SE540314C2 - Method and system for connecting a selectively switchable compressor to an internal combustion engine - Google Patents

Description

Method and system for connecting a selectively switchable compressor to an internal combustion engine.

TECHNICAL FIELD The present invention relates to compressors which can be selectively switched on by means of a coupling and in particular to a method for determining whether a compressor is to be switched on with or without delay. The invention also relates to a system and a vehicle in which the system is used as well as a computer program and a computer program product which implement the method according to the invention.

BACKGROUND AND PRIOR ART Heavy vehicles such as e.g. Trucks and buses are often equipped with pneumatic braking systems, suspension systems and level control systems. Compressed air can also be used to open and close doors on e.g. buses or for air-suspended seats etc. The vehicles may comprise a source of compressed air in the form of a compressor which is usually driven by the internal combustion engine of the vehicle and which is adapted to supply compressed air to one or more compressed air tanks which may be arranged at the vehicle chassis to supply the various systems and components with compressed air. The compressor can be permanently connected to the motor and thus be active all the time the motor is in operation, but it can also be adapted to be selectively connected to the motor but by means of a coupling, e.g. a vane coupling so that the motor can be in operation without the compressor having to be active.

It is common to use selective connection because the compressed air requirement is not normally such that continuous operation of the compressor is necessary. When the compressed air tanks are full and the vehicle does not consume compressed air, the pressure in the tanks is equal to or above a predetermined limit value. When the vehicle consumes compressed air, e.g. during braking, the pressure in the tanks drops to a lower limit value at which the compressor is switched on to fill the tanks to a predetermined pressure above the limit value. When the predetermined pressure is reached, the compressor is switched off. This means that the compressor can be switched off for long periods, especially during e.g. highway driving as the use of compressed air consuming systems is often small.

An advantage of selective connection is that the wear on the compressor can be reduced at the same time as the motor's energy consumption can be reduced by not unnecessarily applying the motor to the load that the compressor constitutes. A disadvantage is that the clutch wears with each clutch and that it wears the most when it is engaged at high engine speeds because the wear increases quadratically in relation to the engine speed.

It is known to replace wear parts in the coupling if necessary, but this requires a workshop visit and that the coupling is dismantled, which is relatively expensive, especially as the vehicle cannot be used in the meantime.

SUMMARY OF THE INVENTION An object of the present invention is to minimize the number of compressor connections at high speeds. Another purpose is to prevent the clutch that engages and disconnects from the engine operation of the compressor from being subjected to unnecessary wear. Another purpose is to extend the life of the coupling. These and other objects are achieved by the features set forth in the appended claims.

Compressor clutches at high speeds wear significantly more on the clutch than clutches at lower speeds and should therefore be avoided to increase the life of the clutch. Since the compressor is controlled by the pressure in the vehicle's compressed air system, it can receive a request for connection from the compressed air system and be switched on at virtually any time regardless of engine speed. It can e.g. is switched on at a speed stop just before shifting, even though it could just as easily have been switched on at a significantly lower speed after the clutch actually took place, etc. To reduce the number of compressor connections at speed peaks, a system in the vehicle includes means that detect the engine speed when a request for compressor connection is made. The detected speed is then used to determine whether the compressor should be switched on with or without delay. In this way, it is possible to control the connection of the compressor so that it is not switched on at a speed stop but when the speed is lower. At certain times when the demand for compressed air is great, it is necessary to switch on the compressor even though the speed is relatively high, in order to ensure air supply to the compressed air system.

In the invention, switching on the compressor is delayed if the engine speed is equal to or above a limit value for the engine speed. The limit value can vary depending on the type of vehicle and in an advantageous embodiment can be between 800-1000 rpm. In a further advantageous embodiment, the limit value can be in the order of 800 rpm.

In order to determine a suitable length of the delay, e.g. type of vehicle and gearbox but in an advantageous embodiment of the invention the engagement can be delayed 0.1-3 seconds but preferably 0.5-1 second. By delaying the connection, speed peaks are avoided and the wear on the clutch becomes significantly less than it otherwise would have been. Since the speed peaks are often relatively short-lived, the probability is high that the speed is significantly lower within the said time interval after the respective speed peaks. However, if a lower speed is not present after the delay, the compressor is still switched on to ensure air supply to the compressed air system.

In a further advantageous embodiment, it is only possible to delay the connection of the compressor if the pressure in the compressed air system is equal to or above 9 bar to ensure that the pressure does not become too low in the compressed air system.

Other features and advantages of the invention will be apparent from the claims, the description of embodiments and the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, embodiments of the invention are described by way of example with reference to the accompanying drawings, in which: Fig. 1 schematically shows a vehicle driven by an internal combustion engine.

Fig. 2 schematically shows a compressor driven by the internal combustion engine.

Fig. 3 schematically shows a control unit in a control system for vehicles.

Fig. 4 shows a graph illustrating an example from actual operation where the compressor is switched on at a relatively high engine speed.

Fig. 5 schematically shows a flow diagram of an embodiment of a method.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Fig. 1 schematically shows a vehicle 1 driven by an internal combustion engine 2. The vehicle 1 is advantageously a heavy vehicle and the internal combustion engine 2 may be a diesel engine or an otto engine. In alternative embodiments, the internal combustion engine 2 may be intended for industrial or marine use. The internal combustion engine 2 is via a flywheel 3, a gearbox 4, a drive shaft 5, a differential gear 6 and drive shafts 7,8 adapted to drive two or more drive wheels 9,10 and adapted to be controlled by a control system included in the vehicle via at least one control unit 12.

The vehicle 1 comprises a source of compressed air in the form of a compressor 13 which is driven by the internal combustion engine 2 and which is adapted to supply compressed air to one or more compressed air tanks 14 which may be arranged at the chassis of the vehicle to supply air consumers 15 with compressed air. The air consumers 15 can consist of a compressed air-driven brake system, level control system, suspension system or arrangement for opening and closing doors on e.g. a bus or air-suspended seats etc. The compressor 13 can be permanently connected to the internal combustion engine 2 and thus be active all the time the internal combustion engine 2 is in operation but is in this exemplary embodiment adapted to be selectively connected to the internal combustion engine 2 by means of a coupling 17 so that the internal combustion engine 2 can be operated without the compressor 13 need to be active. The coupling 17 can then be switched by means of signals 28 from a control unit 18.

Fig. 2 schematically shows a gear transmission 20 driven by the internal combustion engine 2. The gear transmission 20 may be arranged to be driven by the flywheel 3 or be power-transmitted connected to the internal combustion engine 2 in another suitable manner. The gear transmission 20 is adapted to drive a first clutch part 21 so that it rotates when the internal combustion engine 2 is in operation. The coupling 17 comprises a second coupling part 22 which is rotationally connected to the compressor 13 and a coupling member 23 arranged between the two coupling parts 21, 22. 13 with the internal combustion engine 2 or to disengage the two coupling parts 21, 22 from each other so that the compressor 13 is not driven by the internal combustion engine 2.

The compressed air control comprises a first passage 24 extending between the coupling 17 and a valve 26 and a second passage 25 extending between the valve 26 and the compressed air tank 14. The valve 26 is controlled by the signals 28 from the control unit 18. The signals 28 may be based on pressure signals 29 from the compressed air tank. 14 and / or from another suitable position in the vehicle's compressed air system.

The coupling member 23 may be a friction coupling e.g. a lamella coupling comprising one or more lamellae with friction pads which are pressed against a pressure plate of strong springs to transmit driving force between the two coupling parts 21,22 and thus also between the internal combustion engine 2 and the compressor 13. When compressed air is supplied to the coupling 17 from the compressed air tank 14 via the first and the second passage 24, 25 the pressure force of the pressure plate against the lamella is gradually reduced, which leads to the two coupling parts 21, 22 being disengaged from each other and the compressor 13 thereby being disengaged from the internal combustion engine 2.

When the internal combustion engine 2 is in operation at the same time as the two coupling parts 21, 22 are connected, driving force is transmitted from the flywheel 3 of the internal combustion engine 2 via the gear transmission 20 and the coupling 17 to the compressor 13. The compressor 13 compresses air which is supplied via a line 16. the different air consumers 15 in the vehicle 1. When the compressed air tank 14 is pressed to a predetermined first pressure, the control unit 18 emits a signal 28 to the valve 26 which closes the connection between the first and the second passage 24,25 and interrupts the supply of compressed air from the compressed air tank 14 to the coupling 17.

Residual air in the coupling member 23 is then drained via a third passage 27 and the compressor 13 is switched off.

When the vehicle 1 consumes compressed air, e.g. during braking, the pressure in the compressed air tank 14 drops to a predetermined second pressure. The control unit 18 emits a signal 28 to the valve 26 which opens the connection between the first and the second passage 24,25 between the compressed air tank 14 and the coupling 17 and closes the third passage 27. The coupling 17 is thereby pressurized and the compressor 13 is switched on to fill the compressed air tank 14 to the predetermined first pressure. When the predetermined first pressure is reached, the compressor 13 is switched off again.

The coupling means 23 can be of such a type that in the pressure-relieved state it connects the two coupling parts 21, 22 to each other to ensure that the compressor 13 always starts when the internal combustion engine 2 is started so that the required compressed air structure can be ensured at vehicle start.

The vehicle 1 shown in Fig. 1 comprises a control system for controlling the various functions of the vehicle 1. The control system consists of a communication bus system consisting of one or more communication buses which connect a number of electronic control units (ECU) or controllers and various components on the vehicle 1.

The control units communicate with different sensors and actuators and continuously read signals from these and are connected to each other in such a way that they can act as sensors and actuators for each other. The control system can thus comprise a large number of control units and the responsibility for a specific function can be divided into more than one control unit. For the sake of simplicity, only two control units 12,18 are shown in Fig. 1, but in practice the number of control units can be substantially larger than what is shown.

The invention may be adapted to be carried out by any suitable control unit in the control system e.g. of the control unit 18 or of the control unit 12. The invention may also be adapted to be performed by a control unit dedicated to the task or by a combination of different control units.

The control of the various functions of the vehicle is performed by programmed instructions which consist of computer programs which when executed in a control unit cause the control unit to perform the desired control such as e.g. procedural steps in a procedure.

The computer program forms part of a computer program product where the computer program product comprises an appropriate digital storage medium which may comprise a volatile and / or a non-volatile memory on which the computer program is stored. The storage medium 33 shown in Fig. 3 can e.g. consists of someone from the group ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically Erasable PROM), a hard disk drive etc. and be arranged in or in connection with the control unit, the computer program being executed by the control unit. By changing the programmed instructions, the behavior of the vehicle in a specific situation can thus be adapted.

Fig. 3 shows as an example that the control unit 18 may comprise a calculation unit 32 which may be constituted by any suitable type of processor or microcomputer, e.g. a Digital Signal Processor (DSP) or an Application Specific Integrated Circuit (ASIC). The computing unit 32 is connected to the storage medium 33 which may provide the computing unit 32 with the stored program code and / or the stored data the computing unit 32 needs to be able to perform calculations. The calculation unit 32 may also be arranged to store partial or final results of calculations on the storage medium 33.

The control unit 18 comprises devices 34,35 for receiving input signals and devices 36,37 for transmitting output signals which input and output signals may contain waveforms, pulses or other attributes. The input signals are detected by the devices 34,35 as information for processing the calculation unit 32. The devices 36,37 for transmitting output signals are adapted to convert calculation results from the calculation unit 32 into output signals for transmission to other parts of the vehicle control system and / or to the component or components for which signals are intended.

Each of the connections to the devices 34,35 for receiving input signals and the devices 36,37 for transmitting output signals may be constituted by one or more of a cable, a data bus such as a CAN bus (Controller Area Network bus), a MOST -bus (Media Oriented Systems Transport) or any other bus configuration or of a wireless connection.

The function of the control unit 18 or the function of the control unit or units where the invention is implemented may depend on signals from different sensors or on signals from one or more other control units. Data 30 about the engine speed can e.g. obtained from a sensor that senses the engine speed or from one or more other control units e.g. from the control unit 12 (Fig. 1) which is part of the control system of the vehicle 1 for controlling the engine 2. The control unit, e.g. the control unit 18 in which the invention may be implemented is further adapted to receive signals 29 (Fig. 3) regarding the compressor e.g. a request for switching on or off the compressor and adapted to send output signals 28 e.g. to switch the compressor on or off.

The gearbox 4 shown in Fig. 1 can cooperate with a control unit (not shown) which is arranged to initiate automatic disengagement of a gear in the gearbox 4 and loading of another gear when the engine speed exceeds an upper limit value or when it falls below a lower limit value. With each gear change, the speed changes to different extents. In an alternative embodiment, the gearbox 4 can be shifted manually.

Figure 4 shows the change in speed during an actual gearing process of the vehicle from the time it is started until the vehicle reaches cruising speed.

The vehicle speed is shown with a line 40. The corresponding change in speed occurs during a downshift process. In the figure, the x-axis shows time and the y-axis motor speed. An engine speed curve 41 grows from a first speed n1 of about 500-600 rpm at time t1 to a second speed n2 of 1397 rpm at time t2 where the control unit cooperating with the gearbox initiates disengagement of a first gear and loading of a second higher gear. In connection with the gear change, the speed drops to a third speed n3 of 984 rpm at time t3 and then rises to a fourth speed n4 at time t4 where another gear change to a higher gear takes place and the speed drops to a fifth speed n5 at time t5 for to then rise to a sixth speed n6 at time t6 where a further change of gear to a higher gear takes place, and so on. After a number of gear changes and in connection with these occurring changes in speed, the vehicle reaches cruising speed and the engine speed stabilizes.

A line extends parallel to the x-axis between the higher engine speeds n2, n4, n6 and the lower engine speeds n1, n3, n5 and marks a limit value 42 for the speed. In the present application, the limit value 42 may be in the order of 1000 rpm. However, the invention is not limited to this particular speed, but other values may occur depending on the application in question. In other applications, the limit value 42 can e.g. be in the order of 800 rpm or be between 800 and 1000 rpm.

Fig. 4 also shows a line 43 which illustrates when the compressor was switched on and off in the described operating case. Since the compressor is controlled by the air pressure in the vehicle's compressed air system, it could have been switched on at virtually any time independent of engine speed, but in this operating case it was switched on at time t2 at speed n2 above the limit value 42 even though it could just as easily have been switched on below the limit value 42 before or after the connection actually owned etc. In this operating case, the compressor was switched on just before the time t6 where it was switched off due to the predetermined second pressure being reached in the compressed air system. Since the compressor was engaged at a speed stop, the clutch that engages and disconnects from the engine operation of the compressor was subjected to unnecessary wear.

In order to avoid compressor clutches at high speeds and thereby reduce wear on the clutch, the invention delays the connection of the compressor for a certain time (39) if the speed is equal to or exceeds the limit value 42. In the operating mode shown, the speed can be reduced the connection is delayed only 0.72 seconds. The speed change is shown by a bidirectional arrow 38 in the figure. By delaying the connection, the speed peak is avoided and the wear on the clutch becomes significantly less than it otherwise would have been. Since the speed peaks are often relatively short-lived, it is likely that the speed is lower for a short time after the respective speed peaks, but if a lower speed is not present after the delay, the compressor is still switched on to ensure air supply to the compressed air system.

In order to determine a suitable length of the delay, account must be taken of e.g. type of vehicle and gearbox but in an advantageous embodiment of the invention the engagement is delayed 0.1-3 seconds but preferably 0.5-1 second. In a further advantageous embodiment, it is only possible to delay the connection of the compressor if the pressure in the compressed air system is equal to or higher than 9 bar to ensure that the pressure does not become too low in the compressed air system. In yet another advantageous embodiment, one or more control units in the vehicle detect whether the speed is rising, falling or stable. In the event that the speed is above the limit value at the same time as some control unit senses that the speed is rising, the delay is not activated because the speed in such a situation may be higher after a possible delay than before. The delay is thus activated only if the engine speed is falling or stable.

Fig. 5 shows a flow chart of a method for determining whether the compressor 13 should be switched on with or without delay. At 45, the control unit 18 receives a request for switching on the compressor 13. The request may be based on pressure signals 29 from the compressed air tank 14 and / or from another suitable position in the vehicle's compressed air system. At 46, the control unit 18 receives information about the current engine speed. The control unit 18 receives such information continuously or at short time intervals from e.g. a sensor that senses the speed or from one or more other control units e.g. from the control unit 12 which is part of the control system of the vehicle 1 for controlling the internal combustion engine 2. At 47, the control unit 18 checks how the current speed relates to the limit value 42. If the current speed is equal to or above the limit value 42, the control unit at 48 initiates a delay of the compressor connection by a predetermined time after which the compressor 13 is switched on at 49. At 50, the control unit 18 receives a request to switch off the compressor 13. The request may be based on pressure signals 29 from the compressed air tank 14 and / or from another suitable position in the vehicle's compressed air system. At 51, the compressor 13 is switched off.

If the current speed is lower than the limit value 42, the compressor 13 is switched on without delay at 52. At 53 the control unit 18 receives a request to switch off the compressor 13. The request may be based on pressure signals 29 from the compressed air tank 14 and / or from another suitable position in the vehicle. compressed air system. At 54, the compressor 13 is switched off.

The invention is not limited to the described embodiments, but a number of possibilities for modifications thereof are obvious to the person skilled in the art without the latter deviating from the basic idea of the invention as defined in the claims. For example, the invention can be used with different types of vehicles e.g. cars, trucks, buses, boats, loaders and other vehicles that include a selectively connectable compressor for supplying a compressed air system.

In an alternative embodiment, it is not necessary to use the actual engine speed to determine whether the compressor should be switched on with or without delay but a calculated speed can be used. Map data is used in today's vehicles e.g. in different systems for automatic shifting in which shift selections are made based on e.g. road slope. With map data and knowledge of the slope of the road, one or more control units on the vehicle can calculate when the next change will take place and engine speed before and after the change. This information can then be used by any control unit in the vehicle to decide whether the compressor should be switched on with or without delay. In one embodiment, e.g. the connection is delayed when map data informs about upcoming change within said time interval but is not delayed when map data informs about upcoming change outside the time interval.

In a further alternative embodiment, a combination of map data and sensors and / or control units is used to sense and / or calculate a speed that can be used to determine whether the compressor is to be switched on with or without delay.

Claims (18)

A method of coupling a selectively switchable compressor (13) to an internal combustion engine (2) by utilizing a coupling (17), the method comprising the step of coupling the compressor (13) when a signal (29) for coupling is emitted, characterized of the steps of detecting an engine speed of the internal combustion engine (2) and by using the detected engine speed determining whether the compressor (13) is to be switched on with or without delay (39). Method according to Claim 1, characterized by the step of delaying the connection of the compressor (13) if the engine speed is equal to or above a limit value (42) for the engine speed. Method according to one of the preceding claims, characterized by the step of delaying the connection of the compressor (13) if the engine speed is between 800 and 1000 rpm. Method according to one of the preceding claims, characterized by the step of delaying the connection of the compressor (13) if the engine speed is 800 rpm. Method according to one of the preceding claims, characterized by the step of delaying the connection of the compressor by 0.1-3 seconds. Method according to one of the preceding claims, characterized by the step of delaying the connection of the compressor by 0.5-1 s. Method according to one of the preceding claims, characterized by the step of delaying the connection of the compressor (13) if the pressure in a compressed air system which supplies the coupling (17), which is compressed air, with compressed air is equal to or higher than 9 bar. Method according to one of the preceding claims, characterized by the steps of sensing whether the motor speed is rising, falling or stable and delaying the switching on of the compressor (13) if the motor speed is falling or stable. Method according to one of the preceding claims, characterized by the step of detecting engine speed by means of map data. Method according to claim 9, characterized by the step of delaying switching on of the compressor (13) when map data informs of upcoming changeover within said time interval. Method according to one of the preceding claims, characterized by the step of controlling the connection of the compressor (17) to a control unit (18). Computer program comprising program code which when the program code is executed in a computer causes the computer to perform the method according to any one of claims 1-10. A computer program product comprising a computer readable medium and a computer program according to claim 12, wherein the computer program is included in the computer readable medium. System for coupling a selectively switchable compressor (13) to an internal combustion engine (2) by using a coupling (17) which compressor (13) is adapted to be switched on when a signal (29) for switching is emitted, characterized by that the system comprises means (18) for detecting an engine speed of the internal combustion engine (2) when the signal (29) for switching on the compressor (13) is emitted and by using the detected engine speed determining whether the compressor (13) is to be switched on with or without delay (39). System according to Claim 14, characterized in that the coupling (17) is a friction coupling. System according to Claim 15, characterized in that the friction coupling is a lamella coupling. System according to Claim 14, characterized in that the coupling (17) is a compressed air-controlled coupling. Vehicle, characterized in that it comprises a system according to claim 14.