Locking in VTM-4

[Jet-Pilot-64]

Went to Lake Tahoe this weekend in a decent snowstorm. The roads at one point were very icy. Traffic came to a stop because a Toyota Tacoma was moving sideways rather than forward when accelerating. When I tried to accelerate, the same thing happend and I was moving toward hitting the car next to me. I quickly popped the car into first gear and hit the VTM-4 lock. Got traction immediately and made my way around the Tacoma.

Can anyone explain why it worked when I locked it in, but not when it wasn't locked in? Shouldn't it have sensed wheel slippage and provided the correct torque on each wheel to get me out with having to lock it in?

[2muchfun]

Originally posted by Jet-Pilot-64


Can anyone explain why it worked when I locked it in, but not when it wasn't locked in? Shouldn't it have sensed wheel slippage and provided the correct torque on each wheel to get me out with having to lock it in?

Good question....

[ecsw]

The only thing I can think of is, when locking VTM-4, u force the power distribution to 50/50 front/back. But for VTM-4 to detect slippage, it might not be sending all the 50% of the traction to the rear wheel since it doesn't think it needs all of them?


maybe, it's just my guess.

[Jet-Pilot-64]

But it was really nice to have the option to lock in. I'm telling you all, this is a great go to the snow vehicle. It won't go where a CJ-5 will go, but I have had several occasions where the AWD kicked butt! Really great peace-of-mind when taking your family to places where weather can be an issue. Now, if they could just put a toilet in these things for when traffic is stopped due to an accident. Man, it sucks having to whip it out with 40 cars around you...

[jestmaty]

Went to Galveston, Tx. beach on Sunday and have a somewhat interesting story to tell about "not getting stuck in deep, dry sand".

A friend and his wife and new baby drove their 2004 VW Jetta, and my family took our pilot.

The first cool story involves his high performance kites, the kind that cost a bunch of money... We flew two kites that were steerable and those were neat. Now keep in mind that I havent mentioned how windy it was that day.......

He brings out one kite that looks like a parachute foil, about 2 feet tall and 8 feet wide. Four strings to fly that puppy.

I watched him literally get dragged around the sand and get pulled over face first in the sand. Cool!!!!

I also neglected to mention his weight, 310 lbs and not a bit of muscle on him. He knows he is obese and has tried over the years to lose it, I just encourage him and supports whatever he tries.

Back to the story. I get ahold of that same kite, don't know how to fly it all that well either. The only problem is that I weigh 185 lbs

Long story short is that I literally got lifted maybe 4 feet off the ground and flew about 10 feet before I let go. It was awsome!!! I had his wife and my wife and 2 boys laughing histerically at me after I hit the sand and rolled head over heels...

My friend and I had enough and decided to leave the same way we drove in.... through some really deep, dry and unpacked sand.

He got a running start and sort of skipped over the sand to the concrete road. Good for him...

I just left the Pilot in D and kept a steady foot on the gas, made it through without any problem either.

Watched a Chevy pickup follow right behind me get stuck, deep....

Luckily a brutally stout 4 wheel drive truck saw the guy get stuck and offered to pull him out. Of course, being Texans, there was no request for compensation for the service

Hooray for the Pilot, all bow down to the VW for his accomplishments also.

Thank God I didn't break my neck with the kites either, my friend had said, "By all means, drop the handles if the kite gets out of control."


Later.... Jestmaty

[onu2002]

that's great about the pilot, but the important question is, did you get the kite back?

[sjlee]

Originally posted by ecsw
The only thing I can think of is, when locking VTM-4, u force the power distribution to 50/50 front/back. But for VTM-4 to detect slippage, it might not be sending all the 50% of the traction to the rear wheel since it doesn't think it needs all of them?


maybe, it's just my guess.

My guess is something similar. When you start to accelerate without having VTM-4 locked, there is more power to the front than to the rear, which caused your Pilot to slide sideways. If you were able to keep going, eventually the VTM-4 would have allocated enough power to the rear to get you going straight... but at that point, you probably would've hit the guy next to you. By locking VTM-4, the Pilot will distribute equal power to the front and back right away.

[Jet-Pilot-64]

Originally posted by sjlee


My guess is something similar. When you start to accelerate without having VTM-4 locked, there is more power to the front than to the rear, which caused your Pilot to slide sideways. If you were able to keep going, eventually the VTM-4 would have allocated enough power to the rear to get you going straight... but at that point, you probably would've hit the guy next to you. By locking VTM-4, the Pilot will distribute equal power to the front and back right away.

Makes sense!

[2004 PILOT]

If I remember correctly, the VTM-4 doesnt actually come on till after 18-20 MPH in the unlocked mode if slippage is detected. Thats why you can lock it out in "L" "2" "R" after you are stopped. In the locked mode the VTM-4 will shut off once you hit 18-20 MPH.

[rocky]

The Toy, which does come with a locking read diff in certain models, probably had an open rear diff. If one rear wheel got traction and the other had none, the vehicle will skip to one side as all the power goes to the side with no traction.
Because a locked vtm4 keeps the power output even there is less tendancy to skip to one side

[sjlee]

Originally posted by 2004 PILOT
If I remember correctly, the VTM-4 doesnt actually come on till after 18-20 MPH in the unlocked mode if slippage is detected. Thats why you can lock it out in "L" "2" "R" after you are stopped. In the locked mode the VTM-4 will shut off once you hit 18-20 MPH.

I've never heard VTM-4 doesn't engage until a certain speed. I thought that it only allowed you to engage the lock in the lower gears (1, 2 or R)was to keep the transmission from shifting into a higher gear.

[2004 PILOT]

This is what the dealer told me.

[xGS]

Originally posted by 2004 PILOT
If I remember correctly, the VTM-4 doesnt actually come on till after 18-20 MPH in the unlocked mode if slippage is detected. Thats why you can lock it out in "L" "2" "R" after you are stopped. In the locked mode the VTM-4 will shut off once you hit 18-20 MPH.

For those who are unclear regarding the distinction between the VTM-4 system and the VTM-4 lock mode, once again:

"Variable Torque Management 4-wheel-drive (VTM-4)

The Pilot's innovative VTM-4 four-wheel drive system was designed to deliver outstanding traction, stability and control in all weather conditions as well as good medium-duty off-road performance. It was also designed to minimize the weight and packaging penalties associated with conventional four-wheel drive systems.

The VTM-4 system is unique in its operation. Unlike many competitive systems that use an engagement strategy triggered by wheel slippage, VTM-4 anticipates the need for all-wheel drive and engages the rear wheels whenever the vehicle is accelerating. Additional torque is applied to the rear wheels when wheel slip is detected, up to an approximate maximum of 50-percent in low gear. Another unique feature of the system is the VTM-4 Lock function.

Activated by a button on the instrument panel, the VTM-4 Lock mode delivers maximum torque transfer to the rear wheels to aid extraction from extremely slippery or "stuck" conditions. The feature works only when the vehicle is in first, second or reverse gears, and automatically disengages at speeds above 18 miles per hour.

When cruising under normal conditions, the Pilot provides front-wheel drive power for improved efficiency. Torque is proactively distributed to the rear wheels when the vehicle is accelerating or wheel slip is detected. The level of torque delivery, front to rear, is determined by the amount of acceleration (rate of change in velocity) and wheel slip (difference in rotational speed) and is controlled by a dedicated CPU with sensors in the braking, engine and transmission systems.

To avoid the weight and bulk of a conventional transfer case, VTM-4's torque transfer unit is a compact cast-aluminum housing bolted directly to transaxle. The transfer case is a single-speed, permanently engaged device without a low-range, reducing weight and space penalties while maintaining excellent on- and off-road capabilities. Attached to the front wheel differential's ring gear is a helical gear that provides input torque to the transfer unit. A short horizontal shaft and a hypoid gear set within the case turn the drive ninety degrees, move it to the vehicle center line and lower its axis by approximately 3.75-inches.

VTM-4 Engagement Modes

There are three distinct modes of VTM-4 engagement:

(1) The first mode, called Acceleration Torque Control (ATC), works whenever the vehicle's throttle is depressed, even on dry pavement - a feature unique to the VTM-4 system. Sensors in the engine and transmission monitor vehicle speed and acceleration. The amount of torque applied, as directed by the system's ECU, is determined according to vehicle speed, the amount of acceleration and transmission status (gear setting). This benefits not only the Pilot's ability to gain traction from a standing start, before wheel slip occurs, but also its overall dynamic stability on both dry and slippery roads. Reducing the propulsive force carried by the front tires under acceleration reduced torque steer and cornering adhesion. Rear wheel torque rises smoothly from zero to a preset maximum in proportion to vehicle acceleration (both forward and reverse). During constant-speed driving, all power is driven to the front wheels for improved fuel efficiency.

(2) The second engagement mode occurs when wheel slip is detected. Differences in rotational speed between front and rear wheels are measured by sensors in the ABS system and monitored by the ECU. In response, the ECU commands an increase in torque delivery to the rear wheels. Torque application is adjusted according to the amount and the rate of change in wheel slip. As slip increase, more power is delivered to the rear wheels for improved traction.

(3) The third mode of engagement is VTM-4 Lock. Lock mode occurs when the driver shifts into first, second or reverse gears and depresses the VTM-Lock button on the instrument panel. When lock mode is selected at vehicle speeds below 18-mph, the system ECU commands a preset maximum amount of rear-drive torque to be delivered to the rear wheels for improved traction in very low-speed, low-traction, conditions. As control is regained and vehicle speed increases, the system gradually reduces rear axle torque until it is completely disengaged.

The maximum torque delivered to the rear wheels is sufficient to climb the steepest grade observed on any public road in America - 31-degrees (60 percent slope) - with a two-passenger load on board. The Pilot will also move from rest up a 28-degree (53 percent slope) dirt grade. On a split-friction grade (different amounts of traction at each wheel), VTM-4 automatically provides sufficient rear-wheel torque to help the vehicle climb a steep, slippery driveway to enter a garage."

[paw5306]

Originally posted by Jet-Pilot-64
Went to Lake Tahoe this weekend in a decent snowstorm. The roads at one point were very icy. Traffic came to a stop because a Toyota Tacoma was moving sideways rather than forward when accelerating. When I tried to accelerate, the same thing happend and I was moving toward hitting the car next to me. I quickly popped the car into first gear and hit the VTM-4 lock. Got traction immediately and made my way around the Tacoma.

Can anyone explain why it worked when I locked it in, but not when it wasn't locked in? Shouldn't it have sensed wheel slippage and provided the correct torque on each wheel to get me out with having to lock it in?

VTM-4 only works in 1st, 2nd and reverse gears; and then only up to 18 mph.
My understanding is that it locks the rear differential like posi-traction or a Detroit Locker.
I haven't used it myself ...yet.

[ctobio]

Originally posted by paw5306


VTM-4 only works in 1st, 2nd and reverse gears; and then only up to 18 mph.
My understanding is that it locks the rear differential like posi-traction or a Detroit Locker.
I haven't used it myself ...yet.

Just to clarify, VTM-4 manual lock only works in 1st, 2nd and reverse gears. VTM-4 will work its magic at any speed and modulate the torque distribution as it sees fit automagically in all circumstances when not in manual lock.