WO2003078197A1

WO2003078197A1 - Motor vehicle drive unit

Info

Publication number: WO2003078197A1
Application number: PCT/SE2003/000455
Authority: WO
Inventors: Anders Eriksson; Marcus STEÉN
Original assignee: Volvo Lastvagnar Ab
Priority date: 2002-03-20
Filing date: 2003-03-18
Publication date: 2003-09-25
Also published as: AU2003211650A1; SE0200845D0; SE0200845L; SE521540C2

Abstract

Drive unit for motor vehicles, comprising an internal combustion engine (1) and a unsynchronised stepped automated gearbox (9) connected to the engine via a clutch (3). The clutch and the gearbox are controlled by an electronic control unit (45), which communicates with an engine control unit (48) to which there are fed signals representing the selected gear from a gear selector (46) and signals representing various engine and vehicle data. The engine control unit is disposed, when the synchronization with the engine when shifting demands a lower engine speed than the engine idle speed determined by the engine control unit for the selected gear, to steer the engine speed to a lower rpm than idle rpm. The transmission control unit is disposed to engage the selected gear when the engine speed has reached a speed lower than idle speed, which is suitable for engaging the selected gear.

Description

Motor vehicle drive unit

The present invention relates to a drive unit for motor vehicles, comprising an internal combustion engine and a step gear box input shaft connected via an disc clutch to the engine crankshaft, said step gear box having at least one intermediate shaft mounted in a housing, said intermediate shaft having at least one gear in engagement with a gear on the input shaft, a main shaft which is mounted in the housing and has gears engaging gears on the intermediate shaft, at least one gear in each pair of interengaging gears on the intermediate shaft and the main shaft being rotatably mounted on its shaft and lockable by engaging means of which at least some forward gears lack a synchronization function, and operating means cooperating with the engaging means and being controlled by a transmission control unit, which is joined to a gear selector and which communicates with an engine control unit, signals being fed to said transmission control unit representing the selected gear and various engine and vehicle data, at least including engine speed, vehicle speed, clutch position and accelerator pedal position.

Drive units of this type with so-called automatic multi-step gearboxes have become more and more common in heavy vehicles as microcomputer technology has been developed and made it possible, with the aid of a control computer and a number of control means, e.g. servomotors, to precision-regulate engine speed, engagement and disengagement of the clutch and gearbox coupling means relative to each other, so as to always provide smooth shifting, even when shifting between unsynchronized gear steps. The synchronization during shifting is achieved in this type of gearbox by controlling the engine speed to the speed of the gearbox input shaft with the aid of the engine control unit. The advantage of a step-geared automatic transmission over a traditional automatic transmission, made up of a planet gear stage with a hydrodynamic torque converter on the input side, is, on the one hand, particularly when used in heavy vehicles, that it is simpler and more reliable and can be manufactured at a substantially lower cost than traditional automatic transmission, and, on the other hand, that it has a higher efficiency, making lower fuel consumption possible. In a gearbox made up of a non-synchronized stepped main group and a synchronized 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.

In such a gearbox, in contrast with an automatic gearbox of planetary type, there is a break in the driving force during shifting. This is one reason for skipping, if load and road conditions permit, at least one of the lower gears when shifting up, i.e. shifting directly from first to third or even to fourth gear. The problem is however that the engine control unit controls the engine rpm to the lowest rpm, which is the idle speed, typically 600 rpm. The risk is then that if several gear steps are skipped, then the selected gear speed will require a lower rpm than the idle speed in order to synchronized the engine speed to the speed of the input shaft, which is directly dependent on the vehicle speed. Especially in an uphill incline the risk is great that the vehicle speed and thus the speed of the gearbox input shaft during the break in driving power will drop below a speed below the idle speed so that it will not be possible to engage the desired gear and a lower gear must be selected instead.

The purpose of the present invention is to solve the above described problem and make it possible for example from starting the vehicle and during acceleration up to cruising speed, to reach the desired cruising speed with fewer shifts than was plreviously possible, to thereby achieve increased comfort and performance.

This is achieved according to the invention by virtue of the fact that the control means are arranged - when synchronization with the engine when shifting demands a lower engine speed then the engine idle speed determined by the control means for the selected gear - to steer the engine speed towards a rotational speed which is lower than the idle speed and that the control means are disposed to engage the selected gear, when the engine speed has reached a suitable speed for engaging the selected gear, which is lower than the idle speed. By making it possible to steer the engine speed to an rpm lower than idle speed, not only is it possible to skip gear speed steps when shifting up, but it is also possible to shift up to a new higher gear earlier than if the lowest engine speed were idle speed. Furthermore the safety margins in relation to changes in the vehicle surroundings (travel resistance, road incline) can be increased when shifting up if the engine can be steered to a lower rpm than idle speed. This means that shifting can take place under normal conditions even if the indata should be unreliable.

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 and Fig. 2 shows the clutch and the gearbox of Fig. 1 on a larger scale, Fig. 3 is a diagram of engine speed and gearbox input rpm as a function of time when shifting up in a steep uphill incline, Fig. 4 is a corresponding diagram when shifting up on level ground and Fig. 5 is a diagram illustrating required shifting up speeds in order to end up at idle speed after shifting, for four gear steps.

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, gene-rally 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. Displacement 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 Geartronic^®. The servo means are controlled by an electronic control unit 45 (Fig. 1), comprising a microcomputer depending on signals fed into the control unit representing 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. Supplementary apparatus driven by the intermediate shaft, e.g. an oil pump for lubricating the gearbox, is driven in this position. The control unit 45 is also programmed, when the vehicle is standing still 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.

If the next gear step which is selected -either directly by the driver or automatically depending on a shifting strategy stored in the transmission control unit 45, and which can take into account how the vehicle surroundings will appear a bit into the future- is two or three steps higher than the starting off gear, the situation can occur that the rpm of the gearbox input shaft, which is directly dependent on vehicle speed, will require a lower rpm than idle speed for synchronization with the engine. The same thing can occur when shifting to the adjacent higher gear, if the shifting takes place on a steep uphill incline. In the diagram in Fig. 3 this situation is illustrated when shifting in a steep uphill incline, where the vehicle loses so much speed from the beginning of the shifting manoeuvre until the engine speed and the gearbox input shaft speed (vehicle speed) are synchronous, that this φm will be below the idle speed. By programming, in accordance with the invention, the engine control unit 48 so that it reduces in such a situation the lowest permissible engine φm to an φm below idle φm, as illustrated in Fig. 3, e.g. from an idle speed of ca 600 φm or in certain cases 700 φm, with a cold engine, to a lowest φm of ca 500 φm, the synchronisation takes place in the φm range between said speeds so that synchronisation can be completed and shifting take place without any scraping in the gear box.

The lowering of the idle speed makes it possible to shift up on very steep hills, where shifting up was previously not possible with the idle speed as the lowest φm limit. The driver was forced to remain in a low gear until the end o f the hill. This is particularly important when starting off, since the first shifting manoeuvre is the most critical since the gearbox input shaft retards rapidly due to the large gear ratio. The torque is usually sufficient (due to the large gear ratio), which means that if one can make the first up- shifting, it will usually be possible to shift up additional steps. On a long uphill incline, much can be gained by being able to drive in a gear which is a few steps higher.

The diagram in Fig. 4 shows In a corresponding manner shifting on level ground. During shifting, the vehicle speed and thus the gearbox input shaft speed are, in principle, constant. The time from when shifting is initiated until the speeds of the engine and the gearbox input shaft are synchronous, so that shifting can be completed, depends of course on how rapidly the engine φm drops, but there is never any problem in getting the gear to finally engage. In order to rapidly reduce the engine φm, it is possible to use existing engine braking devices such as exhaust brakes or decompression brakes, which are common in engines for heavy trucks.

The diagram in fig. 5 illustrates the relationships between the various engine speeds required to end up at idle speed when shifting up. "a" marks the φm for ending up at idle speed when shifting to the next gear, "b", "c" and "d" mark the corresponding engine speeds when skipping one, two and three gear steps respectively. As can be seen in the diagram it is not possible, while retaining the φm idle limit, to skip three gear steps when shifting up, since the maximum engine φm would then have to be exceeded in order to come up to idle speed. By temporarily lowering, in accordance with the invention, the lower φm limit below idle speed, four steps can be taken at once when shifting, as illustrated by the dash-dot bar in the diagram.

Generally, lower engine speed provides increased comfort. It is thus advantageous to reduce the engine φm where possible. Instead of shifting up without lowering the engine φm below idle speed, the same shifting up steps can be taken but with the shifting speeds moved downwards.

Claims

1. Drive unit for motor vehicles, comprising an internal combustion engine (1) and a step gearbox input shaft (7) connected via a disc clutch (3) to the engine crankshaft (2), said step gearbox (9) having at least one intermediate shaft (11) mounted in a housing, said intermediate shaft (11) having at least one gear (16, 17) in engagement with a gear (12, 15) on the input shaft, a main shaft (10) which is mounted in the housing and has gears (15, 21, 22, 23) engaging gears (17, 18, 19, 20) on the intermediate shaft, at least one gear in each pair of interengaging gears on the intermediate shaft and the main shaft being rotatably mounted on its shaft and lockable by engaging means (13, 24, 25) of which at least some forward gears lack a synchronization function, and operating means (40,41,42), cooperating with the engaging means and being controlled by control means (45,48) which are connected to a gear selector (46) and have transmission control function and engine control function, signals being fed into said control means representing the selected gear and various engine and vehicle data, at least including engine speed, input shaft speed, vehicle speed, clutch position and accelerator pedal position, characterized in that the control means (45,48) are arranged - when synchronization with the engine when shifting demands a lower engine speed then the engine idle speed determined by the control means for the selected gear - to steer the engine speed to a rotational speed which is lower than the idle speed and that the control means are disposed to engage the selected gear, when the engine speed has reached a suitable speed for engaging the selected gear, which is lower than the idle speed.

2. Drive unit according to claim 1, characterized in that said control means (45, 48) comprise a transmission control unit (45) and an engine control unit (48) which communicate with each other.

3. Drive unit according to claim 1 or 2, characterized in that the idle speed determined by the engine control unit (48) is ca 600 φm and that the engine control unit is arranged under said pre-conditions when shifting to lower the lowest engine speed to ca. 500 φm.

4. Drive unit according to claim 3, characterized in that the engine control unit (48) is arranged under certain conditions, e.g. cold engine, to steer the engine speed to an elevated idle speed , e.g. ca 700 φm, and when shifting under said preconditions, to lower the lowest permissible engine φm to a speed below the original idle speed.