GB2032543A

GB2032543A - An electronic circuit device for the actuation of an overdrive

Info

Publication number: GB2032543A
Application number: GB7933759A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1978-09-29
Filing date: 1979-09-28
Publication date: 1980-05-08
Also published as: SE7908064L; DE2842390A1; GB2032543B; SE445102B

Abstract

An electronic circuit arrangement (20) for the actuation of an overdrive (23) in a change speed gear (22) of a motor vehicle driven by a combustion engine (21) is proposed in which the overdrive is automatically switched in or out in accordance with different predetermined threshold values of the inlet manifold negative pressure ( DELTA P). To avoid operation at low revolutions or over revving of the combustion engine, engine speed nM or vehicle speed limiting values are provided which produce a switching pattern for the switching over of the overdrive (23) by means of a logic gating circuit (33, 34, 35). Finally, it is guaranteed that the overdrive (23) can only be switched in when fourth gear is engaged. <IMAGE>

Description

SPECIFICATION An electronic switching device for the actuation of an overdrive The invention originates from a switching device according to the type set forth in the main claim.

With motor vehicles comprising change speed drives it is known to provide, in addition to the usual speeds, a fast speed (overdrive) which has a particularly low transmission ratio and permits the retention of medium speeds of the combustion engine at high vehicle speeds. Wear on the combustion engine is reduced thereby and the fuel consumption falls. As a result of the lower transmission ratio when the overdrive is switched in the maximum power available at the particular speed is also certainly reduced so that with an increased power requirement, for example, during overtaking or on long hills, the drive must be changed down.

An overdrive is normally actuated by the driver by an additional switch in the gear lever whereby, by means of a contact in the drive, it is guaranteed that the overdrive can only be switched in when the highest speed has been previously selected.

From the periodical "Automotive Engineer" April-May 1978 page 92, a control device for the actuation of an overdrive in an automatic change speed gear is known in which the overdrive is switched in, in accordance with the inlet manifold negative pressure and is again switched out above a predetermined throttle valve opening or displacement of the accelerator pedal.

Furthermore, a speed switch is provided which prevents the switching in of the overdrive below a predetermined vehicle speed. Controlling the disengagement of the overdrive by the displacement of the accelerator pedal has the disadvantage, however, that the accelerator pedal always has to be depressed very considerably although, especially at low and medium speeds, this scarcely produces an increase in power whereas it produces a considerable increase in fuel consumption. On the other hand, if the threshold of the accelerator pedal displacement for disengaging the overdrive is arranged at a low value this can lead to hunting in the changed speed drive at high speeds because the two switching thresholds then lie very close to one another over this range of the family of characteristic engine curves.Furthermore, hunting can likewise occur with small fluctuations about the threshold value in the neighbourhood of the permissible lowest speed. Finally, the known apparatus has no means to prevent an overrunning of the motor on disengagement of the overdrive and high vehicle speeds.

Advantages of the invention As opposed to this, the switching apparatus in accordance with the invention comprising the characterising features of the main claim has the advantage of guaranteeing an adequate switching hysteresis between a limit value of the inlet manifold negative pressure causing a changeover and the engine speed or vehicle speed. In addition, the ratios at the upper and lower limits of the operating ranges of the combustion engine are taken into consideration in such a manner that a standard pattern is provided by which travelling at low revolutions during switching in of the overdrive and with it a drop in engine speed and on the other hand and an overrunning of the combustion engine during disengagement of the overdrive and with it an increasing engine speed is prevented.Finally, a change in the switching pattern is possible by adjusting the limit speed (saving programme). In this manner, the driver of the motor vehicle can adjust the changeover requirements of the overdrive correspondingly according as to whether an economical or a sporty mode of travel is desired.

Drawings Embodiments of the invention are illustrated in a drawing and are described in more detail in the following specification.

Figure 1 shows a family of engine curves; Figure 2 is a block diagram of a first embodiment of a switching apparatus in accordance with the invention; Figure 3 is a block diagram of a second embodiment of a switching apparatus in accordance with the invention; Figure 4 shows a first switching pattern (saving programme); Figure 5 shqws a second switching pattern (power programme); Figure 6 is the circuit diagram of a first embodiment of a threshold value switch provided with a variable response threshold; Figure 7 is the circuit diagram of a second embodiment of a threshold value switch provided with a variable response threshold; Figure 8 is the circuit diagram of a third embodiment of a threshold value switch provided with a variable response threshold.

Description of the embodiments The family of engine curves 10 of a combustion engine is illustrate in Figure 1. The curve of maximum power in fourth gear and the fourth gear is overdrive are inference 11 and 1 Ia respectively.

in a corresponding manner, 12 and 1 2a respectively characterise first curves of constant inlet manifold negative pressure A P1 for the fourth gear or the fourth gear with overdrive respectively, 13 or 1 3a respectively characterise second curves of a higher constant inlet manifold negative pressure A P2. In this connection, the difference between inlet manifold pressure Ps and atmospheric pressure P0 is understood as a constant inlet manifold negative pressure A P.

Finally, the curves for optimal fuel consumption of the combustion engine are referenced with 14 and 1 4a. As is readily apparent from Figure 1, the curves of constant inlet manifold negative pressure 12, 1 2a; 13, 1 3a have a similar shape and similar behaviour as the curves for optimal fuel consumption 14, 1 4a. The operating parameter: inlet manifold negative pressure AP is therefore a preferable criterion for the actuation of a change speed gear with a fuel saving mode of travel.

Accordingly, the invention seeks to detect the inlet manifold negative pressure A P, to compare established limit values in a preferred manner and to effect a gear change when these limit values are exceeded especially the engagement or disengagement respectively of an overdrive.

If, for example, the motor vehicle is at first operating point 1 5 with the overdrive disengaged and the accelerator pedal is released, the inlet manifold negative pressure A P is increased. On reaching an upper value of the inlet manifold negative pressure A P2 corresponding to the second operating points 16, the overdrive is switched in. Since the throttle pedal position and the vehicle's speed remain constant, the inlet manifold negative pressure is again somewhat increased due to the switching in of the overdrive.

With the provision of a fixed inlet manifold negative pressure threshold, this would mean that the overdrive would be disengaged once again immediately thereafter. However, in accordance with the invention, a lower inlet manifold negative pressure A P1 is established as a switching out threshold so that the overdrive is only disengaged once again with a fresh actuation of the accelerator pedal and with it an increase in power and attainment of a value A P1 corresponding to the third operating point 1 7.

In order to prevent operation of the combustion engine at the low revolutions during low engine speeds and engagement of the overdrive and on the other hand to prevent an overrunning of the combustion engine at high engine speeds and with the overdrive disengaged, it is necessary to limit the changeover characteristics to the limits of the operating range of the combustion engine.

An electronic switching device 20, for example, is suitable for this purpose as is illustrated in Figure 2. The electronic switching device 20 is associated with a motor vehicle drive, consisting of a combustion engine 21 a transmission 22, an overdrive 23 in series with the transmission and an output 24. The transmission 22 has a transmission switching contact 220 which when the highest gear is selected, generates a positive logic signal. The overdrive 23 is controlled through a control import 230 through which engagement of the overdrive 23 can be effected by the application of a positive signal.

In addition to operating parameters, a signal from the combustion engine 21 corresponding to the engine speed nM, is fed to the electronic switching device 20, for example derived from the ignition coil, as well as signals corresponding to the inlet manifold pressure Ps and to atmospheric pressure P0 supplied through terminals 25 and 26 respectively. The pressure signals arrive at a summing point 27 to the output from which is applied the inlet manifold negative pressure signal A P which is fed to a first convertor 28 at the output from which appears a DC voltage proportional to the inlet manifold negative pressure A P. However, it is obviously also possible to generate the inlet manifold negative pressure signal A P in a mechanical manner.For this purpose, normal commercial negative pressure sensors can be used for example, in which the pressures PS and PO are on both sides of a diaphragm the deflection of which is converted into a voltage. In a similar manner a voltage proportional to the engine speed is produced in a second convertor 29 from the engine speed signal nM the signal proportional to the inlet manifold negative pressure A P arrives at a first threshold value switch 30, the signal proportional to the engine speed nM arrives at a second threshold value switch 31 as well as a third threshold value switch 31 as well as a third threshold value switch 32.The threshold value switches 30, 31,32 can be switched in accordance with their response thresholds, their control inputs being arranged in parallel with the control input 230 to the overdrive 23 for this purpose. The outputs from the first threshold value switch 30 and from the second threshold value switch 31 are fed to a first AND gate 33 the output from which is connected to one input to a first OR gate 34. The third threshold value switch 32 is connected to the second input to the first OR gate 34 its output is connected to one input to a second AND gate 35 the further input to which is connected to the transmission switching contact 220.The output from the second AND gate 35 is connected through a delay member 36 to an amplifier 37 the output from which is finally connected to the control input 230 for the overdrive 23 and two the control inputs to the threshold value switches 30, 31, 32 previously referred to. Beyond this, the third threshold value switch 32 also has a further control input which can be controlled by means of a programme switch 38. A control of this further control input to the third threshold value switch 32 operates so that the two values of the response thresholds are displaced as regards their value by a particular fraction.

The method of operation of the circuits illustrated in Figure 2 is as follows: In order to engage the overdrive 23, a positive signal is necessary at its control input 230 which is determined by the series logic circuit in accordance with certain operating conditions. The values of the inlet manifold negative pressure A P1, A P2 are established in the first threshold value switch 30 and which are derived from the family of engine curves 10 according to Figure 1 in such a manner that the combustion engine 21 is, as much as possible, always operated in the neighbourhood of the curves for optimal fuel consumption 1 4, 1 4a. With the overdrive 23 disengaged, the response threshold of the first threshold value switch 30 is A P2 with the overdrive 23 engaged it is A P,. In a corresponding manner, engine speed threshold values N1, N2 relating respectively to an engaged and disengaged overdrive 23, are established in the second threshold value switch 31. The logic connection through the first AND gate 33 is effected so that a switching procedure, for example with the overdrive 23 disengaged, can only take place if the inlet manifold negative pressure A P2 and the engine speed N2 are exceeded simultaneously. The speed threshold values N1, N2 lie at the lower operating range of the combustion engine 21. The speed threshold values N3, N4, which are added to the signal flow through the first OR gate 34, lie in the upper operating range of the combustion engine 21. The logic gating of the gates 33, 34 acts so that below a certain minimum speed the overdrive 23 cannot be engaged and must be engaged above a certain highest speed.The additional requirement that the overdrive 23 can be engaged only when fourth gear is engaged, is provided by the second AND gate 35. Since the switching conditions referred to above are generally met when the accelerator pedal has not yet been actuated shortly after engaging the fourth gear, it is necessary, in this case, to prevent an immediate engagement of the overdrive 23 in order to prevent an all too frequent to-and-fro switching. For this purpose, the timing member 36 is provided which operates so that the overdrive 23 is only switched in when the operating parameter configuration determined by the previous logic gating as existed for a predetermined period.

Finally, it is possible to change over the speed threshold valuers N3, N4 as regard their value by a predetermined percentage through the programme switch 38. As is further explained below, the switching procedure for the overdrive 23 at high speeds can, in this way, be provided in the sense of a programme selection: Power programme-fuel saving programme.

Figure 3 shows the circuit diagram of a variant of the electronic switching device illustrated in Figure 2. Moreover, a signal proportional to the vehicle's speed v, is evaluated instead of the engine speed signal NM. This is derived from the output shaft through a tachometer generator 40 and is converted by a third converter 41 in known manner into a vehicle speed proportional voltage.

This voltage arrives at a fourth threshold value switch 42 and a fifth threshold value switch 43 in which vehicle speed-threshold values v1, v2, v3, v4 are established. Moreover, the fifth threshold value switch 43 has an additional control input through which the threshold value-pair of values can be transposed. For the rest, the method of operation of the electronic switching device inserted in Figure 3 corresponds to that of Figure 2.

A first switching pattern 50 is illustrated in Figure 4, such as can be achieved with one of the arrangements according to Figure 2 or 3. A first range 51 with the overdrive disengaged, a second range 52 with the overdrive engaged and an intermediate neutral range 53 can be produced by the logic 1 8 of the inlet manifold negative pressure values and of the respective engine speeds and vehicle speeds.This means that, in the ranges 51, 52, the overdrive is always engaged or disengaged, whereas, in the neutral range 53, it remains in the switching position which was associated with the operating point for the combustion engine 21 when leaving one of the two ranges 51, 52. As can be seen quite clearly, engagement of the overdrive below the speed threshold value n, and disengagement of the overdrive above the speed threshold value n4 is no longer possible. Moreover, the speed-threshold value n4 is so designed that an operation takes place with the highest possible saving in fuel.

By transposing the pair of values n3, n4to values'3, n'4 by means of the programme switch 38, a second switching pattern 60 can be produced as is illustrated in Figure 5. In this manner, a third range 61 exists with the overdrive disengaged and a fourth range 62 with the overdrive engaged including an intermediate neutral range 63. Thereby, the upper most speedthreshold value nt4 is arranged in the vicinity of the maximum permissible speed for the combustion engine 21.As can be seen from the second switching pattern 60, the vehicle with the overdrive disengaged can be operated, in this case, up to the limit of the permissible engine speed whereas, with the first switching pattern 50 according to Figure 4, that was not possible since, on reaching the speed threshold value n4, the overdrive 23 would be automatically switched in.

Thus, the first switching pattern 50 according to Figure 4 represents a "saving programme", the second switching pattern 60 according to Figure 5 represents a "power programme". The driver of the vehicle can then select whether he desires a former fuel saving or sporty mode of travel by means of the programme switch 38.

Figure 6 shows the circuit diagram of a first embodiment of a change-over threshold value switch as can be used, for example, for the threshold value switches 30, 31, 32, 42, 43. For example, a speed signal n from an input terminal 70 is thread in parallel to the inputs to a sixth threshold value switch 71 and a seventh threshold value switch 72 one of which has a fixed high speed threshold value n2 and the other of which has a lower fixed speed threshold value n,. The output from the sixth threshold value switch 71 is fed to the first input to a second OR gate 73, the output from the seventh threshold value switch 72 is connected through a third AND gate 74 to its second input.The output from the second OR gate 73 is connected to the output terminal 76, the second input to the third AND gate 74 can be supplied with the switching signal S through a terminal 75. if the change over signal S equals 0, the third AND gate 74 is blocked and the response threshold of the entire arrangement is produced from the response threshold of the sixth threshold value switch 71. However, if a change over signal S is present, the threshold value of the entire arrangement is determined by the lower response threshold of the seventh threshold value switch 72. Figure 7 shows the circuit diagram of a second embodiment of a threshold value switch which can be changed over. Herein, an operational amplifier 80 is connected at its non-inverting input to the speed signal n or to the inlet manifold negative pressure signal A P to a terminal 81.The inverting input to the operational amplifier 80 is connected to the centre cap of a voltage divider 83, 84 which is connected between the supply voltage and earth by means of a terminal 82. The portion of the voltage divider at the earth end is connected in parallel with the series circuit comprising a resistor 85 and a transistor 86 wherein the transistor 86 is controlled through a resistor 87 and a terminal 88 to which the switching signal S can be applied. The output from the operational amplifier 80 is connected to the input terminal 89. If the switching signal S is zero, the transistor 86 is blocked and the response threshold of the operational amplifier 80 serving as a threshold value switch is determined by the voltage divider ratio 83/84.However, if a positive switching signal S is present the transistor 86 is made conductive and the response threshold is then determined by the ratio between the resistor 83 on the one hand and the parallel circuit of the resistors 84, 85 on the other hand.

Finally, Figure 8 shows the circuit diagram of a third embodiment of a threshold value switch which can be changed over. With this embodiment, the inlet manifold negative pressure signal A P is fed through a terminal 90 to an eighth threshold value switch 91 as well as to a ninth threshold value switch 92 wherein the eighth threshold value switch 91 once again has a higher response threshold than has the ninth threshold value switch 92. The threshold value switches 91, 92 actuate switches 93, 94 through which a reference voltage is switched to the output terminal 97 through a terminal 95 or the switching signal S is switched, through a terminal 96, to the output terminal 97 from which a resistor 98 is connected to earth. A diode 99 is connected in the supply line from the terminal 96 to the terminal 97.With this arrangement, the switch 94 is closed on reaching the lower response threshold and, insofar as a switching signal S is applied to the terminal 96, the latter is conducted to the output. If no switching S prevails, closure of the switch 94 produces no results. In this case, the switch 93 is only closed on reaching the higher response threshold and the reference voltage arrives from the terminal 95 at the output terminal 97. As has already been expressly stated above, the threshold value switches 91,92 can obviously also be constructed as purely mechanical negative pressure sensors to which the pressures P6 P0 are applied. Since, in this case, no conversion of the inlet manifold negative pressure signal A P into an electrical voltages takes place, the first converter 28 is omitted when using such mechanical negative pressure sensors.

Claims

1. An electronic circuit arrangement for the actuation of an overdrive in a change speed gear of a motor vehicle driven by a combustion engine comprising switching means for detecting the inlet manifold negative pressure, characterised in that, the signal proportional to the inlet manifold negative pressure (A P) is applied to a first threshold value switch which is in operative first communication with a control input to the overdrive wherein the response threshold of the first threshold value switch can be changed over in accordance with the switched condition of the overdrive.

2. The circuit arrangement according to claim 1 characterised in that the response threshold of the first threshold responsive switch with the overdrive engaged is adjustable to a lower value (h P,) and with the overdrive disengaged is adjustable to a higher value (A P2).

3. A circuit arrangement according to claim 1 or 2 characterised in that between the first threshold value switch and the control input to the overdrive there is connected a first AND gate the further input of which is connected to a second threshold value switch influenced by an engine speed signal (nm) and the response threshold of which lies in the lower operating range of the combustion engine and with the overdrive engaged can be adjusted to a lower value (nm) and with the overdrive disengaged can be adjusted to a higher value (n2).

4. A circuit arrangement according to claim 1 or 2 characterised in that between the first threshold value switch and the control input to the overdrive there is connected a first AND gate the further input to which is connected to a fourth threshold value switch influenced by a vehicle speed signal (Fv) and the response threshold of which is adjustable to a lower value (v1) with the overdrive engaged and is adjustable to a higher value (v2) with the overdrive disengaged.

5. A circuit arrangement according to claims 1 to 3 characterised in that, furthermore, between the first AND gate and the control input to the overdrive there is connected a first OR gate the further input to which is connected to a third threshold value switch influenced by the engine speed signal (nM) and the response threshold of which lies in the upper operating range of the combustion engine and is adjustable to a lower value (n3) with the overdrive engaged and is adjustable to a higher'value (n4) with the overdrive disengaged.

6. A circuit arrangement according to one of claims 1,2 and 4 characterised in that, furthermore, between the first AND gate and the control input to the overdrive there is connected a first OR gate the further input to which is connected to a fifth threshold value switch influenced by the vehicle speed signal (v and the response threshold of which is adjustable to a lower value (V3) with the overdrive engaged and is adjustable to a higher value (V4) with the overdrive disengaged.

7. A circuit arrangement according to one of the preceding claims characterised in that between the first OR gate and the control input to the overdrive there is connected a second AND gate the further input to which is connected to a transmission switching contact.

8. A circuit arrangement according to claim 7 characterised in that a delay member is connected upstream of the control input.

9. A switching circuit according to one of claims 5 to 8 characterised in that the pairs of values for the response threshold (n3, n4; v3, v4) of the threshold value switch are transposable (n'3 n'4; v'3, v'4) by means of a programme switch.

10. A circuit arrangement according to one of claims 2 to 9 characterised in that the threshold value switches which can be switched over are formed as two threshold values switches connected in parallel on the input side and having fixed but different switching thresholds, wherein the output from one of the threshold value switches is fed directly to one input to a second OR gate and the output from the other threshold value switch is fed through a third AND gate which is controllable on the other hand by the signal (S) deviating from the threshold value.

11. A circuit arrangement according to one of claims 2 to 9, characterised in that the threshold value switches which can be switched over are formed as operational amplifiers one input to which is connected to the centre cap of a voltage divider arranged between two operating voltages wherein the resistor of one voltage divider element can be changed over in accordance with the signal (S) changing over the response threshold.

1 2. A circuit arrangement according to one of claims 2 to 9 characterised in that the first threshold value switch has two threshold value switches with different switching thresholds formed as negative pressure sensors and which act on switches by means of which a reference voltage (uO) or a signal (S) switching over the response thresholds is switchable to the output from the first threshold value switch.

13. An electronic circuit arrangement for the actuation of an overdrive in a change speed gear of a motor vehicle driven by a combustion engine characterised by first switching means for generating logic signals on attaining a first inlet manifold negative pressure value (h P1) with the overdrive engaged and a second inlet manifold negative pressure value (d P2) with the overdrive disengaged; second switching means for generating logic signals on attaining a first engine speed value (n,) with the overdrive engaged and a second engine speed value (n2) with the overdrive disengaged third switching means for generating logic signal on attaining a third engine speed value (n3) with the overdrive engaged and a fourth engine speed value (n4) with the overdrive disengaged; fourth switching means for generating a logic signal with the highest gear of the change speed gear engaged (49); a logic gating circuit the output signal (A) from which with the overdrive disengaged fulfills the condition: A = 4.G.An4V4.G AdP2 A n2 and the overdrive engaged fulfils the condition: A = 4.G. An3 v 4.G. A AP1 An1 and a delay member connected between the output from the logic gating circuit and the control input to the overdrive.

14. An electronic circuit arrangement for the actuation of an overdrive in a change speed gear of a motor vehicle driven by a combustion engine characterised by first switching means for generating logic signals on attaining a first inlet manifold negative pressure value (d P1) with the overdrive engaged and a second inlet manifold negative pressure value (S P2) with the overdrive disengaged; second switching means for generating logic signals on attaining a first vehicle speed valve (v1) with the overdrive engaged and a second vehicle speed value (V2) with the overdrive disengaged, third switching means for generating logic signals on attaining a third vehicle speed value (V3) with the overdrive engaged and a fourth vehicle speed value (V4) with the overdrive disengaged; fourth switching means for generating a logic signal with the highest gear engaged (4th G); a logic gating circuit the output signal (A) from which will the overdrive disengaged fulfills the condition.

A = 4.G.An4V4.G.AP2An2 and with the overdrive engaged fulfills the condition A = 4.G.An3V4.G.AAP1An1 and a delay member connected between the output from the logic gating circuit and the control input to the overdrive.