GB2465979A

GB2465979A - A shift-by-wire system with a dedicated communication bus

Info

Publication number: GB2465979A
Application number: GB0822035A
Authority: GB
Inventors: Thomas Magnusson; Christian Rubsam; Jan Sporleder
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2008-12-03
Filing date: 2008-12-03
Publication date: 2010-06-09
Anticipated expiration: 2028-12-03
Also published as: GB0822035D0; GB2465979B; WO2010063340A1

Abstract

A bus system for a motor vehicle comphises a first bus 101, a transmission control unit 103 connected to said first bus an engine control unit 104, and a first actuator 108 for driving a shifting operation in a gearbox of the vehicle under control of the transmission control unit(TCU)103. The transmission control unit is connected to a gear selector 106 and to a clutch 111 by a second bus 102. Preferably the second bus has a greater bandwidth than the first bus. The TCU is preferably disposed between a clutch pedal and said clutch for controlling the clutch with respect to the said pedal position. The said gear selector shift-by-wire system simulates such a mechanical shifting system by use of the gear shifter as shown in figure 2.

Description

Bus System for a Motor Vehicle

Description

The present invention relates to a bus system for a motor vehicle by which various electronic devices of the vehicle can exchange information. In conventional bus systems of this type, based e.g. on the CAN standard, a huge number of devices, comprising controllers of vital functions of the vehicle as well as e.g. entertainment electronics devices can communicate indiscriminately.

Since only one device can transmit a message on the bus at a given time, there is a risk that due to excessive bus traffic messages of the vital components cannot be transmitted at short notice, and that response times may become intolerably long. This may cause problems in a vehicle of the shift-by-wire type, if an appropriate synchronisation of operations of a gear selector operated by the driver, of an actuator for driving a shifting operation in a gearbox of the vehicle, and of a clutch cannot be ensured.

The present invention solves this problem by means of a bus system for a motor vehicle comprising a first bus, a plurality of devices connected to said first bus, a transmission control unit and a first actuator for driving a shifting operation in a gearbox of the vehicle under control of the transmission control unit in which the transmission control unit is connected to a gear selector and a clutch by a second bus. By keeping this second bus free from messages of non-vital devices, which are assigned to the first bus, an unnecessary delay of communication between the devices connected to the second bus is avoided.

In order to achieve still shorter response times, the second bus may have a greater bandwidth than the first bus.

The gear selector preferably comprises a shift lever which is displaceable by the driver between various positions associated to different gears and a position sensor for detecting the position of the shift lever and communicating the detected position on said second bus.

The gear selector further preferably comprises a second actuator for impeding a displacement of said shift lever based on an instruction received via said second bus. The actuator may thus block an undesired displacement completely, or it may merely provide an increased resistance against displacement, in order to warn the driver that a shifting movement he is attempting is inadequate, e.g. because it is leading to a position associated to a gear which is ill-adapted to the present speed of the vehicle or because the first actuator is not able to follow the movement of the gear selector, e.g. due to a synchronization process in the gearbox being unfinished.

The first actuator may be connected to the transmission control unit by a dedicated line, for receiving instructions and/or providing feedback to the transmission control unit.

If the bandwidth of the second bus is high enough, the first actuator may as an alternative be connected to the transmission control unit by said second bus.

In particular, if a mismatch between positions of the shift lever and the first actuator is detected, e.g. by the transmission control unit, the second actuator may be activated in order to impede a displacement of the gear selector.

The transmission control unit is further preferably connected between a clutch pedal and said clutch, in order to be able to control the clutch at variance with the clutch pedal. This measure may be appropriate in particular if the driver releases the clutch pedal before synchronisation between upstream and downstream gearwheels in the gearbox has been achieved.

The transmission control unit may further be adapted to address a torque request to an engine control unit. By an appropriate torque request, damage to the gearbox which might be caused by an inappropriate shifting operation can be prevented, even if the transmission control unit is not adapted to control the clutch at variance with the clutch pedal or if such a control has failed. To this effect, a torque request from the transmission control unit should override a torque request from another device, in particular from an accelerator pedal.

In order to enable communication between the devices connected to the second bus and others connected to the first bus, the transmission control unit preferably forms a message gateway between said first and second buses.

Among the devices connected to the first bus, there may be the engine control unit. In that case the above-mentioned torque request would have to be transmitted on the first bus.

Further features and advantages of the invention will become apparent from the subsequent description of embodiments thereof referring to the appended drawings.

Fig. 1 is a block diagram of a bus system according to an embodiment of the invention; and Fig. 2 is a diagram of a gear selector which can be used in the invention.

In the block diagram of Fig. 1, two CAN buses are assigned reference numerals 101, 102. Bus 101 interconnects a transmission control unit (TCU) 103, an engine control unit (ECU) 104, a dashboard display device and various other devices of the vehicle, not shown, such as sensors providing input information for the ECU 104, e.g. an accelerator position pedal sensor, a driving speed sensor, a rotation speed sensor for detecting the crankshaft rotation speed of an engine of the vehicle, etc., or devices which have operation status data to display on display device 105, e.g. the above mentioned speed sensors, an air conditioner, and others.

Bus 102 is faster than bus 101, but the number of devices connected to it is smaller. In the embodiment shown in Fig. 1, only a gear selector 106, a clutch control unit 107 for controlling a clutch 111 mounted between the engine and a gearbox, and transmission control unit 103 are connected to bus 102. Actuators 108 for driving shift and select movements of a shifting rod in the gearbox, not shown, may be connected to the bus 102 or may communicate directly with TCU 103 via a dedicated line 109, shown in phantom in Fig. 1.

Optionally, a mode switch 110 is connected to TCU 103. The mode switch 110 allows a driver to select between manual or automatic shifting operation modes, 0 between different algorithms for gear selection when in automatic operation mode, e.g. a sport mode in which downshifting is carried out liberally when the driver accelerates, and/or synchronization times are short, and a comfort mode in which a threshold for downshifting is higher than in the sport mode and/or synchronization times are longer.

In an elementary embodiment of the invention, the gear selector 6 might be a simple pushbutton which is depressed by the driver in order to initiate an upshifting or downshifting process. The shifting operation itself is then carried out by the TCU 103 by sending a clutch opening instruction to clutch control unit 107, controlling the actuators 108 to carry out the appropriate shifting movement and then sending another instruction to clutch control unit 107 to close the clutch again. In such an embodiment the duration of a shifting process is always the same, or the driver can be given the possibility of setting a more or less sporty or more or less comfortable duration of the shifting process using mode switch 110.

In a conventional mechanical shifting system, the driver determines the duration of each shifting process by the speed with which he moves a gearshift lever. According to a preferred embodiment of the invention, the shift-by-wire system simulates such a mechanical shifting system by use of the gear selector 106 shown in Fig. 2. This gear selector comprises a shifter-selector lever 1 having an articulation ball 2, a rod 3 extending upwards from said ball 2, a handle 4 at the upper end of rod 3 and a spring cartridge 5 extending downwards from ball 2. Ball 2 is caught between a housing plate 6 which is mounted stationary with respect to the passenger compartment of the motor vehicle and a bearing plate 7 which is slightly displaceable with respect to housing plate 6. Housing plate 6 and bearing plate 7 have aligned passages which together form a space in which articulation ball 2 is received substantially without play.

Bearing plate 7 is urged against housing plate 6 by springs, in the present case by two compressed coil springs 8, each of which is arranged around a pin 10 fixed to housing plate 6 and extending from there through a bore 9 of bearing plate 7 in a downward direction. Each spring 8 is supported by a head 11 formed at a lower end of pin 10. The strength of the springs 8 is chosen so that due to friction between the articulation ball 2 and surfaces of the passages of housing plate 6 and bearing plate 7 the shift/select lever 1 is not displaceable at all or only by applying substantial force.

Between housing plate 6 and bearing plate 7 two actuators 12 are provided which are adapted to overcome the force of springs 8 and to displace bearing plate 7 off housing plate 6, so that articulation ball 2 becomes easily moveable. The required stroke of actuators 12 is small, so that piezoelectric actuators can be used; other types of actuators can also be used, in particular if they have short response times.

The spring cartridge 5 comprises an outer sleeve 13 which is fixed to articulation ball 2, an inner sleeve 14 which is telescopically displaceable within outer sleeve 13, a ball 15 at the tip of inner sleeve 14 and a coil spring 16 which urges ball 15 away from articulation ball 2.

The outer sleeve 13 extends through slots of a slotted plate 17 which define the possibilities of displacement of lever 1. Spring 16 urges ball 15 against a contour 18 which, in the section of Fig. 2, has the shape of a circular arc centred upon articulation ball 2 and having three recesses 19, 20, 19. The shape of contour 18 guarantees that the orientation of lever 1 shown in Fig. 1, in which ball 15 engages central recess 20, is stable, just like an orientation in which the lever 1 is tilted around an axis perpendicular to the plane of Fig. 1 and ball 15 engages one of recesses 19.

In a way familiar to the man of the art, the slots of slotted plate 17 comprise a selection slot and a plurality of shifting slots which extend at right angles from the selection slot. While the lever 1 is in the selection slot, ball 15 engages recess 20, and if the lever 1 is at the end of a shifting slot, ball 15 is in one of recesses 19.

A position sensor for sensing the orientation of lever 1 comprises e.g. two potentiometers which are coupled to the lever 1 so that the resistance of one of the two potentiometers is representative of the position of lever 1 in the selection slot and the other is representative of its position in a shifting slot. The two potentiometers are coupled to CAN bus 102 by a CAN interface, not shown, for converting, at regular time intervals or upon receipt of a request from bus 102, the resistance value of one or both potentiometers into a CAN message which is output to bus 102. The same CAN interface also controls the piezoelectric actuators 12 based on received CAN messages.

As a default, piezoelectric actuators 12 are off, and shift lever 1 is fixed in its position. If TCU 3 detects that the clutch pedal is depressed, it sends an instruction to gear selector 106 by which the actuators 12 are activated and shift lever 1 becomes displaceable.

In a subsequent displacement of the shift lever 1 by the driver, TCU 103 continuously monitors the shift lever positions detected by the two potentiometers, and controls actuators 108 accordingly. In this way, the speed of the shifting rod of the gearbox that is displaced by the actuators 108 corresponds to the speed with which the driver operates the shift lever 1, just as it would in a conventional mechanic shifting system. If TCU 103 detects that shift lever 1 is entering a shifting slot, it checks whether the gear associated to this slot is compatible with the present vehicle speed and rotation speed. If yes, it allows the displacement to proceed; if not, it controls a voltage applied to the piezoelectric actuators 12 so that the lever 1 is blocked or experiences a continuously increasing resistance, so that the driver can immediately feel that the gear selected by him is not appropriate and might cause damage to the gearbox.

If the driver pushes the lever 1 so hard that the blocking effect is overcome, TCtJ 103 issues a torque request to ECU 4 which overrides any concurrent torque request from the accelerator pedal. In this way, the speed of the motor can be adapted in a short time so that if the inappropriate gear is indeed engaged, damage to the gearbox is avoided or at least minimized.

If the gear selected by the driver is judged to be appropriate by TCU 103, it allows *the lever to be pushed forward into the shifting slot freely, until the actuator 108 associated to a shifting movement of the gearbox reaches a synchronizing position. In this position, according to a first alternative TCU 103 blocks further displacement of lever 1 until synchronization is achieved and the actuator 8 is free to move on and actually engages the selected gear in the gearbox.

According to a second alternative the resistance of the shift lever 1 against displacement is only increased, so that the driver can bring the lever into the position associated to the selected gear but knows from the resistance that the gear is not yet engaged but that synchronization is in course.

Since each shifting process requires position data of shift lever 1 to be supplied to TCU 103 at a high rate and the actuators 12 should be controlled with short response times in the millisecond range, it is readily apparent that a high bandwidth for communication between TCU 103, gear selector 106 and actuators 108 is desirable. Such a high bandwidth is best ensured by dedicated bus 102.

If the TC[J 103 detects from position feedback information provided by actuators 108 that a shifting process in the gearbox has terminated properly, it forwards clutch pedal position data from a clutch pedal 112 directly to clutch control unit 107, allowing the latter to set a degree of closure of the clutch 111 corresponding to the current position of clutch pedal 112. If a shifting process is not terminated properly before the clutch pedal 112 is released, TCU 103 does not forward the clutch pedal position information to clutch -10 -control unit 107 but controls the clutch 111 autonomously, instructing clutch control unit 107 to keep the clutch lii open until position information from actuators 108 indicates that a new gear was successfully selected in the gearbox.

Advantageously, clutch control unit 107 continuously provides feedback information concerning the position of the clutch 111 and/or an internal failure of clutch control unit 107 to TCU 103, and TCU 103 in that case outputs a torque request to ECU 104 via 101 overriding any current torque request from the accelerator pedal, so as to control the engine of the vehicle in a way in which the failure of the clutch 111 or its control unit 107 will not cause subsequent damage in the gearbox.

Another condition in which the TCU 103 may send instructions to clutch control unit 107 which are at variance from the current position of the clutch pedal 112 is if the driver releases the pedal 112 very quickly.

In this case, the TCU 103 can control the closing of the clutch lii to be slowed down, in order to avoid a high torque peak from occurring at the clutch 111 upon closing, which peak would cause unnecessary wear of the clutch lii and/or an uncomfortable jolt of the vehicle.