Crawler excavator travel motor speed control system and method

Abstract

The present disclosure provides a kind of track excavator walking motor speed control system and method, it is related to walking motor speed control technical field, on the basis of the control of original two point variable walking motor, increase a swash plate limiting valve, swash plate limiting valve is controlled by swash plate limiting valve control valve and control oil circuit Pr2, control oil circuit Pr2 takes system high pressure oil from the rear of second one-way valve, when motor is at small displacement, swash plate limiting valve control valve is in right position when control oil circuit Pr2 has no hydraulic oil, when this swash plate limiting valve left oil cavity is high pressure, motor displacement has no change, when the motor speed needs to increase, connect control oil circuit Pr2 oil circuit, swash plate limiting valve control valve is in left position, swash plate limiting valve left cavity is connected with mailbox and releases oil, swash plate limiting valve moves to left under the action of spring force, motor swash plate angle becomes small, motor displacement reduces, when swash plate limiting valve is in left cavity limit position, motor displacement is minimum, when flow is unchanged, motor speed can increase in set range.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of walking motor speed control, in particular to a walking motor speed control system and method for a crawler excavator. BACKGROUND

[0002] The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.

[0003] The walking motor is a walking driving system for a crawler excavator, which drives the motor to rotate by supplying hydraulic oil from a pump to the walking motor through a main valve, so as to realize the walking function of the crawler excavator. Generally, two walking motors with the same configuration are provided for each crawler excavator, which are arranged on the crawler of the excavator and cooperate with a speed reducer and a crawler to realize the walking function of the excavator. The walking motor is divided into upper and lower parts, the lower part is a shell, the cavity bears the main components, and the rear cover is a multifunctional sealing cover which integrates most of the control functions of the motor. The function valve controls the flow and direction of the hydraulic oil through the valve core and oil passage openings, so as to realize the control of the motor function.

[0004] The existing walking motor for a crawler excavator is a two-point variable walking motor, and the speed of the two-point variable walking motor is divided into first and second speeds, i.e. the commonly known turtle gear and rabbit gear, which realizes fast and slow walking of the excavator. However, in the existing scheme, the speed cannot be adjusted when the system flow is constant, and the fast and slow speeds are fixed values, so the speed cannot be adjusted. SUMMARY

[0005] In order to solve the above problems, the present disclosure provides a walking motor speed control system and method for a crawler excavator, which is applied to a two-point variable walking motor, realizes swash plate limiting through a swash plate limiting valve and a control oil path, so as to make the motor realize smaller displacement, and increase the motor speed within a certain range when the flow is constant.

[0006] According to some embodiments, the present disclosure adopts the following technical scheme:

[0007] A walking motor speed control system for a crawler excavator, comprising a two-point variable walking motor, a swash plate limiting valve, a swash plate limiting valve control valve and a control oil path Pr2, the swash plate limiting valve control valve is connected with the swash plate limiting valve through the control oil path Pr2, the swash plate limiting valve is connected with a servo piston through the control oil path Pr2, the swash plate limiting valve controls the two-point variable walking motor, the pressure in the servo piston cavity is changed by changing the swash plate limiting valve and the control oil path Pr2, and then the angle of the motor swash plate is changed, so that the motor realizes smaller displacement, and the motor speed can be increased within a certain range when the flow is constant.

[0008] Further, the control oil circuit further comprises a motor oil inlet and a motor oil outlet, the motor oil inlet is connected to the oil tank, and the motor oil outlet is connected to the oil tank through a pipeline.

[0009] Further, the motor can rotate in both directions, and the balance valve in the oil circuit is reversed, and the high-pressure oil in the motor passes through the overflow valve and the throttle oil pipeline to reach the upper cavity of the buffer sleeve to achieve the buffering effect.

[0010] Further, the overflow valve is connected to the second one-way valve through a pipeline, the second one-way valve is connected to the two-speed valve core, and the second one-way valve is opened, and the main oil of the motor oil inlet is at the oil inlet of the two-speed valve core.

[0011] Further, the two-point variable walking motor is connected to the spring brake, when the balance valve is reversed, the oil entering the motor oil inlet reaches the spring brake deactivation cavity, and the pressure oil acts on the corresponding pressure oil effective surface of the brake piston to overcome the brake spring force and remove the mechanical brake of the walking motor.

[0012] Further, the main oil of the motor oil inlet reaches the control side of the two-speed valve core, when the two-speed valve core has oil in the pilot control oil circuit and the motor operating oil pressure reaches a certain pressure, the two-speed valve core is forced to reverse, the automatic speed reduction and torque increase of walking is realized, at this time, the motor works normally to realize walking, and the maximum working pressure of the oil in the motor oil inlet is adjusted by the overflow valve.

[0013] Further, a swash plate limiting valve and a control oil circuit are added to the original oil circuit, the swash plate limiting valve is controlled by a swash plate limiting valve control valve and a control oil circuit Pr2, and the control oil circuit Pr2 takes high-pressure oil from the system through the swash plate limiting valve control valve after the second one-way valve.

[0014] Further, when the two-point variable walking motor is in small displacement, the swash plate limiting valve control valve is in the right position when there is no hydraulic oil in the control oil circuit Pr2, and at this time, the left oil chamber of the swash plate limiting valve is high pressure, and the displacement of the motor does not change.

[0015] Further, when the motor speed needs to be increased, the control oil circuit Pr2 oil circuit is connected, the swash plate limiting valve control valve is in the left position, the left chamber of the swash plate limiting valve is connected to the oil tank, the swash plate limiting valve moves to the left under the action of the spring, the angle of the swash plate of the motor becomes smaller, the displacement of the motor decreases, and the speed increases.

[0016] According to some embodiments, the present disclosure adopts the technical scheme as follows:

[0017] A control method of a walking motor speed control system of a crawler excavator, comprising:

[0018] On the basis of the control of the original two-point variable walking motor, a swash plate limiting valve is added, the swash plate limiting valve is controlled through a swash plate limiting valve control valve and a control oil circuit Pr2, the control oil circuit Pr2 takes system high-pressure oil after a second one-way valve, when the motor is in small displacement, the swash plate limiting valve control valve is in the right position when there is no hydraulic oil in the control oil circuit Pr2, at this time, the left oil cavity of the swash plate limiting valve is high pressure, and the motor displacement does not change, when the motor speed needs to be increased, the control oil circuit Pr2 oil circuit is connected, the swash plate limiting valve control valve is in the left position, the left cavity of the swash plate limiting valve is connected to the oil tank to release oil, the swash plate limiting valve moves to the left under the action of the spring force, the swash plate angle of the motor becomes smaller, the motor displacement decreases, and when the swash plate limiting valve is in the left limit position, the motor displacement is the smallest, and the motor speed can be increased within a set range when the flow is unchanged.

[0019] Compared with the prior art, the beneficial effects of the present disclosure are:

[0020] The walking motor speed control system of the crawler excavator provided by the present disclosure is for a two-point variable walking motor, the present disclosure adds a swash plate limiting valve to the original oil circuit control, the swash plate limiting valve is controlled through a swash plate limiting valve control valve and a control oil circuit Pr2, when the motor is in small displacement, the swash plate limiting valve control valve is in the right position when there is no hydraulic oil in the control oil circuit Pr2, at this time, the left oil cavity of the swash plate limiting valve is high pressure, and the motor displacement does not change, when the motor speed needs to be increased, the control oil circuit Pr2 oil circuit is connected, the swash plate limiting valve control valve is in the left position, the left cavity of the swash plate limiting valve is connected to the oil tank to release oil, the swash plate limiting valve moves to the left under the action of the spring force, the swash plate angle of the motor becomes smaller, the motor displacement decreases, and when the swash plate limiting valve is in the left limit position, the motor displacement is the smallest, and the motor speed can be increased within a set range when the flow is unchanged; the swash plate limiting valve and the control oil circuit can be used to realize swash plate limiting, so that the motor can realize smaller displacement, the motor speed can be increased within a certain range when the flow is unchanged, the speed can be increased faster under the same conditions, the working efficiency is improved, and speed regulation is realized. BRIEF DESCRIPTION OF DRAWINGS

[0021] The drawings accompanying the specification of the present disclosure serve to provide further understanding of the present disclosure, the illustrative embodiments of the present disclosure and the description thereof serve to explain the present disclosure, and do not constitute improper limitations on the present disclosure.

[0022] Figure 1 The walking motor control principle diagram of the embodiment of the present disclosure;

[0023] Figure 2 The swash plate limiting valve working principle diagram of the embodiment of the present disclosure.

[0024] Wherein, 1, speed reducer; 2, spring brake, 3, overflow valve orifice, 4, first check valve, 5, balance valve, 6, third check valve, 7, buffer sleeve, 8, overflow valve, 9, second check valve, 10, two-speed valve core, 11, swash plate limiting valve control valve, 12, orifice, 13, spring, 14, swash plate limiting valve, 15, servo piston, 16, first spring, 17, two-point variable walking motor. DETAILED DESCRIPTION

[0025] The present disclosure is further illustrated by the following examples in conjunction with the accompanying drawings.

[0026] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the present disclosure. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0027] It is to be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments consistent with the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, devices, components and / or combinations thereof, but do not preclude the presence or addition of one or more other features, steps, operations, devices, components and / or combinations thereof.

[0028] Example 1

[0029] In an embodiment of the present disclosure, a walking motor speed control system for a crawler excavator is provided, wherein the walking motor refers to a driving system for the walking of the crawler excavator, and the walking function of the crawler excavator is realized by driving the rotation of the motor through the hydraulic oil provided by the pump to the walking motor through the main valve. Generally, two walking motors with the same configuration are provided for each crawler excavator, which are arranged on the crawler of the excavator and realize the walking function of the excavator in cooperation with the speed reducer and the crawler. The walking motor is divided into upper and lower parts, the lower part is a shell, and the cavity bears the main components. The rear cover is a multifunctional sealing cover, which integrates most of the control functions of the motor. The function valve controls the flow and direction of the hydraulic oil through the valve core and oil passage opening, thereby realizing the control of the motor function.

[0030] The device driving the whole vehicle to walk, namely the transmission device, is actually composed of driving wheels, guide wheels, supporting wheels, drag chain wheels and tracks, wherein the driving wheels are actually two groups of straight shaft type axial piston motor driving reducer parts driving the track wheels, which are called left and right walks. The walk motor displacement is variable, when the motor displacement is the smallest, high speed walking can be realized, and when the motor displacement is the largest, low speed walking with increased torque can be realized. Therefore, in actual work, the walk motor can realize the high and low speed walking function of the whole vehicle, namely the walking two speed function. The reducer of the walk motor assembly used by the excavator is a two-stage planetary gear reducer 1, and in structure, the outer cover of the reducer serves as the mounting flange of the motor. The left and right walk motors are variable displacement motors, namely the walk motor swash plate angle is variable, and the motor displacement is variable, but the displacement can only be in the two displacement states of the smallest displacement and the largest displacement. Among them, when the walk motor is in the smallest displacement state, it is in the high speed walking state of the walk motor, and when the walk motor is in the largest displacement state, it is in the low speed walking state of the walk motor. The two walk motors have basically the same structure, and the displacement change process and mode are also the same. Therefore, the present disclosure proposes a new walk motor speed control system for the above problems, which realizes faster speed under the same conditions and improves work efficiency.

[0031] As shown in Figure 1 , A and B are motor oil inlets and motor oil outlets (the walk motor can move forward and backward, the motor can rotate in two directions, and the A and B oil ports are oil inlets and outlets), T1 and T2 are oil return ports connected with the oil tank, MsA and MsB are pressure measuring ports, and Pr1 is a two-speed control.

[0032] As shown in Figure 2 , the walk motor speed control system of the present disclosure sets two-point variable walk motor 17, swash plate limiting valve 14, swash plate limiting valve control valve 11 and control oil way Pr2 on the basis of the original control of the walk motor, the swash plate limiting valve control valve 11 is connected with the swash plate limiting valve 14 through the control oil way Pr2, the swash plate limiting valve 14 is connected with the servo piston 15 through the control oil way Pr2, the first spring 16 is arranged in the servo piston, the swash plate limiting valve 14 connects and controls the two-point variable walk motor 17, changes through the swash plate limiting valve 14 and the control oil way Pr2, changes the pressure in the cavity of the servo piston 15, and then changes the angle of the motor swash plate, so that the motor realizes smaller displacement, and the flow rate can be increased within the set range when the flow rate is unchanged.

[0033] Further, the walk motor speed control system of the present disclosure, as shown in Figure 1Also shown, there is a motor oil inlet A and a motor oil outlet B, the motor oil inlet A is connected to the oil tank through a pipeline, the motor oil inlet A is connected to the first one-way valve 4 through a pipeline after oil, the first one-way valve 4 is opened, and the oil entering the motor left cavity through a pipeline.

[0034] The motor can rotate in both directions, and the balance valve 5 in the oil circuit is reversed. The high-pressure oil in the motor passes through the overflow valve 8 and the throttle oil pipeline above it to the upper cavity of the buffer sleeve 7 to achieve the buffering effect. The overflow valve 8 is connected to the second one-way valve 9 through a pipeline, and the second one-way valve is connected to the two-speed valve core 10. When the second one-way valve 9 is opened, the main oil of the motor oil inlet A is waiting for oil at the oil inlet of the two-speed valve core 10.

[0035] The two-point variable walking motor 17 is connected to the spring brake 2. When the balance valve 5 is reversed, the oil entering the motor oil inlet A reaches the spring brake 2 to remove the brake cavity. The pressure oil acts on the corresponding pressure oil effective surface of the brake piston to overcome the brake spring force and remove the mechanical brake of the walking motor. The reversal of the balance valve 5 makes the right side of the two-point variable walking motor 17 connected to the pipeline where the motor outlet B is located. The A inlet oil reaches the spring brake 2 to remove the brake cavity, and the pressure oil acts on the corresponding pressure oil effective surface of the brake piston to overcome the brake spring force and remove the mechanical brake of the walking motor. The main oil of the motor oil inlet A reaches the control side of the two-speed valve core 10. When the two-speed valve core 10 has oil in the pilot control pipeline and the motor working oil pressure reaches a certain pressure, it forcibly pushes the two-speed valve core to reverse to the initial left position shown in the figure, realizing the "automatic speed reduction and torque increase" function of walking. At this time, the motor works normally to realize the walking function, and the maximum working pressure of the oil in the motor oil inlet A is adjusted by the buffer overflow valve.

[0036] The buffer overflow valve is composed of the buffer sleeve 7 and the overflow valve 8. The overflow valve 8 is provided with an overflow valve throttle hole 3 between the buffer sleeve 7 and the overflow valve 8. When the oil flows back to the motor outlet B, it flows back to the motor outlet B through the third one-way valve 6.

[0037] Specifically, the basic control principle of the walking motor is as follows: if the walking motor hand lever is pushed to make the corresponding main reversing valve core reverse, and finally let the motor oil inlet A inlet oil, and the motor oil outlet B is connected to the oil tank pipeline, then the main oil of the motor oil inlet A will make: the first one-way valve 4 is opened to make the motor oil inlet A inlet oil reach the left cavity of the two-point variable walking motor 17; the balance valve 5 is reversed to the left position, and the oil from the motor oil inlet A reaches the buffer sleeve 7 upper cavity through the overflow valve 8 and the throttle oil way above it to realize the buffering effect; the second one-way valve 9 is opened, and the A main oil is waiting for oil at the oil inlet of the two-speed valve core 10.

[0038] The reversing of the balance valve 5 makes the right side oil return line of the two-point variable walking motor 17 communicate with the oil return line; the A port oil enters the spring brake 2 brake release cavity, and the pressure oil then acts on the brake piston corresponding pressure oil effective surface to overcome the brake spring force to release the mechanical brake of the walking motor; the A port main oil reaches the two-speed valve core 10 control side, and when the two-speed valve core 10 pilot control line has oil and the motor working oil pressure reaches a certain pressure, the two-speed valve core is forced to reverse to the initial left position shown in the figure to realize the “automatic speed reduction and torque increase” function of walking. At this time, the motor works normally to realize the walking function, and the maximum working pressure of the A port oil is adjusted by the buffer overflow valve.

[0039] When the walking control handle is released and the motor bleeds, the balance valve 5 will return to the initial middle position under the action of the spring force, and the two ends are provided with two first and second buffer orifices to slowly recover from the left position to the middle position. Due to the inertia of the motor, high pressure will be generated on the right side of the motor, and the high pressure oil can realize the buffering effect through the overflow valve 8 and the buffer sleeve 7; the left side of the two-point variable walking motor 17 will produce a sharp decrease in pressure cavity, which can be supplemented through the opening of the first one-way valve 4 in the system main oil return oil channel. At the same time, the brake piston of the spring brake 2 is slowly pressed against the friction plate and the separation plate under the action of the brake spring to provide mechanical force to lock the motor cylinder, and the brake cavity bleeds through the slowly closed balance valve to return oil, and the motor is braked.

[0040] When the “rabbit gear” is selected on the cab control panel, i.e. the two-speed electromagnetic valve is reversed, the two-speed valve core 10 control line has a pilot 4MPa oil, the two-speed valve core is reversed to the right position, and then the main oil can reach the two-speed control piston first spring 16 through the two-speed valve core 10 to make the motor swash plate inclination angle smaller, realizing the high-speed walking state of the motor at the minimum displacement (part of the walking motor has the “automatic speed reduction” function, i.e. in the high-speed walking state, when the motor main oil pressure reaches the set pressure, the two-speed valve core 10 control left oil pressure also rises to the main oil pressure, at this time, the left side of the two-speed valve core is affected by the spring force and the set pressure oil on the certain surface, and the right side is affected by the pilot 4MPa pressure on the certain area, the valve core is reversed to the left position, making the motor swash plate inclination angle larger, and the motor is in the maximum displacement state, finally realizing the “automatic speed reduction” of walking).

[0041] As shown in Figure 2 , Figure 2 is Figure 1The winning line frame encircles the part, on the basis of the original control of the walking motor (Pr1 is not oil, control valve 1 left position is connected, servo plunger is connected with T, the motor is in large displacement; Pr1 is oil, inclined disc limiting valve control valve 11 is in right position, the right cavity of servo plunger is high pressure, the motor is in small displacement), a kind of inclined disc limiting valve 14 is increased, inclined disc limiting valve is controlled by inclined disc limiting valve control valve 11 and control oil path Pr2, there is orifice 12 between inclined disc limiting valve and inclined disc limiting valve control valve, control oil path Pr2 takes system high pressure oil (by two-position three-way valve control) from the second one-way valve 9. When the motor is in small displacement, two-position three-way valve (inclined disc limiting valve control valve 11) is in right position when there is no hydraulic oil in control oil path Pr2, at this time, the left oil cavity of inclined disc limiting valve 14 is high pressure, and the motor displacement is unchanged, when the motor speed needs to be increased, Pr2 oil path is connected, inclined disc limiting valve control valve 11 is in left position, the left cavity of inclined disc limiting valve is connected with mailbox to release oil, inclined disc limiting valve 14 moves to left under the action of spring 13, the angle of motor inclined disc becomes small, the motor displacement is reduced (when inclined disc limiting valve is in left cavity limit position, the motor displacement is minimum), and the speed is increased.

[0042] Embodiment 2

[0043] A kind of control method of the walking motor speed control system of the tracked excavator of the present disclosure, including: based on the control system described in embodiment 1, on the basis of the control of original two-point variable walking motor, a kind of inclined disc limiting valve is increased, inclined disc limiting valve is controlled by inclined disc limiting valve control valve and control oil path Pr2, control oil path Pr2 takes system high pressure oil from the second one-way valve, when the motor is in small displacement, inclined disc limiting valve control valve is in right position when there is no hydraulic oil in control oil path Pr2, at this time, the left oil cavity of inclined disc limiting valve is high pressure, and the motor displacement is unchanged, when the motor speed needs to be increased, control oil path Pr2 oil path is connected, inclined disc limiting valve control valve is in left position, the left cavity of inclined disc limiting valve is connected with mailbox to release oil, inclined disc limiting valve moves to left under the action of spring, the angle of motor inclined disc becomes small, the motor displacement is reduced, when inclined disc limiting valve is in left cavity limit position, the motor displacement is minimum, and when the flow is unchanged, the motor speed can be increased in the set range.

[0044] The present disclosure is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present disclosure. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to produce a machine, so that the instructions executed by the computer or other programmable data processing devices generate a device for implementing the functions described in the flowcharts and / or block diagrams. Figure 1 A flow or multiple flows and / or blocks Figure 1means for performing the function specified by the block or blocks.

[0045] These computer program instructions can also be loaded into computer or other programmable data processing devices, so that a series of operational steps are performed on the computer or other programmable data processing devices to generate a computer-implemented process, so that the instructions executed on the computer or other programmable data processing devices provide a process for implementing the flowchart Figure 1 one or more flowcharts and / or blocks Figure 1 steps of a function specified by a block or blocks.

[0046] Although the specific embodiments of the present disclosure are described above with reference to the drawings, the description is not a limitation on the scope of protection of the present disclosure, and those skilled in the art should understand that various modifications or changes made on the basis of the technical solutions of the present disclosure without creative labor are still within the scope of protection of the present disclosure.

Claims

1. A track-type excavator travel motor speed control system, characterized by, Two-point variable walking motor, swash plate limiting valve, swash plate limiting valve control valve and control oil circuit Pr2, the swash plate limiting valve control valve is connected with the swash plate limiting valve through the control oil circuit Pr2, the swash plate limiting valve is connected with the servo piston through the control oil circuit Pr2, the swash plate limiting valve controls the two-point variable walking motor, the swash plate limiting valve and the control oil circuit Pr2 are changed, the pressure in the servo piston cavity is changed, and then the angle of the motor swash plate is changed, so that the motor realizes smaller displacement, and the motor speed can be increased in the set range when the flow is unchanged. The control oil circuit further comprises a motor oil inlet and a motor oil outlet, the motor oil inlet is connected to the oil tank through the pipeline, and the motor oil inlet is connected to the first one-way valve through the pipeline after the oil inlet. The main oil of the motor oil inlet reaches the two-speed valve core control side, when the two-speed valve core pilot control oil circuit has oil and the motor working oil pressure reaches a certain pressure, the two-speed valve core is forced to change direction, the automatic speed reduction and torque increase of walking are realized, at this time, the motor works normally, walking is realized, and the maximum working pressure of the oil in the motor oil inlet is adjusted by the overflow valve.

2. A track-type excavator travel motor speed control system as claimed in claim 1, characterized in that, The overflow valve is connected to the second one-way valve through the pipeline, the second one-way valve is connected to the two-speed valve core, and the second one-way valve is opened.

3. A track-type excavator travel motor speed control system as claimed in claim 1, wherein, The two-point variable walking motor is connected to the spring brake, when the balance valve changes direction, the oil in the motor oil inlet reaches the spring brake deactivation cavity, and the pressure oil acts on the corresponding pressure oil effective surface of the brake piston to overcome the brake spring force and remove the mechanical brake of the walking motor.

4. A track-type excavator travel motor speed control system as claimed in claim 1, wherein, The swash plate limiting valve and the control oil circuit are added to the original oil circuit, the swash plate limiting valve is controlled through the swash plate limiting valve control valve and the control oil circuit Pr2, and the control oil circuit Pr2 takes the system high-pressure oil through the swash plate limiting valve control valve after the second one-way valve.

5. A track-type excavator travel motor speed control system as claimed in claim 4, wherein, When the two-point variable walking motor is in small displacement, the swash plate limiting valve control valve is in the right position when there is no hydraulic oil in the control oil circuit Pr2, at this time, the left oil cavity of the swash plate limiting valve is high pressure, and the motor displacement does not change.

6. A track-type excavator travel motor speed control system as claimed in claim 5, wherein, When the motor speed needs to be increased, the control oil circuit Pr2 oil circuit is connected, the swash plate limiting valve control valve is in the left position, the left cavity of the swash plate limiting valve is connected to the oil tank, the swash plate limiting valve moves to the left under the action of the spring force, the angle of the motor swash plate becomes smaller, the motor displacement decreases, and the speed increases.

7. A control method for a track-type excavator travel motor speed control system according to any one of claims 1 to 6, characterized by, Comprise: On the basis of the original two variable walking motor control, increase a swash plate limit valve, swash plate limit valve through swash plate limit valve control valve and control oil circuit Pr2 control, control oil circuit Pr2 from the second check valve after taking system high pressure oil, when the motor is in small displacement, swash plate limit valve control valve in control oil circuit Pr2 no hydraulic oil when right, the swash plate limit valve left oil cavity for high pressure, motor displacement no change, when the need for motor speed increase, connect control oil circuit Pr2 oil circuit, swash plate limit valve control valve in left, swash plate limit valve left cavity mailbox oil, swash plate limit valve under the action of spring force to the left, motor swash plate angle is small, motor displacement decreases, swash plate limit valve in left cavity limit position, motor displacement is minimum, when the flow can be in the set range within the motor speed increases.

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