| 摘要 |
<p>A motor vehicle is provided having an engine 11 as its prime mover, at least first and second groups of one or more wheels and a driveline to connect the prime mover to the groups of wheels in one of two modes. The first group of wheels 12, 13 is driven by the prime mover 11 when the driveline is in a first mode of operation and the second group of wheels 14, 15 is additionally driven by the prime mover 11 when in a second mode of operation. The driveline includes releasable torque transmitting means 22, 27 operable to connect the second group of wheels 14, 15 to the prime mover 11. When in the first mode, the vehicle is operable to control the driveline to assume the second mode responsive to a speed of the vehicle. This typically occurs when the vehicle slows to below a first speed threshold. When the vehicle speed increases, reversion to the first mode is delayed until a second speed threshold is exceeded. This provides control hysteresis and thus decreases the risk of rapid fluctuation between modes which would cause chatter.</p> |
