The key hint: the principle of automatic control of engine speed of Cat E240 excavator and fault detection: the AEC system is an automatic control system for high and low two speed throttle, which uses worm and worm to change the movement of the throttle lever and control the engine speed, so that the engine throttle is in high speed position when working. The engine throttle is in a low speed position when it is loaded.
Cat E240 excavator's engine speed automatic control system.
Working principle of 1 AEC system
The AEC system is an automatic control system for high and low two speed throttle, which uses worm and worm to change the movement of the throttle lever and control the engine speed, so that the engine throttle is in high speed position and the engine throttle is in low speed position when it is no-load.
1.1 when the 1.1 accelerates the joystick moving, the hydraulic signal is passed to the pressure switch 8, the switch 8 is closed, the AEC switch 9 sets the oN bit, the mode switch 10 sets the I (or II, III II I) bits, the three signal is input to the controller 7, and the controller 7 handles the signal after the output current to the standby switch 4 (0FF) ABC relay 6, and the relay 6 works, often touching the contact. Point a is closed, and often closed contact B disconnects. The current is composed of a battery eleven power switch 2, a fuse box 3, a limit contact C, a relay contact a - AEC motor 5 winding, and a closed loop. The motor 5 turns, driving the worm wheel to rotate 180. Push the accelerator to the high speed position to accelerate the engine to 2380 R / m5n. Due to the mechanical linkage of motor 5, the contact C is broken and the contact D is closed after acceleration to high speed position. The closed circuit of motor 5 accelerates, the motor stops turning, and the engine throttle is kept in high speed position. At this time the engine works at the rated speed.
1.2 when the speed control lever returns to the middle position, there is no hydraulic signal to AEC pressure to turn ABC off 8 and switch 8 to disconnect. When the controller 7 receives the signal 3S, if the switch 8 is still disconnected, the output current of the ten terminal of the SOL.B is cut off. The relay 6 is out of power, the contact a is disconnected, and the normally closed contact B is closed. The current of the battery consists of a contact D, a contact B - AEC motor 5 winding, and a closed loop is formed. The motor 5 rotates and drives the worm wheel to rotate 1800, pushing the throttle from the high speed position to the low speed position, so that the engine speed is reduced to 1300 r/min. Because of mechanical interaction, the contact D disconnects, the contact C closes the closed loop of the motor 5 reducing speed, the motor 5 stops working and the engine runs at low speed in order to save fuel.
2 failure detection Carter E240 type excavator engine throttle automatic control system common faults are:
(1) the engine throttle can not fall to the low speed automatically until it reaches the middle position.
(2) when the joystick moves, the engine throttle can not be automatically accelerated and has been in a low speed position. According to the circuit principle of AEC system, the following steps can be used for fault detection:
First, check whether fuse motor AEC and fuse controller fuse in fuse box 3.
Check AEC pressure switch 8. When the engine is running, when the joystick is in working position, the AEC pressure switch should be closed. When the s lever is in the middle position, the AEC pressure switch should be broken. If there is no movement reaction, the hydraulic signal should be detected first. When the AEc pressure switch is working, the signal oil pressure is the pilot oil pressure. When working normally, the oil pressure should be between the 4.25-4.55MPa and the lever back to the middle, and the signal oil pressure is the oil back pressure. The AEC pressure switch will be closed when signal oil pressure is greater than 2.45MPa, and will be disconnected when 2.45MPa. If the oil pressure of the detected signal is normal, the AEC pressure switch has no action response. The AEc pressure switch is damaged and should be replaced. If the detected oil pressure is abnormal, further check the signal oil pressure.
Check whether the AEc switch 9, the standby switch 4, the working mode switch 10 are damaged. Check the corresponding contact points, whether there is a short-circuit, if damaged, should be replaced.
Check AEC relay 6. The resistance of the AEC relay coil is 170 Omega, which can be measured. Check the closing of AEC relay contacts by direct power and power failure. If the damage is damaged, it should be replaced.
Check AEc motor 5, can be directly through the instant check, that is, I line iron, instant power to the f line, such as the AEc motor action, the AEC motor is perfect; conversely, should be removed or replaced. Check linkage contacts C and D, such as AEc motor in high speed position, e line and H line are connected (resistance is 0Q), e line and g line are disconnected (resistance is). ): if the AEC motor is in low speed position, the e line and the H line are disconnected (the resistance is infinity). The e line and the g line are connected (resistance is 09). If they do not meet the requirements, the contact points and linkage mechanisms should be inspected.
Check connections between wires and plugs and see if there are any circuit breakers or short circuits.
The detection controller 7. According to the contents of Table 1, the voltage parameters of each terminal of the controller are detected. AEC system for short. If the test results do not correspond to the damage of the control part of the controller (computer board), the whole controller should be replaced, the standby switch is used for emergency or the AEc control system is reformed.
3 AEC control system for the emergency reloading of the Cat E240 type excavator engine oil throttle automatic control system if the AEc motor relay control failure is caused by the internal failure of the controller. As an emergency measure, a simple time relay control loop time relay 7 can be used to select the Ds22c type electromagnetic time relay. The specifications of electrical appliances are DC 24V and normally open contacts. The setting delay range is 1.5 - 5S. According to the control function of the controller's delay 3s of the AEC relay, the DS22C power delay indication is transferred to the 3S scale position. Make a mounting bracket and install the DS22C type time relay into the electrical cabinet on the right side of the cab. According to figure 2, connect the AEC pressure switch, AEC switch, AEC relay coil, controller fuse e, cab lighting fuse F and DS22C time relay. The other original lines are unchanged. It should be specially stated that this line modification is limited to the control function of the AEC relay instead of the controller, and the original other functions of the controller remain unchanged. According to this scheme, our unit has changed two units. The effect is good. To achieve the AEC function, that is to install a time relay 7, and its power delay is 3S, instead of the control function of controller 7 in Figure 1 to relay 6.
