GB2333618A

GB2333618A - Non-volatile power supply disconnection indicator

Info

Publication number: GB2333618A
Application number: GB9826810A
Authority: GB
Inventors: Thomas Reindl
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1997-12-04
Filing date: 1998-12-04
Publication date: 1999-07-28
Anticipated expiration: 2018-12-04
Also published as: GB2333618B; GB9826810D0; FR2772943B1; FR2772943A1; DE19753840C1

Abstract

A microprocessor-supported control unit for petrol engines and diesel engines is provided with a central microprocessor (2), a voltage regulator (3) for supplying the microprocessor (2) with its operating voltage (VCC), and a battery terminal (4) for feeding the vehicle battery voltage (VB) into the voltage regulator (3). Furthermore, there is provided a memory circuit (5), which is connected to the battery terminal (4) and is also connected to the microprocessor (2) by way of a read-out output (6) and a reset input (7). It is designed as a one-bit memory on the basis of a thyristor function circuit (T1, T2), in such a way that after a temporary disconnection of the vehicle battery voltage (VB), this event can be displayed at the read-out output (6) by a logic signal which can be detected by the microprocessor (2) and used for the further control of the program flow. The read-out output (6) of the memory circuit (5) can be logically reset by a reset signal of the microprocessor (2) via the reset input (7). The advantage is that the controller detects and stores information regarding the disconnection of the battery even when the controller is switched off.

Description

MICROPROCESSOR-SUPPORTED CONTROL UNIT FOR PETROL ENGINES AND DIESEL ENGINES The invention relates to a microprocessorsupported control unit for petrol engines and diesel engines.

With respect to the background of the invent ion, it is to be noted that modern motor vehicle engines have an "intelligent" engine management which, as a rule, makes available a plurality of diagnostic functions. Thus, for example, exhaust-gas-related data or fundamentally occurring faults on components are detected by appropriate sensors and stored in appropriate memories by the control program of the control unit. During a service or repair, the workshop personnel can, by means of an appropriate diagnostic unit, read out the data and messages stored in the memories, carry out the associated repairs and maintenance work, and reset the memories to erase the data messages or fault messages which have now been serviced.

In workshops which are less well equipped, problems can arise because of the housekeeping sequence which has just been described, to the extent that the appropriate maintenance work is indeed carried out, but because of the lack of a diagnostic unit, the corresponding fault messages in the memories cannot be reset. In this respect, the driver is constantly irritated by an uncancelled request to carry out a service, for example, even though everything is in perfect order in maintenance terms.

In earlier generations of electronic control units for petrol engines and diesel engines, volatile memory chips in the form of RAMs were used, which had to be supplied constantly by the vehicle battery in order to hold the data. This admittedly had the disadvantage of a high current consumption, but in the case of an interruption in the supply, all fault messages and data messages stored in the memories were automatically erased. The corresponding memories could therefore be reset by disconnecting the vehicle battery.

In the course of new memory techniques, nonvolatile memories, such as flash memories or EEPROM memories, for example, were developed, which memories hold their data even without a voltage supply.

Furthermore, in accordance with relevant statutory regulations in various countries, the erasing of certain data is not permitted.

It has now emerged that from a practical point of view, many automobile and engine manufacturers still contemplate the possibility of erasing the fault memories - at least within legally permitted limits by disconnection of the vehicle battery voltage to be desirable in order to render possible a resetting of fault messages etc even if a diagnostic unit is not available.

In his scientific treatise "Mehr Sicherheit für Mikrokontroller-Applikationen", which was published in the periodical DESIGN & ELEKTRONIK, issue 1/2 of 15.01.1991 on pages 58, 59, Johann Stelzer describes a check unit which is provided with a chip. This chip basically comprises the functions of a 5-V voltage regulator, a low-voltage monitor, a power-on-resetpulse generator and a watchdog. With this arrangement, it is intended to ensure that the check unit does not lose its rhythm in the event of disturbances, or at least that a defined restart will be possible.

A computer system which can store the state of a failed voltage supply in a one-bit-memory, the logic signal of which can be detected by the microprocessor and used for the further control of the program flow is known from the US periodical - IBM Technical Disclosure, Bulletin, Vol. 33, No. 12, May 1991, pages 309 to 311.

The invention thus seeks to provide a circuit which recognises and stores a disconnection of the battery. This function must be available even when the control unit is switched off, in which case upon a system start, for example when the engine is restarted, the temporary disconnection of the battery that took place previously can be recognised and processed accordingly by the software. Furthermore, this circuit must have only a low current consumption when the control unit is inactive. High current consumptions, such as those which occurred when RAMs were used, are no longer acceptable to the users of such control units.

According to the invention there is provided a control unit for petrol engines and diesel engines, having: a central microprocessor; a voltage regulator, for supplying the microprocessor with its operating voltage; a battery terminal for feeding the vehicle battery voltage into the voltage regulator; and a memory circuit, which is connected to the battery terminal on the one hand and, on the other hand, is connected to the microprocessor by way of a read-out output and a reset input, the memory circuit being designed as a one-bit memory on the basis of a thyristor function circuit, in such a way that after a temporary disconnection of the vehicle battery voltage, this event can be indicated at the read-out output by a logic signal which can be detected by the microprocessor and used for the further control of the program flow, and the read-out output of the memory circuit can be logically reset by a reset signal of the microprocessor via the reset input.

Thus a disconnection of the battery is recognised by the interrogation of the read-out output of the memory circuit by the microprocessor, which interrogation is controlled by software, and is made available to the microprocessor as a one-bit-wide item of information after the system run-up. As a result of implementation in the control software of the microprocessor, all further erasing processes, and possibly additionally provided measures, can be carried out independently of the hardware once this item of information has been recognised. Data which must not be erased, for example because of statutory exhaust-gas regulations, can thereby be excluded from an erasing and therefore remains securely stored, because the erasing process is not triggered by the hardware.

As becomes even more clear from the description of the exemplary embodiment, by the term thyristor function circuit" is meant a circuit which has thyristor-like characteristics, i.e. is to be triggered by voltage pulses and turned off by interruption of the voltage supply. As a result of this triggering and turning off, corresponding logic states can be generated at the read-out output, i.e. a logic signal "high" (= high level), for example, which can be logically reset via the reset input, i.e. converted into "low" (= low level).

In accordance with a preferred development of the control unit, the memory circuit is provided with a buffer stage for the electrical isolation between readout output and thyristor function circuit. As a result of this, the current consumption of the memory circuit is very low, something which makes itself positively noticeable particularly when the control unit is switched off (for instance in the state "engine off").

The thyristor function circuit is preferably formed by two bipolar transistors connected back to back. The buffer stage can be formed by a MOSFET transistor.

For a better understanding of the present invention, and to show how it may be brought into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a heavily schematised block diagram of a control unit; and Figure 2 shows a connection diagram of the memory circuit of the control unit.

As is clear from Figure 1, the basic components of the control unit 1 are a central microprocessor 2 which, in the usual way, has at least one central processor, a main memory, a program memory, a data memory and corresponding interfaces to the peripherals.

Provided for the power supply of the microprocessor is a voltage regulator 3, the input side of which is coupled to the vehicle battery voltage VB. On the output side, for example, the voltage regulator 3 has at its disposal 5 V, which is currently standard for the value of the operating voltage for microprocessors.

Connected to the battery terminal 4 of the control unit 1 is now a memory circuit, the whole of which is denoted with 5. This has a read-out output 6 and a reset input 7, by way of which output and input the memory circuit 5 is connected to the microprocessor 2.

As also becomes clear in the following from the explanation of the connection diagram according to Figure 2, the memory circuit 5 is designed as a one-bit memory on the basis of a thyristor function circuit, in such a way that after a temporary disconnection of the battery voltage VB from the battery terminal 4, this event is indicated at the read-out output 6, for example by a logic signal "high". This in turn can be detected by the microprocessor 2 and used for the further control of the program flow. In the case of this control of the program flow, the detection of a disconnection event is then, for instance, manifested in the erasing of certain memory contents in the data memory of the microprocessor 2. Furthermore, the software execution routine in the microprocessor provides that after the engine has been switched off, and thus after the control unit 1 has been deactivated, a reset signal is transmitted by the microprocessor 2 to the reset input 7 of the memory circuit 5, so that the read-out output 6 is logically reset again. In this way, a recent disconnection of the battery terminal 4 from the vehicle battery voltage VB can be detected and logically indicated.

The structure and function of the memory circuit 5 can be explained with the aid of Figure 2. Thus, the vehicle battery voltage VB is fed in by way of the battery terminal 4 between a pair of oppositely connected diodes D1, D2, which protect against a polarity reversal. By way of an R-C element which comprises the resistor R7 and capacitor C2, the vehicle battery voltage VB is passed on to the actual heart of the memory circuit 5, namely to the thyristor function circuit which comprises the two bipolar transistors T1, T2. As is clear from Figure 2, the two transistors T1, T2 are connected back to back, the emitter terminal 8 of the input-side bipolar transistor T1 being connected to the vehicle battery voltage VB. Furthermore, the base terminal 9 is also connected to the battery terminal 4 by way of a resistor R4; the base-emittersection of the bipolar transistor T1 and the resistor R4 are therefore parallel. The base terminal 9 is furthermore connected to the collector terminal 10 of the output-side bipolar transistor T2. The base terminal 11 of the latter is connected to the centre tap 12 of a voltage divider R2, R3, which in turn is connected to the collector terminal 13 of the inputside transistor T1. Finally, the emitter terminal 14 is connected to the gate terminal 15 of a MOSFET transistor T3, which serves as a buffer stage. The input voltage of the gate terminal 15 is restricted by way of a Zener diode D3 having a parallel resistor R5.

The drain terminal 16 forms the read-out output 6 of the memory circuit 5, which output 6 is connected to an appropriate input of the microprocessor 2.

Furthermore, the operating voltage VCC from the voltage regulator 3 is made available to the drain terminal 16 by way of a corresponding resistor R6.

The thyristor function circuit which comprises the two transistors T1, T2 furthermore has a reset input 7, which is driven by the microprocessor 2. The reset input 7 is connected to the centre tap 12 of the voltage divider R2, R3 by way of an R-C element R1, C1 and a pair of protective diodes D4, D5. The reset function which can be realised in this way becomes clear from the following description of the manner of operation of the whole memory circuit 5: The starting point is the situation in which the engine has been switched off and the control unit 1 is therefore inactive. If the vehicle battery voltage VB is now disconnected, the whole arrangement is currentless and voltageless. After the reconnection of the voltage VB, the same voltage prevails at the emitter terminal 8 and base terminal 9 of the transistor T1, and the transistor T1 is therefore blocked. This means that the base terminal 11 of the transistor T2 that is connected to the collector terminal 13 of the transistor T1 is at a low level, and the transistor T2 is therefore blocked. This in turn means that the gate terminal 15 of the MOSFET transistor T3 is likewise at a low level and is blocked. As a result of this, the operating voltage VCC at the read-out output 6 is fully available, something which is defined as a logic signal "high".

When the engine is switched on again, i.e. when the control unit 1 is activated, the microprocessor 2 is controlled by software in such a way that the readout output 6 of the memory circuit 5 is interrogated.

By means of the logic signal "high", the microprocessor 2 is informed that a disconnection of the battery has taken place. Consequently, the corresponding fault memories and other permissible data in the microprocessor 2 are then erased in a manner controlled by the software.

During the operation of the control unit, i.e. while the engine is running, the event of a battery disconnection is naturally not important. The event does not have to be enquired about anew until after the engine has been switched off. In order to ensure this, the control program of the microprocessor 2 is designed in such a way that after each switching off, a voltage pulse goes from the microprocessor 2 to the reset input 7. The base terminal 11 is thus at a high level and the bipolar transistor T2 is conductive. As a result of this, a current flows through the resistor R4, which current in turn puts the bipolar transistor T1 into a conductive state. As a result of this, the second bipolar transistor T2 stays in a conductive state, although there is no more voltage across the reset input 7. In all, both transistors T1, T2 therefore remain conductive and in the sense of a thyristor function circuit are therefore "triggered".

This in turn results in the gate terminal 15 being at a high level and the section between drain terminal 16 and source terminal 17 becoming conductive. In this way, the read-out output 6 goes to logic "low" and remains there, provided that the vehicle battery VB is not disconnected and the operational sequence that is linked with this and described above does not commence.

Upon reactivation of the control unit 1, the microprocessor 2 recognises a logic signal "low" at the read-out output 6, which means that a disconnection of the battery did not take place.

Claims

Claim

1. A control unit for petrol engines and diesel engines, having: a central microprocessor; a voltage regulator, for supplying the microprocessor with its operating voltage; a battery terminal for feeding the vehicle battery voltage into the voltage regulator; and a memory circuit, which is connected to the battery terminal on the one hand and, on the other hand, is connected to the microprocessor by way of a read-out output and a reset input, the memory circuit being designed as a one-bit memory on the basis of a thyristor function circuit, in such a way that after a temporary disconnection of the vehicle battery voltage, this event can be indicated at the read-out output by a logic signal which can be detected by the microprocessor and used for the further control of the program flow, and the read-out output of the memory circuit can be logically reset by a reset signal of the microprocessor via the reset input.

2. Control unit according to claim 1, wherein the memory circuit is provided with a buffer stage for the electrical isolation between read-out output and thyristor function circuit.

3. Control unit according to claim 1 or 2, wherein the thyristor function circuit is formed by two bipolar transistors connected back to back.

4. Control unit according to claim 3, wherein the emitter terminal and the base terminal of the inputside bipolar transistor are connected to the vehicle battery voltage, and the base terminal of the said bipdlar transistor is connected to the collector terminal of the second bipolar transistor.

5. Control unit according to claim 4, wherein the base terminal of the output-side bipolar transistor is connected to the reset input and the collector terminal of the first bipolar transistor, and the emitter terminal of the said bipolar transistor is connected to the buffer stage.

6. Control unit according to one of the claims 1 to 5, wherein the buffer stage is formed by a MOSFET transistor, the gate terminal of which is connected to the output of the thyristor function circuit.

7. A control unit substantially as herein described, with reference to the accompanying drawings.

8. A motor vehicle including a control unit as claimed in any preceding claim.