Patent ID: 6504474
Filing Date: 2003-01-07
Classification: B01D,F01M,F16H,Y10T

Abstract:
A method of warning a vehicle operator of the need to service a vehicle transmission having a hydraulic pump and filter downstream from the pump and a filter bypass valve, the method comprising the steps of:sensing a first pressure on a first side of the filter and a second pressure on a second side of the filter; comparing the first and second pressures to determine a pressure differential across the filter;activating activating a first alarm when the pressure differential exceeds a first predetermined value; opening the filter bypass valve in the event the pressure differential across the filter exceeds a second predetermined value and wherein the first predetermined value is less than the second predetermined value whereby the first alarm is activated prior to the filter being bypassed and wherein the first alarm is activated only when the transmission input speed is above a first predetermined speed level and the transmission oil temperature is above a predetermined amount; activating a second alarm when the pressure differential across the filter exceeds the second pressure by a third predetermined value wherein if the engine speed is above a second predetermined speed level when the second alarm is activated, the engine speed is reduced to below the second predetermined speed level whereby the pump pressure is reduced; reducing the engine speed to a low idle speed if after the engine speed is reduced to below the second predetermined speed level the pressure differential across the filter remains above the third predetermined value; and, wherein the second and third predetermined values are approximately equal whereby the second alarm is activated when the filter is bypassed.