GB2271399A

GB2271399A - Control blocking distributor gearbox shift senses speed downstream of clutch

Info

Publication number: GB2271399A
Application number: GB9318949A
Authority: GB
Inventors: Gerhard Josef Fruehwirh
Original assignee: Steyr Daimler Puch AG
Current assignee: Steyr Daimler Puch AG
Priority date: 1992-09-16
Filing date: 1993-09-14
Publication date: 1994-04-13
Anticipated expiration: 2013-09-14
Also published as: FR2695701A1; FR2695701B1; GB2271399B; IT1272607B; ITMI931952A1; AT408971B; DE4230989C2; GB9318949D0; ITMI931952A0; ATA166493A; DE4230989A1

Abstract

An engine (1) drives a motor vehicle by way of a clutch (2), a main gearbox (3) and a synchronized distributor gearbox (6). Shifting into cross-country speed is initiated by operating a preselection switch (31) and the clutch pedal. The control device (25) calculates an advanced shifting point from the rotating speed drop of a transmission input shaft (4) and an anticipated shifting time. By this, shifting is cleared before the rotating speed at which the engine overspeed is reached. This enables an early and easy downshift into cross-country speed. The control device inputs one preferably additionally a speed engaged signal (sS), and an oil temperature signal (sT). There may be a warning lamp (32) and/or an audible warning (33) operating when a change is requested and the speed is low. <IMAGE>

Description

CONTROL DEVICE FOR SHIFTING IN A DISTRIBUTOR GEARBOX The invention relates

to a control device for shifting a distributor gearbox with an input shaft driven by an engine by means of a clutch and a main gearbox and comprising a sleeve with synchronizing means shiftable by means of an actuator, shifting being initiated by preselecting a speed of the distributor gearbox and disengaging the clutch, an actual rotational speed being measured, the actuator being activated and therewith the speed engaged if the actual rotational speed attains a clearing rotational speed and thereafter, the clutch being released.

Such a control device is described in DE-A 38 35 644. It relates to a synchronized distributor gearbox with preselection, shifting between a road speed and a cross-country speed and with a downshift-lock. The latter is linked to an engine overspeed monitor and only allows shifting into crosscountry speed if engine speed is in a predetermined lower range when the clutch is released.

The fact that in control devices according to the state of the art engine speed at the moment of opening the clutch is decisive has the disadvantage that the actual driving state after that moment is not recorded and therefore disregarded. Downshifting into cross-country speed is necessary when tractive resistances increase (by an ascent or by ground conditions) these resistances bringing about deceleration of the ve- hicle when the clutch is disconnected. The driver cannot shift down before the downshift lock has given clearance, i.e. engine speed has attained the predetermined lower range. When the vehicle is in cross- country speed at last, it may have lost much of its speed or may even have stopped entirely. Restarting an immobilized vehicle under such circumstances causes heavy wear of the clutch and may be dangerous. The long duration of shifting due to inertia and the large step between the speeds add to these diffculties.

The object of the invention is thus to improve the aforementioned device with simple means so as to enable the speed range of the engine to be fully exploited with a maximum of safety and service life of the distributor gearbox and it's synchronizing elements in particular.

The object set is achieved according to the invention in that the actual rotational speed is measured downstream of the clutch, and in that the clearing rotational speed'is calculated from the drop of the actual rotational speed during a predefined time interval from an engine rotational speed limit and from a shifting time.

In other words, the deceleration of the vehicle by the various tractive resistances after disengaging the clutch is measured and clearance for shifting is advanced by the amount of the anticipated shifting time.

In this way, clearance for shifting is given before the predetermined lower range of the engine rotary speed or the rotational speed of the output shaft is attained, that is already when the higher clearing rotary speed is attained and synchronization, which due to inertia and the large step between the speeds takes some time, starts. When synchronization is accomplished, rotative speed of the drive train will have been reduced by the tractive resistances to the allowed value. Overspeeding of the engine can only occur after synchronization when the clutch is reengaged. Clearance is not given after a certain time but after the rotating speed of the drive train has diminished to clearing speed. This offers the advantage that clearance is given at the right moment, even if the brakes have been operated in the meantime or if tractive resistances have varied in the meantime.

Preferably the clearing rotational speed is calculated by calculating a rotational speed of the output shaft of the distributor gearbox by dividing the engine rotational speed limit by the transmission ratio between the point of measurement of the rotational speed and the output shaft in the speed to be shifted into, by predicting from the drop of the rotational speed in the interval the time required for the speed to attain the rotational speed of the output shaft, and by determining the clearing rotational speed from the shifting time and the time until the output shaft rotational speed will be reached.

This means in geometrical terms, that the rotative speed curve is extrapolated beyond the measuring interval and intersected with the horizontal line corresponding to the maximum rotative speed of the distributor gear box output shaft in the speed to be shifted into, thus taking into consideration the reduction ratio in the cross-country speed. This is the output shaft rotational speed. Interpolation with the predicted shifting time leads to the clearing rotational speed. By the assumption of a linear development a reliable value is quickly obtained, this value being unadulterated by shorter disturbances.

For reasons of safety it is advantageous that the clearing rotational speed equals the output shaft rotational speed if the measured actual speed increases.

This means that in this state of operation clearance to shift is not advanced. This assures safe shifting into cross-country speed, e.g. in order to increase the effect of engine-braking, even when going downhill and operating the brakes.

Within the context of the invention, measurement of the actual rotational speed can be performed anywhere downstream of the clutch, whereby the gear ratios must be taken account of. In a particularly simple embodyment, actual rotational speed is measured at the input shaft of the main gearbox. Accordingly, the gear ratios of the main gearbox can be disregarded unless shifting in both gearboxes at the same time is considered, and the reduction ratio of the cross-country-speed of the distributor gearbox can be stored forever. If shifting in both gearboxes at the same time is considered, a shifting lever position pick-up and entry of the gear ratios into memory is required or even measuring rotary speeds of the engine and of the distributor gearbox output shaft.

The fact that the ratios of the main gearbox need not be considered nor even known makes the whole shifting process very simple, safe and precise. It offers the further advantage that no modification whatsoever needs to be made on the main gearbox, which often originates from a different supplier, nor does it need to be known at all. Only in the rare cases that no speed pick-up be provided it would need to be fitted.

Shifting time could be a value calculated from masses and dimensions of the accelerated parts or a value measured for a certain combination of main gearbox and distributor gearbox and stored in the memory. But it is much easier to measure and store the actual shifting time and to correct the stored shifting time in dependance of the actual shifting time.

Preferably, correction of the shifting time is performed by weighing the stored shifting time and the measured shifting time and to average the weighed values. Such an algorithm allows the automatic adjustment of shifting time to the drive drain of the individual vehicle and to the wear of the synchronizing elements. This offers an invaluable advantage for mass production: The distributor gearboxes can be manufactured without knowledge of their future application and are simply initiated with a unique value that will adapt to their particular drive train.

If the measured shifting time (tSE) is weighed heavily when the difference between stored shifting time and measured shifting time is positive, and weighed lightly when this difference is negative, adaptation to the vehicle will be fast and adaptation to the slow wear of the syncronizing elements will be undisturbed by stochastic influences.

This means that when the actual shifting time is shorter than forecast the forecast for the next shift will be corrected very quickly. If the new gearbox is initiated with a very short shifting time and the actual shifting time is longer, the forecast shifting time is quickly increased. If the actual shifting time is longer due to slow wear of the synchrnizing elements, the forecast is increased very slowly.

The accuracy of the forecast can be increased by correcting the stored shifting time in dependence of a temperature, preferably the oil temperature of the distributor gearbox.

In a preferred embodyment, first the desired speed of the distributor gearbox is preselected and only then shifting is triggered by releasing the clutch. It is advantageous to provide that preselection is only valid for a limited time and is erased if the clutch is not released within that time. This avoids undesired shifting in both gearboxes if the driver has preselected the cross-country speed and forgotten about it.

As a further refinement, a signal invites reengaging the clutch when de selected speed is engaged. If it is provided that the actuator remains activated for a certain time when reengaging the clutch before engagement of the selected speed is accomplished, even too early release of the clutch does not have any 6- consequences for safety. Furthermore synchronization can be assisted by operating the accelerator or the brake.

The subject matter of the invention is illustrated by way of the drawings in which:

Figure 1 is a schematic representation of the drive train of a motor vehicle and a control device for shifting the distributor gearbox.

Figure 2 is a time chart of the shifting process of the control device.

Figure 3 is a flow chart of a control cycle of the control device.

Figure 4 is a flow chart of a cycle for the correction of shifting time.

The drive train of the vehicle represented in Fig.1 consists of an engine 1, a clutch 2, a main gearbox 3 with input shaft 4, a distributor gearbox 5 with input shaft 5, a front axle driving shaft 7 and a rear axle driving shaft 8.

The distributor gearbox 6 contains an input shaft 5 carrying two gears 10, 11 with coupling means, coupled to the shaft 5 at will by sleeve 12 with synchronizing means, an intermediate shaft 13 with gears meshing with gears 10,11 and an output shaft 14 with drive gear and a coupling 15 for engaging the front wheel drive. Depending on the position of the sleeve 12, either the road speed or the cross-country speed is engaged, as customary. The transmission ratio of the cross-country speed is about 1,7 to 2,0 times (UVG) that of the road speed.

The described distributor gearbox is only an example. Various other types are within the scope of the invention, for instance with a differential, lockable or not, with a different disposition of the shafts, of the gears or of the shifting sleeve, provided there is a sleeve with synchronizing means at all. This sleeve 12 is-shiftable by means of a shifting fork 16 attached to a shifting rod 17, for example. The shifting rod 17 is actuated by a control-cylinder 18, preferably a cylinder with three positions.

The control-cylinder 18 is supplied by compressed air from an air reservoir 24 by means of three solenoid-valves 19,20,21. Furthermore, there is a shifting valve 22 and a throttling valve 23 allowing the control-cylinder to be supplied with varying pressure in order to achieve different shifting times. In particular, the consideration of shifting time provided by the invention allows its extension by reducing air pressure in order to extend the service life of the synchronizing means. The shifting rod could be actuated just as well by hydraulic or electromagnetic means.

The central control device 25 executes the shifting process by emitting signals to the solenoid-valves 19,20,21. It could be a micro-processor or a taylored digital processor (ASIC) or a hybrid device.

Signals are supplied to the central control device 25 by the following sensors:

- a main gearbox input shaft rotary speed nGE from the speed sensor 26, a clutch signal sK from clutch pickup 27 reporting that the clutch pedal 28 is depressed, - a speed engaged signal sS from the position pickup 29 stating wether the road speed, the cross country speed or even no speed at all is engaged in the distributor gearbox, - a temperature signal sT from the oil temperature pickup 30, - a preselection signal sG from the preselecting switch 31.

Furthermore, there are pilot lamps 32 and an audible warning device 33.

Fig.2 shows a time chart of the process of shifting the distributor gearbox 6 from the road speed into the cross-country speed, the time axis being horizontal. Curve 40 repre-sents the rotary speed nGE of the main gearbox input shaft 4. The interrupted lines represent in turn: the maximum admissible engine speed nMOTMAX, the maximum speed (nGAG) of the distributor gearbox output shaft being the maximum admissible engine speed nMOTMAX divided by the ratio UVG of the distributor gearbox in cross-country speed, and the clearing rotational speed (nGEG) being the speed higher than nGAG at which shifting is allowed to commence.

Curve 45 is the speed of the vehicle, curve 46 the position of the clutch pedal 28 (the clutch is engaged when the curve is on the time axis). The signal of the clutch position pickup 32 is sK, sV is the control signal activating solenoid valve 19 and therewith movement of the sleeve 12 into cross-country speed and sS is the answering signal indicating that shifting is accomplished. The humps 50 indicate the audible signal inviting release of the clutch pedal 28.

Shifting proceeds as follows: The vehicle is travelling in whichever speed of the main gearbox and in road speed of the distributor gearbox. The driver notices a strong increase of tractive resistance, operates the preselecting switch 31 (Fig.1) and releases clutch 2 (ramp 46' of the curve 46). At tO the clutch pedal is depressed to the extent that clutch sensor 27 (Fig.1) responds and emits the signal sK.

This leads to a first measurement and storage of the speed n1GE of the main gearbox entry shaft 4 at the moment tl and to a second measurement, an interval dt later at the moment tl, of the speed n2GE. These values nl,n2 and the interval dt determine the slope of the curve 40, assumed to be a straight line 401. This straight line 40' intersects the horizontal line corresponding to the speed nGAG in a point at the instant t4. According to the invention, the increased clearing speed nGEG taking into account the shifting time tSE is determined by linear interpolation. The point of intersection of the curve 40' and the time ordinate t4 is the speed nGAG at which, in a distributor gearbox according to the state of the art, shifting would be cleared. The time span tSE corresponds to an advance of clearance, more precisely an increase of the speed of the gearbox output shaft nGAG to clearance speed nGEG.

As the speed of the input shaft of the main gearbox is measured continuously, the actual shifting can be cleared as soon as it has attained the clearing speed nGEG by supplying the solenoid valve with an activation signal sV, visible on the respective curve as a step. Now, synchronization is executed and it is assumed that it will take as long (tSE) as predicted. As soon as the synchronization is finished, the shifting rod 17 has assumed its end position and position pickup 29 emits the answering signal sS.

The fact that synchronization is accomplished can be seen by curve 40 having attained the maximum engine speed nMOTMAX exactly at the moment t4. In the time span between t4 and t5 engine speed drops slightly until the clutch is engaged again. Curve 4W is steeper than curve 40' due to the different transmission ratio and shows the slight drop of the engine speeed.

Speed engaged signal sS at t4 triggers an audible signal, two short hoots or cheeps for instance, inviting the driver to reengage the clutch and the driver follows suit -see the descending ramp of curve 46. For shifting upward into road speed again, no special measures are required as the driver will of course accelerate the engine close to the upper limit before shifting.

Figure 3 is a flow chart of a control cycle of the control device: As long as the vehicle circulates in road speed, the waiting loop 40 containing the decision box 42 is circled until the cross country speed is preselected ("preselected speed = LOW V1). If so box 42 decides YES (Y) and the waiting loop 41 is circled until pickup 27 reports that the clutch is released (tO in Fig.2). This is answered by the decision YES (V) in box 43 ( "clutch released V') and a short waiting time dtO follows in box 44 in order to give possible torsional vibrations in the drive train the time to die down. This is indicated by a waiting loop 46 which is circled until (t - tO) > 0 (t being the lapsing time).

This means YES and the next decision is made in box 47: If the measured rotating speed n (short for nGE) is already lower than the rotating speed of the output shaft (this is nMOTMAX divided by UVG), the decision in box 47 is NO and a jump to box 57 is made. causing immediate clearance for the shifting process.

If, however, the measured speed n is higher than the speed limit for the gearbox output shaft (which according to the state of the art would cause a downshift-lock), nl is measured and stored in box 48 and a time span dtl is defined. Now, the waiting loop 50 is circled until t2 which equals (tl + dtl) and in box 51 the speed n2 at the moment t2 is measured and stored as well as the time span dt.

In the decision box 52, the two speeds nl and n2 are compared. If the speed n has dropped in this time span (nl > n2), the decision is YES (Y) and clearing speed nGEG is calculated in box 53 according to the following equation:

nGEG = nMOTMAX/UVG + (nl-n2)/dt.tSE If the speed has increased in this time span (nl < n2), the decision is NO (N) and clearing speed nGEG is calculated according to the following equation:

nGEG = nMOTMAX/CVG Subsequently, the waiting loop 56 is circled until the measured speed n has reached clearing speed nGEG. If so, the decision in box 55 is YES (y) and moves to box 57 in which it is checked wether the clutch is still released. If it is not, waiting loop 40 is reverted to. If it is, the activating signal is given to the solenoid valve 19 in box 58 and so the synchronization starts.

When synchronization is accomplished, the position pickup 29 reports execution ("report LOW") and after circling the waiting loop 60 the next step is made from decision box 59 to box 61. Here, the audible signal 50 for reengaging the clutch is generated and a pilot lamp indicates that the cross-country speed is engaged. These are the essential steps of shifting according to a progra.m, further decisions, checks and details can be added.

For instance, the predicted shifting time t2 can be corrected by comparison with the measured shifting time tV, as shown in Fig.4: The virgin gearbox is initiated with a minimum and a maximum shifting time tSEMIN and tSEMAX, the predicted shifting time being set equal to the minimum time tSEMIN. This is shown in box 70.

After each shift into cross-country speed, it is decided in box 71 whether the actual shifting time tS has been as forecast or different ("new value tS ?"). As long as the decision is NO, the waiting loop 80 is circled. If it is YES, it is decided whether the measured shifting time is sufficiently different from the forecast. In order to do this, two coefficients kl and U are chosen, for example kl = 1.03 et U = 0.97. In the boxes 72 and 73 it is decided whetherthis is the case and wether the new value is higher or lower.

Next, a corrected shifting time t'SE is calculated in boxes 74,75 according to the following equations; if the new value is higher than the forecast according to the first, if it is lower according to the second:

tISE = k3.tSE + (1-k3).tS wherein 0.8 < k3 < 0.99 tISE = k4.tSE + (1-k4).tS wherein 0.2 < k3 < 0.01 It will be apparent, that in the first case correction will be very slow and in the second case very fast. Chosen values would be, for example, k3 = 0,9 and k4 = 0,1.

Finally, in the boxes 76,77 a check is made, whether the corrected values are outside the set values tSEMIN and tSEMAX and, if they happened to be, they would be replaced by these set values in the following boxes 78,79.

Claims

1. A control device for shifting a distributor gearbox with an input shaft driven by an engine by means of a clutch and a main gearbox and comprising a sleeve with synchronizing means shiftable by means of an actuator, shifting being initiated by preselecting a speed of the distributor gearbox and disengaging the clutch, - an actual rotational speed being measured, - the actuator being activated and therewith the speed engaged, if the actual rotational speed attains a clearing rotational speed, thereafter, the clutch being released, characterized in that - the actual rotational speed is measured downstream of the clutch, and - the clearing rotational speed is calculated from the drop of the actual rotational speed during a predefined time interval, from an engine rotational speed limit and from a shifting time.

2. A control device according to claim 1, wherein the clearing rotational speed is calculated by:

14 calculating a rotational speed of the outpuit shaft of the distributor gearbox by dividing the engine rotational speed limit by the transmission ratio between the point of measurement of the rotational speed and the output shaft in the speed to be shifted into, - predicting, from the drop of the rotational speed in the interval, a time until the rotational speed of the output shaft will be attained, and determining the clearing rotational speed from the shifting time and the time until the output shaft rotational speed will be reached.

3. A control device according to claim 1, wherein the clearing rotational speed equals the output shaft rotational speed if the measured actual speed increases.

4. A control device according to any one of the preceding claims, wherein the actual rotational speed is measured at the primary shaft of the main gearbox.

5. A control device according to any one of the preceding claims, wherein the shifting time is a stored value, the actual shifting time being measured, and that the stored shifting time is corrected in dependence on the actual shifting time.

6. A control device according to claim 5, wherein correction of the shifting time is performed by weighing the stored shifting time and the measured shifting time and averaging the weighed values.

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7. A control device according to claim 6, wherein the measured shifting time is weighed heavily if the difference between stored shifting time and measured shifting time is positive, and weighed lightly if this difference is negative.

8. A control device according to claim 5, wherein the stored shifting time is corrected in dependence on a temperature, preferably the oil temperature of the distributor gearbox.

9. A control device according to any of the preceding claims, wherein first the desired speed of the distributor gearbox is preselected and only then shifting is triggered by releasing the clutch.

10. A control device according to claim 9, wherein preselection is only valid for a limited time and is erased if the clutch is not released within that time.

11. A control device according to any one of the preceding claims, wherein a signal invites reengaging of the clutch when a selected speed is engaged.

12. A control device according to any one of the preceding claims, wherein the actuator remains activated for a certain time when reengaging the clutch before engagement of the selected speed is achieved.

13. A control device substantially asd herein described with reference to the accompanying drawings.