192 clutches and power-stop control – Transmission control and clutch control – Common control
Reexamination Certificate
2002-06-25
2003-09-16
Rodriguez, Saul (Department: 3681)
192 clutches and power-stop control
Transmission control and clutch control
Common control
C192S003620, C192S1030FA
Reexamination Certificate
active
06619451
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to power take-off shafts on tractors, and, more particularly, to a control system for the starting and running down of a power take-off shaft on a tractor.
Such control systems vary the quantity and hence the pressure build-up and pressure decay respectively in the hydraulic fluid supplied to a hydraulically actuated clutch. For this the said hydraulically actuated clutch of whatever kind required is located in the drive train on a shaft between the engine and the power take-off shaft (PTO shaft) of the tractor, onto one end of which a cardan shaft is attached and its other end is connected to the PTO shaft of a tool suspended on the lift of the tractor so that it can be driven.
For such control systems a number of variant versions are already known, one of which is explained in more detail in WO 99/56978 A1. There a control device is fixed on the tractor, which contains a processor, which depending upon the input signals fed to it runs a special control program and produces appropriate output signals. In so-called normal operation mode the input signals come each from one push-button for switching on and off the PTO shaft and from a sensor for monitoring the speed of the PTO shaft. The operator can optionally switch over to a so-called management operation mode, where further input signals are fed to the controller via a push-button for switching on management operation mode, and via sensors for monitoring the speed of the rear axle and the status of the lift (controlling and transport).
The said output signals are passed on to a solenoid valve functioning as a switching valve, which in this case is a pulse-width-modulated ON/OFF valve. This solenoid valve admits the adjacent pressure of the hydraulic fluid from the hydraulic circuit of the tractor to the hydraulically actuated clutch, so that according to the special control program of the control device this engages and disengages smoothly over a specified period of time. One part of the input signals ensures the trouble free course of these functions and another part in management operation controls automatically in addition the engagement and disengagement of the hydraulically actuated clutch in according to the status of the lift of the tractor and its speed of travel, in which additional safety circuits are installed for the protection of the operator.
A disadvantage of this control system is that since it was conceived for optimum engagement and disengagement, which means engagement as fast and smoothly as possible for the avoidance of wear and tear on the hydraulically actuated clutch and the transmission of high torques harmlessly to the clutch, important conditions of use were not taken into account. On the one hand these include changes in viscosity of the hydraulic fluid through varying ambient temperatures. On the other hand through the special control program in the control device, on the clutch no influences are felt when at the moment of starting up very different tools are employed. Likewise the initial speed of the engine is not taken account of in the control program at the moment of starting or stopping of the PTO shaft, although it is known that in consequence of differing amounts of power being taken from the engine it can fluctuate markedly. Finally, a further disadvantage is seen in this control system in that no facility for variable manual setting for the smoothness of engagement and disengagement is envisaged. Therefore in this variant it is a question of a quite normal control, which cannot by a long way react so variably as a control system.
All the said disadvantages are the reason that a hydraulically actuated clutch controlled in such a way under these conditions has only a limited service life, since starting proceeds too abruptly. Furthermore, it is still to be criticised in this control that in management mode of operation engagement and disengagement of the hydraulically actuated clutch is not influenced by the desired height of lift of the tool, which, however, would certainly be desirable in view of the variability in the tools employed. As a result damage to the cardan shaft can sometimes occur, if this is not stopped in time before the attainment of a high angle of flexion when the lift is raised, or if already in the presence of a high angle of flexion it is switched on again too soon. If on the other hand in the reverse case, the cardan shaft is not switched on again in good time when the lift is lowered, loss of time occurs, which reduces the effective time of use of the tractor and with it the danger exists that in the event that the engine stalls, because the tool is already in contact with the ground before the PTO shaft starts turning.
A further variant implementation of a control system for starting and running-down a PTO shaft on a tractor has been disclosed in EP 0 443 325 A1, the main objective of which for the hydraulically actuated clutch and for critical operating conditions in the subsequent driving elements up to the tool, consists in avoiding increased wear and in the extreme case destruction of all the drive elements. The construction of this control system, which also works only as a control, agrees fully with the solution described in the foregoing, as it likewise possesses a controller which receives input signals and produces output signals, in which the output signals are passed on to a solenoid valve functioning as a switching valve for the engagement or disengagement of the magnetically actuated clutch in the drive train to the cardan shaft.
In a preferred implementation the solenoid valve is a proportional valve, which is driven by timed pulses from the control unit and thereby actuated. As input signal first the engine speed is monitored, in which the hydraulically actuated clutch is disengaged by the control unit when the engine speed falls below a set value and is reengaged when this value is exceeded. As a further input signal the speed of the input shaft and of the output shaft of the hydraulically actuated clutch is detected with sensors, from which the controller calculates the existing slip from the differences that occur. If this exceeds a set value, then the hydraulically actuated clutch is disengaged and when it falls below this value it is engaged again. In the same way the speed fluctuations on the input shaft and the output shaft of the hydraulically actuated clutch are processed as input signals. Finally the height of the lift on the tractor is followed and when a set limiting value is attained the clutch is disengaged.
For the purpose of engagement that is as rapid and smooth as possible, yet another characteristic curve is stored in the controller, the function of which is comparable with the control program from the controller in accordance with WO 99/56978 A1. As regards the disadvantages of this controller, to avoid a recapitulation of the disadvantages of the controller first described one is referred to these, as these are identical. A further disadvantage is added for this controller, as it does not provide for management operation mode.
SUMMARY OF THE INVENTION
For that reason the objective of the invention is based upon a control system for the starting and running-down of a power take-off shaft on an agricultural vehicle, in particular a tractor, for which normal operation and management operation modes are to be provided, which achieves a rapid and smooth engagement of an hydraulically actuated clutch located between the engine and the power take-off shaft, of such a kind that on the one hand the hydraulically actuated clutch and the other hand the drive elements connected to it and on the other hand also tools differing markedly in behaviour at the moment of starting attain a maximum service life under all conditions of use. In addition, it should in both normal operation and also in management operation protect the cardan shaft from destruction through too great an angle of flexion. Finally in the management operation mode it should prevent the occurrence of lost time for ev
Henkel Rebecca L.
New Holland North America Inc.
Rodriguez Saul
Stader John William
LandOfFree
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