EP1577443A1

EP1577443A1 - Vibratory screed for a paving machine

Info

Publication number: EP1577443A1
Application number: EP04006487A
Authority: EP
Inventors: Marco Gerardo
Original assignee: Bitelli SpA
Current assignee: Caterpillar Prodotti Stradali SRL
Priority date: 2004-03-18
Filing date: 2004-03-18
Publication date: 2005-09-21

Abstract

A screed assembly (14) for a paving machine (10) is provided. The screed assembly (14) includes at least one screed plate (22) having an electrically actuated vibratory unit (26) positioned at a location sufficient to controllably vibrate the screed plate (22). The vibratory unit (26) is a self-contained vibratory system having an electric motor (30) driving a rotating mass (34). Each screed plate (22) included in the screed assembly (14) may be provided with a respective electronically actuated vibratory unit (26).

Description

Technical Field

The present invention relates to paving machines having screed assemblies and, more particularly, to paving screed assemblies having associated oscillatory mechanisms.

Background

Paving machines are used for depositing, spreading, compacting, and smoothing a paving material on a roadbed in such a manner that a uniform and drivable surface is produced. In the case of an asphalt paving machine, the paving material is typically an aggregate filled bituminous mixture that is deposited while hot on a roadbed. Once the mixture cools, after being suitably compacted and smoothed, a hardened pavement surface results.

The service life of a pavement, in particular of an asphalt pavement, depends significantly upon the successful reduction of voids in the bituminous mixture. The process of compaction of the asphalt layer or mat controls and minimizes voids in the material. Paving machines use screed assemblies to smooth and compact the paving material. The screed assembly is typically drawn behind the paving machine, and is adjustable to establish the thickness of the deposited layer of paving material.

A screed assembly typically includes main and may include auxiliary screed portions. Each screed portion typically has at least one steel screed plate mounted to the screed portion in such a manner that the plates smooth and compress the deposited paving material, leaving behind a mat of the desired thickness. In the case of asphalt paving, the screed plates are often heated, typically using gas-fired burners, to prevent the bituminous material from clinging to the steel plates and to produce a desired finish on the pavement. It is also known and becoming more common to use electrical resistance heaters instead of gas fired burners to heat the screed plates.

To aid in compacting the paving material, it is known to vibrate the screed plates. A typical vibratory screed may be represented by US patent 5,868,522 issued to Campbell. The Campbell system uses a motor driven shaft attached in a linear manner via a plurality of bearing journals to each of the multiplicity of screed plates in a screed assembly. Eccentric weights mounted on the shaft cause the shaft and, indirectly, each of the screed plates to vibrate when the shaft is rotated by the motor.

In certain applications it has been found to be advantageous to pre-compact the paving material using tamper or compactor bars mounted on the screed assembly in front of the screed plates. As is further discussed in Campbell, the tamper bars may be reciprocated vertically in a manner similar to the vibration of the screed plates, using a linear shaft commonly mounted to the plurality of tamper bars.

Motor driven linear vibrator and reciprocator shafts are bulky, difficult to optimally position in the tight confines of a screed assembly, and are not readily adapted to apply a controlled motion to the most advantageous location on a screed plate or tamper bar because the shaft can only be positioned in a linear manner on the respective device.

Because the screed assembly is typically towed behind a paving machine, it is desirable to minimize the number of connections that must be made between the machine and the screed assembly. Screed and tamper bar heating units using natural gas burners disposed about the screed assembly require a network of tubing both within the screed assembly and between the screed assembly and a source of combustible fuel, typically carried under pressure in a tank on the paving machine. The fuel supply also must be replenished frequently. Screed and tamper bar shafts that are rotationally driven by hydraulic motors, as is typical because pressurized hydraulic fluid is commonly available on paving machines, also require the provision of high-pressure hydraulic plumbing within the screed assembly and between the screed assembly and the paving machine proper. A hydraulic pump and control system of suitable capacity must also be carried by the paving machine. Electrical heater assemblies and electric motors may be advantageously employed to avoid the disadvantages of combustible fuel and hydraulic systems, but normally require the availability of a high capacity electric power system.

The present invention is directed to overcoming one or more of the problems set forth above.

Summary of the Invention

In one aspect of the present invention, a screed assembly for a paving machine includes at least one screed plate and a respective electrically actuated vibratory unit associated with and positioned relative to the screed plate at a location sufficient to controllably vibrate the screed plate. The vibratory unit is a self-contained vibratory system having an electric motor driving a rotating mass.

In a second aspect of the present invention, a paving machine includes an engine coupled to a system for producing electrical power. The machine includes a screed assembly having at least one screed plate. An electrical heater assembly is associated with and positioned at a location sufficient to controllably heat at least a portion of the screed plate, and an electrically actuated vibratory unit is associated with and positioned at a location sufficient to controllably vibrate the screed plate. The electrically actuated vibratory unit is a self-contained vibratory system having an electric motor driving a rotating mass, and the heating element and vibratory units are controllably connectable to the system for producing electrical power.

In a third aspect of the present invention, a method is disclosed for providing an electrical screed assembly for a paving machine. The screed assembly includes a screed plate and the paving machine includes an electrical power source. The method comprises the steps of positioning at least one electrical heater assembly and an electrically actuated vibratory unit in proximity to the screed plate. The heater assembly is controllably connectable to the electric power source during a preheat time period while the electrical vibratory unit is disconnected from the power source, and both the heater assembly and the vibratory unit is connected to the power source during at least a portion of an operational time period.

Brief Description of the Drawings

Fig. 1 one is a diagrammatic side view of a paving machine including a screed assembly;

Fig. 2 is a partial plan view of the screed assembly of Fig. 1 as viewed from the front of the screed assembly;

Fig. 3 is a partial plan view of the screed assembly of Fig. 1 as viewed from the rear of the screed assembly; and

Fig. 4 is an embodiment of an electrically actuated vibratory unit suitable for use with the screed assembly of Fig. 1.

Detailed Description

Referring generally to the figures, a paving machine 10 is shown having an attached screed assembly 14. The screed assembly 14 may be connected to the paving machine 10 via draw bars 18 or in other conventional manners known in the art. The screed assembly 14 may be a single fixed-width assembly, or may be separated into left and right side units. Such split screed assemblies are advantageously used to form road surfaces having special characteristics such as a crowned center. In addition, each screed assembly portion may include one or more auxiliary or extension portions permitting adjustment of the paving width as desired.

The screed assembly 14 has at least one screed plate 22. In the depicted preferred embodiment, the screed assembly 14 includes first and second main screed

portions

46, 50, and first and second auxiliary screed

portions

54, 58. Each screed portion includes a respective screed plate 22.

An electrically actuated vibratory unit 26 is associated with and positioned relative to each screed plate 22 at a location sufficient to controllably vibrate the screed plate 22. The vibratory unit 26 is a self-contained vibratory system having an electric motor 30 driving a rotating mass 34. In a preferred embodiment, both of the motor 30 and mass 34 are contained within a single enclosure 42. The vibratory units 26 may be mounted to the screed plates 22 with mounting flanges 38. To reduce the bearing load on the motor 30, the mass 34 may be divided on opposite ends of the motor shaft and may be rotationally adjustable on the shaft. Self contained vibratory units of such a construction are commercially available, for example from Italvibras SpA, Sassuolo, Italy.

In a preferred embodiment, the screed assembly 14 includes first and second main screed

portions

46, 50, each having a respective screed plate 22 and electrically actuated vibratory unit 26 associated with and positioned relative to the respective screed plate 22 at a location sufficient to controllably vibrate the screed plate 22. The screed assembly 14 may also include first and second auxiliary screed

portions

54, 58, extendable from respective ones of the first and second main screed

portions

46, 50. Each of the auxiliary screed

portions

54, 58 also has a respective screed plate 22 and electrically actuated vibratory unit 26 associated with and positioned relative to the respective screed plate 22 at a location sufficient to controllably vibrate the respective screed plate 22.

The screed assembly 14 may also include a respective tamper bar 62 associated with each included screed

portion

46, 50, 54, 58. Each tamper bar 62 has an electrically actuated eccentric drive unit 28 operatively associated with and positioned relative to the respective tamper bar 62 at a location sufficient to controllably reciprocate the tamper bar 62. The eccentric drive units 28 are preferably discrete electric motor drive eccentric shaft devices, and may be connected to the tamper bars 62 with connecting links 40. Consequently, each included screed plate 22 and tamper bar 62 in a given screed assembly 14 may have an associated respective vibratory or

eccentric drive unit

26, 28 mounted thereon.

In a preferred embodiment, the screed plates 22 and tamper bars 62 may also include respective electrically powered heater assemblies 66 positioned at locations sufficient to controllably heat at least a portion of the associated screed plate 22 or tamper bar 62. The paving machine 10 and screed assembly 14 includes an electrical power source 70. Each of the electrically actuated vibratory and

eccentric drive units

26, 28 and the electrically powered heater assemblies 66 are connectable to and controllably and commonly powered by the electrical power source 70. At least one of the frequency and amplitude of vibration produced by the electrically actuated vibratory units 22 and the frequency of tamper bar motion produced by the electrically actuated eccentric drive units 28 may be controllably variable in response to the power supplied by the electrical power source 70. The electrical power source 70 includes an electrical generator 74 configured with appropriate control and power conditioning circuitry sufficient to produce the magnitude and type of electrical power required by the selected electrical heater assemblies 66 and electrically actuated vibratory and

eccentric drive units

26, 28. The generator 74 is typically driven by a combustion engine 82 associated with the paving machine 10.

In a preferred embodiment, the electrical power source 70 controllably delivers power to the heater assemblies 66 during both a preheat time period and an operational time period, and controllably delivers power to the electrically actuated vibratory and

eccentric drive units

26, 28 only during the operational period and not during the preheat period.

Industrial Applicability

A screed assembly 14 for a paving machine 10 may be relatively simple having only a single portion containing a single screed plate 22, or may be more complex. In a preferred embodiment, the screed assembly 14 may have both first and second

main screed portions

46, 50 and first and second

auxiliary screed portions

54, 58. In any case, each screed portion will include a respective screed plate 22 and may or may not include a respective tamper bar 62. It is desirable to heat the screed plates 22 and, under some conditions, the tamper bars 62 to prevent paving material from clinging to them, and it is desirable to vibrate the screed plates 22 and, if present, to reciprocate the tamper bars 62, to compact the paving material to produce a firm road surface.

In the embodiment described, each screed plate 22 includes a discrete associated electrically actuated vibratory unit 26 that is positioned relative to the respective screed plate 22 at a location sufficient to controllably vibrate the associated screed plate 22. Each vibratory unit 26 is self-contained and can be positioned for optimal vibration of the respective screed plate 22. In like manner, if tamper bars 62 are present in a particular embodiment, each tamper bar 62 may have an electrically actuated eccentric drive unit 28 associated with and positioned relative to the tamper bar 62 at a location sufficient to controllably reciprocate the respective tamper bar 62. The drive units 28 associated with the tamper bars 62 are of a similar self-contained construction to those associated with the screed plates 22, although they might differ in certain design characteristics such as size and shape.

The use of discrete, self-contained

units

26, 28 associated with respective screed plates 22 and tamper bars 62 permits precise and controllable positioning of the

units

26, 28 in a manner sufficient to obtain the most satisfactory motion characteristics. The use of electrical heater assemblies 66 associated with respective screed plates 22 and tamper bars 62 also allows the best control of the application of heat. The combination of electrically actuated vibratory and drive

units

26, 28 and electrical heater assemblies 66 eliminates or reduces the need for fluid and fuel connections between the screed assembly 14 and the paving machine 10.

Where electrical heater assemblies 66 are used, the overall required electrical generating capacity of the electric power source 70 can be minimized by controlling the times during which power is supplied to the electrical heater assemblies 66 and the electrically actuated vibratory and

eccentric drive units

26, 28. This opportunity is available because the screed plates 22 and tamper bars 62 are generally preheated before using the screed assembly 14 with hot paving material. After such preheating and once the screed assembly 14 is being operated with hot material, very little, if any, additional heat need be applied to the screed plates 22 and tamper bars 62. Therefore, most of the electrical power required by the electrical heater assemblies 66 is during a preheat stage of operation.

To the contrary, there is normally no need to operate the electrically actuated vibratory and

eccentric drive units

26, 28 except when paving material is actually being laid down. Therefore, during the preheat operational time period there is no need to apply electrical power to the

units

26, 28. However, during the operational time period while paving material is being applied, the

units

26, 28 typically require continuous electrical power. Consequently, in a preferred embodiment, the electrical heater assemblies 66 are connected to the electric power source 70 during a preheat time period, and the electrical vibratory and drive

units

26, 28 are not supplied with power during this time. During an operational time period, the heater assemblies 66 are either disconnected or are connected only for brief periods of time, while the

units

26, 28 are in operation. Therefore, by avoiding or minimizing the need to apply full electrical power to both the electrical heater assemblies 66 and the vibratory and drive

units

26, 28 simultaneously, the overall required power capacity of the electrical power source 70 is advantageously minimized.

Although there are obvious benefits obtained from the provision of a screed assembly 14 having all electrical components and no need for gas-fired fuel heaters, the use of individual, discrete electrically actuated vibratory and

eccentric drive units

26, 28 in place of traditional linear shaft type devices remains valuable even where traditional gas or other fuel powered heater units are employed. The use of electrically actuated

units

26, 28 that may be individually positioned on respective screed plates 22 and tamper bars 62 provides flexible and accurate application of motion to these elements regardless of the type of heater assemblies employed.

Although the invention has been described with reference to a preferred embodiment, it is clear in light of the overall disclosure that one skilled in the relevant arts may readily recognize or conceive modifications, variations, and alternative constructions not specifically addressed in detail above. For example, the particular selection of the number and orientation of screed assembly segments, and the positioning of electrical power or combustible fuel sources, might be readily modified in accordance with a particular paving machine. These and other adaptations are intended to be covered by the appended claims.

Other aspects, objects, and advantages of this invention may also be obtained from a study of the drawings, the disclosure, and the appended claims.

Claims

A screed assembly (14) for a paving machine (10), said screed assembly (14) having at least one screed plate (22), comprising:

an individual electrically actuated vibratory unit (26) associated with and positioned relative to each of said screed plates (22) at a location sufficient to controllably vibrate said screed plates (22), and wherein said vibratory unit (26) has an electric motor (30) driving a rotating mass (34).
A screed assembly (14), as set forth in claim 1, including first and second main screed portions (46, 50), each of said main screed portions (46, 50) having a respective main screed plate (22) and associated electrically actuated vibratory unit (26) positioned relative to said respective main screed plate (22) at a location sufficient to controllably vibrate said respective screed plate (22).
A screed assembly (14), as set forth in claim 2, including first and second auxiliary screed portions (54, 58) extendable from respective ones of said first and second main screed portions (46, 50), each of said auxiliary screed portions (54,58) having a respective auxiliary screed plate (22) and associated electrically actuated vibratory unit (26) positioned relative to said respective auxiliary screed plate (22) at a location sufficient to controllably vibrate said respective screed plate (22).
A screed assembly (14), as set forth in claim 2 or 3, including a respective tamper bar (62) associated with each of said screed portions (46, 50, 54, 58), each of said tamper bars (62) having an associated electrically actuated eccentric drive unit (28) positioned relative to said respective tamper bar (62) at a location sufficient to controllably reciprocate said respective tamper bar (62).
A screed assembly (14), as set forth in any of claims 2-4, wherein each of said screed plates (22) and/or tamper bars (62) includes a respective electrically powered heater assembly (66) positioned at a location sufficient to controllably heat at least a portion of said respective associated screed plate (22) and tamper bar (62).
A screed assembly (14), as set forth in claim 5, wherein said paving machine (10) includes an electrical power source (70), and wherein each of said electrically actuated vibratory and/or eccentric drive units (26, 28) and said electrically powered heater assemblies (66) are connected to and controllably and commonly powered by said electrical power source (70).
A screed assembly (14), as set forth in claim 6, wherein at least one of the frequency and amplitude of motion produced by said electrically actuated vibratory and/or eccentric drive units (26, 28) is controllably variable in response to the power supplied by said electrical power source (70).
A screed assembly (14), as set forth in claim 6, wherein said electrical power source (70) controllably delivers power to said heater assemblies (66) during both a preheat time period and an operational time period, and controllably delivers power to said electrically actuated vibratory and/or eccentric drive units (26, 28) only during said operational time period and not during said preheat time period.
A paving machine (10) having a combustion engine (82) coupled to a system for producing electrical power (70), and including a screed assembly (14) having at least one screed plate (22), comprising:

at least one electrical heater assembly (66) associated with and positioned at a location sufficient to controllably heat at least a portion of said at least one screed plate (22), and at least one electrically actuated vibratory unit (26) associated with and positioned relative to said at least one screed plate (22) at a location sufficient to controllably vibrate said at least one screed plate (22), and wherein said electrically actuated vibratory unit (26) is self contained having an electric motor (30) driving a rotating mass (34), said heater assemblies (66) and vibratory units (26) being controllably connectable to said system for producing electrical power (70).
A paving machine (10), as set forth in claim 14, wherein said screed assembly (14) includes at least one tamper bar (62), said tamper bar (62) having at least one electrically actuated eccentric drive unit (26, 28) associated with and positioned relative to said at least one tamper bar (66) at a location sufficient to controllably reciprocate said at least one tamper bar (66).
A paving machine (10), as set forth in claim 9 or 10, wherein said system for producing electrical power (70) controllably delivers power to said at least one electrical heater assembly (66) during both a preheat time period and an operational time period, and controllably delivers power to said at least one electrically actuated vibratory and/or eccentric drive unit (26, 28) only during said operational time period and not during said preheat time period.
A method for providing a screed assembly (14) for a paving machine (10), said screed assembly (14) including a screed plate (22) and said paving machine (10) including an electrical power source (70), comprising the steps of:

positioning at least one electrical heater assembly (66) in operative proximity to said screed plate (22);

positioning at least one electrical vibratory unit (26) in operative proximity to said screed plate (22);

controllably connecting said at least one electrical heater assembly (66) to and disconnecting said at least one electrical vibratory unit (26) from said electrical power source (70) during a preheat time period; and

controllably connecting said at least one electrical heater assembly (66) and said at least one electrical vibratory unit (26) to said electrical power source (70) during at least a portion of an operational time period.
A method, as set forth in claim 12, wherein said screed assembly (14) includes a tamper bar (62), including the steps of:

positioning at least one electrical heater assembly (66) in operative proximity to said tamper bar (62);

positioning at least one electrical eccentric drive unit (28) in operative proximity to said tamper bar (62);

controllably connecting said electrical heater assemblies (66) to and disconnecting each of said electrical eccentric drive units (28) from said electrical power source (70) during a preheat time period; and

controllably connecting said electrical heater assemblies (26) and said electrical eccentric drive units (28) to said electrical power source (70) during at least a portion of an operational time period.