Patent ID: 6397138
Filing Date: 2002-05-28
Classification: F16H,Y10T

Abstract:
A safety system for an electrohydraulically controlled automatic transmission (2) driven by an internal combustion engine (1), said safety system comprising:an electronic control unit (5) for determining a reduction ratio (i(K), K=1 . . . 5) via a shift characteristic field (i(K)=f (DKI, nAB)), with said reduction ratio depending on a throttle valve position (DKI) and a transmission output speed (nAB), and each of said characteristic fields having a line of constant reduction ratio included within a reduction ratio range (B(K), K=1 . . . 5); a selector lever (21) coupled to the automatic transmission (2) for facilitating control of said automatic transmission (2) during use by a driver; said electronic control unit (5) including a mechanism for determining, while driving (nAB>limit value), whether a first change of said selector lever (21) occurs, from a forward driving position to a neutral position, and whether the first change is followed by a second change of the selector lever (21) from the neutral position to the forward driving position; said electronic control unit (5) includes means for deriving, upon detection of the first change and said selector lever (21) being moved to the neutral position, a virtual reduction ratio (iV) from a transmission input speed (nT) and the transmission output speed (nAB), and said electronic control unit, upon detection of the second change, including means for determining a set reduction ratio (iSOLL) with the set reduction ratio (iSOLL) containing the virtual reduction ratio (iV); when the virtual reduction ratio (iV) is between first and second reduction ratio ranges, said electronic control unit (5) including means for determining a first difference (DIFF) of the virtual reduction ratio (iV) and the first reduction ratio range and a second difference (DIFF) of the virtual reduction ratio (iV) and the second reduction ratio range; and said electronic control unit (5) including means for selecting the set reduction ratio (iSOLL) based upon a lesser of the first difference (DIFF) and the second difference (DIFF).