US20160186389A1

US20160186389A1 - Method of warming paving machines

Info

Publication number: US20160186389A1
Application number: US15/065,863
Authority: US
Inventors: Luke E. Graham; Jameson M. Smieja; Ricky L. Mings; Toby A. Frelich
Original assignee: Caterpillar Paving Products Inc
Current assignee: Caterpillar Paving Products Inc
Priority date: 2016-03-10
Filing date: 2016-03-10
Publication date: 2016-06-30

Abstract

A method to warm a paving machine is disclosed. The method includes activation of a tamper speed control mode associated with a tamper bar in a screed section of the paving machine. A temperature of hydraulic oil of a tamper hydraulic circuit is detected. In addition, a temperature of the screed section is detected. A speed of operation of the tamper bar is set to a predetermined threshold if a temperature of the hydraulic oil is greater than a first oil temperature limit and a temperature of the screed section is greater than a screed temperature limit. The paving machine transitions to a paving mode, if the hydraulic oil temperature exceeds a second oil temperature limit and a minimum operational screed temperature is attained.

Description

TECHNICAL FIELD

The present disclosure generally relates to operation of screeds applied in paving machines. More particularly, the present disclosure relates to a method of warming a tamper system that has a restrained initial speed to ascertain low temperature compensation in paving machines.

BACKGROUND

Laying of asphalt paving material for preparing road surfaces includes a spread of paving material, constituted by an aggregate filled bituminous mixture, on a pre-prepared roadbed. The paving material is typically spread while it is hot and is then compacted so that upon cooling a hardened paved surface is formed. Conventional paving machines utilize a screed section, Which is drawn behind the paving machine during a paving operation. The screed section includes a screed plate assembly that facilitates a smooth spread of an even layer of the paving material on the roadbed. Weight of the screed section helps in minimal compaction of the paving material. Screed sections (not shown) generally include vibratory mechanisms placed directly on or adjacent the screed plate assembly. The vibratory mechanisms generally include tamper bars that are connected in tandem with the screed plate assembly, and which aid in the initial compaction of the paving material.
To facilitate laying of the paving material, screed assemblies are typically heated to a temperature in the range of about 82° to 171° C. (180° to 340° F.). Heating the screed assemblies enables the paving material to generally easily flow under the screed plate assembly and reduces adhesion of the paving material to the screed plate assembly. If the screed plate assembly is not adequately heated, the bituminous mixture may contact a bottom of the screed plate assembly and may harden, resulting in a buildup of the paving material and excessive drag, during operations. Such a build-up may also creep into a space defined between the screed plate assembly and the tamper bar, which may harden over time. When paving machines are operated after a prolonged period, particularly in relatively low temperature conditions, such a hardened build-up in-between the screed plate assembly and the tamper bar may cause the tamper bar to stick to the screed plate assembly or corresponding screed frame. With inadequate heating of the screed assemblies, there is an increased initial effort required to operate or reciprocate) the tamper bar relative to the screed plate assembly, as it requires overcoming the forces of adhesion between the tamper bar and the screed plate assembly. As a result, components such as those belonging to related hydraulic systems facilitating operation of the tamper bar relative to the screed plate assembly, and which are connected and operated in conjunction with the screed plate assembly, are increasingly prone to become degraded relatively quickly.
U.S. Pat. No. 8,998,530 discloses a screed for road pavers with a compaction unit. The compaction unit has a tamper bar that is drivable in cyclical work cycles with a selectable stroke and a selectable frequency for pre-compacting a pavement made from paving material. However, the '530 reference includes no discussion pertaining to easing out the strain sustained by the hydraulic components, particularly when a paving operation is initiated.
Accordingly, the system and method of the present disclosure solves one or more problems set forth above and other problems in the art.

SUMMARY OF THE INVENTION

The disclosure provides a method to warm a paving machine. The method includes activation of a tamper speed control mode associated with a tamper bar in a screed section of the paving machine. Temperature of hydraulic oil of tamper hydraulic circuit associated with an operation of the tamper bar, is detected. Further, the temperature of the screed section is detected. A speed of operation of the tamper bar is set to a predetermined threshold if a temperature of the hydraulic oil is greater than a first oil temperature limit and a temperature of the screed temperature is greater than a screed temperature limit. The paving machine is then transitioned to a paving mode, if the hydraulic oil temperature exceeds a second oil temperature limit and a minimum operational screed temperature is attained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary paving machine installed with a tamper system and a screed plate assembly, in accordance with the concepts of the present disclosure;

FIG. 2 is a perspective view of the tamper system of the paving machine of FIG. 1, in accordance with the concepts of the present disclosure;

FIG. 3 is a schematic layout of an electronic control system of the tamper system and the screed plate assembly of FIG. 2, in accordance with the concepts of the present disclosure; and

FIG. 4 is a flowchart depicting an exemplary method of operation of the electronic control system of the tamper system of FIG. 3, in accordance with the concepts of the present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown an exemplary embodiment of a paving machine 10 with a forward end 12 and a rear end 14. The paving machine 10 includes a tractor section 16 positioned at the forward end 12 and a screed section 18 positioned at the rear end 14.
The tractor section 16 includes a frame 20, a prime mover 22, one or more traction devices 24, an operator station 26, a hopper 28, and one or more conveyors 30. The frame 20 supports the prime mover 22, the traction devices 24, the hopper 28, and the conveyors 30.
The prime mover 22 may include, for example, a diesel engine, a gasoline engine, a natural gas engine, or other type of combustion engine commonly used to generate power. The prime mover 22 drives the traction devices 24 in conventional manner. The traction devices 24 may include one or more driven tracks, wheels, or other suitable propulsion mechanisms to cause movement of the paving machine 10.
The tractor section 16 includes the operator station 26, which is supported by the frame 20. The operator station 26 includes a seat and a console (not shown), which may include various controls for directing operations of the paving machine 10.
The tractor section 16 further includes the hopper 28 and the conveyors 30. The hopper 28 is arranged at the forward end 12 of the tractor section 16. The hopper 28 stores a paving material, such as asphalt, which is received by a dump vehicle (not shown). The hopper 28 is equipped with the conveyors 30, which are arranged at a bottom of the hopper 28, The conveyors 30 are configured for conveying the paving material from the hopper 28 in a rearward manner relative to the paving machine 10. More particularly, the conveyors 30 move the paving material rearward towards the screed section 18.
The screed section 18 may be towed or otherwise coupled to the tractor section 16, for instance, by a pair of tow arms 32, or the like. The screed section 18 is configured to spread and compact paving material into a layer or mat 34 of desired thickness, size, and uniformity on a paving surface 36. The screed section 18 includes an auger assembly 38, a screed frame 40, a screed plate assembly 42, a tamper system 44, and a wear plate 46 (shown in FIG. 2).
The auger assembly 38 is arranged near the forward end 12 of the screed section 18. The auger assembly 38 is provided to receive the paving material supplied by the conveyors 30. The auger assembly 38 laterally and more evenly spreads the paving material along the width of the screed section 18, particularly, beneath the screed plate assembly 42. Although only one auger is shown in FIG. 1, the paving machine 10 most typically includes two sets of augers (not shown) that can be independently controlled left and right to distribute the material as needed to each side of the screed plate assembly 42. If the paving machine 10 includes multiple auger sections to increase the width of the auger assemblies, the augers may be aligned end-to-end, and situated crossways within the screed section 18.
Referring to FIG. 2, there is shown the screed section 18 with the screed frame 40, the screed plate assembly 42, the tamper system 44, and the wear plate 46. The screed frame 40 is a metallic structure generally enclosed in a screed housing (not shown). The screed frame 40 is structured for support and attachment of the screed plate assembly 42, the tamper system 44, and the wear plate 46.
The screed plate assembly 42 is attached to a bottom portion of the screed frame 40. The screed plate assembly 42 may be constructed of a suitable steel. The screed plate assembly 42 floats over the paying surface 36 (FIG. 1), to spread the smooth and even mat 34 (FIG. 1) of paving material on the paying surface 36. Weight of the screed section 18 compresses the paving material and initially compacts a paving material layer. Certain vibratory mechanisms are placed directly on the screed plate assembly 42 or the screed frame 40 to aid in the initial compaction of the paving material. In the exemplary embodiment, the tamper system 44 is a vibratory tamper system, which is connected in tandem with the screed plate assembly 42.
The tamper system 44 is supported by the screed frame 40. The tamper system 44 is disposed between the conveyors 30 and the screed plate assembly 42. The tamper system 44 includes a tamper bar 48 and a tamper drive mechanism 50. The tamper bar 48 is an elongated rectangular member with a generally flat paving material engagement surface along a lower edge thereof. The tamper system 44 is used to pre-compact the paving material as the paying machine 10 moves forward, or in the direction opposite the direction denoted by arrow, A. The tamper bar 48 is supported so as to be movable up and down so as to be able strike the paving material layer upon deposition by the auger assembly 38. An upward and downward movement of the tamper bar 48 is powered by the tamper drive mechanism 50. The tamper drive mechanism 50 includes a tamper hydraulic circuit 52 (FIG. 3) that includes one or more tamper drive members operatively connected to the tamper bar 48, which is further explained in description of FIG. 3. To further aid in compaction of the paving material, the screed section 18 may include other vibratory mechanisms (not shown) arranged on an upper side of the screed plate assembly 42, which are configured to drive a vibratory movement of the screed plate assembly 42.
The wear plate 46 is perpendicularly attached to the screed frame 40, such that a portion of the wear plate 46 is in contact with the screed plate assembly 42. The wear plate 46 is partially disposed between the tamper bar 48 and the screed frame 40. The wear plate 46 is also partially disposed between the tamper bar 48 and the screed plate assembly 42. The wear plate 46 is provided to reduce wearing of screed plate assembly 42 during movement of the tamper bar 48.
Referring to FIG. 3, there is shown a layout of an electronic control system 54 to control vibration of the tamper system 44 and a warm-up sequence of the screed plate assembly 42. The electronic control system 54 includes an interactive display unit 56, a controller 58, afloat mode switch 60, a park brake switch 62, the tamper hydraulic circuit 52, and one or more screed temperature sensors 63, 64, 66, and 68.
The interactive display unit 56 is equipped with a series of switches, function keys, for different functions of the screed section 18 and the tractor section 16. The interactive display unit 56 includes a warm-up switch 70 and a tamper speed control switch 72. The warm-up switch 70 facilitates initiation of the warm-up sequence of the screed plate assembly 42. The tamper speed control switch 72 facilitates activation of a tamper speed control mode during the warm-up sequence. In the tamper speed control mode, the electronic control system 54 sets a speed of operation for the tamper to a predetermined threshold. This implies that the controller 58 commands the tamper bar 48 to be restricted to a tamper speed of 200 revolutions per minute (rpm), which is referred to as the predetermined threshold.
Inputs given to the interactive display unit 56 via one or more of the above-mentioned switches are communicated to the controller 58. The controller 58 is responsive to inputs from the switches of the interactive display unit 56, the park brake switch 62, the tamper hydraulic circuit 52, and the screed temperature sensors 63, 64, 66, and 68. The controller 58 may include a typical microprocessor (not shown) and memory (not shown). and can be programmed or hard-wired to provide the functions discussed below.
The float mode switch 60 is located on the operator station 26. The float mode switch 60 determines a float condition of the screed plate assembly 42 relative to the paving surface 36. The float mode switch 60 is in control communication with the controller 58.
The park brake switch 62 is communication with the electronic control module 58. State of the park brake switch 62 determines if a park brake 74 for the paving machine 10 is in an active state or a passive state.
The tamper hydraulic circuit 52 is associated with the tamper drive mechanism 50 of the tamper system 44. The tamper hydraulic circuit 52 includes a solenoid 76, a hydraulic pump 78, a hydraulic motor 80, a tamper bar speed sensor 84, and an oil temperature sensor 86. The solenoid 76 is connected to the hydraulic pump 78 which drives the hydraulic motor 80. The oil temperature sensor 86 may be located in a hydraulic oil tank (not shown) and may measure a temperature of hydraulic oil in the tamper hydraulic circuit 52 from that location. The oil temperature sensor 86 generates a temperature signal indicative of temperature of hydraulic oil flowing in the tamper hydraulic circuit 52. The oil temperature sensor 86 sends the temperature signal to the controller 58 and the interactive display unit 56.
The hydraulic motor 80 is operably coupled to the tamper drive mechanism 50. The tamper drive mechanism 50 is attached to the tamper bar 48, such that rotation of the tamper drive mechanism 50 facilitates movement of the tamper bar 48.
The tamper bar speed sensor 84 is associated with the tamper drive mechanism 50 of the tamper system 44. The tamper bar speed sensor 84 produces a tamper bar speed signal indicative of rotational velocity of the tamper drive mechanism 50. The tamper bar speed sensor 84 is in control communication with the controller 58 and the interactive display unit 56, which thereby receive the tamper bar speed signal, It may be contemplated that although the most accurate way to measure and display the tamper bar speed is through a dedicated speed sensor of a magnetic type or otherwise, the tamper bar speed may also be calculated and controlled via an advanced hydraulic control system calibration (not shown) for the tamper hydraulic circuit 52.
Typically, the screed plate assembly 42 includes four screed plate sections(not shown). The four screed plate sections (not shown)are equipped with the screed temperature sensors 63, 64, 66, and 68. The screed temperature sensors 63, 64, 66, and 68 provide current temperatures of the respective screed sections (not shown). It will be understood that during initial start-up, although each of the screed sections (not shown) (not shown) may be at substantially similar temperatures, very minute temperature differences between the screed sections (not shown) (not shown) may still exist, which the screed temperature sensors 63, 64, 66, and 68 sense and provide to the controller 58. The controller 58 extracts temperatures from the different sections of the screed plate assembly 42 by reading inputs from the screed temperature sensors 63, 64, 66, and 68 located on the screed sections (not shown) (not shown). The temperature of the screed plate assembly 42 is communicated to the interactive display unit 56.
Referring to FIG. 4, there is shown a flowchart for a method 88 to start the tamper system 44 that has a restrained initial speed to ascertain low temperature compensation in the paving machine 10. The method 88 starts with step 90.
At step 90, an operator may actuate the warm-up sequence and the tamper speed control mode, via the warm-up switch 70 and the tamper speed control switch 72, respectively. Prior to initiation of the warm-up sequence, the controller 58 determines whether few conditions are met for optimum warm-up operation. The controller 58 determines whether the park brake 74 is in a proper state, based on the park brake switch 62. The controller 58 receives and processes signal from the float mode switch 60 to infer the position of the screed section 18 to determine whether the screed section 18 is in the proper state, that is, not in float condition. Upon confirming that the park brake 74 is in the active state and the screed assembly 18 is not in the float condition, the warm-up sequence is initiated. The method 88 proceeds to step 92.
At step 92, the controller 58 detects the temperature of the hydraulic oil via the oil temperature sensor 86. The controller 58 receives an oil temperature signal and determines whether the temperature is equal to or greater than a first oil temperature limit, which may be selectable from a set of low temperature limits. The controller 58 detects the temperature of the screed sections (not shown), via the screed temperature sensors 63, 64, 66, and 68. The controller 58 determines whether the temperature of the screed section 18 is greater than a screed temperature limit, which may be selectable from a set of screed temperature limits. The method 88 proceeds to step 94.
At step 94, the controller 58 processes the oil temperature signal and determines whether the temperature is equal to or greater than the first oil temperature limit. Also, the controller 58 determines whether the temperature of the screed section 18 is greater than the screed temperature limit, that is, 50° C. If the temperature of the hydraulic oil is equal to or greater than the first oil temperature limit and the temperature of the screed section 18 is greater than the screed temperature limit, the method 88 proceeds to step 96. Otherwise, the method 88 goes to step 92, whereby not allowing the tamper system 44 to actuate and attempt to rotate in an attempt to prevent a hydraulic stall condition and thus protecting the hydraulic components from potential damage and degradation of service life.
At step 96, the tamper speed limit control mode initiates. Movement of the tamper bar 48 is actuated at the speed of operation, which is equal to 200 rpm. The method 88 proceeds to step 98.
At step 98, the controller 58 checks operational parameters, that is, positions of the park brake 74 and the screed section 18 (the screed plate assembly 42), via the park brake switch 62 and the float mode switch 60, respectively. If the park brake 74 is in the passive state and the screed section 18 is in the float condition, the method 88 proceeds to step 100, otherwise the method 88 goes to step 99.
At step 99, the controller 58 sends signals to de-activate the warm-up sequence on detecting that the park brake 74 is in the active state and the screed section 18 is in the float condition. The method 88 proceeds to step 104.
At step 100, the controller 58 determines whether the temperature of the at least one section of the screed plate assembly 42 is at a minimum operational screed temperature. Further, the controller 58 determines whether the temperature of the hydraulic oil exceeds a second oil temperature limit, which may be selectable from a set of high temperature limits. If the screed plate assembly 42 is at a minimum operational screed temperature and the temperature of the hydraulic oil exceeds the second oil temperature limit, the method 88 proceeds to step 102, otherwise the method 88 goes to step 104.
At step 102, the electronic control system 54 operates the controller 58 to allow the paving machine 10 to transition to a paving mode. In the paving mode, the screed plate assembly 42 and the tamper bar 48 operate at desired configured temperatures and speeds.
At step 104, the electronic control system 54 operates the controller 58 to turn-off the tamper system 44. This results in termination of movement of the tamper bar 48.

INDUSTRIAL APPLICABILITY

In operation, an on/off switch in the operator station 26 selectively connects a power supply to the electronic control system 54. An operator activates the warm-up sequence by the warm-up switch 70 on the interactive display unit 56. The warm-up sequence is initiated when the controller 58 determines that the park brake 74 is in the active state and the screed plate assembly 42 is in float condition. At this instant, the tamper bar 48 is stationary and is not operational. During the warm-up sequence, the controller 58 detects that the hydraulic oil temperature is greater than the first oil temperature limit and the temperature of the screed section 18 is greater than the screed temperature limit. In such conditions, the tamper speed control mode is initiated by the controller 58 during the warm-up sequence. In the tamper speed control mode, the controller 58 limits the speed of operation of the tamper bar 48 to 200 rpm. The controller 58 produces a tamper bar control signal corresponding to the rotational speed of 200 rpm. The controller 58 sends the tamper bar control signal to the solenoid 76. The solenoid 76 being in control communication with the hydraulic pump 78 controls flow of the hydraulic oil to the hydraulic motor 80, based on the tamper bar control signal. The hydraulic motor 80 controls the rotational speed of the tamper drive mechanism 50 for 200 rpm, based on the flow of the hydraulic oil. The tamper drive mechanism 50 moves the tamper bar 48 such that the speed of operation is limited to 200 rpm. The tamper system 44 operates the tamper bar 48 in the tamper speed control mode until the operator manually turns-off using the tamper speed control switch 72, or the above mentioned temperature conditions are met. Further, the electronic control system 54 continues to monitor signals from the oil temperature sensor 86 and the screed temperature sensors 63, 64, 66, and 68. At some point in time, the controller 58 senses that the temperature of the hydraulic oil in the tamper hydraulic circuit 52 is equal to the second oil temperature limit and temperature of at least one section of the screed plate assembly 42 is at a predetermined set point. Thereafter, the controller 58 sends signal to turn-off the tamper speed control drive. The paving machine 10 then starts to transition the tamper speed to the higher pre-set tamper speed more representative of a paving application, where the taper bar and the screed plate assembly 42 function at the desired temperatures and speeds. Changing the state of the screed section 18 to the float condition and/or switching the park brake 74 to the passive state will shut down this warm-up sequence and turn off the tamper system 44.
In instances after prolonged use, there is residual hardened deposit of the asphalt between the tamper bar 48 and the screed plate assembly 42. In such cases, the tamper bar 48 is operated at the tamper speed which is limited to 200 rpm. This is done until the tamper bar 48 and the screed plate assembly 42 is heated to adequate temperatures, which in this case is the screed temperature limit. As the tamper bar 48 and the screed plate assembly 42 are adequately heated, adhesion forces between the tamper bar 48 and the screed plate assembly 42 weaken. Further, the speed of the tamper bar 48 is increased to the desired speed. Hence, there is no pressure build-up in the tamper hydraulic circuit 52 as compared to the existing tamper systems, as reduced force is required to remove the tamper bar 48 from the screed plate assembly 42. Hence, undesired degradation of the tamper hydraulic circuit 52 is eliminated.
The many features and advantages of the disclosure are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the disclosure that fall within the true spirit and scope thereof. Further, since numerous modifications and variations will readily occur to those skilled in the art. It is not desired to limit the disclosure to the exact construction and operation illustrated and described, and, accordingly, all suitable modifications and equivalents may be resorted to that fall within the scope of the disclosure.

Claims

What is claimed is:

1. A method of warming a paving machine, the method comprising:

activating a tamper speed control mode associated with a tamper bar in a screed section of the paving machine;

detecting a temperature of a hydraulic oil of a tamper hydraulic circuit associated with an operation of the tamper bar;

detecting a temperature of the screed section;

allowing the tamper bar to actuate at a speed of operation equal to a predetermined threshold if a temperature of the hydraulic oil is greater than a first oil temperature limit and a temperature of the screed section is greater than a screed temperature limit; and

transitioning the paving machine to a paving mode if the hydraulic oil temperature exceeds a second oil temperature limit and a minimum operational screed temperature is attained, wherein in the paving mode the tamper bar is operated at a desired speed of operation,

wherein the warming of the paving machine via a warm-up sequence may be de-activated if the park brake and the screed section are not in the proper state to facilitate safe operation of the tamper system.