JPH0530615U - Transmission for construction vehicles - Google Patents

Abstract

(57) [Summary] [Purpose] To downsize a transmission and facilitate switching between constant speed control and automatic transmission control. [Structure] A variable displacement motor 6 is provided with a control cylinder 1 for speed control and a solenoid valve 11 for operating the control cylinder, and hydraulic pumps PSA, PSB are provided in operating pipe lines 12A, 12B of the variable displacement motor 6, When the load in the second speed running increases and the hydraulic pressure in the work lines 12A, 12B rises, the hydraulic switches 12A, 12B switch the solenoid valve 11 and the control cylinder switches the variable displacement motor 6 to the first speed. A switch for switching between constant speed control and speed change control is attached to the shift lever.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a transmission for a construction vehicle such as a wheel loader.

[0002]

[Prior Art]

 As shown in FIG. 4, a transmission of a conventional construction vehicle is a hydraulic transmission in which a variable displacement motor 6 is provided with a control cylinder 1, a pressure control valve 2, a shuttle valve 3, a low pressure communication valve 4, and a low pressure relief valve 5. The device is being used. Pressure oil is supplied to one of the main ports A and B of the variable displacement motor 6 from a hydraulic pump (not shown), and the variable displacement motor 6 is supplied depending on which of the main ports A and B the pressure oil is supplied from. The rotation direction of the motor body 7 is determined. The switching is performed by operating the shift lever 15 shown in FIG.

When the pressure oil is supplied from the main port B, the oil pressure of the main port B is guided from the port B _{1 to the} shuttle valve 3 to shut off the port A ₁ and at the same time, from the port C ₁ to the pressure control valve 2. Although guided to the pilot port C ₄ , the position shown in the figure is maintained while the pressure at the main port B is low. Therefore, the oil pressure of the main port B acts on one oil chamber RB of the control cylinder 1, and the other oil chamber RA communicates with the tank T via the pressure control valve 2, so that the piston 8 of the control cylinder 1 Sets the tilt angle of the motor body 7 to the minimum capacity position. At this time, the speed stage of the construction vehicle 10 becomes the second speed.

Under operating conditions such that the running load of the construction vehicle 10 becomes large, the pressure of the main port B rises, and when the set pressure of the pressure control valve 2 is reached, the pressure control valve 2 is switched, Port C ₂ and port C ₃ communicate with each other. Therefore, the hydraulic pressure from the main port B also acts on the oil chamber RA of the control cylinder 1, but since the pressure receiving area of the oil chamber RA is larger than the pressure receiving area of the oil chamber RB, the piston B of the control cylinder 1 is mounted on the motor main body. The inclination angle of 7 is the maximum capacity position. At this time, the speed stage of the construction vehicle 10 becomes the first speed.

When pressure oil is supplied from the main port A, the rotation direction of the motor body 7 is reversed. Also, the hydraulic pressure of the main port A is₁From shuttle port 3 to port B ₁ Shut off port C at the same time₁Is applied to the pressure control valve 2 and the control cylinder 1 to perform the same shift control as in the case where the pressure is supplied from the main port B. The low-pressure communication valve 4 connects the low-pressure side of the main ports A and B to the low-pressure relief valve 5 to drain a part of the hydraulic oil to prevent an abnormal rise in the hydraulic temperature of the hydraulic oil in the closed circuit. Remove foreign matter inside.

In some cases, it may be more convenient to fix the speed of the construction vehicle 10 to the first speed without performing the above-described automatic shift control during work or the like. Therefore, conventionally, as shown in FIG. 5, the dashboard 16 is provided with a dedicated control changeover switch CS for switching between the constant speed control which is fixed to the first speed and the automatic speed change control.

[0007]

[Problems to be solved by the device]

 Conventional hydraulic transmissions have a built-in pressure control valve and shuttle valve for automatic shifting, so the variable displacement motor becomes large, especially for small construction vehicles such as small wheel loaders where space is limited. As a result, assembly and maintenance are difficult and inappropriate, and the cost is high.

Further, since the control changeover switch is provided at a position apart from the forward / reverse shift lever, the shift lever is used to switch between forward / backward movement, while at the same time fixing the first speed and automatically shifting. Switching is difficult. This invention solves the above-mentioned problem in the transmission of a construction vehicle, and makes it possible to reduce the size of a variable displacement motor, to facilitate assembly and maintenance on a small construction vehicle, and to reduce the cost. It is an object of the present invention to provide a transmission for a construction vehicle that can be performed, and also provide a transmission for a construction vehicle in which a switching operation between constant speed control and shift control is easy.

[0009]

[MEANS FOR SOLVING THE PROBLEMS] To solve the above-mentioned problems, a transmission apparatus for a construction vehicle according to the present invention is provided with a variable displacement motor, a control cylinder for speed control, and an electromagnetic valve for switching a control line to this control cylinder. And a hydraulic switch for switching the solenoid valve at a predetermined pressure in the actuation pipe of the variable displacement motor.

Further, a control changeover switch for changing over between constant speed control and speed change control is provided on the shift lever for forward and backward switching.

[0011]

[Action]

 When performing shift control, when the traveling load of the construction vehicle is small, the working line of the variable displacement motor is at low pressure and the hydraulic switch is off. At this time, the tilt angle of the variable displacement motor is at the minimum displacement position. . When the running load of the construction vehicle increases, the pressure in the working line of the variable displacement motor rises, the hydraulic switch is turned on at a predetermined pressure, the solenoid valve is switched, and the tilt angle of the variable displacement motor is set to the maximum displacement position. Change the speed stage of the construction vehicle to 1st speed.

When performing constant speed control, the shift lever for forward / reverse switching is operated to switch the control switching switch to the constant speed side, whereby the solenoid valve is turned on regardless of whether the hydraulic switch is ON or OF. The construction vehicle is run at a constant speed by holding it at a fixed position and fixing the tilt angle of the variable displacement motor. Switching between forward and backward movement is performed by operating a shift lever for forward and backward movement to change the direction of supply of pressure oil to the working pipe of the variable displacement motor.

[0013]

【Example】

 FIG. 1 is a hydraulic circuit diagram of a transmission for a construction vehicle according to an embodiment of the present invention, and FIG. 2 is an electric circuit diagram thereof. Here, in the variable displacement motor 6 that drives the construction vehicle 10, the control cylinder 1 that controls the speed by changing the inclination angle of the motor body 7 from the minimum displacement position to the maximum displacement position, and the piston 8 of this control cylinder 1. And a solenoid valve 11 for switching the control lines 9A and 9B to the oil chambers RA and RB on both sides of. Further, pressure switches PSA and PSB for switching the solenoid valve 11 at a predetermined pressure are provided in the operation pipe lines 12A and 12B of the variable displacement motor 6.

The solenoid S of the solenoid valve 11 is connected to the power source E via the normally closed contact NC1 of the relay R1, and the coil C _{1 of the} relay R1 is connected to the first speed fixed side terminal X of the control changeover switch CS. It is connected to the normally open contact NO2 of the relay R2. The hydraulic switches P SA and PSB are connected in parallel to the ground side of the coil C ₂ of the relay R2. Moreover, a diode D is connected between the hydraulic switches PSA and PSB and the coil of the relay R2 to prevent the hydraulic switches PSA and PSB from being damaged by an overcurrent. The power source side terminal COM of the relay R2 is connected to the speed change side terminal Y 1 of the control changeover switch CS.

FIG. 3 is an explanatory view showing the operating position of the shift lever to which the control changeover switch CS is attached. The shift lever 15 is attached near the steering wheel 18 above the steering column 17 which is provided upright after the dashboard 16. The shift lever 15 can move up and down and back and forth around the fulcrum 0. The upper position is the first speed fixed position PX, the lower position is the shift position PY, the front position is the forward position PF, and the rear position is the reverse position PR. , The center is the neutral position PN.

When the shift lever 15 is lowered to the shift position PY, the shift side terminal Y of the control changeover switch CS is turned on. The forward / backward movement of the construction vehicle 10 can be arbitrarily selected by moving the shift lever 15 back and forth in this state. If in-line construction vehicle 10 is low-load run, operating line 12A, 12B is the oil pressure of lower than the set value, the oil pressure switch PSA, since PSB is the OFF state, the coils C ₂ of the relay R2 to the ground side Continuity is cut off. Thus, the normally open contact NO2 is open or Mananode of the relay R2, the coil C ₁ of the relay R1 is also a de-energized state. Therefore, the solenoid S of the solenoid valve 11 is in an excited state, and the solenoid valve 11 supplies pressure oil from the control line 9B to one oil chamber RB of the control cylinder 1 to set the tilt angle of the motor body 7 to the minimum displacement position. Therefore, the traveling speed of the construction vehicle 1 is maintained at the second speed.

When the construction vehicle 10 is in a high-load running state, the hydraulic pressure of one of the operation pipe lines 12A, 12B of the variable displacement motor 6 reaches the set pressure, and one of the pressure switches PSA, PSB is in the ON state. Since the coil C _{2 of the} relay R2 is energized and excited, the normally open contact NO2 of the relay R2 is closed and the coil C _{1 of the} relay R1 is also energized. Then, the normally closed contact NC1 of the relay R1 is opened and the solenoid S of the solenoid valve 11 is de-energized, and the solenoid valve 11 supplies pressure oil from the control line 9A to the other oil chamber RA of the control cylinder 1 to supply the motor main body. Since the inclination angle of 7 is the maximum capacity position, the speed of the construction vehicle 10 is switched to the 1st speed.

When the speed of the construction vehicle is fixed to the 1st speed, if the shift lever 15 is raised to the 1st speed fixed position PX, the 1st speed fixed terminal X of the control changeover switch CS is turned on. Then, the coil C _{1 of the} relay R1 is excited, the normally-closed contact NC1 of the relay R1 is opened, the solenoid S of the solenoid valve 11 is de-energized, and the solenoid valve 11 supplies the pressure oil from the control line 9A to the control cylinder. The oil is supplied to the first oil chamber RA and the speed of the construction vehicle 10 is set to the first speed. At this time, the coil C _{1 of the} relay R1 continues to be excited regardless of the ON / OFF operation of the hydraulic switches PSA, PSB and the relay R2, so that the variable displacement motor 6 is always held at the maximum displacement position, and the construction vehicle 10 has a large displacement. The running speed is fixed at 1st speed.

[0019]

[Effect of the device]

 As described above, the transmission for a construction vehicle according to the present invention is equipped with a hydraulic switch in the working line of the variable displacement motor to convert hydraulic pressure into an electric signal. Can be done easily. Further, since the variable displacement motor can be downsized without providing a pressure control valve, a shuttle valve, etc., it can be easily mounted on a small construction vehicle and the cost can be reduced.

Further, by providing the shift lever with a changeover switch for switching between the constant speed control and the shift control, the operability is improved.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram of a transmission of a construction vehicle according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of a transmission of a construction vehicle.

FIG. 3 is an explanatory diagram of an operation position of a shift lever equipped with a control changeover switch.

FIG. 4 is an explanatory diagram of a conventional transmission for a construction vehicle.

FIG. 5 is an explanatory view of the arrangement of a conventional shift lever and a control changeover switch.

[Explanation of symbols]

 1 Control Cylinder 6 Variable Capacity Motor 9A Control Pipeline 9B Control Pipeline 10 Construction Vehicle 11 Solenoid Valve 12A Actuating Pipeline 12B Actuating Pipeline 15 Shift Lever PSA Hydraulic Switch PSB Hydraulic Switch CS Control Changeover Switch

Claims (2)

[Scope of utility model registration request] 1. A hydraulic transmission for a construction vehicle capable of controlling forward and backward movement and speed stages, wherein a variable displacement motor includes a control cylinder for speed control, and a solenoid valve for switching a control line to the control cylinder. And a hydraulic switch for switching the solenoid valve at a predetermined pressure is provided in the actuating pipe of the variable displacement motor. 2. The transmission apparatus for a construction vehicle according to claim 1, wherein a control changeover switch for switching between constant speed control and shift control is provided on a shift lever for forward / backward movement.