Method of and system for controlling hydraulic power system

A method of controlling a hydraulic power system comprising an internal combustion engine receiving a supply of fuel from a fuel injection pump, and at least one variable displacement hydraulic pump driven by the internal combustion engine, the method comprising the steps of:

• (a) obtaining an engine speed deviation from the difference between a target speed set by an accelerator operation of the internal combustion engine and an output speed of the engine;
• (b) obtaining a fuel injection target value based on at least said engine speed deviation, said fuel injection target value being in a predetermined functional relationship to said deviation;
• (c) controlling a fuel injection rate of said fuel injection pump based on said fuel injection target value;
• (d) determining, at the same time, a displacement volume target value of said hydraulic pump based on at least said engine speed deviation and an actual discharge pressure of the hydraulic pump in such a manner that an input torque of the hydraulic pump decreases as the engine speed deviation increases;
• (e) controlling the displacement volume of the hydraulic pump based on the displacement volume target value;
• and
• wherein step (b) comprises:
• (i) judging whether said target speed is in an idling range, an intermediate speed range, or a high speed range;
• (ii) obtaining said fuel injection target value from said engine speed deviation based on a first function set beforehand when the target speed is in the idling speed range;
• (iii) obtaining said fuel injection target value from said engine speed deviation based on a second function set beforehand when the target speed is in the intermediate speed range;
• and
• (iv) obtaining said fuel injection target value from the engine based on a present third function when the target speed is in the high speed range.

A method of controlling a hydraulic power system comprising an internal combustion engine receiving a supply of fuel from a fuel injection pump, and at least one variable displacement hydraulic pump driven by the internal combustion engine, the method comprising the steps of:

• (a) obtaining an engine speed deviation from the difference between a target speed set by an accelerator operation of the internal combustion engine and an output speed of the engine;
• (b) obtaining a fuel injection target value based on at least said engine speed deviation, said fuel injection target value being in predetermined functional relationship to said deviation;
• (c) controlling a fuel injection rate of said fuel injection pump based on said fuel injection target value;
• (d) determining, at the same time, a displacement volume target value of said hydraulic pump based on at least said engine speed deviation and an actual discharge pressure of the hydraulic pump in such a manner that an input torque of the hydraulic pump decreases as the engine speed deviation increases;
• (e) controlling the displacement volume of the hydraulic pump based on the displacement volume target value;
• and
• wherein step (d) comprises:
• (i) calculating the displacement volume target value from said engine speed deviation and said actual discharge pressure of the hydraulic pump based on a preset functional relationship in such a manner that as the engine speed deviation increases the product of the actual discharge pressure of the hydraulc pump and the displacement volume target value thereof decreases.

A system for controlling a hydraulic power system comprising an internal combustion engine receiving a supply of fuel from a fuel injection pump, and at least one variable displacement hydraulic pump driven by the internal combustion engine, the system comprising:

• (a) means for obtaining an engine speed deviation from the difference between a target speed set by an accelerator operation of the internal combustion engine and an output speed of the engine;
• (b) means for obtaining a fuel injection target value based on at least said engine speed deviation, said fuel injection target value being in predetermined functional relation to said deviation;
• (c) means for controlling a fuel injection rate of said fuel injection pump based on said fuel injection target value;
• (d) means for determining, at the same time, a displacement volume target value of said hydraulic pump based on at least said engine speed deviation and an actual discharge pressure of the hydraulic pump in such a manner that the input torque of the hydraulic pump decreases as the engine speed deviation increases;
• and
• (e) means for controlling the displacement volume of the hydraulic pump based on the displacement volume target value.

A method of controlling a hydraulic power system comprising an internal combustion engine receiving a supply of fuel from a fuel injection pump, and at least one variable displacement hydraulic pump driven by the internal combusion engine, the method comprising the steps of:

• (a) obtaining an engine speed deviation from the difference between a target speed set by an accelerator operation of the internal combustion engine and an output speed of the engine;
• (b) obtaining a fuel injection target value based on at least said engine speed deviation, said fuel injection target value being in a predetermined functional relationship to said deviation;
• (c) controlling a fuel injection rate of said fuel injection pump based on said fuel injection target value;
• (d) determining, at the same time, a displacement volume target value of said hydraulic pump based on at least said engine speed deviation and an actual discharge pressure of the hydraulic pump in such a manner that an input torque of the hydraulic pump decreases as the engine speed deviation increases;
• (e) controlling the displacement volume of the hydraulic pump based on the displacement volume target value;
• and
• wherein in step (b), said fuel injection target value is in the functional relationship to said engine speed deviation in such a manner that the target value increases until the deviation reaches a predetermined value and the increase in the target value is restricted thereafter, and in step (d), the decrease in the input torque of the hydraulic pump is initiated when the deviation at least approximately reaches said predetermined value at least when said target speed is in a high speed range.