Patent Application
20170073907
The present disclosure relates generally to a paving machine. In particular, the present disclosure relates to a cushioning system for a screed of a paving machine.
A paving machine, commonly known as a paver, is used in combination with a screed to lay a paved surface, also referred to as a mat or paving mat. A paving machine is generally a self-propelled machine designed to receive, convey, distribute, and compact paving material, such as asphalt, to create a flat, consistent surface over which vehicles may travel. A paving machine typically has a tractor with a hopper at its front end for receiving paving material. A conveyor system on the machine transfers the paving material from the hopper towards a screed mounted rearwards of the tractor. Screw augers positioned behind the tractor and in front of the screed assist in moving the paving material so that a relatively uniform volume of paving material is distributed in front the screed.
The screed is a heavy assembly towed behind the paving machine by a pair tow arms for smoothing out and compacting the paving material distributed by the screw augers. When the paving machine moves, the screed physically levels any paving material lying higher than a predetermined height above the roadway surface, leaving a generally uniform thickness of the paving material. The screed also compacts the paving material in order to provide a uniform, smooth, durable pavement surface.
The screed is generally connected to the frame of the paving machine by tow arms. These tow arms have one end coupled to the frame of the machine and the other end coupled to the screed. Typically, hydraulic actuators are coupled to the screed or the tow arms in order to raise or lower the screed relative to the surface being paved. When the paving machine is engaged in paving a mat on a desired surface, the paving machine travels at a very slow speed with the screed floating above the ground surface in order to provide a mat of a specified thickness and to level and compact the material being paved. For travelling or transportation of the paving machine while the machine is not engaged in paving, the screed is raised to a higher or a transport position in order to avoid the screed from hitting the ground surface or objects lying on the ground. While moving, the screed may bounce or there may be unwanted movements in the screed due to uneven road conditions or due to other forces acting on the screed. The weight of the screed causes these movements to be transmitted back to the main body of the paver, resulting in imbalance of the paver and difficulty in handling the paver while travelling. These movements may also deteriorate the ride quality of the paver. Also, the bouncing screed may damage the paved surface.
U.S. Pat. No. 5,556,227 discloses providing an elastic support for a screed of a paver. The paver uses an accumulator to damp the movement of screed by providing an accumulator connected to the lifting cylinder when the paver is travelling. When such cushioning systems are switched on, there may be some unwanted movements in the screed or unevenness in switching the screed to the cushioned state. The sudden shift from a normal raised position to a cushioned state may lead to sudden downward motion of the screed. This motion may lead to a momentary feel of an unstable paver.
The present disclosure provides for a paver including a screed, an actuator coupled to the screed and configured to raise the screed to a transport position by pressurizing a raise end of the actuator. An accumulator is selectively connected to the actuator. A control valve is configured to switch the screed in the transport position between a non-cushioned state and a cushioned state by connecting the accumulator to the raise end of the actuator in the cushioned state. The accumulator hydraulic pressure is equalized to actuator hydraulic pressure before the control valve switches the screed from the non-cushioned state to the cushioned state.
The present disclosure further provides for a paver including a screed, an actuator coupled to the screed and configured to move the screed between a raised position and a lowered position. The paver further includes a control valve configured to switch the screed between a non-cushioned state and a cushioned state in the raised position. A controller is configured to raise the screed to the raised position and switch the screed to a cushioned state when the screed is in the raised position.
The present disclosure provides for a method of cushioning a screed. The method includes raising the screed from a lowered position to a raised position. The method further includes equalizing an actuator pressure to an accumulator pressure and placing the screed in a cushioned state by connecting the actuator to the accumulator.
Actuators 30 are coupled to the screed 20 and the frame 14. As one of skilled in the art will appreciate, the actuators 30 may be any type of structure or mechanism responsible for moving a component. For example, the actuators 30 may be hydraulic or pneumatic actuators. In the embodiment illustrated in
The paver 10 may include a position detection device 40 operatively connected to the actuator 30 to detect the position of the screed 20. In the illustrated embodiment, position detection device 40 is coupled to the actuator 30 and is configured to detect the position of the screed 20 based on the position of the actuator 30. In an alternate embodiment, the position detection device 40 may be configured to detect the position of the screed 20 based on the position of the tow arms 22.
The paver 10 further includes a locking system 50 to lock the screed 20 in a transport position or raised position.
A head end conduit 102 connects the head end 32 of the actuators 30 to the control module 200. A rod end conduit 104 connects the rod end 34 of the actuators 30 to the damping system 400, the cushioning system 300 and the control module 200. Two rod end valves 130 are connected between the rod end 34 and the damping system 400 for controlling the flow of fluid to and from the rod ends 34 of the actuators 30.
Referring to
The control module 200 further includes a first valve 260 and a second valve 270. The first valve 260 and the second valve 270 regulate the flow of hydraulic fluid to and from the head end conduit 102 and the rod end conduit 104, respectively. Proportional pressure reducing valve 230 is connected to the first valve 260 and the second valve 270. The first valve 260 and the second valve 270 work in tandem with the proportional pressure reducing valve 230, the stop valve 240 and the rod end valves 130 to control the raising or lowering of the screed 20. Tank 220 is connected to the first valve 260 and the second valve 270 via a parallel tank conduit 224, in order to receive hydraulic fluid from the head end conduit 102 or the rod end conduit 104. The first valve 260 is connected to the head end 32 via the head end conduit 102, and the second valve 270 is connected to the rod end 34, rod end valves 130 and the cushioning system 300 via rod end conduit 104. Pressure sensors 60 may be connected to the hydraulic circuit to measure pressure in the hydraulic circuit. The pressure sensor output may be used to provide signal or feedback to the controller 500, in order to provide closed loop control of system pressure. The pressure sensor feedback may also be used to maintain cushioned state.
Further, a damping system 400 is connected to the rod end conduit 104. The damping system 400 includes a damping orifice 410 and a one way check valve 420. The damping orifice 410 damps the downward motion of the screed 20 by restricting the free flow of hydraulic fluid from the rod end 34 of the actuator 30. Whereas, the check valve 420 allows for free flow of hydraulic fluid towards the rod end 34 for raising the screed 20. In the embodiment illustrated, the damping system 400 includes a set of a check valve 420 and a damping orifice 410 connected in parallel, to the rod end 34 of each actuator 30.
For switching the screed 20 to the cushioned state, the cut-off valve 310 is switched to block the flow of fluid between the rod end 34 and the control module 200, and the rod end valves 130 and the accumulator valve 320 are switched to connect the accumulator 330 to the rod end 34. Whereas, for switching the screed 20 to a non-cushioned state, the cut-off valve 310 is switched to allow the flow of fluid between the rod end 34 and the control module 200, and the rod end valves 130 and the accumulator valve 320 are switched to disconnect the accumulator 330 from the rod end 34.
In the embodiment as illustrated in
Further, a pressure equalization passage 340 connects the rod end 34 of the actuator 30 to the accumulator 330. The pressure equalization passage 340 while restricting any substantial flow of fluid between the rod end 34 and the accumulator 330, ensures that the pressure in the rod end 34 and the accumulator 330 are equalized. Thus, when the screed 20 is switched to the cushioned state from a non-cushioned state, the transition can take place smoothly as there is no pressure equalization needed at the time of the transition. Similarly, due to the pressure equalization passage 340, the transition of the screed 20 from a non-cushioned state to a cushioned state can also take place smoothly due to pressure equalization between the accumulator 330 and the rod end 34 of the actuators 30. In other embodiments, alternate pressure equalization mechanisms known in the art such as using pressure sensors and valve actuation may be used to match actuator pressure to the accumulator pressure.
A controller 500 is connected to the hydraulic circuit and is configured to control various modules, valves and devices in the hydraulic circuit in order to perform the operation of the screed control system 100. The controller 500 may include a single microprocessor or multiple microprocessors that include a means for controlling an operation of various systems and valves in the hydraulic circuit. Commercially available microprocessors can be configured to perform the functions of the controller 500. The controller 500 may include a memory, a secondary storage device, a processor, and other components for running an application. Various other electrical or electronic circuits may be associated with the controller 500 such as power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and other types of circuitry. Additionally, there may be several measuring and monitoring devices, for example pressure sensors, position sensors or motion sensors, coupled to different parts of the screed control system 100 and the controller 500 to sense various parameters needed in order to effectively control the screed control system 100.
The controller 500 ensures that the valves of the screed control system 100 work in tandem to achieve different positions of the screed 20. The controller 500 generates signals to switch the various valves in different positions in order to control the raising, lowering, cushioning or locking of the screed 20.
The controller 500 may be coupled to the position detection device 40 for detecting the position of the screed 20. Further, the controller 500 may be configured to determine whether the screed 20 is in a cushioned state or a non-cushioned state. The controller 500 may be configured to determine the screed 20 in a transport position or above a certain predetermined height and automatically engage the cushioned state. Further, the controller 500 may be configured to automatically lock the screed 20 in the transport position when the screed 20 is in a cushioned state.
The screed control system 100 operates as follows. The controller 500 may be configured to generate signals for actuation of the various valves in the required positions for effecting different operations on the screed 20.
In the embodiment in accordance with
When the screed 20 is switched to a cushioned state there is no difference in pressure in the rod end 34 and the accumulator 330, as the pressure equalization passage 340 equalizes the hydraulic pressure of the accumulator 330 with the current hydraulic pressure of the actuator 30 at the rod end 34. This enables smooth transition of the screed 20 from the non-cushioned state to a cushioned state.
In accordance with an embodiment, the controller 500 may be configured to automatically switch the screed 20 into a cushioned state on detecting the transport position or raised position of the screed 20. The controller 500 may further engage the locking system 50 to automatically switch or move the stop member 52 to an operating position when the screed 20 is determined in a transport position or in a cushioned state. In an embodiment, the controller 500 may move the stop member 52 based on an operator input.
In an alternate embodiment, when the screed 20 is switched to a cushioned state, the controller 500 may be configured to raise the screed 20 to a transport position, engage the screed 20 to a cushioned state and lock the screed 20 in the transport position.
Industrial Applicability
The present disclosure provides for a screed control system 100 that facilitates the cushioning of the screed 20 during travel of the paver 10. The disclosure also facilitates locking of the screed 20 in cushioned state during travel of the paver 10. The disclosure provides for enabling a smooth transition of the screed 20 from a non-cushioned state to a cushioned state.
Further, the present disclosure provides for a method 600 of cushioning a screed 20 of a paver 10. Referring to
The disclosed method 600 may further include determining whether the screed 20 is in the raised position. The position detection device 40 may detect the position of the screed 20. Based on the feedback from the position detection device 40, the controller 500 may determine position of the screed 20. When the screed 20 is in the raised position, the stop member 52 may be extended to restrict or lock the screed 20 in the raised position. The controller 500 may determine the raised or lowered position of the screed 20 based on signal from the position detection device 40.
In alternate embodiments, once the screed 20 is placed in the cushioned state, travel of the screed 20 out of the transport or raised position may be restricted by extending a stop member 52. The stop member 52 restricts or locks the downward travel of the screed 20 when the screed 20 is in a transport position and/or a cushioned state. In an embodiment, the method 600 may further include providing a damping orifice 410 between the rod end 34 of the actuator 30 and the accumulator 330. The damping orifice 410 restricts free flow of the hydraulic fluid in the rod end conduit 104 and thus damps any downward movement of the screed 20.
In an embodiment, the method 600 may further include determining an operator request to move the screed 20 to a lowered position. On receiving a request to lower the screed 20, the stop member 52 may be retracted and the screed 20 may be moved to the lowered position.
Using the method and system according to the present disclosure, the screed 20 may be switched to a cushioned state smoothly, as the pressure of the accumulator 330 is equalized with the pressure of the rod end 34 of the actuators 30 before switching the screed 20 into the cushioned state. This way, when the accumulator 330 is connected to the rod end 34 of the actuator 30 for cushioning the screed 20, absence of any pressure difference between the rod end 34 and the accumulator 330 leads to smooth transitioning of the screed 20 into the cushioned state.
Also, the present disclosure provides for switching the screed 20 to the cushioned state once the screed 20 is raised to a transport position. The screed control system 100 may include a controller 500 that is coupled to the control module 200, cushioning system 300, damping system 400 and locking system 50, and a position detection device 40. The position detection device 40 may determine when the screed 20 is in a raised position, a transport position or above a certain predetermined height and send a signal to the controller 500. The controller 500 may, on receiving the signal that the screed 20 is in a transport position, control various valves in the screed control system 100 to switch the screed 20 to the cushioned state by connecting the rod end 34 of the actuator 30 to the accumulator 330, allowing the screed 20 to be automatically switched to a cushioned state once the screed 20 is detected in a transport position.
In an alternate embodiment, the controller 500 may be configured to receive instructions from the operator to put the screed 20 into a transport state. Upon receiving such instructions, the controller 500 may be configured to raise the screed 20 to a transport position and then engage the cushioned state. For raising the screed 20, the controller 500 may signal the control module 200 to send pressurized hydraulic fluid towards the rod end 34 of the actuator 30. Once the screed 20 is raised to a transport position, the controller 500 may signal the cushioning system 300 to switch the screed 20 to a cushioned state by actuating the accumulator valve 320 and cut-off valve 310 to connect the rod end 34 of the actuator 30 to the accumulator 330.
Further, the screed control system 100 according to the present disclosure provides for locking of the screed 20 in the transport position when the screed 20 is switched into a cushioned state. In an embodiment, the position detection device 40 may send signal to the controller 500 once the screed 20 is raised to a transport position. On receiving such signal, the controller 500 may be configured to switch the screed 20 to a cushioned state and extend the stop member 52 to a locking position in order to lock the screed 20 in the transport position. This way the screed 20 may be automatically locked into the transport position once the screed 20 is raised to a transport position and switched to a cushioned state. Thus the present disclosure provides for an easy operation of the screed 20 of a paver 10. In an embodiment, switching the screed 20 to a transport state may include engaging the locking system 50 once the screed 20 is switched to a cushioned state.
