Question about power delivery while moving.

[DEWFPO]

I believe what I am describing below is normal but I don't understand how or why it happens. Maybe someone who understands the hydraulic system on the 5600D can explain.

Driving up a steep grade in Work Mode, Low Speed Range, Full throttle, Full Go Pedal and Attachment(s) Power OFF, the Toolcat always mimics what I would call a "transmission downshift" as I press the pedal down to the floor. At the same time the vehicle speed slows some as it climbs up the grade.

I've got HP Management on the default ON setting. I tried turning HP Mgmt OFF once and couldn't wait to turn it back on again.

I'd just like to understand what causes the "downshift feeling" to occur?

DEWFPO

 

[ruffdog]

I can't answer your question BUT, would switching HP mngmt off change how it acted? How?

 

[aczlan]

IIRC, that has a variable displacement hydraulic pump on the engine driving fixed displacement wheel motors and the "downshift" you feel is the ECU reducing the displacement of the pump (reducing your ground speed) so that the engine doesn't get overloaded.

Aaron Z

 

[DEWFPO]

I can't answer your question BUT, would switching HP mngmt off change how it acted? How?

It's too easy to bog the engine down with the HP Mgmt Off. I tried it once.

I live at 7,200' elevation and I know that having a turbo on the engine should theoretically "make up" for the altitude but I never operated a Toolcat at sea level so I can't access whether the turbo takes altitude completely out of the equation or just makes up for it "some". My gut is that at 7,200' my Toolcat engine does not make the same HP as a similar model at seal level, regardless of RPM. I've always wanted more power from the engine in my Toolcat.

DEWFPO

 

[DEWFPO]

IIRC, that has a variable displacement hydraulic pump on the engine driving fixed displacement wheel motors and the "downshift" you feel is the ECU reducing the displacement of the pump (reducing your ground speed) so that the engine doesn't get overloaded.

Aaron Z

That makes sense Aaron, but it 'feels' like the adjustment is like flipping a switch (hence the downshift feeling) versus a graduated adjustment.

DEWFPO

 

[ruffdog]

Thanks guys....

 

[SSdoxie]

The downshifting you experience is the Horsepower Management working. When pressure/torque load at the pump rises greater than engine torque @ desired RPM the HPMgt de-strokes the HST pump to increase torque output of the pump.
How HPM works: Bobcat controller monitors throttle position, engine RPM, and HST pump stroke, and travel peed at the motor. When it senses slowing of the engine speed without change in throttle position the HPM reduces pump stroke to help bring engine back to throttle RPM setting. All machines prior to G-series T4 have mechanical injection so the governor is only load adjustment on the engine and governor usually doesn't start shift fuel rack for more until approximately 200 RPM reduction occurs.

Turbo engine performs much better at high altitude the aspirated engine however there are still limitations due to oxygen levels.
One advantage of the G-series Tier4 is the engine ECM has a barometric pressure sensor built in it to aide the ECM in adjusting fuel injection & timing to perform at possible power range. Plus the ECM can adjust for torque loads faster than a mechanically injected engine with governor.

Make sure the turbo waste gate is functioning so you are getting max boost when you need it.

 

[aczlan]

That makes sense Aaron, but it 'feels' like the adjustment is like flipping a switch (hence the downshift feeling) versus a graduated adjustment.

DEWFPO

It is probably graduated, but the graduations may be fairly coarse.

Aaron Z

 

[ruffdog]

Is there ever a situation that it would be beneficial to have HPM shut off?

 

[Spudgunner]

@ruffdog...IIRC, yes. My engine speed sensor failed at one point to provide accurate measurements...the tach was all over the place and my TC started "lurching" like crazy. Couldn't really be driven effectively but I was able to limp home. After some research, I turned HP Management off and the problem stopped. So this gave me time to get to the Bobcat dealer at my leisure, more or less, and get a new speed sensor. After I installed the new sensor I turned HP management back on and all was well. Having said that, I can't say that I found HP management turned off to be a problem. All this happened quite a few years ago but this is my recollection of what happened.