BRAKE STOP LIGHT CIRCUITRY FOR A VEHICLE HAVING ELECTRONIC DIESEL CONTROL

Abstract: A brake light switch circuitry has an additional switch (S2) which opens upon actuation of the brake pedal (13) but only after the first switch (S1) closes. The signals from the two switches are processed by gating circuitry (16, 17, 18) to produce brake signals (BS1 and BS2) which are used respectively to provide a stand-by idle-running or idle-setting signal (LL<*>) and to switch off constant vehicle velocity control (FGR) by the main computer (30) of the EDC. It is thereby prevented that, in the event of the brake switch (S1) becoming faulty and remaining closed during an overtaking maneuvre, the EDC does not reduce the injected fuel quantity to the idling quantity, even though the accelerator pedal is depressed. It is also prevented that, in the event of a fault in the brake switch (S1), while the accelerator pedal is released, constant vehicle velocity control by the EDC is not switched off.

Description: DESCRIPTION BRAKE STOP LIGHT CIRCUITRY FDR A VEHICLE HAVING ELECTRONIC DIESEL CONTROL State of the Art The present invention relates to a brake stop light circuitry for a vehicle fitted with a diesel engine having electronic diesel control (EDC), in accordance with the pre-chara ter z ng clause of claim 1. As described in DE-A-3531198 , the brake light signal, that is to say, the switching on off the brake lights upon depression of the brake pedal, is processed in the safety system as an additional or stand-by sional indicating idling control, i.e. reduction of the injected fuel quantity to the dling quantity for the purpose of using the engine as a brake. In the event of a fault such that an idle running signal FFR-LL is not produced when the accelerator pedal is completely released, a too-large an injected fuel quantity can be switched off by actuating the brakes. However, this brings with it the danger that, in the event of the brake light switch being defective in that t remains closed, it can lead to a reduction of the injected fuel quantity in critical driving situations, e.g. during overtaki.ng. Also, upon actuation of the brakes and operation of the diagnosis sw tch of the fault memory in the EDC, fault diagnosis and removal of the fault become more d fficult. Advantages of the invention The above disadvantages can be avoided in a brake stop light circuitry havin the features of the charact¬ erizing clause of claim 1. This has the advantage that it is possible to monitor the brake signal. A particularly simple circuit is obtained by adopting the features of claim 2. In the case of a vehicle whose EDC has provision for the vehi le to be driven automatically at constant velocity, irrespective of the position of the accelerator pedal, also as described in the above-mentioned DE-A-3531198 the velocity control (FGR) is switched off upon actuation of the brake pedal. However, should the brake light switch be defective in that it does not close, the FGR does not react, which can frighten the driver and lead to a critical situation. This disadvantage is avoided by adopting the features of claim 3. There may be occasions when both the accelerator and brake pedals are depressed simultaneously, and faulty operation of the safety system under such circumstances can be avoided by adopting the features of claims 4 and 5. Drawing The invention is further described, by way of example, with reference to the accompanying drawing, which is a circuit diagram of a brake light circuitry for a vehicle having EDC and of related parts of the EDC. Descr .ption of the preferred embodi ent The usual brake lights 10 are connected between one pole 11 of a brake light switch S, and earth, the other pole 12 of the switch S, being connected to a battery terminal U p . The pole 12 is also connected to a terminal 45 of the EDC, of which only a few components, including a main computer 3D, are shown in the drawing. Other details of the EDC can be obtained from the above-mentioned DE-A-353119C. Suffice it to say, the main computer 30 receives various input variables (not all shown) and delivers various output variables (not all shown). One input variable is the position of the accelerator pedal. A pedal position transducer is connected to a terminal 35 and thereby delivers a pedal position signal FFG to the main computer 30. Included in the signal FFG is a distinct signal FFG-LL indicating that the accelerator pedal is completely released, i.e. in the idling position. The main computer 30 receives an engine speed signal n and a brake signal B ς7 , the latter indicating that the brakes are operated. The main computer 30 delivers a desired value signal RW ,, indicating the desired injected fuel quantity, that is to say, the desired delivery setting of t e injection pump (not shown). The main computer 30 also delivers a signal FGRein, indicative that velo ity control is in operation. In accordance with the invention, the brake stop light circuitry further comprises a second sw t h S„ which s independent of the brake lights 10 and which is shown as being connected between earth and a separate terminal 45a of the EDC. Whereas the switch S, is normally open and is closed upon depression of the brake pedal 13, the second switch S_ is shown as being normally closed and is opened upon depression of the brake pedal 16 Furthermore, to avoid ambiguity, it s ensured thai the pedal travel required to open the s tch S ? is slightly greater than that required to close the s itch S, . The terminal 45 is connected v a a h gh resistance 14 to earth and the terminal 45a s connected v ε. a h gh resistance 15 to the battery terninεl L ) g. Each switch thereby delivers an 0 signal to the respect ve terminal when the brake pedal is released and a 1 signal when the brake pedal is operated. Ho ever, hen the brakes are very lightly operated, the switches S, and S„ could deliver respectively a 1 signal and an 0 signal. The various possibilities for normal operation and the occurrence of faults can be tabulated as follows:- Switch State Indications Consequences S l 5 2 0 0 Brakes not operated FGR possible No safety operation. 0 1 Fault in brake FGR not possible light circuit No safety operation (Transient state FGR not possible possible) See No safety operation. below for fault indication. Brakes operated FGR not possible Safety operation if FFG>0 To achieve the above operation, the terminals 45,45a are connected to gating circuitry as follows:- Both terminals are connected to non-invertory inputs of an AND gate 16 whose output brake signal B,-., is applied to further gating circuitry 46 where it is combined with the signal FGRein from the main computer 30 and the signal FFG-LL from the accelerator pedal transducer to produce the stand-by idle-running signal LL*. The terminal 45 is also connected to inverting and non-inverting inputs, respectively, of AND gates 17,18 and the terminal 45a to non-inverting and inverting inputs respectively, of the AND gates 17, 18. In addition, the outputs of the AND gate 16,17 are connected directly to an OR gate 19 and the output of the AND gate 18 is connected via a delay circuit 20 to the OR gate 19. It is possible for the second switch S ? to be connected to the battery voltage U p , instead of to earth. It is also possible for the second switch S2 to be a normally-open switch instead of a normally-closed switch. Such changes would entail alternating of the connections of the resistor 15 and the inputs to the gates 16,17,18. The brake signal B gl and the velocity control "on" signal FGRein are applied to respective inputs of an AND gate 46a to produce a stand-by idle-running signal LL* via an OR gate 47, in the event that the brakes are actuated while the velocity control is switched on. The signals FGRein and FFG-LL are applied respectively to inverting and non-invert ng inputs of an AND gate 46b to produce the idle-running signal LL* via the OR gate 47 in the event of failure of the pedal travel transducer, or at least that part adapted to produce the signal FFG-LL when the pedal is in its fully raised position. These poss bilities 5 and the processing of the stand-by idle-running signal LL* are described more fully in the above-mentioned DE-A-R20192. It can be seen that the brake signals B ς , and B-„ are produced and processed in accordance with the 10 above table. The delay produced by the delay circuit is of the order of 20 seconds which is longer than the period for which there is any likelihood of the brake pedals being held continuously but only lightly depressed. The second condition, S.=0, S =l can only 15 occur when the brake sw tch S, is defective and this can be indicated by the fault diagnosis. The third condition S,=l, S„=0 takes place at least momentarily each time the brake is operated and continues during light braking. It s therefore a permissible condition ~- ~ and is not to be taken as indicating a fault unless it lasts too long, i.e. over 20 seconds. The likelihood of a fault occurring during this 20 second period is remote. If the s itching sequence becomes irregular, both of the second and third conditions can occur. 5 Once the 20 second delay has elapsed, a fault is indicated. A fault is also indicated if the third condition S,=l, S„=0 lasts for more than 20 seconds. The invention can be realized by suitable soft are or hardware. The stand-by signal is also monitored 0 and it is used only during emergency operation of the EDC. The system safety is improved by the invention.

Claims: CLAIM5 1. Brake stop light circuitry for a vehicle fitted with a diesel engine having electronic diesel control, in which a signal is derived from the brake light switch (S.) for producing a back-up idle-running signal (LL*) in the event of failure of an idle- running signal (FFG-LL) from an accelerator pedal transducer, characterized by a second switch (S„) actuated upon operation of the brake pedal (13) and in a circuit independent of the brake lights (10). 2. Brake stop light circuitry according to claim 1, characterized in that the two switches (S-.,S„) are connected to a gating circuit (16) to enable the back-up idle-running signal (LL*) to be produced when neither switch is defective or when the brake light switch ( ^) is defective in that it reπains closed when the brakes are released. 3. Brake stop light circuitry according to claim 2, for a vehicle whose electronic diesel control has provision for vehicle velocity control, in which the brake light s i.tch (S, ) is connected to a main computer (30) of the electronic diesel control for automatically switching off the velocity control upon actuation of the foot brake pedal (13), characterized in that a gating circuit (16,17,18) connects both switches (S, , S„) to the main computer (30) so that the velocity control is switched off upon brake actuation, even if one switch is faulty, yet the velocity control is not switched off in the absence of brake actuation, even if one switch is faulty. 4. Brake stop light circuitry according to claim 3, characterized in that the second switch (S„) is closed when the brake pedal (13) is released and opens upon operation of the brake pedal, but only after the brake light switch (S. ) has closed. 5. Brake stop light circuitry according to claim 4, characterized in that a delay circuit (20) is provided to prevent a fault in the brake light circuit being diagnosed in the event of short period light actuation of the brakes .

Inventors: BERGER JOACHIM, GERSTUNG ULRICH, BERGER, JOACHIM, GERSTUNG, ULRICH
Applicants: BOSCH GMBH ROBERT, ROBERT BOSCH GMBH
Application year: 1988
Main classification: F02D41
IPC codes: B60K31, B60Q1, F02B3, F02D11, F02D29, F02D41, F02D45