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Thread: More transmission questions and info

  1. #1
    Tuner in Training
    Join Date
    Jun 2004
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    Posts
    12

    More transmission questions and info

    Would there be any way of more directly controlling shift pressure than the 'desired shift time v. torque' setting? Aside, of course from raising the line pressure wholesale via the force motor current settings... :


    From my friend at GM Powertrain:

    You are mentioning the shift times as if
    it is an input. The FWD transmissions adapt on the shift time by modifying
    the shift line pressure from one shift to the next. However, the 4L60 has
    never used the adapts. That is because there is no input speed sensor, so
    the 'shift time' can only be calculated by looking at the engine speed
    pulldown, which is not good enough. The 4L60 shift line pressure and
    torque management are whatever they are calibrated to be, and the shift
    time that results is the shift time - an output, not an input, is what I am
    saying here. So I don't fully get it.
    As for line pressure, there are 7 tables that are in the calibration.
    The first column of each is 'gearbox torque' from zero to some large
    number. Gearbox torque is continuously calculated using engine airflow,
    engine speed, and trans output speed. The second column in tables 1-4 is
    the line pressure command in gears 1-4 respectively if no shift is taking
    place, called 'steady state line pressure.' The second column in tables
    5-7 is the line pressure command in shifts 1-2, 2-3, and 3-4, respectively,
    called 'shift line pressure.' The shift line pressure is always much lower
    than the steady-state line pressure surrounding it.
    So one of these tables is being used at all times. Which entry in
    the table is being used to create the line pressure command at a given
    moment depends on the gearbox torque calculation at that moment.
    So if you followed all that, here is my advice. Don't increase the
    steady state line pressure. It won't get you anything but extra heat in
    the fluid, and maybe wear out the pump. If you reduce the steady-state
    line pressure, clutches might slip, and that can be very hard to perceive
    until it is too late and you smell it. Bump up the shift line pressure as
    far as you want. If you only bump up the entries corresponding to higher
    levels of gearbox torque, the light throttle shifts can be smooth, but the
    heavy throttle shifts can make that pleasing tire squawk noise. The amount
    of tie-up in the 2-3 is controlled by hardware, so it is ok to add huge
    amounts to the line pressure for the 2-3 if you want to.

    The last stage of the calibration
    is the table that represents the response of the line pressure to the
    solenoid current. I did not even mention that, because that is the least
    logical to change, although maybe the easiest to backwards engineer for
    these aftermarket folks. The problem is that different gears and different
    shifts require different amounts of line pressure for a given amount of
    engine torque, such as full throttle. So a full throttle 1-2 might be only
    using 45% of the max current, but a full throttle 3-4 would use 90% of the
    max current. But then a light throttle 3-4 would use 45% of the max
    current. So you would have no way to get a firm full throttle 1-2 without
    also getting a firm light throttle 3-4, by modifying that table. That is
    what I think these guys are referring to. The 18x18 table that you have
    there must be the lookup for that based on temperature or something. A lot
    more job security goes with a 2-d lookup than just a 1-d lookup.
    I'm guessing that the vertical axis of that table is temperature and the
    horizontal axis corresponds to line pressure, and the values in the table
    are milliamps. Clear enough? Ok, just jack up the pressure all the time
    and have at it.

    Also, beware of aftermarket shift kits for the 4L60. There is an orifice
    they have you open up to make a faster 2-3. The problem with that, is that
    the fluid going through this orifice to move the 34 clutch piston is also
    the same fluid that is holding on the 24 band, but before the orifice. The
    downstream of orifice fluid acts against the other side of the 24 band
    piston to push it off, once the 34 clutch piston actually contacts the
    clutch and some pressure builds up. Unfortunately, the fluid before the
    orifice , which is keeping the band on, has some pressure drop already from
    going through the manual valve. While the fluid is moving the 34 piston
    against only the return spring, the orifice is like an open drain in the
    system. So when you open up that orifice, the pressure drop through the
    manual valve becomes enough that the band starts slipping, before you have
    torque capacity on the 34 clutch. So aftermarket folks then give you a new
    band piston with more area. That fixes the above problem, but then when
    the 34 clutch starts to get capacity, the band has way too much force on
    it, and you get terrible tie-up. But it's a firm shift, darn it.

    You can successfully use the orifice changes in a shift kit to get a really
    firm 1-2 and 3-4 however. But it is much more logical to do it with line
    pressure.

    On the 4L60, and all the other current transmissions, one solenoid event
    causes a shift. In the transmission hardware, only the 2-3 shift requires
    something to come off for the shift to occur, in D4 anyway. The off-and-on
    for the 2-3 and 3-2 are coordinated in hydraulic hardware, using the method
    patented by Simpson, around 1950, which is really quite interesting, but
    too hard to put into words, although I tried anyway in the previous email.
    So anyway, that can't be the shift time.
    We could drive around your jeep using alligator clip wires to the solenoids
    and a battery sliding around on the floor to make the shifts, and it would
    work just fine, as long as we didn't, for example, put it into 2nd at 120
    mph.


    Lots to digest, but I thought it might be useful, especially in dispelling the 'setting the desired shift time to 0 sec = sorta two gears at once' myth Last I talked to him, he was working on the 5 speed Caddy automatics, but I'm not sure what he's doing now.

    -Anton
    1973 AMG Postal Jeep powered by:&&1998 Chevy Camaro 3800 Series II V6/4L60E&&Adjustable fuel pressure, K&N clamped to TB, AMC Pacer front suspension (makes it LHD+disc brakes), Explorer 3.55 rear axle

  2. #2
    Advanced Tuner
    Join Date
    Oct 2002
    Posts
    206

    Re: More transmission questions and info

    Quote Originally Posted by athet
    Would there be any way of more directly controlling shift pressure than the 'desired shift time v. torque' setting? Aside, of course from raising the line pressure wholesale via the force motor current settings... :


    From my friend at GM Powertrain:

    You are mentioning the shift times as if
    it is an input. The FWD transmissions adapt on the shift time by modifying
    the shift line pressure from one shift to the next. However, the 4L60 has
    never used the adapts. That is because there is no input speed sensor, so
    the 'shift time' can only be calculated by looking at the engine speed
    pulldown, which is not good enough. The 4L60 shift line pressure and
    torque management are whatever they are calibrated to be, and the shift
    time that results is the shift time - an output, not an input, is what I am
    saying here. So I don't fully get it.
    As for line pressure, there are 7 tables that are in the calibration.
    The first column of each is 'gearbox torque' from zero to some large
    number. Gearbox torque is continuously calculated using engine airflow,
    engine speed, and trans output speed. The second column in tables 1-4 is
    the line pressure command in gears 1-4 respectively if no shift is taking
    place, called 'steady state line pressure.' The second column in tables
    5-7 is the line pressure command in shifts 1-2, 2-3, and 3-4, respectively,
    called 'shift line pressure.' The shift line pressure is always much lower
    than the steady-state line pressure surrounding it.
    So one of these tables is being used at all times. Which entry in
    the table is being used to create the line pressure command at a given
    moment depends on the gearbox torque calculation at that moment.
    So if you followed all that, here is my advice. Don't increase the
    steady state line pressure. It won't get you anything but extra heat in
    the fluid, and maybe wear out the pump. If you reduce the steady-state
    line pressure, clutches might slip, and that can be very hard to perceive
    until it is too late and you smell it. Bump up the shift line pressure as
    far as you want. If you only bump up the entries corresponding to higher
    levels of gearbox torque, the light throttle shifts can be smooth, but the
    heavy throttle shifts can make that pleasing tire squawk noise. The amount
    of tie-up in the 2-3 is controlled by hardware, so it is ok to add huge
    amounts to the line pressure for the 2-3 if you want to.

    The last stage of the calibration
    is the table that represents the response of the line pressure to the
    solenoid current. I did not even mention that, because that is the least
    logical to change, although maybe the easiest to backwards engineer for
    these aftermarket folks. The problem is that different gears and different
    shifts require different amounts of line pressure for a given amount of
    engine torque, such as full throttle. So a full throttle 1-2 might be only
    using 45% of the max current, but a full throttle 3-4 would use 90% of the
    max current. But then a light throttle 3-4 would use 45% of the max
    current. So you would have no way to get a firm full throttle 1-2 without
    also getting a firm light throttle 3-4, by modifying that table. That is
    what I think these guys are referring to. The 18x18 table that you have
    there must be the lookup for that based on temperature or something. A lot
    more job security goes with a 2-d lookup than just a 1-d lookup.
    I'm guessing that the vertical axis of that table is temperature and the
    horizontal axis corresponds to line pressure, and the values in the table
    are milliamps. Clear enough? Ok, just jack up the pressure all the time
    and have at it.

    Also, beware of aftermarket shift kits for the 4L60. There is an orifice
    they have you open up to make a faster 2-3. The problem with that, is that
    the fluid going through this orifice to move the 34 clutch piston is also
    the same fluid that is holding on the 24 band, but before the orifice. The
    downstream of orifice fluid acts against the other side of the 24 band
    piston to push it off, once the 34 clutch piston actually contacts the
    clutch and some pressure builds up. Unfortunately, the fluid before the
    orifice , which is keeping the band on, has some pressure drop already from
    going through the manual valve. While the fluid is moving the 34 piston
    against only the return spring, the orifice is like an open drain in the
    system. So when you open up that orifice, the pressure drop through the
    manual valve becomes enough that the band starts slipping, before you have
    torque capacity on the 34 clutch. So aftermarket folks then give you a new
    band piston with more area. That fixes the above problem, but then when
    the 34 clutch starts to get capacity, the band has way too much force on
    it, and you get terrible tie-up. But it's a firm shift, darn it.

    You can successfully use the orifice changes in a shift kit to get a really
    firm 1-2 and 3-4 however. But it is much more logical to do it with line
    pressure.

    On the 4L60, and all the other current transmissions, one solenoid event
    causes a shift. In the transmission hardware, only the 2-3 shift requires
    something to come off for the shift to occur, in D4 anyway. The off-and-on
    for the 2-3 and 3-2 are coordinated in hydraulic hardware, using the method
    patented by Simpson, around 1950, which is really quite interesting, but
    too hard to put into words, although I tried anyway in the previous email.
    So anyway, that can't be the shift time.
    We could drive around your jeep using alligator clip wires to the solenoids
    and a battery sliding around on the floor to make the shifts, and it would
    work just fine, as long as we didn't, for example, put it into 2nd at 120
    mph.


    Lots to digest, but I thought it might be useful, especially in dispelling the 'setting the desired shift time to 0 sec = sorta two gears at once' myth Last I talked to him, he was working on the 5 speed Caddy automatics, but I'm not sure what he's doing now.

    -Anton
    Wow, that is a awesome write up. I wish you would email him and get the same info on the 4T65eHD and how it works.

    Thanks,

    Loyde

  3. #3
    Advanced Tuner
    Join Date
    Jun 2008
    Posts
    539
    Quote Originally Posted by athet View Post
    Would there be any way of more directly controlling shift pressure than the 'desired shift time v. torque' setting? Aside, of course from raising the line pressure wholesale via the force motor current settings... :


    From my friend at GM Powertrain:

    You are mentioning the shift times as if
    it is an input. The FWD transmissions adapt on the shift time by modifying
    the shift line pressure from one shift to the next. However, the 4L60 has
    never used the adapts. That is because there is no input speed sensor, so
    the 'shift time' can only be calculated by looking at the engine speed
    pulldown, which is not good enough. The 4L60 shift line pressure and
    torque management are whatever they are calibrated to be, and the shift
    time that results is the shift time - an output, not an input, is what I am
    saying here. So I don't fully get it.
    As for line pressure, there are 7 tables that are in the calibration.
    The first column of each is 'gearbox torque' from zero to some large
    number. Gearbox torque is continuously calculated using engine airflow,
    engine speed, and trans output speed. The second column in tables 1-4 is
    the line pressure command in gears 1-4 respectively if no shift is taking
    place, called 'steady state line pressure.' The second column in tables
    5-7 is the line pressure command in shifts 1-2, 2-3, and 3-4, respectively,
    called 'shift line pressure.' The shift line pressure is always much lower
    than the steady-state line pressure surrounding it.
    So one of these tables is being used at all times. Which entry in
    the table is being used to create the line pressure command at a given
    moment depends on the gearbox torque calculation at that moment.
    So if you followed all that, here is my advice. Don't increase the
    steady state line pressure. It won't get you anything but extra heat in
    the fluid, and maybe wear out the pump. If you reduce the steady-state
    line pressure, clutches might slip, and that can be very hard to perceive
    until it is too late and you smell it. Bump up the shift line pressure as
    far as you want. If you only bump up the entries corresponding to higher
    levels of gearbox torque, the light throttle shifts can be smooth, but the
    heavy throttle shifts can make that pleasing tire squawk noise. The amount
    of tie-up in the 2-3 is controlled by hardware, so it is ok to add huge
    amounts to the line pressure for the 2-3 if you want to.

    The last stage of the calibration
    is the table that represents the response of the line pressure to the
    solenoid current. I did not even mention that, because that is the least
    logical to change, although maybe the easiest to backwards engineer for
    these aftermarket folks. The problem is that different gears and different
    shifts require different amounts of line pressure for a given amount of
    engine torque, such as full throttle. So a full throttle 1-2 might be only
    using 45% of the max current, but a full throttle 3-4 would use 90% of the
    max current. But then a light throttle 3-4 would use 45% of the max
    current. So you would have no way to get a firm full throttle 1-2 without
    also getting a firm light throttle 3-4, by modifying that table. That is
    what I think these guys are referring to. The 18x18 table that you have
    there must be the lookup for that based on temperature or something. A lot
    more job security goes with a 2-d lookup than just a 1-d lookup.
    I'm guessing that the vertical axis of that table is temperature and the
    horizontal axis corresponds to line pressure, and the values in the table
    are milliamps. Clear enough? Ok, just jack up the pressure all the time
    and have at it.

    Also, beware of aftermarket shift kits for the 4L60. There is an orifice
    they have you open up to make a faster 2-3. The problem with that, is that
    the fluid going through this orifice to move the 34 clutch piston is also
    the same fluid that is holding on the 24 band, but before the orifice. The
    downstream of orifice fluid acts against the other side of the 24 band
    piston to push it off, once the 34 clutch piston actually contacts the
    clutch and some pressure builds up. Unfortunately, the fluid before the
    orifice , which is keeping the band on, has some pressure drop already from
    going through the manual valve. While the fluid is moving the 34 piston
    against only the return spring, the orifice is like an open drain in the
    system. So when you open up that orifice, the pressure drop through the
    manual valve becomes enough that the band starts slipping, before you have
    torque capacity on the 34 clutch. So aftermarket folks then give you a new
    band piston with more area. That fixes the above problem, but then when
    the 34 clutch starts to get capacity, the band has way too much force on
    it, and you get terrible tie-up. But it's a firm shift, darn it.

    You can successfully use the orifice changes in a shift kit to get a really
    firm 1-2 and 3-4 however. But it is much more logical to do it with line
    pressure.

    On the 4L60, and all the other current transmissions, one solenoid event
    causes a shift. In the transmission hardware, only the 2-3 shift requires
    something to come off for the shift to occur, in D4 anyway. The off-and-on
    for the 2-3 and 3-2 are coordinated in hydraulic hardware, using the method
    patented by Simpson, around 1950, which is really quite interesting, but
    too hard to put into words, although I tried anyway in the previous email.
    So anyway, that can't be the shift time.
    We could drive around your jeep using alligator clip wires to the solenoids
    and a battery sliding around on the floor to make the shifts, and it would
    work just fine, as long as we didn't, for example, put it into 2nd at 120
    mph.


    Lots to digest, but I thought it might be useful, especially in dispelling the 'setting the desired shift time to 0 sec = sorta two gears at once' myth Last I talked to him, he was working on the 5 speed Caddy automatics, but I'm not sure what he's doing now.

    -Anton
    Interesting five year old post. Quoted for max irritability.

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