SE1550551A1

SE1550551A1 - A method for shifting to a reverse gear in a hybrid vehicle,a hybrid vehicle, a computer program for shifting to a reverse gear and a computer program product comprising program code.

Info

Publication number: SE1550551A1
Application number: SE1550551A
Authority: SE
Inventors: Mats Liwell; Fredrik Sunden; Mattias Nilsson; Afram Kourie
Original assignee: Scania Cv Ab
Priority date: 2015-05-04
Filing date: 2015-05-04
Publication date: 2016-03-23

Abstract

The invention relates to a method for shifting to a reverse gear while moving forward in a hybrid vehicle (1) comprising an internal combustion engine(2), an electric machine (6), a clutch (4) arranged between the electric machine (6) and the combustion engine (2) and a gearbox (8), wherein the gearbox (8) comprises an input shaft (14) connected to the electric machine (6), a main shaft (15), an output shaft (16), and a lay shaft (18) connected to the input shaft (14) and the main shaft (15). The method comprises the steps of a) identifying a request for shifting to a reverse gear; b) ensuring that specific starting criteria are fulfilled;. c) gradually reducing the electric machine torque (T) to zero and disengaging an engaged gear; d) synchronizing the lay shaft speed and the main shaft. speed and engaging the reverse gear; and e) increasing the electric machine torque (T) until a requested output torque (Tq) is reached.The invention also relates to a hybrid vehicle (1).(Fig. 2)

Description

A method for shifting to a reverse gear in a hybrid vehicle, a hybrid vehicle, a computer program for shifting to a reverse gear and a computer program product comprising program code.

TECHNICAL FIELD The present invention relates to a method for shifting to a reverse gear in a hybrid vehicle according to the preamble of claim 1. The invention also relates to a hybrid vehicle according to claim 7, a computer program for shifting to a reverse gear according to claim 8 and a computer program product comprising program code according to claim 9.

BACKGROUND Operators driving vehicles for transporting and delivering goods often operate under stress when stopping and unloading the goods in heavy city traffic. In order to avoid hindering the traffic it is important that the operator quickly and efficiently can shift from a forward gear to a reverse gear when the operator is forced to drive the vehicle backwards into an unloading location. Vehicles with conventional powertrains, non-hybrid powertrains, must stand substantially still before the reverse gear can be engaged. This is due to the fact that input shaft and the lay shaft in the gearbox rotate in the wrong direction compared to the requested reverse direction when the vehicle is moving forward with a gear engaged. Such shifting procedure from a forward gear to a reverse gear is time consuming and will add stress to an already stressful work environment.

Electric machines are commonly known in vehicle powertrains, for example as propulsion means in hybrid vehicles, as starter motors for combustion engines and as pump drives etc. Electric machines may also be used for synchronization during gear shifting, in particular in conventional manual transmissions and dual clutch transmissions. Shifting between gears in a hybrid vehicle may thereby be performed in a more efficient way compared to 2 vehicles with conventional powertrains. Document US8251867 B2 discloses a method for operating a powertrain comprising an internal combustion engine, a manual transmission and an electric machine, wherein the electric machine is adapted to handle irregular changes in the direction of rotation of transmission shafts. This way, the electric machine may improve gear changes in specific operating situations, such as when changing gear when driving uphill and the vehicle rolls back while shifting gear. However, this solution does not consider the problem to achieve efficiency when shifting from a forward gear to a reverse gear.

SUMMARY OF THE INVENTION Despite known solutions in the field, there is still a need to develop a method for shifting to a reverse gear in a hybrid vehicle, which is quick and efficient and thus minimizes the stress for the operator of the vehicle.

An object of the present invention is thus to achieve a method for shifting to a reverse gear in a hybrid vehicle, which is quick and efficient.

Another object of the invention is to achieve a method for shifting to a reverse gear in a hybrid vehicle, which minimizes the stress for the operator of the vehicle.

A further object of the invention is to achieve a method for shifting to a reverse gear in a hybrid vehicle, which is suitable particularly for operating situations in heavy traffic.

A further object of the invention is to achieve a method for shifting to a reverse gear in a hybrid vehicle, where the accelerator pedal may be depressed throughout the method. 3 Another object of the present invention is to achieve a new and advantageous computer program for shifting to a reverse gear in a hybrid vehicle.

The herein mentioned objects are achieved by a method characterized by the features in the characterizing part of claim 1.

The herein mentioned objects are also achieved by a vehicle characterized by the features in the characterizing part of claim 7.

The herein mentioned objects are also achieved by a computer program for starting an internal combustion engine characterized by the features in the characterizing part of claim 8.

The herein mentioned objects are also achieved by a computer program product for starting an internal combustion engine characterized by the features in the characterizing part of claim 9.

According to an aspect of the present invention a method for shifting to a reverse gear in a hybrid vehicle is provided, the vehicle comprising an internal combustion engine, an electric machine, a clutch arranged between the electric machine and the combustion engine and a gearbox, wherein the gearbox comprises an input shaft connected to the electric machine, a main shaft, an output shaft, and a lay shaft connected to the input shaft and the main shaft. The method comprises the steps of: a) identifying a request for shifting to a reverse gear; ensuring that specific starting criteria are fulfilled; gradually reducing the electric machine torque to zero and disengaging a previously engaged gear; synchronizing the lay shaft speed and the main shaft speed and engaging the reverse gear; and increasing the electric machine torque until a requested output torque is reached. 4 The main shaft of the gearbox is connected to the output shaft and the output shaft speed thus depends on the main shaft speed. The lay shaft is connected to the output shaft via the main shaft. The output shaft is connected to the driving wheels of the vehicle.

An operator of a vehicle driving forward may in specific situations need to quickly change direction and drive the vehicle backwards. Such situations may occur for example for vehicles transporting goods in urban environments with heavy traffic or for snowploughs which repeatedly drives forwards and backwards moving snow. By controlling the electric machine torque to zero and disengaging the engaged gear, and then synchronizing the lay shaft speed and the main shaft speed, the reversed gear can be engaged while the vehicle is moving forward. This way, the shift time between a forward gear and a reverse gear is minimized and a method for shifting to a reverse gear in a hybrid vehicle is achieved, which is quick and efficient.

A control unit is preferably arranged in communication with the combustion engine, the electric machine, the clutch and the gearbox. The control unit thus controls the combustion engine, the electric machine, the clutch and the 20 gearbox.

The request to shift to a reverse gear is preferably provided by the operator of the vehicle through a lever, push button or similar. The request to shift to a reverse gear may alternatively be provided as a signal request in the case where the vehicle is an unmanned vehicle, such as remotely controlled or autonomous vehicle. The control unit suitably receives the request and then determines if it is allowable or not.

The control unit preferably determines if the specific starting criteria are fulfilled and thus determines if the shifting to a reverse gear should be allowed or not.

It is this way ensured that the shifting process only is started under safe conditions and the safety of the operator of the vehicle and the surrounding traffic is thereby guaranteed. If the control unit determines that any of the starting criteria is not fulfilled when the request for shifting to a reverse gear is identified, the steps c)-e) will not be performed. However, if a request for shifting to a reverse gear has been identified, the steps c)-e) will be performed when the control unit at a later stage has determined that all starting criteria are indeed fulfilled. Thus, the starting criteria do not have to be fulfilled at the same time as the request for shifting is identified, but the shifting will not be initiated unless they are.

Suitably, if any of the starting criteria is not fulfilled, the decision not to allow automatic shifting to a reverse gear may be presented to the operator of the vehicle on a display device. Alternatively, when all starting criteria are fulfilled, the decision to allow the automatic shifting to a reverse gear may be presented to the operator on a display device.

Preferably, the step c) comprises ensuring that the clutch is disengaged before gradually reducing the electric machine torque. A hybrid vehicle may be propelled by a combustion engine and/or an electric machine depending on the operating situation. When a request from the operator of the vehicle to shift to a reverse gear is identified, the control unit determines if the clutch is disengaged or not. If the clutch is engaged and the vehicle thus is propelled at least partly by the combustion engine, the combustion engine torque is first reduced to zero and the control unit subsequently controls the clutch such that it is disengaged. This way, the electric machine may be controlled without affecting the combustion engine. The combustion engine may at this stage be controlled to an idle speed. When the clutch is disengaged, the electric machine is controlled such that the electric machine torque is gradually reduced to zero. Thus, the torque provided by the combustion engine and/or the torque provided by the electric machine are gradually reduced to zero before disengaging the gear. Reducing the electric machine torque will have substantially no effect on the input shaft speed and the vehicle will still move forwards. When the electric machine no longer provides any torque, the output 6 shaft is rotated by means of the inertia of the driving wheels and the output shaft thus rotates the main shaft, the lay shaft and the input shaft. At this stage, the forces acting on the engaged gear, that is, the forces acting between the gear on the lay shaft and the gear on the main shaft, are reduced to zero. The previously engaged gear may thereby easily be disengaged.

Preferably the step d) comprises controlling the electric machine such that the direction of rotation of the electric machine is changed. When the electric machine torque is zero and the previously engaged gear is disengaged, the electric machine is controlled to change direction from a first direction to a second direction. When the electric machine starts rotating in the second direction the input shaft will be braked and the input shaft speed will be gradually reduced. After a while the input shaft speed will have decreased to zero whereby the input shaft subsequently starts rotating in the second direction together with the electric machine. The lay shaft always rotates in a direction opposite to the input shaft. When a forward gear is engaged and the vehicle is driving forwards, the lay shaft rotates in a direction opposite to the main shaft and the output shaft. Thus, when driving forwards, the input shaft, the main shaft and the output shaft rotates in the first direction and the lay shaft rotates in the second direction. However, when a reverse gear is engaged and the vehicle is driving backwards, the main shaft and the output shaft rotate in the same direction as the lay shaft, the second direction. This is possible due to an intermediate shaft with a reverse gear arranged between the main shaft and the lay shaft. In order to be able to engage the reverse gear while moving forwards, the lay shaft and the main shaft must rotate in the same direction and the lay shaft speed and the main shaft speed need to be synchronized. By changing the direction of rotation of the electric machine, and thus the input shaft, to the second direction, the lay shaft will start rotating in the first direction. The main shaft and the output shaft still rotate in the first direction since no gear is engaged and the output shaft rotates by means of the driving wheels rolling forwards. Thus, the lay shaft and the main shaft now rotate in the same direction. The electric machine is thereafter controlled such 7 that the lay shaft speed is synchronized with the main shaft speed, whereby the reverse gear may be engaged.

When the reverse gear has been engaged, the electric machine is controlled such that the direction of rotation of the electric machine is changed back to the first direction. The electric machine torque is thereafter gradually increased until a requested output torque is reached. The requested output torque is preferably determined by means of sensor devices arranged in connection to the accelerator pedal sensing the output torque requested by the operator.

Alternatively, the requested output torque is predetermined and stored in the control unit. When the electric machine once again is rotating in the first direction and the torque is increased, the input shaft speed in the second direction will be gradually reduced to zero and eventually the input shaft will start rotating in the first direction. When the input shaft speed in the second direction is reduced to zero the lay shaft speed in the first direction is reduced to zero, whereby the main shaft speed and the output shaft speed in the first direction is reduced to zero. This way, the vehicle speed is reduced to zero and the vehicle stands substantially still. But as the input shaft starts rotating in the first direction again, the lay shaft starts rotating in the second direction and the main shaft and the output shaft thus start rotating in the second direction.

This way, the vehicle speed is increased and the vehicle is propelled backwards. Hence, the inventive method for shifting to a reverse gear automatically brakes the forward movement of the vehicle and changes the driving direction of the vehicle while the operator of the vehicle depresses the accelerator pedal. This way, a method for shifting to a reverse gear is achieved, which is quick and efficient and which minimizes the stress for the operator of the vehicle.

According to an aspect of the invention a starting criterion is that the vehicle speed is equal to or lower than a maximum speed. An operator driving a vehicle forwards, which intends to change direction and drive the vehicle backwards, typically propels the vehicle with a relatively low vehicle speed. 8 However, since the inventive method means that the vehicle keeps moving forward for a while during the shifting to a reverse gear, the operator might feel uncomfortable and unsecure if the vehicle is moving with too high speed. Also, it might tear on the gearbox if the vehicle speed is too high when starting the shifting method. The maximum speed is preferably 1 2-1 3 km/h. If the control unit determines that the vehicle speed is higher than the maximum speed, the steps c)-e) will not be performed.

According to an aspect of the invention a starting criterion is that if the vehicle speed is between the maximum speed and a threshold speed, the brake pedal of the vehicle must be depressed. The threshold speed is preferably between 7-8 km/h. If the vehicle speed thus is lower than or equal to the maximum speed but higher than the threshold speed, the brake pedal of the vehicle must be depressed in order for the steps c)-e) to be performed. The depressed brake pedal indicates that the operator of the vehicle wants to reduce the vehicle speed and thus that the operator indeed intends to change direction of the vehicle. Whether the brake pedal is depressed or not is determined by means of sensor devices arranged in connection to the brake pedal. The sensor devices are arranged in communication with the control unit such that the control unit may determine if the brake pedal is depressed or not.

If the control unit determines that the vehicle speed is lower than or equal to the maximum speed and not higher than the threshold speed, the steps c)-e) may be performed.

According to an aspect of the invention a starting criterion is that the energy level in an energy storage connected to the electric machine must be higher than a predetermined minimum level. When the electric machine is controlled to change direction of rotation to the second direction, the input shaft speed will first be reduced until the input shaft is still and then the input shaft will start rotating in the second direction and the input shaft speed will increase. When the electric machine is rotating in the second direction and the input shaft 9 speed is gradually reduced, energy will be stored in the energy storage since the electric machine will operate as a generator. However, when the input shaft starts rotating in the second direction and the input shaft speed increases, electric energy is needed for the electric machine to be able drive the input shaft. Therefore, if there is not enough energy in the energy storage, the shifting to a reverse gear cannot be performed and the shifting steps c)-e) will not be initiated.

With the same reasoning, a starting criterion may be that the energy level in the energy storage must be lower than a predetermined maximum level. Since energy is generated when the electric machine brakes the input shaft speed, there must be space for that energy in the energy storage. If the control unit determines that the energy level is higher than the maximum level the steps c)-e) will not be performed. Alternatively, if the control unit determines that the energy level in the energy storage is higher than the maximum level, the control unit may control the energy storage to burn off energy such that the energy level becomes lower than the maximum level. The energy may be burnt off by a brake resistor in which energy is converted into heat. When the energy level is low enough, the steps c)-e) are performed.

Preferably all starting criteria mentioned herein must be fulfilled in order to initiate the steps c)-e).

The torque provided by the electric machine is preferably increased by increasing the current and/or power supply to the electric machine.

According to an aspect of the invention, a computer program is provided, wherein said computer program comprises programme code for causing an electronic control unit or another computer connected to the electronic control unit to perform the steps according to the herein mentioned method for shifting to a reverse gear.

According to an aspect of the invention a computer programme product is provided, comprising a programme code stored on a computer-readable medium for performing the method steps according to the herein mentioned method for shifting to a reverse gear, when said computer programme is run on an electronic control unit or another computer connected to the electronic control unit.

Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following details, and also by putting the invention into practice. Whereas the invention is described below, it should be noted that it is not restricted to the specific details described. Specialists having access to the teachings herein will recognise further applications, modifications and incorporations within other fields, which are within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS For fuller understanding of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which: Figure 1schematically illustrates a vehicle according to an embodiment of the invention; Figure 2schematically illustrates a hybrid powertrain according to an embodiment of the invention; Figure 3illustrates a flow chart for a method for shifting to a reverse gear according to an embodiment of the invention; Figure 4illustrates a diagrams of torque and speed variations during a method for shifting to a reverse gear according to an embodiment of the invention; and 11 Figure schematically illustrates a control unit or computer according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 schematically shows a side view of a hybrid vehicle 1 according to an embodiment of the invention. A hybrid vehicle is considered to be a vehicle with a hybrid powertrain, such that the vehicle may be propelled by a combustion engine and/or an electric machine. The vehicle 1 comprises a hybrid powertrain 3 with a combustion engine 2, a clutch 4 (not shown), an electric machine 6 (not shown) and a gearbox 8. The electric machine 6 is connected to the gearbox 8. The gearbox 8 is also connected to the driving wheels 10 of the vehicle 1 through an output shaft 16. The vehicle 1 may be a heavy vehicle, e.g. a truck or a bus. The vehicle 1 may alternatively be a passenger car.

Figure 2 schematically shows a hybrid powertrain 3 of a vehicle 1 according to an embodiment of the invention. The hybrid powertrain 3 comprises a combustion engine 2, a clutch 4, an electric machine 6 and a gearbox 8. The crankshaft 12 of the combustion engine 2 is connected to one side of the clutch 4 and the electric machine 6 is connected to the other side of the clutch 4. The clutch 4 is thus arranged between the combustion engine 2 and the electric machine 6. The gearbox 8 comprises an input shaft 14 connected to the electric machine 6 and an output shaft 16 connected to the driving wheels of the vehicle 1. The gearbox 8 further comprises a lay shaft 18 arranged in connection to the input shaft 14 and a main shaft 15. The main shaft 15 is connected to the output shaft 16. Only two driving wheels 10 are illustrated in Figure 2, however, any number of driving wheels 10 may be driven by the hybrid powertrain 3 within the scope of the invention. 12 The combustion engine 2, the clutch 4, the electric machine 6 and the gearbox 8 are arranged in connection to a control unit 20. The control unit 20 is adapted to control the combustion engine 2, the clutch 4, the electric machine 6 and the gearbox 8, for example for shifting to a reverse gear while the vehicle 1 is moving forwards. A computer 22 may be connected to the control unit 20.

In order to drive the driving wheels 10 and thus propel the vehicle 1, the combustion engine 2 and/or the electric machine 6 generates a torque which is transferred via the gearbox 8 to the output shaft 16. The torque on the output shaft 16, called output torque, is the torque that propels the vehicle 1. When the combustion engine 2 provides output torque and propels the vehicle 1, the clutch 4 is engaged and a gear is engaged. The electric machine 6 may in this case either provide additional output torque on the output shaft 16 or it may operate as a generator. When the electric machine 6 solely provides the output torque, the clutch 4 is disengaged and a gear is engaged. When the vehicle 1 is driven forwards by the combustion engine 2 and/or the electric machine 6, a forward gear is engaged and the input shaft 14 is rotating in a first direction and the main shaft 15 and the output shaft 16 are rotating in the same first direction. The lay shaft 18 is always rotating in the opposite direction to the input shaft 14, thus when the vehicle 1 is driven forwards the lay shaft 18 rotates in a second direction. When the vehicle 1 is driven backwards, a reverse gear is engaged and the main shaft 15 and the output shaft 16 are rotating in the second direction. An intermediate shaft 24 with a gear is arranged between the lay shaft 18 and the main shaft 15. This constitutes the reverse gear and when it is engaged to the main shaft 15 and the lay shaft 18 it allows the output shaft 16 to rotate in the second direction while the input shaft still rotates in the first direction. When the vehicle 1 is driven backwards the lay shaft 18 thus rotates in the same direction as the main shaft 15 and the output shaft 16. Since the lay shaft 18 and the main shaft 15 rotates in different directions when the vehicle 1 is moving forwards it is difficult to engage the reverse gear. Conventionally the vehicle 1 must stand still such that the main 13 shaft 15 and the lay shaft 18 are substantially still before the reverse gear can be engaged.

Figure 3 shows a flowchart for a method for shifting to a reverse gear in a hybrid vehicle 1 comprising an internal combustion engine 2, an electric machine 6, a clutch 4 arranged between the electric machine 6 and the combustion engine 2 and a gearbox 8, wherein the gearbox 8 comprises an input shaft 14 connected to the electric machine 6, a main shaft 15, an output shaft 16, and a lay shaft 18 connected to the input shaft 14 and the main shaft 15. The vehicle is suitably configured as described in Figure 2. The method comprises the steps of a) identifying a request for shifting to a reverse gear; b) ensuring that specific starting criteria are fulfilled; c) gradually reducing the electric machine torque Te to zero and disengaging a previously engaged gear; d) synchronizing the lay shaft speed and the main shaft speed and engaging the reverse gear; and e) increasing the electric machine torque Te until a requested output torque Treq is reached. The method steps are also illustrated by torque and speed variations in Figure 4.

In the step a), the request for shifting to a reverse gear is preferably identified by the control unit 20 by means of a lever or push button or similar, through which the operator of the vehicle 1 indicates the desire to shift to a reverse gear. The request to shift to a reverse gear may alternatively be provided as a signal request in the case where the vehicle 1 is an unmanned vehicle, such as remotely controlled or autonomous vehicle.

In the step b), the control unit 20 preferably determines if the starting criteria are fulfilled and thus decides if the following method steps are allowed to be performed or not. This way, it is ensured that the shifting is performed under safe conditions and the safety of the operator of the vehicle and the surrounding traffic is thereby guaranteed. If one or several starting criteria are not fulfilled and a request for shifting to a reverse gear has been identified, the steps c)-e) will be performed at a later stage when the control unit 20 has 14 determined that all starting criteria are indeed fulfilled. Thus, the starting criteria must not be fulfilled at the same time as the request for shifting is identified, but the starting criteria must be fulfilled in order to proceed with the shifting.

The step c) to gradually reduce the electric machine torque Te to zero and disengage a previously engaged gear, preferably comprises ensuring that the clutch 4 is disengaged before gradually reducing the electric machine torque Te to zero. When a request to shift to a reverse gear is identified and all starting criteria are fulfilled, the control unit 20 determines if the clutch 4 is disengaged or not. If the clutch 4 is engaged and the vehicle 1 thus is propelled at least partly by the combustion engine 2, the combustion engine torque is reduced to zero and the control unit 20 controls the clutch 4 such that it is disengaged. This way, the electric machine 6 may be controlled without affecting the combustion engine 2. The combustion engine 2 may at this stage be controlled to an idle speed. When the clutch 4 is disengaged, the electric machine 6 is controlled such that the electric machine torque T. is gradually reduced to zero. The reduce of electric machine torque Te will have substantially no effect on the input shaft speed ninput and the vehicle 1 will still move forwards. This is further illustrated in Figure 4. When the electric machine 6 no longer provides any torque Te, the output shaft 16 is rotated in the first direction by means of the driving wheels 10 and the output shaft 16 thus rotates the main shaft 15 and the lay shaft 18 in the second direction and the input shaft 14 in the first direction. At this stage, the forces acting on the engaged gear, that is, the forces acting between the gear on the lay shaft 18 and the gear on the main shaft 15, are reduced to zero. The previously engaged gear may thereby easily be disengaged.

The step d) to synchronize the lay shaft speed and the main shaft speed and engage the reverse gear preferably comprises controlling the electric machine 6 such that the direction of rotation of the electric machine 6 is changed. When the electric machine torque T. is zero and the previously engaged gear is disengaged, the electric machine 6 is controlled to change direction from the first direction to the second direction. When the electric machine 6 starts rotating in the second direction the input shaft 14 will initially be braked and the input shaft speed ninput will be gradually reduced to zero (see figure 4). The input shaft 14 will subsequently start rotating in the second direction together with the electric machine 6. By changing the direction of rotation of the electric machine 6, and thus the input shaft 14, to the second direction, the lay shaft 18 will start rotating in the first direction. The main shaft 15 and the output shaft 16 still rotates in the first direction since no gear is engaged and the output shaft 16 rotates by means of the driving wheels 10 rolling forwards. Thus, the lay shaft 18 and the main shaft 15 now rotate in the same direction. The electric machine 6 is thereafter controlled such that the input shaft speed ninput, and thus the lay shaft speed, is synchronized with the main shaft speed, whereby the reverse gear is engaged.

The step e) to increase the electric machine torque Te until a requested output torque Treq is reached preferably comprises controlling the electric machine 6 such that the direction of rotation of the electric machine 6 is changed back to the first direction. The electric machine torque Te is thereafter gradually increased until a requested output torque Treq is reached. The requested output torque Treq is preferably determined by means of sensor devices arranged in connection to the accelerator pedal sensing the output torque Treq requested by the operator. When the electric machine 6 once again is rotating in the first direction and the torque Te is increased, the input shaft speed ninput in the second direction will be reduced to zero and eventually the input shaft 14 will start rotating in the first direction. When the input shaft speed ninpui in the second direction is reduced to zero the lay shaft speed in the first direction is reduced to zero, whereby the main shaft speed and the output shaft speed in the first direction is reduced to zero. This way, the vehicle speed Vvehicle is reduced to zero and the vehicle stands substantially still. But as the input shaft 14 starts rotating in the first direction again, the lay shaft 18 starts rotating in the second direction and the main shaft 15 and the output shaft 16 thus start 16 rotating in the second direction. This way, the vehicle speed Vvernde is increased and the vehicle 1 is propelled backwards.

One starting criterion may be that the vehicle speed Vvehicie is equal to or lower than a maximum speed Vmax. The maximum speed Vmax is preferably 12-13 km/h. If the control unit determines that the vehicle speed Vvehicie is higher than the maximum speed Vmax, the steps c)-e) will not be performed.

Another starting criterion may be that if the vehicle speed Vvehicle is between the maximum speed Vmax and a threshold speed Vth, the brake pedal of the vehicle 1 must be depressed. The threshold speed Vih is preferably between 7- 8 km/h. If the vehicle speed Vvenide thus is lower than or equal to the maximum speed Vmax but higher than the threshold speed Vth, the brake pedal of the vehicle 1 must be depressed in order for the steps c)-e) to be performed. The depressed brake pedal indicates that the operator of the vehicle 1 wants to reduce the vehicle speed Vvehicle and thus that the operator indeed intends to change direction of the vehicle 1. Whether the brake pedal is depressed or not is determined by means of sensor devices arranged in connection to the brake pedal. The sensor devices are arranged in communication with the control unit 20 such that the control unit 20 may determine if the brake pedal is depressed or not.

Another starting criterion may be that the energy level in an energy storage connected to the electric machine 6 must be higher than a predetermined minimum level. When the electric machine 6 is controlled to change direction of rotation to the second direction, the input shaft speed ninput will first be reduced until the input shaft 14 is still and then the input shaft 14 will start rotating in the second direction and the input shaft speed ninput will increase. When the electric machine 6 is rotating in the second direction and the input shaft speed ninput is gradually reduced, energy will be stored in the energy storage since the electric machine 6 will operate as a generator. However, when the input shaft 14 starts rotating in the second direction and the input shaft speed ninput increases electric energy is needed for the electric machine 6 17 to be able drive the input shaft 14. Therefore, if there is not enough energy in the energy storage, the shifting to a reverse gear cannot be performed and the shifting steps will not be initiated.

Yet another starting criterion may be that the energy level in the energy storage must be lower than a predetermined maximum level. Since energy is generated when the electric machine 6 brakes the input shaft speed ninpul, there must be room for that energy in the energy storage. If the control unit 20 determines that the energy level is higher than the maximum level the steps c)- e) will not be performed. Alternatively, if the control unit 20 determines that the energy level in the energy storage is higher than the maximum level, the control unit 20 may control the energy storage to burn off energy with a brake resistor, such that the energy level becomes lower than the maximum level. When the energy level is low enough, the steps c)-e) are performed.

Figure 4 shows a diagram of the electric machine torque Te, input shaft speed ninput and vehicle speed Vvehicie variations during a method for shifting to a reverse gear according to an embodiment of the invention. The method for shifting to a reverse gear is described in Figure 3 and is here further illustrated by the diagram over the torque and speed variations over time.

The top curve illustrates the electric machine torque Te variations over time measured in seconds. The middle curve illustrates the input shaft speed ninput variations over time measured in seconds and the bottom curve illustrates the vehicle speed Vvehicle variations over time measured in seconds.

The vehicle 1 is propelled forwards and a gear is thus engaged. Typically the vehicle 1 is propelled by both the combustion engine 2 and the electric machine 6 whereby the clutch 4 is engaged. The time t1 represents the time when all starting criteria are fulfilled and a request for shifting to a reverse gear has been identified. At the time t1 the clutch 4 is disengaged. The time ti thus 18 represents the time when the step c) to gradually reduce the electric machine torque Te to zero and disengage a previously engaged gear is initiated.

The time t2 represents the time when the electric machine torque Te is zero and the engaged gear is disengaged. At t2 the vehicle speed Vvehide might have been slightly reduced. When the electric machine torque Te is zero and the previously engaged gear is disengaged, the electric machine 6 is controlled to change direction from the first direction to the second direction. This is illustrated with a negative electric machine torque Te in the top curve. When the electric machine 6 starts rotating in the second direction the input shaft speed ninput in the first direction will be gradually reduced as can be seen in the middle curve. After a while the input shaft speed ninput will have decreased to zero after which the input shaft 14 also starts rotating in the second direction. This is illustrated with a negative input shaft speed ninput. By changing the direction of rotation of the electric machine 6, and thus the input shaft 14, to the second direction, the lay shaft 18 will start rotating in the first direction. The main shaft 15 and the output shaft 16 still rotate in the first direction since no gear is engaged and the vehicle speed Vvehicie is thus not affected. The electric machine 6 is controlled such that the input shaft speed ninput, and thus the lay shaft speed, is synchronized with the main shaft speed. The time t3 represents the time when the lay shaft speed and the main shaft speed are synchronized and when the reverse gear is engaged.

When the reverse gear has been engaged, the electric machine 6 is changed back to rotate in the first direction. The electric machine torque Te is thereafter gradually increased until it corresponds to a requested output torque Treq. When the electric machine 6 once again is rotating in the first direction and the electric machine torque Te is increased, the input shaft speed ninput in the second direction will first be reduced to zero by the braking effect of the electric machine 6 and eventually the input shaft 14 will start rotating in the first direction. The time t4 represents the time when the input shaft 14 starts rotating in the first direction. When the input shaft speed ninput in the second direction is 19 reduced to zero the lay shaft speed in the first direction is reduced to zero, whereby the main shaft speed and the output shaft speed in the first direction is reduced to zero since the reverse gear is engaged. This way, the vehicle speed Vvehicie is reduced to zero as illustrated in the bottom curve. At the time tt the input shaft 14 starts rotating in the first direction again and the input shaft speed hinput in the first direction is increased. This means that the lay shaft 18 starts rotating in the second direction and the main shaft 15 and the output shaft 16 thus starts rotating in the second direction. This way, the vehicle speed Vvehipie is increased and the vehicle 1 is propelled backwards.

Figure 5 is a diagram of a version of a device 500. The control unit 20 and/or computer 22 described with reference to Figure 2 may in a version comprise the device 500. The term "link" refers herein to a communication link which may be a physical connection such as an optoelectronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link. The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile memory 520 has a first memory element 530 in which a computer programme, e.g. an operating system, is stored for controlling the function of the device 500. The device 500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.

There is provided a computer programme P which comprises routines for shifting to a reverse gear. The computer programme P comprises routines for identifying a request for shifting to a reverse gear. The computer programme P comprises routines for ensuring that specific starting criteria are fulfilled. The computer programme P comprises routines for gradually reducing the electric machine torque Te to zero and disengaging an engaged gear. The computer programme P comprises routines for disengaging the clutch 4. The computer programme P comprises routines for synchronizing the lay shaft speed and the main shaft speed and engaging the reverse gear. The computer programme P comprises routines for changing the direction of rotation of the electric machine 6. The computer programme P comprises routines for increasing the electric machine torque Te until a requested output torque Treq is reached.

The programme P may be stored in an executable form or in a compressed form in a memory 560 and/or in a read/write memory 550.

Where the data processing unit 510 is described as performing a certain function, it means that the data processing unit 510 effects a certain part of the programme stored in the memory 560 or a certain part of the programme stored in the read/write memory 550.

The data processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit 510 via a data bus 511. The read/write memory 550 is adapted to communicating with the data processing unit 510 via a data bus 514.

When data are received on the data port 599, they are stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 is prepared to effect code execution as described above.

Parts of the methods herein described may be effected by the device 500 by means of the data processing unit 510 which runs the programme stored in the memory 560 or the read/write memory 550. When the device 500 runs the programme, methods herein described are executed.

The foregoing description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended 21 to be exhaustive or to restrict the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and its practical applications and hence make it possible for specialists to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims

22 Claims

1. A method for shifting to a reverse gear while moving forward in a hybrid vehicle (1) comprising an internal combustion engine(2), an electric machine (6), a clutch (4) arranged between the electric machine (6) and the combustion engine (2) and a gearbox (8), wherein the gearbox (8) comprises an input shaft (14) connected to the electric machine (6), a main shaft (15), an output shaft (16), and a lay shaft (18) connected to the input shaft (14) and the main shaft (15), characterized by the steps of: a) identifying a request for shifting to a reverse gear; b) ensuring that specific starting criteria are fulfilled; 3. gradually reducing the electric machine torque (Te) to zero and disengaging an engaged gear; 4. synchronizing the lay shaft speed and the main shaft speed and engaging the reverse gear; and e) increasing the electric machine torque (Te) until a requested output torque (Treq) is reached.

2. A method according to claim 1, characterized in that step c) comprises disengaging the clutch (4) before gradually reducing the electric machine torque (Te).

3. A method according to claim 1 or 2, characterized in that step d) comprises controlling the electric machine (6) such that the direction of rotation of the electric machine (6) is changed.

4. A method according to any of the preceding claims, characterized in that a starting criterion is that the energy level in an energy storage connected to the electric machine (6) must be higher than a predetermined minimum level.

5. A method according to any of the preceding claims, characterized in that a starting criterion is that the vehicle speed (Vvehicie) is equal to or lower than a maximum speed (Vmax). 23

6. A method according to claim 5, characterized in that a starting criterion is that if the vehicle speed (Vvehicie) is between the maximum speed (Vmax) and a threshold speed (Vth), the brake pedal of the vehicle (1) must be depressed.

7. A hybrid vehicle (1), characterized in that shifting to a reverse gear in the vehicle (1) may be performed according to the method in any of the claims 1-6.

8. A computer program (P), wherein said computer program comprises programme code for causing an electronic control unit (20; 500) or another computer (22; 500) connected to the electronic control unit (20; 500) to perform the steps according to any of the claims 1-6.

9. A computer programme product comprising a programme code stored on a computer-readable medium for performing the method steps according to any of claims 1-6, when said computer programme is run on an electronic control unit (20; 500) or another computer (22; 500) connected to the electronic control unit (18; 500). I. 'bld C 0 1. 171- 9 9 1- 9tr .b! 3/