How a simple reactive balance beam tandem axle suspension system helps maintaining the ground contact between wheels and uneven road surfaces for multi axle trucks and trailers – that you may already know. Although, the simple tandem axle suspension systems works fine in case the vehicle is moving at (almost) constant speed, but it fails to serve the purpose while the vehicle is in acceleration and deceleration. Why?
Limitations of the simple tandem axle suspension suspension:
Look at the below figure, it is showing the momentary situation of a simple balance beam tandem axle suspension system while the vehicle is accelerating. Ta1 and Ta2 are the applied torques to the wheels by the axles and Tr1 and Tr2 are the reaction torques by the wheels to the axles.
The reaction torques Tr1 and Tr2 creates a couple in the reactive balance beam by applying two equal and opposite force shown as F in the above figure. As a result of the applied on the reactive balance beam, the front wheel goes downward and the rear wheel comes closer to the frame (or chassis) and the rear wheel losses its contact with the ground while acceleration.
The opposite situation is created in case of applying brakes, the front wheel losses its contact.
How a Reactive Balance Beam Tandem Axle Suspension with Slipper Contact Blocks and Torque Arms can help in above situation: The below picture is showing the overall arrangement of this type of suspension systems.
The most distinguishing feature from this configuration of the suspension system from the earlier one is Sliper block and torsion rod. The ends of the leaf springs connected with the slipper blocks causes the leaf springs to have oscillating motion as shown by the blue arrows. In this type of suspension system as the created couple (by F as explained in the above paragraph) tries to push the front wheel downward, the torsion rod converts that movement to the oscillating movement through the slipper block. Thus no wheel losses contacts in case of the reactive balance beam tandem axle suspension with slipper contact blocks and torque arms.