Electrically controlled pressure relief valve system and method

An agricultural combine with an electrically controlled pressure relief valve system for varying the maximum allowable line pressure in an associated hydraulic fluid line in response to an electrical signal, comprising:

• an inlet line for containing hydraulic fluid under pressure;
• a tank line leading to a hydraulic fluid tank at a relatively low pressure to that normally contained in said inlet line;
• a proportional, pressure relief valve located in line between said inlet line and said tank line, blocking the two off when a relatively low pressure exists in said inlet line, said pressure relief valve including
• a cartridge,
• a longitudinally extended cage held by said cartridge and associated with said inlet line,
• a longitudinally movably, centrally open pilot spool located within said cage and in fluid communication with said inlet line, said spool having a front orifice associated with the centrally open area of said spool and communicating with said inlet line and having a substantially smaller cross-sectional area than the most adjacent part of said inlet line, causing a pressure drop across said spool as fluid passes through said orifice from said inlet line, and said cage having a back orifice associated with said centrally open area through which fluid can flow under certain pressure conditions to said tank line,
• a valve element seat surrounding said back orifice,
• a longitudinally movable valve element associated with said seat tending to close off said back orifice tending to prevent fluid flow through it, and
• biasing spring means associated with said movable valve element for applying an initial, minimum resistive biasing force against said valve element tending to keep it seated in said seat;
• a direct, side port leading from said inlet line to said tank, said port having a cross-sectional area substantially greater than said front orifice and being located in juxtaposition to the side of said pilot spool and being normally blocked off by said spool under the action of said biasing spring at least until the pressure in said inlet line at least equals the resistive biasing force but, as the inlet pressure increases, said pilot spool tending to allow hydraulic fluid to flow from said inlet line through said front orifice to said centrally open area through said back orifice overcoming the biasing force of said spring to said tank, upon which said spool begins to move back until it exposes said port to said inlet line, causing the relatively high pressure of said inlet line to be limited by the relatively low pressure in said tank line;
• electrical means associated with said valve element for applying a supplemental resistive force to it, increasing the resistive pressure upon it over the initial, biasing spring force, further tending to keep said valve element seated, closing off any fluid flow through said back orifice;
• electrical signal means associated with said electrical means for varying the amount of resistive force applied by said electrical means to said valve element, allowing the maximum allowed pressure allowed in said inlet line before its is exhausted to said tank line to be variously set by utilizing said electrical signal;
• and
• work means associated with said inlet line, which work means is caused to do desirable work at a rate set in accordance with the varying set maximum pressure levels in said inlet line, said electrical signal means effectively controlling said work means in accordance with the electrical signal produced by said electrical signal means, said work means including:
• an agricultural combine;
• a combine header carried by said combine;
• an hydraulic circuit associated with said inlet line, said tank line and said pressure relief valve;
• hydraulic lift means included in said circuit and connected to said header for moving said combine header to a vertical position off of the ground and at a speed dependent upon the hydraulic pressure existent in said inlet line, said hydraulic lift means including
• a gravity lowered hydraulic ram connected to said combine head;
• and
• an "on/off" control valve connected between said hydraulic ram and said inlet line controlling the hydraulic fluid pressure supplied to said ram controlling its direction and speed of movement in conjunction with said pressure relief valve,
• ground contour sensing means associated with said combine measuring the changing contour of the ground over which said combine travels as the combine travels over the ground and is being operatively used, said ground contour sensing means including a ski sled carried by said combine in contact with the ground;
• and
• computer means associated with said combine for interpreting the output of said ground sensing means and controlling said electrical signal means producing appropriate electrical signals to be sent to said electrical means appropriately changing the set maximum allowed pressure allowed in said inlet line, appropriately moving said combine header in response thereto.

A method of varying the maximum allowable line pressure in an associated fluid line in response to an electrical signal, comprising the following steps:

• (a) utilizing an electrically controlled pressure relief valve system, including
• an inlet line for containing fluid under pressure;
• a tank line leading to a fluid tank at a relatively low pressure to that normally contained in said inlet line;
• a proportional, pressure relief valve located in line between said inlet line and said tank line, blocking the two off when a relatively low pressure exists in said inlet line, said pressure relief valve having
• a cartridge,
• a longitudinally extended cage held by said cartridge and associated with said inlet line,
• a longitudinally movably, centrally open pilot spool located within said cage and in fluid communication with said inlet line, said spool having a front orifice associated with the centrally open area of said spool and communicating with said inlet line and having a substantially smaller cross-sectional area than the most adjacent part of said inlet line, causing a pressure drop across said spool as fluid passes through said orifice from said inlet line, and said cage having a back orifice associated with said centrally open area through which fluid can flow under certain pressure conditions to said tank line,
• a valve element seat surrounding said back orifice,
• a longitudinally movable valve element associated with said seat tending to close off said back orifice tending to prevent fluid flow through it, and
• biasing spring means associated with said movable valve element for applying an initial, minimum resistive biasing force against said valve element tending to keep it seated in said seat;
• a direct, side port leading from said inlet line to said tank, said port having a cross-sectional area substantially greater than said front orifice and being located in juxtaposition to the side of said pilot spool and being normally blocked off by said spool under the action of said biasing spring at least until the pressure in said inlet line at least equals the resistive biasing force but, as the inlet pressure increases, said pilot spool tending to allow fluid to flow from said inlet line through said front orifice to said centrally open area through said back orifice overcoming the biasing force of said spring to said tank, upon which said spool begins to move back until it exposes said port to said inlet line, causing the relatively high pressure of said inlet line to be limited by the relatively low pressure in said tank line;
• electrical means associated with said valve element for applying a supplemental resistive force to it, increasing the resistive pressure upon it over the initial, biasing spring force, further tending to keep said valve element seated, closing off any fluid flow through said back orifice;
• electrical signal means associated with said electrical means for varying the amount of resistive force applied by said electrical means to said valve element, allowing the maximum allowed pressure allowed in said inlet line before its is exhausted to said tank line to be variously set by utilizing said electrical signal;
• and
• work means associated with said inlet line, which work means is caused to do desirable work at a rate set in accordance with the varying set maximum pressure levels in said inlet line, said electrical signal means effectively controlling said work means in accordance with the electrical signal produced by said electrical signal means;
• and
• (b) varying the electrical signal to said electrical means to vary the maximum allowed pressure allowed in said inlet line, controlling said work means in accordance with the electrical signal produced by said electrical signal means.