WO2002049870A1

WO2002049870A1 - Motor vehicle drive unit

Info

Publication number: WO2002049870A1
Application number: PCT/SE2001/002827
Authority: WO
Inventors: Marcus STEÉN
Original assignee: Volvo Lastvagnar Ab
Priority date: 2000-12-20
Filing date: 2001-12-19
Publication date: 2002-06-27
Also published as: AU2002216560A1; SE0004727L; SE0004727D0; SE518029C2

Abstract

Motor vehicle drive unit, comprising an internal combustion engine (1), a disc clutch (3) manually operated by a clutch pedal (15), a gearbox (4) and an electronic control unit (10) for controlling the engine torque and rpm. A first sensor (16) signals to the control unit whether or not the clutch pedal is depressed, while a second sensor (11) coupled to the gearbox signals to the control unit whether a gear higher than a predetermined gear is selected in the gearbox. The control unit is disposed to limit engine torque to a level below maximum torque when the first sensor indicates that the clutch pedal is depressed at the same time as the second sensor indicates that a higher gear than said predetermined gear is selected.

Description

Motor vehicle drive unit

The present invention relates to a drive unit for motor vehicles, comprising an internal combustion engine, a disc clutch manually operated by a clutch pedal, a gearbox connectable to the engine crankshaft via the disc clutch, an electronic control unit for controlling engine torque and engine speed, and a first sensor coupled to the control unit, said sensor sensing and providing signals to the control unit representing a released and a depressed clutch pedal, respectively.

In vehicles equipped with disc clutches, which are manually operated with a clutch pedal, it is important that the driver release the clutch pedal with the correct gear speed engaged when starting, or when the vehicle is to be accelerated after having coasted slowly with the clutch disengaged. Otherwise, the combined effect of slippage and high torque between the slipping parts of the clutch will be so great as to appreciably shorten the life of the clutch due to unnecessary wear of the friction surfaces of the clutch. The correct starting gear speed is usually first gear or a crawl gear. If the transmission has a main group and an additional group in the form of a spUtter group, the high or low position in the splitter group can be selected depending on the load. If the gearbox also has a range group, the low range should always be engaged when the clutch pedal is released for engaging the clutch after the vehicle has coasted slowly with the clutch disengaged.

In a vehicle with a gearbox, which in addition to the main group, has both a splitter group and a range group, the driver thus has three staffing functions to keep track of. It has been shown that, particularly in certain driving situations, for example when the vehicle has been braked down to low speed at a crossing or a traffic circle and the clutch has been disengaged, that the driver not infrequently retains the previously selected gear, which is now too high in view of the vehicle speed after braking, in a subsequent engagement and acceleration, in order to not have to shift. Especially in fully loaded heavy vehicles, this manner of driving wears down the clutch in a much shorter time than otherwise. The purpose of the present invention is to achieve a drive unit of the type described by way of introduction, which, without using any automatic shifting function, automatically limits the possibilities for the driver to use a manner of driving which will result in abnormally high clutch wear.

This is achieved according to the invention by virtue of the fact that a second sensor is coupled to the control unit, said sensor sensing and providing signals to the control unit indicating whether a gear higher than a predetermined gear is selected in the gearbox, and that the control unit is arranged to limit the maximum engine torque when the first sensor indicates that the clutch pedal is depressed and the second sensor indicates that a higher gear than said predetermined gear is selected.

Said predetermined gear can be first gear or second gear, depending on the number of gear ratios in the gearbox. The torque limitation leder till /hor inte vad du valtfόr ord/tiiQ result that, if a gear is selected which is higher than the predetermined gear, the available engine torque will not be sufficient to accelerate the vehicle and the driver will thus be forced to shift down, at least to said predetermined gear.

In vehicles with cruise control, there is already a sensor which senses whether the clutch pedal has been released or is depressed, which means that, with very simple means, an extra sensor in the gearbox and a simple supplementing of the control function of the control unit, a function is achieved which can substantially increase the life of the clutch.

Gearboxes for heavy trucks often consist of a main group, usually four or five forward gears, a splitter group connected on the input side of the main group and providing a low and a high speed for each gear in the main group, and a range group which is connected to the output side of the main group and which provides an ad- ditional low and high range for each gear in the main group. A number of known gearboxes of this type have today sensors which sense and provide signals to the control unit, representing the shift position in the splitter group and the range group. The recommended starting gear, i.e. the predeteraiined gear pre-programmed in the control unit of such a gearbox, can be first gear in the main group, high in the splitter group and low in the range group. The existing sensors in the split and range groups can thus be used for the torque-limiting function as well according to the present invention, which means that it is sufficient in this type of gearbox to add a single additional sensor, i.e. one which senses the gear position in the transmission main group.

In a preferred embodiment of the drive unit according to the invention, the control unit is also arranged to limit the maximum permissible engine speed to a level below the maximum rpm of the engine, if a gear higher than the predetermined gear is selected and the clutch pedal is depressed. Since the load on the clutch is depending on lutelάmnat av dig? /Has, transmitted engine torque and the difference in rotational speed, this further reduces the wear on the clutch.

The invention will be described in more detail below with reference to examples shown in the accompanying drawings, where the figure shows a schematic representation of one embodiment of a drive unit according to the invention.

In the figure, 1 designates a six-cylinder internal combustion engine, e.g. a diesel engine, the crankshaft 2 of which is coupled to a disc clutch (not shown), the plate of which is joined to the input shaft into a gearbox generally designated 4, which consists of a main portion 5, a splitter portion 6 and a range portion 7. The main portion 5 is preferably a four-ratio-stepped gearbox, while the range portion 7 is preferably a two-ratio planet group providing low and high ranges, with each ratio in the main group being represented. The splitter portion 6 is a two-ratio gearbox, often integrated into the main portion, with high and low diffeiing relatively little in ratio.

The splitter portion 6 and the range portion 7 are each provided in a known manner with sensors 8 and 9, respectively, which sense and indicate by a signal to an electronic control unit 10 whether low or high is engaged in the splitter portion 6 and the range portion 7, respectively. According to the invention, the main portion 5 is also provided with a sensor 11, which senses and provides a signal to the control unit 10 at least when a gear other that a predeteraiined gear is selected in the main portion 4. The predetermined gear can be first gear in a four-speed main group and it is sufficient that the sensor 11 is disposed to provide a signal to the control unit 10 which indicates that first gear is not selected, but, as an alternative, it is also possible to arrange a sensor which provides four different signals, each indicating a spe- cifϊc ratio.

In the figure, 12 designates a portion of an instrument panel of a vehicle. Underneath the panel that_. is an accelerator 13, a brake pedal 14 and a clutch pedal 15, all pivotally mounted. The clutch pedal 15 is associated with a sensor 16, which signals to the control unit 10 whether the clutch pedal 15 is released or depressed.

A typical driving situation, where the control unit 10 limits the available engine torque to a level under the maximum level at a given engine rpm, is when the driver releases the clutch pedal 15 after the sensor 16 has indicated a depressed clutch pedal at the same time as the sensor 11 in the main portion 5 indicates a higher gear than first gear and the sensor 8 in the splitter portion 6 indicates "high". This is the case regardless of whether high or low range is selected as indicated by the sensor 9 in the range portion 7. The engine torque is always limited if the sensor 16 indicates a depressed clutch pedal 15 and the sensor 9 indicates high range selected in the range portion, regardless of the selections in the splitter portion and the main portion, i.e. even if the lowest gear is selected in the main portion. If the sensor 11 is a sensor which provides a specific signal for each gear in the main portion 5, it is possible that the combination of "low" in the splitter portion and a higher gear that first gear in the main portion, e.g. second gear, together with a depressed clutch pedal will not trigger torque limitation. The maximum level of the available limited engine torque is selected so that it is sufficiently high to make it possible to start the vehicle at "high" in the sphtter portion and a higher gear than first gear in the main portion, when the vehicle is unloaded.

Claims

1. Motor vetacle drive unit, comprising an internal combustion engine (1), a disc clutch (3) manually operated by a clutch pedal (15), a gearbox (4) connectable to the engine crankshaft via the disc clutch, an electronic control unit (10) for controlling engine torque and engine speed, and a first sensor (16) coupled to the control unit, said sensor sensing and providing signals to the control unit representing a released and a depressed clutch pedal, respectively, characterized in that a second sensor (11) is coupled to the control unit (10), said sensor sensing and providing signals to the control unit indicating whether a gear higher than a predetermined gear is selected in the gearbox (4), and that the control unit is arranged to limit the maximum engine torque when the first sensor indicates that the clutch pedal is depressed and the second sensor indicates that a higher gear than said predetermined gear is selected.

2. Drive unit according to Claim 1, characterized in that the gearbox (4) consists of a main gearbox (5) and at least one supplementary gearbox (6 or 7), which provides a low ratio and a high ratio for each gear step in the main gearbox, and that a third sensor (8 or 9) is arranged which senses and provides signals to the control unit representing the selected ratio in the supplementary gearbox.

3. Drive unit according to Claim 2, characterized in that the supplementary gearbox is a splitter gearbox (6) coupled to the input side of the main gearbox (5), and that the control unit (10) is arranged, when the clutch pedal (15) is depres- sed, to limit the engine torque when a gear higher than a predetermined lowest gear is selected in the main gearbox at the same time as the high ratio of the splitter gearbox is selected.

4. Drive unit according to Claim 3, characterized in that the control unit (10) is arranged, when the clutch pedal (15) is depressed, to limit the engine torque when a gear higher than first gear is selected in the main gearbox (5) at the same time as the high ratio in the splitter gearbox (5) is selected.

5. Drive unit according to one of Claims 2-4, characterized in that a second supplementary gearbox in the form of a range gearbox (7) with a low range and a high range is connected to the output side of the main gearbox (5), and that a fourth sensor (9) is connected to the control unit (10), said sensor sensing and providing signals to the control unit representing the range selected in the range gearbox.

6. Drive unit according to Claim 5, characterized in that the control unit (10) is arranged, when the clutch pedal (15) is depressed, to limit the engine torque, regardless of the gear selected in the main gearbox (5), when the high range (7) in the range gearbox is selected.

7. Drive unit according to one of Claims 1-6, characterized in that the control unit (10) is arranged to also limit the maximum permissible engine speed to a level below the engine speed of the engine, if a gear higher than a predetermined gear is selected and the clutch pedal (15) is depressed.