Pressure-compensation hydraulic pump, rotation speed control system and control method, and construction machinery

A construction machinery, comprising a heat radiator for cooling hydraulic oil and a rotation speed control system, wherein the rotation speed control system comprises a temperature sensor for detecting the oil temperature of the hydraulic oil, a fan motor for driving a fan to rotate, a controller and a pressure-compensation controlled hydraulic pump, the pressure-compensation controlled hydraulic pump comprises a pressure control device, a hydraulic pump and a displacement adjusting device,

• wherein the displacement adjusting device is adapted to compare a first pressure value generated by the pressure control device with a second pressure value at an oil outlet of the hydraulic pump, and to adjust the displacement of the hydraulic pump according to a result of the comparison, so that the output flow rate of the hydraulic pump is stabilized within a preset flow rate range when the rotation speed of the hydraulic pump varies, and wherein the temperature sensor is electrically connected to the controller, and the controller is arranged to receive a signal from the temperature sensor and control the first pressure value generated by the pressure control device according to the signal, and the pressure generated by the fan motor when driving the fan is fed back to the oil outlet of the hydraulic pump to form the second pressure value, and wherein the fan motor is arranged to drive the fan to rotate to cool the heat radiator,
• wherein the displacement adjusting device comprises a hydraulic control reversing valve and a servo cylinder for adjusting the displacement of the hydraulic pump, the oil outlet of the hydraulic pump is connected to an internal output oil path, an oil inlet of the hydraulic pump is connected to an internal input oil path, a first hydraulic control port of the hydraulic control reversing valve is connected to an internal oil drain path via the pressure control device, a piston chamber of the servo cylinder is connected to the internal output oil path and the internal oil drain path respectively via the hydraulic control reversing valve, a pressure difference between the pressure control device and an oil outlet pressure of the hydraulic pump acts on a valve spool of the hydraulic control reversing valve via the first hydraulic control port and a second hydraulic control port of the hydraulic control reversing valve to drive the hydraulic control reversing valve to perform reversing, thereby selectively enables the piston chamber of the servo cylinder to be in communication with the internal output oil path or the internal oil drain path, and
• wherein the first hydraulic control port is connected to the internal output oil path through a hydraulic control oil inlet path provided with a first throttle valve, and the second hydraulic control port of the hydraulic control reversing valve is connected to the internal output oil path.