WO1994008157A1 - Process and device for controlling an automatic gearbox with lockup free-wheel - Google Patents

Abstract

Proposed is a process and a device for implementing the process for controlling an automatic gearbox with lockup free-wheel. With this process and device the second clutch is not engaged until after a first clutch, which is parallel to the free-wheel, has been disengaged. During the gear shift the free-wheel takes over the load.

Description

 Method and device for controlling an automatic gearbox with bridged freewheel

The invention relates to a method and a device for controlling an automatic transmission with a bridged freewheel according to the preamble of the first and fifth claims.

In automatic gearboxes, freewheels are used to suppress load switching surges and to make the shifting process manageable. A freewheel can only transmit a moment in one direction. When the power flow is reversed, the freewheel is overrun.

An automatic manual transmission with freewheel is known from a publication, ZF automatic transmission for passenger cars and light commercial vehicles, page 7, of ZF Getriebe GmbH Saarbrücken. Here, a clutch is arranged parallel to a freewheel. This clutch is closed in selector lever position 1. The purpose of this clutch is to prevent the freewheel from rolling over when the force flow is reversed. Da¬ by remains a frictional connection between the transmission input and output ^~ exist, so that the motor is transmitted in thrust operation the brake torque. Upshifts are not permitted in selector lever position 1. This prevents overlap circuits from occurring. An overlap shift occurs when a second clutch, which is to be engaged, is already transmitting a torque during a shutdown process of a first clutch. In the other selector lever positions 2, 3 and D the control of the clutch is hydraulically locked. The lock prevents that the clutch can be closed due to a defect, since this could lead to safety-critical driving situations.

The invention has for its object to realize a thrust connection in the selector lever positions 2, 3 and D for the first gear.

According to the invention, the object is achieved by the characterizing features of the first and fifth claims.

The solution according to the invention includes an increase in the time interval between the switching-off process of the first clutch, which bridges the freewheel, and the take-over process of the second clutch. The switch-off process and the takeover process take place sequentially. Overlaps between the first and the second coupling do not occur. During the shift transition, the freewheel takes over the load so that there is no interruption in the tractive force. In the case of a shift from the first gear stage, the freewheel takes over the load from the first clutch arranged in parallel after it has switched off. If a sufficiently high pressure level has built up on the second clutch, this takes over the load from the freewheel. When shifting back to the first gear, the freewheel takes over the load from the second clutch, which is now disengaged. If a sufficiently high pressure level has built up on the first clutch that is now engaged, this takes over the load from the freewheel, it bridges the freewheel.

These measures ensure that there is no need for hydraulic locking of the first clutch, which is parallel to the freewheel. A safety-critical engagement of the first clutch cannot take place since the freewheel takes over the load first. • The time interval between the first and the second clutch is increased by accelerating the switch-off process of the first clutch and delaying the filling process of the second clutch.

A device for accelerating the shutdown process is a piston return spring, the z. B. can be a plate spring. This causes the pressure piston to release a clutch plate set more quickly.

The filling process of the second clutch is influenced by two measures:

On the one hand, the mass flow of a first pressure is limited by a device in the pressure supply of the clutch. This facility can e.g. B. be a throttle.

As a further measure, a second pressure, the modulation pressure, is set at a lower level. The second pressure acts on a clutch damper, which is a spring damper system. In the clutch damper, the second pressure causes a force that is directed against the direction of force of the filling pressure of the clutch.

The pressure level of the second pressure is set via an electromagnetic pressure regulator. The pressure regulator is controlled by an electronic control unit.

In an embodiment of the invention it is proposed that the reduction of the second pressure at a low level takes place only above a limit speed. This ensures that in the area of high torque conversion, the clutch is pressurized with sufficiently high pressure, for. B. when starting. As a further measure, the reduction is limited in time. A blocking time prevents that after an upshift can be changed back to the same gear. The blocking time is determined so that the pressure reduction in the first clutch can take place completely during this period.

Another advantage is the setting of limit speeds. A downshift to a lower gear level requested via the selector lever is only carried out if the current engine speed is lower than the limit value. The downshift protection prevents the engine from over-revving. A safety-critical downshift caused by a defect, e.g. B. a downshift from the highest to the lowest gear is also prevented by the Rückschalt¬ fuse.

An exemplary embodiment is shown in the drawing, in which:

Fig. 1 is a system diagram of an automatic transmission;

2 shows a clutch damper;

Fig. 3 shows a coupling element.

Fig. 1 shows an automatic transmission 3, which is connected to a motor 1 through a drive shaft 2. The automatic transmission 3 contains clutches, not shown, which are actuated by electromagnetic valves, not shown, which are contained in a hydraulic control device 4. Also located in the hydraulic control unit 4 is an electromagnetic pressure regulator (not shown) which sets the modulation pressure 10. The electromagnetic valves and the electro

REPLACEMENT LEAF Magnetic pressure regulators are controlled by an electronic control unit 5. The electronic control unit 5 contains the usual components of a microprocessor system, such as input and output part, working memory and computing unit. The input variable for the electronic control unit 5 is an engine speed signal 6, a speed signal which stands for the vehicle speed 7 and the signal from a driving position switch 8.

2 shows a clutch damper 12. The engagement behavior of the clutch 20 is predetermined via the clutch damper 12 and the throttle 21. The clutch damper 12 consists on the one hand of a valve slide 13 and its control piston 14 and 15 and on the other hand of a piston 16 and a compression spring 17. Connected to the clutch damper 12 are a first pressure 9 and a second pressure 10, the modulation print. A third pressure 11 is set from the pressure 9 via the control pistons 14 and 15 in connection with the compression spring 17. The pressure medium supply of the third pressure 11 to the clutch 20 is limited by the throttle 21. Delayed closing of the clutch 20 is thereby achieved.

The outside of the piston 16 is acted upon by the third pressure 11 via a check throttle valve 19. The second pressure 10 ~ acts on the inside of the piston 16, which is connected to the valve slide 13 via the compression spring 17 and the plate spring 18. An increase or decrease in the second pressure 10 thus causes an increase or decrease in the third pressure 11 and the pressure level in the clutch 20. The level of the second pressure 10 is set by the electromagnetic pressure regulator, which is in the hydraulic control unit 4 sits.

REPLACEMENT LEAF The deactivation of a clutch is explained with reference to FIG. 3,

Fig. 3 shows a coupling element. The initial state is shown, i. that is, the clutch is open and transmits no moment. The coupling element consists of a non-rotatably held housing part 22, outer plates 23, inner plates 24, the plate carrier 25, a piston 26, the piston return spring 27 and an intermediate space 28 which is formed from the housing 22 and piston 26. The outer plate 23 is non-rotatably connected to the housing 22 and can be displaced in the axial direction. The inner lamella 24 is connected to the lamella carrier 25 in a rotationally fixed manner and can also be displaced in the axial direction. If a pressure medium is supplied to the intermediate space 28, the piston 26, which is displaceable in the axial direction, moves in the direction of the outer and inner plates. The outer plates 23 and inner plates 24 form a friction clutch. At a sufficiently high pressure level, the piston 26 clamps the outer plates against the inner plates, the axial path of which is limited. A positive connection is created.

If the intermediate space 28 is ventilated, the piston return spring 27 pushes the piston 26 back into its rest position. The piston 26 releases the outer and inner plates. The spring force of the piston return spring 27 causes the clutch to open more quickly.

reference numeral

REPLACEMENT LEAF

Claims

Expectations 1. A method for controlling an automatic gearbox (3) with an electronic control unit (5) which controls or regulates a switching process by means of electromagnetic valves by switching off at least one first clutch with parallel freewheeling and at least a second one Coupling engages, an electromagnetic pressure regulator which specifies a modulation pressure (10), a sensor (7) which detects the vehicle speed and a sensor (6) which detects the engine speed and a driving position switch (8), characterized in that that the second clutch is activated after the first clutch has deactivated. 2. The method according to claim 1, characterized in that the filling of the second clutch is influenced by lowering the modulation pressure (10). 3. The method according to claim 2, characterized in that the modulation pressure (10) is reduced only above a limit speed. 4. The method according to claim 2, characterized in that the lowering of the modulation pressure (10) is limited in time. 5. Device for performing the method according to claim 1, characterized in that the temporal behavior of the first clutch is determined by mechanical means, for. B. by return springs (27). 6. Device for carrying out the method according to claim 1, characterized in that the filling of the second clutch is determined by mechanical means, for. B. by a throttle point (21) in the pressure supply of the clutch (20). 7. The method according to claim 1, characterized in that after an upshift to the same gear stage, shifting can take place only after a blocking time has elapsed. 8. The method according to claim 1, characterized g e e n n ¬ z e i c h n e t that a downshift is carried out only below a predetermined limit speed.