Power transmission device for construction machinery

Abstract

Various embodiments of the present invention provide a power transmission device for engineering machinery, which transmits the driving force of the engine to the wheels. The power transmission device of the engineering machinery may include: a travel pump, which is driven by the engine to discharge working hydraulic pressure in one of a first direction and a second direction; an auxiliary pump, which forms a pilot hydraulic pressure; a main pilot flow path, which supplies the pilot hydraulic pressure supplied from the auxiliary pump to the direction conversion valve; a travel motor, whose rotation direction is determined according to the discharge direction of the travel pump; and a first pilot flow path, which branches from one side of the main pilot flow path and supplies the pilot hydraulic pressure in a manner that controls the volume of the travel motor.

Description

Technical Field

[0001] The present invention relates to a power transmission device for construction machinery, and more particularly, to a power transmission device for construction machinery that prevents a sudden increase in the volume of a travel motor when the construction machinery is switched to a stopped state during travel. Background Art

[0002] Typically, a closed-loop hydraulic power transmission system (CLHT) utilizes working fluid discharged from a travel pump driven by the engine to rotate the travel motor. This refers to a hydraulic system in which the working fluid discharged from the pump, after passing through the travel motor, does not return to the hydraulic tank but instead flows back to the hydraulic pump. Summary of the Invention

[0003] Technical issues

[0004] The present invention has been conceived to solve the above-mentioned problem, and an object of the present invention is to provide a power transmission device for a construction machine that prevents a sudden increase in the displacement of a travel motor when the construction machine is stopped during travel.

[0005] Technical Solution

[0006] Various embodiments of the present invention provide a power transmission device for engineering machinery, which transmits the driving force of the engine to the wheels. The power transmission device of the engineering machinery may include: a travel pump, which is driven by the engine to discharge working hydraulic pressure in one of a first direction and a second direction; an auxiliary pump, which forms a pilot hydraulic pressure; a direction conversion valve, which is switched by a direction conversion signal and controls the swash plate of the travel pump by the pilot hydraulic pressure; a main pilot flow path, which supplies the pilot hydraulic pressure supplied by the auxiliary pump to the direction conversion valve between the auxiliary pump and the direction conversion valve; a travel motor, whose rotation direction is determined according to the discharge direction of the travel pump; and a first pilot flow path, which branches from one side of the main pilot flow path to supply the pilot hydraulic pressure to the travel motor.

[0007] Preferably, the pilot hydraulic pressure supplied through the first pilot flow path can reduce the displacement of the travel motor.

[0008] Preferably, the pilot hydraulic pressure can change the displacement of the travel motor in inverse proportion to the rotation speed of the engine.

[0009] Preferably, when the direction change signal is in neutral, the first pilot flow path may supply the pilot hydraulic pressure to the travel motor.

[0010] Preferably, when the direction change signal is changed from one of forward and reverse to neutral, the first pilot flow path may supply the pilot hydraulic pressure to the travel motor.

[0011] Preferably, when the directional control valve is released, the first pilot flow path may supply the pilot hydraulic pressure to the travel motor.

[0012] Preferably, the direction switching valve may control at least one of a tilting direction and a tilting angle of a swash plate of the travel pump.

[0013] Preferably, the travel motor may include a volume control piston for performing volume control of the travel motor, and a travel motor valve for supplying the working hydraulic pressure to the volume control piston when the pilot hydraulic pressure is applied thereto.

[0014] The power transmission device of the engineering machinery of the present invention may further include: an electronic proportional pressure reducing valve, which is arranged in the main pilot flow path to control the pilot hydraulic pressure supplied to the directional control valve; and a control unit, which controls the electronic proportional pressure reducing valve according to the operation amount of the accelerator pedal.

[0015] Preferably, the control portion may control the electronic proportional pressure reducing valve in a direction in which the pilot hydraulic pressure is reduced as the operation amount of the accelerator pedal decreases.

[0016] Preferably, the control portion senses whether a cruise mode is activated, and fixedly controls the electronic proportional pressure reducing valve so as to maximize the pilot hydraulic pressure when the cruise mode is activated (ON).

[0017] Preferably, it also includes an FNR operating lever, which generates an FNR operating signal through the operator's operation. When the current FNR state of the construction machinery and the FNR operating signal are different from each other, the control unit can control the electronic proportional pressure reducing valve in a manner that minimizes the pilot hydraulic pressure.

[0018] Preferably, the power transmission device of the engineering machinery also includes a working machine pump, which is driven by the engine to make the working machine work. When the travel pump and the working machine pump are driven simultaneously, as the operation amount of the accelerator pedal decreases, the control unit can control the electronic proportional pressure reducing valve in the direction in which the pilot hydraulic pressure is reduced.

[0019] Effects of the Invention

[0020] The power transmission device for construction machinery according to various embodiments of the present invention can prevent a sudden increase in the displacement of the travel motor when the construction machinery is shifted to neutral to stop during high-speed travel, thereby preventing the travel motor from applying excessive load to the engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a hydraulic circuit diagram of a power transmission device in the prior art.

[0022] Figure 2 It is a hydraulic circuit diagram of a power transmission device according to various embodiments of the present invention.

[0023] Figure 3 This is a hydraulic circuit diagram for controlling a travel pump of a construction machine according to various embodiments of the present invention.

[0024] Figure 4 This is a block diagram illustrating the relationship between components for controlling a travel pump of a construction machine according to various embodiments of the present invention.

[0025] Reference numerals

[0026] 1: Engine, 110: Travel pump, 120: Auxiliary pump, 131: Main pilot flow path, 135: First pilot flow path, 140: Direction change valve, 145: Direction change piston, 151: First working fluid supply flow path, 152: Second working fluid supply flow path, 160: Electronic proportional pressure reducing valve, 170: Travel motor, 180: Travel motor valve, 185: Volume control piston, 190: Control unit. DETAILED DESCRIPTION

[0027] Hereinafter, for the convenience of description, some embodiments of the present invention are described with reference to exemplary drawings. When describing the components of each figure with reference numerals, the same components will be marked with the same reference numerals as much as possible even if they are marked in different figures.

[0028] The terms or words used in this specification and claims should not be limited to the common or dictionary meanings, but should be interpreted as the meanings and concepts that conform to the technical ideas of the present invention, based on the principle that the inventor can appropriately define the concept of terms in order to best illustrate his invention. In addition, when describing the constituent elements of the embodiments of the present invention, terms such as first, second, A, B, (a), (b) may be used. Such terms are only used to distinguish the constituent elements from other constituent elements, and the essence, order or sequence of the constituent elements are not limited by the terms. When it is recorded that a certain constituent element is "connected" or "coupled" to another constituent element, it should be understood that the constituent element may be directly connected or coupled to the other constituent element, but the constituent element and the other constituent element may also be "connected" or "coupled" to another constituent element.

[0029] Therefore, the embodiments described in this specification and the components shown in the drawings are merely the most preferred embodiments of the present invention and do not represent the entire technical concept of the present invention. Therefore, it should be understood that at the time of this application, various equivalents and modifications may exist that can replace these. In addition, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the main purpose of the present invention will be omitted.

[0030] Hereinafter, a wheeled excavator will be described as an example of a construction machine to which the hydraulic system of the present invention is applied. However, it is obvious that the concept includes various construction machines used at construction sites, such as bulldozers, loaders, and forklifts.

[0031] The present invention aims to provide a closed-loop hydraulic power transmission device (Closed Loop Hydro Static Transmission) applied to construction machinery such as wheeled excavators, which is used to prevent the volume of the travel motor 170 from increasing sharply when the construction machinery changes to neutral gear to stop during high-speed travel, thereby preventing the travel motor 170 from applying an excessive load to the engine 1.

[0032] Hereinafter, a power transmission device for construction machinery according to various embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0033] Figure 2 It is a hydraulic circuit diagram of a power transmission device according to various embodiments of the present invention.

[0034] The power transmission device for construction machinery according to various embodiments of the present invention may include a travel pump 110 utilizing a variable swash plate and a travel motor 170 with a fixed swash plate rotated by hydraulic fluid discharged from the travel pump 110. The device is configured to transmit power generated by the engine 1 to the wheels. The power transmission device for construction machinery according to the present invention may include the travel pump 110, an auxiliary pump 120, a directional control valve, a main pilot flow path 131, the travel motor 170, and a first pilot flow path 135. Furthermore, the power transmission device for construction machinery according to the present invention may further include an electronic proportional pressure reducing valve and a control unit 190.

[0035] The travel pump 110 may be configured to be driven by the engine 1 to discharge working hydraulic pressure. The travel pump 110 may include a double-tilt hydraulic pump using a variable swash plate whose tilt direction can be changed to a first direction (e.g., a forward or (+) direction) or a second direction (e.g., a reverse or (-) direction).

[0036] Hereinafter, the term "first direction" may refer to the direction in which the operating hydraulic pressure of the travel pump 110 is discharged, which causes the rotation direction of the travel motor 170 to be the forward direction, and / or the direction in which the directional switching valve 140 of the travel pump 110, described later, is switched. Furthermore, the term "second direction" may refer to the direction in which the operating hydraulic pressure of the travel pump 110 is discharged, which causes the rotation direction of the travel motor 170 to be the reverse direction, and / or the direction in which the directional switching valve 140 of the travel pump 110 is switched.

[0037] The swash plate of the travel pump 110 can be tilted in either a first or second direction by a direction switching valve 140. When the direction switching valve 140 is switched to the first or second direction in response to a direction switching signal corresponding to an operator's operation, pilot hydraulic pressure is supplied to the direction switching piston 145, thereby changing the tilt direction of the swash plate of the travel pump 110.

[0038] In one embodiment, when the direction switching valve 140 is switched to the first direction in response to a forward signal, pilot hydraulic pressure is supplied to the direction switching piston 145. As the piston moves, the tilting direction of the swash plate is changed to the first direction. The hydraulic pressure discharged from the travel pump 110 in the first direction is supplied to the travel motor 170 via the first working fluid supply path 151, thereby changing the rotation direction of the travel motor 170 to the forward direction.

[0039] In one embodiment, when the direction-switching valve 140 is switched to the second direction in response to a reverse signal, pilot hydraulic pressure is supplied to the direction-switching piston 145. As the piston moves, the tilting direction of the swash plate is changed to the second direction. The hydraulic pressure discharged from the travel pump 110 in the second direction is supplied to the travel motor 170 via the second working fluid supply path 152, thereby shifting the travel motor 170 to the reverse direction.

[0040] The travel pump 110 is driven by the engine 1. The faster the rotation speed of the engine 1, the larger the tilting angle of the swash plate, thereby increasing the volume of the travel pump 110. Conversely, the tilting angle of the swash plate of the travel motor 170 decreases, and the volume of the travel motor 170 decreases, which increases the rotation speed.

[0041] Typically, wheeled construction machinery is equipped with a working machine pump separately from the travel pump for transmitting power to the working machine. Under high-load conditions, a higher engine RPM is required to increase the output of the working machine pump. However, if a higher RPM is used in this way, the travel pilot pressure of the travel pump increases, resulting in an increase in volume, making low-speed travel difficult.

[0042] Therefore, in the present invention, an electronic proportional pressure reducing valve 160 capable of controlling the travel pilot pressure supplied by the auxiliary pump 120 according to the operator's operation amount of the accelerator pedal 105 may be provided on the main pilot flow path 131 between the auxiliary pump 120 and the directional control valve 140 .

[0043] Refer to the following Figure 3 and Figure 4 A method of controlling the pilot hydraulic pressure using the electronic proportional pressure reducing valve 160 will be described.

[0044] An electronic proportional pressure reducing valve 160 (hereinafter referred to as an EPPR valve) can be installed in the main pilot flow path 131 between the auxiliary pump 120 and the direction-shifting solenoid valve. The EPPR valve 160 can be controlled by a control current output by the controller 190 based on the operator's operation amount (%) of the accelerator pedal 105. When the accelerator pedal 105 is operated at a minimum (e.g., 0%), the EPPR valve 160 can perform pressure reduction control to minimize the pilot hydraulic pressure supplied to the direction-shifting solenoid valve. Conversely, when the accelerator pedal 105 is operated at a maximum (e.g., 100%), the EPPR valve 160 can perform pressure reduction control to maximize the pilot hydraulic pressure supplied to the direction-shifting solenoid valve.

[0045] When the engine of the construction machinery rotates at high speed, the pilot hydraulic pressure supplied by the auxiliary pump 120 forms a higher pressure according to the engine speed. In the present invention, an EPPR valve 160 that controls the opening amount according to the operation amount of the accelerator pedal 105 is provided in the main pilot flow path 131 at the front end of the direction conversion solenoid valve, thereby allowing low-speed driving even when using a higher RPM of the engine.

[0046] The control unit 190 of various embodiments of the present invention can control the EPPR valve 160 and the directional control valve 140. The specific control method of the control unit 190 of the present invention on the EPPR valve 160 and the directional control valve 140 is described in detail below.

[0047] The control unit 190 can receive the amount of operation of the accelerator pedal 105 sensed by various sensors. The amount of operation of the accelerator pedal 105 can be input as a percentage (%) of the pressure relative to the initial state, ranging from an initial state (0%) where the operator does not operate the pedal to a state (100%) where the pedal is pressurized to the maximum as the operator operates the pedal.

[0048] The control unit 190 may control the electronic proportional pressure reducing valve 160 according to the operation amount of the accelerator pedal 105. As the operation amount of the accelerator pedal 105 decreases, the electronic proportional pressure reducing valve 160 may be controlled in a direction in which the pilot hydraulic pressure is reduced.

[0049] In one embodiment, the control unit 190 can sense whether the cruise mode is active and, when the cruise mode is on, can fixedly control the electronic proportional pressure reducing valve 160 to maximize the pilot hydraulic pressure. Furthermore, the present invention may include an FNR operating lever 101 that generates an FNR operating signal through operator operation. When the current FNR state of the construction machine differs from the FNR operating signal, the control unit 190 can control the electronic proportional pressure reducing valve 160 to minimize the pilot hydraulic pressure.

[0050] In one embodiment, when the pilot hydraulic pressure is controlled by the electronic proportional pressure reducing valve 160, the control unit 190 may also control the electronic proportional pressure reducing valve 160 so that the pilot hydraulic pressure has the smallest value among a first value of the pilot hydraulic pressure determined in a direction of being reduced as the operation amount of the accelerator pedal 105 decreases, a second value of the pilot hydraulic pressure determined based on whether the cruise mode is engaged, or a third value of the pilot hydraulic pressure determined when the current driving state and the signal of the operating lever are different from each other.

[0051] In an exemplary embodiment, when the operation amount (%) of the accelerator pedal 105 is input, the control unit 190 may convert it into a control current for controlling the electronic proportional pressure reducing valve 160 and output it. The control unit 190 may control the opening amount of the electronic proportional pressure reducing valve 160 using the output control current.

[0052] When a cruise mode that automatically controls the travel speed according to the distance to the preceding vehicle is turned on, the control unit 190 may output a fixed control current at a minimum value (200 mA) so that the output of the travel pump 110 may be maintained at a maximum.

[0053] In addition, when the current FNR state of the construction machine and the FNR operation signal input by the operator's FNR operating lever 101 are different from each other, the control unit 190 can decelerate the driving speed to a minimum by fixedly outputting the control current to a maximum value (1500mA). For example, when the current FNR state of the construction machine is judged to be forward, and the FNR operation signal input by the operating lever is not a forward signal, the control unit 190 can fixedly output the control current to a maximum value (1500mA). When the current FNR state of the construction machine is judged to be reverse, and the FNR operation signal input by the operating lever is not reverse, the control unit 190 can also fixedly output the control current to a maximum value (1500mA). In addition, when the current FNR state of the construction machine is judged to be neutral or the FNR operation signal input by the operating lever is neutral, the control unit 190 can also fixedly output the control current to a maximum value (1500mA).

[0054] Furthermore, when outputting the control current to the changed value, the control unit 190 may output the control current so that the control current has a predetermined slope when the current value increases. For example, when the current value increases, the control unit 190 may output the control current so that the slope has a value of 500 mA / sec.

[0055] In addition, the present invention may include a working machine pump driven by the engine 1 to operate the working machine. When the travel pump 110 and the working machine pump are driven simultaneously, as the operation amount of the accelerator pedal 105 decreases, the control unit 190 can control the electronic proportional pressure reducing valve 160 in the direction in which the pilot hydraulic pressure is reduced.

[0056] The auxiliary pump 120 can be located on either side of the travel pump 110 and can be driven by the engine 1 to generate a pilot hydraulic pressure. The pilot hydraulic pressure generated by the auxiliary pump 120 can be supplied to the directional control valve 140 via the main pilot flow path 131. When the directional control valve 140 is switched to the first or second direction by a direction switching signal, the pilot hydraulic pressure is supplied to the directional control piston 145, thereby moving the piston. Furthermore, in the present invention, the pilot hydraulic pressure supplied by the auxiliary pump 120 can be supplied to the travel motor 170 via the first pilot flow path 135. This will be described in detail later.

[0057] The auxiliary pump 120 is directly connected to the engine 1. When the user shifts the vehicle into neutral, the engine speed decreases to approximately 800 RPM. At this time, the RPM of the auxiliary pump 120 also decreases proportionally, and the displacement of the travel motor 170 can be controlled at this RPM. Alternatively, when the engine 1 is turned off, the engine 1 does not immediately stop at 0 RPM. Therefore, the displacement of the travel motor 170 can be gradually controlled in conjunction with the engine 1.

[0058] The directional control valve 140 can be controlled by a directional control signal to supply pilot hydraulic pressure to the directional control piston 145. The directional control valve 140 may include a solenoid valve. When powered by a forward signal in the directional control signal, the valve switches to a first direction, thereby moving the directional control piston 145 in the corresponding direction. Furthermore, when powered by a reverse signal, the valve switches to a second direction, thereby moving the directional control piston 145 in the corresponding direction. When the directional control signal is a neutral signal, the solenoid valve is de-energized, and in this case, no pilot hydraulic pressure is supplied to the directional control piston 145.

[0059] The main pilot flow path 131 is formed between the auxiliary pump 120 and the directional control valve 140, and can supply the pilot hydraulic pressure generated by the auxiliary pump 120 to the directional control valve 140. According to various embodiments of the present invention, a first pilot flow path 135, described later, can be formed by branching from one side of the main pilot flow path 131. Thus, the pilot hydraulic pressure supplied by the auxiliary pump 120 is not only supplied to the directional control valve 140, but can also be supplied to the travel motor 170 to control the travel motor 170's displacement.

[0060] On the other hand, refer to Figure 1 In a typical closed-loop hydraulic power transmission system, the pilot hydraulic pressure supplied by the auxiliary pump 12 can be supplied from the rear end of the directional control valve to the travel motor 17. Specifically, when the directional control valve 14 is switched to the first direction, the pilot hydraulic pressure can be supplied to the directional control piston 14a, and at the same time, it can be supplied through the second pilot flow path 13a to control the volume of the travel motor 17. Furthermore, when the directional control valve 14 is switched to the second direction, the pilot hydraulic pressure can be supplied to the travel motor 17 through the third pilot flow path 13b.

[0061] However, if Figure 1 As shown, when the flow path for supplying the pilot hydraulic pressure to the travel motor 17 side is formed downstream of the directional control valve 14, when the directional control signal is in neutral, the power supply to the directional control valve 14 is released, thereby cutting off the supply of the pilot hydraulic pressure to the directional control piston 14a and the travel motor 17 side.

[0062] Therefore, when a neutral signal is applied to the directional control valve 14 to change direction while the construction machine is traveling at high speed, the directional control valve 14 is released, causing the pilot hydraulic pressure originally supplied to the travel motor 17 to decrease rapidly. In this case, the travel pump 11's capacity is reduced to its minimum, while the travel motor 17's capacity is increased to its maximum. Due to the inertia of the equipment in the current driving state, the travel motor 17 connected to the wheels functions as the travel pump 11, while the travel pump 11 functions as a motor. This creates the problem of excessive torque (load) being applied to the engine 1.

[0063] Refer again Figure 2 In the present invention, even when a neutral signal is applied to the directional control valve 140 to change direction during high-speed travel of the construction machine, thereby releasing the directional control valve 140, a pilot hydraulic pressure can be supplied to the travel motor 170 through the first pilot flow path 135. In the present invention, the pilot hydraulic pressure can be supplied so that the displacement of the travel motor 170 is changed in inverse proportion to the rotational speed of the engine 1.

[0064] The first pilot flow path 135 proposed in the present invention can be formed to supply pilot hydraulic pressure from the front end of the directional control valve 140 to the travel motor 170. The first pilot flow path 135 can be formed by branching from the main pilot flow path 131 formed between the auxiliary pump 120 and the directional control valve 140. One end of the first pilot flow path 135 can be connected to the main pilot flow path 131, and the other end can be connected to the travel motor valve 180. This allows the pilot hydraulic pressure supplied by the auxiliary pump 120 to be supplied from the front end of the directional control valve 140 to the travel motor 170.

[0065] That is, according to various embodiments of the present invention, when the direction needs to be changed during high-speed driving of the engineering machinery, a neutral signal may be applied to the directional conversion valve 140 to stop the equipment. At this time, the power supply to the directional conversion valve 140 is released. Therefore, even if the pilot hydraulic pressure is supplied through the main pilot flow path 131, the connection to the downstream may be cut off.

[0066] However, in the present application, since the first pilot flow path 135 is formed upstream of the directional control valve 140, the pilot hydraulic pressure generated by the auxiliary pump 120 can be supplied to the travel motor 170 via the main pilot flow path 131 and the first pilot flow path 135 branching therefrom. According to various embodiments of the present invention, even when a neutral signal is applied to the directional control valve 140 during high-speed travel of the construction machine, pilot hydraulic pressure can continue to be supplied to the travel motor 170 via the first pilot flow path 135, thereby preventing the travel motor 170 from reaching its maximum capacity. In other words, by reducing the travel motor 170's capacity to prevent it from reaching its maximum capacity, the inertia of the construction machine can be prevented from applying excessive rotational force to the engine 1.

[0067] The travel motor 170 can be configured to be connected to a gearbox (not shown) at the bottom of the construction machinery to transmit driving force to the wheels (not shown). The rotation direction of the travel motor 170 can be determined by the direction in which the working hydraulic pressure is discharged by the travel pump 110. In one embodiment, when the direction switching valve 140 is switched to the first direction, so that the discharge direction of the travel pump 110 is changed to the first direction, the working hydraulic pressure is supplied to the travel motor 170 through the first working fluid supply path 151, so that the rotation direction of the travel motor 170 can be the forward direction (FWD). In addition, when the direction switching valve 140 is switched to the second direction, so that the discharge direction of the travel pump 110 is changed to the second direction, the working hydraulic pressure is supplied to the travel motor 170 through the second working fluid supply path 152, so that the rotation direction of the travel motor 170 can be the reverse direction (REV).

[0068] The travel motor 170 may include a travel motor valve 180 and a volume control piston 185. The travel motor valve 180 may be connected to the first pilot flow path 135 to supply a pilot hydraulic pressure generated by the auxiliary pump 120. When the pilot hydraulic pressure is applied to the travel motor valve 180, the working hydraulic pressure supplied from the travel pump 110 flows into the large-diameter chamber of the volume control piston 185, causing the tilt angle of the swash plate to decrease, thereby reducing the volume of the travel motor 170.

[0069] As described above, in the case of a general closed-loop hydraulic power transmission device, when the direction change signal is converted to neutral, the direction change valve 140 is released, resulting in the inability to apply pilot hydraulic pressure to the valve of the travel motor 170. Therefore, as the pressure formed in the large-diameter cavity of the volume control piston 185 is discharged, the tilting angle of the swash plate becomes larger, and the volume of the travel motor 170 increases.

[0070] However, in the present invention, the pilot hydraulic pressure can be continuously applied to the travel motor valve 180 via the first pilot flow path 135 branching from the main pilot flow path 131 . Therefore, even if a neutral signal is suddenly applied during high-speed travel, the volume of the travel motor 170 can be prevented from increasing.

[0071] Just because all the constituent elements constituting the embodiments of the present invention are described above as being combined into one or combined into one to act, it does not mean that the present invention must be limited to such embodiments. That is, as long as it is within the scope of the purpose of the present invention, all its constituent elements can be selectively combined into more than one to act. In addition, unless otherwise stated to the contrary, the terms "including", "constituting" or "having" described above mean that the constituent elements can be inherent therein, and should therefore be interpreted as also including other constituent elements, rather than excluding their constituent elements. Unless otherwise defined, all terms including technical or scientific terms have the same meaning as commonly understood by a person skilled in the art of the art to which the present invention belongs. Commonly used terms, such as terms defined in dictionaries, should be interpreted as being consistent with the meaning in the context of the relevant technology and, unless clearly defined in the present invention, should not be interpreted as ideal or overly formal meanings.

[0072] The above description is merely an exemplary explanation of the technical idea of ​​the present invention, and a person skilled in the art in the art to which the present invention belongs can make various modifications and variations without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of ​​the present invention, but to illustrate the technical idea of ​​the present invention, and the scope of the technical idea of ​​the present invention is not limited by such embodiments. The scope of protection of the present invention should be interpreted by the claims, and all technical ideas within the scope equivalent to them should be interpreted as falling within the scope of the rights of the present invention.

Claims

1. A power transmission device for construction machinery, which transmits the driving force of an engine to wheels, the power transmission device for construction machinery comprising: a travel pump driven by the engine to discharge working hydraulic pressure in one of a first direction and a second direction; Auxiliary pump, which forms the pilot hydraulic pressure; a direction switching valve that controls a swash plate of the travel pump via the pilot hydraulic pressure according to a direction switching signal; a main pilot flow path for supplying the pilot hydraulic pressure supplied from the auxiliary pump to the directional control valve; a travel motor, the rotation direction of which is determined by the discharge direction of the travel pump; as well as a first pilot flow path branching from one side of the main pilot flow path and supplying the pilot hydraulic pressure in a manner to control the displacement of the travel motor; When the direction change signal is in neutral, the first pilot flow path supplies the pilot hydraulic pressure to the travel motor.

2. The power transmission device for construction machinery according to claim 1, characterized in that: The auxiliary pump is directly connected to the engine.

3. The power transmission device for construction machinery according to claim 1, characterized in that: The pilot hydraulic pressure supplied through the first pilot flow path reduces the displacement of the travel motor.

4. The power transmission device for construction machinery according to claim 1, characterized in that: The pilot hydraulic pressure changes the displacement of the travel motor in inverse proportion to the rotation speed of the engine.

5. The power transmission device for construction machinery according to claim 1, characterized in that: The first pilot flow path supplies the pilot hydraulic pressure to the travel motor when the direction change signal is changed from one of forward and reverse to neutral.

6. The power transmission device for construction machinery according to claim 1, characterized in that: When the directional control valve is released, the first pilot flow path supplies the pilot hydraulic pressure to the travel motor.

7. The power transmission device for construction machinery according to claim 1, characterized in that: The direction switching valve controls at least one of a tilting direction and a tilting angle of a swash plate of the travel pump.

8. The power transmission device for construction machinery according to claim 1, characterized in that: The travel motor includes a volume control piston for performing volume control of the travel motor, and a travel motor valve that supplies the working hydraulic pressure to the volume control piston when the pilot hydraulic pressure is applied thereto.

9. The power transmission device for construction machinery according to claim 1, characterized in that: Also includes: an electronic proportional pressure reducing valve, disposed in the main pilot flow path to control the pilot hydraulic pressure supplied to the directional control valve; as well as A control unit controls the electronic proportional pressure reducing valve according to an operation amount of an accelerator pedal.

10. The power transmission device for construction machinery according to claim 9, characterized in that: The control unit controls the electronic proportional pressure reducing valve in a direction in which the pilot hydraulic pressure is reduced as the operation amount of the accelerator pedal decreases.

11. The power transmission device for construction machinery according to claim 9, characterized in that: The control portion senses whether a cruise mode is activated, and fixedly controls the electronic proportional pressure reducing valve so that the pilot hydraulic pressure becomes maximum when the cruise mode is activated.

12. The power transmission device for construction machinery according to claim 9, characterized in that: It also includes an FNR operating lever, which generates an FNR operating signal through the operator's operation. When a current FNR state of the construction machine and the FNR operation signal are different from each other, the control portion controls the electronic proportional pressure reducing valve so as to minimize the pilot hydraulic pressure.

13. The power transmission device for construction machinery according to claim 9, characterized in that: Also included is a working machine pump driven by the engine to operate the working machine. When the travel pump and the working machine pump are driven simultaneously, the control unit controls the electronic proportional pressure reducing valve in a direction in which the pilot hydraulic pressure is reduced as the operation amount of the accelerator pedal decreases.

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