Fan Drive System

Abstract

A fan drive system for driving an engine cooling fan mounted in a working machine is described. The fan drive system includes a variable displacement pump that supplies oil to an actuator and is also used as a hydraulic pump for the hydraulic motor that drives the cooling fan. A pump displacement of a variable displacement pump can be controlled in accordance with the load of the working machine, and when a load is not generated in the working machine, the pump displacement of the variable displacement pump can be controlled in accordance with a load pressure of a hydraulic motor which drives a cooling fan. Examples of such working machines include a forklift, a skid steer loader (SSL) and a crawler dump.

1 . A fan drive system comprising:
 a load pressure sensitive variable displacement pump;   a work machine circuit and a flow rate control valve to which a discharge flow rate from the variable displacement pump is supplied;   a load pressure separation valve which is controlled by a maximum load pressure in the working machine circuit;   a hydraulic motor which drives a cooling fan;   a first discharge oil path which connects the variable displacement pump and the working machine circuit with each other;   a second discharge oil path which is branched from the first discharge oil path and which is connected to the flow rate control valve with each other;   a supply oil path which connects the flow rate control valve and the hydraulic motor with each other;   a first pilot oil path which takes out the maximum load pressure in the working machine circuit;   a second pilot oil path which takes out a load pressure that drives the hydraulic motor; and   a shuttle valve which selects a high-pressure-side load pressure between the maximum load pressure in the first pilot oil path and the load pressure in the second pilot oil path,   wherein a pump displacement of the variable displacement pump is controlled in accordance with a differential pressure between the high-pressure-side load pressure selected by the shuttle valve and a pump pressure of the variable displacement pump,   wherein, the load pressure separation valve is disposed in the second pilot oil path,   wherein the load pressure separation valve is controlled in accordance with a differential pressure between a pressing force by the maximum load pressure taken out by the first pilot oil path and a biasing force of a spring applied to the load pressure separation valve,   wherein, when the pressing force by the maximum load pressure is greater than the biasing force of the spring, the load pressure separation valve is switched from a position where the second pilot oil path is brought into communication with the shuttle valve to a position where the second pilot oil path is brought into communication with a tank, and a tank pressure is led to the shuttle valve, and   wherein, when the pressing force by the maximum load pressure is smaller than the biasing force of the spring, the load pressure separation valve is switched from the position where the second pilot oil path is brought into communication with the tank to the position where the second pilot oil path is brought into communication with the shuttle valve, and the load pressure which drives the hydraulic motor is led to the shuttle valve.   
     
     
         2 . A fan drive system comprising:
 a load pressure sensitive variable displacement pump;   a working machine circuit and a flow rate control valve to which a discharge flow rate from the variable displacement pump is supplied;   a load pressure separation valve which is controlled by a maximum load pressure in the working machine circuit;   a hydraulic motor which drives a cooling fan;   a first discharge oil path which connects the variable displacement pump and the working machine circuit with each other;   a second discharge oil path which is branched from the first discharge oil path and which is connected to the flow rate control valve with each other;   a supply oil path which connects the flow rate control valve and the hydraulic motor with each other;   a first pilot oil path which takes out the maximum load pressure in the working machine circuit;   a second pilot oil path which takes out a load pressure that drives the hydraulic motor; and   a throttle disposed in the second pilot oil path; and   a shuttle valve which selects a high-pressure-side load pressure between the maximum load pressure in the first pilot oil path and the load pressure in the second pilot oil path,   wherein a pump displacement of the variable displacement pump is controlled in accordance with a differential pressure between the high-pressure-side load pressure selected by the shuttle valve and a pump pressure of the variable displacement pump,   wherein, the second pilot oil path is branched into two oil paths downstream of the throttle, one of the branched oil paths is connected to the shuttle valve,   wherein, the load pressure separation valve is disposed at an intermediate portion of the other oil path, and the other oil path is connected to a tank,   wherein, the load pressure separation valve is controlled in accordance with a differential pressure between a pressing force by the maximum load pressure taken out from the first pilot oil path and a biasing force of a spring applied to the load pressure separation valve,   wherein, when the pressing force by the maximum load pressure is greater than the biasing force of the spring, the load pressure separation valve is switched to a position where the other oil path is brought into communication with the tank, and a tank pressure is led to the shuttle valve, and   wherein, when the pressing force by the maximum load pressure is smaller than the biasing force of the spring, the load pressure separation valve is switched from the position where the other oil path is brought into communication with the tank to a position where a communication is shut off, and the load pressure which drives the hydraulic motor is led to the shuttle valve.   
     
     
         3 . A fan drive system comprising:
 a load pressure sensitive variable displacement pump;   a steering circuit, a working machine circuit and a flow rate control valve to which a discharge flow rate from the variable displacement pump is supplied;   a priority valve which supplies the discharge flow rate from the variable displacement pump preferentially to the steering circuit using the steering circuit as a priority circuit with respect to the working machine circuit;   a load pressure separation valve which is controlled by a maximum load pressure in the working machine circuit;   a hydraulic motor which drives a cooling fan;   a third discharge oil path which connects the variable displacement pump and the priority valve with each other;   a fourth discharge oil path which connects the priority valve and the steering circuit with each other;   a fifth discharge oil path which connects the priority valve and the working machine circuit with each other;   a sixth discharge oil path which is branched from the third discharge oil path and which is connected to the flow rate control valve;   a supply oil path which connects the flow rate control valve and the hydraulic motor with each other;   a first pilot oil path which takes out the maximum load pressure in the working machine circuit;   a second pilot oil path which takes out a load pressure for driving the hydraulic motor;   
       a third pilot oil path which takes out a load pressure in the steering circuit;
 a first shuttle valve which selects a high-pressure-side load pressure between the maximum load pressure in the first pilot oil path and the load pressure in the third pilot oil path; and 
 a second shuttle valve which selects a high-pressure-side load pressure between the high-pressure-side load pressure selected by the first shuttle valve and the load pressure in the second pilot oil path, 
 wherein a pump displacement of the variable displacement pump is controlled in accordance with a differential pressure between the high-pressure-side load pressure selected by the second shuttle valve and a pump pressure of the variable displacement pump, 
 wherein, the load pressure separation valve is disposed in the second pilot oil path, 
 wherein, the load pressure separation valve is controlled in accordance with a differential pressure between a pressing force by the maximum load pressure taken out from the first pilot oil path and a biasing force of a spring applied to the load pressure separation valve, 
 wherein, when the pressing force by the maximum load pressure is greater than the biasing force of the spring, the load pressure separation valve is switched from a position where the second pilot oil path is brought into communication with the second shuttle valve to a position where the second pilot oil path is brought into communication with a tank, and a tank pressure is led to the second shuttle valve, and 
 wherein, when the pressing force by the maximum load pressure is smaller than the biasing force of the spring, the load pressure separation valve is switched from the position where the second pilot oil path is brought into communication with the tank to the position where the second pilot oil path is brought into communication with the second shuttle valve, and the load pressure for driving the hydraulic motor is led to the second shuttle valve. 
 
     
     
         4 . A fan drive system comprising:
 a load pressure sensitive variable displacement pump; a steering circuit, a working machine circuit and a flow rate control valve to which a discharge flow rate from the variable displacement pump is supplied;   a priority valve which supplies the discharge flow rate from the variable displacement pump preferentially to the steering circuit using the steering circuit as a priority circuit with respect to the working machine circuit;   a load pressure separation valve which is controlled by a maximum load pressure in the working machine circuit;   a hydraulic motor which drives a cooling fan;   a third discharge oil path which connects the variable displacement pump and the priority valve with each other;   a fourth discharge oil path which connects the priority valve and the steering circuit with each other;   a fifth discharge oil path which connects the priority valve and the working machine circuit with each other;   a sixth discharge oil path which is branched from the third discharge oil path and which is connected to the flow rate control valve;   a supply oil path which connects the flow rate control valve and the hydraulic motor with each other;   a first pilot oil path which takes out the maximum load pressure in the working machine circuit;   a second pilot oil path which takes out a load pressure for driving the hydraulic motor;   a third pilot oil path which takes out a load pressure in the steering circuit;   a throttle disposed in the second pilot oil path;   a first shuttle valve which selects a high-pressure-side load pressure between the maximum load pressure in the first pilot oil path and the load pressure in the third pilot oil path; and   a second shuttle valve which selects a high-pressure-side load pressure between the high-pressure-side load pressure selected by the first shuttle valve and the load pressure in the second pilot oil path,   wherein a pump displacement of the variable displacement pump is controlled in accordance with a differential pressure between the high-pressure-side load pressure selected by the second shuttle valve and a pump pressure of the variable displacement pump,   wherein, the second pilot oil path is branched into two oil paths downstream of the throttle, one of the branched oil paths is connected to the second shuttle valve,   wherein, the load pressure separation valve is disposed in an intermediate portion of the other oil path, and the other oil path is connected to a tank,   wherein, the load pressure separation valve is controlled in accordance with a differential pressure between a pressing force by the maximum load pressure taken out from the first pilot oil path and a biasing force of a spring applied to the load pressure separation valve,   wherein, when the pressing force by the maximum load pressure is greater than the biasing force of the spring, the load pressure separation valve is switched to a position where the other oil path is brought into communication with the tank, and a tank pressure is led to the second shuttle valve, and   wherein, when the pressing force by the maximum load pressure is smaller than the biasing force of the spring, the load pressure separation valve is switched from the position where the other oil path is brought into communication with the tank to a position where a communication is shut off, and the load pressure for driving the hydraulic motor is led to the second shuttle valve.   
     
     
         5 . The fan drive system according to  claim 1 , wherein the flow rate control valve is controlled in accordance with a temperature of a coolant. 
     
     
         6 . The fan drive system according to  claim 2 , wherein the flow rate control valve is controlled in accordance with a temperature of a coolant. 
     
     
         7 . The fan drive system according to  claim 3 , wherein the flow rate control valve is controlled in accordance with a temperature of a coolant. 
     
     
         8 . The fan drive system according to  claim 4 , wherein the flow rate control valve is controlled in accordance with a temperature of a coolant.