Abstract:
A system and method are provided for monitoring a vehicle hydraulic system having a plurality of hydraulic function elements. The hydraulic system includes a hydraulic pump for supplying pressurized hydraulic fluid to the plurality of hydraulic function elements via a corresponding plurality of hydraulic element control valves, an electronic control unit for controlling the element control valves. The pump also supplies lube fluid to a lubrication circuit if requirements of the hydraulic function elements are met. The method includes sensing a hydraulic pressure (preferably the lube pressure of lube fluid in the lube circuit), and comparing the sensed pressure to a threshold pressure. If the sensed pressure is less than threshold pressure, then actively engaged hydraulic elements are tested by disengaging the elements in a predetermined manner, checking to see if the sensed low pressure condition is eliminated. If the sensed low pressure condition is eliminated after disengaging an element, then the leaking hydraulic function element (the last element disengaged) is deactivated (locked-out) and a corresponding message is generated and stored.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a system for monitoring and protecting a vehicle hydraulic system. 
     BACKGROUND OF THE INVENTION 
     Serious damage can result when a drivetrain in a tractor is not operated at a proper operating temperature, with a proper clutch engagement pressure or with proper lubrication. Therefore, various systems have been used to protect transmissions from such conditions. For example, gages have been used to display conditions to an operator so that the operator could take appropriate action if the transmission oil temperature became higher than a threshold or if system pressure drops below a threshold. Some gages are augmented with flashing lights or audible alarms. 
     Another approach is a “Murphy switch” which automatically shuts an engine down if transmission oil temperature becomes higher than a threshold or if system pressure falls below a threshold. 
     The hydraulic system pressure level is set so that engaged transmission clutches will not slip even when transmitting full engine torque. Hydraulic system pressure is set by a pressure regulating valve. The pressure regulating valve ensures that system pressure remains above a set level even under low pump flow conditions, as is the case when the tractor is running at low idle. A system which monitors system hydraulic pressure with respect to a single warning level may be sufficient to prevent transmission clutch slippage and large hydraulic system leaks, but it may not detect low to medium sized hydraulic leaks which may result in a loss of lubrication fluid. In order to detect a full range of hydraulic leaks, the lube system needs to be monitored. However, monitoring lube pressure with respect to a single pressure level would be unsatisfactory because a transmission lube circuit will normally operate under low pressure conditions, not just when little or no lube oil is available. For example, normal lube pressure is low when the lube oil is warm and engine speed is low. Thus, using low lube pressure as a warning level will not detect leaks when the engine speed is operating at higher speeds. 
     A known system, marketed by Case, detects critically high engine and transmission temperature and low engine oil pressure, and shuts down the engine if these parameters are above certain thresholds. 
     U.S. Pat. No. 4,489,305, Lang, et al., issued in 1984 and is assigned to the assignee of this application. The Lang et al. patent describes a monitoring system for a vehicle, such as an agricultural tractor, which includes a hydraulic assist-type transmission with fluid control and lubricating circuits. The monitoring system senses the fluid pressure in the lubricating circuit, the hydraulic fluid temperature and the engine speed. The sensed pressure is compared to a temperature and engine speed-compensated alarm value. Alarm signals are generated when the sensed pressure is continuously below the alarm value for a certain period. The alarm is disabled when the engine speed falls below a non-zero threshold level. However, this system and the previously mentioned systems do not automatically shut off any hydraulic functions to determine the source of the leak, nor does it isolate or lock-out only the hydraulic function(s) that are determined to be the cause of the leak and any other affected hydraulic functions. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of this invention is to provide a system which detects and protects against small and medium size oil leaks in vehicle hydraulic systems. 
     A further object of the invention is to provide such a system which also determines which vehicle system is the source of the problem while the vehicle is in operation without the operator having to place the vehicle into a special mode. 
     A further object of the invention is to provide such a system which is responsive to recent operational status of the transmission or of other hydraulic functions to aid in determining which vehicle system is the source of the problem. 
     A further object of the invention is to deactivate (lock-out) only the hydraulic element(s) found to be causing a leak and any other hydraulic elements affected by the leak, while allowing all other non-affected hydraulic functions of the tractor to remain operational. 
     A further object of the invention is to automatically engage a limp home mode under certain low lube conditions. 
     These and other objects are achieved by the present invention, wherein a system and method are provided for monitoring a vehicle hydraulic system having a plurality of hydraulic function elements. The hydraulic system includes a hydraulic pump for supplying pressurized hydraulic fluid to the plurality of hydraulic function elements via a corresponding plurality of hydraulic element control valves, an electronic control unit for controlling the element control valves. The pump also supplies lube fluid to a lubrication circuit via a lube line if requirements of the hydraulic function elements are met. The method includes sensing a lube pressure of lube fluid in the lube line, and comparing the lube pressure to a threshold pressure. If the sensed lube pressure is less than threshold pressure, then actively engaged hydraulic elements are tested by disengaging the elements in a predetermined manner while the vehicle is in operation, checking to see if the sensed low lube pressure condition is eliminated. If the sensed low lube pressure condition is eliminated after disengaging an element, then the leaking hydraulic function element (the last element disengaged) is deactivated (locked-out) and a corresponding message is generated and stored. By locking-out the leaking hydraulic function element, lube pressure is returned to normal allowing all non-affected hydraulic function elements on the tractor to remain operable. In many cases, this would allow the operator to continue operating the tractor for the rest of the day until taking the tractor to the dealer for service. If after testing the previously engaged hydraulic elements, the sensed lube pressure is still below threshold pressure, then all elements are deactivated and a limp home mode is automatically enabled. Limp home mode allows the tractor to only be driven in a pre-selected forward or reverse gear. This allows the tractor to be driven onto a truck or to the dealer for service. The pre-selected forward and reverse gear is chosen so that the bearings in the transmission are moving at a relatively low speed so there is minimal risk of transmission damage under low lube conditions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified schematic diagram of a vehicle hydraulic control and lubrication system according to the present invention; and 
     FIG. 2 is a simplified schematic diagram of a valve assembly of FIG. 1; and 
     FIGS. 3 a - 3   d  comprise a logic flow diagram illustrating an algorithm executed by the control unit of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A vehicle hydraulic system  10 , such as for an agricultural tractor, includes a hydraulic supply pump  12  which supplies system pressure hydraulic fluid to various hydraulic functions or elements, such as MFWD control element  50 , a park brake element  52 , a differential lock control element  54 , etc., via a corresponding solenoid operated control valve  16 A,  16 B,  16 C, etc. The MFWD control element  50  is preferably a spring engaged, pressure released unit, and which is normally engaged during field operation of the tractor. The park brake element  52  is preferably a spring engaged, pressure released park brake, which is released when the tractor is moving. The differential lock control element  54  is preferably a pressure engaged, spring disengaged differential lock unit which is normally disengaged. 
     The pump  12  also supplies system pressure to a plurality of other hydraulic elements, such as transmission control clutch elements  60 ,  62 , of a conventional powershift transmission  64 , such as the powershift transmission on 8000 Series John Deere tractors, and/or a PTO control clutch element  70 . Each of these further elements is coupled to the pump  12  via a corresponding conventional element control valves  20 A,  20 B,  20 C, etc. The term hydraulic function or element should be understood to include other known hydraulically operated functions which are used on vehicles such as agricultural tractors or other agricultural work vehicles or machines. Although only two transmission control clutch elements  60 ,  62  are shown it should be understood that there would be as many such elements as are part of a typical powershift transmission. With a transmission  64  as described above, two clutch elements must be engaged (an input clutch and output clutch) to transmit torque. Most of the shifts of the transmission  64  require only a single element clutch swap. However, some shifts require dual element clutch shifts, wherein two clutch elements are disengaged and two different clutch elements engaged to obtain a new gear ratio. 
     As seen in FIG. 2, each element control valve  20 A,  20 B,  20 C, etc., includes a solenoid operated valve section  21  and a pilot operated section  23 . The pilot operated section  23  is normally spring biased to a position which blocks communication between pump  12  and the element, and valve section  21  normally connects the pilot side of valve section  23  to sump. When the solenoid of valve section  21  is energized, communication is blocked between sump and the pilot side of valve section  23 . This pressurizes the pilot side of valve section  23  and valve section  23  moves to a position connecting pump  12  to the element. 
     The pump  12  also supplies lubrication fluid to a transmission lube circuit  22  via a pressure regulating and system priority valve  24 , an oil cooler  26  and hydraulic lube line  28 . The monitoring and control system of the present invention includes an oil temperature sensor  30  which senses the temperature of lube fluid in line  28 , a pressure sensor  32  which senses the pressure P of lube fluid in line  28  and an engine speed sensor  34 . A control unit  40  receives signals from sensors  30 ,  32  and  34 , supplies control signals to valves  16  and  21 , and supplies information to a display  42  via a conventional data bus  44 . The control unit  40  executes an algorithm  100  represented by the flow chart set forth in FIGS. 3 a - 3   d.  The conversion of this flow chart into a standard language for implementing the algorithm described by the flow chart in a digital computer or microprocessor, will be evident to one with ordinary skill in the art. 
     After starting in step  102 , step  104  determines whether the lube pressure P from sensor  32  is less than a threshold pressure Pt for a predetermined time period. If not, step  104  is repeated. Preferably, the threshold pressure Pt varies as a function of engine speed and oil temperature, as sensed by sensors  34  and  30 , respectively. For example, the oil pump  12  is driven by the engine (not shown), therefore as engine speed goes up the pump provides more oil, therefore normal lube pressure is higher with higher engine speed. As an example, with oil temperature at 55 degrees C., normal lube pressure is higher than 240 kpa at 2000 engine rpm but at 1000 engine rpm, normal lube pressure is higher than 60 kpa. The colder the oil, the higher the oil viscosity which raises the normal oil pressure. Therefore the colder the oil, the normal oil pressure will also be higher. At 2000 engine rpm, normal oil pressure is greater than 240 kpa at 55 degrees C., at 25 degrees C., normal lube pressure is greater than 360 kpa. 
     If, in step  104  the lube pressure P from sensor  32  is less than threshold pressure Pt, then step  106  recalls from a memory the last element which was changed, and step  108  determines whether the element changed within a predetermined time period of lube pressure dropping below threshold pressure. If yes, step  110  determines whether the last element changed was a dual element transmission shift (meaning two elements in the transmission were changed at the same time to engage a gear). If not, step  108  directs the algorithm to step  122 . 
     If, in step  110 , the last element changed was not a dual element transmission shift, step  118  depressurizes the single element that changed within the predetermined time period (closes communication between that element and the pump  12 ). If, in step  110 , the last element changed was a dual element transmission shift, step  112  downshifts the transmission  64  and depressurizes one of the pair of elements involved in the dual element transmission shift, and step  114  again compares the lube pressure P from sensor  32  to the threshold pressure Pt. 
     If, in step  114 , the lube pressure P is less than threshold pressure Pt, control is directed to step  116  which downshifts the transmission  64 , depressurizes the other element involved in the dual element transmission shift when lube pressure became less than threshold pressure and directs the algorithm to step  120 . If, in step  114 , the lube pressure P is not less than threshold pressure Pt, control is directed to step  124  which disables and locks out that transmission element from pump  12  until the tractor is serviced. 
     Step  120  is performed after either step  118  or  116 , and again determines whether the lube pressure P from sensor  32  is less than a threshold pressure Pt. for a predetermined time period. If, in step  120 , the lube pressure P is not less than threshold pressure Pt, control is directed to step  124 . If, in step  120 , the lube pressure P is less than threshold pressure Pt, control is directed to step  122  which engages the MFWD  50  by closing valve  16   a  and disconnecting MFWD  50  from pump  12 . 
     Step  123  is performed after step  122 , and again determines whether the lube pressure P from sensor  32  is less than a threshold pressure Pt for a predetermined time period. If, in step  123 , the lube pressure P is not less than threshold pressure Pt, control is directed to step  124  which disables and locks out the disengagement of the MFWD. Step  124  directs the algorithm to step  125  which stores, transmits and displays a corresponding warning message or signal. Step  125  transmits on bus  44  a message that certain element(s) have been disabled and causes display  42  to flash a corresponding indication that element(s) have been disabled, including element(s) effecting transmission gears, and stores this message in memory. Step  125  then directs the algorithm back to step  104 . 
     If, in step  123 , the lube pressure P is less than threshold pressure Pt, control is directed to step  126 . Step  126  depressurizes the differential lock  54 , if the differential lock  54  was engaged. 
     Step  128  again determines whether the lube pressure P from sensor  32  is less than a threshold pressure Pt for a predetermined time period. If not, it is assumed that there is a leak in the circuit to differential lock  54 , and steps  124  and  125  are executed. If yes, step  130  downshifts the transmission  64  by one gear ratio. 
     If, in step  132 , the lube pressure P is not less than threshold pressure Pt, control is directed to step  134 . If, in step  132 , the lube pressure P is less than threshold pressure Pt, control is directed to step  150 . 
     In step  134 , the transmission downshift is checked to see if the shift was a dual element transmission shift (meaning two elements in the transmission were changed at the same time to engage the new gear). If no, the downshift is a single element shift (meaning only one clutch element was changed to engage the new gear). As a result, the one clutch element that was disengaged (depressurized) in the shift is now identified as the element causing low lube pressure. Step  136  clears the transmission gears and elements shifted through and directs the algorithm to steps  124  and  125  to lock-out the element, store that the element is locked-out and generate and transmit a message. If, in step  134 , the transmission downshift is determined to be a dual element shift, then step  138  recalls the elements which have already been shifted through while downshifting and directs the algorithm to step  140 . By recalling the elements already shifted through in step  130  the controller may be able to diagnose which clutch element is causing a system leak even during a dual element shift. For example, if 6 th  gear is engaged (6 th  gear in the transmission  64  engages a C 1  input clutch (not shown) and a C output clutch (not shown)) and the lube pressure is below threshold pressure, then step  130  downshifts the transmission to 5 th  gear. Shifting from 6 th  gear to 5 th  gear is a single element clutch swap. In 5 th  gear input clutch C 1  (not shown) and output clutch B (not shown) is engaged. If the low lube pressure condition is not eliminated, the controller then downshifts the transmission to 4 th  gear. Shifting from 5 th  gear to 4 th  gear is a duel element transmission shift. In 5 th  gear, input clutch C 1  (not shown) and output clutch B (not shown) is engaged. In 4 th  gear, C 4  (not shown) and Ab (not shown) are the two elements engaged. If after shifting from 5 th  gear to 4 th  gear, the low lube pressure condition is eliminated, then either C 1  (not shown) or B (not shown) clutch elements could be the possible cause of the leak. However, by looking at the elements already shifted through, the controller can determine that C 1  (not shown) clutch is the source of the leak since C 1  (not shown) was engaged in both 6 th  gear and 5 th  gear under the low lube condition. Step  140  checks for this type of situation by looking to see if one element was shifted through twice. 
     If yes, step  140  directs the algorithm to steps  136 ,  124  and  125 . If no element was shifted through twice, step  140  directs the algorithm to step  142 , which downshifts the transmission  64  to a gear that engages one of the clutch elements that was engaged before the dual element transmission shift that eliminated the low lube pressure condition. 
     Step  144  again compares the lube pressure P from sensor  32  to the threshold pressure Pt. If, in step  144 , the lube pressure P is not less than threshold pressure Pt, control is directed to step  146 . If, in step  132 , the lube pressure P is less than threshold pressure Pt, control is directed to step  152 . 
     Step  146  downshifts the transmission  64  to a gear that engages the other clutch element that was engaged before the dual element transmission shift that eliminated the low lube pressure condition, and directs the algorithm to step  148 . 
     Step  148  again compares the lube pressure P from sensor  32  to the threshold pressure Pt. If, in step  148 , the lube pressure P is not less than threshold pressure Pt, control is directed to step  104 . If, in step  148 , the lube pressure P is less than threshold pressure Pt, control is directed to step  152 . 
     Returning to step  150 , if the transmission is not in neutral, control is directed to step  152 , else control is directed to step  154 . 
     Step  152  stores in a memory of the VCU  40  the transmission elements which were shifted through when downshifting to neutral and directs control to step  130 . 
     In step  154 , if the PTO  70  is not engaged, control is directed to step  162 , else control is directed to step  156 . 
     Step  156  depressurizes or disengages the PTO  70  by causing valve  20  to close communication between pump  12  and PTO  70 . 
     Step  158  compares the lube pressure P from sensor  32  to the threshold pressure Pt. If the lube pressure P is not less than threshold pressure Pt, control is directed to step  160  which locks out the PTO  70  and directs the algorithm to step  125 . If the lube pressure P is less than threshold pressure Pt, control is directed to step  162 . 
     Step  162  engages the park brake by closing valve  16   b.    
     Step  164  again compares the lube pressure P from sensor  32  to the threshold pressure Pt. If the lube pressure P is not less than threshold pressure Pt, control is directed to step  166  which disables or locks-out neutral and the transmission gears. This is because the park brake release system is causing the leak. The algorithm then goes to step  125 . If the lube pressure P is less than threshold pressure Pt, control is directed to step  168 . 
     Step  168  disables all elements and enables a limp home mode wherein only a pre-selected forward and reverse gear can be accessed by the operator. This allows the vehicle to be driven onto a truck or to the dealer for service. The forward and reverse gear is chosen so that the bearings in the transmission are moving at a relatively low speed so there is minimal risk of transmission damage under low lube conditions. 
     Step  170  stores, transmits and displays a warning message, after which the algorithm  100  ends. 
     While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. For example, the algorithm described above could be used together with monitoring of hydraulic system pressure, instead of monitoring lube pressure. However, the resulting system would only detect large hydraulic system leaks, not small to medium size leaks which can still cause system failure due to lack of lubrication. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.