electronic throttle

On Sun, 07 Mar 2010 22:24:45 -0800, jim beam > wrote:

>On 03/07/2010 02:47 PM, wrote:
>> On Sun, 07 Mar 2010 08:24:21 -0800, jim > wrote:
>>
>>> On 03/07/2010 08:10 AM, Bill Putney wrote:
>>>> jim beam wrote:
>>>>> On 03/06/2010 08:26 PM, Bill Putney wrote:
>>>>
>>>>>> I don't necessarily disagree with the rest of your post, but that part
>>>>>> of your post is definitely incorrect. Have you ever played with your
>>>>>> power brakes while simultaneously pressing the accelerator? Anything
>>>>>> more than one or two initial stabs at the brakes depletes the vacuum
>>>>>> stored in the booster, and with even slight power simultaneously being
>>>>>> demanded of the engine, the vacuum is not enough to directly power the
>>>>>> brakes, much less re-charge the vacuum in the booster.
>>>>>
>>>>> i have done this. with the engine off, the vacuum remains until the
>>>>> pedal is released - thus if you stomp the pedal and keep it there, you
>>>>> don't need to keep replenishing the vacuum. and you will stop the car.
>>>>> with the engine running, there is no vacuum issue, and the brakes are
>>>>> still powerful enough to stop the car. on my honda anyway.
>>>>
>>>> I have real trouble believing that a large majority of people would, in
>>>> a sudden inadvertent acceleration situation, be content to press the
>>>> brakes one time and not try to pump them once or twice.
>>>
>>> why? if the car in front of you suddenly jams on their brakes, do you
>>> apply then release your pedal? i think your answer is "no" - unless
>>> you're skidding and know what cadence braking is. and if you know what
>>> cadence braking is, you should know that to stop a car with the engine
>>> on full throttle, you apply the brakes hard and quickly - you don't
>>> monkey about with multiple brake applications that can cause excess
>>> heating and fade.
>>>
>>>
>>>> After that, the
>>>> brakes will be almost totally ineffective because of loss of vacuum.
>>>
>>> no. fade maybe, but vacuum is always present if the engine is running.
>>> even if it's not, you still have vacuum reserve for three applications.
>>>
>>>
>>>>
>>>>>> People don't believe that, but try it on your car: On a deserted road at
>>>>>> highway speed, stab the brake pedal a couple of times while holding the
>>>>>> gas pedal down a little bit to load the engine slightly (this works
>>>>>> anywhere from slight to WOT throttle). I guarantee you (unless your
>>>>>> brake booster gets its vacuum from something besides the intake vacuum -
>>>>>> like a separate electric motor-driven vacuum pump) that after two or
>>>>>> more stabs at the brake pedal, the braking power will be extremely low -
>>>>>> so low that the engine will have no trouble overpowering the brakes. No
>>>>>> vacuum in the booster essentially equals no brakes.
>>>>>
>>>>> with respect, i think you're confusing vacuum with fade...
>>>>
>>>> No - I'm not. While you could certainly induce fade with a certain
>>>> prolonged script of usage of the brakes, what I'm talking about is true
>>>> over what I would say would be the real world typical scenario (before
>>>> the fade issue becomes real - which - yes - it would over a longer
>>>> period, but not likely if the 2 or 3 stabs had already occurred in the
>>>> relatively short period that I would expect). It is a fact that the
>>>> vacuum cannot recharge with almost no vacuum in the intake - it doesn't
>>>> recharge by magic. I guarantee you that after a third stab of the brakes
>>>> on an engine vacuum-driven power brake car, the brakes will loose the
>>>> fight with the engine - fade has nothing to do with that over the first
>>>> few seconds that we would be talking about (during which the first 2 or
>>>> 3 stabs would occur real world).
>>>
>>> if that is your experience, then i think you must have a vacuum leak.
>>> even with wide open throttle, there is sufficient vacuum in the manifold
>>> to create significant braking assist.
>>>
>>
>> Sorry Jim - but you are wrong.
>> A diesel engined vehicle with a mechanical vacuum pump would work as
>> you envision - but under any substantial load there is not enough
>> manifold vacuum produced to provide full braking assist.
>
>i didn't say "full".


OK then - lets be accurate and say "adequate". Won't get that either.
>
>
>> With both
>> feet on the brake pedal a strong man MAY be able to provide enough
>> brake line pressure to stop the car at half throttle.
>
>/if/ the driver has pressed and released the pedal a couple of times.
>why they would do that though is something i don't follow.

On 03/08/2010 04:28 PM, wrote:
> On Sun, 07 Mar 2010 22:24:45 -0800, jim > wrote:
>
>> On 03/07/2010 02:47 PM, wrote:
>>> On Sun, 07 Mar 2010 08:24:21 -0800, jim > wrote:
>>>
>>>> On 03/07/2010 08:10 AM, Bill Putney wrote:
>>>>> jim beam wrote:
>>>>>> On 03/06/2010 08:26 PM, Bill Putney wrote:
>>>>>
>>>>>>> I don't necessarily disagree with the rest of your post, but that part
>>>>>>> of your post is definitely incorrect. Have you ever played with your
>>>>>>> power brakes while simultaneously pressing the accelerator? Anything
>>>>>>> more than one or two initial stabs at the brakes depletes the vacuum
>>>>>>> stored in the booster, and with even slight power simultaneously being
>>>>>>> demanded of the engine, the vacuum is not enough to directly power the
>>>>>>> brakes, much less re-charge the vacuum in the booster.
>>>>>>
>>>>>> i have done this. with the engine off, the vacuum remains until the
>>>>>> pedal is released - thus if you stomp the pedal and keep it there, you
>>>>>> don't need to keep replenishing the vacuum. and you will stop the car.
>>>>>> with the engine running, there is no vacuum issue, and the brakes are
>>>>>> still powerful enough to stop the car. on my honda anyway.
>>>>>
>>>>> I have real trouble believing that a large majority of people would, in
>>>>> a sudden inadvertent acceleration situation, be content to press the
>>>>> brakes one time and not try to pump them once or twice.
>>>>
>>>> why? if the car in front of you suddenly jams on their brakes, do you
>>>> apply then release your pedal? i think your answer is "no" - unless
>>>> you're skidding and know what cadence braking is. and if you know what
>>>> cadence braking is, you should know that to stop a car with the engine
>>>> on full throttle, you apply the brakes hard and quickly - you don't
>>>> monkey about with multiple brake applications that can cause excess
>>>> heating and fade.
>>>>
>>>>
>>>>> After that, the
>>>>> brakes will be almost totally ineffective because of loss of vacuum.
>>>>
>>>> no. fade maybe, but vacuum is always present if the engine is running.
>>>> even if it's not, you still have vacuum reserve for three applications.
>>>>
>>>>
>>>>>
>>>>>>> People don't believe that, but try it on your car: On a deserted road at
>>>>>>> highway speed, stab the brake pedal a couple of times while holding the
>>>>>>> gas pedal down a little bit to load the engine slightly (this works
>>>>>>> anywhere from slight to WOT throttle). I guarantee you (unless your
>>>>>>> brake booster gets its vacuum from something besides the intake vacuum -
>>>>>>> like a separate electric motor-driven vacuum pump) that after two or
>>>>>>> more stabs at the brake pedal, the braking power will be extremely low -
>>>>>>> so low that the engine will have no trouble overpowering the brakes. No
>>>>>>> vacuum in the booster essentially equals no brakes.
>>>>>>
>>>>>> with respect, i think you're confusing vacuum with fade...
>>>>>
>>>>> No - I'm not. While you could certainly induce fade with a certain
>>>>> prolonged script of usage of the brakes, what I'm talking about is true
>>>>> over what I would say would be the real world typical scenario (before
>>>>> the fade issue becomes real - which - yes - it would over a longer
>>>>> period, but not likely if the 2 or 3 stabs had already occurred in the
>>>>> relatively short period that I would expect). It is a fact that the
>>>>> vacuum cannot recharge with almost no vacuum in the intake - it doesn't
>>>>> recharge by magic. I guarantee you that after a third stab of the brakes
>>>>> on an engine vacuum-driven power brake car, the brakes will loose the
>>>>> fight with the engine - fade has nothing to do with that over the first
>>>>> few seconds that we would be talking about (during which the first 2 or
>>>>> 3 stabs would occur real world).
>>>>
>>>> if that is your experience, then i think you must have a vacuum leak.
>>>> even with wide open throttle, there is sufficient vacuum in the manifold
>>>> to create significant braking assist.
>>>>
>>>
>>> Sorry Jim - but you are wrong.
>>> A diesel engined vehicle with a mechanical vacuum pump would work as
>>> you envision - but under any substantial load there is not enough
>>> manifold vacuum produced to provide full braking assist.
>>
>> i didn't say "full".
>
>
> OK then - lets be accurate and say "adequate". Won't get that either.

not for casual comfort, no. but this is academic unless we're buying
bills "panic pump" theory, which is not observed in reality.



>>
>>
>>> With both
>>> feet on the brake pedal a strong man MAY be able to provide enough
>>> brake line pressure to stop the car at half throttle.
>>
>> /if/ the driver has pressed and released the pedal a couple of times.
>> why they would do that though is something i don't follow.
>


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