Speed changing device, speed changer and speed changing method of hydraulic engineering machinery

The invention discloses hydraulic engineering machinery and a speed changer thereof. The speed changer comprises a shell, a sun wheel, at least one planet wheel, a double-faced gear ring and an output gear, and further comprises a planet carrier connected with the planet wheel, wherein the sun wheel, the planet wheels, the double-faced gear ring and the output gear are arranged in the shell and are sequentially meshed, an inner circle and an outer circle of the double-faced gear ring are provided with mesh teeth, an input shaft of the speed changer is arranged on the planet carrier. The speed changer further comprises a first clutch and a second clutch. When the first clutch and the second clutch are disengaged, the rotating speed of the input shaft is zero, and the speed changer is located at a neutral position; when the first clutch is engaged and the second clutch is disengaged, the planet wheels, the sun wheel and the gear ring are connected into a whole, and the speed changer is located at the low position; when the first clutch is disengaged and the second clutch is engaged, the rotating speed of the sun wheel is zero, and the speed changer is located at the high position. The speed changer can achieve the intelligent change of the transmission speed ratio of a prime motor and a hydraulic pump, the load rate of the prime motor can be increased when the load of the hydraulic pump is small, and the purpose of saving energy is achieved. The invention further discloses a speed changing method of the hydraulic engineering machinery.