Control device for controlling functions of a motor vehicle during a load dump

Control device for controlling functions of a motor vehicle for a load dump having a computer for generating at least one control signal that is dependent on the level of the operating voltage feeding the control device. A power supply system generates an operating voltage that is supplied to a threshold switch. As long as the operating voltage is above a limit value in the load dump case, the threshold switch outputs a response signal to an evaluator. The latter then only supplies an output signal and thus reports the load dump case to a computer unit when the response signal lasts longer than a set time span.

BACKGROUND OF THE INVENTION 
The present invention is directed to a control device for controlling 
functions of a motor vehicle for a load dump. The device has a computer 
for generating at least one control signal that is dependent on the level 
of an operating voltage. 
For example, such functions are the open time of an injection valve, the 
position of a throttle valve regulator and/or the charging time of an 
ignition coil. The length of the control signals controlling these units 
is dependent on the operating voltage applied to them in order to achieve 
a desired condition, such as quantity of fuel injected, position of the 
throttle valve or stored ignition energy, independently of the level of 
the operating voltage. 
Since the operating voltage in a motor vehicle is supplied by a battery 
with a generator connected in parallel thereto and since the battery 
voltage can change only slowly, it has been sufficient for control devices 
with a computer to sense the operating voltage only from time to time and 
to base the calculation of the control signals on the value that was most 
recently sampled. 
The present invention is based on the recognition that this procedure leads 
to unsatisfactory results under special operating conditions: namely, it 
can occur that the connection between the battery and generator is briefly 
or permanently broken. This then results in a significantly increased 
operating voltage for a sudden load dump whose size, among other things, 
is dependent on the speed of the generator (load dump). Since this 
operating situation is unpredictable but must be immediately taken into 
consideration, the computer would practically have to sense the operating 
voltage every millisecond. This, however, would result in a 
correspondingly costly design of the computer which however cannot be 
justified since the operating situations that have been described occur 
rarely. 
SUMMARY OF THE INVENTION 
An object of the present invention is therefore to immediately recognize a 
load dump without having to design the performance capability of the 
computer therefore. Further, the case of the load dump is to be 
distinguished from extremely short, non-critical increased levels of the 
operating voltage. 
The control device of the present invention has a threshold switch to which 
the operating voltage is applied at an input side and that outputs a 
response signal as long as the operating voltage lies above a limit value. 
An evaluator is provided that is driven with the response signal and 
generates an output signal on which the control signal is dependent and 
that starts offset by a time span after the beginning of the response 
signal and ends with the response signal. A timer in the evaluator defines 
the time span such that it is longer than the response signal for short, 
non-critical levels of the operating voltage and is shorter than the 
response signal for the shortest load dump. 
Without laying claim to the computer, the present invention provides an 
output signal only in the case of a load dump. A temporary disconnection 
of the control signal (SG) or an immediate sensing of the operating 
voltage and a recalculation of the control signal based thereon can thus 
then be initiated by the computer. 
To this end, the output signal can initiate the normal control program or a 
special load dump routine during which the operating voltage is sensed at 
points in time that follow relatively quickly after one another and the 
last sample is used for the calculation of the control signals until the 
load dump has decayed. Otherwise, the computer calculates the curve of the 
operating voltage during the load dump, proceeding from the sample at the 
beginning of the load dump, according to a stored characteristic or an 
equation and uses the operating voltage values calculated in this fashion 
for calculating the control signals. 
In the present invention, the output signal signaling a load dump is only 
generated when a real load dump is present and is not generated for only a 
brief, high noise voltage (noise pulse). A timer serves the purpose of 
distinguishing between these cases, this timer defining a time span whose 
length is selected such that it is longer than the duration of such 
non-critical noise pulses but is shorter than the duration of the shortest 
load dump that occurs. The latter is identified by measuring the 
conditions in a motor vehicle under real conditions. To this end, the 
duration during which the operating voltage occurs above a limit value due 
to a load dump is measured and the shortest of these times is selected. 
The limit value preferably is at the upper tolerance limit of the normal 
operating voltage. 
It is thereby especially advantageous to also switch a limiter on with the 
output signal, this limiter limiting the operating voltage at the units to 
a limit value that is permissible for them. Since brand-new vehicles are 
sometimes started with an auxiliary voltage source that supplies a higher 
operating voltage (referred to as a jump start), this limit value must be 
selected correspondingly higher, practically twice as great as the normal 
operating voltage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 3 shows a chronological curve of the limited operating voltage UBB. In 
the normal case, the operating voltage UBB has a normal value UB that is 
supplied by a voltage source 13 of a power supply system 1. (see FIG. 1). 
The voltage source 13 is composed of a generator that is connected in 
parallel to a battery. In case of a malfunction, the connection between 
the battery and generator is interrupted. A load dump then results and the 
generator generates a load dump signal SS (entered in broken lines in FIG. 
3 for unlimited operating voltage) whose amplitude can rise to 60-100 
volts and can last a few hundred milliseconds. However in addition to this 
critical noise signal, brief, harmless noise pulses SPI (shown with broken 
lines in FIG. 3) also occur, for example, resulting from a windshield 
wiper motor, that can reach amplitudes of up to 200 volts but only last 
about 100 nanoseconds. A noise source 12 is indicated in FIG. 1 as a 
source of the noise signals. 
The effective impedance value of the internal resistance 11 of the power 
supply system 1 normally amounts to only a few hundred milliohms. In case 
of a malfunction, however, it can amount from a few ohms up to a few 
hundred ohms depending on the range of the disturbances 
The illustrated load dump signal SS has exactly the calculated minimum 
signal duration TS. The noise pulse SPI has the calculated maximum pulse 
duration TI that is analogous to the calculation of the signal duration TS 
of the load dump signal SS. 
Proceeding from the power supply system 1, the operating voltage UBB is 
supplied to a threshold switch 2, to a limiter 8, to a typical load 
circuit that has a user 7 and a load switch 6, and to a power diode 9 that 
suppresses the negative portions of the operating voltage UBB. 
The threshold switch 2 has a first series branch having a drop resistor 22 
and a Zener diode 21. A resistor 24, a resistor 25 and an 
emitter-collector path of a pnp transistor 23 are in the second series 
branch. The operating voltage UBB is supplied to both series branches. The 
control path of the pnp transistor 2 is connected in parallel to the drop 
resistor 22. 
The limiter 8 has a limiter branch having a load resistor 82 and a 
self-inhibiting MOSFET 81 of the type whose drain-source channel lies in 
series with the load resistor 82. The MOSFET 81 has a fast switch behavior 
and a positive temperature coefficient that prevents an overload of the 
MOSFET 81. The gate-source path of the MOSFET 81 is connected in parallel 
to the resistor 25. A damping capacitor 83 that suppresses hunting is 
connected in parallel to the resistor 24. 
The voltage drop across the resistors 24 and 25 is equal to the response 
signal SW that is supplied to the input side of the evaluator 3. The 
response signal SW is supplied to a logic element 34 via an input resistor 
31 and is supplied to a mono-stable circuit of the timer 33 via an 
amplifier 32. With the beginning of the response signal SW, the monostable 
circuit emits a trigger signal SK at its output side whose duration 
corresponds to a time span TZ. The logic element 34 generates an output 
signal SA from the inverted trigger signal SK and from the response signal 
SW by an AND operation, this output signal SA being supplied to the reset 
input of a computer unit 4. The latter inhibits all control signals at its 
outputs as long as the output signal SA is present at the reset input. The 
computer unit 4 controls the load switch 6 with a control signal SG via a 
final stage 5. 
The computer 4 is shown in more detail in FIG. 4. In an internal combustion 
engine, a speed emitter arrangement 110 is composed of serrated rotating 
disk 111 preferably connected to the crankshaft of the internal combustion 
engine (not shown) whose tooth marks are sensed by a pick-up means 112. 
The output frequency that is generated is converted into a binary number 
in a following frequency-to-number converter 113 and is supplied to the 
computer 4. Any other speed acquisition that generates a speed-dependent 
numerical value, of course, is also possible instead of such a speed 
acquisition. Three parallel memory matrices 115, 116, 117, are selected in 
parallel in the computer 4 by this speed-dependent numerical value, 
whereby the speed-dependent numerical value respectively serves as an 
address. The selected memory contents are respectively supplied to a 
counter means 121 via switch devices 118, 119, 120, the counter means 121 
having a counterclock frequency f. In this embodiment an instruction line 
122 connects the counter mechanism 121 to an ignition output stage 123 
that usually has an electronic switch 124 in the primary current circuit 
of an ignition coil 125 in whose secondary circuit at least one spark plug 
126 is inserted. The electronic switch 124 is controlled via the 
instruction line 122. 
The supply voltage UBB supplied to terminal 127 is also supplied to the 
computer 4 via an analog-to-digital converter 128. Therein, the binary 
value dependent on the supply voltage that is generated by the 
analog-to-digital converter 128 is decoded in a decoder means 129 and 
actuates one of the switches 118, 119, 120 dependent on this supply 
voltage UBB. 
In the computer 4 a defined address y in each of the three memory matrices 
115, 116, 117 is addressed for a defined speed n. These memory matrices 
are usually fashioned as read-only memories (ROM) whose plurality is 
defined by the storage capacity and by the plurality of information to be 
stored. For example, a characteristic that is required for a supply 
voltage of 10 volts is stored in the memory matrix 115, while a 
corresponding characteristic for 12 volts is stored in the memory matrix 
116 and on for 14 volts is stored in the memory matrix 117. 
Let it also be pointed out that, for example the decoder means 129 and the 
switch devices 118, 119, 120 in the computer 4 of course, are not present 
discretely per se. The selection of one of the memory values x1 through x3 
occurs under program control, just as does the interrogation of the 
numerical value at the output of the analog-to-digital converter 128. A 
circuit-oriented realization, of course, is also conceivable as an 
alternative to the computer 4. 
The computer 4 as shown in FIG. 4 controls the ignition time and the closed 
duration of the primary winding of the ignition coil 125. The beginning of 
the closed time is varied as a function of the battery voltage UBB. The 
computer 4 samples the battery voltage UBB for this purpose with an 
appropriate programming of the computer 4 and a signal that corresponds to 
the signal SG in FIG. 1 is output on line 122 to the electronic switch 
124. 
In the present invention, this computer 4 is programmed to sample the 
battery voltage at greater time intervals for no load dump than when a 
load dump occurs. When a load dump does occur, the signal SA is sent to 
the computer 4 wherein the computer 4 is programmed to sample the battery 
voltage UBB in every calculating cycle as long as the signal SA is 
present. 
Many different microcomputers or microprocessors are available in the prior 
art for use as the computer 4. The programming of such computers is also 
well known to those skilled in the art. 
As long as the operating voltage UBB remains under the limit value UG, the 
Zener diode 21 is inhibited and the base of the pnp transistor 23 is at a 
high potential. The pnp transistor 23 is then inhibited and no response 
signal SW is generated. As long as the response signal SW is not present 
at the input side of the evaluator 3, it does not output an output signal 
SA to the computer unit 4. 
When the operating voltage UBB reaches the limit value UG, the Zener diode 
21 breaks down in the reverse direction and the pnp transistor 23 of the 
threshold switch 2 becomes conductive. A voltage drop that corresponds to 
the response signal SW therefore occurs at the resistor 24 and at the 
resistor 25. 
With the start of the response signal SW the monoflop 33 outputs the 
trigger signal SK on its output, the duration thereof corresponding to the 
time span TZ that is between the pulse duration TI of the longest noise 
pulse SPI and the signal duration TS of the shortest load dump signal SS. 
When a load dump signal SS is present, the response signal SW is present 
at the logic element 34 longer than is the trigger signal SK. After the 
removal of the trigger signal SK, the logic element 34 thus outputs the 
output signal SA to the computer unit 4 until the end of the response 
signal SW. When, by contrast, the noise pulse SPI that only lasts a short 
time is present, the response signal SW will already be removed from the 
input of the logic element 34 during the duration of the trigger signal 
SK, i.e., during the time span TZ, the logic element 34 then not 
outputting an output signal SA. 
As soon as the output signal SA is present at the computer unit 4, the 
latter removes the control signal SG at its output and the load switch 6 
in the load circuit is opened. 
With the beginning of the response signal SW, the MOSFET 81 is driven by 
the voltage drop across the resistor 25 and a current flows through the 
load resistor 82 of the limiter 8. The voltage drop across the load 
resistor 82 and the drain-source voltage at the MOSFET 81 together are of 
the same size as the limit value UG. The operating voltage UBB (see FIG. 
3) is thus limited to the limit value UG. In the limiting case, a 
considerably greater voltage drop occurs across the load resistor 82 than 
across the MOSFET 81, the latter being thereby considerably relieved. 
FIG. 2 shows an evaluator 3.1 that has a timer 33.1 and a switch 35 and to 
which the response signal SW is supplied at the input side via an input 
resistor 31. 
The timer 33.1 has a RC element composed of a timer capacitor 33.11 and a 
resistor 33.12 that is connected to the timer capacitor 33.11 and to the 
switch 35. The RC-element is followed by a Schmitt trigger 33.13 that has 
a trigger threshold UT. The switch 35 is composed of the two 
series-connected inverters 351, 352. 
When the response signal SW appears at the input of the evaluator 3.1, the 
timer capacitor 33.11 is charged to a trigger voltage ST via the resistor 
33.12 and this trigger voltage ST is supplied to the Schmitt trigger 
33.13. The time span TZ is defined by the duration that the trigger 
voltage ST requires in order to reach the trigger threshold UT of the 
Schmitt trigger 33.13 beginning from 0. The Schmitt trigger 33.13 outputs 
the output signal SA (FIG. 3) as long as the trigger voltage ST is above 
the trigger threshold UT. When the response signal SW is removed from the 
input of the evaluator 3.1, the inverter 352 discharges the timer 
capacitor 33.11 via the resistor 33.12. The inverter 352 keeps the timer 
capacitor 33.11 in its discharged condition as long as no response signal 
SW is present at the evaluator 3.1. 
The invention is not limited to the particular details of the apparatus 
depicted and other modifications and applications are contemplated. 
Certain other changes may be made in the above described apparatus without 
departing from the true spirit and scope of the invention herein involved. 
It is intended, therefore, that the subject matter in the above depiction 
shall be interpreted as illustrative and not in a limiting sense.