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KR-20260063237-A - HYDROSTATIC TRANSMISSION

KR20260063237AKR 20260063237 AKR20260063237 AKR 20260063237AKR-20260063237-A

Abstract

According to the present invention, a hydrostatic transmission is provided comprising: a hydraulic pump (110) for discharging fluid; a hydraulic motor (120) that operates by the fluid discharged by the hydraulic pump (110) and outputs a torque that varies according to the tilt angle of the swash plate (121); a piston (130) capable of adjusting the tilt angle of the swash plate (121) by moving back and forth in a forward/backward section (Sar); and a piston body (140) for housing the piston (130).

Inventors

  • 정승호
  • 이수윤

Assignees

  • 엘에스엠트론 주식회사

Dates

Publication Date
20260507
Application Date
20241030

Claims (7)

  1. A hydraulic pump (110) that discharges fluid; A hydraulic motor (120) that operates by the fluid discharged by the above hydraulic pump (110) and outputs a torque that varies according to the tilt angle of the swash plate (121); A piston (130) capable of adjusting the tilt angle of the sway plate (121) by moving back and forth in the advance/retreat section (Sar); and It includes a piston body (140) that accommodates the above piston (130), and The above piston body (140) A placement space (141) in which the above piston (130) is placed; A supply passage (142) that connects the outside (OR) and the placement space (141) so that working fluid can be supplied to the piston (130); and A discharge passage (143) is formed to connect the outside (OR) and the placement space (141) so that working fluid can be discharged from the piston (130), and The above piston (130) moves back and forth by the hydraulic pressure of the operating fluid supplied through the supply path (142), and When the piston (130) moves back and forth in the buffer section (Sd), which is part of the above-mentioned advance/retreat section (Sar), the working fluid is discharged into the discharge passage (143). Hydrostatic transmission (100).
  2. In paragraph 1 The above piston (130) A hydraulic chamber (131) for filling with hydraulic fluid capable of applying hydraulic pressure; An inlet hole (132) connecting the supply channel (142) and the hydraulic chamber (131); and As the piston (130) moves back and forth, the hydraulic chamber (131) and the discharge passage (143) are connected in the buffer section (Sd), and a discharge hole (133) is formed that is shielded by the piston body (140) in the section excluding the buffer section (Sd). The hydraulic fluid supplied through the above supply channel (142) is filled into the hydraulic chamber (131) through the above inlet hole (132) to apply hydraulic pressure to the piston (130), and In the above buffer section (Sd), a portion of the hydraulic fluid filled in the above hydraulic chamber (131) is discharged through the above discharge port (133) to the above discharge path (143). Hydrostatic transmission (100).
  3. In paragraph 2 The above buffer section (Sd) includes the point where the piston (130) begins to advance, and When the piston (130) advances in the above buffer section (Sd), the communication area (CF) in which the discharge hole (133) and the discharge passage (143) communicate with each other gradually narrows. Hydrostatic transmission (100).
  4. In paragraph 2 The above buffer section (Sd) includes a point where the piston (130) ends its forward movement, and When the piston (130) advances in the above buffer section (Sd), the communication area (CF) in which the discharge hole (133) and the discharge passage (143) communicate with each other gradually widens. Hydrostatic transmission (100).
  5. In paragraph 2 The above discharge hole (133) has an expanded diameter on the side of the piston body (140). Hydrostatic transmission (100).
  6. In paragraph 2 The apparatus further includes an elastic spring (ES) connected to the piston (130) and applying an elastic force in a retracting direction to the piston (130) that has advanced. Hydrostatic transmission (100).
  7. In paragraph 2 The tilt angle of the above plate (121) decreases as the above piston (130) advances. Hydrostatic transmission (100).

Description

Hydrostatic Transmission The present invention relates to a hydrostatic transmission capable of two-speed control. Hydrostatic transmissions (HSTs) facilitate the maintenance of high torque output because they transmit power via hydraulics. Additionally, they enable easy implementation of continuously variable speeds, making them suitable for fine-tuning the output delivered to implements via a Power Take-Off (PTO). Accordingly, it is mainly adopted by work vehicles such as tractors. The hydrostatic transmission includes a hydraulic pump and a hydraulic motor. In a hydraulic pump, a piston linked to a rotating input shaft slides on a swash plate, thereby inducing a change in volume inside the piston block into which the piston is inserted, and accordingly discharges hydraulic fluid. The hydraulic fluid discharged from the hydraulic pump is supplied to the hydraulic motor through a path extending to the hydraulic motor. The hydraulic pressure resulting from the fluid supply causes a change in volume within the hydraulic motor's piston block, and as the piston slides on the swash plate, the piston block rotates to transmit power to the output shaft. Hydrostatic transmissions typically controlled output torque by rotating the pump-side swash plate. However, a wider range of output control was required, and accordingly, hydrostatic transmissions capable of 2-speed control (switching) that also varied the motor-side swash plate emerged. Hydrostatic transmissions capable of 2-speed control have a problem in that the shifting shock is large when the motor-side swash plate is switched. Prior art recognizing this problem has been disclosed (Registered Patent Publication No. 10-1988413). Figure 1 is a cross-sectional view of a conventional hydrostatic transmission capable of 2-speed control. Referring to FIG. 1, the conventional hydrostatic transmission discloses a hydraulic pump (10') and a hydraulic motor (20'). The hydraulic pump (10') performs speed change by discharging a flow rate that varies according to the angle of inclination of the pump swash plate (12'). The hydraulic motor (20') is driven by hydraulic fluid from the hydraulic pump (10') and rotates in a low-speed mode or a high-speed mode as the angle of the motor swash plate (22') is operated between the maximum tilt angle (a2) or the minimum tilt angle (a1) to drive the hydraulic equipment. At this time, hydraulic fluid supplied from the hydraulic pump (10') through the flow path (Ls) and port (A) flows into the lower outer surface of the motor plate (22') and acts as a control pressure. Figure 2 shows the rotational speed of the hydraulic motor - load pressure - torque of the hydraulic motor according to Figure 1. As shown in FIG. 2, when the load pressure exceeds a certain value, the rotational speed and torque of the hydraulic motor change rapidly. In other words, the hydrostatic transmission according to FIG. 1 experiences significant shifting shock when switching between two speeds. Accordingly, the prior art attempts to solve this problem by proposing the following hydrostatic transmission. Figure 3 is a cross-sectional view of a hydrostatic transmission according to the prior art. According to FIG. 3, a hydrostatic transmission according to the prior art discloses a hydraulic motor (20) comprising a hydraulic pump (10) and a swash plate (22) capable of turning at two turning angles. In addition to this, the prior art discloses a proportional control valve (30) that takes hydraulic pressure supplied from a hydraulic pump (10) as input and outputs a control pressure for controlling a swash plate (22). The description of the operation of the proportional control valve (30) is replaced with the content disclosed in the prior art document (Registered Patent Publication No. 10-1988413). This specification describes the effects of the prior art by introducing a proportional control valve (30). Figure 4 shows the rotational speed - load pressure - torque of the hydraulic motor (20) according to Figure 3. As shown in FIG. 4, the hydraulic motor (20) has a proportional control section in which the rotational speed gradually decreases and the torque increases as the load pressure increases. That is, according to the prior art, a technology is provided that can mitigate shifting shock when switching between two speeds of a hydrostatic transmission. However, according to Fig. 4, the curves of rotational speed and torque show a bending shape at both ends of the proportional control section. That is, even according to the prior art, shifting shock still occurs in the hydraulic motor when entering the proportional control section and when exiting the proportional control section. 2-speed control technology has a clear advantage in that it expands the shifting range of hydrostatic transmissions. However, the shifting shock during 2-speed switching is a factor that undermines the advanced advantage of hydrostatic transmissions, which enables precise output contro