the car is accelerating as it is then being used as a generator it's output being supplied either to MG2 or the HV battery. In this mode it controls the engine revs, and hence the "apparent" gear ratio

John.

It was just a high level overview.......

Zotto · January 22, 2017

Remember that regenerative braking works alone without use of pads if you gently slow down keeping the indicator in !charge zone without reaching top low zone; from that point, pads work and you have more braking effect but loose some energy. So, to have best mpg the most important driving suggestion is to achieve max regeneration making soft braking (and doing so preserves brake pads).

Jedimaster65 · January 25, 2017

My front pads and disks all just been replaced at 70k miles and were totally knackered, though probably due to car being unused for 7 months and a lot of rust on them, but also badly lipped.

It had horrible, very poor brakes with no real bite, no servo assistance and a very solid pedal feel (little pedal movement).

Brake fluid resevoir has also been replaced as the built-in braking pressure sensor was also faulty.

After weeks of problems, it's now fixed.

This explanation furnished by Lexus stoke.

Britprius · January 25, 2017

The CT being front wheel drive can regenerate to a much greater degree than rear wheel drive such as the GS450H and the GS300H. This is because when braking wieght transfers to the front of the car meaning the front wheels have more grip and regen can be harder. With the rear wheel drive cars to much regen could result in the rear wheels locking up in a bend causing the car severe over steer (swapping ends).

I have not seen a 4 wheel drive GS in the UK although they are available I believe in the US. This would allow much more regen capability.

John

Britprius · January 25, 2017

22 minutes ago, Jedimaster65 said:

My front pads and disks all just been replaced at 70k miles and were totally knackered, though probably due to car being unused for 7 months and a lot of rust on them, but also badly lipped.

It had horrible, very poor brakes with no real bite, no servo assistance and a very solid pedal feel (little pedal movement).

Brake fluid resevoir has also been replaced as the built-in braking pressure sensor was also faulty.

After weeks of problems, it's now fixed.

This explanation furnished by Lexus stoke.

The CT does not have a servo. The reason being the engine does not run all the time to produce a vacuum. It has an electric hydraulic pump that pumps brake fluid into a nitrogen pressure chamber. This pressurised fluid is released under control by the brake pedal. You can often hear this pump start after opening the drivers door. This is so the brakes are ready for use as soon as the driver gets in the car.

John

Britprius · January 25, 2017

On 10/10/2016 at 1:57 PM, rayaans said:

Instead of doing the coasting in neutral down a hill I'd suggest some emergency braking instead when no one is behind you, its more controllable IMO. In neutral the car just seems to run away from you.

Granted I dont have a CT but my RX has done 42k miles and its got half its brakes left. Pretty good IMO considering the thing weighs 2 tonnes

The snag with emergency braking is the wheels go round once and you have stopped. With putting the car in nuetral you can brake gently over some distance giving the chance for the rust to be worn away.

John.

Zotto · January 26, 2017

12 hours ago, Britprius said:

The CT being front wheel drive can regenerate to a much greater degree than rear wheel drive such as the GS450H and the GS300H. This is because when braking wieght transfers to the front of the car meaning the front wheels have more grip and regen can be harder. With the rear wheel drive cars to much regen could result in the rear wheels locking up in a bend causing the car severe over steer (swapping ends).

I have not seen a 4 wheel drive GS in the UK although they are available I believe in the US. This would allow much more regen capability.

John

Sorry, it' s a physics nonsense: energy of braking is recovered whatever wheel brakes, no difference till wheels don't slip, and in that evenience they are not in regeneration, using traditional pads.

Britprius · January 26, 2017

41 minutes ago, Zotto said:

Sorry, it' s a physics nonsense: energy of braking is recovered whatever wheel brakes, no difference till wheels don't slip, and in that evenience they are not in regeneration, using traditional pads.

As long as the tyre do not slip on the road surface, and the current limit of the generator or batteries is not exceeded all the braking on the CT200H is done by regeneration. The hydraulic brakes are not activated until these limits are reached or the car travels at less than 7 mph where there is insufficient regen to be of use.

There were many complaints from customers "especially on the gen3 Prius on which the CT is based but also on the gen2" of momentary loss of brakes on the transition from regen to friction braking. Toyota altered the software to reduce this effect. The change over to friction brakes is very evident on the CT and Prius as you slow through 7mph while braking.

It is a physical fact that some of the weight in any vehicle transfers to the front during braking.

With the GS being rear wheel drive the front friction brakes are used when slowing down using the brakes, and regen is used on the rears to recover as much energy as possible.

This being the CT part of the forum is the area under discussion, and the GS as stated above uses a slightly different arrangement, but still uses regen to slow the car, and recover some kinetic energy.

John.