Patent Application
20200003191
The present invention relates to a hydraulic pump and a motor.
A hydraulic pump and a hydraulic motor have been widely used in, for instance, a construction machine and a working vehicle. The hydraulic pump is actuated to be rotated by a motor, an engine and the like, thereby discharging hydraulic oil to a hydraulic circuit. In contrast, the hydraulic motor converts a pressure of the hydraulic oil supplied from the hydraulic circuit into rotational movement. Among such hydraulic pump and motor, variable displacement hydraulic pump and motor with a swash plate have been known.
For instance, Patent Literature 1 discloses a variable displacement pump with a swash plate, in which a control valve is disposed in parallel to a working direction of a servo piston configured to tilt the swash plate, and a single lever is disposed on a common plane including working axial lines of the servo piston and the control valve, whereby the servo piston and the control valve are operable in conjunction with each other. This technique allows a product (horsepower) of a pump discharge rate and a pump discharge pressure to be controlled to a constant level by a compact and simple structure of the pump.
In the variable displacement pump, there has also been known a technique of detecting a tilt angle of the swash plate for determining the pump discharge rate, and controlling the variable displacement pump using the detected tilt angle. For instance, Patent Literature 2 discloses a variable displacement pump including a swash plate and a potentiometer disposed on an exterior of a housing, in which a rotation transmission mechanism transmits rotation of the swash plate disposed inside the housing to the potentiometer. According to this technique, the tilt angle of the swash plate can be detected at a high accuracy using the potentiometer and the potentiometer can be easily adjusted.
However, when the rotation of the swash plate is directly transmitted to the detector as described in Patent Literature 2, it is necessary to concentrically arrange the transmission mechanism and a tilt axis of the swash plate, which restricts a design of the pump. This also applies to the variable displacement motor with the swash plate.
In light of the above, an object of the invention is to provide a variable displacement hydraulic pump and a variable displacement hydraulic motor each being provided with a swash plate and capable of detecting a tilt angle of the swash plate and reducing restriction on designs.
According to an aspect of the invention, variable displacement hydraulic pump or motor includes: a swash plate; a lever supported by a housing and configured to rotate in conjunction of tilting of the swash plate; and a sensor configured to detect a displacement amount of the lever.
According to the above aspect of the invention, the displacement generated by tilting the swash plate is converted into the rotation of the lever in contact with the swash plate. Accordingly, the influence of micro-vibration of the swash plate is reducible and the tilt angle is detectable at a high accuracy. In addition, since it is not necessary to dispose the lever concentrically with the tilt axis of the swash plate, restriction on a device design is reducible.
1. Overall Arrangement of Work Machine
In the above-described wheel loader 1, an output from the engine is distributed into a travelling system for driving tires 7 and a hydraulic system for driving the working equipment 3. In the hydraulic system, the hydraulic pump is driven by the output from the engine to supply a pressure oil to the working equipment 3 through a hydraulic circuit. A bucket cylinder 35 and a boom cylinder 36 are extended and contracted using the pressure oil, thereby moving the bucket 31 between a loading position and a tilt position and vertically moving the boom 32.
2. Structure of Hydraulic Pump
The swash plate 13 is a plate member having a through hole 131 at the center. The swash plate 13, while the rotary shaft 12 is placed in the through hole 131, is attached to the base end wall 111a of the housing body 111 through a pair of ball retainers (supports) 132. The swash plate 13 can be tilted relative to the housing 11 and the rotary shaft 12 with the ball retainers 132 serving as a fulcrum. The swash plate 13 has, on both sides, a first slide surface 133 facing the housing cap 112 and a second slide surface 134 facing the housing body 111. The first slide surface 133 is a flat surface to contact with a later-described piston shoe and is annularly formed around the through hole 131. The second slide surface 134 is a flat surface to contact with a later-described servo piston shoe and is formed at a part of the swash plate 13 facing the servo piston shoe.
The cylinder block 14 is a cylindrical member having at the center a through hole 141 for the rotary shaft 12. The cylinder block 14, which is coupled to the rotary shaft 12 by a spline formed on the through hole 141, rotates in conjunction with the rotary shaft 12. An end of the cylinder block 14 near the housing cap 112 is in contact with an inner wall of the housing cap 112 through a valve plate 142. The valve plate 142, which is a plate member having a suction port 142a and a discharge port 142b, is fixed to the housing cap 112. The suction port 142a of the valve plate 142 communicates with a suction passage 112a formed in the housing cap 112. The discharge port 142b communicates with a discharge passage 112b formed in the housing cap 112.
Moreover, the cylinder block 14 includes a plurality of cylinders 143 formed therein. The cylinders 143 are annularly arranged around the rotary shaft 12. Each of the cylinders 143 has a communication port 143a penetrating a side near the valve plate 142 to reach an end surface of the cylinder block 14 near the valve plate 142. While the cylinder block 14 rotates in conjunction with the rotary shaft 12, the valve plate 142 is fixed to the housing cap 112. Accordingly, the communication port 143a of each of the cylinders 143 is to alternately communicate with the suction port 142a and the discharge port 142b.
Meanwhile, a piston 151 is inserted from a side near the swash plate 13 in each of the cylinders 143 and is slidably received therein. A piston shoe 153 is coupled through a ball joint 152 to a side of the piston 151 near the swash plate 13. A press force of a press spring 144 whose one end is fixed to the cylinder block 14 is transmitted through a rod 145, a retainer guide 146, and a press plate 147 to the piston shoe 153, whereby the piston shoe 153 is brought into contact with the first slide surface 133 of the swash plate 13. With this operation, when the cylinder block 14 rotates in conjunction with the rotary shaft 12, a position of the piston 151 relative to the corresponding one of the cylinders 143 changes along the tilted swash plate 13, whereby oil is discharged from the hydraulic pump 10. Specifically, the piston 151 is drawn from the corresponding cylinder 143 while the corresponding cylinder 143 is in communication with the suction passage 112a, and the piston 151 is pushed into the corresponding cylinder 143 while the corresponding cylinder 143 is in communication with the discharge passage 112b. Accordingly, the oil sucked from the suction passage 112a is delivered to the discharge passage 112b.
A discharge rate of the oil in the above-described hydraulic pump 10 is determined in accordance with a tilt angle of the swash plate 13. At the larger tilt angle, a stroke of the piston 151 relative to each of the cylinders 143 becomes large, thereby increasing the discharge rate of the oil. On the other hand, at the smaller tilt angle, the stroke of the piston 151 relative to each of the cylinders 143 becomes small, thereby decreasing the discharge rate of the oil. It should be noted that, when the tilt angle is zero and the swash plate 13 is perpendicular to the rotary shaft 12, the stroke of the piston 151 becomes zero, whereby no oil is discharged.
The tilt angle of the swash plate 13 is adjusted by operating a servo piston 161 shown in
3. Structure of Tilt State Detector
In the exemplary embodiment, the lever 22 has a first arm 223 and a second arm 224. As shown in the figure, the first arm 223 extends downward from the rotary shaft 222 in the figure. Specifically, the first arm 223 extends from a hollow portion of the servo valve housing 21a to a hollow portion of the housing body 111 of the hydraulic pump 10, so that a contact point 223a provided at an end of the first arm 223 is brought into contact with the ball 221. In an intermediate portion of the first arm 223, a servo valve 25 is in contact with a servo valve contact portion 223b. The servo valve 25 has a spring box 251 configured to press the servo valve 25 onto the servo valve contact portion 223b with a spring 25b. The second arm 224 extends from the rotary shaft 222 rightward in the figure, in other words, in a direction different from the first arm 223. A measurement portion 224a of the second arm 224 is in contact with a contact piece 231 of the stroke sensor 23. In the exemplary embodiment, the lever 22 is disposed on a first plane perpendicular to the rotary shaft 222 (i.e., a plane in parallel to a plane of paper in
Herein, in the example shown in the figure, the contact piece 231 and the spring box 251 are attached in such a direction as to generate moment in the same direction around the rotary shaft 222 of the lever 22. Specifically, the contact piece 231 and the spring box 251 are attached so as to generate moment clockwise in the figure around the rotary shaft 222.
The stroke sensor 23, which is exemplified by a contact stroke sensor, generates an output signal in accordance with a displacement of the contact piece 231 in a direction along the shaft 232. The stroke sensor 23 has a spring 233 for pressing the contact piece 231 onto the measurement portion 224a of the lever 22. At this time, since the contact piece 231 in contact with the second arm 224 of the lever 22 is displaced by the lever 22 rotating around the rotary shaft 222, it can be said that the stroke sensor 23 also detects a displacement amount, specifically, a rotation amount of the lever 22.
4. Structure of Servo Mechanism
Herein, in the servo valve 25 that is a three-port two-position directional control valve, a spool 252 is switched between a communication position and a drain position depending on a balance between a pressure of an oil supplied from the discharge passage 112b of the hydraulic pump 10 to the hydraulic pilot 25a and a biasing force of the spring 25b in contact with the lever 22 through the spring box 251. At the communication position, the large-diameter pressurized chamber 166a of the servo piston 161 communicates with the discharge passage 112b. At the drain position, the large-diameter pressurized chamber 166a is blocked out of the discharge passage 112b and communicates with a tank.
For instance, when the servo valve 25 is at the communication position, the oil is supplied to the large-diameter pressurized chamber 166a, so that the servo piston 161 moves in such a direction as to reduce the tilt angle of the swash plate 13. As the tilt angle is reduced, the lever 22 rotates rightward in
Herein, when the discharge pressure of the hydraulic pump 10 is increased by an increase in a load pressure in the working equipment 3, the servo valve 25 is not switched to the drain position unless the lever 22 compresses the spring 25b by a large amount. Accordingly, in this case, the tilt angle is maintained smaller than before the discharge pressure is increased. On the other hand, when the discharge pressure of the hydraulic pump 10 is decreased, the servo valve 25 is switched to the drain position with the lever 22 compressing the spring 25b only by a small amount. Accordingly, in this case, the tilt angle is maintained larger than before the discharge pressure is decreased. The servo valve 25 and the servo piston 161 thus maintain a constant product (horsepower) of the discharge rate from the hydraulic pump 10 determined by the tilt angle of the swash plate 13 and the discharge pressure from the hydraulic pump 10 determined by the load pressure.
Although not shown in
5. Structure of Controller
The tilt angle calculator 241 calculates the tilt angle of the swash plate 13 on a basis of the output signal of the stroke sensor 23. Specifically, the tilt angle calculator 241 calculates a rotation angle of the lever 22 on a basis of displacement of the contact piece 231 indicated by the output signal of the stroke sensor 23 and a distance between the measurement portion 224a and the rotary shaft 222. Further, the tilt angle calculator 241 calculates the tilt angle of the swash plate 13 on a basis of a distance between the contact point 223a and the rotary shaft 222 of the lever 22 and a relative positional relationship between the ball 221 and a tilt axis of the swash plate 13.
The angle difference calculator 242 calculates a difference between a control-target tilt angle determined based on a state of an engine driving the hydraulic pump 10 and operation amounts and the like of an operation lever, a pedal and the like disposed in the cab 6 and the like, and the tilt angle of the swash plate 13 calculated by the tilt angle calculator 241. The angle difference calculator 242 refers to data of a control pattern and the like stored in the memory 245 in order to determine the control-target tilt angle.
The control signal generator 243 generates a control signal on a basis of the angle difference calculated by the angle difference calculator 242. The control signal output portion 244 converts the control signal generated by the control signal generator 243 into a current value and a voltage value and outputs the current value and the voltage value to the electromagnetic proportional pilot valve annexed to the servo piston 161.
In the exemplary embodiment with the above arrangement, the displacement of the end of the swash plate 13 caused by the tilting of the swash plate 13 is converted into the rotation of the lever 22 in contact with the swash plate 13 through the ball 221, and the tilt angle of the swash plate 13 is calculated based on the rotation amount of the lever 22. Since the displacement of the swash plate 13 by the tilting occurs at any portion of the swash plate 13 except for the tilt axis, the displacement of the swash plate 13 can be detected when the lever 22 is in contact with any portion of the swash plate 13 in place of the above-exemplified end of the swash plate 13.
Herein, for instance, the tilt angle of the swash plate 13 can also be detected by contacting the contact piece 231 of the stroke sensor 23 with swash plate 13 without using the lever 22. However, at this time, it is not easy to detect the tilt angle of the swash plate 13 at a high accuracy due to micro-vibration generated by the rotation of the cylinder block 14 in contact with the swash plate 13. In the exemplary embodiment, the influence of the micro-vibration is reduced by contacting the contact piece 231 of the stroke sensor 23 to the lever 22 that is a member independent of the swash plate 13, thereby enabling a highly accurate detection of the tilt angle.
Moreover, even when the generated rotation amount of the lever 22 is the same, the displacement of the contact piece 231 is different depending on the distance between the rotary shaft 222 and a contact position of the contact piece 231 with the lever 22. Specifically, as the contact position of the contact piece 231 is closer to the rotary shaft 222, the displacement is smaller. As the contact position of the contact piece 231 is remote from the rotary shaft 222, the displacement is larger. By using the above, a resolution of the detection value of the stroke sensor 23 can be changed by adjusting the contact position of the contact piece 231 with the lever 22.
In the illustrated example, the lever 42 has a single arm 423. The arm 423 extends downward from the rotary shaft 422 in
By contacting the contact piece 231 with the inclined surface 424 as described above, for instance, the contact piece 231 and the spring box 251 of the servo valve 25 in contact with a servo valve contact portion 423b of the lever 42 can contact with the arm 423 in different directions at longitudinally close positions. With this arrangement, the tilt state detector can be more compact in size. Since the second exemplary embodiment has the same structures as those in the first exemplary embodiment except for the above structures, overlapping descriptions of the same structures will be omitted.
In the illustrated example, the lever 52 has a first arm 523 and a second arm 524. The arm 523 extends downward from the rotary shaft 522 in
In the above example, since the stroke sensor 23 is disposed in parallel to the servo valve 25, the tilt state detector can be more compact in size in a height direction in
As exemplarily described in the first to fourth exemplary embodiments, the stroke sensor 23 of the invention can be provided to the hydraulic pump 10 in various directions and various postures. Accordingly, for instance, the arrangement of the stroke sensor 23 can be changed suitably for a shape of a usable space around the hydraulic pump 10, or, when an additional stroke sensor 23 is attached to the existing hydraulic pump 10, a direction or a posture of the additional stroke sensor 23 for an easy attachment can be selected.
The invention is not limited to the above-described embodiments, but includes modifications and improvements as long as an object of the invention can be achieved.
Although the hydraulic pump is exemplified in the above exemplary embodiments, for instance, in some embodiments, a tilt angle of a swash plate is detected in the same manner in a variable displacement hydraulic motor with the swash plate. Alternatively, in some embodiments, a tilt angle of a bent axis is detected in the same manner in a bent axis variable displacement hydraulic pump or hydraulic motor. A working fluid of the hydraulic pump or motor is not limited to oil but other kinds of fluids are usable.
In the above exemplary embodiments, the lever is in indirect contact with the swash plate through the ball. However, for instance, in some embodiments, the lever is in direct contact with the swash plate without using the ball. Moreover, for instance, in some embodiments, the lever is in indirect contact with the swash plate through a single member or a plurality of members other than the ball.
In the above exemplary embodiments, the stroke sensor, which is a contact displacement gauge, is used for detecting the rotation amount of the lever. However, for instance, in some embodiments, a non-contact displacement gauge is used for detecting the rotation amount of the lever. Alternatively, for instance, in some embodiments, a rotary encoder disposed near the rotary shaft of the lever is used for detecting the rotation amount of the lever on a basis of the rotation angle.
In the above exemplary embodiments, the servo piston, which is driven by the hydraulic pressure, is used for changing the tilt angle of the swash plate. However, for instance, in some embodiments, a non-hydraulic driving unit is used for changing the tilt angle of the swash plate. Specifically, for instance, in some embodiments, the servo piston is replaced by a proportional solenoid valve. In this case, the servo valve is unnecessary and the control signal generated in the controller is inputted to the proportional solenoid valve.
In the above exemplary embodiments, the hydraulic pump for driving the working equipment of the wheel loader is exemplarily described. However, for instance, a fluid pressure rotary device in some embodiments is applicable to other work machines such as a hydraulic excavator, bulldozer and forklift.
1 . . . wheel loader, 2 . . . 3-port, 2 . . . vehicle body, 3 . . . working equipment, 31 . . . bucket, 32 . . . boom, 33 . . . bell crank, 34 . . . connecting link, 35 . . . bucket cylinder, 36 . . . boom cylinder, 5 . . . rear vehicle body frame, 6 . . . cab, 7 . . . tires, 10 . . . hydraulic pump, 11 . . . housing, 12 . . . rotary shaft, 13 . . . swash plate, 135 . . . recess, 14 . . . cylinder block, 161 . . . servo piston, 21, 41, 51, 61 . . . housing, 22, 42, 52 . . . lever, 221 . . . ball, 222, 422, 522 . . . rotary shaft, 223, 523 . . . first arm, 224, 524 . . . second arm, 423 . . . arm, 424 . . . inclined surface, 23 . . . stroke sensor, 231 . . . contact piece, 24 . . . controller, 241 . . . tilt angle calculator, 242 . . . angle difference calculator, 243 . . . control signal generator, 244 . . . control signal output portion, 245 . . . memory, 25 . . . servo valve, 251 . . . spring box.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-122348 | Jun 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/021308 | 6/4/2018 | WO | 00 |
