Steven Holmes

Hi

I have a 2003 AWD CR-V. I know how the system works technically, but what I
am wondering is, when wheels begin to slip, and the AWD kicks in, how long
does the car stay in AWD for? In other words, once AWD starts up, does it
stay there until I brake, until the car slows to a stop again, until the
engine is turned off and then on?

Curious.

SAH

null_pointer@nowhere.com.net.edu.gov.de

On Sat, 03 Apr 2004 16:15:12 GMT, Steven Holmes
<stevenaholmes@earthlink.net> wrote:

>Hi
>
>I have a 2003 AWD CR-V. I know how the system works technically, but what I
>am wondering is, when wheels begin to slip, and the AWD kicks in, how long
>does the car stay in AWD for? In other words, once AWD starts up, does it
>stay there until I brake, until the car slows to a stop again, until the
>engine is turned off and then on?
>
>Curious.
>
>SAH
I recently read somewhere that there are two small oil pumps, one
driven by the drive shaft, the other by the rear wheels. Their output
is directed to opposing sides of a piston. When the front wheels slip
the drive shaft pump turns faster causing the piston to move causing a
clutch pack to engage the rear wheels. As soon as the wheels are
turning at the same speed the oil pressure on both sides of the piston
equalizes and the piston returns to it's central position and the rear
wheels disengage. Don't take this as the gospel truth...it's just
something I read on the internet.

Scott MacLean

> I recently read somewhere that there are two small oil pumps, one
> driven by the drive shaft, the other by the rear wheels. Their output
> is directed to opposing sides of a piston. When the front wheels slip
> the drive shaft pump turns faster causing the piston to move causing a
> clutch pack to engage the rear wheels. As soon as the wheels are
> turning at the same speed the oil pressure on both sides of the piston
> equalizes and the piston returns to it's central position and the rear
> wheels disengage. Don't take this as the gospel truth...it's just
> something I read on the internet.

Almost right. If that was the case, as soon as it engaged, it would then
disengage again, slip, re-engage, and so on.

There are two pumps, as you mentioned, pumping differential fluid from the
rear diff. One pump is in the transmission, the other runs off the rear
diff. The drive shaft to the rear diff turns continuously, but is not
connected to the wheels in normal driving, which keeps mileage up. When the
front wheels turn faster than the rear, there is a pressure differential
between the pumps, and a multiplate clutch in the rear diff system engages,
transferring torque to the rear wheels. This clutch remains engaged as long
as there is torque available. As soon as you let up off the gas, the clutch
disengages and you are back in FWD mode.

'Curly Q. Links'

Steven Holmes wrote:
>
> Hi
>
> I have a 2003 AWD CR-V. I know how the system works technically, but
> what I am wondering is, when wheels begin to slip, and the AWD kicks
> in, how long does the car stay in AWD for? In other words, once AWD
> starts up, does it stay there until I brake, until the car slows to a
> stop again, until the engine is turned off and then on?
>
> Curious.
>
> SAH

================

Nul_pointer is right.. (if it's the same as the 1st generation CRV) two
opposing pumps inside the rear diff. If front or rear wheels spin
faster, the rear diff locks up to transfer torque to whatever is
slipping. It's over as soon as it starts because your wheels all start
turning the same speed right away. Great at icy intersections and
snowbanks.

If you lock up the rear wheels on a AWD CRV, the fronts will lock up too
(almost completely). In other words, you can't put it into one of those
'park-brake-skids' that I used to find so handy for burning a U-turn on
my icy driveway. :-(



Honda.com has resources that explain this.