Air spring stiffness controller

For a vehicle having a frame suspended on wheels by a suspension system, an apparatus for adaptively controlling relative motion between the wheels and the frame, the apparatus comprising:

• an air spring disposed between the frame and at least one of the wheels, wherein the air spring comprises a primary reservoir for holding air and a piston adapted to act upon the air in the reservoir to compress the air and thereby provide support for the frame;
• an auxiliary reservoir that holds air wherein the auxiliary reservoir can be placed in fluid communication with the primary reservoir to increase an effective volume of air upon which the piston acts;
• and
• a valve that selectively places the auxiliary reservoir in communication with the primary reservoir in response to variations in pressure in the primary reservoir, wherein the valve comprises a moveable plunger that moves away from the primary reservoir when the primary reservoir pressure exceeds a threshold pressure to place the primary reservoir in communication with the auxiliary reservoir, and wherein when the pressure in the primary reservoir is reduced, the plunger returns to an original position relative to the primary reservoir under force of gravity.