JP2007315419A - Front wheel drive circuit for asphalt finisher - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a crack or the like caused by shocking abutment by making a roller on the cylinder tip of a cam motor for front wheel drive contact with a cam surface shock-absorbingly when a front wheel of an asphalt finisher is changed over from a free wheel state to a drive state. <P>SOLUTION: In a hydraulic circuit constituted to operate a cam motor 5 by supplying pressurized oil to a pressurized oil line 6 for driving from a hydraulic pump 1 via an electromagnetic selector 4 and sending the pressurized oil to the cam motor 5 driving front wheels from the pressurized oil line 6 for driving, a spring type accumulator 8 is connected and made to communicate with the pressurized oil line 6 for driving via a branched line 6a, and a pressing force by the pressurized oil is lowered by the accumulator 8 to make a piston 54 contact with the cam surface 51 at gentle speed shock-absorbingly at a time of change over from the free wheel state to the drive state by moving the piston 54 of the cam motor 5 forward by the pressurized oil and making the piston abut on the cam surface 51. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a drive circuit for a hydraulic cam motor that drives a front wheel of an asphalt finisher in a wheel type asphalt finisher.

  In the wheel type asphalt finisher, a cam motor, which is a type of hydraulic motor for driving the front wheels, has been conventionally used so that the front wheels also have a driving force to increase the traction force during construction and the rear wheels do not slip. For example, as described in Patent Document 1, a front wheel drive motor composed of a cam motor is configured to control the amount of hydraulic oil and pressure flowing into the cam motor by a computer or the like so that the asphalt finisher travels smoothly. Yes.

On the other hand, the cam motor includes a plurality of fixed cam rings having a continuous-wave-shaped cam surface on an inner peripheral surface, and pistons disposed in a space surrounded by the fixed cam ring and capable of moving back and forth toward the cam surface. This cylinder consists of a cylinder block that is radially provided at equal intervals in the circumferential direction and a front wheel drive shaft that is fixed to the center of the cylinder block. The hydraulic oil is supplied to the cam motor to sequentially operate the pistons. Thus, the front wheel drive shaft is rotated by pressing a roller provided integrally with the tip of the piston against the cam surface.
JP-A-10-183525

  As described above, the wheel-type asphalt finisher paved the road surface with a screed disposed at the rear end while driving the front wheel and the rear wheel at a low speed and running on the road surface as described above. However, when moving to the construction site or on the return path after the construction, the front wheels are set in a free wheel state and the rear wheels are driven to rotate at high speed. Therefore, if a cam motor having a structure in which the back surface of the piston is constantly pressed toward the cam surface by a spring, pressure oil, etc. is used, the front end roller of the piston will be The piston frequently moves back and forth while sliding on the cam surface, and a failure occurs in a short period of time despite the fact that the cam surface and the roller surface are cured and heat-treated.

  Therefore, the cam motor used for driving the front wheel of the wheel type asphalt finisher has a structure in which the piston is retracted into the cylinder and the roller at the tip of the piston is kept away from the cam surface when the front wheel is in a free wheel state. However, when switching from the free wheel state to the driving state by pressing the piston during paving, the tip roller of the piston impacts against the cam surface and cracks the cam surface and roller surface that are hardened. And the like, the cracks gradually progressed, and the cured surface was peeled off, making it unusable.

  For this reason, in the above-mentioned Patent Document 1 and the like, an electrical control circuit and a hydraulic control device are incorporated to suppress a shock pressure increase against the piston at the time of switching from the freewheel state to the drivable state. Control circuits such as a hydraulic circuit and an electric circuit are extremely complicated and costly, and there is a problem in that stable control cannot be obtained and reliability is lowered.

  The present invention has been made in view of such problems, and an object of the present invention is to simplify a roller at the tip of a cylinder of a cam motor that rotationally drives a front wheel when the front wheel is switched from a free wheel state to a driving state. It is an object of the present invention to provide a front wheel drive circuit for an asphalt finisher which can be brought into contact with a cam surface in a shock-absorbing manner and which enables stable front wheel drive control.

  In order to achieve the above object, a front wheel drive circuit for an asphalt finisher according to the present invention is a wheel-type asphalt finisher using a cam motor for driving a front wheel, as described in claim 1, from a hydraulic pump to the cam motor. The hydraulic circuit for supplying hydraulic oil has a structure in which an accumulator is provided for alleviating the impact caused by the collision between the cam surface of the cam motor and the piston when switching from the free wheel state to the traveling drive state.

  In the front wheel drive circuit of the asphalt finisher configured as described above, the invention according to claim 2 connects the front wheel drive hydraulic circuit to a discharge line and an oil tank connected to a discharge port of a hydraulic pump. The pressure oil return line is connected to a drive motor pressure oil line and a drive release line of a cam motor that drives the front wheel via an electromagnetic switching valve, and an accumulator is connected to the drive pressure oil line. In addition, the pressure holding pipe line is connected to the cam motor, the pressure holding pipe line is connected to the oil tank via a flow rate adjusting valve composed of a slow return valve, and a check valve is connected to the drive release pipe line. The invention according to claim 3 is characterized in that a spring-type accumulator is used as the accumulator.

  According to the first aspect of the present invention, since the accumulator is connected in the hydraulic circuit that supplies the hydraulic oil from the hydraulic pump to the front-wheel drive cam motor, the hydraulic oil is supplied to the cam motor by operating the hydraulic pump from the free wheel state. When driving the front wheel by supplying (hereinafter referred to as pressure oil), the pressure of the pressure oil that presses the back of the piston of the cam motor can be absorbed by the accumulator, and the piston can be advanced at a slow speed, Therefore, the roller at the tip of the piston can be brought into contact with the cam surface in a buffering manner, and cracks can be prevented from occurring on the roller surface and the cam surface. As described above, the cam motor can be operated smoothly and stably so that the front wheels are driven from the free wheel state by a simple structure in which the accumulator is disposed in the hydraulic circuit from the hydraulic pump to the front wheel drive cam motor. . In addition, even if the pressure at the front wheel is increased or the pressure fluctuates after the roller at the tip of the piston comes into contact with the cam surface, there is no problem with the cam motor.

  According to the invention of claim 2, as the hydraulic circuit, a discharge line connected to the discharge port of the hydraulic pump and a pressure oil return line connected to the oil tank are connected to the front wheel via an electromagnetic switching valve. Since the drive pressure oil line and the drive release line of the cam motor for driving are connected to each other and an accumulator is connected to the drive pressure oil line, the electromagnetic switching valve is excited to By connecting the discharge line to the drive oil pressure line side of the cam motor, the pressing force acting on the back surface of the piston of the cam motor due to the pressure oil from the hydraulic pump is absorbed by the accumulator, so that the piston of the cam motor is loosened as described above. The free wheel state can be changed to the driving state by contacting the cam surface.

  Further, since the pressure holding pipe is communicated with the cam motor and the pressure holding pipe is connected to the oil tank via a flow rate adjusting valve composed of a slow return valve, the pressure relaxation action by the accumulator is reduced and the back surface of the piston When the pressure of the pressure oil acting on the pressure increases, a part of the pressure oil is released to the flow rate adjusting valve side consisting of the slow return valve through the pressure holding pipe, and the pressure oil is set at a constant pressure set by the flow rate adjusting valve. The roller at the tip of the piston is pressed against the cam surface, and the cam motor can be stably operated with a constant rotational driving force. Further, when the discharge line of the hydraulic pump is communicated with the drive release line by releasing the excitation of the electromagnetic switching valve, the pressure oil enters the casing of the cam motor and pushes back the piston to easily and reliably separate from the cam surface. And the front wheels can be held in the freewheel state. At this time, since the check valve is disposed in the drive release pipe line, the piston can be pushed back smoothly with a constant pressure while allowing the pressure oil to flow into the tank through the check valve.

  According to the invention of claim 3, since a spring-type accumulator is used as the accumulator, the accumulator has a function of preventing a sudden pressure increase in a hydraulic circuit that supplies hydraulic oil from the hydraulic pump to the cam motor. Pressure oil that acts on the back of the piston in the cam motor without using a set pressure valve or the like, and without any decrease in service life due to gas leakage due to deterioration of the rubber part, unlike the Prada accumulator. Therefore, the asphalt finisher front wheel drive circuit can be configured with high reliability so that the piston can be accurately and stably set to a constant pressure that allows the piston to move forward slowly.

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a hydraulic circuit diagram for driving a front wheel 31 of a wheel type asphalt finisher 30, and FIG. 2 is a simplified side view of the wheel type asphalt finisher 30. Asphalt finisher 30, as is well known, front wheel 31 and rear wheel 32 are configured to be driven by independent hydraulic motors, and rear wheel 32 is formed with a larger diameter than front wheel 31, and is driven. Although the rear wheel 32 has a larger force, the front wheel 31 is driven at a slightly higher peripheral speed than the rear wheel 32 to generate a traction force when the pavement construction proceeds.

  Further, the asphalt mixture is put into a hopper 33 installed on the front portion of the asphalt finisher 30 and the asphalt mixture is moved backward from the lower end of the hopper 33 by a conveyor (not shown) such as a bar conveyor. By conveying and discharging from the terminal end of the conveyance onto the road surface, spreading the composite material outwardly by the spreading screw 34 and leveling it to a predetermined thickness by the screed 35 disposed at the rear end of the asphalt finisher 30 It is configured to perform paving. The asphalt finisher 30 is provided with a hydraulic circuit that drives the front wheel 31.

  As shown in FIG. 1, this hydraulic circuit has a discharge oil line 2 connected to a discharge port of a hydraulic pump 1 for driving front wheels, and a pressure oil return line 3 communicating with the discharge line 2 and an oil tank 10. Are connected to the drive pressure oil line 6 of the cam motor 5 that drives the front wheel 31 via the electromagnetic switching valve 4 and the drive release line 7 that communicates with the cam surface side of the cam motor 5. Further, a branching line 6a is provided in the driving pressure oil line 6 of the cam motor 5, and a spring type accumulator 8 is connected to the branching line 6a, and the drive release line 7 is connected to the check valve through the branch line 7a. 11 communicates with the oil tank 10. Further, a pressure holding pipe 9 is communicated with a chamber on the back side of a piston, which will be described later, in each cylinder of the cam motor 5, and the pressure holding pipe 9 is connected to oil through a flow rate adjusting valve 12 comprising a slow return valve. A relief valve 13 is connected between the discharge pipe 2 and the pressure oil return pipe 3 while communicating with the tank 10.

  As shown in FIG. 4, the cam motor 5 includes a plurality of convex arc surfaces and concave arc surfaces in the circumferential direction on the inner peripheral surface of the cylindrical casing 50 (six in the drawing), and is a cam that is alternately continuous. A cylindrical cylinder block 52 is rotatably disposed in a space surrounded by the cam surface 51 and the surface 51 is formed, and the cylinder block 52 is directed radially toward the outer periphery of the cylinder block 52. A plurality of (eight in the figure) cylinders 53 are provided radially at regular intervals in the circumferential direction, and the open ends of the cylinders 53 are connected to the front ends (front ends) of the pistons 54 slidably fitted in the cylinders 53. A roller 55 that protrudes and protrudes from and comes into contact with and separates from the cam surface 51 is integrally provided.

  Further, the rotation drive shaft 36 of the front wheel 31 of the asphalt finisher 30 is integrally fixed to the center of the cylinder block 52, and communicates with the cylinder block portion around the rotation drive shaft 36 in the bottom of each cylinder 53. A plurality (eight) of driving hydraulic oil supply holes 56 are provided, and a pair of cylinders 53, 53 facing in the diametrical direction is paired into each pair of cylinders 53, 53 from the driving hydraulic oil pipe 6 to these. The rotary drive shaft 36 of the front wheel 31 is obtained by sequentially distributing and supplying the pressure oil to the drive pressure oil supply holes 56, 56 communicating with each pair of cylinders 53, 53 and pressing the rollers 55, 55 at the piston tip against the cam surface. Is configured to rotate integrally with the cylinder block 52.

  In addition, the pressure holding conduit 9 is communicated with the inner bottom of the cylinder chamber on the back side of the piston 54, and at the front side of the piston 54, that is, in the space 57 between the piston 54 and the cam surface 51. The drive release pipe line 7 is communicated and pressure oil is supplied to the space 57 through the pipe line 7, whereby the piston 54 is retracted into the cylinder 53 and the roller 55 is separated from the cam surface 51. is doing.

  As shown in FIG. 5, the spring type accumulator 8 has a piston body 8b slidably disposed in a cylindrical cylinder 8a, and the piston body 8b is always placed in the cylinder 8a at the tip of the cylinder 8a. In the normal state, a coil spring 8c is provided on the inner surface of the front end surface of the cylinder 8a so that the piston body 8a is in contact with the inner surface of the cylinder 8a. A through hole 8d for connecting the branch pipe 6a of the path 6 in a communicating state is provided. Further, a stopper 8e is provided in the cylinder chamber on the back side of the piston body 8a to receive the piston body 8a and prevent further backward movement.

  With this configuration, when asphalt pavement is performed on the road surface, the front wheel 31 of the asphalt finisher 30 excites the electromagnetic switching valve 4 from the free wheel state, and the discharge line 2 is pressurized to the driving pressure oil line 6. When the oil return line 3 is in communication with the drive release line 7, the pressure oil from the hydraulic pump 1 is supplied to the drive pressure oil line 6, and the cam motor is further supplied through the drive pressure oil line 6. The pressure oil is supplied to the pair of cylinders 53, 53 opposed to each other in the diametrical direction through the driving pressure oil supply holes 56, 56, and the piston 54 remains in the inner space 57 of the cam surface 51. Is moved toward the cam surface 51 while being pushed out toward the drive release conduit 7.

  At this time, since the spring-type accumulator 8 is connected to the driving pressure oil pipe 6 via the branch pipe 6a, a part of the pressure oil supplied to the cam motor 5 side is stored in the cylinder 8a of the accumulator 8. The piston body 8b is pressed into the distal end portion through the through hole 8d and retracted while compressing the coil spring 8c against the elastic force of the coil spring 8c to absorb the pressure of the pressure oil supplied to the cam motor 5. Then, the piston 54 of the cam motor 5 is advanced toward the cam surface 51 at a moderate speed, and the tip roller 55 of the piston 54 is abutted against the cam surface 51 in a buffering manner. Further, when the piston body 8b of the accumulator 8 moves backward and is received by the stopper 8e, the pressure of the pressure oil supplied to the cam motor 5 side through the driving pressure oil pipe 6 rapidly rises and comes into contact with the cam surface 51. The pushing force of the piston 54 against the cam surface 51 is increased to the motor driving pressure, and the cylinder block 52 of the cam motor 5 having the rotation driving shaft 36 fixed thereto is rotated to drive the front wheel 31.

  FIG. 6 is a diagram showing the operating state of the pressure oil, and point a is a point in time when the discharge valve 2 of the hydraulic pump 1 is switched to the drive pressure oil line 6 by exciting the electromagnetic switching valve 4. From this point of time, the pressure oil is supplied to the drive pressure oil pipe 6 and is received while the piston body 8b is retracted against the coil spring 8c in the cylinder 8a of the accumulator 8 until the pressure oil reaches the cam motor 5. The pressure is reduced, and the piston 54 of the cam motor 5 is advanced toward the cam surface 51 at a low speed with the low pressure. After contacting the cam surface 51 at the point b, the piston body 8b in the accumulator 8 is stopped by the stopper 8e. When the point c is received and received, the pressure absorbing function of the accumulator 8 is lost, and the pressure of the pressure oil supplied from the driving pressure oil pipe 6 to the cam motor 5 increases rapidly. Reached a certain point d rapidly Then, the cam motor 5 is rotationally driven.

  When the piston 54 advances toward the cam surface 51 at a low speed, the pressure oil in the space 57 on the cam surface 51 side flows out from the drive release line 7 into the pressure oil return line 3 through the electromagnetic switching valve 4. And collected in the oil tank 10. In the figure, a line e indicated by a dotted line is the drain pressure acting in the space portion 57.

  As described above, the cam motor 5 is operated as a pair of diametrically opposed cylinders 53, 53, and the drive pressure oil supply holes 56, 56 from the drive pressure oil pipeline 6 into each pair of cylinders 53, 53. Then, the pressure oil is distributed and supplied sequentially, and the pair of rollers 55 and 55 are sequentially pressed against the cam surface 51. At this time, when the pressing force of the rollers 55, 55 that press the cam surface 51 reaches the motor driving pressure, a part of the pressure oil flows out from the bottom of the cylinder 53 to the pressure holding conduit 9 side, and consists of a slow return valve. The flow regulating valve 12 is pushed open and returned to the oil tank 10. Accordingly, the cam motor 5 can be driven while the motor driving pressure is always kept constant.

  Next, when the asphalt compound paving work on the road surface is completed or when moving to a new road to be paved, the electromagnetic switching valve 4 is de-energized to drive the discharge pipe roller 552 of the hydraulic pump 1. When the electromagnetic switching valve 4 is switched so that the pressure oil return line 3 communicates with the drive pressure oil line 6 side on the release line 7 side, the pressure oil from the hydraulic pump 1 is released from the discharge line 2. It is supplied to the space 57 between the piston 54 and the cam surface 51 of the cam motor 5 through the pipe line 7 side, and the piston 54 is pushed back into the cylinder 53 by the hydraulic pressure to be separated from the cam surface 51. When the piston 54 moves backward, the pressure oil remaining in the cylinder chamber on the bottom side of the cylinder 53 passes through the pressure oil return line 3 from the driving pressure oil line 6 through the electromagnetic switching valve 4 or the pressure holding line. 9 is collected in the oil tank 10.

  As described above, when the piston 54 is moved backward to separate the tip roller 55 from the cam surface 51 and the rear wheel 32 is driven to rotate in this state to run the asphalt finisher 30 at a high speed, the front wheel 31 is in a free wheel state. There is no possibility that the cam surface 51 and the roller surface of the cam motor 5 will be cracked or worn by rotating.

Front wheel drive circuit diagram. Side view of asphalt finisher. The enlarged front view of a front-wheel part. Sectional drawing which shows the internal structure of a cam motor. Sectional drawing of a spring type accumulator. The pressure line figure which shows the pressure change of pressure oil.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydraulic pump 2 Discharge line 3 Pressure oil return line 4 Electromagnetic switching valve 5 Cam motor 6 Drive pressure oil line 7 Drive release line 8 Spring type accumulator 9 Pressure holding line
11 Check valve
12 Flow control valve
30 Asphalt finisher
31 Front wheels
51 Cam surface
52 Cylinder block
53 cylinders
54 Piston
55 Laura

Claims (3)

  In a wheel-type asphalt finisher that uses a cam motor for driving the front wheels, the cam surface and piston of the cam motor at the time of switching from the free wheel state to the traveling drive state in a hydraulic circuit that supplies hydraulic oil from the hydraulic pump to the cam motor A front wheel drive circuit for an asphalt finisher, wherein an accumulator is provided to alleviate an impact caused by a collision with the asphalt finisher.   The hydraulic circuit is a pressure oil line for driving a cam motor that drives a front wheel via an electromagnetic switching valve between a discharge line connected to a discharge port of a hydraulic pump and a pressure oil return line connected to an oil tank. And an accumulator is connected to the driving pressure oil line, and a pressure holding line is connected to the cam motor to connect the pressure holding line to a slow return valve. 2. The front wheel drive circuit for an asphalt finisher according to claim 1, wherein a check valve is provided in the drive release pipeline while being connected to an oil tank through a flow rate adjusting valve.   3. The front wheel drive circuit for an asphalt finisher according to claim 1, wherein the accumulator is a spring type accumulator.

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