GB2530633A - Method for operating a gaseous-fuel engine for a vehicle as well as drive unit for a vehicle - Google Patents

Abstract

Disclosed is a method for operating a gaseous-fuel engine 12 for a vehicle, the method comprising detecting a pressure in a gaseous fuel tank 14, 24, 26 for storing gaseous fuel for the gaseous-fuel engine 12, using that data in an electronic control unit, ECU 18, to limit the total amount of torque allowed to be requested from the gaseous-fuel engine 12, and the rate of change of torque to be provided by the gaseous-fuel engine 12. The method may be used to prevent engine stall and may also utilise geographic data when determining the torque limit. A drive unit 10 using the method of operation is also disclosed.

Description

Method for Operating a Gaseous-Fuel Engine for a Vehicle as well as Drive Unit for a Vehicle The invention relates to a method for operating a gaseous-fuel engine for a vehicle as well as a drive unit for a vehicle.

US 7 661 409 B2 shows a method for a gas-operated internal combustion engine, which is also referred to as a gaseous-fuel engine. The method comprises an electronic control unit defining a desired gas pressure in a gas-injection system of the internal combustion engine as a function of operating conditions of the internal combustion engine, the operating conditions including at least one of a rotational speed, a torque, and a load of the internal combustion engine. The electronic control unit matches the desired pressure in the gas-injection system at least by evaluating signals from a pressure sensor and a temperature sensor, and generating actuating signals for controlling a shut-off valve, a pressure reducer or pressure controller, and a pressure release valve.

Moreover, DE 10 2008 019 466 Al shows a method for operating a gas tank, in which a gas is stored under pressure. In said method, a current discharge of gas out of the gas tank is controlled, in particular reduced, when falling below at least one predeterminable temperature threshold value in and/or on the gas tank.

It is an object of the present invention to provide a method and a drive unit by means of which a particularly advantageous operation of a vehicle can be realized.

This object is solved by a method having the features of patent claim 1 as well as a drive unit having the features of patent claim 5. Advantageous embodiments with expedient developments of the invention are indicated in the other patent claims.

A first aspect of the present invention relates to a method for operating a gaseous-fuel engine for a vehicle, in particular a commercial vehicle. The gaseous-fuel engine is also referred to as a gas-driven or gas-operated internal combustion engine. In the method according to the present invention, at least one pressure in at least one gas tank for storing gaseous fuel for the gaseous-fuel engine is detected by means of at least one pressure sensor. Moreover, the total amount of torque allowed to be requested from the gaseous-fuel engine is limited by means of an electronic control unit on the basis of the detected pressure. Alternatively or additionally, the rate of change of torque to be provided by the gaseous-fuel engine is limited by means of the electronic control unit on the basis of the detected pressure.

A second aspect of the invention relates to a drive unit for a vehicle, in particular a commercial vehicle. The drive unit comprises a gaseous-fuel engine for driving the vehicle as well as at least one gas tank for storing gaseous fuel for the gaseous-fuel engine. The drive unit further comprises at least one pressure sensor configured to detect pressure in the gas tank. Moreover, the drive unit comprises an electronic control unit configured to limit, on the basis of the detected pressure, at least one of the total amount of torque allowed to be requested from the gaseous-fuel engine, and the rate of change of torque provided by the gaseous-fuel engine. Advantages and advantageous embodiments of the first aspect of the invention are to be regarded as advantages and advantageous embodiments of the second aspect of the invention and vice versa.

The idea behind the invention is that vehicles with gaseous fuels, such as compressed natural gas, that use only the pressurization of the gaseous fuel as the motive force to move the gaseous fuel into the engine, can lose some of that force when the fuel tank pressure drops. This can cause the engine to stutter and stall either due to a transient loss in fuel pressure when a large amount of power is requested at once or during steady state operation if the fuel rate requested is higher than it can be consistently provided from the gas tank. These problems can be solved by limiting the transient power ramp-up and limiting the steady state flow rate to the engine at various pressures. In the method and the drive unit according to the present invention, the range of the gas fuel vehicle can be increased. This is achieved by reducing the tendency for the vehicle to stall when the gas pressure in the gas tank is low.

The background of the present invention is that usually, in most compressed gaseous fuel systems, such as a compressed natural gaseous fuel vehicle or a hydrogen fuel cell vehicle, fuel pressure is created solely from the pressure of the gas in the gas tank. Said gas is said gaseous fuel for operating the gaseous-fuel engine. There is no additional fuel pump to regulate fuel pressure. Hence, when the pressure in the gas tank is low, e.g. below 500 psi, there is less pressure to force the gaseous fuel into the engine. If a large amount of torque is requested quickly, e.g. quickly going to wide open throttle (WOT) to accelerate from a stop, then the throttle is opened all the way and a set amount of air is sent to the cylinders of the engine. The engine will measure this amount of the air and attempt to inject the correct amount of gaseous fuel into the airstream. However, if the gas pressure is too low, not enough gas will be able to go into this mix and it will lean out the mixture to the point of stuttering or stalling the engine. According to the present invention, two possible solutions to this problem are: reducing the total amount of torque allowed to be requested from the engine and/or reducing the rate of change of torque request so that the engine can adjust and compensate. A combination of these two solutions could be possible.

Further advantages, features, and details of the invention derive from the following description of a preferred embodiment as well as from the drawings. The features and feature combinations previously mentioned in the description as well as the features and feature combinations mentioned in the following description of the figures and/or shown in the figures alone can be employed not only in the respectively indicated combination but also in other combination or taken alone without leaving the scope of the invention.

The drawings show in: Fig. 1 a schematic view of a drive unit for a vehicle, the drive unit comprising a gaseous-fuel engine, at least one pressure sensor configured to detect a pressure in a gas tank for storing gaseous fuel for the gaseous-fuel engine, and an electronic control unit configured to limit, on the basis of the detected pressure, at least one of the total amount of torque allowed to be requested from the gaseous-fuel engine, and the rate of change of torque to be provided by the gaseous-fuel engine; Fig. 2 a flow chart illustrating a method for operating said drive unit, in particular the gaseous-fuel engine; Fig. 3 a diagram illustrating a stepped torque limit; Fig. 4 a diagram illustrating a continuous torque limit; and Fig. 5 a schematic view of a buffer tank system of the drive unit.

In the figures the same elements or elements having the same functions are indicated by the same reference signs.

Fig. 1 shows, in a schematic view, a drive unit 10 for a vehicle such as a commercial vehicle, in particular a truck. The drive unit 10 comprises a gaseous-fuel engine 12 for driving the vehicle, wherein the gaseous-fuel engine 12 is also referred to as an engine or an internal combustion engine. The drive unit 10 further comprises at least one gaseous fuel tank 14 for storing gaseous fuel for the gaseous-fuel engine 12. Moreover, the drive unit 10 comprises at least one pressure sensor 16 configured to detect a pressure in the gaseous fuel tank 14. The drive unit 10 further comprises a stall prevention system electronic control unit 18 (SPS ECU) configured to limit, on the basis of the detected pressure, at least one of the total amount of torque allowed to be requested from the gaseous-fuel engine 12, and the rate of change of torque to be provided by the gaseous-fuel engine 12. For example, said limitation is transmitted to and received by a further engine electronic control unit (ECU) 20 configured to adjust the respective limitation.

By limiting the total amount of torque and/or the rate of change of torque a stall prevention system is realized. The high-level function of the stall prevention system is that a SPS ECU 18 constantly reads in the pressure in the gaseous fuel tank 14 from the pressure sensor 16 on the at least one gaseous fuel tank 14 which is also referred to as a tank, a fuel tank or a CNG tank (CNG -compressed natural gas). When the tank pressure is below a predetermined level, but above a level at which the system will begin to affect the available torque, the driver is given a warning, that the fuel is low and that the stall prevention system will activate soon, so they should refuel as soon as possible.

When the tank pressure is below a predetermined level, for example 500 psi, then the system will activate and initiate one or more functions described below. The SPS ECU 18 then dictates some form of speed or torque limit to the engine ECU 20.

In the following, key system components are described: One of said key system components is the SPS ECU 18. The SPS ECU 18 can be a stand-alone unit or could be integrated into an existing vehicle ECU such as the fuel management module, engine or transmission. The SPS ECU 18 has inputs of: -CAN (Controller Area Network) or other communication protocol connector for reading current engine torque, engine speed, torque requested from the driver, and other parameters, -tank pressure from the pressure sensor 16 or CAN.

A further key system component is the pressure sensor 16 attached, for example, to the high pressure gaseous fuel tank 14 to give a constant and accurate temperature-compensated pressure reading to the SPS ECU 18. Il may be necessary to filler the pressure signal to remove excessive measurement noise. For example, said pressure signal is a signal provided by the pressure sensor 16 and indicative of the detected pressure in the gaseous fuel tank 14.

In the following, system functions will be described. One of said system functions is transient stall prevention. The engine may stall if a large transient power is requested.

This is due to inertia of the gas. For example, if the driver wants to accelerate quickly from a stop and depresses the accelerator pedal fully very quickly, the torque request will increase rapidly. Because the airflow to the engine is less restricted than the fuel flow, there will be more air than prescribed by the required fuel/air mixture causing the mixture to be lean.

To prevent the torque request from increasing too quickly, the SPS ECU 18 uses the current torque request level as read from the CAN bus and compares it to any new torque request. If the changes are too high for the amount of tank pressure remaining (as determined by a look-up table, equation or other method), then the system will limit the torque to a certain rate of change (expressed as a torque percent delta per second), but could use absolute limits as well. The following table gives example fuel pressure and effective rate of change limits: Fuel Pressure [psi] Rate of Change Limit >500 No limit 400-500 20%/s 300-400 1 5%/s 200-300 10%/s <200 5%/s A further system function is steady-state stall prevention. In the steady-state stall prevention a determination of steady-state torque limitation is executed. Fuel flow rate to the engine is related to the power the engine produces as illustrated in a fuel rate versus torque and speed map. Assuming that the engine can only be limited by torque or speed and speed is not changing rapidly, torque will be the easier of the two to control. This process is described below and illustrated in Fig. 2.

First, the tank pressure is read into the controller, i.e. the SPS ECU 18, for example. The controller contains a flow rate look-up table which contains the maximum allowable flow rate to the engine for every tank pressure. This look-up table can vary depending on the tank system installed, the fuel management module, how dirty the filters are, and other variables. The controller also contains a fuel look-up table for the fuel flow rate for every speed and torque. Using the inputs of current engine speed (available on the CAN bus) and the maximum allowable fuel flow rate (from the flow rate look-up table, e.g. 100 gallons per hour), the torque corresponding to the speed and flow rate can be determined. This torque is the value that corresponds to the maximum flow rate at the current speed. The maximum torque for the engine should ideally be this maximum torque multiplied by a safety factor (e.g. 0.95) to ensure it is not exceeded.

Moreover, in the steady-state stall prevention, a steady-state flow limitation implementation is provided. Two possible ways to implement the torque or speed limitation are stepped limitation or linear limitation. Said stepped limitation is shown in Fig. 3, wherein said linear limitation is shown in Fig. 4. For example, in the stepped torque limit case shown in Fig. 3, if the pressure drops from 500 to 499 psi, the SPS ECU 18 would send a request to the engine ECU 20 requesting that the engine be limited to 95% of its maximum torque. When the pressure drops to 449 psi, the engine would be limited to 90% of its maximum torque and so on as the fuel is depleted.

Similarly, the continuous limit case shown in Fig. 4 works in the same way, but there is a function that relates any given tank pressure to a torque limit that is given to the engine.

This function could be linear or non-linear depending on what the optimal setting for the engine performance is, i.e. not stalling or stuttering and acting predictably. This is the preferred method for limiting the steady-state engine power and thus fuel flow rate because the changes will be gradual and therefore less apparent to the driver.

In the following, methods of limiting engine torque and/or speed are described. Vehicle engines use a CAN bus to accept torque, speed, and other limits from other devices, e.g. automated manual transmissions and anti-lock braking systems (ABS). These signals are typically send as TSC1 (torque speed control) requests and are used by the transmission and ABS to perform speed matching and limiting torque. The engines typically have a torque arbitration schedule that determines which devices have priority for which TSC1 requests. This arbitration allows the engine to override less critical systems when necessary. The SPS ECU 18 can be set up to work with the engine at a certain high priority level to limit the torque and/or speed of the engine. It is through this communication to the engine that the SPS ECU 18 will instruct the engine to limit torque and/or speed. The described method and drive unit 10 could also be built into engines, eliminating the need for a separate control unit and communication with such a computer.

In the following, additional features are described. One of said additional features is a driver alert. The driver should be alerted whenever the system is activated. This can include a visual light, icon or text message; audible tone or spoken message; or any other way the driver could be alerted to the fact that the available power will be or is currently reduced. The amount of power reduction can also be displayed. In other words, at least one signal is output in the interior of the vehicle, the signal being configured to inform the driver of the vehicle about said limitation.

A further one of the additional features is an anti-stall interlock. When the tank pressure gets below a certain point, likely when the torque/speed limitation will begin to extremely limit vehicle performance, the vehicle will give a warning to the driver that the vehicle will shut down in a certain amount of time or distance and will not be able to be turned back on again without a refuel. Using, for example, a satellite-based navigation system such as a Global Positioning System (GPS) navigation system, the system can recommend a location that would be ideal for either refuel or pull over to wait for help.

A further additional feature is a learning ability. If the system detects that the vehicle is beginning to stall when the tank pressure indicates that there should be adequate flow, the system can warn the driver and then adjust either the look-up tables or the safety factor for the torque limit to the real performance of the system. Thus, the system learns and adapts to changes in the system due to changes in fuel flow due to filter quality or other factors. The warning to the driver will also inform the driver that there may be a problem with the system, such as a dirty filter.

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A further additional feature is hybrid drive train integration, lithe vehicle is equipped with another power generating source, e.g. electric motor, flywheel, second combustion engine, etc., then some of the power required when the primary, gaseous fuel tank is low on pressure can be supplemented by the secondary power generating source. For example, if the above system will reduce the available power to 90% due to the gaseous fuel tank being low on pressure, then the secondary power generating source could make up the remaining 10% to make the normal 100% of power available.

When the pressure in the tank drops below a certain pressure that is low, but still above the point at which the stall prevention system would reduce the available power, then more power from the engine and kinetic energy should be used to fill up the capacity of the secondary energy storage device. For example, when the tank pressure drops below 800 psi, the charging system on a natural gas/electric hybrid will request more power to charge the batteries from the engine and also recover more energy when the vehicle is going downhill. This prepares the system to have more energy available when the primary fuel tank gets low as described above.

A further additional feature is use of geo-fencing.. There may be certain locations where it would be desired that the vehicle not stall under any circumstances. Examples may be in a train yard, crossing train tracks, in a dangerous stretch of road or in any other spaces. If these "no-stall zones" are defined in a digital map with Global Positioning System coordinates, then a virtual fence or a "geo-fence" can be established around these zones.

If the vehicle is equipped with a satellite-based navigation system, then the system can determine the physical location of the vehicle. Using this information and comparing it to the no-stall zone geo-fence map, it can reduce the available power of the vehicle whenever the vehicle enters a no-stall zone. The driver will be notified via visual and/or audible warning when they are approaching a zone in which their power will be reduced to prevent a stall from occurring in the designated no-stall zone.

Location based predictive technology can also be used for power-dependent routing. So-called fuel-efficient routing using GPS is a known feature. Power-dependent routing is a method of improving the routing using the stall prevention system. If the vehicle is running low on fuel or is predicted to be low on fuel, then the GPS navigation system, using road grade information that is available to them, can predict which roads and routes will require the highest peak power based on at least one event such as the grade of the route, length, and/or grade transitions. The system can then suggest alternate routes that may require a lower peak torque, e.g. less steep routes, so that the vehicle does not stall. If the vehicle is equipped with a system to measure or estimate the weight of the vehicle (e.g. an inertial measuring device in the transmission) then this information can be used to calculate the predicted peak torque and speed needed on a given grade.

In mapping a route from start to finish, the system can integrate with the OPS and telematics system on the vehicle to determine the approximate fuel consumption rate over the route and determine if at any point on the route the vehicle will be approaching the lower limit of the fuel capacity in which the stall prevention system could be activated before reaching a fueling station. In this case, power-dependent routing can be used for the latter section of the route to avoid high-load situations such as hills to avoid stalling the vehicle and ensuring it reaches its destination. Fuel-efficient, shortest time, shortest distance or other routing algorithms can be used for the section of the route before the vehicle gets low on fuel.

Location based predictive technology can also be used to provide an advance vehicle speed change warning to the operator. If the vehicle is approaching a hill or other high torque situations, as determined using the aforementioned predictive technology, the system can issue a warning or reminder that the maximum torque will be limited and that the vehicle will need to travel slowly up the hill.

Fig. 5 shows a schematic view of a buffer tank system 22 of the vehicle. The buffer tank system 22 is also referred to simply as a buffer tank. On a compressed gas vehicle with more than one fuel tank in which each tank valve may be independently opened or closed using an electronic solenoid or other method, stalls caused by dynamic losses of pressure may be prevented by supplying high pressure gas from one reserve tank when a dynamic fuel request occurs. For example, in a four tank system such as the buffer tank system 22, three of the tanks would be primary tanks and the fourth would be the reserve tank. In Fig. 5, the primary tanks are indicated by 24, and the reserve is indicated by 26. The primary tanks 24 are used during normal operation and the reserve tank 26 remains out of the system (e.g. isolated by a valve) so that the gas in the reserve tank 26 remains at high pressure. When the primary tanks 24 reach a pressure below that at which a stall may occur and there is a rapid throttle request, the primary tank gas supply is changed from the primary tanks 24 to the reserve tank 26. This can be achieved by using a two position, three port solenoid valve which is also referred to as a controllable solenoid in Fig. 5. Once the primary tanks 24 are depleted such that they can no longer maintain steady-state fuel flow, the reserve tank 26 is selected and the reserve tank fuel is utilized as a normal fuel tank would be.

In the following, an application for cryogenically liquefied gas vehicles is described.

Liquefied natural gas (LNG) is an example of a cryogenically liquefied gas to which this invention can also apply. The gas is cryogenically chilled to a liquefied state and is thus stored at much lower pressures (50 to 150 psi) than compressed natural gas (ONG).

Because of this low storage pressure, the gas may enter the engine at a low pressure and that could cause an engine stall if too much power is requested.

Compared to CNG, the pressure of LNG does not directly correlate with the filling level (fill volume) of the tank but mainly with the temperature of the cryogenic fluid (i.e. the saturation pressure). If fluid is taken at a higher flow rate for some time, the temperature and therefore the pressure may fall below the lower limit. By using an inline pressure sensor after the high pressure regulator or other location, the system can determine if the pressure in the line may be too low to supply the system with enough pressure for a high power request, i.e. high flow request. If the line pressure is determined to be low, then the available power to the driver can be reduced similarly to the description for the compressed gas. Alternatively the sensor data may be used to control a heating device to raise the fluid temperature (and therefore pressure). This may be done by taking part of the evaporated fluid downstream of the evaporator and lead it back to the tank to mix with the remaining liquid.

list of reference signs drive unit 12 gaseous-fuel engine 14 gaseous fuel tank 16 pressure sensor 18 stall prevention system electronic control unit engine electronic control unit 22 buffer tank system 24 primary tank 26 reserve tank

Claims (5)

1. Claims A method for operating a gaseous-fuel engine (12) for a vehicle, the method comprising: -by means of at least one pressure sensor (16), detecting at least one pressure in at least one gas tank (14, 24, 26) for storing gaseous fuel for the gaseous-fuel engine (12), -by means of an electronic control unit (18), limiting, on the basis of the detected pressure, at least one of: o the total amount of engine torque allowed to be requested from the gaseous-fuel engine (12), and o the rate of change of engine torque to be provided by the gaseous-fuel engine (12).
2. 2. The method according to claim 1, wherein the method comprises: -by means of a satellite-based positioning system, determining at least one position of the vehicle, and -limiting the total amount of allowable engine torque and/or the rate of change of torque on the basis of the determined position.
3. 3. The method according to claim 1 or 2, wherein the method comprises: -by means of a satellite-based positioning system, determining at least one upcoming event on a route the vehicle is currently travelling, and -limiting the total amount of engine torque and/or the rate of change of engine torque on the basis of the determined event.
4. 4. The method according to any one of the preceding claims, wherein at least one signal is output in the interior of the vehicle, the signal being configured to inform the driver of the vehicle about the limitation.
5. 5. A drive unit (10) for a vehicle, the drive unit (10) comprising: -a gaseous-fuel engine (12) for driving the vehicle, -at least one gas tank (14, 24, 26) for storing gaseous fuel for the gaseous-fuel engine (12), -at least one pressure sensor (16) configured to detect a pressure in the gas tank (14, 24, 26), -an electronic control unit (18) configured to limit, on the basis of the detected pressure, at least one of: o the total amount of engine torque allowed to be requested from the gaseous-fuel engine (12), and o the rate of change of engine torque to be provided by the gaseous-fuel engine (12).