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Auto Transmission : Engine Braking Vs Brakes


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#11
bigal26

Posted 01 June 2010 - 08:44 AM

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QUOTE (TheGunner @ May 30 2010, 09:59 AM) <{POST_SNAPBACK}>
Well... I do use engine braking to slow down for corners as well. As long as you downshift to the right gear, you'll be fine.

Bro
You mentioned earlier that heat generated when braking will boil the brake fluid. How does brake fluid work anyway to assist braking?

#12
rallychamp

Posted 01 June 2010 - 01:28 PM

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QUOTE (bigal26 @ Jun 1 2010, 08:44 AM) <{POST_SNAPBACK}>
Bro
You mentioned earlier that heat generated when braking will boil the brake fluid. How does brake fluid work anyway to assist braking?



u normally would see brake cable on bicycle brake...when u pull the lever so does the cable will pull the brakepad....

while in brake fluid (hyraulic system) where u step on the brake pedal so the fluid move towards brake caliper and push the piston so that the caliper will "clamp"/grip the disc and braking happens...


but since when fluid boils it turns into gas/steam so does the your brake system will turn from a solid hydraulic-pressure into sponge-gas pressure....and this weaken the pressure as your caliper cannot grip that disc tightly to help u stop in time....

*above statement explain why u would see most heavy lorry/busses have accident when going a steep downhill....heavy loads=heavy braking=brake fluid temp overheated=fluid turned into gas/steam=less braking pressure=cannot stop in time=crash
smile_approve.gif



-in fact when going down a steep hill it is advisable to use engine braking in order to keep the brake loads to a minimum level and keep brake fluid in its stable temp. thus optimum brake to ensure your own safety....


in proton cars, with displacement above from wira generation 1.6/1.8/2.0 all utilizing fuzzy logic adapted from mitsubishi INVECS-1 (the first version) that have its own ecu to help the gearbox do its decision wether to step-down or step-up gear position...

while gen2/waja/persona/exora/neo generation (campro models) also utilizing fuzzy logic concept also came from mitsubishi and newer version which is called INVECS-2...giving a more active gearbox work hence some people not used to it and complain....in fact this version will learn your driving style....and soon u will adapted to it


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#13
bigal26

Posted 02 June 2010 - 08:46 AM

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QUOTE (rallychamp @ Jun 1 2010, 01:28 PM) <{POST_SNAPBACK}>
u normally would see brake cable on bicycle brake...when u pull the lever so does the cable will pull the brakepad....

while in brake fluid (hyraulic system) where u step on the brake pedal so the fluid move towards brake caliper and push the piston so that the caliper will "clamp"/grip the disc and braking happens...


but since when fluid boils it turns into gas/steam so does the your brake system will turn from a solid hydraulic-pressure into sponge-gas pressure....and this weaken the pressure as your caliper cannot grip that disc tightly to help u stop in time....

*above statement explain why u would see most heavy lorry/busses have accident when going a steep downhill....heavy loads=heavy braking=brake fluid temp overheated=fluid turned into gas/steam=less braking pressure=cannot stop in time=crash
smile_approve.gif



-in fact when going down a steep hill it is advisable to use engine braking in order to keep the brake loads to a minimum level and keep brake fluid in its stable temp. thus optimum brake to ensure your own safety....


in proton cars, with displacement above from wira generation 1.6/1.8/2.0 all utilizing fuzzy logic adapted from mitsubishi INVECS-1 (the first version) that have its own ecu to help the gearbox do its decision wether to step-down or step-up gear position...

while gen2/waja/persona/exora/neo generation (campro models) also utilizing fuzzy logic concept also came from mitsubishi and newer version which is called INVECS-2...giving a more active gearbox work hence some people not used to it and complain....in fact this version will learn your driving style....and soon u will adapted to it

Bro Rallychamp
Thanks for this info. Fully understand how it works now. As an ignorant driver, I only know how to step gas and brake..haha.
Can you also advise on the downshifting of gears. If i'm going say 100 and I have to slow down suddenly, will it spoil the gears if i go straight from 4 to 2? Usually i just slam the brakes but will a combination of downshifting and braking make the car stop faster?

#14
shermansee

Posted 02 June 2010 - 07:02 PM

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QUOTE (bigal26 @ Jun 2 2010, 08:46 AM) <{POST_SNAPBACK}>
Bro Rallychamp
Thanks for this info. Fully understand how it works now. As an ignorant driver, I only know how to step gas and brake..haha.
Can you also advise on the downshifting of gears. If i'm going say 100 and I have to slow down suddenly, will it spoil the gears if i go straight from 4 to 2? Usually i just slam the brakes but will a combination of downshifting and braking make the car stop faster?



Yes, I wanted to know as well, particularly on whether engine braking will damage the car, in any way, short and long-term.

This is because when I do engine brake from, say, 80km/h at 4th gear to 3rd, I can see my rev shoots up to over 3k/rpm+ even though I'm off the acceleration paddle. I'm just worried that the high rev and the slow down the tyre spin will, in some mechanical way, wear down the engine in the long term? The sounds from the high rev seem "forceful" at time..

#15
Newkelisa

Posted 04 June 2010 - 02:45 PM

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I look at this way.

Brakes are designed for SOLE purpose to slow down and stop the car. Brake pads are wear items and meant to be kena makan as when braking. Engines and transmission are not designed for braking per se.

A lot of research have been done for better brakes over the decades. I say use the brake always as they are designed for that. Engine braking has its uses such as going down a long downhill road but I would not say for normal town or highway driving.

Horror stories of buses with overboiled brake fluid - in first place, did they have good brake fluid to start off with? Are the brake fluid renewed regularly? Brake fluid over time absorbs moisture in the air causing the boiling point to become lower. I suspect going from my experience with workshops the brake fluid in most buses and lorries in M'sia are not changed annually or even 2 yearly as recommended. I suspect they change it by the color of the fluid which is very inaccurate and maybe too late.



#16
rallychamp

Posted 04 June 2010 - 04:41 PM

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QUOTE (bigal26 @ Jun 2 2010, 08:46 AM) <{POST_SNAPBACK}>
Bro Rallychamp
Thanks for this info. Fully understand how it works now. As an ignorant driver, I only know how to step gas and brake..haha.
Can you also advise on the downshifting of gears. If i'm going say 100 and I have to slow down suddenly, will it spoil the gears if i go straight from 4 to 2? Usually i just slam the brakes but will a combination of downshifting and braking make the car stop faster?


QUOTE (shermansee @ Jun 2 2010, 07:02 PM) <{POST_SNAPBACK}>
Yes, I wanted to know as well, particularly on whether engine braking will damage the car, in any way, short and long-term.

This is because when I do engine brake from, say, 80km/h at 4th gear to 3rd, I can see my rev shoots up to over 3k/rpm+ even though I'm off the acceleration paddle. I'm just worried that the high rev and the slow down the tyre spin will, in some mechanical way, wear down the engine in the long term? The sounds from the high rev seem "forceful" at time..


braking with help of engine brake during heavy braking situation (steep downhill/race) proved was valuable to help the brake doing its work.....

but on the other side yes the engine would risk to overheat/overstress when engine braking was does too frequent/too heavy/too dependent on engine brake/skipping ratio where it would lead to engine operating beyond optimum rev range (over-revved)...

thats why u will see how frequent race driver would do "heel n toe" to blip the throttle before shifting down the gear...this was done to ensure the engine rev match to gearbox synchronizer range...helps reducing transmission/drivetrain shocking-load....if not...sure the gearbox and engine as well as drive shaft would stressed to their limits....

#but thats during race situation..where abuse is normal....in normal daily like approaching traffic light, a soft engine braking doing very little to none harm on your engine/drivetrain....(of course approaching with low speed reccomended in this situation)








QUOTE (Newkelisa @ Jun 4 2010, 02:45 PM) <{POST_SNAPBACK}>
I look at this way.

Brakes are designed for SOLE purpose to slow down and stop the car. Brake pads are wear items and meant to be kena makan as when braking. Engines and transmission are not designed for braking per se.

A lot of research have been done for better brakes over the decades. I say use the brake always as they are designed for that. Engine braking has its uses such as going down a long downhill road but I would not say for normal town or highway driving.

Horror stories of buses with overboiled brake fluid - in first place, did they have good brake fluid to start off with? Are the brake fluid renewed regularly? Brake fluid over time absorbs moisture in the air causing the boiling point to become lower. I suspect going from my experience with workshops the brake fluid in most buses and lorries in M'sia are not changed annually or even 2 yearly as recommended. I suspect they change it by the color of the fluid which is very inaccurate and maybe too late.



-but....there's still one thing for sure....no matter how frequent or how good u maintain your brake fluid,as well as using superior brake fluid (dot4 and above)..there's very little or nothing u can do once the brake overheated as the brakepads material won't grip anymore and your brake fluid becomes vapor.....try it during trackdays if u didn't believe me....(there is a reason why race-metallic/carbon brake pad compounds have higher optimum operating temp. compared to stock standard brake pads...but it was rubbish during cold/below operating temp.)

*this issue is well taken care by modern heavy trucks/buses by utilizing water cooling-spray system on their brakes....<<<more visible if u watch truck race video.....(u will see a cloud of steam coming out from their wheels during braking attempts... trink39.gif

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#17
bigal26

Posted 04 June 2010 - 11:55 PM

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QUOTE (rallychamp @ Jun 4 2010, 04:41 PM) <{POST_SNAPBACK}>
braking with help of engine brake during heavy braking situation (steep downhill/race) proved was valuable to help the brake doing its work.....

but on the other side yes the engine would risk to overheat/overstress when engine braking was does too frequent/too heavy/too dependent on engine brake/skipping ratio where it would lead to engine operating beyond optimum rev range (over-revved)...

thats why u will see how frequent race driver would do "heel n toe" to blip the throttle before shifting down the gear...this was done to ensure the engine rev match to gearbox synchronizer range...helps reducing transmission/drivetrain shocking-load....if not...sure the gearbox and engine as well as drive shaft would stressed to their limits....

#but thats during race situation..where abuse is normal....in normal daily like approaching traffic light, a soft engine braking doing very little to none harm on your engine/drivetrain....(of course approaching with low speed reccomended in this situation)

Bro
Thanks again for explaining. When we downshift, what rpm range should we be in? I always hear of drivers redlining before every shift up. Doesn't it work the same way down?

#18
Gunnerzz

Posted 05 June 2010 - 02:11 PM

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QUOTE (bigal26 @ Jun 4 2010, 11:55 PM) <{POST_SNAPBACK}>
Bro
Thanks again for explaining. When we downshift, what rpm range should we be in? I always hear of drivers redlining before every shift up. Doesn't it work the same way down?

It all depends on the gear ratio and the speed u are travelling.
Different car hav different gear ratio so the matching rev for a smoother downshift is also different.

"Heel-n-toe" like bro rallychamp mention is a great technique to do braking and engine braking at the same time.
If done properly,it will be so smooth instead of a surge of rev causing weight being transferred to the front and disturbing comfort and balance during cornering.
Corner will also feels like straight and soon u wont believe the speed u took a corner.
If u are used to your car,u will instinctively know the suitable rev to match with the suitable gear.

On automatic gearbox which do downshift to aid braking,it all depends to the gearbox to quickly accelerate again.
For example,with the Wira 1.5,its soo slow to accelerate again bcoz it just using an old age autobox.
With the Waja 1.8,when doing hard braking,the gearbox will downshift to the correct gear to make sure u are always in the right gear to accelerate again.
It all depends on the tech that are in the gearbox.

On revving up to the redline,this also depends to the engine characteristic.
With the Waja 1.8,revving to redline is almost useless as the engine is tuned for loads of low-end torque.
Revving it to redline only results in more noise but not much go.
In racing,its normal to keep the rev as close to the redline as possible bcoz race engine are tuned for loads of power on the higher rev so race driver will keep the rev high even when shifting to lower gear.
This is unnecessary for for everyday driving unless u want to blow your engine.

For example,i will heel-n-toe to keep the rev between 3k rpm ant 4k rpm when i want to hav a fun drive with the Neo CPS.
I can keep it above the 4400rpm-CPS kicks-in-point but as i'm driving not that fast and on public road and i hav to be safe to others as well.

#19
bigal26

Posted 05 June 2010 - 02:35 PM

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QUOTE (Gunnerzz @ Jun 5 2010, 02:11 PM) <{POST_SNAPBACK}>
It all depends on the gear ratio and the speed u are travelling.
Different car hav different gear ratio so the matching rev for a smoother downshift is also different.

"Heel-n-toe" like bro rallychamp mention is a great technique to do braking and engine braking at the same time.
If done properly,it will be so smooth instead of a surge of rev causing weight being transferred to the front and disturbing comfort and balance during cornering.
Corner will also feels like straight and soon u wont believe the speed u took a corner.
If u are used to your car,u will instinctively know the suitable rev to match with the suitable gear.

On automatic gearbox which do downshift to aid braking,it all depends to the gearbox to quickly accelerate again.
For example,with the Wira 1.5,its soo slow to accelerate again bcoz it just using an old age autobox.
With the Waja 1.8,when doing hard braking,the gearbox will downshift to the correct gear to make sure u are always in the right gear to accelerate again.
It all depends on the tech that are in the gearbox.

On revving up to the redline,this also depends to the engine characteristic.
With the Waja 1.8,revving to redline is almost useless as the engine is tuned for loads of low-end torque.
Revving it to redline only results in more noise but not much go.
In racing,its normal to keep the rev as close to the redline as possible bcoz race engine are tuned for loads of power on the higher rev so race driver will keep the rev high even when shifting to lower gear.
This is unnecessary for for everyday driving unless u want to blow your engine.

For example,i will heel-n-toe to keep the rev between 3k rpm ant 4k rpm when i want to hav a fun drive with the Neo CPS.
I can keep it above the 4400rpm-CPS kicks-in-point but as i'm driving not that fast and on public road and i hav to be safe to others as well.

Bro Gunnerzz
Can you tell me more about "heel-n-toe" and how it works exactly. Btw, I don't rev to redline..I just read about some forumers talking about it. My aim is to have a smooth yet spirited drive.

#20
TheGunner

Posted 06 June 2010 - 12:00 PM

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QUOTE (shermansee @ Jun 2 2010, 07:02 PM) <{POST_SNAPBACK}>
Yes, I wanted to know as well, particularly on whether engine braking will damage the car, in any way, short and long-term.


As long as not done excessively, it's fine. For sedated driving, engine braking for automatic transmission isn't absolutely necessary.

QUOTE (shermansee @ Jun 2 2010, 07:02 PM) <{POST_SNAPBACK}>
This is because when I do engine brake from, say, 80km/h at 4th gear to 3rd, I can see my rev shoots up to over 3k/rpm+ even though I'm off the acceleration paddle. I'm just worried that the high rev and the slow down the tyre spin will, in some mechanical way, wear down the engine in the long term? The sounds from the high rev seem "forceful" at time..


Revs going up when you downshift is normal even if u lift off.
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