Patent ID: 7004456
Filing Date: 2006-02-28
Classification: B66D,E21B

Abstract:
1. A mobile service rig with a hoist for exerting an upward force that varies while servicing a well, comprising: a truck frame; a drive wheel coupled to the truck frame and being adapted to propel the mobile service rig; a hoist drum supported by the truck frame; a hoist derrick coupled to the truck frame; a cable supported by the hoist derrick and wrapped around the hoist drum; a block suspended from the cable for transmitting the upward force; an engine supported by the truck frame; a engine speed adjuster coupled to the engine for adjusting the speed thereof; a transmission driven by the engine and selectively coupled to the hoist drum and the drive wheel; a load sensor providing a load signal that varies in response to the upward force varying; and a controller having an input connected to receive the load signal and an output coupled to the engine speed adjuster, wherein the output commands the engine speed adjuster to limit the speed of the engine in response to the load signal reaching a predetermined limit.