CA2121536A1

CA2121536A1 - Control system for operating a comminuting machine

Info

Publication number: CA2121536A1
Application number: CA 2121536
Authority: CA
Inventors: Werner Doppstadt
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-04-20
Filing date: 1994-04-18
Publication date: 1994-10-21
Also published as: DE9305834U1

Abstract

INVENTION: Control System For Operating A Comminuting Machine INVENTOR: Werner Doppstadt ABSTRACT OF THE DISCLOSURE

The comminuting machine contains two disintegration shafts which comminute infed material. The two disintegration shafts are connected to respective pressure fluid operated drive motors which, in turn, are connected to respective pressure fluid main pumps like axial piston pumps drivingly coupled to a prime mover. A control valve acts upon an adjusting actuator for controlling the amount and the feed direction of pressure fluid delivered by the pressure flud main pumps and permit independent control of the pressure fluid operated drive motors. Pressure sensing means are responsive to excess pressure in feed lines leading to the drive motors and cause transient reversals of the pressure fluid main pumps and drive motors for removing blockage of the disintegration shafts. After a preset number of reversals an alarm is triggered.

Description

^~ Z~21~3B

.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to my copending United States Patent Application Serial No. .. ......, filed .. ......, entitled "Mobile Machine Containing Displaceably Mounted Power Unit Or Power Unit Components", United States Patent Application Serial No. ....... , filed ....... , entitled "Mobile Material Processing Machine With Tandem Axle", United States Patent Application Serial No. ......... , filed ........ , entitled "Dual Disintegration Shaft Comminuting Machine", and United States Patent Application Serial No. .......... , filed ........ , and entitled "Conveying System For Mobile Processing Machine".

BACKGROUND OF THE INVENTION

The present invention relates to a new and improved construction of a control system for operating a comminuting machine. The present invention also relates to a comminuting machine including such control system.

In its more particular aspects, the present invention relates to a new and improved construction of a control system for operating a comminuting machine and a comminuting machine containing such control system and which comminuting machine generally includes comminuting means comprising two cooperating disintegration shafts equipped with disintegrating members acting upon material infed into the infeed hopper.

It is known in the art to drive the two cooperating disintegrating shafts using a common drive motor and mechanically coupling the two disintegration shafts. As a result, the disintegration shafts always rotate in opposite rotational directions and at the same rotational speed. In such arrangement it is virtually impossible to vary the rotational speed and the rotational speed of the two disintegration shafts independent of each other.

,.. , - :
.: .. . :

, `~` 212~i3~

A further great disadvantage of the known comminuting machine is caused by the fact that infed pieces of hard or high-strength material which cannot be comminuted under the action of the two disintegration shafts, tend to damage the disintegration shafts or the disintegrating members with which these shafts are equipped. Furthermore, the rotating movement of the disintegration shafts may be blocked by infed material pieces which assume a position in which their disintegration can not be effected and further rotation of the disintegration shafts is inhibited by these material pieces. In such events, time and effort must be invested to repair the damage or remove the blocking pieces of material, as the case may be, which causes a highly undesirable interruption in the operation of the machine.

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is a primary object of the present invention to provide a new and improved construction of a control system for operating a comminuting machine and a comminuting machine which includes such control system and which is not afflicted with the drawbacks and limitations of the prior art constructions heretofore 2S discussed.

Another and more specific object of the invention is directed to providing a new and improved construction of a control system for operating a comminuting machine and a comminuting machine which includes such control system and which permits readily adapting the operation of the comminuting machine to diferent comminution requrements.

Another quite important object of the present invention is directed to a new and improved construction of a control system for operating a comminuting machine and a comminuting machine which includes such control system and enables the ,;~; ' ~ - .
. " ' .. . .. .
.",, ~ , , 2~2~ ~3~

.

comminuting machine to be operated at variable rotational speed of the disintegration shafts.

It is a further important object of the present invention to provide a new and improved construction of a control system for operating a comminuting machine and a comminuting machine which includes such control system and which renders possible driving the two disintegration shafts independent of each other and at different rotational speeds and even at opposite rotational directions.

A further, highly significant object of the present resides in providing a new and improved construction of a control system for operating a comminuting machine and a comminuting machine which includes such control system and which very effective prevents damage to the disintegration shafts of the comminuting machine during operation thereof.

It is another quite important object of the invention to provide a new and improved construction of a control system for operating a comminuting machine and a comminuting machine which includes such control system and which permits ready removal of blockage of the disintegration shafts during operation of the comminuting machine.
Now, in order to implement these and still further objects of the invention, which will become more apparent as the description proceeds, the control system for operating a comminuting machine and a comminuting machine which includes such control system, of the present development is manifested by the features that, among other things, the disintegration shafts are drivlngly connected to respective pressure fluid operated drive motors which, in turn, are powered by at least one pressure fluid main pump. Preferably, the at least one pressure fluid main pump can be adjusted with respect to the amount and the direction of pressure fluid delivered to the pressure fluid operated drive motors.

2121.~

Advantageously, two pressure fluid main pumps are provided and each one of the pressure fluid operated drive motors is powered by a respective one ot the two pressure fluid main pumps.

In an advantageous further development of the inventive control system for operating a comminuting machine and a comminuting machine which includes such control system, pressure sensing means are provided and subjected to the operating fluid pressure which is effective at the pressure fluid operated drive motors. The pressure sensing means are designed such as to permit transient reversal of the pressure fluid operated drive motor at the occurrence of an overload, i.e. a working pressure which exceeds a predetermined threshold value. Due to such transient reversal in the rotational direction, any piece of material which offers resistance against further rotation of the disintegration shafts in the original rotational direction, will be temporarily released from the disintegration shafts. Upon return to the original rotational direction, the piece of material will assume a different position with respect to the disintegration shafts and thus become accessible for comminution by the disintegrating members present at the disintegration shafts.
The aforementioned pressure sensing means may include a single pressure sensor which is connected to the working pressure side of both pressure fluid operated drive motors via a pressure sensitive switch valve by means of which the highest existing working pressure is applied to the pressure sensor.

In a still further development of the inventive control system for operating a comminuting machine and a comminuting machine which includes such control system, the aforementioned reversals may be repeated a number of times. Corresponding switching signals issue from the pressure sensing means and -~ 21~ ~3~

may be applied to counting and time control means which produce an alarm signal whenever a predetermined number of reversals, i.e. switching signals has occurred within a predetermined time period. If the blockage continues in spite of repeated reversals and returns of the disintegration shafts to the original rotational direction, such occurrence provides an indication that the piece of material present at the comminuting means can not be comminuted. The alarm signal thus produced may also result in shut-off of the drive means driving the comminuting means.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes references to the annexed drawings wherein the same or analogous components are designated by the same reference characters and wherein:

Figure 1 is a side view of an exemplary embodiment of the inventive comminuting machine;

Z5 Figure 2 i9 a partially sectional rear view of the comminuting machine as shown in Figure 1;

Figure 3 is a side view illustrating the cooperation between disintegrating discs mounted at cooperating disintegration shafts of the comminuting machine as shown in Figure 1;

Figure 4 is a detailed rear view of a first conveyor in the comminuting machine as shown in Figure 2;
Figure 5 is a view into an open side of a pressing body used in the comminuting machine as shown in Figure 1;

212~33~

Figure 6 is a front view of the pressing body as shown in Figure 5;

Figure 7 is a view of a link connection provided between conveyor sections of a second conveyor in the comminuting machine as shown in Figure 1;

Figure 8 is a schematic top plan view of the comminuting machine as shown in Figure 1; and ~' Figure 9 is a schematic block circuit diagram showing a control system controlling the operation of the comminuting ~
machine as shown in Figure 1. ~-DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Describing now the drawings, it is to be understood that only enough of the construction of the control system for operating a comminuting machine and a comminuting machine which includes such control system, has been shown as needed for those skilled in the art the readily understand the underlying principles and concepts of the present development while simplifying the showing of the drawing. While the illustrated exemplary embodiment is concerned with a mobile comminuting machine including a wheel-supported chassis, it will be understood that the inventive construction is not limited to mobile comminuting machines but can also be realized in stationary comminuting machines.
Turning attention now to Figure 1, there ha~ been shown a side view of an exemplary embodiment of the inventive comminuting machine which is mounted at a wheel-supported chassis 10. The chassis 10 defines a front end 11 which is provided with coupling means 13 of conventional construction for connection to a towing vehicle like a tractor or truck, and a rear end 14 of the comminuting machine. During operation _~ 2~21~3~

of the comminuting machine, the front end 11 of the chassis 10 is supported on ground by means of a standard 8 which is removed for travel of the comminuting machine between different working locations. For wheel support, a rear half of the chassis 10 is connected to a tandem axle carriage 12, preferably in a lengthwisely adjustable manner of the type as described in the second initially cross-referenced United States patent application the disclosure of which is herein incorporated by reference.

The front end 11 of the chassis 10 carries a power unit 1 for driving the comminuting machine above the tandem axle carriage 12. The power unit 1 is of conventional construction and will be described further hereinbelow with reference to Figure 8.

The actual comminuting means 15 is secured to a support frame 16 which is mounted at the chassis 10. As will be evident from Figure 2, which is a partially sectional view of the comminuting machine from its rear end 14, the comminuting means 15 encompasses two disintegration shafts 17 and 19 which cooperate by defining respective overlapping cylindrical areas 18 and 20 of action. The disintegration shafts 17,19 are driven by respective pressure fluid operated drive motors 21 and 22 which are drivingly connected to the aforementioned power unit 1. In the illustrated exemplary embodiment, the pressure fluid operated drive motors 21 and 22 are coupled to opposite ends of the respective disintegration shafts 17,19, however, in a preferred embodiment, the pressure fluid operated drive motors 21 and 22 are arranged in juxtaposition and coupled to respective front ends of the disintegration shafts 17,19.

The comminuting means 15 specifically comprise a plural number of disintegrating discs 23 exchangeably mounted at each one of the disintegration shafts 17 and 19. The disintegrating discs 23 are substantially identically constructed and, -- 2~ 2~ ~3~

therefore, it will be sufficient to describe only one of the disintegrating discs 23 shown in Figure 3. The disintegrating disc 23 has as its base a wear resistant, high strength metal disc which defines an aperture 24 of a contour corresponding to that of the disintegration shaft for receiving the respective disintegration shaft 17 or 19, as the case may be, and a circumference 25. Protruding from the circumference 25 is a circumferential sequence of a multitude of disintegrating members, namely at least one lacerating member 27 and a plural number of protruding rounded bulges 26 in a sequence which extends along a predetermined part of the circumference 25, preferably in the range of one half to three quarters, i.e. in the range of 180 to 270 degrees of the circumference 25. In the illustrated exemplary embodiment, a single lacerating member 27 is disposed between the ends of the bulge sequence, preferably, as illustrated, close to one end of the sequence of bulges 26. The lacerating member 27 has a base 28 which is securely affixed such as by welding to the circumference 25, and has a generally arcuate shape which protrudes from the circumference 25 and ends in a sharp lacerating edge 29 from which the lacerating member 27 recedes toward the circumference 25 and defines a recess 30.

Each disintegrating shaft 17,19 is provided with a plural number of such disintegrating discs 23 which are exchangeably mounted thereat at a predetermined spacing by means of spacer rings (not shown) between adjacent pairs of disintegrating discs 23. The spacer rings are of substantially circular shape and have a smaller diameter than the disintegrating discs 23 such that the spacer rings do not interfere with the cooperation between the disintegrating discs 23 of the ad~acent disintegration ~hafts 17,19. The thickness of the ~pacer rings which determines the number of disintegrating discs 23 mounted at the disintegration shafts 17,19, is dependent upon the type of material to be comminuted. For example, for comminuting wood material the spacer rings may have a thickness which is greater than that used in the case ~ ' '.. : ~ . ! ,, -- ^` 212~

of plastic material. In the latter case, the disintegrating discs 23 are mounted with less space therebetween and the laterally overlapping lacerating members 27 and rounded bulges 26 of the adjacent disintegrating shafts 17,19 perform more of a cutting action.

The plural number of disintegrating discs 23 is mounted at the respective disintegration shafts 17,19 in a manner such that the lacerating members 27 are circumferentially offset from each other by by a predetermined angle, preferably by 30 degrees. As indicated in Figure 3, the disintegrating discs 23 are mounted at the adjacent disintegration shafts 17 and 19 in a manner such that the disintegrating discs 23 on one of the two shafts have a staggered relationship to the disintegrating discs 23 mounted at the respective other one of the two disintegrating shafts. In other words, the disintegrating discs 23 mounted at one of the two shafts are aligned to the spacer rings at the other one of the two shafts. This ensures that the lacerating members 27 and the rounded bulges 26 do not interfere with each other during rotation of the disintegration shafts 17 and 19 but are arranged at a partial lateral overlap of the type which is indicated in Figure 3 and which ~esults in a further comminuting action.

The disintegrating discs 23 and the spacer rings are exchangeably mounted at the disintegration shafts 17 and 19 in conventional manner by placing the same in alternating manner from one end onto the disintegration shafts which are supported in position at the comminuting machine. After placement of the disintegrating discs 23 and spacer rings, a conventional shaft nut i9 threaded onto the free ends of the disintegration shafts 17 and 19 whereby the disintegrating discs and spacer rings are tlghtened together. The exact alignment on the disintegration shafts 17,19 is favorably affected by a polygonal, preferably hexagonal cross-section of these shafts and the aperture 24 of the disintegrating discs 23.

. .,.,.:, 2~2~ ~.33~

During operation of the comminuting machine, the lacerating members 27 act upon coarse infed material or larger pieces thereof to comminute the infed material by breaking off pieces therefrom and thereby whittling the same down to smaller size. The rounded bulges 26 actually fulfill two main functions: (i) firstly, by acting upon the infed material during rotation of the disintegration shafts 17,19, such material is forced toward the nip which is defined by the two disintegrating shafts 17,19. Thus, the infed material is very effectively prevented from bouncing off the surface formed by the substantially cylindrical areas 18 and 20 of action defined by the disintegrating discs 23. (ii) Secondly, and due to the partial latera~ overlap between axially adjacent ones of the rounded bulges 26, the infed material and particularly ths smaller pieces thereof and/or the smaller pieces present as a result of the lacerating action of the lacerating members 27, are forced into the aforementioned nip and become crushed or cut between the cooperating axially adjacent rounded bulges 26. This results in a highly effective further comminuting process and, at the same time, assists in forcing the infed material through the comminuting means 15.

Further supported at the support frame 16 is an infeed hopper 31 which has a front wall 32, a rear wall 33 and two opposite side walls 34 and 35. All of the aforenoted walls extend at a non-vertical inclination toward the comminuting means 15.

A first conveyor 36 is disposed below the comminuting means 14 and extends in the lengthwise direction of the chassis 10. The first conveyor 36 is constructed substantially in the manner of a conventional band or belt conveyor of which the conveying band or belt 37 and a deflection roll 38 are schematically indicated in Figure 2. Both ends of the deflection roll 38 are journalled in bearings 39. A drive roll (not shown) is placed at the other end of the first conveyor and drivingly connected to, for example, a pressure fluid ..,.. ,,, .j . , ,. : , ' ' . . ,, :. , ;~, ,, , , , ~ . , .
,,,, ,,, , , ., .,, ,, i " .. , .. ;~

2 1 2 ~

operated drive motor which may be constructed as a conventional flange motor and which is not shown in the drawing for reasons of clarity. The drive motor is drivingly connected to the aforementioned power unit 1. The first conveyor 36 receives comminuted material which has passed through the comminuting means 15, and conveys the throughpassed material to a second or rear conveyor 59 to be described further hereinbelow.

Instead of the the construction as a band or belt conveyor, the first conveyor 36 may also be constructed in the manner of a conventional scraper conveyor. Such scraper conveyor receives the comminuted material and comprises a plate extending the conveying length. A chain drive contains two chains extending along opposite lateral sides of the plate and carrying transverse ledges which extend across the plate and scrape the comminuted material along the plate during operation of the chain drive.

The first conveyor 36 is mounted at the chassis 10 by means of frame members 40 which extend alongside the first conveyor 36 and which have an inverted U-shape. The frame members 40 are secured to the support frame 16 on an underside thereof. The frame members 40 accommodate suspension spring assemblies one of which is schematically indicated by the block 41 and which bear at respective tandem axles of the tandem axial carriage 12 by means of respective support blocks 42. The rear axle of the tandem axle carriage 12 is shown in broken lines in Figure 2 of the drawing.
As schematically illu8trated in Figure 4, the first conveyor 36 is part of an assembly including carrier3 43 which extend along both opposite lateral sides of the first conveyor 36. Each one of the carriers 43 is provided with a bent-off carrier member 44 which is slidably held between retainer members 45 and 46 which protrude toward the carrier member 44.
The lower retainer member 45 is formed by a guide rail affixed ,; ' ' "
~ :

-- '' 2~21v9~

to an inner leg 47 of the U-shaped frame member 40. The upper retainer member 46 is in the form of a guide member mounted at the support frame 16. The retainer member 46 also has a guide surface 48 cooperating with a guide surface 49 at the carrier 43 in order to guide the comminuted material passing through the comminuting means 15 toward the first conveyor 36. The rear ends of the bent-off carrier members 44 are affixed to the support frame 16 by conventional securing means such as respective bolts and linchpins (not shown). After releasing the linchpins and withdrawing the bolts, the first conveyor 36 can be removed from the support frame 16 by rearwardly sliding the same between the retainer members 45 and 46. Thereby, the underside of the comminuting machine as well as the first conveyor 36 become readily accessible for inspection and, if need be, maintenance and repair. Also, the arrangement of the first conveyor 36 below the support frame 16 is a space and height saving arrangement.

In the illustrated exemplary embodiment, the comminuting machine further includes at least one pressing body which, if required, can be pivoted to act upon infed material to be comminuted and urge the same into comminuting contact with the disintegration shafts 17,19.

The pressing body 50 is pivotably mounted by means of a pivot shaft 51 which, in turn, is pivotably mounted in slide bearing~ 52 provided at the upper part of the support frame 16, see Figure 1. Specifically, the rear slide bearing 52 has a divided construction in which an upper part of the slide bearing 52 can be removed, for example, by unscrewing a fastening ~rew. After removal of this upper bearing part, the entire pressing body 50 can be removed by sllding the same in the rearward direction for relea~e from the front slide bearing 52 and by laterally removing the same from the support frame 16. The associated side wall 35 of the infeed hopper 31 is provided with an aperture 53 for receiving the pressing body 50 in its inoperative or retracted position.

~, . ...................... .

- . ~

2~21~3~

The pressing body 50 is constructed from a plural number of reinforcing discs 54 which are firmly secured such as by welding to the pivot shaft 51, see Figure 5. In the illustrated exemplary embodiment, six such reinforcing discs 53 are provided and have a substantially circular sector shape. The reinforcing discs 54 are fixedly connected such as by welding to a shell plate 55 substantially along their entire circumference so that the pressing body 50 actually assumes the shape of a hollow, substantially cylindrical sector body. The entire side facing the comminuting means 15, is covered by a cover or pressing plate 56 which is affixed such as by welding to the respective edge of the shell plate 55, the edges of the reinforcing discs 54 and the pivot shaft 51. In this manner, there is formed the pressing body 50 which is closed on the side facing the material to be comminuted and which can be pressed thereupon.

The intermediate reinforcing discs 54 are pairwisely arranged and provided with mounting means 57 for connection to an actuator 58 as shown in Figure 2 and disposed between the reinforcing discs 54 of the respective pair. The actuator 58 of the illustrated exemplary embodiment is constructed as a conventional pressure fluid operated cylinder-piston unit which is powered by means of the power unit 1. The cylinder is linked to the support frame 16 whereas the piston is linked to the mounting means 57 of the reinforcing discs 54.
Consequently, the pressing body 50 assumes an inoperative or retracted position when the piston is retracted, and an operative or pressing position when the piston is extended.
Power is stepwisely applied such that, at relatively low power, the pivoting movement is carried out whereas, in the operative position, relatively high power can be applied in order to exert a pre~ing actlon on the infed materlal by means of the pressing body 50. As will be apparent from Figure 5, the pressing body 50 is connected to two actuators 58.

' . `', ' ' ' " '.:

'.

2121~

The pressing body 50 is constructed in adaptation to the aperture 53 in the associated side wall 35 of the infeed hopper 31. In particular, the pressing body 50 assumes an inoperative or retracted position such that the pressing plate 56 extends in the plane of the side wall 35 and the aperture 53 is substantially completely closed. It is thereby ensured that all of the material infed into the infeed hopper 31 will be directed to the comminuting means 15 and no parts or pieces of the material are allowed to exit from the infeed hopper 31 other than through the comminuting means 15.

In the illustrated preferred embodiment, two substantially identical pressing bodies 50, which are of basically the same construction as described hereinbefore, are placed in a mirror-image relationship in respective apertures 53 in the opposite side walls 34 and 35 of the infeed hopper 31. As explained hereinbefore, the pressing plates 56 are flush with the respective side walls 34 and 35 in the inoperative or retracted position of the pressing bodies 50.
In the operative position, the pressing plates 56 extend across the comminuting means 15 close toward each other, as illustrated in Figure 2 of the drawing by broken lines.

A second conveyor 59 constituting, for example, likewise a band or belt conveyor, is mounted at the rear end 14 of the comminuting machine, see Figure 1. The arrangement is such that the second conveyor 59 cooperates with the first conveyor 36 for receiving comminuted material therefrom and further conveying the ~ame. The second conveyor 59 includes a first conveyor section 60 and a second conveyor section 61 which are interconnected by a link or hinge connection 62 which is illustrated in detail in Figure 7 in an expanded condition.

The first conveyor section 60 is provided with bushes 63 at the four corners or along top and bottom rims of its end 64 which is remote from the rear end 14 of the comminuting machine. The bushes 63 protrude from this end 64. The second , :,. .

2~2~36 conveyor section 61 has an end 65 facing the end 64 of the first conveyor section 60. This end 65 is provided with a substantially circular disc 66 on one of its lateral sides and a disc 67 of substantially semicircular shape on the opposite lateral side. The discs 66 and 67 are provided with aligned throughbores 68. The ends 64,65 of the first and second conveyor sections 60,61 are linked to each other by placing the bushes 63 of the end 64 of the first conveyor section 60 in between the discs 66 and 67 of the end 65 of the second conveyor section 61, particularly in a manner such that the bushes 63 are aligned with the throughbores 68. Then, conventional locking means such as, for example, bolts and associated linchpins are employed to lock the first and second conveyor sections 60,61 to each other. To this end, the bolts are pas~ed through the bushes 63 and the aligned throughbores 68 and locked by the linchpins. In this condition, the mutually facing ends 64,65 of the first and second conveyor sections 60,61 are locked to each other in a manner such that the second conveyor ~ection 61 extends substantially in straight continuation of the first conveyor section 60. If the linchpin is removed from the bolt which extends through the upper bushes 63 and throughbores 68, and the bolt is also removed, then, the two conveyor sections 60,61 remain linked to each other merely by the bolt extending through the lower bushes 63 and throughbores 68.

Furthermore, the second conveyor section 61 contains a cable mount 69 from which a cable or rope 70 or the like extends and is fixed to the rear end 14 of the comminuting machine at a further cable mount 71. The cable or rope 70 is guided along a guide surface provided at the circumference of the circular disc 66. The cable or rope 70 exerts a pull on the end 65 of the second conveyor section 61 so a~ to ensure, in addition to the locked link connection 62, the aforementioned position of this conveyor section 61 in substantially straight continuation of the first conveyor section.

~ .

.

.
..:...
.. -, . :

- r~
2~2~33~

The receiving end 73 of the second conveyor 59 is mounted at the bottom of the rear end 14 of the comminuting machine.
To this end, a link 74 is linked to a link carrier 75 at the rear end 14. Actuator means 76 includes a pressure fluid operated cylinder-piston unit. The cylinder of the actuator means 76 is linked to a cylinder carrier 77 which is secured to the bottom of the chassis 10. The piston of the actuator means 76 is linked to the free end of the link 74. The purpose of this arrangement is as follows:
During operation of the comminuting machine, the second conveyor 59 assumes the operative or extended position which is illustrated in Figure 1. In this position, the two conveyor sections 60 and 61 follow each other and extend substantially in ~traight continuation at an upward inclination from the rear end 14 of the comminuting machine. It would be undesirable to leave the second conveyor 59 in this operative, extended position during travel of the comminuting machine from one working location to another. Therefore, the second conveyor 59 is constructed such that the conveyor sections 60 and 61 can be folded into an inoperative, folded position as indicated by broken lines in Figure 1.

In order to place the second conveyor 59 into the inoperative, folded condition, the upper bolt and linch pin of are removed from the link connection 62. The second conveyor section 61 is, then, subject to the action of gravity but held in position due to the tensioned cable 70. When, now, the actuator means 76 is actuated by extending the piston and thereby pivoting the link 74 upwardly toward the position as shown by broken lines, the tension of the cable 70 is reduced and the second conveyor section 61 is permitted to pivot in a downward direction. During further extension of the piston and the resulting further pivoting movement, part of the cable 70 is "wound up" on the cable guide surface provided at the circular disc 66 and the second conveyor section 61 is permitted to pivot further downward while the first conveyor ",; ~
. ~ , . .... ..
, 2121~3~

section 60 continues to be upwardly pivoted. At the end of the movement, the two conveyor sections 60 and 61 of the second conveyor 59 are located parallel to each other and the rear end 14, i.e. depend substantially vertically in an arrangement S in which the first conveyor section 60 extends upwardly and the second conveyor section 61 extends downwardly. The dimensions of the first and second conveyor sections 60,61 are selected such that their extended length satisfies the operating requirements while their folded condition satisfies existing traffic regulations.

For returning the second conveyor 59 into the operating condition, the aforenoted sequence of movements is reversed which is effected by retracting the piston of the actuator means 76.

According to the schematic top plan view of Figure 8, the power unit 1 comprises a prime mover 78 like a diesel engine or an electric motor, if the comminuting machine is exclusively used in places where electric power is available, and at least one pressure fluid main pump 79 like, for example, an axial piston pump for powering the various pres~ure fluid operated components of the comminuting machine.
The at least one pressure fluid main pump 79 is coupled to the prime mover 78 by conventional coupling means (not shown) capable of compensating for rotational and axial offsets. A
cooler 80 is pivotably connected to the prime mover 79 by means of a hinge connection 81. More specifically, the power unit 1 preferably may be constructed in the manner of the power unit as disclosed in the first initially mentioned cross-referenced United States Patent Application the disclo~ure of which is incorporated herein by reference.

Furthermore, preferably two pres~ure fluid main pumps 79 of the same type, namely axial piston pumps, are drivingly connected to respective pressure fluid operated drive motors 21 and 22 driving the front ends of the respective .; ;
, ..

21~ ~3~

disintegration shafts 17 and 19. Also powered thereby are the other pressure fluid operated drive motors which are present in the comminuting machine and which drive the first and second conveyors 36 and 59, and the actuator means 58 and 76 which are present in the comminuting machine and which respectively act upon pressing bodies 50 and the second conveyor 59. This arrangement has the advantage that the pressure fluid main~ pumps 79, the pressure fluid operated drive motors 21 and 22 and further pressure fluid pumps can be arranged conjointly in a readily accessible part of the comminuting machine.

It should be noted that in this arrangement the two disintegration shafts 17 and 19 are independently driven and thus may rotate at different rotational speeds and in different rotational directions. If only one pressure fluid main pump and an associated control valve are provided, both of the pressure fluid operated drive motors are driven at the same rotational speed but their rotational direction can still be reversed. Also, in the case of an overload, one or both of the two disintegration shafts 17,19 may even be reversed so as to thereby clear the nip defined by the two disintegration shafts 17,19 from infed material and subject the same to comminution upon return of the disintegration shafts 17 and 19 to the original rotational directions.

Figure 9 shows, in the form of a schematic block circuit diagram, a control sy~tem for controlling the operation of the aforedescribed comminuting machine and its connection with the various pressure fluid operated components which have been described hereinbefore.

In Figure 9, there will recognized the prime mover 78 at the bottom on the left. The prime mover 78, as explained hereinbefore, is in driving connection through conventional coupling means (not shown) with two pressure fluid main pumps, namely 79a and 79b, which may be constructed as axial piston ' ' :. ' ' ' ~' , . ' ', . ~
;, .

. .

" 2~2~33~

pumps. A common drive shaft 82 interconnects the pressure fluid main pumps 79a, 79b with the associated pressure fluid operated drive motors 21,22 and further pressure fluid pumps 210,216 and 222 for respectively powering pressure fluid operated drive motors of the first and second conveyors 212,218 and the actuators 58 and 76 which respectively act upon the pressing bodies 50 and the second conveyor 59. Leaked pressure fluid from the pressure fluid operated drive motors 21,22 is passed to a pressure fluid reservoir 174 through lines or conduits 184,182 and a pressure fluid cooler 172.

Starting with the control of the pressure fluid operated drive motors 21 and 22 which are drivingly to the respective front ends of the disintegration shafts 17 and 19, it will be noted that the pressure fluid main pumps 79a,79b are conventional axial piston pumps containing a swash plate which is conventionally adjustable for varying the pressure fluid flow and its direction.

The adjustment of the swash plates is effected by means of respective actuators 126,128 which are constructed in the manner of double-acting pressure fluid cylinders. In the following, there will only be described the actuator 126 and it will be understood that the actuator 128 is constructed and oper-ated essentially in the same manner. The cylinder is subdivided into two cylinder chambers by means of an adjusting piston. Control pressure can be selectively applied either to the left-hand or the right-hand cylinder chamber, as the case may be, while correspondingly either the right-hand or the left-hand cylinder chamber is connected to the pressure fluid reservoir 174. As a result, such actuator may exert pressure fluid forces in two opposlte directions.

The operation of the actuator 126 is governed by means of an electromagnetically operable control valve 130. The control valve 130 is conventionally constructed in the manner of a 4/3-way valve. Two connectors of the control valve 130 are , .

, 2 ~ 3 ~

connected to respective ones of the two cylinder chambers in the actuator 126, a further connector receives the control pressure and a still further connector leads to the reservoir 174.

The control valve is spring-loaded and normally held in a neutral, central position in which all four of the connectors are blocked. Two magnet coils are provided for adjusting the control valve in basically two different limiting valve positions. In a first limiting valve position, control pressure is applied to the right-hand cylinder chamber of the actuator 126 whereas the left-hand cylinder chamber of the actuator 126 is connected to the reservoir 174. In a second limiting valve position, control pressure is applied to the left-hand cylinder chamber in the actuator 126 whereas the right-hand cylinder chamber is connected to the reservoir 174.
A valve housing 132 of the control valve 126 is mechanically coupled through a conventional and, therefore, only schematically indicated mechanical connection 134 to the adjusting piston of the actuator 126.

As a result, and in the aforementioned first limiting valve position which the control valve 130 assumes upon energization by the respective magnet coil, control pressure is applied to the right-hand cylinder chamber whereas the right-hand cylinder chamber will be connected to the reservoir 174. Consequently, the adjusting piston of the actuator 126 will move to a left limiting position in Figure 9. The valve housing 132 will follow the movement of the adjusting piston, i.e. the valve housing 132 will also move to the left until the control valve again assumes the neutral, central position and the connection to the cylinder chambers i8 blocked. To acieve the second limiting valve position, opposite movements occur in essentially the same manner with the result that the adjusting piston is moved in the opposite direction into the opposite limiting position. The application of control pressure to the respective cylinder chambers and thus the 2~2~'3 ~

corresponding displacement of the respective adjusting pistons may be continuously variable or in a preselected number of steps in conventional manner.

Since the displacement of the adjusting piston in one or the other direction causes corresponding tilting of the swash plate in one or the other corresponding direction, pressure fluid will flow in one or the other direction depending upon the direction of displacement of the adjusting piston of the actuator 126. The amount or extent of displacement will also be governed by the electromagnetically controlled control valve 130. The pressure fluid operated drive motor 22 which is in driving connection with the disintegration shaft 19, is connected to the pressure fluid main pump 79a through the lines or conduits 136 and 138. Therefore, the drive motor 22 will rotate the disintegration shaft 19 in a rotational direction determined by the direction of displacement of the adjusting piston in the actuator 126 and at a rotational speed determined by the amount of displacement of the adjusting piston in the actuator 126.

Essentially corresponding movements occur upon electromagnetic adjustment of the control valve 129 and application of control pressure to the actuator 128. The valve housing 129 likewise is mechanically coupled to the adjusting piston of the actuator 128 by means of a mechanical connection 133. The pressure fluid operated drive motor 21 which is in driving connection with the disintegration shaft 17, is connected to the pressure fluid main pump 79b through the lines or conduits 140 and 142. Therefore, the drive motor 21 will rotate the disintegration shaft 17 in a rotational direction determined by the direction of displacement of the adjusting piston in the actuator 128 and at a rotational speed determined by the amount of displacement of the adjusting piston in the actuator 128.

2~21~3~

It should be noted that the control valves 129 and 130 as well as the actuators 126 and 128 are operated independently of each other. As a consequence, the pressure fluid operated drive motors 21 and 22 the respective disintegration shafts 17 and 19 are also operated independent of each other.

The control pressure effective at the actuator 126 and the associated control valve 130 is supplied by means of a control pressure pump 140 which likewise is driven by means of the common drive shaft 82. A pressure limiter 146 limits the control pressure to a predetermined value. A pressure accumulator 150 is provided to maintain the control pressure.
Correspondingly, a control pressure pump 147, a control pre~sure limiter 148 and a pressure accumulator 152 are provided in conjunction with the actuator 128 and the control valve 129.

A pressure limiter 154 is connected to both the lines or conduits 136 and 138 interconnecting the pressure fluid main pump 79a and the pressure fluid operated drive motor 22. The pressure limiter 154 thus limits the working pressure prevailing at the pressure fluid operated drive motor 22 independent of the feed direction of the pressure fluid main pump 79a and the rotational direction of the drive motor 22 resulting therefrom. In corresponding manner, a pressure limiter 158 is connected to both the lines or conduits 140 and 142 intercoonecting the pressure fluid main pump 79b and the pressure fluid operated drive motor 21. The pressure limiter 15~ thus limits the working pressure prevailing at the pres~ure fluid operated drive motor 21 independent of the feed direction of the pressure ~luid main pump 79b and the rotational direction of the drive motor 21 resulting therefrom.

Furthermore, a pressure responsive switch 164 is controlled by means of a pressure responsive switch valve 162 which interconnects the lines or conduits 136 and 140 which ,, ' ~,' ,.
,. ' ~ "

2~21~3~

respectively connect the pressure fluid main pump 79a with the pressure operated drive motor 22 and the pressure fluid main pump 79b with the pressure fluid operated drive motor 21. The pressure responsive switch valve 162 provides connection between the two lines or conduits 136 and 140 in the reversed operating condition in which the disintegration shaft 19 rotates in clockwise direction and the disintegration shaft 17 in counterclockwise direction because under such condition the working pressure exists in both lines or conduits 136 and 140.
The pressure responsive switch 164 reacts to the occurrence of a predetermined excess pressure by causing emergency shut-off of the comminuting machine.

A further pressure responsive switch valve 166 is connected between lines or conduits 136 and 138. The purpose of this pressure responsive switch valve 166 is to apply the working pressure, i.e. the higher pressure of the pressures prevailing in the lines or conduits 136 and 138 to a pressure limiter 168. The pressure limiter 168 passes any pressure fluid which is relieved as a result of a pressure limiting action, to the pressure fluid reservoir 174 through a line or conduit 170 and the pressure fluid cooler 172. In corresponding manner, a further pressure responsive switch valve 176 is connected between lines or conduits 140 and 142.
The purpose of this pressure responsive switch valve 176 is to apply the working pressure, i.e. the higher pressure of the pressures prevailing in the lines or conduits 140 and 142 to a pressure limiter 178. The pressure limiter 178 passes any pressure fluid which is relieved as a re~ult of a pressure limiting action, to the pressure fluid reservoir 174 through a line or conduit 180,182 and the pressure fluid cooler 172.

The two l~nes or conduits 138 and 142 are feed lines or conduits in which the working pressure prevails when the pressure fluid operated drive motor 22 rotates the disintegration shaft 19 in counterclockwise direction and the pressure fluid operated drive motor 21 rotates the ....
,. , : , ~.

2121-~3~

disintegration shaft 17 in clockwise direction. A pressure responsive switch valve 190 is connected to the lines or conduits 138 and 142 through respective lines or conduits 186 and 188. The pressure responsive switch valve 190 connects that one of the two lines or conduits 138,142 which has the higher pressure, with a pressure sensor 192. In the event that the rotation of the disintegration shafts 17,19 is blocked by a non-disintegrable piece of infed material, the working pressure experiences a strong rise which is detected by the pressure sensor 192. The pressure sensor 192 will respond if a pressure threshold value is exceeded which is distinctly above the standard operating pressure.

In the event of a response of the pressure sensor 192 to an excessive pressure build-up above the working pressure in the line or conduit 138, the control valve 130 is reversed for a predetermined period of time T. As a consequence, the displacement of the adjusting piston in the actuator 126 is reversed and thus also the feed direction of the pressure fluid main pump 79a. The working pressure now is applied to the line or conduit 136 and also the rotational direction of the pressure fluid operated drive motor 22 and the associated disintegration shaft 19 is reversed. The clamped, blocking piece of material is thereby released and, after the predetermined time period T has elapsed, the control valve 130 and the adjusting piston of the actuator 126 are returned into their original position. As a result, the pressure fluid main pump 79a assumes the original feed direction and the drive motor 22 and its disintegration shaft 19 are rotated in the original rotational direction so that the comminuting operation is restarted. The circuit producing this sequence of events, is illustrated in the block diagram shown in the top left-hand corner of Figure 4 where there are shown the pressure sensor 192, the reversing switch 198 which receives the output signal of the pressure sensor 192 via an input 194 and which produces at a first output 196 an output signal for effecting reversal of the control valve 130.

: , ,~ . ..................... . . .. .
. . : ,. .. , ; . :
. . , .:, .
.
,. . ...
,: ' , , , , : :
"

2~2~3 5~

If the excessive pressure build-up occurs in the line or conduit 142, the corresponding sequence of events is effected at the pressure fluid main pump 79b and the associated pressure fluid operated drive motor 21 and disintegration shaft 17. In the event that the control means 130 ccontrols both of the pressure fluid main pumps 79a,79b or a common pressure fluid main pump is provided for both the pressure fluid operated drive motors 21 and 22, both of the pressure fluid operated drive motors 21,22 and the associated disintegration shafts 17,19 will be temporarily reversed.

It may occur that even after repeated reversal the comminuting means 15 remain blocked, for example, because the clamped piece of material which produces the blockage, is not released by repeated reversal, because the piece of material can not be disintegrated at all even if repeatedly subjected to the comminuting action, or because the piece of material offers an unduely high resistance to the comminuting action.
Therefore, the aforedescribed operation would repeat itself endlessly without producing any result if no countermeasures are taken. For this reason, an alarm signal is triggered and brings the comminuting machine to standstill, after multiple repetitions of the transient reversal have occurred within a pre~etermined period of time. Instead or additionally, the alarm signal may be or may include an optical or acoustic alarm indication.

The circuit for producing this sequence of events, is shown by the block diagram at the top left-hand corner of Figure 9. Thus, a second output 202 of the reversing switch 198 produces a signal which i~ applied to a counter 200 which counts the number of switching or reversing operations and in which a predetermined number of counts is pre~et. At the occurrence of each reversing operation, a pulse appears at a 3s third output 204 of the reversing switch 198. This pulse will set a timer 206 which is connected to a reset input of the counter 200 and which may be, for example, a monostable .. . .

. . ~

~ .

212~ ~3~

multivibrator, which sets a predetermined counting period.
After this counting period has elapsed, the counter 200 will be reset to zero. If during this counting period the preset count nO is exceeded, the alarm signal will be produced at an output 208 of the counter 200.

Each reversing ~aoperation will produce a pulse at the third output 204. This pulse determines the start of the predetermined counting period and sets the timer 206. Further pulses will not affect the timer 206 as long as the timer 206 has not been rese~ to the original state or condition. If less than nO pulses appear during the predetermined counting period, the counter 200 will be reset to 0 and an alarm signal will not occur. The alarm signal will only be triggered if the number nO of pulses, which appear during the predetermined counting period which is preset by the timer 206, is exceeded.

Furthermore, a pressure fluid pump 210 is connected to the cGmmon drive shaft 82 and feeds pressure fluid to a pressure fluid operated drive motor 212. A pressure limiter 214 is provided for limiting the pressure which is effective at the drive motor 212. The pressure fluid operated drive motor 212 i8 in driving connection with the drive roll of the first conveyor 36 which is located below the comminuting means 15. A still further pressure fluid pump 214 is connected to the common drive shaft 82 and feeds pressure fluid to a pressure fluid operated drive motor 218. A pressure limiter 220 is provided for limiting the pres~ure which is effective at the drive motor 218. The pressure fluid operated drive motor 218 is in driving connection with the drive roll of the second conveyor S9 which is located at the rear end 14 of the comminuting machine.

Yet a further pressure fluid pump 222 is connected to the common drive shaft 82 and feeds pressure fluid to the actuator means 58 and 76 respectively operating upon the pressing bodies 50 and the first conveyor section 60 of the second . .
;, ..
.. ' '', '' ~
..
.. . .. , ~,.. ~; ~ . .

:::

2121~

conveyor 59 for producing the desired pivoting movements thereof. The pressure fluid is delivered to the respective pressure fluid operated cylinder-piston units of the actuator means 58 and 76. Such units include double acting cylinders as schematically indicated in Figure 9. The pressure fluid feed thereto is controlled by means of respective 4/3-way valves 224 and 230 via respective twin check valves 226,228 and 232,234. The 4/3-way valve 224 is mechanically switched in correspondence with the pivoting movements of the pressing 10bodies 50. The 4/3-way valve 230 is mechanically switched in correspondence with the pivoting movements of the first conveyor section of the second conveyor 59.

A number of modifications are envisaged in the aforedescribed control system. Thus, instead of providing separate control valves 129 and 130 for each one of the pressure fluid main pumps 79a and 79b, only one control valve such as the control valve 130 may be provided as a common control valve conjointly with additional lines or conduits leading from the common control valve to the cylinder chambers of the actuator 128. Also, in a simplified version, the control valves 129,130 or the common control valve may just apply control pressure to the cylinder chambers of the respective actuators and thus displace the adjusting pistons merely between the neutral, central position and the selected one of the two limiting positions. In such arrangement, the pressure fluid supply to the pressure fluid operated drive motors 21 and 22 can only be varied between zero and a maximum value in either rotational direction, i.e. the pressure fluid operated drive motors 21 and 22 and their associated disintegration shafts 19 and 17 can only be driven at the ~ame, namely the maxlmum rotational speed and in the selected one of the two rotational directions.

35In a further variant, the circuitry for operating the control valve and thereby the actuator for reversing the pressure fluid main pump and thereby the pressure fluid : . .. .
' '' ,' : : ' . . .. , :

.. , . ~ .
: .. . . . . .. . . .
, 2~21~

operated drive motor of the disintegration shafts may be displaced by correspondingly operating mechanical devices.
Such mechanically operated devices may include, for example, angle transmitters or cam members.

While there are shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims. Accordingly, ... . .

.

Claims

1. A control and operating system for a comminuting machine containing comminuting means composed of two cooperating disintegration shafts for comminuting infed material and drive means for driving the two disintegration shafts, said control and operating system comprising:

at least one pressure fluid main pump;

two pressure fluid operated drive motors drivingly connected to said at least one pressure fluid main pump and driving respective ones of two disintegration shafts.

2. The control and operating system as defined in claim 1, further including control means for adjusting said at least one pressure fluid main pump with respect to amount and direction of pressure fluid delivered thereby.

3. The control and operating system as defined in claim 1, wherein said at least one pressure fluid main pump encompasses two pressure fluid main pumps connected to respective ones of said two pressure fluid operated drive motors for powering the same.

4. The control and operating system as defined in claim 3, wherein:

said two pressure fluid main pumps being adjustable with respect to amount and direction of pressure fluid delivered by said two pressure fluid main pumps; and control means for controlling said two pressure fluid main pumps with respect to said amount and said direction of pressure fluid delivered by said two pressure fluid main pumps and thereby controlling said two pressure fluid operated drive motors and the associated disintegration shafts with respect to rotational speed and with respect to rotational direction.

5. The control and operating system as defined in claim 4, wherein said control means are common control means for controlling both said two fluid pressure main pumps.

6. The control and operating system as defined in claim 4, wherein said control means include two independent control means for independently controlling respective ones of said two pressure fluid main pumps.

7. The control and operating system as defined in claim 4, wherein said control means is continuously adjustable in order to provide continuous adjustment of said amount of pressure fluid delivered by said two pressure fluid main pumps to said two pressure fluid operated drive motors.

8. The control and operating system as defined in claim 4, wherein said control means is stepwisely adjustable in order to provide stepwise adjustment of said amount of pressure fluid delivered by said two pressure fluid main pumps to said two pressure fluid operated drive motors.

9. The control and operating system as defined in claim 3, further including:

two pressure fluid feed lines leading from said two pressure fluid main pumps to respective ones of said two pressure fluid operated drive motors for feeding pressure fluid at a predetermined working pressure to said two pressure fluid operated drive motors;

pressure sensing means connected across said feed lines and defining a threshold pressure above said working pressure;

said pressure sensing means being operatively connected to said control means; and said control means transiently reversing said feed direction of at least one of said two pressure fluid main pumps at the occurrence of a pressure in excess of said threshold pressure in said feed lines.

10. The control and operating system as defined in claim 9, wherein:

said pressure sensing means includes a single pressure sensor;

said pressure sensing means further including a pressure responsive switch valve interconnecting said two feed lines and connected to said pressure sensor; and said pressure responsive switch valve connecting to said pressure sensing means, the pressure prevailing in that one of said two feed lines which has the higher working pressure.

11. The control and operating system as defined in claim 9, further including:

a reversing switch connected to said pressure sensing means and receiving therefrom an input signal indicative of an excess pressure above said working pressure in one of said two feed lines;

said reversing switch having a first output connected to said control means for transiently reversing the rotational direction of at least one of said two pressure fluid main pumps during a predetermined time period;

a counter containing means for presetting a predetermined count;

said reversing switch having a second output connected to said counter for counting the number of reversing operations;

a timer;

said reversing switch having a third output connected to said timer for setting a predetermined counting period;

said timer having an output connected to said counter for resetting said counter after said predetermined counting period;

alarm means;

said counter having an output connected to said alarm means; and said counter triggering said alarm means when the number of said reversing operations counted by said counter within said predetermined counting period, exceeds said predetermined count preset in said counter.

12. A comminuting machine comprising:

comminuting means for comminuting infed material;

said comminuting means including two cooperating disintegration shafts extending substantially parallel to each other;

two pressure fluid operated drive motors drivingly connected to respective ones of said two disintegration shafts;

a power unit;

said power unit comprising a prime mover and at least one pressure fluid main pumps drivingly connected to said prime mover; and said at least one pressure fluid main pump being drivingly connected to said two pressure fluid operated drive motors.

13. The comminuting machine as defined in claim 12, further including control means for adjusting said at least one pressure fluid main pump with respect to amount and direction of pressure fluid delivered thereby.

14. The comminuting machine as defined in claim 12, wherein said at least one pressure fluid main pump encompasses two pressure fluid main pumps drivingly connected to respective ones of said two pressure fluid operated drive motors for powering the same.

15. The comminuting machine as defined in claim 14, wherein:

said two pressure fluid main pumps being adjustable with respect to amount and direction of pressure fluid delivered by said two pressure fluid main pumps; and control means for controlling said two pressure fluid main pumps with respect to said amount and said direction of pressure fluid delivered by said two pressure fluid main pumps and thereby controlling said two pressure fluid operated drive motors and the associated disintegration shafts with respect to rotational speed and with respect to rotational direction.

16. The comminuting machine as defined in claim 15, wherein said control means are common control means for controlling both said two fluid pressure main pumps.

17. The comminuting machine as defined in claim 15, wherein said control means include two independent control means for controlling respective ones of said two pressure fluid main pumps.

18. The comminuting machine as defined in claim 15, wherein said control means is continuously adjustable in order to provide continuous adjustment of said amount of pressure fluid delivered by said two pressure fluid main pumps to said two pressure fluid operated drive motors.

19. The comminuting machine as defined in claim 15, wherein said control means is stepwisely adjustable in order to provide stepwise adjustment of said amount of pressure fluid delivered by said two pressure fluid main pumps to said two pressure fluid operated drive motors.

20. The comminuting machine as defined in claim 14, further including:

two pressure fluid feed lines leading from said two pressure fluid main pumps to respective ones of said two pressure fluid operated drive motors for feeding pressure fluid at a predetermined working pressure to said two pressure fluid operated drive motors;

pressure sensing means connected across said feed lines;

said pressure sensing means being operatively connected to said control means; and said control means transiently reversing said feed direction of at least one of said two pressure fluid main pumps at the occurrence of a pressure in excess of said threshold value in said feed lines.

21. The comminuting machine as defined in claim 20, wherein:

said pressure sensing means includes a single pressure sensor;

said pressure sensing means further including a pressure responsive switch valve interconnecting said two feed lines and connected to said pressure sensor; and said pressure responsive switch valve connecting to said pressure sensing means, the pressure prevailing in that one of said two feed lines which has the higher working pressure.

22. The comminuting machine as defined in claim 20, further including:

a reversing switch connected to said pressure sensing means and receiving therefrom an input signal indicative of an excess pressure above said working working pressure in one of said two feed lines;

said reversing switch having a first output connected to said control means for transiently reversing the rotational direction of at least one of said two pressure fluid main pumps during a predetermined time period;

a counter containing means for presetting a predetermined count;

said reversing switch having a second output connected to said counter for counting the number of reversing operations;

a timer;

said reversing switch having a third output connected to said timer for setting a predetermined counting period;

said timer having an output connected to said counter for resetting said counter after said predetermined counting period;

alarm means;

said counter having an output connected to said alarm means; and said counter triggering said alarm means when the number of said reversing operations counted by said counter within said predetermined counting period, exceeds said predetermined count preset in said counter.

23. The comminuting machine as defined in claim 12, further including:

at least one pressing body containing a pressing plate for exerting a pressing action upon material to be comminuted and infed into said infeed hopper;

said at least one pressing body having the shape of a substantially cylindrical sector body defining an axis and a circumference;

a pivot shaft extending along said axis of said substantially cylindrical sector body;

actuator means connected to said substantially cylindrical sector body for pivoting the same between an inoperative position in which said pressing plate is spaced from said comminuting means and an operative position in which said pressing plate faces said comminuting means.

24. The comminuting machine as defined in claim 23, wherein:

said actuator means includes at least one pressure fluid operated cylinder-piston unit containing a double-acting cylinder;

a pressure fluid pump powering said double acting cylinder through a 4/3-valve via a twin check valve; and said pressure fluid pump being drivingly connected to said prime mover via a common shaft with said pressure fluid main pumps.

25. The comminuting machine as defined in claim 12, further including:

a support frame supporting said comminuting means and said power unit;

conveying means carried by said support frame;

said conveying means comprising a first conveyor and a second conveyor following said first conveyor;

said first and second conveyors including respective pressure fluid operated drive means for driving said first and second conveyors;

two pressure fluid pumps connected to respective ones of said pressure fluid operated drive means;

said two pressure fluid pumps being drivingly connected to said prime mover via a common shaft with said pressure fluid main pumps.

26. The comminuting machine as defined in claim 25, further including:

a rear end;

dependant frame members depending from said support frame and carrying said first conveyor below said comminuting means;

said second conveyor containing a first conveyor section mounted at said rear end and a second conveyor section linked to said first conveyor section remote from said rear end;

actuator means connected to said first conveyor section for pivoting the same between an inoperative position and an operative position;

said actuator means including a pressure fluid operated cylinder-piston unit containing a double-acting cylinder;

a pressure fluid pump powering said double acting cylinder through a 4/3-valve via a twin check valve; and said pressure fluid pump being drivingly connected to said prime mover via a common shaft with said pressure fluid main pumps.