Drive means for motor vehicles The present invention relates to a drive means for motor vehicles, comprising an internal combustion engine and, connected to the crankshaft of the engine via a disc clutch, an input shaft of a stepped gearbox which has at least one intermediate shaft which is mounted in a casing and has at least one gear wheel in engagement with a gear wheel on the input shaft, a main shaft, mounted in the casing, with gear wheels which engage with gear wheels on the intermediate shaft, at least one gear wheel in each pair of mutually engaging gear wheels on the intermediate shaft and the main shaft being mounted rotatably on its shaft and being lockable on its shaft by engaging means, of which the engaging means for at least some of the forward gears lack synchronisation function, and also operating means which interact with the engaging means and are controlled by a transmission control means, connected to a gear selector and communicating with an engine control unit and to which signals are fed representing the selected gear and various engine and vehicle data, which include at least engine speed, rotational speed of the gearbox input shaft and vehicle speed.

Drive means of this type with automated stepped gearboxes, known as autoshift gearboxes, have become increasingly common in heavy-duty vehicles as microcomputer technology has developed further and made it possible to use a control computer and a number of actuators, for example servo motors, to precision- regulate engine speed, engagement and disengagement of the clutch and also the engaging means of the gearbox in relation to one another, so that smooth shifting is always obtained even when shifting between unsynchronised gear steps. The synchronisation during shifting is done in this gearbox type by controlling the engine speed. The advantage of this type of automatic gearbox compared with a conventional automatic gearbox constructed with planetary gear stages and with a hydrodynamic torque converter on the input side is, firstly, especially as far as use in heavy-duty vehicles is concerned, that it is simpler and more robust and can be produced at a considerably lower cost than the conventional automatic gearbox, and,

secondly, it has greater efficiency, which means that lower fuel consumption is possible. In a gearbox consisting of an unsynchronised stepped main group and a range group the absence of synchronizations reduces costs even further. The absence of synchronization means makes it possible to make the gearbox shorter or, alternatively, with a set length, make the gears wider than in a synchronized gearbox of the same length, to thereby make it possible to transmit higher torque.

Generally, at least three control parameters, namely: engine rpm, torque on the gearbox input shaft and vehicle speed determine when shifting shall occur according to a shifting strategy stored in an engine and transmission control computer. The torque on the gearbox input shaft is equated here with the engine torque, i. e. the load on the engine, which is obtained from sensors indicating the amount of fuel supplied to the engine, for example a flowmeter or sensor indicating accelerator pedal position. When initiating shifting, i. e. disengagement of an engaged gear, the torque transmission between the engine and the gearbox must be as small as possible.

Preferably the drive chain should be torqueless to achieve jerk-free disengagement.

In to the control computer there are programmed values of how large the supplied fuel amount should be for different shifting points so that the torque on the gearbox input shaft will be close to zero or in any case so low that an engaged gear can be disengaged without any unpleasant jerking. After disengagement of the gear, the control computer controls the engine speed for synchronisation with the rpm of the gear to be engaged. When the rotational speeds have been synchronized, the new gear is engaged.

With the known method of estimating torque equal to zero or pratically zero between the engine and the gearbox, there is no feedback. Since the level is tuned to fit a certain vehicle, there is no guarantee that it will be tuned for all vehicles.

Furthermore, the engine torque varies depending on the inner engine friction losses, which are temperature dependent. If auxiliary units, such as a power take-off, air compressor, cooing fan and or AC compressor are engaged, the engine torque signal

will indicate torque transmission even when the torque transmission between the engine and the gearbox is zero. Also variations in fuel quality (with variations in energy content) will effect the possibility of controlling the drive chain to a torque- less state. The torque levels to the auxiliary units must therefore be estimated and stored in the control computer and the engine control must take into account whether one of more auxiliary units are engaged or disengaged.

One purpose of the present invention is to achieve a drive unit of the type described by way of introduction, in which it is possible to always exactly determine a torque- less state in the vehicle drive chain, to make possible-regardless of variations in the engine's own sluggishness, depending on variations in engine temperature, and regardless of whether or not one or more auxiliary units are engaged-jerk free disengagement of the current gear without disengaging the drive chain clutch.

A further purpose of the present invention is to achieve such a drive unit in which it precision control is possible of the engine rpm reduction or increase to achieve rapid, exact and jerk free shifting.

This is achieved according to the invention by virtue of the fact that the input shaft of the gearbox is coordinated with a torque sensor, which sends a signal, dependent on the torque on the input shaft, to said control means and that the control means are disposed, upon shifting to an unsynchronised gear, to initiate shifting only when the torque sensor indicates that the torque on the input shaft is zero or at least practically zero.

By using a torque sensor, there is a torque feedback loop and the torque in the drive chain can be brought to zero regardless of temperature-dependent engine sluggishness and regardless of whether or not auxiliary units are in use.

According to a preferred embodiment of the drive unit according to the invention, the control means are disposed to register the fuel amount supplied to the engine when the input torque to the gearbox is zero or practically zero. When adapting the rpm during shifting, the engine is controlled taking into account the engine torque corresponding to the registered amount of fuel.

By basing the rpm control of the engine during shifting on the registered engine load, when the rpm is to be adapted to the next gear ratio, a more rapid and exact adjustment can be achieved.

The invention will be described in more detail with reference to examples shown in the accompanying drawings, where Fig. 1 shows a schematic representation of a drive unit according to the invention, Fig. 2 shows the clutch and the gearbox of Fig.

1 on a larger scale and Fig. 3 is a diagram of engine torque and gearbox torque as a function of time during shifting.

In Fig. 1,1 designates a six-cylinder internal combustion engine, e. g. a diesel engine, the crankshaft 2 of which is coupled to a single-disc dry-disc clutch, generally designated 3, which is enclosed in a clutch bell 4. Instead of a single disc clutch, a dual disc clutch can be used. The crankshaft 2 is solidly joined to the clutch housing 5, while its disc 6 is solidly joined to an input shaft 7 (Fig. 2) which is rotatably mounted in the housing 8 of a gearbox, generally designated 9. A main shaft 10 (Fig.

2) and an intermediate shaft 11 (Fig. 2) are rotatably mounted in the housing 8.

As is most clearly evident from Fig. 2, a gear 12 is rotatably mounted on the input shaft 7 and can be locked to such shaft with the aid of an engaging sleeve 13 provided with synchronizing means. Said engaging sleeve 13 is non-rotatably but axially displaceably mounted on a hub 14 non-rotatably connected to the input shaft.

With the aid of the engaging sleeve 13, a gear 15, rotatably mounted on the main shaft 10, is lockable relative to the input shaft 7. The gears 12 and 15, respectively,

engage gears 16 and 17, respectively, which are non-rotatably joined to the intermediate shaft 11. Additional gears 18,19 and 20, respectively, are non-rotatably joined to the intermediate shaft 11 and engage gears 21,22 and 23, respectively, on the main shaft 10 and lockable to the main shaft with the aid of engaging sleeves 24 and 25, respectively, which in the example shown do not have synchronizing means.

On the main shaft 10, an additional gear 28 is rotatably mounted and engages an intermediate gear 30 rotatably mounted on a separate shaft 29. The intermediate gear 30 engages in turn an intermediate shaft gear 20. The gear 28 is lockable to its shaft with the aid of an engaging sleeve 26.

The gear pairs 12,16 and 15,17 and the engaging sleeve 13 form a splitter group with a low stage LS and a high stage HS. The gear pair 15,17 together with the gear pairs 21, 18, 22,19, 23,20 and 28,30 form a main group with four speeds forward and one reverse. At the output end of the main shaft 10, a gear 31 is non-rotatably mounted to form the sun gear in a two-range group of planetary type, generally designated 32, the planet carrier 33 of which is non-rotatably mounted to a shaft 34, forming the output shaft of the gearbox. The planet gears 35 of the range group 32 engage a ring gear 36 which, with the aid of an engaging sleeve 37, can be locked relative to the gearbox housing 8 for low range LR and relative to the planet carrier 33 for high range HR. The engaging sleeve 37 also has a neutral position NR lying between low range LR and high range HR, in which neutral position the output shaft 34 is released from the main shaft 10.

The engaging sleeves 13,24, 25,26 and 37 are displaceable as indicated by the arrows in Fig. 2, providing the gear positions indicated above the arrows. Displace- ment is achieved by servo means 40,41, 42,43 and 44, schematically indicated in Fig. 2, which can be pneumatically operated piston-cylinder devices of the type used in a gearbox of the above described type, which is marketed under the name Geartronico. The servo means are controlled by an electronic control unit 45 (Fig. 1), comprising a microcomputer depending on signals fed into the control unit represent-

ing various engine and vehicle data, including at least engine speed, vehicle speed, clutch and accelerator pedal position and, where applicable, engine brake on-off, when an electronic gear selector 46 coupled to the control unit 45 is in its automatic position. When the selector is in its position for manual shifting, the shifting occurs at the command of the driver via the gear selector 46. The control unit 45 also controls the fuel injection, i. e. the engine speed, depending on the accelerator pedal position and the air supply to a pneumatic piston-cylinder device 47, by means of which the clutch 3 is engaged and disengaged.

The transmission control unit 45 is programmed in a known manner so that the clutch 3 is held engaged when the vehicle is standing still and the gear selector 46 is in the neutral position. This means that the engine is driving the input shaft 7 and thus also the intermediate shaft 11, while the output shaft 34 is disengaged. Auxiliary apparatus driven by the intermediate shaft, e. g. an oil pump for lubricating the gear- box, is driven in this position. The control unit 45 is also programmed, when the vehicle is standing still and the gear selector is moved from the neutral position to a gear engaging position, either a position from automated shifting or to a position with a driver-selected starting off gear, to first disengage the clutch and then brake the intermediate shaft 11 to stop with the aid of the intermediate shaft brake 50 indicated in Fig. 2, and which can be a braking device of a type known per se and controlled by the control unit 45. With the intermediate shaft 11 braked to stop or at least nearly to stop, the control unit 45 now initiates shifting in the main group a starting off gear which provides the total gear ratio selected by the automatic transmission or by the driver. When the driver, after engagement of the selected starting off gear, e. g. first gear, depresses the accelerator, the accelerator pedal will function as a reversed clutch pedal, which, via the transmission control unit successively increases the clutch engagement with increasing throttle opening.

When shifting-initiated either directly by the driver or by automatic control means in accordance with a gear selection strategy stored in the transmission control unit 45,

which can take into account hw the vehicle surroundings will appear in the immediate future-the transmission control unit 45 first controls the engine control unit 48 to regulate the fuel supply to the engine, so that a torqueless or practically torqueless state is created in the vehicle drive chain. In other words, the torque transmission from the engine crankshaft 2 to the input shaft 7 of the gearbox 9 must be zero or at least practically zero. The transmission control unit 45 receives continuous information on, and registers the current engine torque via, the amount of fuel injected and current torque on the input shaft 7 via a torque meter 60 coupled to the shaft. The torque meter can be of a known type, hitherto used in the laboratory.

The torque can be computed for example on the bsis of measured torsion in the shaft 7. When the registered torque is zero or practically zero on the input shaft 7 the current gear is disengaged.

Starting from the registered amount of fuel, which indicates the current engine load at this point in time, the transmission control unit 45 directs the engine control unit 48 to regulate the amount of fuel to the engine for rpm synchronisation with the rpm of gearbox rpm for the new gear, whereafter the new gear is engaged. 61 designates generally an auxiliary unit, which can be an engine driven/engine mounted power take-off, which can be engaged or disengaged by a driver actuated control coupled to the engine control unit 48. If one or more auxiliary units 61 are engaged via the driver actuated control, the engine load will be increased and more fuel will be required for synchronisation than if no auxiliary unit were engaged. By registering and starting from the actual engine load when the drive chain is without torque, rapid and jerk free shifting can be achieved.

The transmission control unit 45 is also disposed during driving, when there is no shifting, to register which auxiliary unit (s) 61 is/are engaged (fuly or partially), together with the difference between the engine torque and the torque on the gearbox input shaft. A number of different combinations are registered. The control unit 45 is arranged to compute the engine load attributable to each auxiliary unit.

Fig. 3 shows the control process in connection with shifting in the gearbox, where the curve"a"illustrates the engine torque during the drop in torque when shifting with an engaged auxiliary unit 61 while the curve"b"illustrates the torque on the gearbox input shaft 7 during the same time period. As can be seen in the figure, the engine torque does not coincide with the input shaft torque, since a torque must be maintained to drive the auxiliary unit (s). As is also evident from the figure, the input shaft 7 will become torqueless onlya certain time after the engine torque has reached its minimum.

The transmission control unit 45 is arranged, even during driving when there is no shifting, to register the inner friction of the engine as a function of engine temperature, by registering the difference between the engine torque and the torque on the gearbox input shaft.

The transmission control unit 45 is also arranged to order the engine control unit 48, when regulating the fuel supply to the engine during the shifting process, to compensate, based on the engine torque, the torque on the input shaft 7 and the engine temperature, for variations in engine inner friction caused by temperature variations.