Hydrostatic drive system and control method for a motor grader

Abstract

This invention belongs to the field of motor grader technology and discloses a hydrostatic transmission system and control method for a motor grader. The hydrostatic transmission system includes a power source, a variable pump, a controller, a first motor, a second motor, multiple gear sets with different transmission ratios, a first shaft, a second shaft, an intermediate shaft, an output shaft, a third gear, a fourth gear, and an output gear. The power source provides power to the variable pump, which in turn provides power to the first and second motors. The first shaft is fixedly mounted at the output end of the first motor, and the second shaft is fixedly mounted at the output end of the second motor. The intermediate shaft and the output shaft are both parallel to the first and second shafts, and the output shaft drives the drive axle. The third gear is fixedly mounted on the intermediate shaft, the fourth gear is fixedly mounted on the second shaft, and the output gear is fixedly mounted on the output shaft. Both the third and fourth gears mesh with the output gear. This invention allows for the selection of different gear sets under different working conditions, effectively improving work efficiency.

Description

Technical Field

[0001] This invention relates to the field of grader technology, and in particular to a hydrostatic transmission system and control method for a grader. Background Technology

[0002] There are currently two types of hydrostatic drive systems used in graders: one is a bridgeless structure with a variable displacement pump and dual motors for independent wheel-side drive; the other is a structure with a variable displacement pump, a single motor, a two-speed mechanical gearbox, and a drive axle. The former hydrostatic drive structure suffers from a narrow speed range and poor synchronization performance. While the latter expands the speed range to some extent, the two-speed gearbox, due to both traction requirements and speed limitations, requires shifting in both medium and light load conditions, leading to significant pressure fluctuations in the system. Furthermore, the large difference in transmission ratios between the two gears in the two-speed mechanical gearbox can easily cause shocks during shifting. Summary of the Invention

[0003] The purpose of this invention is to provide a hydrostatic transmission system and control method for a grader, which can select different gear sets for different working conditions to suit different working conditions, avoid frequent gear shifting, and is highly economical.

[0004] To achieve this objective, the present invention adopts the following technical solution:

[0005] The hydrostatic transmission system of the grader includes:

[0006] The system comprises a power source, a variable pump, a controller, a first motor, a second motor, multiple sets of gears with different transmission ratios, a first shaft, a second shaft, an intermediate shaft, and an output shaft. The power source provides power to the variable pump, which in turn provides power to the first and second motors. The controller controls the displacement of the variable pump, the first motor, and the second motor. The first shaft is located at the output end of the first motor, and the second shaft is located at the output end of the second motor. The intermediate shaft is parallel to the first shaft, and the output shaft is connected to a drive axle. Each set of gears includes a first gear and a second gear that mesh with each other. The first gear is fixedly mounted on the first shaft, and the second gear is connected to the intermediate shaft via a clutch. The clutch is configured to control the connection and disconnection of the second gear from the intermediate shaft.

[0007] The system comprises a third gear, a fourth gear, and an output gear. The third gear is fixedly mounted on the intermediate shaft, the fourth gear is fixedly mounted on the second shaft, and the output gear is fixedly mounted on the output shaft. Both the third gear and the fourth gear mesh with the output gear.

[0008] As an alternative, the gear set is provided with two sets, including two first gears and two second gears. The two first gears are a first left gear and a first right gear, and the two second gears are a second left gear and a second right gear. The second left gear is connected to the intermediate shaft through a left clutch, and the second right gear is connected to the intermediate shaft through a right clutch.

[0009] As an alternative, the system also includes a first speed sensor for detecting the rotational speed of the first motor and a second speed sensor for detecting the rotational speed of the second motor.

[0010] As an alternative, the power source is an electric motor or an engine.

[0011] The hydrostatic transmission control method for a grader, applied to the hydrostatic transmission system of the grader described in any of the above schemes, includes the following steps:

[0012] To determine the working condition of the grader, when the grader is determined to be in a non-light load condition, firstly, the clutch in a gear set with the transmission ratio corresponding to the non-light load condition is controlled to close; then, the first motor and the second motor are controlled to be at maximum displacement, and the displacement of the variable pump is zero; when the grader starts, the displacement of the variable pump is controlled to increase to the maximum displacement, the displacement of the first motor is reduced to a first set value, and the second motor maintains the maximum displacement unchanged;

[0013] When the grader is determined to be operating under light load, firstly, the clutch in the gear set with the smallest transmission ratio among the multiple gear sets is controlled to close; then, the first motor and the second motor are controlled to be at maximum displacement, and the displacement of the variable pump is zero; after the grader starts, the displacement of the variable pump is controlled to increase to the maximum displacement, the displacement of the first motor is reduced to a second set value, and the second motor remains at its maximum displacement; then, the closed clutch is controlled to disengage, and the displacement of the first motor is controlled to decrease to zero, the second motor remains at its maximum displacement, and the variable pump decreases from its maximum displacement to a third set value; finally, the displacement of the variable pump is controlled to increase from the third set value to the maximum displacement, and the displacement of the second motor decreases to a fourth set value.

[0014] As an alternative, a pressure sensor is used to monitor the pressure of the hydrostatic transmission system of the grader in real time. When the pressure sensor detects that the pressure in the hydrostatic transmission system of the grader is higher than the maximum allowable value, the displacement of the first motor is increased until the pressure in the hydrostatic transmission system of the grader is lower than the maximum allowable value. If the pressure in the hydrostatic transmission system of the grader is still higher than the maximum allowable value even after the first motor is increased to its maximum displacement, the displacement of the variable pump is decreased until the pressure in the hydrostatic transmission system of the grader is lower than the maximum allowable value.

[0015] As an optional solution, the non-light load conditions include heavy load conditions and medium load conditions.

[0016] As an optional solution, the first set value under the heavy load condition is:

[0017] a = (37.7 * V) p1 *n e *η pv *r*η mv2 -v1*i q *i4*V m2 )*η mv1 *100 / (v1*i q *i1*i3*η mv2 *V m1 );

[0018] The first set value under medium load conditions is:

[0019] b = (37.7 * V) p2 *n e *η pv *r*η mv2 -v1*i q *i4*V m2 )*100 / (v1*i q *i2*i3*η mv2 *V m1 );

[0020] Under the aforementioned light load condition:

[0021] The second setting is c = 20;

[0022] The third setting value is:

[0023] d=(v3*i q *i4*V m2 *100) / (37.7*η pv *r*η mv2 );

[0024] The fourth setting value is:

[0025] e = (37.7 * V) p2 *n e *η pv *r*η mv2 *100) / (v4*i q *i4*V m1 );

[0026] Among them, V p1 V represents the actual displacement of the variable pump under heavy load conditions. p2 n represents the actual displacement of the variable pump under medium load conditions. e η is the rotational speed of the power source. pv Let r be the volumetric efficiency of the variable pump, r be the tire radius, and η be the displacement efficiency. mv1 η is the volumetric efficiency of the first motor. mv2 v1 represents the volumetric efficiency of the second motor, v1 represents the required vehicle speed under heavy load conditions, and i represents the volumetric efficiency of the second motor. q V is the speed ratio of the drive axle. m2 V is the maximum displacement of the second motor. m1 i1 is the maximum displacement of the first motor, i2 is the gear ratio of the gear set under heavy load, i3 is the ratio of the output gear to the third gear, i4 is the ratio of the output gear to the fourth gear, v3 is the vehicle speed when the right clutch is disengaged, and v4 is the required vehicle speed under light load.

[0027] As an alternative, the power source is an engine, and the engine has multiple power curves. The actual output power of the engine is P, and the power curve of the engine is selected according to P*(1+m%), where m% is the power reserve.

[0028] As an optional solution, the power required by the hydrostatic transmission system of the grader is P1 = V. pa *n*η p *p s / 600000, the actual output power of the engine is P=P1 / (η1*η2);

[0029] Among them, V pa Let n be the actual displacement of the variable pump under any operating condition, and η be the rotational speed of the variable pump under any operating condition. p p represents the volumetric efficiency of the variable pump under any operating condition. s η1 is the actual pressure of the hydrostatic transmission system of the grader, η2 is the total efficiency of the variable pump, and η3 is the ratio of the input power of the variable pump to the actual output power of the engine.

[0030] The beneficial effects of this invention are:

[0031] This invention provides a hydrostatic transmission system for a grader. By setting multiple sets of gears with different transmission ratios, the grader has multiple different gears, allowing it to select different gears under different working conditions. This avoids frequent gear changes. Furthermore, the difference in speed ratio between adjacent gears is smaller than the difference in speed ratio between two-speed gearboxes, thus effectively reducing shift shock. In addition, by controlling the displacement of the variable pump, the first motor, and the second motor through a controller, the power source of the grader can operate within the range of highest efficiency, improving the grader's economy.

[0032] This invention provides a hydrostatic transmission control method for a grader, which allows the grader to be set to a corresponding gear when not under light load conditions. When the grader starts, the first and second motors are controlled to be at maximum displacement, while the variable displacement pump is at zero displacement, enabling the grader to start quickly. After the grader starts, the variable displacement pump is increased to its maximum displacement, the first motor's displacement is reduced to a first set value, and the second motor maintains its maximum displacement, allowing the grader to rapidly increase its speed after starting. This enables the grader to work efficiently in that gear, and the overall speed control of the grader does not require changing the speed of the power source, improving the grader's economy.

[0033] When the grader is operating under light load, set the gear corresponding to light load conditions. When the grader starts, control the first and second motors to their maximum displacement and the variable displacement pump to zero to enable the grader to start quickly. After the grader starts, control the variable displacement pump to increase to its maximum displacement, reduce the displacement of the first motor to the second set value, and keep the second motor at its maximum displacement to enable the grader to increase its speed rapidly after starting. After the grader starts, perform a gear shifting operation. At this time, control the displacement of the first motor to decrease to zero, keep the second motor at its maximum displacement, and reduce the variable displacement pump from its maximum displacement to the third set value. Finally, control the displacement of the variable displacement pump to increase from the third set value to its maximum displacement, and reduce the displacement of the second motor to the fourth set value to enable the grader to maintain high speed for quick site transfer and minimize the impact during gear shifting. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the hydrostatic transmission system of the grader provided in an embodiment of the present invention;

[0035] Figure 2 This is a control flowchart of the grader involved in the embodiments of the present invention when the working condition is heavy load;

[0036] Figure 3 This is a control flowchart of the grader involved in the embodiments of the present invention when the working condition is medium load.

[0037] Figure 4This is a control flowchart of the grader involved in the embodiments of the present invention when the working condition is light load.

[0038] Figure 5 This is a schematic diagram of the power curve of the engine involved in the embodiments of the present invention.

[0039] In the picture:

[0040] 1. Power source; 2. Variable pump; 3. First motor; 4. Second motor; 5. First shaft; 6. Second shaft; 7. Intermediate shaft; 8. Output shaft; 9. Drive axle; 10. First gear; 101. First left gear; 102. First right gear; 11. Second gear; 111. Second left gear; 112. Second right gear; 12. Clutch; 121. Left clutch; 122. Right clutch; 13. Third gear; 14. Fourth gear; 15. Output gear. Detailed Implementation

[0041] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar components or components having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0042] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; a mechanical connection or an electrical connection; a direct connection or an indirect connection through an intermediate medium; or the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0043] In the description of this invention, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0044] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0045] like Figure 1As shown, this embodiment of the invention provides a hydrostatic transmission system for a grader, including a power source 1, a variable displacement pump 2, a controller, a first motor 3, a second motor 4, multiple sets of gears with different transmission ratios, a first shaft 5, a second shaft 6, an intermediate shaft 7, an output shaft 8, a third gear 13, a fourth gear 14, and an output gear 15. The power source 1 is configured to provide power to the variable displacement pump 2, driving its operation. The variable displacement pump 2 is configured to provide power to the first motor 3 and the second motor 4, driving their rotation. The first shaft 5 is fixedly mounted on the output end of the first motor 3, and the second shaft 6 is fixedly mounted on the output end of the second motor 4. The first motor 3 and the second motor 4 can respectively drive the rotation of the first shaft 5 and the second shaft 6. The intermediate shaft 7 and the output shaft 8 are rotatably mounted on the grader's body and are both parallel to the first shaft 5 and the second shaft 6. The output shaft 8 is used for... The drive axle 9 is driven; the third gear 13 is fixedly mounted on the intermediate shaft 7, the fourth gear 14 is fixedly mounted on the second shaft 6, and the output gear 15 is fixedly mounted on the output shaft 8, with both the third gear 13 and the fourth gear 14 meshing with the output gear 15; each gear set includes a first gear 10 and a second gear 11 meshing with each other, the first gear 10 is fixedly mounted on the first shaft 5, and the second gear 11 is connected to the intermediate shaft 7 through a clutch 12. The clutch 12 can control the connection and disconnection between the second gear 11 and the intermediate shaft 7. By closing and opening the clutch 12, different gear sets can be selected under different working conditions, that is, the optimal gear can be selected for work, avoiding frequent gear changes and improving work efficiency; the grader is equipped with a controller, which is used to control the displacement of the variable pump 2, the first motor 3 and the second motor 4, effectively avoiding the need to change the displacement of the variable pump 2 through the power source 1.

[0046] The hydrostatic transmission system of this grader utilizes multiple gear sets with different transmission ratios to provide multiple gear positions. This allows the grader to select different gears under varying working conditions, thus avoiding frequent gear shifting. Furthermore, the difference in gear ratios between adjacent gears is smaller than that of a two-speed gearbox, effectively reducing shift shock. Additionally, by controlling the displacement of the variable pump 2, the first motor 3, and the second motor 4, the power source 1 of the grader can operate within its most efficient range, improving the grader's economy. Moreover, the first motor 3 can use a smaller displacement motor, effectively reducing costs.

[0047] The grader's gearbox is a multi-speed gearbox, which can be three-speed, four-speed, or even higher. The following explanation uses a three-speed gearbox as an example. The first motor (3) is a high-torque motor, and the second motor (4) is a high-speed motor. The grader's operating conditions are divided into heavy-load, medium-load, and light-load conditions. (Continue referring to...) Figure 1The gear set has two sets, including two first gears 10 and two second gears 11. The two first gears 10 are a first left gear 101 and a first right gear 102, which are fixedly arranged on the first shaft 5 at intervals. The two second gears 11 are a second left gear 111 and a second right gear 112. The clutch 12 includes a left clutch 121 and a right clutch 122. The second left gear 111 is connected to the intermediate shaft 7 through the left clutch 121, and the second right gear 112 is connected to the intermediate shaft 7 through the right clutch 122. The first left gear 101 and the second left gear 111 mesh with each other, and the first right gear 102 and the second right gear 112 mesh with each other. When the grader is in heavy-load operation, the left clutch 121 is engaged and the right clutch 122 is disengaged. The transmission path is as follows: the first motor 3 drives the first shaft 5 to rotate, the first left gear 101 drives the second left gear 111 to rotate, the second left gear 111 drives the intermediate shaft 7 to rotate, the intermediate shaft 7 drives the third gear 13 to rotate, the third gear 13 drives the output gear 15 to rotate, which in turn causes the output shaft 8 to drive the drive axle 9 to rotate; and the second motor 4 drives the second shaft 6 to rotate, the fourth gear 14 drives the output gear 15 to rotate, which in turn causes the output shaft 8 to drive the drive axle 9 to rotate. When the grader is in medium-load operation, the left clutch 121 is disengaged and the right clutch 122 is engaged. The transmission path is as follows: The transmission path is as follows: the first motor 3 drives the first shaft 5 to rotate; the first right gear 102 drives the second right gear 112 to rotate; the second right gear 112 drives the intermediate shaft 7 to rotate; the intermediate shaft 7 drives the third gear 13 to rotate; the third gear 13 drives the output gear 15 to rotate; and so on, causing the output shaft 8 to drive the drive axle 9 to rotate. Additionally, the second motor 4 drives the second shaft 6 to rotate; the fourth gear 14 drives the output gear 15 to rotate; and so on, causing the output shaft 8 to drive the drive axle 9 to rotate. When the grader is operating under light load, the transmission path after the grader's speed stabilizes is as follows: the second motor 4 drives the second shaft 6 to rotate; the fourth gear 14 drives the output gear 15 to rotate; and so on, causing the output shaft 8 to drive the drive axle 9 to rotate. In this structure, the first motor 3 and the second motor 4 are matched with a three-speed gearbox to achieve different transmission ratios for heavy load, medium load, and light load conditions, meeting the requirements of each working condition, and with minimal shift shock.

[0048] Preferably, in order to prevent the rotational speed of the first motor 3 and the second motor 4 from exceeding the maximum limit, the hydrostatic transmission system of the grader also includes a first speed sensor and a second speed sensor. The first speed sensor is used to detect the rotational speed of the first motor 3 to prevent the first motor 3 from overspeeding; the second speed sensor is used to detect the rotational speed of the second motor 4 to prevent the second motor 4 from overspeeding.

[0049] Optionally, the power source 1 is an electric motor or an engine. When the grader is electrically driven, the power source 1 is an electric motor; when the grader is hydraulically driven, the power source 1 is an engine.

[0050] This invention also provides a hydrostatic transmission control method for a grader, applied to the hydrostatic transmission system of the grader described above. The hydrostatic transmission control method for the grader includes the following steps:

[0051] To determine the working condition of the grader, when the grader is determined to be in a non-light load condition, firstly, the clutch 12 in a gear set with the transmission ratio corresponding to the non-light load condition is controlled to close; then, the first motor 3 and the second motor 4 are controlled to be at maximum displacement, and the displacement of the variable pump 2 is zero, to provide the grader with a large traction force so that the grader can start quickly; after the grader starts, the displacement of the variable pump 2 is controlled to increase to the maximum displacement, the displacement of the first motor 3 is reduced to the first set value, and the second motor 4 is kept at the maximum displacement, so that the grader can further accelerate;

[0052] When the grader is determined to be operating under light load, and based on the condition that the grader can start quickly, the clutch 12 in the gear set with the smallest transmission ratio among the multiple gear sets is first controlled to close. Then, the first motor 3 and the second motor 4 are controlled to be at maximum displacement, and the displacement of the variable pump 2 is zero, providing a large traction force for the grader to start quickly. After the grader starts, the displacement of the variable pump 2 is increased to the maximum displacement, the displacement of the first motor 3 is reduced to the second set value, and the displacement of the second motor 4 remains unchanged at the maximum displacement, so as to further increase the speed of the grader. Then, the closed clutch 12 is controlled to open. At this time, the displacement of the first motor 3 is reduced to zero, the displacement of the second motor 4 remains unchanged at the maximum displacement, and the displacement of the variable pump 2 is reduced from the maximum displacement to the third set value to ensure the speed of the grader. Finally, the displacement of the variable pump 2 is controlled to increase from the third set value to the maximum displacement, and the displacement of the second motor 4 is reduced to the fourth set value, so that the grader can work or move at a higher speed, improving efficiency.

[0053] The hydrostatic transmission control method of this grader allows for setting a corresponding gear when the grader is not under light load. When the grader starts, the first motor 3 and the second motor 4 are controlled to be at maximum displacement, while the displacement of the variable pump 2 is zero, so that the grader can start quickly. After the grader starts, the variable pump 2 is controlled to increase to maximum displacement, the displacement of the first motor 3 is reduced to a first set value, and the second motor 4 is kept at maximum displacement, so that the grader speed increases rapidly after starting. This allows the grader to work efficiently in that gear, and the overall speed control of the grader does not require changing the speed of the power source 1, thus improving the grader's economy.

[0054] When the grader is operating under light load, the gear corresponding to light load is set. When the grader starts, the first motor 3 and the second motor 4 are controlled to be at maximum displacement, and the displacement of the variable pump 2 is zero, so that the grader can start quickly. After the grader starts, the variable pump 2 is controlled to increase to maximum displacement, the displacement of the first motor 3 is reduced to the second set value, and the second motor 4 is kept at maximum displacement, so that the grader speed increases rapidly after starting. After the grader starts, a gear shifting operation is performed. At this time, the displacement of the first motor 3 is controlled to decrease to zero, the second motor 4 is kept at maximum displacement, and the variable pump 2 is reduced from maximum displacement to the third set value. Finally, the displacement of the variable pump 2 is controlled to increase from the third set value to maximum displacement, and the second motor 4 is reduced to the fourth set value, so that the grader maintains high speed for quick site transfer. This hydrostatic transmission control method of the grader only requires gear shifting under light load conditions, effectively avoiding frequent gear shifting, and the impact during gear shifting operation is small.

[0055] like Figure 2 As shown, when the grader is under heavy load: starting the power source 1, the left clutch 121 in the control gear set is engaged, the right clutch 122 in the control gear set is disengaged, and the first motor 3 and the second motor 4 are controlled to be at maximum displacement, while the displacement of the variable pump 2 is zero; after the grader starts, the displacement of the variable pump 2 is increased to the maximum displacement, the displacement of the first motor 3 is reduced to the first set value a under heavy load conditions, and the second motor 4 maintains the maximum displacement.

[0056] like Figure 3 As shown, when the grader is in medium load condition: starting the power source 1, the right clutch 122 in the control gear set is engaged, the left clutch 121 in the control gear set is disengaged, and the first motor 3 and the second motor 4 are controlled to be at maximum displacement, while the displacement of the variable pump 2 is zero; after the grader starts, the displacement of the variable pump 2 is increased to the maximum displacement, the displacement of the first motor 3 is reduced to the first set value b under medium load condition, and the second motor 4 maintains the maximum displacement.

[0057] like Figure 4 As shown, when the grader is under light load: Power source 1 is started, the left clutch 121 in the control gear set is disengaged, the right clutch 122 is engaged, and the first motor 3 and the second motor 4 are controlled to operate at maximum displacement, while the displacement of the variable pump 2 is zero. After the grader starts, the displacement of the variable pump 2 is increased to its maximum displacement, the displacement of the first motor 3 is reduced to the second set value c, and the second motor 4 maintains its maximum displacement. When the right clutch 122 is disengaged, the displacement of the first motor 3 is reduced to zero, the second motor 4 maintains its maximum displacement, and the variable pump 2 decreases from its maximum displacement to the third set value d. Finally, according to the actual speed requirement of the grader, the displacement of the variable pump 2 is increased from the third set value to its maximum displacement, and the displacement of the second motor 4 decreases to the fourth set value e.

[0058] Specifically, the first setpoint a under heavy load conditions is (37.7 * V) p1 *n e *η pv *r*η mv2 -v1*i q *i4*V m2 )*η mv1 *100 / (v1*i q *i1*i3*η mv2 *V m1 ); The first setpoint b under medium load conditions = (37.7 * V) p2 *n e *η pv *r*η mv2 -v1*i q *i4*V m2 )*100 / (v1*i q *i2*i3*η mv2 *V m1 Under light load conditions, the second setpoint c = 20, and the third setpoint d = (v3 * i) q *i4*V m2 *100) / (37.7*η pv *r*η mv2 The fourth setpoint e = (37.7 * V) p2 *n e *η pv *r*η mv2 *100) / (v4*i q *i4*V m1 V p1 V represents the actual displacement of variable pump 2 under heavy load conditions. p2 n represents the actual displacement of variable pump 2 under medium load conditions. e η is the rotational speed of power source 1. pv Let r be the volumetric efficiency of variable pump 2, r be the tire radius, and η be the volumetric efficiency. mv1 η is the volumetric efficiency of the first motor 3. mv2 v1 represents the volumetric efficiency of the second motor 4, v1 represents the required vehicle speed under heavy load conditions, and i q For the speed ratio of drive axle 9, V m2 V is the maximum displacement of the second motor 4. m1 i1 is the maximum displacement of the first motor 3, i2 is the speed ratio of the gear set under heavy load, i3 is the speed ratio of the gear set under medium load, i4 is the ratio of the output gear 15 to the third gear 13, v3 is the vehicle speed when the right clutch 122 is disengaged, and v4 is the required vehicle speed under light load.

[0059] It should be noted that the first setting value 'a' is the displacement of the first motor 3 as a% of the total displacement of the first motor 3 under the current heavy load condition; the first setting value 'b' is the displacement of the first motor 3 as b% of the total displacement of the first motor 3 under the current medium load condition; the second setting value 'c' = 20, that is, the displacement of the first motor 3 as 20% of the total displacement of the first motor 3 under the current light load condition; the third setting value 'd' is the displacement of the variable pump 2 as d% of the total displacement of the variable pump 2 under the current light load condition; and the fourth setting value 'e' is the displacement of the second motor 4 as e% of the total displacement of the second motor 4 under the current light load condition.

[0060] Preferably, when the grader is operating under heavy load, medium load, and light load conditions, a pressure sensor is used to detect the actual pressure p of the grader's hydrostatic transmission system in real time. s When the pressure sensor detects the actual pressure p in the hydrostatic transmission system of the grader s If the pressure exceeds the maximum allowable value, the displacement of the first motor 3 is increased first, until the actual pressure p of the hydrostatic transmission system of the grader is detected. s If the first motor 3 is increased to its maximum displacement, the actual pressure p in the hydrostatic transmission system of the grader will be lower than the maximum allowable value. s If the pressure is still higher than the maximum allowable value, reduce the displacement of variable pump 2 until the actual pressure p of the grader's hydrostatic transmission system is reached. s Below the maximum permissible value. This design effectively protects the hydraulic components of the grader's hydrostatic transmission system, ensuring that the grader's hydrostatic transmission system always operates within a relatively efficient working pressure range.

[0061] When the grader is oil-driven, the power source is the engine. The engine has multiple power curves. Assuming the actual output power of the engine is P, the value of P*(1+m%) is compared with the power values ​​of the multiple power curves at the same speed. The power value that is greater than P*(1+m%) and closest is selected as the actual power curve to achieve fuel saving. Here, m% is the power reserve to prevent sudden changes in load demand during actual operation of the grader, effectively avoiding engine stalling.

[0062] For example, if a grader requires 200KW of power, when selecting an engine, it is necessary to choose an engine with a maximum output power of at least 200KW at the speed corresponding to the optimal fuel consumption range (e.g., 1400r / min). Figure 5 As shown, the engine power curves are set to three. At a speed of 1400 r / min, the three power curves correspond to the engine power values ​​Pa, Pb and Pc respectively. By comparing P*(1+m%) with Pa, Pb and Pc respectively, the curve corresponding to the power value that is greater than P*(1+m%) and closest to it is selected as the engine power curve.

[0063] The engine's actual output power P = P1 / (η1*η2) (KW), where P1 is the power required by the grader's hydrostatic transmission system, P1 = V pa *n*η p *p s / 600000, V pa ηp is the actual displacement of variable pump 2 under any operating condition, in ml / r; n is the rotational speed of variable pump 2 under any operating condition, in r / min; ηp is the volumetric efficiency of variable pump 2 under any operating condition; ps is the actual pressure of the hydrostatic transmission system of the grader, in bar; η1 is the total efficiency of variable pump 2; and η2 is the ratio of the input power of variable pump 2 to the actual output power P of the engine.

[0064] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. The hydrostatic transmission system of a grader, characterized in that, include: The system comprises a power source (1), a variable pump (2), a controller, a first motor (3), a second motor (4), multiple sets of gears with different transmission ratios, a first shaft (5), a second shaft (6), an intermediate shaft (7), an output shaft (8), a first speed sensor for detecting the rotational speed of the first motor (3), and a second speed sensor for detecting the rotational speed of the second motor (4). The power source (1) provides power to the variable pump (2), the variable pump (2) provides power to the first motor (3) and the second motor (4), and the controller controls the variable pump (2), the first motor (3), and the second motor (4). The displacement is such that the first shaft (5) is located at the output end of the first motor (3), the second shaft (6) is located at the output end of the second motor (4), the intermediate shaft (7) is arranged parallel to the first shaft (5), the output shaft (8) is connected to the drive axle (9), each gear set includes a first gear (10) and a second gear (11) meshing with each other, the first gear (10) is fixedly located on the first shaft (5), the second gear (11) is connected to the intermediate shaft (7) through a clutch (12), and the clutch (12) is configured to control the connection and disconnection of the second gear (11) and the intermediate shaft (7); The third gear (13), the fourth gear (14), and the output gear (15) are fixedly mounted on the intermediate shaft (7), the fourth gear (14) is fixedly mounted on the second shaft (6), and the output gear (15) is fixedly mounted on the output shaft (8). The third gear (13) and the fourth gear (14) are both meshed with the output gear (15). The gear set is provided in two sets, namely two first gears (10) and two second gears (11). The two first gears (10) are a first left gear (101) and a first right gear (102), respectively. The two second gears (11) are a second left gear (111) and a second right gear (112), respectively. The second left gear (111) is connected to the intermediate shaft (7) through a left clutch (121), and the second right gear (112) is connected to the intermediate shaft (7) through a right clutch (122).

2. The hydrostatic transmission system of the grader according to claim 1, characterized in that, The power source (1) is an electric motor or an engine.

3. A hydrostatic transmission control method for a grader, characterized in that, The hydrostatic transmission system of the grader as described in any one of claims 1-2, wherein the hydrostatic transmission control method of the grader comprises the following steps: To determine the working condition of the grader, when the grader is determined to be in a non-light load condition, firstly control the clutch (12) in a gear set with the transmission ratio corresponding to the non-light load condition to close; then control the first motor (3) and the second motor (4) to be at maximum displacement and the displacement of the variable pump (2) to be zero; when the grader starts, control the displacement of the variable pump (2) to increase to the maximum displacement, the displacement of the first motor (3) to decrease to the first set value, and the second motor (4) to maintain the maximum displacement. When the grader is determined to be in a light-load condition, firstly, the clutch (12) in the gear set with the smallest transmission ratio among the multiple gear sets is controlled to close; then, the first motor (3) and the second motor (4) are controlled to be at maximum displacement, and the displacement of the variable pump (2) is zero; when the grader starts, the displacement of the variable pump (2) is controlled to increase to the maximum displacement, the displacement of the first motor (3) is reduced to the second set value, and the second motor (4) remains at the maximum displacement; then, the closed clutch (12) is controlled to open, and the displacement of the first motor (3) is controlled to decrease to zero, the second motor (4) remains at the maximum displacement, and the variable pump (2) decreases from the maximum displacement to the third set value; finally, the displacement of the variable pump (2) is controlled to increase from the third set value to the maximum displacement, and the displacement of the second motor (4) decreases to the fourth set value.

4. The hydrostatic transmission control method for a grader according to claim 3, characterized in that, The pressure sensor is used to detect the pressure of the hydrostatic transmission system of the grader in real time. When the pressure sensor detects that the pressure in the hydrostatic transmission system of the grader is higher than the maximum allowable value, the displacement of the first motor (3) is increased until the pressure in the hydrostatic transmission system of the grader is lower than the maximum allowable value. If the first motor (3) is increased to the maximum displacement and the pressure in the hydrostatic transmission system of the grader is still higher than the maximum allowable value, the displacement of the variable pump (2) is reduced until the pressure in the hydrostatic transmission system of the grader is lower than the maximum allowable value.

5. The hydrostatic transmission control method for a grader according to claim 3, characterized in that, The non-light load conditions include heavy load conditions and medium load conditions.

6. The hydrostatic transmission control method for a grader according to claim 5, characterized in that, The first set value under the heavy load condition is: ； The first set value under medium load conditions is: ； Under the aforementioned light load condition: The second setting is c=20; The third setting value is: ； The fourth setting value is: ； in, The actual displacement of the variable pump (2) under heavy load conditions. The actual displacement of the variable pump (2) under medium load conditions. The rotational speed of the power source (1) Let r be the volumetric efficiency of the variable pump (2) and r be the tire radius. The volumetric efficiency of the first motor (3) is... For the volumetric efficiency of the second motor (4), To meet the speed requirements of heavy-duty operating conditions, The speed ratio of the drive axle (9), The maximum displacement of the second motor (4) The maximum displacement of the first motor (3) For the speed ratio of gear sets under heavy load conditions, For the gear ratio of the gear set under medium load conditions, The ratio of the output gear (15) to the third gear (13) is given. The ratio of the output gear (15) to the fourth gear (14) is given. The vehicle speed when the right clutch (122) is disengaged. The required vehicle speed under light load conditions.

7. The hydrostatic transmission control method for a grader according to claim 3, characterized in that, The power source (1) is an engine, and the engine has multiple power curves. The actual output power of the engine is P, and the power curves of the engine are based on... To select, m% is the power reserve.

8. The hydrostatic transmission control method for a grader according to claim 7, characterized in that, The power required by the hydrostatic transmission system of the grader The actual output power of the engine ; in, Let n be the actual displacement of the variable pump (2) under any operating condition, and n be the rotational speed of the variable pump (2) under any operating condition. The volumetric efficiency of the variable pump (2) under any operating condition, This refers to the actual pressure of the hydrostatic transmission system of the grader. For the overall efficiency of the variable pump (2), It is the ratio of the input power of the variable pump (2) to the actual output power of the engine.

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