GB2383394A

GB2383394A - Tensioning device that is fixed during engine start-up

Info

Publication number: GB2383394A
Application number: GB0227971A
Authority: GB
Inventors: Michael Bogner
Original assignee: INA Schaeffler KG
Current assignee: IHO Holding GmbH and Co KG
Priority date: 2001-12-01
Filing date: 2002-11-29
Publication date: 2003-06-25
Anticipated expiration: 2022-11-29
Also published as: FR2833058A1; GB0227971D0; GB2383394B; DE10159072A1; FR2833058B1

Abstract

A tensioning device 7 intended for a traction drive 1, which includes a drive for a starter generator 2, and preferably a belt. In the start-up mode of the engine the roller of the tensioning device 7 is pivoted and fixed in a position that increases the prestressing force on the traction means 5. The tensioning device 7 preferably includes an actuator 9 that may consist of a ball and screw 18 and 19 moved by an electric motor 17.

Description

TENSIONING DEVICE FOR A TRACTION DRIVE

The invention relates to a tensioning device which is intended for a traction drive of an internal combustion 5 engine. The traction means provided are preferably a belt which connects belt pulleys of various units. The traction drive also includes, inter alla, the drive of a starter generator. The tensioning device includes a roller which is pivotable relative to a base portion and 10 which is supported on the traction means under the effect of spring force.

Traction drives of this kind are driven by the crankshaft or the belt pulley thereof, the traction 15 means, particularly a belt, connecting the belt pulleys of the units which are to be driven. Internal combustion engines in current use are usually provided with two separate traction drives. A first traction drive, the control drive, is provided for driving the 20 camshaft or camshafts. A second traction drive, also known as the unit drive, serves to drive, for example, the water pump, the injection pump, the starter generator, the air-conditioning compressor and other units. Increasing lengths of traction means and the 25 rotational asymmetry of the crankshaft, as a result of the combustion process of the internal combustion engine, cause dynamic effects, particularly unwanted vibrations, which are transmitted to the traction drive and hence to the traction means. Moreover, there is a 30 change in the material of the traction means caused by temperature, as a result of which the prestressing force of the traction means, the belt tension, changes particularly at high or low temperature limits. Belts tend to expand because of ageing and wear, reducing the 35 prestressing force set in the new state.

A traction drive which also includes the drive of a starter generator requires an effective prestressing force of the traction means or belt both for the start-

up process and also while the engine is running. During 5 the start-up process the starter generator operating as an electric motor drives the engine. Immediately after the engine has started up or while it is running, the starter generator starts to operate as a generator supplying the onboard power supply of the vehicle with 10 electrical energy. Depending on the operating mode of the engine a torque is transmitted from the starter generator or from the engine via the corresponding belt pulleys into the traction means. Associated with this is an alternation of the return strand and pulling 15 strand or an alternation of the direction of torque in the pulling strand between the belt pulleys of the crankshaft and the starter generator.

The patent JP 010059555A discloses a traction drive 20 which includes the drive of a starter generator. In order to produce an adequate prestressing force in the traction means both during start-up and when the engine is running, the known traction drive includes two automatically operating tensioning means. A first 25 tensioning means comprise a tension roller which rests on the pulling strand between the belt pulleys of the crankshaft and those of the starter generator. The tension roller of the second tensioning device is supported on the pulling strand in a section provided 30 after the starter generator. This construction envisages the first tensioning means being blocked or secured in start-up mode in order to achieve a biased traction means between the starter generator and the belt pulley of the crankshaft. When the engine is 35 running the lock is released so that the roller of the tensioning device guided on the traction means is moveable. The double arrangement of tensioning devices

on the known traction drive takes up more room, which is not available in smaller engines. Furthermore, the double arrangement of tensioning devices increases the work and costs involved in assembly and thus cancels out 5 the savings achieved by the starter generator which combines the functions of generator and starter.

SUMMARY OF THE INVENTION

10 Taking account of the disadvantages of the known solution, the problem of the invention is to provide, for a traction drive of this kind, a tensioning device which is optimum in terms of both costs and space and which adequately biases the traction means irrespective 15 of the operating mode of the engine.

To solve this problem the invention proposes that the traction drive be provided with only one tensioning device. For this purpose the tensioning device has an 20 associated locking system by means of which a roller can be fixed in position in one operating mode, particularly the start-up mode of the engine. By dispensing with a second tensioning device there is a cost advantage over the known prior art. Moreover, the tensioning device

25 according to the invention makes it possible to use belt-driven starter generators for smaller engines as the installation space required is significantly reduced thanks to the provision of only one tensioning device.

30 Further advantageous features of the invention are recited in the dependent claims 2 to 21.

According to an advantageous embodiment of the invention, the locking system is constructed so that 35 before the locking process it additionally pivots the roller in order to increase the prestressing force of the traction means. This meets the requirement of

providing a sufficient prestressing force irrespective of the mode of operation of the internal combustion engine. 5 Preferably, the tensioning device according to the invention is arranged, in its installed state, on the pulling strand between the belt pulleys of the starter generator and the crankshaft of the engine. This position of installation of the tensioning device lo compensates for the elastic change in the length of the traction means occurring in start-up mode during operation as a generator, i.e. when the engine is running, on the return strand of the traction drive.

15 According to this embodiment of the invention, the tensioning device or its roller is automatically pivoted and at the same time locked into the position corresponding to start-up when the engine is stationary.

This procedure ensures that the traction means are 20 sufficiently prestressed even at the beginning of the start-up process and thereby prevents disadvantageous slipping of the traction means.

Alternatively, the invention includes a tensioning 25 device in which the roller is pivoted and fixed in position synchronously with the start-up process of the engine, in order to increase the prestressing force of the traction means.

30 According to an advantageous embodiment, the tension roller or the tensioning device as a whole can be pivoted and locked in position by means of an actuator or an active control member. Preferably, an electromagnetic or electrohydraulic actuator is suitable 35 for this purpose. A control member of this kind, provided with spring means, for example, allows automatic adjustment and locking in order to ensure non

- 5 - slipping drive in the start-up mode. Alternatively, the invention also includes a pneumatically operating actuator and other modes of activity of active control members or actuators which are not specified here.

The invention further includes a tensioning device the actuator of which comprises a ball screw, in which a threaded spindle of the ball screw can be adjusted by means of an electric motor.

Another preferred embodiment of the invention comprises an electronic system with which the effective length of the actuator can be influenced. The actuator is operated taking account of at least one parameter which 15 affects the prestressing force of the traction means.

The electronic system is preferably constructed so that it alters the effective length of the actuator as a function of the generator power, the prestressing force of the traction means, the direction of effect of the 20 torque in the traction means or the speed of a belt pulley and thus directly influences the prestressing force of the traction means. Moreover, the invention also includes the adjustment of the effective length of the actuator as a function of a resetting moment of an 25 electric motor which drives a ball screw integrated in the actuator, for example.

The electronic system is also constructed so as to ensure a permanently constant prestressing in the 30 traction means independently of any lengthening of the traction means caused by wear, for example.

The structure of the tensioning device according to the invention is preferably provided with an actuator which 35 can be operated in at least two positions, an operating position which corresponds to the start-up mode of the engine and a neutral position which is adopted when the

engine is running. As a deviation from this, the invention also includes an actuator which is smoothly variable between the operating position and the neutral position. s The invention can advantageously be applied to tensioning devices of different constructions. For example, it may be used on tensioning devices the base portion of which is connected via a rotary bearing to a 10 pivot arm on whose free end is mounted the roller resiliently supported on the traction means.

The invention can also be combined with a tensioning device wherein the roller resiliently supported on the 15 traction means is connected to the base portion via an eccentric. For tensioning devices of this kind it is useful to secure the base portion rotatably to an engine 20 component, for example the crank case of an engine, and to mount the actuator between the engine component and the base portion.

Instead of an actuator fixed directly to the base 25 portion of the tensioning device or its pivot arm, the invention also provides an indirect link. This might be, in particular, a toggle lever the ends of which are fixed to the engine component and the base portion or pivot arm and the actuator of which is preferably 30 jointed in the region of a toggle joint. This measure allows the actuator force to be stepped up, which is beneficial for the design of the actuator or its control force. Preferably, a stop is provided for the toggle lever by means of which the lever can be precisely 35 positioned in an end position. This feature provides a defined position for the toggle lever and the base

- 7 - portion connected thereto or the pivot arm of the tensioning device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained more fully by means of an embodiment illustrated in two Figures, wherein: Figure 1 diagrammatically shows the structure of a lo traction drive having a tensioning device according to the invention; Figure 2 is a detail, on a larger scale, of the structure of the tensioning device according 15 to the invention.

DETAILED DESCRIPTION OF 1n DRAWINGS

The traction drive 1 shown in Figure 1 serves to drive 20 various units in an internal combustion engine, such as the starter generator 2, water pump 3 and air conditioning compressor 4, which are driven by means of traction means 5, particularly a belt, from the crankshaft 6 of the engine. In addition, the traction 25 drive 1 is associated with a tensioning device 7 the pivotable roller 8 of which abuts on the pulling strand between the crankshaft 6 and the starter generator 2.

The starter generator 2 combines the functions of two previously separate units, the starter and the 30 generator. During the start-up process the starter generator 2 operating as an electric motor drives the engine. Then, when the engine is running, the starter generator 2 begins to operate as a generator, supplying electrical energy to the onboard power supply of the 35 vehicle.

Irrespective of the operating mode of the engine, a torque is transmitted from the starter generator 2 or the engine, i.e. the crankshaft 6, through the corresponding belt pulleys into the traction means 5.

5 In association with this, the return strand and pulling strand alternate or there is an alternation of the direction of torque in the traction means between the starter generator 2 and the crankshaft 6. In order to achieve a sufficient prestressing force in start-up mode 10 in which the starter generator 2 rotating clockwise drives the engine 6, the tensioning device 7 is provided with an actuator 9 or an active control member. In the start-up operation the actuator 9 pivots the roller 8 about the rotation axis 10 of the tensioning device 7.

15 In the end position "a" shown by a dotted line, the roller 8 is locked or fixed in position in order to achieve a "fixed" roller which ensures a constant prestressing force on the traction means 5 during the start-up operation. Immediately after the engine has 20 started up, the actuator 9 is released, as a result of which the roller 8 resiliently bearing on the traction means 7 operates automatically and compensates for any vibrationinduced deflection of the traction means 7 and is able to pivot between the position shown and position 25 "b" shown by dotted lines. In the generating mode, i.e. when the engine is running, the tensioning device 7 is associated with the return strand.

Figure 2 essentially shows the structure of the 30 tensioning device 7 on a larger scale. The tensioning device 7 is connected to a base portion 12 via the rotation axis 10 to an engine component 11, e.g. the crank case of an internal combustion engine. The base portion 12 forms a rotary bearing 14 with a pivot arm 35 13, associated with a torsion spring 15 which ensures that the roller 8 mounted at the end of the pivot arm 13 positively bears against the traction means 5. The

- g - active control member, the actuator 9, by means of which the tensioning device 7 can be pivoted clockwise and fixed in position in order to increase the prestressing force of the traction means 5 in startup mode, is 5 constructed as a ball screw 16. The structure of the ball screw 16 comprises a threaded spindle 18 driven by an electric motor 17, on which a nut 19 is guided. A lever 20 is hinged between the base portion 12 of the tensioning device 7 and the nut 19. The threaded 10 spindle 18 which is to be driven in both directions of rotation allows the nut 19 to be moved axially as shown by the double arrow. In this way the effective length "s" between the threaded spindle 18 and an articulation point 21 of the lever 20 on the base portion 12 can be 15 influenced directly. The electric motor 17 is actuated by means of an electronic system 22 having at least one sensor 23. The electronic system can be used, for example, to activate the actuator 9 synchronously with the start-up operation, to move the tensioning device 7 20 into a position corresponding to the start-up position and to achieve a sufficient prestressing force on the traction means 7 in the start-up mode of the starter generator 2.

- 10 LIST OF REFERENCE NUMERALS

1 Traction drive 2 Starter generator 5 3 Water pump 4 Air conditioning compressor 5 Traction means 6 Crank shaft 7 Tensioning device 10 8 Roller 9 Actuator 10 Rotation axis 11 Engine component 12 Base portion 15 13 Pivot arm 14 Rotary bearing 15 Torsion spring 16 Ball screw 17 Electric motor 20 18 Threaded spindle 19 Nut 20 Lever 21 Articulation point 22 Electronic system 25 23 Sensor

Claims

l CLAIMS

1. A tensioning device intended for a traction drive of an internal combustion engine which includes the 5 drive of a starter generator driven by traction means, wherein a roller of the tensioning device is supported on a traction means and in a start-up mode of the internal combustion engine a locking system fixes the tensioning device in position.

2. A tensioning device according to claim 1, wherein said traction means is a belt.

3. A tensioning device according to claim 1 or 2, 15 wherein said locking system fixes the roller 8 in position.

4. Tensioning device according to any preceding claim, wherein the locking system pivots the roller into a 20 position which increases the prestressing force of the traction means and fixes it in position.

5. Tensioning device according to any preceding claim, wherein the roller abuts on the traction means of the 25 traction drive between the starter generator and the crank shaft of the engine.

6. Tensioning device according to any preceding claim, wherein the roller automatically pivots and locks into 30 the position corresponding to the start-up operation when the engine is stationary.

7. Tensioning device according to any preceding claim wherein, synchronously with the start-up operation of 35 the engine, the roller of the tensioning device pivots and is locked into a position which increases the prestressing force of the traction means.

- 12

8. Tensioning device according to any preceding claim comprising an actuator or an active control element by means of which at least the tensioning roller of the tensioning device can be pivoted and locked.

9. Tensioning device according to claim 8 wherein the actuator is an electromagnetically acting actuator.

10. Tensioning device according to claim 8, wherein the 10 actuator operates electrohydraulically or pneumatically.

11. Tensioning device according to claim 8, wherein the actuator includes a ball screw which can be moved by means of an electric motor.

12. Tensioning device according to claim 11, wherein an operating length "s" obtained between the actuator and the tensioning device can be adjusted by means of an electronic system.

13. Tensioning device according to any of claims 8 to 12, wherein the actuator is operated as a function of at least one of the following parameters: 25 - Generator output; - Tractive force; - Direction of application of the torque in the traction means; - Speed of rotation of a belt pulley; 30 - Resetting moment of the electric motor.

14. Tensioning device according to claim 12, wherein the electronic system ensures a permanently constant prestressing in the traction means, at least during 35 start-up.

15. Tensioning device according to any of claims 6 to

- 13 14, wherein the actuator can be operated in at least two positions.

16. Tensioning device according to any of claims 6 to 5 15 wherein the actuator is smoothly variable.

17. Tensioning device according to any preceding claim, further comprising a base portion which is connected via a rotary bearing to a pivot arm on the free end of which lo is fixed the roller resiliently supported on the traction means.

18. Tensioning device according to claim 17, wherein roller is resiliently guided on the traction means and 15 is connected to the base portion by means of an eccentric.

19. Tensioning device according to any of claims 1 to 16, wherein a base portion of the tensioning device is 20 connected to an engine component via a rotation axis and the actuator is disposed between the base portion and the engine component.

20. Tensioning device according to claim 19, wherein 25 the actuator is indirectly connected to the base portion of the tensioning device via a toggle lever.

21. A tensioning device substantially as hereinbefore described with reference to the drawings.