IMPROVEMENTS IN CYLINDER-TYPE MOWERS

Abstract: A cut-adjusting apparatus for a mower comprising a rotatably mounted cutting cylinder (10) and a stationary blade (18) in grass-cutting relationship therewith, the apparatus comprising means for effecting relative approaching movement of the cylinder and the stationary blade towards each other until they contact each other with a predetermined force, and means for effecting relative movement of the cylinder and blade away from each other to separate them by a predetermined distance, thereby defining the cutting relationship of the cylinder and the blade. The approaching movement is effected hydraulically, and a volume of fluid is trapped when the in-contact datum is established. The separation of the blades is affected by hydraulic pressure acting against a spring (40), preferably via the trapped volume of fluid.

Description: IMPROVEMENTS IN CYLINDER-TYPE MOWERS The invention relates to improvements in cylinder-type mowers, in particular to a method and apparatus for adjusting the cut thereof. A cylinder-type mower comprises a cutting reel or cylinder arranged for rotation about an axis parallel to the ground, from which it is supported by a frame with ground-contacting wheels or rollers. The cylinder is rotatably driven, either from the wheels or from a prime mover (eg. an internal combustion engine or an electric motor). In professional IC powered machines the drive is conveniently taken from the IC engine to the cylinder or cylinders by a hydraulic power transmission system . The cylinder has a number of helical blades (eg. six or eight) defining its periphery, and these blades co-act with a stationary blade beneath the cylinder and parallel to its axis to cut the grass by a shearing or scissors-like action. The gap between the helical blade and the bottom blade is critical to effective and efficient grass cutting. Too large a gap results in poor cutting, but if the gap is too small or non-existent, rapid wear results. Conventionally the gap is adjusted manually either at predetermined service intervals, or On condition' ie when the quality of cut deteriorates. The manual adjustment procedure is time-consuming and requires a degree of skill on the part of the mechanic. It also is potentially dangerous because the mechanic must handle the cutting edges. Further, when being adjusted or awaiting adjustment the mower is out of commission. This is a significant problem for groundsmen and green-keepers of municipal parks, sports grounds, golf courses etc where mowers are intensively used and the need for adjustment is frequent. The present invention seeks to offer, at least in its preferred embodiments, a solution to the foregoing problem by providing a method of and apparatus for the automatic adjustment of a cylinder mower, thereby effectively eliminating adjustment downtime. According to one aspect of the invention there is provided a method of adjusting the cut of a cylinder-type mower comprising supplying hydraulic pressure fluid to a chamber to effect relative approaching movement between the cutting cylinder and the stationary blade until they contact each other, then effecting relative movement of the cylinder and blade in the opposite sense to separate them by a predetermined distance, the relative movement in the opposite sense being effected by closing the chamber to trap the pressure fluid and applying a separating force against a resilient means, the predetermined distance being controlled by the deflection of the resilient means under the action of the separating force. In another aspect the invention provides a cut-adjusting apparatus for a mower comprising a rotatably mounted cutting cylinder and a stationary blade in grass- cutting relationship therewith, the apparatus comprising means for effecting relative approaching movement of the cylinder and the stationary blade towards each other until they contact each other, and means for effecting relative movement of the cylinder and blade away from each other to separate them by a predetermined distance, thereby defining the cutting relationship of the cylinder and the blade, characterised in that the means for effecting relative approaching movement comprises a first pressure chamber of variable volume and adapted to receive pressure fluid, the means for effecting relative separating movement comprising means for trapping pressure fluid in the first chamber, a resilient means and means for applying a separating force to the resilient means so that the predetermined distance is controlled by the deflection of the resilient means under the action of the separating force. The separating force may be greater than the force with which the cylinder and blade are brought into contact. The separating force may be transmitted through the trapped fluid to the resilient means. The separating force may be applied by hydraulic pressure fluid. The separating force may be transmitted through the fluid to a member bounding the chamber and acting upon the resilient means. The means for effecting relative approaching movement and the means for effecting relative separating movement may be respective oppositely-acting hydraulic rams. The rams may be formed by oppositely-directed faces of a piston bounding said first chamber and a further chamber in a common cylinder. Said first chamber may also be bounded by a further piston, whereby pressure applied to the fluid trapped in the first chamber by one said piston is transmitting therethrough to the other piston. Preferably the resilient means may act upon the further piston, setting of the predetermined distance being achieved by applying the separating force to the first piston to pressurise the trapped fluid in the chamber, the pressurised fluid causing the further piston to deflect the resilient means until the separating force is balanced. The resilient means may be a compression spring arranged coaxially with the further piston, means being provided to apply a compressive pre-load to the spring. Preferably the oppositely-directed faces of the first-mentioned piston are of unequal area, the relative approaching movement being effected by applying pressure fluid at the same pressure to both said faces. Thus the compressive pre-load may be greater than the force applied to the first piston when the relative approaching movement is effected. The invention also provides a cylinder type mower having cut-adjusting apparatus as set forth above. Usually the cutting cylinder is mounted for movement towards and away from the stationary blade. Thus the cut-adjusting apparatus may be connected between a mounting of the cutting cylinder and fixed structure of the mower. The mower preferably comprises control means causing the cut-adjusting apparatus to operate between one mowing operation and the next. Thus a mower according to the invention may comprise a cutting unit including the cutting cylinder and the stationary blade, and means for moving the cutting unit between a raised transport position and a lowered grass-cutting position, the control means causing the cut-adjusting device to operate when the cutting unit is moved between the two said positions. 'Professional' powered mowers are usually ride-on machines with a gang of several (eg. three or more) cutting cylinders. Alternatively, a gang of several cutting cylinders may be towed behind a conventional tractor. In both cases the cutting cylinders are usually powered by hydraulic fluid from an engine- driven hydraulic pump. The hydraulic fluid is also used to move the cutting units between a lowered or grass-cutting position and a raised or transport position. Thus when the raising and lowering apparatus is effected hydraulically, the cut-adjusting apparatus may be operated by the hydraulic pressure fluid used for that purpose. There may be means for reducing the pressure of the hydraulic fluid utilised to provide the relative approaching movement. There may be flow-limiting means for restricting the rate of flow of hydraulic fluid utilised to operate the cut-adjusting device. The invention now will be described merely by way of example with reference to the accompanying drawings, wherein Figure 1 shows a conventional cutting unit of a cylindrical mower; Figure 2 shows a method of adjusting the cut employed in the invention; Figure 3 shows one embodiment of a cut-adjusting apparatus according to the invention; Figure 4 and 5 shows another embodiment of the invention; Figure 6 shows an operating cycle of a powered mower; and Figure 7 and 8 show alternative hydraulic circuits of a mower according to the invention. Referring to Figure 1, a conventional cylinder mower comprises a cutting reel or cylinder 10 having a number (in this case six) helical blade 12 equi-angularly distributed around and carried by an axle 14. A surrounding fixed frame or housing 16 carries a bottom blade 18 which co-acts with the helical blades to cut the grass with a scissors-like action. The point of contact 20 (actually a small gap of about 0.05mm) of each helical blade with bottom blade travels along the bottom blade as this cylinder rotates. The spacing and lead angle of the blades 12 is such that several of them (in this case three or four) are in contact with the bottom blade at any one time. The gap between the cylinder and the bottom blade conventionally is adjusted by screw-threaded adjusters 22 mounted between the frame 16 and the hubs 24 of the cylinder, and which move the cylinder towards and away from the bottom blade. Typically, accurate adjustment is achieved by inserting a feeler gauge between the helical blade 12 and the fixed blade 16. More crudely, the adjusters can be advanced until the cylinder contacts the bottom blade, and then can be backed-off by an arbitrary amount. However, this practice is undesirable because there is no control over the degree of contact made between the cylinder and the fixed blade, and the latter can easily be permanently distorted. It then is impossible to set the mower to cut evenly across the full width of the cylinder. Figures 2 and 3 illustrate the novel principle and apparatus of the present invention. At each end of the cylinder 10 the manual adjusters 22 are replaced by coaxial opposed hydraulic rams 26, 28. The arrangement of the cut-adjusting rams at each end of the cylinder 10 is the same. Therefore for simplicity the arrangement at only one end of the cylinder 10 will be described, it being understood that the rams at each end operate in unison so that the axis of the cylinder 10 remains parallel to the blade 18. The rams act in opposite senses on a beam 30 pivotally mounted from the frame 16 at 32. The cylinder is carried in a bearing on the beam at 34. The piston of the ram 28 is connected to the beam 34 by a pivot 36. The piston of the ram 26 carries a rigid cylindrical cage 38. The disc 42 acts upon a pre-loaded compression spring 40 trapped within the cage. The end 44 of the cage 38 to which the ram 26 is connected is screw-threaded in the main body of the cage. Thus the cage is of adjustable length so that the degree of pre-load can be controlled. The ram 26 is pressurised to exert a predetermined (ie. known) force to advance the blades of the cylinder into contact with the bottom blade (stage 1 in Figure 2). The predetermined force is relatively low so that the blades are not distorted. The pre-load in the spring 40 is set to be greater than the predetermined force so that the spring is not further compressed when the cylinder is advanced. The hydraulic fluid (oil) which pressurises the ram 26 is supplied via a non-return valve (80, Figures 7 and 8) and thus once extended the ram 26 is locked by the substantially incompressible fluid trapped therein. To set the cutting gap between the blades the ram 28 is then pressurised at a considerably higher pressure to generate a relatively large force which compresses the spring 40 in the cage 38 against the locked ram 26, allowing ram 28 to displace the pivot 36 and thus move the cylinder 10 away from the blade 18. The deflection characteristic of the spring 40 and the pressure applied to the ram 28 are such that the spring is compressed by an amount related to the required gap between the cylinder 10 and the bottom blade 18 (stage 2 of Figure 2) by the mechanical advantage of the beam 34. The pre-load applied to the spring is chosen to be sufficient to hold the cylinder in its required gap-defining position in all normal circumstances, but to allow it to be displaced should a stone, or other foreign body become trapped between the cylinder 10 and the blade 18. The required piston area of the ram 28 is set so that the working pressure of the hydraulic fluid applied to it just overcomes the pre-loads. Figures 4 and 5 show an engineered version of the apparatus of Figure 3. The two rams 26, 28 are replaced by oppositely-directed faces 46, 48 of a single (primary) piston 50 which bounds respective chambers 52, 54 in a hydraulic ram 56. The spring 40, again pre-loaded, is disposed between a secondary piston 58 (which also bounds the chamber 52) and an end cap 60. The end-cap is screw- threaded in the end of the cylinder 56 and thus may be screwed in or out to adjust the pre-load of the spring 40. The pre-load is transmitted through a flange 59 of the piston to an internal wall 61 of the ram 56. The end cap 60 and the wall 61 thus are equivalent in the cage 38 of Figure 3, and the flange 59 equates to disc 42. The face 62 of the piston 58 bounding the chamber 52 is smaller than face 46 of piston 50. Referring to Figure 5, a ram as shown in Figure 4 secured to the frame 16 at each end of the cutting cylinder 10, the piston rod 64 of piston 50 being pivotally connected at 36 to the beam 30. In this embodiment the frame 16 also carries a trailing roller 66, so that the mown grass exhibits the desirable striped appearance. In operation, relatively low pressure hydraulic fluid is supplied via port 68 to chamber 52, forcing piston 50 leftwards and extending the overall length of the ram 56. The cutting cylinder 10 thereby is pushed against the bottom blade with a moderate predetermined force. As in the Figure 3 embodiment , non-return valve 80 prevents fluid from escaping from chamber 52. The pressure of the fluid in chamber 52 is insufficient to overcome the pre-load of the spring 38, so it is not further compressed. Chamber 54 is then pressurised to a considerably higher pressure than was chamber 52. Piston 50 commences to move to the right, pressurising the substantially incompressible fluid trapped in chamber 52. The increased pressure acts upon face 62 of piston 58 and is sufficient to overcome the pre-load in spring 40. Piston 58 thus moves rightward contracting the ram 56, compressing the spring and permitting piston 50 also to move to the right in response to the high-pressure fluid supplied to chamber 54. Ultimately, the spring 40 is compressed sufficiently for the pressure on face 62 of piston 58 to be balanced. The contraction of the ram 56 at each end of the cylinder 10 thus moves the cylinder away from the bottom blade to define the required cutting gap. Because the ram 56 and the cylinder axis 14 are both on the same side of the pivot 32, the ram 56 contracts by a greater amount than the distance by which the cylinder separates from the bottom blade. Furthermore because the piston face 62 is smaller in area than the face 46, the piston 58 moves through a greater distance than piston 50. If the mechanical advantage of the beam 30 in two and the piston face 46 is twice the diameter of piston face 62 the movement of the cylinder is multiplied by a factor of eight in the deflection of the spring 40. The sensitivity of the set gap to variation in the working pressure of the hydraulic fluid or in the rate of the spring thus is reduced. Figure 6 shows the operating cycle of a ride-on mower. The sequential nature of the steps before and after the cutting operation lend themselves to utilisation for the automatic adjustment of the cut between successive cutting operations. Thus the adjustment cycle could be initiated by the depression of the mow pedal, but it currently is preferred to initiate it by movement of the cutting unit between its transport and cutting position, either lowering it at the start of the cycle, or raising it at the end. Referring to Figure 7, the rams 56 of Figures 4 and 5 are connected to the hydraulic circuit unit for raising and lowering the cutting unit. A hydraulic pump (not shown) supplies hydraulic pressure fluid to line 70 at 35 bar (500 lbf/in 2 ) nominal. The majority of the flow is directed to the ram 72 used for raising and lowering the cutting unit, but a small quantity is diverted via ports P and A of a four-pott two- position valve 74. A 1.3mm diameter restrictor 76 limits the diverted flow so that the lifting and lowering capability is not compromised by the diversion. Downstream of the restrictor 76 a pressure reducing valve 78 reduces the pressure of the diverted flow to 0.7 bar (10 lbf/in 2 ). The low pressure fluid is then supplied to chamber 52 of ram 56 to set the cutting cylinder 10 against the bottom blade 18 as already described. Excess fluid is dumped to return tank 81. The valve 74 is spring-biased into the position shown in Figure 7. Thus on powering-up the hydraulic system the cutting cylinder is automatically set against the bottom blade. Then, as the cutting unit is lowered the valve 74 is displaced leftwards by a cam on the lowering/lifting mechanism (eg. or the lift arm pivot tube or on the piston of ram 72) to cross-connect ports P and B, and A and T of the valve. High pressure hydraulic fluid is then applied via a restrictor 82 to chamber 54 of ram 56, and the cutting cylinder is displaced from the bottom blade, thereby setting the cutting gap as previously described. A variable pressure -regulating valve 84 ensures that the pressure in chamber 54 is maintained accurately at a set value, this being important to ensure that the cutting gap is accurately established. The size of the gap may be controlled either by adjusting the setting of the regulator 84 or by adjusting the preload of the spring 40 by position of the end cap 60 of the ram 56. Adjusting the regulator 84 is preferred because the effect on the rams 56 at each end of the cutting cylinder is equal; if the pre-load of the springs 40 is adjusted, care is necessary to equalise the adjustment to ensure that the cutting gap remains constant across the full length of the bottom blade. Of course, individual adjustment of the springs 40 is necessary of the gap should become non-parallel eg. if the cutting unit has ingested twigs, stones or other foreign objects. Upon completion of mowing the cutting unit is raised to its transport position, the valve 74 being returned to its position shown in Figure 7. Thus when the unit is in the transport position the cutting cylinder is constantly biased against the bottom blade by the low pressure supply via restrictor 76. It thus is prevented from rotating, reducing the risk operator injury if the unit is handled for any reason eg. cleaning. Figure 8 shows a modified version of the circuit of Figure 7. Corresponding parts carry the same reference numbers. In a 'professional' mower the cutting cylinder may be of considerable weight, eg. 35 or 40 kg with the result that even with a pressure in chamber 54 as low as 0.7 bar, the total force on the bottom blade during the first phase of the setting process may be more than 700 N. This considerable loading of the bottom blade is undesirable. The loading can be reduced by approximately counter-balancing the weight of the cutting cylinder with springs. However the force applied during the first stage of the setting procedure must overcome the counter-balancing force, and will vary as the blades wear. This may introduce inaccuracies into the setting procedure. Therefore it is preferred to reduce the downforce exerted by the rams during the first stage of the setting procedure. The valve 74 is modified so that during the first stage of the setting procedure low pressure (0.7 bar) hydraulic fluid is applied via ports P, A and B to both chambers 52 and 54 ie. to both faces 46 and 48 of piston 50. The net force on piston 50 is thus the pressure times the difference in area between faces 46 and 48 ie. the cross-sectional area of piston rod 64. The total downforce is thereby much reduced; in the specific case mentioned above it was more than halved from over 700 N to less than 350 N. The valve 74 is modified so as to use only three of its four ports, the T (tank) port being plugged; adequate drain to tank is provided via the pressure reducing valve 78. Internally, the valve spool is modified so that when the valve is in the position shown in the drawing port P in connected to both ports A and B. hen the valve is switched to its other position (rightward in Figure 8), chamber 54 is applied with high pressure fluid as before via ports B and P. Valve actuation is achieved mechanically eg. by a cam as in the Figure 7 embodiment, or by means of a solenoid controlled by microswitches actuated by the cutting unit left arm when it passes a preset angle. The use of microswitches presents the valve 74 to be disposed remotely from the lift arm at any convenient location. The described embodiments have the further advantage that when the hydraulic system is depressurised eg. when the cylinders are lifted to the transport position the cylinder will tend to settle against their respective stationary blades, thereby locking them against rotation. There is then less danger of injury due to fingers becoming trapped between the cylinder and the blade. Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features. The text of the abstract filed herewith is repeated here as part of the specification. A cut-adjusting apparatus for a mower comprising a rotatably mounted cutting cylinder and a stationary blade in grass-cutting relationship therewith, the apparatus comprising means for effecting relative approaching movement of the cylinder and the stationary blade towards each other until they contact each other with a predetermined force, and means for effecting relative movement of the cylinder and blade away from each other to separate them by a predetermined distance, thereby defining the cutting relationship of the cylinder and the blade. The approaching movement is effected hydraulically, and a volume of fluid is trapped when the in- contact datum is established. The separation of the blades is effected by hydraulic pressure acting against a spring, preferably via the trapped volume of fluid.

Claims: CLAIMS 1. A method of adjusting the cut of a cylinder-type mower comprising supplying hydraulic pressure fluid to a chamber to effect relative approaching movement between the cutting cylinder and the stationary blade until they contact each other, then effecting relative movement of the cylinder and blade in the opposite sense to separate them by a predetermined distance, the relative movement in the opposite sense being effected by closing the chamber to trap the pressure fluid and applying a separating force against a resilient means, the predetermined distance being controlled by the deflection of the resilient means under the action of the separating force. 2. A method as claimed in claim 1 wherein the separating force is greater than a force with which the cylinder and the blade are brought into contact. 3. A method as claimed in claim 1 or 2 wherein the separating force is applied by hydraulic pressure fluid. 4. A method as claimed in claim 3 wherein the separating force is transmitted through the trapped fluid to a member bounding the chamber and acting upon the resilient means. 5. A cut-adjusting apparatus for a mower comprising a rotatably mounted cutting cylinder and a stationary blade in grass-cutting relationship therewith, the apparatus comprising means for effecting relative approaching movement of the cylinder and the stationary blade towards each other until they contact each other, and means for effecting relative movement of the cylinder and blade away from each other to separate them by a predetermined distance, thereby defining the cutting relationship of the cylinder and the blade, characterised in that the means for effecting relative approaching movement comprises a first pressure chamber of variable volume and adapted to receive pressure fluid, the means for effecting relative separating movement comprising means for trapping pressure fluid in the first chamber, a resilient means and means for applying a separating force to the resilient means so that the predetermined distance is controlled by the deflection of the resilient means under the action of the separating force. 6. Apparatus as claimed in claim 6 wherein the separating force is greater than the force with which the cylinder and the blade are brought into contact. 7. Apparatus as claimed in claims 5 or 6 wherein the separating force is transmitted through the trapped fluid to the resilient means. 8. Apparatus as claimed in claim 6 or 7 wherein the means for effecting relative approaching movement and the means for effecting relative separating movement are respective oppositely- acting hydraulic rams. 9. Apparatus as claimed in claim 8 wherein the rams are formed by oppositely- directed faces of a piston bounding said first chamber and a further chamber in a common cylinder. 10. Apparatus as claimed in claims 7 and 9 wherein said first chamber is also bounded by a further piston, whereby pressure applied to fluid trapped in the first chamber by one said piston is transmitting therethrough to the other piston. 11. Apparatus as claimed in claim 10 where the resilient means acts upon the further piston, setting of the predetermined distance being achieved by applying the separating force to the first piston to pressurise the fluid trapped in the chamber, the pressurised fluid causing the further piston to deflect the resilient means until the separating force is balanced. 12. Apparatus as claimed in claims 10 and 11 wherein the resilient means is a compression spring arranged coaxially with the further piston, means being provided to apply a compressive pre-load to the spring. 13. Apparatus as claimed in claim 9 wherein the oppositely-directed faces of the first-mentioned piston are of unequal area, relative approaching movement being effected by applying pressure fluid at the same pressure to both said faces. 14. Apparatus as claimed in claims 10, 12 and 13 wherein the compressive preload is greater than the force applied to the further piston when the relative approaching movement is effected. 15. A cylinder-type mower comprising cut-adjusting apparatus as claimed in any of claims 6 to 14. 16. A mower as claimed in claim 15 wherein the cutting cylinder of the mower is mounted for movement towards and away from the stationary blade, the cut-adjusting apparatus being connected between a cutting cylinder mounting and fixed structure of the mower. 17. A mower as claimed in claim 15 or 16 comprising control means causing the cut-adjusting apparatus to operate between one mowing operation and the next. 18. A mower as claimed in claim 17 comprising a cutting unit including the cutting cylinder and the stationary blade, and means for moving the cutting unit between a raised transport position and a lowered grass-cutting position, the control means causing the cut-adjusting device to operate when the cutting unit is moved between the two said positions. 19. A mower as claimed in claim 18 wherein the cut- adjusting apparatus is as claimed in claim 8, the means for moving the cutting unit between its two positions being a hydraulic circuit, the cut-adjusting apparatus being operated by hydraulic pressure fluid from said circuit. 20. A mower as claimed in claim 19 comprising means for reducing the pressure of fluid utilised to effect the relative approaching movement. 21. A mower as claimed in claim 19 or 20 comprising flow-limiting means for restricting the rate of flow of pressure fluid utilised to operate the cut-adjusting device.

Inventors: BROWN DAVID JOHN, BROWN, DAVID, JOHN
Applicants: BROWN DAVID JOHN, RANSOMES SIMS & JEFFERIES LTD, BROWN, DAVID, JOHN, RANSOMES, SIMS & JEFFERIES LIMITED
Application year: 1998
Main classification: A01D34
IPC codes: A01D34