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Here is a description of the Pilot's VTM-4 System. As you read
you'll see that it is quite different from the CRV and all other
systems and gives you closer to actual 4WD (or is it 3 Wheel?_
Rgds
Variable Torque Management 4-wheel-drive (VTM-4) (back to top)
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 four-wheel-drive and engages the rear
wheels whenever the vehicle is accelerating. In low gear, up to
approximately 50 percent additional torque can be transferred to the
rear wheels when wheel slip is detected. 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 30km/h.
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 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 the 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 can turn
the drive ninety degrees, moving it to the vehicle centre line and
lowering its axis by approximately 95mm.
VTM-4 Engagement Modes (back to top)
There are three distinct modes of VTM-4 engagement:
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 electronic control unit
(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 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 engine power is
delivered to the front wheels for improved fuel efficiency.
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.
The third mode of engagement is VTM-4 Lock. Lock m
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Honda Forums > Honda Models > CR-V Forum
Jan 24 2003, 07:48 PM
