Engine speed control for hoist and tongs

A mobile service rig for servicing a well, comprising:

• an engine having a lower speed mode and a higher speed mode wherein said engine operates within a first speed range in said lower speed mode and operates within a second speed range in said higher speed mode with a first average speed of said first speed range being lower than a second average speed of said second speed range;
• a transmission that includes an input shaft, a first output shaft and a second output shaft with said input shaft being coupled to said engine, said transmission having a low-gear operation and a high-gear operation, wherein a ratio of speed of said first output shaft to said input shaft is greater in said high-gear operation than in said low-gear operation;
• a hoist coupled to said first output shaft;
• a hydraulic pump coupleable to said engine;
• a hydraulic motor hydraulically coupled to said hydraulic pump;
• a tong driven by said hydraulic motor;
• a drive wheel adapted to propel said mobile service rig and being coupled to said second output shaft;
• and
• a flow restriction in fluid communication with said hydraulic pump and said hydraulic motor, said flow restriction being adapted to convey a fluid flow therethrough, said flow restriction having a flow coefficient that increases with a decrease in a pressure differential applied thereacross, wherein said flow coefficient is defined as a ratio of said fluid flow to said pressure differential.

A mobile service rig for servicing a well, comprising:

• an engine having a lower speed mode and a higher speed mode wherein said engine operates within a first speed range in said lower speed mode and operates within a second speed range in said higher speed mode with a first average speed of said first speed range being lower than a second average speed of said second speed range;
• a transmission that includes an input shaft, a first output shaft and a second output shaft with said input shaft being coupled to said engine, said transmission having a low-gear operation and a high-gear operation, wherein a ratio of speed of said first output shaft to said input shaft is greater in said high-gear operation than in said low-gear operation;
• a hoist coupled to said first output shaft;
• a hydraulic pump coupleable to said engine;
• a hydraulic motor hydraulically coupled to said hydraulic pump;
• a tong driven by said hydraulic motor;
• a drive wheel adapted to propel said mobile service rig and being coupled to said second output shaft;
• a flow restriction in fluid communication with said hydraulic pump and said hydraulic motor, said flow restriction being adapted to convey a fluid flow therethrough, said flow restriction having a flow coefficient that increases with a decrease in a pressure differential applied thereacross, wherein said flow coefficient is defined as a ratio of said fluid flow to said pressure differential;
• a pressure relief valve in fluid communication with said hydraulic pump, said pressure relief valve being more open when said engine is at said higher speed mode than when said engine is as said lower speed mode;
• and
• a speed adjuster operatively coupled to said engine and being adapted to selectively determine said lower speed mode and said higher speed mode;
• wherein said engine in said lower speed mode and said transmission in said high-gear operation renders said mobile service rig operable in a reduced power mode suitable for normal tong operation and relatively light hoisting;
• and wherein said engine in said higher speed mode renders said mobile service rig operable in a higher power mode suitable for normal tong operation and relatively heavy hoisting.