Hydrostatic transmission for work vehicle and control method thereof

Abstract

The present invention relates to a hydrostatic transmission for a work vehicle and a control method thereof. In the hydrostatic transmission for a work vehicle, according to the present invention, a swash plate of a hydraulic motor is rotatably provided, and an angle of the swash plate is adjusted according to a current load state by a servo mechanism. According to the present invention, shift shock and engine stalling can be minimized.

Description

Hydrostatic transmission for work vehicles and its control method

[0001] The present invention relates to a hydrostatic transmission applicable to various work vehicles.

[0002] A hydrostatic transmission is a transmission device mainly installed in work vehicles (agricultural tractors, heavy equipment or construction machinery vehicles, combines, rice transplanters, etc.) that frequently change gears due to the nature of their operation.

[0003] The hydraulic transmission is continuously variable and consists of a hydraulic motor and a hydraulic pump.

[0004] A hydraulic motor generates rotational force on an output shaft by hydraulic pressure according to the flow rate of working fluid coming from a hydraulic pump.

[0005] The hydraulic pump is operated by the rotational force output from the engine, and sucks in the fluid and supplies it to the hydraulic motor.

[0006] The hydraulic pump is equipped with a swash plate for speed change, and speed change is performed by rotation of the swash plate.

[0007] Forward or reverse gear shifting can be achieved depending on the direction of rotation of the swash plate in the neutral position.

[0008] In addition, the flow rate provided by the hydraulic motor varies depending on the rotational amount of the swash plate, thereby performing stepless acceleration and deceleration.

[0009] That is, the hydraulic pump is equipped with a variable capacity type in which the speed is changed by varying the flow rate provided by the hydraulic motor. The degree of capacity change is determined by the direction and amount of rotation of the swash plate.

[0010] Therefore, the hydraulic transmission has a servo mechanism for adjusting the angle of the swash plate in the hydraulic pump.

[0011] For example, a servo mechanism may consist of a piston that rotates a swash plate by movement, and a hydraulic valve that moves the piston.

[0012] Hydraulic valves can be used to improve shift shock during driving, prevent engine stall due to sudden load generation during driving or work, or electronic proportional control valves can be applied to increase operator convenience.

[0013] However, controlling the hydraulic pump's swash plate alone was insufficient to prevent shift shock and engine stall. Therefore, a two-stage control technology for the hydraulic motor's swash plate was proposed, but it is still insufficient to prevent shift shock and engine stall.

[0014] In particular, for agricultural work vehicles used in agriculture, constant speed driving is necessary to maintain an appropriate driving speed suitable for the work speed performed by the work machine being towed in many tasks.

[0015] However, shift shock and engine stalling can disrupt steady-state driving and reduce power output to the implement, potentially leading to poor performance. Therefore, better technologies are needed to prevent shift shock and engine stalling, particularly in agricultural work vehicles.

[0016] [Prior Art Literature]

[0017] [Patent Document]

[0018] (Patent Document 1) Republic of Korea Publication No. 10-2018-0090015

[0019] The present invention was conceived from the concern of maintaining constant speed driving and good operating condition of a vehicle by preventing shift shock and engine stall as much as possible in a hydrostatic transmission.

[0020] A hydrostatic transmission for a work vehicle according to the present invention comprises: a hydraulic motor that generates rotational force of an output shaft by hydraulic pressure and has a rotational speed of the output shaft that varies according to an angular position of a first swash plate whose angular position can be varied; a first servo mechanism that is controlled by a controller and varies the angular position of the first swash plate in the hydraulic motor between a minimum angle and a maximum angle; a hydraulic pump that provides hydraulic pressure to the hydraulic motor and varies the flow rate provided to the hydraulic motor according to an angular position of a second swash plate whose angular position can be varied; and a second servo mechanism that is controlled by the controller and varies the angular position of the second swash plate in the hydraulic pump. , and the minimum angle is an angular position that makes the rotation speed of the output shaft the minimum, the maximum angle is an angular position that makes the rotation speed of the output shaft the value ㅗ, and the controller controls the first servo mechanism (120) to vary the angular position of the first swash plate between the minimum angle and the maximum angle in response to the load state of the engine.

[0021] The controller controls the first servo mechanism so that the first swash plate can be selectively positioned at the lowest angle, the highest angle, and at least one angular position between the lowest angle and the highest angle.

[0022] The above controller controls the first servo mechanism so that the first swash plate can be selectively positioned at any angular positions consecutively between the lowest angle and the maximum angle.

[0023] The controller comprises: a collection means for collecting information capable of confirming the load state of the engine; a judgment means for confirming the load state of the engine with the information collected by the collection means and then determining which of at least three load states it is currently in; and a control means for controlling the first servo mechanism in different control modes according to the load state of the engine determined by the judgment means, thereby adjusting the angular position of the first swash plate.

[0024] The load state of the engine is divided into a light load state, a high load state, and a medium load state between the light load state and the high load state, and the control means controls the first servo mechanism so that the first swash plate is positioned at the lowest angle in the light load mode, which is a control mode in the light load state, the first swash plate is positioned at the highest angle in the high load mode, which is a control mode in the high load state, and the first swash plate is positioned at an arbitrary angle position between the lowest angle and the highest angle in the medium load mode, which is a control mode in the medium load state.

[0025] The above control means controls the first servo mechanism to move the angular position of the first swash plate toward the minimum angle direction when the current vehicle speed is higher than the set vehicle speed in the above heavy load mode, and to move the angular position of the first swash plate toward the maximum angle direction when the current vehicle speed is lower than the set vehicle speed.

[0026] A control method for a hydrostatic transmission for a work vehicle according to the present invention comprises: an information collection step for collecting information for determining a load state of an engine; a load judgment step for analyzing the information collected in the information collection step to confirm the load state of the engine and to determine the load state of the engine; and an angular position control step for changing the angular position of a swash plate in a hydraulic motor in a control mode according to the load state of the engine determined in the load judgment step.

[0027] The above load judgment step judges whether the load state of the engine is a light load state, a high load state, or a heavy load state between the light load state and the high load state, and the above angular position control step changes the angular position of the swash plate to a control mode according to the load state of the engine judged in the load judgment step among the light load mode, which is a control mode in the light load state, the high load mode, which is a control mode in the high load state, and the heavy load mode, which is a control mode in the heavy load state.

[0028] The above load judgment step includes a first calculation step of calculating a set speed; a first confirmation step of checking whether the engine torque and the engine speed satisfy the first setting condition for corresponding to the high load state; a second calculation step of calculating a speed difference between the set speed and the current vehicle speed if the first setting condition is not satisfied in the first confirmation step; a second confirmation step of checking whether the engine torque and the speed difference calculated in the second calculation step satisfy the second setting condition for corresponding to the light load state; and a judgment step of determining whether the load state of the engine is the light load state, the high load state, or the heavy load state based on the confirmations in the first confirmation step and the second confirmation step.

[0029] The first setting condition is that the engine torque is equal to or greater than the second specific value as the engine speed decreases, and the second setting condition is that the vehicle speed difference is equal to or less than the setting value or the engine torque is equal to or less than the first specific value that is less than the second specific value.

[0030] In the above-mentioned angular position control step, in the above-mentioned heavy load mode, if the current vehicle speed is higher than the set vehicle speed, the angular position of the swash plate is moved toward the minimum angle direction, and if the current vehicle speed is lower than the set vehicle speed, the angular position of the swash plate is moved toward the maximum angle direction.

[0031] In the above-mentioned angular position adjustment step, in the above-mentioned medium load mode, if the engine torque is greater than the second specific value, the angular position of the swash plate is moved in the direction of the maximum angle.

[0032] The above-mentioned angular position adjustment step adjusts the angular position of the swash plate to the minimum angle in the light load mode, adjusts the angular position of the swash plate to the maximum angle in the high load mode, and adjusts the angular position of the swash plate to an arbitrary angular position between the minimum angle and the maximum angle in the medium load mode.

[0033] The variable value of each position of the above-mentioned swash plate can be determined by the mathematical formula [error compensation constant 1 (set vehicle speed - current vehicle speed)].

[0034] The variable value of each position of the above-mentioned swash plate (111) can be determined by the mathematical formula [error compensation constant 1 (set vehicle speed - current vehicle speed) + maximum value (0, error compensation constant 2 (current engine torque - first specific value))].

[0035] According to the present invention, the angular position of the swash plate in the hydraulic motor can be automatically changed in response to the load condition of the engine, thereby providing the following effects.

[0036] First, the gear shift shock caused by rapid changes in working speed can be minimized.

[0037] Second, engine stalling can be minimized or prevented, improving driving stability (e.g., ride comfort and functional convenience).

[0038] Third, work efficiency is improved because constant-speed driving performance and uniform work performance are secured by the work machine.

[0039] Therefore, the reliability of the work vehicle is ultimately improved.

[0040] Figure 1 is a configuration diagram of a hydrostatic transmission for a work vehicle according to another embodiment of the present invention.

[0041] Figure 2 is a schematic diagram of the hydraulic motor side of the hydrostatic transmission of Figure 1.

[0042] Figures 3 and 4 are reference drawings for explaining a controller that controls the hydrostatic transmission of Figure 1.

[0043] Figure 5 is a reference diagram for explaining the change in angle of the swash plate according to the current load state.

[0044] Figure 6 is a flowchart for explaining a method for controlling a hydrostatic transmission according to one embodiment of the present invention.

[0045] Figure 7 is an excerpt for step S20 in the flowchart of Figure 6.

[0046] Figure 8 is a reference diagram for explaining step S25 of Figure 7.

[0047] A preferred embodiment according to the present invention is described with reference to the attached drawings, but for the sake of brevity, descriptions of well-known components are omitted or compressed as much as possible.

[0048] FIG. 1 is a configuration diagram of a hydraulic transmission for a work vehicle (100, abbreviated as ‘hydraulic transmission’) according to one embodiment of the present invention.

[0049] The hydraulic pressure transmission (100) of FIG. 1 includes a hydraulic motor (110), a first servo mechanism (120), a hydraulic pump (130), and a second servo mechanism (140).

[0050] The hydraulic motor (110) generates rotational force of the output shaft (OS) by hydraulic pressure supplied from the hydraulic pump (120).

[0051] According to the present invention, a hydraulic motor (110) has a first swash plate (111) whose angular position can be varied by rotation. And, the rotational speed of the output shaft (OS) is varied according to the angular position of the first swash plate (111).

[0052] According to the present invention, the first swash plate (111) varies the rotational speed of the output shaft (OS) by moving between the lowest angle and the highest angle. That is, the first swash plate (111) may be positioned at the lowest angle or at the highest angle.

[0053] The lowest angle refers to the angle position at which the discharge flow rate of the hydraulic motor (110) becomes the lowest, theoretically making the rotational speed of the output shaft (OS) the lowest.

[0054] The maximum angle refers to the angle at which the discharge flow rate of the hydraulic motor (110) becomes maximum and theoretically the rotational speed of the output shaft (OS) becomes maximum.

[0055] Additionally, the first swash plate (111) can be selectively positioned at at least one angular position between the lowest angle and the highest angle. At this time, theoretically, the rotational speed of the output shaft (OS) has a value between the lowest rotational speed and the highest rotational speed of the output shaft (OS).

[0056] Preferably, for more precise control of the output, the first swash plate (111) can be selectively positioned at the lowest angle, the maximum angle, and any consecutive angular positions between the lowest angle and the maximum angle. For example, the first swash plate (111) can be positioned at any of the lowest angle, the maximum angle, and any consecutive angular positions from the lowest angle to the maximum angle. Of course, each of the consecutive angular positions from the lowest angle to the maximum angle corresponds one-to-one to the rotational speed values ​​of the theoretical output shaft (OS).

[0057] The first servo mechanism (120) varies the angular position of the first swash plate (111) in the hydraulic motor (110) in response to the current load condition.

[0058] For example, as shown in the schematic diagram of Fig. 2, the first servo mechanism (120) can be implemented with an electronic proportional control valve (121) and a piston (122). Therefore, the first servo mechanism (120) can be electronically controlled by the controller (200).

[0059] When the controller (200) operates the electronic proportional control valve (121), the piston (122) moves linearly by hydraulic pressure (see arrow a), and the angular position of the first swash plate (111) is varied (see arrow b) by an amount corresponding to the amount of movement of the piston (122). Accordingly, the angular position of the first swash plate (111) can be determined depending on the amount of movement of the piston (122). Therefore, the angular position of the first swash plate (111) can be the lowest angle, the highest angle, or any position between the lowest angle and the highest angle.

[0060] The hydraulic pump (130) operates by the rotational force of the input shaft (IS) and provides working fluid that generates hydraulic pressure to the hydraulic motor (110). The rotational force of the input shaft (IS) comes from the engine (E).

[0061] The hydraulic pump (130) has a second swash plate (131) whose angular position can be adjusted. Therefore, the flow rate provided to the hydraulic motor (110) varies depending on the angular position of the second swash plate (131).

[0062] The second servo mechanism (140) varies the angular position of the second swash plate (131) in the hydraulic pump (130). Similarly, the second servo mechanism (140) can be controlled by the controller (200).

[0063] Meanwhile, the controller (200) controlling the first servo mechanism (120) and the second servo mechanism (140) can collect information for determining the variable amount for each position of the first swash plate (110). To this end, the controller (200) collects information from various sensors in the work vehicle.

[0064] According to the present invention, the controller (200) determines the load state of the engine (E) and varies the angular position of the first swash plate (110). Therefore, the collected information is information for determining the load state of the engine (E).

[0065] As shown in FIG. 3, the controller (200) collects information from a foot pedal sensor (310), an engine torque sensor (320), an engine RPM sensor (330), a vehicle speed sensor (340), an oil temperature sensor (350), etc.

[0066] The foot pedal sensor (310) detects the amount of pressure applied to the foot pedal by the driver for gear shifting.

[0067] The engine torque sensor (320) detects the engine torque.

[0068] The engine RPM sensor (330) detects the engine rotation speed (hereinafter referred to as “engine rotation speed”).

[0069] The vehicle speed sensor (340) detects the current vehicle speed of the work vehicle.

[0070] The oil temperature sensor (350) detects the temperature of the working oil.

[0071] According to the present invention, the above sensors (310 to 350) are intended to detect information for checking the load status of the engine (E) in driving and / or working conditions. In particular, information collected from the foot pedal sensor (310), engine RPM sensor (330), and oil temperature sensor (350) among them is used to calculate the set vehicle speed.

[0072] Figure 4 is a configuration diagram for a controller (200) according to an example.

[0073] The controller (200) may include a collection means (210), a judgment means (220), and a control means (230).

[0074] The collection means (210) collects information from the sensors (310 to 350) above.

[0075] The judgment means (220) checks the load status of the engine using the information collected by the collection means (210). In addition, the judgment means (220) determines whether the checked load status of the engine is in one of the plurality of set load states.

[0076] The judgment means (220) may include an operation part (221), a confirmation part (222), and a judgment part (223).

[0077] The calculation part (221) calculates the set vehicle speed using information from the foot pedal sensor (310), engine RPM sensor (330), and oil temperature sensor (350).

[0078] In addition, the calculation part (221) calculates the difference between the set speed and the current speed using information from the speed sensor (340).

[0079] In addition, the operation section (221) calculates variable values ​​for each position of the first swash plate (111). This will be explained in more detail later.

[0080] The verification section (222) verifies whether the first setting condition is satisfied.

[0081] The first setting condition is a condition for the load state of the engine (E) to correspond to a high load state.

[0082] Verification of whether the first setting condition is satisfied can be performed using information from, for example, the engine torque sensor (320) and the engine RPM sensor (330).

[0083] More specifically, the first setting condition may be that the current engine speed is lowered while the engine torque is higher than a second specific value. Here, the second specific value may be set to the maximum torque value that the engine can actually output.

[0084] Additionally, the verification part (222) verifies whether the second setting condition is satisfied.

[0085] The second setting condition is a condition for the load state of the engine (E) to correspond to a light load state.

[0086] Verification of whether the second setting condition is satisfied can be performed, for example, using information from the engine torque sensor (320) and the vehicle speed difference calculated in the calculation section (221).

[0087] More specifically, the second setting condition may be that the speed difference is less than or equal to a setting value or that the engine torque is less than or equal to a first specific value. Here, the first specific value is set to a value less than the second specific value, and may be set based on, for example, a negligible load (theoretically, no load).

[0088] The judgment part (223) determines what load state the engine (E) is currently in depending on whether the first setting condition or the second setting condition is met.

[0089] According to a preferred embodiment of the present invention, the current load state is divided into three load states and set.

[0090] The three load states are light load, high load, and medium load.

[0091] A light load state is a state with a relatively small load, a high load state is a state with a relatively large load, and a medium load state refers to a state between a light load state and a high load state.

[0092] That is, according to one embodiment, the judgment part (223) determines whether the current load state is a light load state, a high load state, or a medium load state depending on whether the first setting condition or the second setting condition is satisfied.

[0093] The control means (230) controls the first servo mechanism (120) by changing the control mode according to the load state of the engine (E) determined by the determination means (220). Of course, the angular position of the first swash plate (111) changes in response to the control of the first servo mechanism (120).

[0094] The control mode under light load is light load mode.

[0095] In the light load mode, the control means (230) controls the first servo mechanism (120) so that the angular position of the first swash plate (111) becomes the minimum angle. Therefore, in the light load mode, the rotational speed of the output shaft (OS) is theoretically controlled to have the minimum value.

[0096] The control mode under high load conditions is high load mode.

[0097] In high load mode, the control means (230) controls the first servo mechanism (120) so that the angular position of the first swash plate (111) becomes the maximum angle. Therefore, in high load mode, the rotational speed of the output shaft (OS) is theoretically controlled to have the maximum value.

[0098] The control mode in medium load mode is medium load mode.

[0099] According to a preferred embodiment of the present invention, in the medium-load mode, the first swash plate (111) is determined to be at an arbitrary angular position between the minimum angle and the maximum angle. Therefore, in the medium-load mode, the rotational speed of the output shaft (OS) is theoretically located between the maximum and minimum values.

[0100] In the medium load mode, if the current vehicle speed is higher than the set vehicle speed, the first swash plate (111) is moved toward the lowest angle direction, and if the current vehicle speed is lower than the set vehicle speed, the first swash plate (111) is moved toward the highest angle direction.

[0101] Additionally, depending on the implementation, if the engine torque is higher than the second specific value in the medium load mode, the first swash plate (111) can be additionally moved in the maximum angle direction.

[0102] Figure 5 shows the change in angle of the first swash plate (111) in a light load section, a high load section, and a medium load section.

[0103] Referring to Fig. 5, the change in the angular position of the first swash plate (111) will be described in more detail.

[0104] In a section under light load, the first swash plate (111) maintains the minimum angle, and in a section under high load, the first swash plate (111) maintains the maximum angle. In addition, in a section under heavy load, the first swash plate (111) can be positioned at any angular position between the minimum angle and the maximum angle. That is, according to a preferred example of the present invention, in a section under heavy load, the first swash plate (111) can be selectively positioned at any consecutive angular positions between the minimum angle and the maximum angle. In addition, the rotational speed of the theoretical output shaft (OS) is determined in response to such angular positions.

[0105] The control method of a hydrostatic transmission (100) having the above configuration will be described with reference to the flow chart of Fig. 6.

[0106] 1. Information collection <s10>

[0107] The collection means (210) collects information for determining the load status according to driving and / or work. The information collected here includes the amount of foot pedal pressure, engine torque, engine RPM, current vehicle speed, and operating fluid temperature received from the foot pedal sensor (310), engine torque sensor (320), engine RPM sensor (330), vehicle speed sensor (340), and oil temperature sensor (350). Of course, any information that can determine the load status of the engine (E) more accurately can be added.

[0108] 2. Load judgment <s20>

[0109] The judgment means (220) analyzes the information collected in step S10 to check the current load status of the engine (E) and determines the current load status of the engine (E).

[0110] The load state of the engine (E) can be divided into, for example, light load state, high load state, and medium load state.

[0111] A light load condition is a condition in which the driving and / or work load is light, theoretically allowing the output shaft (OS) to rotate at its lowest speed. For example, a light load condition may occur when driving downhill due to the incline of the driving surface or when the work surface is low, resulting in a low driving and / or work load.

[0112] A high-load condition is a condition in which the driving and / or work load is high, requiring maximum rotational speed of the output shaft (OS). For example, a high-load condition may occur when driving uphill due to the incline of the driving surface, or when the work surface is hard, resulting in high driving and / or work loads, which slows down the work vehicle.

[0113] The heavy load state is a state between the light load state and the high load state.

[0114] Of course, depending on the implementation, it may be possible to further divide the state into one or more of light load state, high load state, and medium load state.

[0115] This step S20 can be subdivided into more specific steps as shown in the flowchart of Fig. 7.

[0116] 2-1. First operation <s21>

[0117] The calculation part (221) calculates the set vehicle speed using the information collected from the foot pedal sensor (310), engine RPM sensor (330), and oil temperature sensor (350) among the information collected in step S10.

[0118] For example, information from the foot pedal sensor (310) may be the amount of pressure applied to the foot pedal by the driver for shifting.

[0119] For example, information from the engine RPM sensor (330) may be engine speed. The engine speed may be implemented to be set by the driver using the RPM pedal or a separate hand lever.

[0120] For example, the oil temperature sensor (350) may measure the temperature of the working fluid. The viscosity of the working fluid may vary depending on its temperature, which may in turn affect the vehicle speed. In other words, the set speed may be affected by the temperature of the working fluid, and therefore, information collected from the oil temperature sensor (350) is required to accurately calculate the set speed.

[0121] 2-2. First confirmation <s22>

[0122] The verification section (222) verifies whether the first setting conditions regarding engine torque and engine speed are satisfied.

[0123] The first setting condition is the condition for engine torque and engine speed to correspond to a high load state.

[0124] According to a preferred embodiment, the first setting condition may be that the engine torque is greater than or equal to a second specific value while the engine speed is lowered.

[0125] 2-3. Second operation <s23>

[0126] If the first setting condition is exceeded in step S22, the calculation part (221) calculates the speed difference between the set speed and the current speed.

[0127] For example, when the engine speed increases or the engine torque is below the second specific value, the calculation part (221) calculates the vehicle speed difference using the set vehicle speed calculated in step S21 and the current vehicle speed collected from the vehicle speed sensor (340).

[0128] 2-4. Second confirmation <s24>

[0129] The verification section (222) verifies whether the second setting condition regarding the engine torque and the vehicle speed difference calculated in step S23 is satisfied.

[0130] The second setting condition is the condition for the engine torque and vehicle speed difference to correspond to a light load state.

[0131] According to a preferred embodiment, the second setting condition may be that the vehicle speed difference is below a set value or the engine torque is below a first specific value. Here, it is preferable that the setting value for the vehicle speed difference is an optimal value selected through numerous repeated tests.

[0132] For reference, if the setting value is 0.1 km / h, the second setting condition can be satisfied if the vehicle speed difference is less than 0.1 km / h. Also, even if the vehicle speed difference is greater than 0.1 km / h, the second setting condition can be satisfied if the engine torque is less than the first specific value.

[0133] In this embodiment, the speed difference is an absolute value that can only specify its size. That is, when the setting value is 0.1 km / h, in order for the first setting condition to be satisfied, the speed difference must fall within the range of (-) 0.1 km / h to (+) 0.1 km / h.

[0134] 2-5. Judgment <s25>

[0135] The judgment part (223) determines whether the state is light load, high load, or medium load based on the confirmation made in steps S22 and S24.

[0136] Step S25 will be examined in more detail with reference to the reference diagram of FIG. 8.

[0137] According to this example, if it is confirmed that the current first setting condition is satisfied in step S22, the judgment part (223) determines that the current is a high load state.

[0138] According to this example, if it is confirmed that the second setting condition is currently satisfied in step S24, the judgment part (223) determines that the current is a light load state.

[0139] According to this example, if it is confirmed that the first setting condition is not satisfied in step S22 and the second setting condition is not satisfied in step S24, the judgment part (23) determines that the current is a heavy load state between a light load state and a high load state.

[0140] 3. Angle position adjustment <s30>

[0141] When the current load state is determined in step S20, the control means (230) changes the angular position of the first swash plate (111) in a control mode according to the determined load state.

[0142] In a light load state, the angular position of the first swash plate (111) is changed to the light load mode, which is the control mode for the light load state.

[0143] According to this example, in light load mode, the angular position of the first swash plate (111) is adjusted to the minimum angle. Accordingly, the rotational speed of the output shaft (OS) is controlled to the minimum. In light load mode, driving and / or work will be performed primarily based on inertia.

[0144] According to this example, in high load mode, the angular position of the first swash plate (111) is adjusted to the maximum angle. Accordingly, the rotational speed of the output shaft (OS) is controlled to the maximum.

[0145] According to this example, in the heavy load mode, the angular position of the first swash plate (111) is adjusted to any angular position between the minimum angle and the maximum angle. The angular position of the first swash plate (111) in this heavy load mode will be described in more detail.

[0146] In the medium load mode, if the current vehicle speed is higher than the set speed, the angular position of the first swash plate (111) is moved toward the lowest angle. In this case, the rotational speed of the output shaft (OS) decreases, so the current vehicle speed decreases and converges to the set speed.

[0147] In the medium load mode, if the current vehicle speed is lower than the set vehicle speed, the angular position of the first swash plate (111) is moved toward the maximum angle. In this case, the rotational speed of the output shaft (OS) increases, so the current vehicle speed increases and converges to the set vehicle speed.

[0148] In addition, in a working situation, even if the driving load is low and the engine speed is maintained, the engine torque may be higher than the second specific value due to the working load. Therefore, in a case where the engine torque is higher than the second specific value while the engine speed is maintained, the angular position of the first swash plate (111) may be additionally moved toward the maximum angle in order to give weight to the angular position control value of the first swash plate (111).

[0149] Meanwhile, the variable value for each position of the first slab (111) can be determined by mathematical formula (1).

[0150] Mathematical formula (1): Rotational displacement value = error compensation constant 1 (set speed - current speed)

[0151] Furthermore, for more precise control over the angular position of the first slab (111), the variable value for each position can be determined by mathematical formula (2).

[0152] Mathematical formula (2): Rotational displacement value = Error compensation constant 1 (set vehicle speed - current vehicle speed) + maximum value (0, error compensation constant 2 (current engine torque - second specific value))

[0153] In the mathematical formula, error compensation constant 1 and error compensation constant 2 are optimized compensation constants obtained through numerous repeated tests.

[0154] Error compensation constant 1 and error compensation constant 2 can have units such that the units of the values ​​obtained by the mathematical formula are angles.

[0155] In mathematical expression (2), the maximum value can be '0' or 'error compensation constant (current engine torque - second specific value)'. If the current '(engine torque - second specific value)' is less than '0', the maximum value becomes '0', and vice versa, the maximum value becomes '(engine torque - second specific value)'. Therefore, the maximum value can be reflected in the variable value only when '(engine torque - second specific value)' is a positive value.

[0156] The variable value for the angular position of the first swash plate (111) according to the mathematical formula above is obtained by the operation of the operation part (221). Then, the control means (230) controls the first server mechanism (120) to move the angular position of the first swash plate (111) by the determined variable value, thereby adjusting the angular position of the first swash plate (111).

[0157] <Additional Explanation>

[0158] Typically, in work vehicles such as agricultural tractors, both the power required for driving and the power required for the work equipment's operation are generated from the engine (E). Therefore, in situations where both driving and work are performed, both the driving load and the work load act as loads on the engine (E).

[0159] Therefore, if either the driving or working load becomes high, both driving and working will be affected. Accordingly, the engine (E) is typically controlled to increase its RPM for greater output. However, if the engine (E) cannot withstand the high load, it will suddenly stall and stall, ultimately causing the engine (E) to stall.

[0160] Meanwhile, when a hydraulic pressure transmission (100) is applied, the load applied during driving and work is transmitted to the engine (E) through the output shaft (OS) at the rear end of the hydraulic motor (110).

[0161] However, according to one example of the present invention, when the engine (E) is under a high load, the angular position of the first swash plate (111) is controlled to become the maximum angle. Then, theoretically, the rotational speed of the output shaft (OS) should increase. However, the actual rotational speed of the output shaft (OS) may not increase due to the high load transmitted to the engine (E) through the output shaft (OS). However, from a control perspective, since the torque of the output shaft (OS) is recognized to decrease due to the increase in the rotational speed of the output shaft (OS), the appropriate engine rotation speed is also determined to be low. Therefore, the engine (E) has room to operate at a lower speed. Accordingly, the start-off time due to a sudden engine stall phenomenon can be somewhat delayed.

[0162] Once the high-load condition is resolved during this delayed period, the work vehicle can return to normal operating conditions. Here are some examples of how high-load conditions can be resolved.

[0163] First, the high load condition can be relieved through appropriate driving operations by the driver.

[0164]

[0165] For example, if a plow, which is a work piece, is deeply embedded and is under a high load, the high load condition can be relieved by the operator lifting the plow.

[0166] For example, a high load condition can be relieved by the operator manipulating the output shaft (OS) to cut power to the implement or wheels.

[0167] Second, high-load conditions can be naturally relieved during the operation of the work vehicle. For example, high-load conditions can be naturally relieved by passing through and then exiting a high-load section during the driving process.

[0168] If the high load condition is released while the engine stall is delayed in this way, the engine (E) can be switched to a medium load condition or a light load condition.

[0169] Meanwhile, the high load condition may not be relieved while the engine (E) is being turned off. Then, the controller (200) prevents the engine (E) from being turned off at least by cutting off the power between the engine (E) and the hydraulic transmission (100).

[0170] <Note>

[0171] 1. Regarding each position of the first edition

[0172] The present invention is to vary the rotational speed of an output shaft (OS) by moving the angular position of a first swash plate (111) in a hydraulic motor (110) in response to a current load condition. Therefore, the first swash plate (111) may be positioned at a minimum angle and a maximum angle, or may be positioned at any position between the minimum angle and the maximum angle.

[0173] That is, in a preferred example of the present invention, the first swash plate (111) is selectively positioned at successive angular positions between the lowest angle and the maximum angle.

[0174] However, depending on the implementation, it may be considered to set multiple angle positions with equal intervals between the lowest angle and the highest angle, and to implement the first swash plate (111) so that it remains fixed at the multiple angle positions.

[0175] 2. Regarding load status

[0176] In the above example, the load states are divided into light, high, and medium load states. However, for example, the medium load state could be divided into a first heavy load state and a second heavy load state, with the control modes for the first and second heavy load states being implemented differently. Similarly, the light and high load states could be further subdivided. Of course, it would also be perfectly possible to give each load state a different name.

[0177] 3. Regarding setting conditions

[0178] The above first and second setting conditions are only examples for checking the current load status, so they may be replaced with better setting conditions that can accurately check the load status, or additional setting conditions may be added.

[0179] 4. Mathematical formulas

[0180] Mathematical formulas (1) and (2) are only examples, so any formula that can obtain the optimal variable value for each position of the first swash plate (111) can be applied.

[0181] 5. Related to various values ​​set

[0182] The first specific value, second specific value, set value, error compensation constant 1, and error compensation constant 2 mentioned above are constants that can be optimally determined through numerous repeated tests. Of course, these values ​​may vary depending on the horsepower and other specifications of the work vehicle.

[0183] 6. Regarding gear shift shock

[0184] During gear shifting, a sudden change in the rotational speed of the output shaft (OS) can cause shock. However, when the present invention is applied, the rotational speed of the output shaft (OS) is appropriately controlled in response to the current load condition, thereby minimizing shock caused by gear shifting.

[0185] The above-described embodiments merely illustrate preferred examples of the present invention, and it may have various applications. Therefore, the present invention should not be construed as limited to the above-described content. Instead, the scope of the present invention should be construed within the scope of the separately described claims and their equivalents.

Claims

1. A hydraulic motor (110) that generates rotational force of an output shaft (OS) by hydraulic pressure and changes the rotational speed of the output shaft (OS) according to the angular position of a first swash plate (111) whose angular position can be changed; A first servo mechanism (120) for varying the angular position of the first swash plate (111) in the hydraulic motor (110) between the lowest angle and the maximum angle while being controlled by the controller (200); A hydraulic pump (130) that provides hydraulic pressure to the hydraulic motor (110) and whose flow rate provided to the hydraulic motor (110) is variable according to the position of the second swash plate (131) whose position can be varied; and A second servo mechanism (140) for varying the angular position of the second swash plate (131) in the hydraulic pump (130) while being controlled by the controller (200); The above minimum angle is the angle position at which the rotational speed of the output shaft becomes the minimum, and the above maximum angle is the angle position at which the rotational speed of the output shaft becomes the maximum. The above controller (200) controls the first servo mechanism (120) to vary the angle position of the first swash plate (111) between the minimum angle and the maximum angle in response to the load state of the engine. Hydrostatic transmission for work vehicles.

2. In paragraph 1 The above controller (200) controls the first servo mechanism (120) so that the first swash plate (111) can be selectively positioned at the lowest angle, the maximum angle, and at least one angular position between the lowest angle and the maximum angle. Hydrostatic transmission for work vehicles.

3. In paragraph 2 The above controller (200) controls the first servo mechanism (120) so that the first swash plate (111) can be selectively positioned at any angular positions consecutively between the lowest angle and the maximum angle. Hydrostatic transmission for work vehicles.

4. In paragraph 1 The above controller (200) A collection means (210) for collecting information that can check the load status of the engine; A judgment means (220) for checking the load state of the engine using the information collected by the above collection means (210) and then determining which of at least three load states it is currently in; and A control means (230) for controlling the first servo mechanism (120) by controlling the first servo mechanism (120) in different control modes according to the load state of the engine determined by the determination means (220), thereby adjusting the angular position of the first swash plate (111); Hydrostatic transmission for work vehicles.

5. In paragraph 4 The engine load condition is divided into light load condition, high load condition, and medium load condition between the light load condition and high load condition. The above control means (230) controls the first servo mechanism (120) so that the first swash plate (111) is positioned at the lowest angle in the light load mode, which is the control mode in the light load state, the first swash plate (111) is positioned at the highest angle in the high load mode, which is the control mode in the high load state, and the first swash plate (111) is positioned at any angle position between the lowest angle and the highest angle in the heavy load mode, which is the control mode in the medium load state. Hydrostatic transmission for work vehicles.

6. In paragraph 5 The above control means (200) controls the first servo mechanism (120) to move the angular position of the first swash plate (111) in the minimum angle direction when the current vehicle speed is higher than the set vehicle speed in the above heavy load mode, and to move the angular position of the first swash plate (111) in the maximum angle direction when the current vehicle speed is lower than the set vehicle speed. Hydrostatic transmission for work vehicles.

7. Information collection stage to collect information to determine the engine load status. <s10> ;< / s10> The above information collection stage <s10>The load judgment stage analyzes the information collected from the engine to check the engine load status and determine the engine load status. <s20> ; and The above load judgment step <s20>An angular position control step that changes the angular position of the swash plate (111) in the hydraulic motor (110) in a control mode according to the load condition of the engine judged in <s30> ; including Control method of a hydrostatic transmission for a work vehicle.

8. In paragraph 7, The above load judgment step <s20> It determines whether the engine load condition is a light load condition, a high load condition, or a medium load condition between the light load condition and the high load condition. The above angular position adjustment step <s30> The control mode is a control mode according to the load state of the engine judged in the load judgment step among the light load mode, which is a control mode in the light load state, the high load mode, which is a control mode in the high load state, and the heavy load mode, which is a control mode in the medium load state, and changes the angular position of the swash plate (111). Control method of a hydrostatic transmission for a work vehicle.

9. In paragraph 8 The above load judgment step <s20> Is The first calculation step to calculate the set speed <s21> ;< / s21> The first verification step is to check whether the engine torque and engine speed satisfy the first setting condition for the high load condition. <s22> ;< / s22> The above first verification step <s22>If the first setting condition is exceeded, the second calculation step calculates the speed difference between the set speed and the current speed. <s23> ;< / s23> Engine torque and the second operation stage <s23>The second verification step is to check whether the speed difference calculated in satisfies the second setting condition for a light load state. <s24> ; and The above first verification step <s22>And the second confirmation step above <s24>A judgment step for determining whether the engine load condition is the light load condition, the high load condition, or the medium load condition based on the confirmation in <s25> ; including Control method of a hydrostatic transmission for a work vehicle.

10. In paragraph 9 The above first setting condition is that the engine torque is higher than the second specific value as the engine speed decreases. The above second setting condition is that the speed difference is less than or equal to the setting value or the engine torque is less than or equal to the first specific value which is less than the second specific value. Control method of a hydrostatic transmission for a work vehicle.

11. In paragraph 9 The above angular position adjustment step <s30> In the above heavy load mode, if the current vehicle speed is higher than the set vehicle speed, the angular position of the swash plate (111) is moved in the direction of the minimum angle, and if the current vehicle speed is lower than the set vehicle speed, the angular position of the swash plate (111) is moved in the direction of the maximum angle.< / s30> Control method of a hydrostatic transmission for a work vehicle.

12. In paragraph 9, The above angular position adjustment step <s30> In the above-mentioned heavy load mode, if the engine torque is greater than the second specific value, the angular position of the swash plate (111) is moved in the direction of the maximum angle.< / s30> Control method of a hydrostatic transmission for a work vehicle.

13. In paragraph 8 The above angular position adjustment step <s30> In the light load mode, the angular position of the swash plate (111) is adjusted to the lowest angle, in the high load mode, the angular position of the swash plate (111) is adjusted to the highest angle, and in the medium load mode, the angular position of the swash plate (111) is adjusted to any angular position between the lowest angle and the highest angle.< / s30> Control method of a hydrostatic transmission for a work vehicle.

14. In paragraph 7, The variable value of each position of the above-mentioned swash plate (111) is determined by the mathematical formula [error compensation constant 1 (set speed - current speed)]. Control method of a hydrostatic transmission for a work vehicle.

15. In paragraph 7, The variable value of each position of the above swash plate (111) is determined by the mathematical formula [error compensation constant 1 (set vehicle speed - current vehicle speed) + maximum value (0, error compensation constant 2 (current engine torque - second specific value))]. Control method of a hydrostatic transmission for a work vehicle.

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