Method and circuit for preventing oscillations of an automotive vehicle

A method and a circuit for preventing oscillations of the automotive vehicle having an engine, a controlling element controlling the output power of the engine and a desired-value transmitter, wherein, within a predetermined period of time after a rise of the desired value which is faster than takes place with a predetermined rate of rise, it is checked whether there is a decrease in the desired value which takes place faster than with a predetermined rate of decrease. In the case of the presence of a faster decrease of the desired value, the rate of rise of the desired value fed to the adjusting element is temporarily limited.

FIELD AND BACKGROUND OF THE INVENTION 
The present invention relates to a method of preventing oscillations of an 
automotive vehicle having an engine, a controlling element which controls 
the output power of the engine and a desired-value transmitter, as well as 
a circuit for the carrying out of the method. As used herein, a desired 
value of speed is a speed value commanded by an instantaneous position of 
an accelerator pedal of a motor vehicle. 
Particularly in the case of automotive vehicles having a strong engine and 
a soft drive line, oscillations can result upon the sudden giving of gas. 
They are increased by the fact that upon the sudden giving of gas the 
driver is pressed back into his seat and thereby unconsciously pulls his 
foot away from the gas pedal. This, in its turn, has the result that the 
automobile is substantially decelerated and the driver slips forward. In 
this connection, he again depresses the gas pedal more strongly. This is 
repeated several times until either the driver gives full gas, clutches or 
removes his foot from the gas pedal. 
This so-called bonanza oscillation, which can be induced by a single sudden 
giving of gas, is not only experienced as extremely unpleasant but can 
also lead to dangerous situations in traffic. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to prevent these oscillations 
without the accelerating capacity of the vehicle suffering thereby. 
According to the invention, within a predetermined time after a rise in the 
desired speed which takes place faster than with a predetermined rate of 
rise, it is checked whether there is present a decrease in the desired 
speed which takes place faster than with a predetermined rate of decrease 
and, in case of the existence of a faster decrease in the desired speed, 
the rate of rise of the desired speed fed to the controlling element is 
temporarily limited. 
The method of the invention has the advantage that the aforementioned 
oscillations are prevented without the increase in the motor power being 
delayed upon the sudden giving of gas. The motor power is reduced without 
delay also upon a sudden removal of gas. This takes place also within the 
time frame within which the rate of rise is limited. In this connection 
the threshold of the rate of rise or of decrease is selected below the 
value at which the so-called load-alternation jolt takes place. 
The method of the invention is suitable both for gasoline engines with 
carburetor or injection and for diesel engines. Upon the use of the method 
of the invention, time constants of the vehicle in question which are 
controlling for the oscillations are to be taken into account. 
An additional feature of the method of the invention consists in the fact 
that the rate of change of the desired speed is compared with a 
predetermined positive value and a predetermined negative value, that upon 
the exceeding in positive or negative direction of the respective 
predetermined value, a signal of, in each case, a constant duration is 
started and that in the event of coincidence of the signals, the rate of 
rise of the desired value fed to the correcting element is limited. 
In this connection it is particularly advantageous if the limiting of the 
rate of rise of the desired value fed to an adjusting element takes place 
in accordance with a parabolic function. In this way a jerk is avoided 
upon the rapid renewed giving of gas, without, however, excessively 
delaying the total rise. This is obtained independently of the exact time 
of the renewed giving of gas in the manner that the course of the 
parabolic function is started by a rise in the desired value given off by 
the desired-value transmitter. 
In accordance with another additional feature, a transfer to the unlimited 
feeding of the desired value to the adjusting element takes place in the 
manner that the course of the parabolic function is started after a 
predetermined period of time even without rise of the desired value. 
The method of the invention can be carried out with different arrangements. 
Thus, for instance, the method of the invention can be carried out with a 
so-called electric-gas system in which the position of the gas pedal is 
transmitted electrically to the adjusting element. The method of the 
invention can, however, also be carried out with systems which have a 
mechanical connection between gas pedal and correcting element, which 
connection is acted on electrically in order to limit or reduce the engine 
power. In both cases a hard-wired circuit or a suitably programmed 
microprocessor can be provided. In the latter case there is the 
possibility of having the method of the invention in addition to other 
control or regulating tasks carried out by a microprocessor. 
One advantageous circuit for the carrying out of the method of the 
invention consists therein that a rate-of-rise limiter (3) is arranged 
between the desired-value transmitter (2) and the adjusting element (4, 
5), that the speed-of-rise limiter (3) has a control signal input (6); 
that to the desired-value transmitter (2) there is connected the input of 
a differentiator (7) whose output is connected to a window comparator (8); 
that the window comparator has two outputs (9, 10) at which signals are 
present as a function of whether the input voltage of the window 
comparator (8) exceeds a positive threshold and/or drops below a negative 
threshold; that the outputs (9, 10) of the window comparator (8) are each 
connected, via a timing member, to the inputs of the AND circuit (13) 
whose output is connected, via a bistable circuit (14), an integrator (15) 
and a pulse-width modulator (17) to the control input (6) of the 
rate-of-rise limiter (3). In this connection the rate-of-rise limiter (3) 
can comprise another integrator (29, 31).

Identical parts are provided with identical reference numbers in the 
figures. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1(a) shows the variation as a function of time of the position of the 
gas pedal, of a control voltage which transmits the position of the gas 
pedal to the adjusting element, and of the position of the adjusting 
element, for instance the throttle valve itself. The control voltage 
represents the desired value for the position of the throttle valve and is 
produced by a desired-value transmitter which is coupled with the gas 
pedal. Two periods of a bonanza oscillation are shown, the throttle valve 
being in each case moved from the idling position into the full load 
position and back into the idling position where it remains until the next 
period commences. 
The method of the invention will be explained with reference to FIG. 1(b). 
In this connection it is assumed that gas is given very rapidly at the 
time t.sub.0. This is shown by the solid line tangent, while the dot-dash 
line represents a predetermined value of the rate of change of the desired 
value. Since in the embodiment shown the change in speed of the desired 
value S lies above the predetermined value, there is produced a pulse 
shown in FIG. 1(c), which continues until the time t.sub.2. 
At t.sub.1 there is a rapid removal of gas so that the change in speed of 
the desired value (solid-line tangent) is greater than the predetermined 
value (dot-dash line). In this way a second pulse, shown in FIG. 1(d), is 
given off. As long as the rapid decrease of the desired value takes place 
within the time t.sub.0 to t.sub.2, there is temporarily conicidence 
between the pulses shown in FIGS. 1(c) and 1(d), which leads indirectly to 
the pulse shown in FIG. 1(e). The rear edge of this pulse is produced by 
the renewed giving of gas. Even if this renewed giving of gas is as sudden 
as represented by the dashed line in FIG. 1(b), a slower rise is forwarded 
to the adjusting element. This rise is shown as a solid line in FIG. 1(b). 
If no renewed giving of gas should occur up to t.sub.3, then the limiting 
of the rate of rise for the desired value is eliminated, so that a sudden 
giving of gas is again possible. 
In the case of the arrangement shown in FIG. 2, a signal representing the 
desired value is fed from a desired-value transmitter 2 connected to a gas 
pedal 1 via a rate-of-rise limiter 3 to a control circuit 4 which, 
corresponding to the desired value, controls a throttle valve 5 of an 
internal combustion engine, now shown. The rate-of-rise limiter 3 is in 
its nature, a low pass filter which, however, is effective only upon a 
rise in the desired value and only as a function of the control voltage 
which is fed to the input 6. A decline in the desired value is transmitted 
without delay, as well as an increase, if a corresponding control voltage 
is present at the input 6. 
The output voltage of the desired-value transmitter is furthermore fed to a 
differentiator 7 the output of which is connected to a window comparator 8 
which, in its turn has two outputs 9, 10 which are connected to 
corresponding inputs of a monostable trigger circuit 11, 12. An output of 
each of the monostable trigger circuits 11, 12, is connected to the inputs 
of an AND circuit 13. 
The output voltage of the differentiator 7 corresponds to the rate of 
change of the desired value. Upon the depressing of the gas pedal 1 a 
negative pulse is produced, while release of the gas pedal results in a 
positive pulse. The faster the gas pedal is moved, the greater the 
amplitudes of the pulses. If the movements are sufficiently fast then the 
amplitude of the negative pulse exceeds a negative threshold present in 
the window comparator 8 while a positive threshold is exceeded if the gas 
pedal is released sufficiently suddenly. 
By means of the output pulses of the window comparator, the two monostable 
trigger circuits 11, 12 are brought into the unstable condition so that 
there are produced at the outputs the pulses shown in FIGS. 1(c) and (d) 
which have a predetermined width and the lead edge of which depend on the 
time of the occurrence of the corresponding movement of the gas pedal. In 
this connection, in a preferred embodiment the width of the output pulse 
of the monostable trigger circuit 11 is about 200 ms, while the other 
output pulse is of lesser width. 
By the connecting of two pulses by means of the AND circuit 13 the 
following then takes place: In case of slow movements of the gas pedal the 
thresholds are not exceeded in positive or negative direction in the 
window comparator, so that no output signals occur there. If the pedal is 
depressed rapidly, then the monostable trigger circuit 11 is set. If, 
within the duration of the output pulse of the monstable trigger circuit 
11 the gas pedal is suddenly released, then the monostable trigger circuit 
12 will also be set within this time, so that for a certain period of time 
both pulses will be present at the inputs of the AND circuit 13 and an 
output pulse will be produced. Upon subsequent sudden release of the gas 
pedal no coincidence arises and thus also no limiting of the rate-of-rise 
of the desired value. 
The output signal of the AND circuit 13 is fed to a set input of a 
flip-flop 14 the reset input of which is connected to the output of the 
differentiator 7. The output signal (FIG. 1(e)) of the flip-flop 14 
controls an integrator 15 whose output signal again modulates, by means of 
a pulse width modulator 17, a triangular voltage fed at 16. The 
pulse-width modulated pulses are fed to the control input 6 of the 
rate-of-rise limiter 3. As will be explained in greater detail in 
connection with FIG. 3, the flip-flop 14 serves to place the circuit in a 
condition of rest upon each giving of gas, even if it does not take place 
so rapidly that a bonanza oscillation is induced. Merely for a 
predetermined period of time after the sudden giving of gas and the sudden 
removal of gas shortly thereafter is the rate-of-rise limiter 3 so 
controlled by means of the integrator 15 and the pulse-width modulator 17 
that the desired value rises slowly corresponding to a predetermined 
function even in the event that gas is suddenly given shortly thereafter. 
FIG. 3 shows a more detailed circuit diagram of the circuit shown as a 
block diagram in FIG. 2. The input 21 is connected to the output of the 
desired-value transmitter 2 (FIG. 2), while the output 22 is connected to 
the control circuit 4 (FIG. 2). The input voltage is fed to the inverting 
input of an operational amplifier 23 whose output is connected, via a 
resistor 24, with positive operating voltage and, via two series circuits 
each consisting of a diode 25, 26 and a resistor 27, 28, to the inverting 
input of another operational amplifier 29. In the branch formed of the 
diode 26 and the resistor 28 there is inserted a transistor 34 which is 
controlled via a resistor 30 by a control voltage fed at 6. 
The operational amplifier 29 is connected as integrator with the capacitor 
31, a constant voltage being fed to the non-inverting input via a voltage 
divider 32, 33. The output of the operational amplifier 29 forms the 
output 22 and is connected via a resistor 36 to battery voltage and via a 
capacitor 35 to ground potential. Furthermore, the non-inverting input of 
the operational amplifier 23 is connected to the output of the operational 
amplifier 29. By this negative feedback coupling the result is obtained 
that the output 22 of the voltage follows the input 21, in which 
connection, however, depending on the integration time constant, there is 
a reduction in the rate of change. The circuit is so designed that upon a 
drop of the desired value, the output voltage follows so rapidly that no 
perceptible delay occurs upon the removal of gas. An increase in the 
desired value is also transmitted practically without delay if the 
transistor 34 is conductive--and therefore the input 6 is fed a voltage 
which is less than the voltage at the inverting input of the operational 
amplifier 29 less the base-emitter voltage of the transistor 34 and the 
voltage drop on the resistor 30. 
However, if the control voltage fed at 6 is greater--for example U+--then 
the transistor 34 is blocked and the voltage at the output 22 remains 
despite the increasing desired value. By the feeding of a pulse-width 
modulated signal, intermediate values for the rate of change of the output 
voltage can be set. 
The differentiator 7 (FIG. 2) is formed in the circuit of FIG. 3 by an 
operational amplifier 41 the inverting input of which is connected via a 
series connection consisting of a resistor 42 and a capacitor 43 to the 
input 21. The non-inverting input receives a voltage which corresponds to 
half of the positive operating voltage and is produced by means of a 
voltage divider 44, 45. Furthermore, the operational amplifier 41 is fed 
back by means of a resistor 46 and a capacitor 47. At the output of the 
operational amplifier 41 there is produced, during a rise in the desired 
value, a negative voltage and during a decrease, a positive voltage, 
referred to the potential at the non-inverting input. 
The amplitude is the higher the faster the decrease or rise takes place. 
The operational amplifiers 51 and 52 form a window comparator, for which 
purpose constant voltages of different value are fed via a voltage divider 
48, 49, 50 to the inverting input of the operational amplifier 51 and the 
non-inverting input of the operational amplifier 52. The differentiated 
desired value is fed from the output of the operational amplifier 41 to 
the non-inverting input of the operational amplifier 51 and to the 
inverting input of the operational amplifier 52. Insofar as digital 
signals are mentioned in the following, such as, for instance, the output 
signals of the window comparator, a positive level is designated by H and 
a negative level or ground level by L. 
The output voltage of the operational amplifier 52 assumes the level H if 
the rate of rise is greater than the predetermined value. If the desired 
value drops faster than at a predetermined rate then the output signal of 
the operational amplifier 51 assumes the level H. With these signals two 
monostable trigger circuits, which are formed in the embodiment shown by 
an integrated circuit of type 4528, are placed in the unstable state. By 
means of the RC members 54, 55 and 56, 57 the duration of the pulse 
occurring at each output Q1 and Q2 is fixed. 
A network consisting of the resistors 58, 59, 60 serves, together with the 
operational amplifier 61 and a voltage divider 62, 63, as AND circuit 13 
(FIG. 2). Adjoining the AND circuit there is the differentiating member, 
consisting of a capacitor 64 and a resistor 65. The pulse which is thus 
differentiated controls the non-inverting input of an operational 
amplifier 67 via a resistor 66 in such a manner that its output assumes 
the level H, as a result of which the diode 68 becomes conductive and 
maintains this condition, for which purpose operating voltage is fed over 
a resistor 69. The inverting input of the operational amplifier 67 
receives, via a voltage divider 70, 71, a bias voltage which is equal to 
half the operating voltage. 
The operational amplifier 67 fulfills the function of a flip-flop which is 
set by the pulses fed. A resetting is effected by another operational 
amplifier 72 the inverting input of which receives a bias voltage via a 
voltage divider 73, 74 and the non-inverting input of which is acted on by 
the differentiated desired value. 
The operational amplifiers 67 and 72 have so-called open collector outputs, 
with the result that the level H is present simultaneously on both of them 
only if both operational amplifiers are controlled accordingly. A positive 
voltage corresponding to level H is fed via the resistor 75 to the base of 
a transistor 76 whose emitter-collector path lies in series with a 
resistor 77 between the inverting input and the output of an operational 
amplifier 78. Furthermore, a capacitor 79 is arranged within said negative 
feedback branch so that the operational amplifier 78 operates as 
integrator. A fixed potential is fed via a voltage divider 80, 81 to the 
non-inverting input, while the inverting input is connected with ground 
potential via a resistor 82. 
The voltage at the output of the integrator tends, when the transistor 34 
is non-conducting, towards an end value which corresponds to the voltage 
potential of the supply voltage. If this end value is fed to the inverting 
input of the operational amplifier 85 and a triangular voltage is fed to 
the non-inverting input with such a portion of dc voltage that the 
triangular voltage is continuously more negative than the output voltage 
of the operational amplifier 78, then the transistor 34 is conductive. A 
rapid change in the desired value fed to the adjusting element 5 (FIG. 2) 
is possible. 
By controlling the output of the operational amplifier 67 at the level H, 
the transistor 76 however becomes conductive and the integrator is thus 
placed at a given initial value. In this connection, the voltage at the 
inverting input of the operational amplifier 85 is continuously more 
negative than the triangular voltage, so that a level H which results in a 
blocking of the transistor 34 is produced at the output of the operational 
amplifier 85. 
Upon the subsequent giving of gas, the transistor 76 is brought by the 
output level L of the operational amplifier 72 into the non-conducting 
state, so that the output voltage of the integrator rises linearly to the 
highest possible positive potential. In this connection it passes through 
the voltage range of the triangular signal, so that at the output of the 
operational amplifier 85 there are produced pulses whose width increases 
linearly with time. The period of the triangular voltage is small as 
compared with the other time constants of the system, so that a pulse-like 
control of the transistor 34 becomes perceptable only continuously with 
increasing pulse width. If one presupposes a sudden rise of the voltage at 
the input 21 then the parabolic function shown in FIG. 1(b) is obtained 
from the linear rise with time of the pulse-width-like control of the 
transistor 34 by the action of the integrator which is formed by the 
operational amplifier 29. The speed of rise of the desired value fed to 
the correcting element is limited more strongly at first and then less so. 
By the circuit shown in FIG. 3 and, in particular, by the starting of the 
integration process by the giving of gas itself, the result is obtained 
that the parabolic limitation only commences when gas is given. In this 
way, one avoids that upon the giving of gas (after sudden giving and 
removal of gas) there is a jump in the output signal or a jump in the 
change with time of the output signal because a transition between the 
uninfluenced forwarding of the desired value and the limiting of the speed 
of rise has been introduced already prior to the giving of gas. 
For the event that the renewed giving of gas does not occur directly after 
the sudden giving and removal of gas, it is provided that, via a diode 86 
which is connected between the output Q2 of the one monostable trigger 
circuit and the base of the transistor 76, the integration process is 
brought about even if no renewed giving of gas takes place within a 
predetermined time. Then no limiting of the rate of rise occurs as long as 
the transistor is not brought into the conductive state by sudden giving 
of gas and shortly thereafter removal of gas, and the integrator is thus 
placed at the initial value.