GB2517075A

GB2517075A - Compressed air system for a vehicle

Info

Publication number: GB2517075A
Application number: GB1411600.8A
Authority: GB
Inventors: Stefan Bartelmes; Shivkumar Duraiswamy
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2014-06-30
Filing date: 2014-06-30
Publication date: 2015-02-11
Also published as: GB201411600D0

Abstract

A compressed air system for a vehicle, the compressed air system comprising at least one compressor for compressing air, at least one clutch via which the compressor is drivable by means of an engine of the vehicle, at least one air dryer for drying the air compressed by the compressor, and preferably at least two solenoid valves for independently initiating the clutch to open or close and the air dryer to purge. A control device capable of independently controlling the clutch and a purging of the air dryer is also used along with a control strategy intelligently shifting charge events based on current system states and prediction of future system states based on map data comprising information about a route along which the vehicle travels. Control of the clutch operation may be based on three operating ranges of the engine which are themselves based on the respective drive torques provided by the engine.

Description

Compressed Air System for a Vehicle The invention relates to a compressed air system for a vehicle, in particular a commercial vehicle.

US 2012/0216533 Al shows a method of operating a vehicle equipped with a pneumatic booster system configured to inject compressed air into an intake of an engine of the vehicle during a pneumatic boost event and configured to adjust at least two of compressed air injection rate, duration and timing of at least two air injection pulses within said pneumatic event. In said method, a position and a direction of movement of the vehicle are determined. Moreover, an anticipated upcoming vehicle route is determined from the position and direction of movement of the vehicle. Based on the anticipated upcoming vehicle route, it is determined whether to initiate compressed air injection to facilitate vehicle's traverse of the anticipated upcoming vehicle route. Based on the anticipated upcoming vehicle route, a compressed air injection pattern is determined to alter a target engine torque output to correspond to a route terrain of the anticipated upcoming vehicle route as the vehicle traverses the route terrain.

The pneumatic boost event is initiated to inject compressed air into the engine using the determined compressed air injection pattern. At least one operating parameter of the vehicle is monitored. It is determined whether the at least one operating parameter is within a predetermined range. Furthermore, at least one of air injection rate, duration and timing of the compressed air injection pattern is adjusted as the vehicle traverses the route terrain based on the determination of whether the at least one operating parameter is within the predetermined range to maintain the at least one operating parameter within the predetermined range.

Conventionally, a compressor for compressing air is powered by an internal combustion engine of the vehicle so that a portion of the energy provided by the engine is used for driving the compressor instead of driving the vehicle. During downhill terrain, the engine is usually operated in a zero fuel mode in which a fuel supply of the engine is cut off and engine friction torque is overcome by road forces as the vehicle travels downhill, the forces being transmitted through the wheels and driveline to the engine. To maximize fuel efficiency, it is desirable to power the compressor by means of the engine during the zero fuel mode, and operate the compressor as little as possible during a fuelling mode in which the engine is supplied with fuel.. Conventionally, it is possible to activate or deactivate the compressor based on current system pressure and current road grade and/or engine state. However, this is not always an optimal strategy due to certain hardware and system limits which must be observed. For instance, there may be a certain minimum activation time for the air compressor imposed for hardware durability.

US 6990401 B2 (Predictive Speed Control for a Motor Vehicle) shows a method of utilizing upcoming terrain information to adjust cruise speed of the vehicle to minimize fuel consumption. This upcoming terrain information is used in a part (PAC) of the present invention to minimize power lost from the engine to drive an air compressor by controlling a compressor clutch and purging events predictively.

Therefore, it is an object of the present invention to provide a compressed air system which can be operated in a particularly effective and efficient way.

This object is solved by a compressed air system having the features of patent claim 1.

Advantageous embodiments with expedient developments of the invention are indicated in the other patent claims.

The invention relates to a compressed air system for a vehicle, the compressed air system comprising at least one compressor for compressing air. The compressed air system further comprises at least one clutch via which the compressor is drivable by means of an engine of the vehicle. For example, the clutch can be switched between at least one closed state and at least one open state. In the open state, the compressor is decoupled from the engine so that the compressor is not driven by the engine thus not compressing air. In the closed state, the compressor is coupled to the engine so that the compressor is driven by the running engine thereby compressing air. The compressed air system further comprises at least one air dryer configured to dry the air compressed by the compressor. Thereby, humidity contained in the compressed air can be removed at least partially.

Furthermore, the compressed air system comprises a control device which is capable of independently controlling the clutch and a purging of the air dryer. By effecting a purging of the air dryer, a so called purging event is effected in which compressed air is discharged from the air dryer. By means of the control device of the compressed air system according to the present invention, free energy provided by the engine of the vehicle can be utilized particularly effectively and efficiently to drive the compressor and, thus, compress air. Thereby, it is possible to operate the compressor as little as possible during a traction mode of the engine in which the engine is supplied with fuel. Moreover, it is possible to power the compressor during a zero fuel mode or a coasting mode during which the engine is not supplied with fuel. Thereby, air can be compressed particularly efficiently and effectively so that the fuel consumption of the vehicle can be kept particularly low while, simultaneously, certain hardware and system limits can be considered as discussed above.

For example, the control system comprises two solenoid valves allowing an independent pressure actuated control of the clutch and the purge event. In other words, a first one of the solenoid valves is used for pressure actuating the clutch, and the second solenoid valve is used to control the purging of the air dryer.

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 respective indicated combination but also in any other combination or taken alone without leaving the scope of the invention.

The drawings show in: Fig. 1 a diagram for illustrating a method for operating a compressed air system for a vehicle, in particular a commercial vehicle, the compressed air system comprising a control device capable of independently controlling a clutch a purging of an air dryer of the compressed air system within said method; Fig. 2 a diagram for illustrating the interfaces of a further, predictive strategy and its integration into said method; Fig. 3 two diagrams which illustrate a first use case of the further, predictive strategy augmenting the efficiency of the method in simulation; and Fig. 4 two diagrams which illustrate a second use case of the predictive enhancement of the method in simulation.

Fig. 1 shows a diagram with the help of which a method for operating a compressed air system for a vehicle, in particular a commercial vehicle or a truck, is illustrated. The compressed air system comprises at least one compressor for compressing air.

Moreover, the compressed air system comprises at least one clutch via which the compressor is drivable by means of an engine of the vehicle. For example, the engine is an internal combustion engine and configured to drive the vehicle in a traction mode which is also referred to as a fuelling mode in which the engine is supplied with fuel. The engine can be operated in a costing mode which is also referred to as a zero fuel mode in which fuel supply of the engine is cut off. This means the engine is not supplied with fuel during the coasting mode in which the engine is driven through the wheels and the drivetrain of the moving vehicle.

The compressed air system further comprises at least one air dryer for drying the air compressed by the compressor. For example, the compressed air system, in particular the air dryer, can comprise at least one lank in which the compressed and dried air can be stored. Moreover, the compressed air system comprises a control device capable of independently controlling the clutch and a purging of the air dryer. By purging the air dryer, a so called purge event is processed in which the compressed air is released from the air dryer or the tank and, for example, injected into an intake of the engine. In order to allow an independent control of the clutch and the purging of the air dryer, the control device comprises a first module in the form of an Instantaneous Air compressor Control (lAO) and a second module in the form of an IAC purge control. Thereby, the IAC strategy realizes an instantaneous and independent compressor and purge. For example, said two modules are components of an electronic control unit (ECU) of the control device, the ECU being configured to control both the clutch for the compressor and the purge event.

For example, two solenoid valves are provided to allow an independent pressure actuated control of the clutch and the purge event. As can be seen from Fig. 1, the lAO compressor control comprises a three mode strategy which allows a particularly efficient and effective utilization of free energy provided by the engine on the basis of vehicle and especially engine operating conditions. The control strategy thereby only needs the compressed air pressure in the air tanks and the current engine torque as inputs. The IAC compressor control comprises a standard mode (STD mode) which is activated when the engine provides a drive torque which is more than 0% and less than 90% of the maximum torque which can be provided by the engine. In the standard mode, the compressor is activated by engaging the clutch when the air tank pressure goes below a low threshold, for example, of 110 PSI. The air tanks are then recharges until a cut-out threshold of, for example, 130 PSI is reached. Thus, in the standard mode, air pressure is kept within a defined range and only by exceeding the low or high pressure threshold is (dis- )engagement of the clutch by the lAG controller realized.

The lAG compressor control further comprises a coasting mode which corresponds to the coasting mode of the engine in which the engine provides no drive torque. In the coasting mode, the clutch is engaged two seconds after the coasting mode of the engine is activated. By engaging the clutch, the clutch is closed so that the air compressor is coupled to the engine and starts to fill the air tanks with compressed air. Additionally, the pressure thresholds of the air tanks are set to, for example, 140 (cut-in) and 145 PSI (cut out). Thus, a recharge of the air tanks starts after two seconds of coasting and the pressure is kept at a maximum between, for example, 140 and 145 PSI as long as the engine remains in coasting mode ensuring air system component protection.

Moreover, the lAG compressor control comprises a high torque mode which is activated for a drive torque higher than 90 % of its maximum. In the high torque mode, the clutch is disengaged immediately. By disengaging the clutch, the clutch is open so that the compressor is decoupled from the engine and does not consume energy from the engine.

During a period of sustained high levels of engine torque, it is desirable to minimize activation of the air compressor and, thus, minimize parasitic load on the engine. Parasitic loads at partial torque can be compensated by commanding additional engine torque, whereas parasitic loads at full torque reduce the overall driving force available and, reduce the vehicle speed. However, if the pressure of the compressed air in the air tank is below the low threshold of the high torque mode of, for example, 105 PSI, the compressor is activated by engaging the clutch so as to compress the air up to the cut-out threshold of the high torque mode of, for example, 120 PSI.

As can be seen from Fig. 1, the ECU with the IAC strategy is configured to control the clutch on the basis of at least three operating ranges in the form of the standard mode, the coasting mode and the high torque mode, said operation modes being activated for different drive torques provided by the engine. In the standard mode and the high torque mode, the engine is in its traction mode. Based on the drive torque. lAG controls the pressure thresholds for clutch (dis-)engagement as well as pressure-independent and immediate (dis-)engagement of the clutch.

The IAC purge control integrates compressed airflow through the air dryer and commands the purging of the air dryer only after a certain processed air volume of, for example, litres is reached. The air dryer only needs to be purged after such a volume of air has been dried and not after each charging, which can be a potentially short period.

Charge cycles may become shorter with the present solution thus a need arises to trigger a purge after a volume threshold instead of after each charge.

As can be seen from Figs. 2 to 4, said method can further comprise a third module in the form of a predictive air control (FAG). The FAG additionally uses, for example, a GFS (GPS -Global Positioning System) module and a 3D map data base which can exist with other predictive technologies to be implemented in the vehicle. The 3D map data base can provide prediction horizon information to predictive applications. Fig. 2 shows an interaction between the FAG and the lAG in the vehicle. The RAG utilizes a simplified vehicle powertrain model to first calculate powertrain signal buffer for use in an air system energy model. The air system energy model predicts the air pressure and air compressor charge events in the future within a certain prediction horizon. The PAC uses this prediction data and categorizes its control strategy into several different use cases to modify cut-in and cut-out thresholds as following: A first one of said use cases is a standard operation with an upcoming predicted high torque period. The predictive first use case shown in Fig. 3 identifies periods of sustained high levels of engine torque, for example, when climbing a long grade. The RAG strategy predicts the drop in air pressure over the high torque region, and calculates a needed starting pressure at the beginning of the high torque period such that the system air pressure will be just above the minimum threshold at the end of the high torque event.

The RAG strategy then initiates a pre-charge of the air system during the low torque region and sets the backwards calculated cut-out pressure to only just overcome the high torque region without charging. Fig. 3 further shows a comparison of the first use case to a base line IAC operation which is referred to as IAC in Fig. 3.

A second one of said use cases is a standard operation with an upcoming coasting period, the predictive second use case being shown in Fig. 4 under certain downhill driving conditions; the engine operates on the so called friction curve when no fuel is injected into combustion chambers of the engine. During this time, energy used to drive the accessories is considered free. Thus, fuel economy is improved when the air compressor operation is maximized during downhill coasting and mininiized during standard operation in which the engine is fired, i.e. the engine is in its traction mode. If the system air pressure is nearing the standard cut-in threshold during standard operation and the predictive horizon detects an upcoming coasting period, the RAG can take one of two actions: a first one of said actions is to temporarily lower the cut-in threshold to such a level that the system recharge will not be activated until the downhill coasting begins. In the second action, if the lowered threshold calculated in the first action is below a safe minimum pressure, the PAC will initiate a short recharge event with a cut-out threshold calculated such that the system air pressure will be adjustable of the minimum safe pressure at the beginning of the coasting event.

A third one of the use cases comprises a reduction of the lAO charging delay. The prediction horizon can also be used to decrease this IAC clutching delay of two seconds, because the duration of the coasting event is known. The IAC clutch delay inhibits charging until some time after a coasting event begins. This is to prevent compressor cycling during very short coasting events (e.g. during gear shifts, see Figs 3 and 4).

However, the PAC knows in advance exactly how long the coasting event will be, and does not need a delay before engaging the compressor during sufficiently long coasting events. The delay time can thus be used to recharge the air tanks with free energy due to zero-fuelling.

The control device can be configured to integrate compressed air flow through the air dryer and effect the purging of the air dryer when the integrated compressed air flow exceeds a predetermined threshold value. The control device predicts a purge event for the prediction horizon according to lAG purge logic, where initiation (advancement/postponement) of the purge event is optimized to minimize compressor activation during fuelling. Alternatively or additionally, the control device can comprise a map data base comprising information about a route along which the vehicle travels.

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Moreover, the control device can comprise a positioning module configured to determine a position of the vehicle in relation to the route, wherein the control device is configured to control the clutch and the purging on the basis of at least an upcoming portion of the route along which portion the vehicle will travel. Thereby, a predictive control of the clutch and the purge event can be realized. Simulations have been conducted and have shown that a reduction of fuel consumption can be realized by using said method to control or operate the compressed air system.

Claims

Claims A compressed air system for a vehicle, the compressed air system comprising: -at least one compressor for compressing air; -at least one clutch via which the compressor is drivable by means of an engine of the vehicle; -at least one air dryer for drying the air compressed by the compressor; and -a control device capable of independently controlling the clutch and a purging of the air dryer.
2. The compressed air system according to claim 1, characterized in that the control system comprises: -at least one first solenoid valve for pressure actuating the clutch; and -at least one second solenoid valve for controlling the purging of the air dryer.
3. The compressed air system according to any one of claims 1 or 2, characterized in that the control device comprises an electronic control unit configured to control the clutch on the basis of at least three operating ranges of the engine, the operation ranges based on the respective drive torques provided by the engine.
4. The compressed air system according to any one of the preceding claims, characterized in that the control device is configured to integrate compressed air flow through the air dryer and effect the purging of the air dryer when the integrated compressed air flow exceeds a predetermined threshold value.
5. The compressed air system according to any one of the preceding claims, characterized in that the control device comprises: -a map data base comprising information about a route along which the vehicle travels; and -a positioning module configured to determine a position of the vehicle in relation to the route, wherein the control device is configured to control the clutch and the purging on the basis of at least an upcoming portion of the route along which portion the vehicle will travel.
6. A method for operating a compressed air system according to any one of the preceding claims.