Arrangement for automatically changing the transmission ratio of a speed-change gearbox of a motor vehicle with the effect of changing to a higher gear

Claim 1

Circuit for a speed-change gearbox which is coupled downstream of a drive engine in a power train of a motor vehicle, the circuit providing a changing-up signal for changing the speed-change gearbox to a higher gear, comprising: an electronic control unit (21) forms a changing-up signal as a function both of a load (10) of the drive engine and of a driving speed (70) of the motor vehicle; an electro-hydraulic changing device (22) connected by a changing-up line (212) to the electronic control unit (21) and receiving from the electronic control unit (21) the changing-up signal (HS); a first switch (102) connected in the changing-up line (212), the first switch (102) being opened when the changing-up signal (HS) and an inhibiting signal (SP v1 ) is present; a bistable multivibrator (108) having a setting input (S) and a resetting input (R), and coupled to the first switch (102), said first switch (102) preventing the changing-up by setting the bistable multivibrator (108) when the inhibiting signal is present; a detection stage (V4) responsive to a change in level of the inhibiting signal (SP v1 ) for preventing the changing-up and outputting a signal (V4A) for setting the bistable multivibrator (108), with the resetting input (R) of the bistable multivibrator (108) for a re-authorization of the changing-up by closure of the first switch (102) being provided with a signal (N11A) which corresponds to a threshold position of an accelerator pedal (10) and which is output when the accelerator pedal has been actuated to at least the threshold position after the setting of the bistable multivibrator (108); a displacement transducer controllably connected to the accelerator pedal (10); a threshold value stage (N11) coupled between the displacement (10) transducer and the resetting input (R), the threshold value stage determining the threshold position; a delay element (106, N1) switched on in response to the changing-up signal (HS) and coupled to a second switch (101), the second switch (101) being coupled in series in the changing-up line (212) with the first switch (102), the delay element (106, N1) during its delay time driving the second switch (101) in an opening direction; wherein the threshold value stage (N11) has a threshold value which varies as a function of a position of the accelerator pedal (10) and is set to a constant offset above an instantaneous position of the accelerator pedal and is locked onto when the delay element (106, N1) is switched on, so that the threshold position deviates by a constant offset from an instantaneous position in which the accelerator pedal was located when the second switch (101) opens, and wherein the second switch (101) is additionally driven by a first delay device (106, N1, N3, N11) which operates as a function both of the delay element (106, N1), and of the threshold value stage (N11) such that the second switch (101) remains opened over a delay time determined by the first delay device (106, N1, N3, N11) when the signal corresponding to the threshold position occurs and switches on the first delay device (106, N1, N3, N11).