Method for operating an exhaust gas turbocharger, exhaust gas turbocharger and use

Abstract

A method for operating an exhaust gas turbocharger (14) of a motor vehicle is provided, in which the exhaust gas turbocharger (14) has a compressor (16) for drawing in and compressing a fresh air volume flow, and in the event that actual or imminent operation of the compressor (16) of the exhaust gas turbocharger (14) at a surge limit is detected, an additional volume flow is supplied to a compressor inlet of the compressor (16), wherein the additional volume flow is diverted from a region downstream of the compressor (16) of the exhaust gas turbocharger (14), wherein a driving operating condition of the motor vehicle is determined and imminent operation of the compressor (16) at the surge limit is detected when a low-speed LET driving operation is determined.By recirculating charged air and / or exhaust gas to the compressor inlet, pumping of the compressor (16) can be avoided simply and effectively, thus enabling reliable and efficient operation of an exhaust gas turbocharger (14).

Description

[0001] The invention relates to a method for operating an exhaust gas turbocharger, by means of which fresh air for an internal combustion engine can be charged with the energy content of an exhaust gas. Furthermore, the invention relates to an exhaust gas turbocharger and the use of a bypass valve, by means of which a compressor of an exhaust gas turbocharger can be short-circuited during overrun operation of the motor vehicle.

[0002] From EP 2 634 393 A2 it is known to return exhaust gas to an outlet of a compressor of an exhaust gas turbocharger by means of an exhaust gas recirculation valve connected to an exhaust manifold of an internal combustion engine of a commercial vehicle.

[0003] From DE 10 2009 033 871 A1 and DE 10 2015 008 291 A1 it is known to return compressed air downstream of the compressor to a compressor inlet in order to avoid pumping in a compressor of an exhaust gas turbocharger of a motor vehicle.

[0004] There is a constant need to operate an exhaust gas turbocharger reliably and efficiently.

[0005] The purpose of the invention is to demonstrate measures that enable the safe and efficient operation of an exhaust gas turbocharger.

[0006] The problem is solved according to the invention by a method with the features of claim 1, an exhaust gas turbocharger according to claim 4, and a use with the features of claim 5. Preferred embodiments of the invention are specified in the dependent claims and the following description, each of which can individually or in combination represent an aspect of the invention, the scope of protection being determined by the claims.

[0007] One aspect of the invention relates to a method for operating an exhaust gas turbocharger, particularly in an EGR system of a motor vehicle, in which the exhaust gas turbocharger has a compressor for drawing in and compressing a fresh air volume flow, and in the event that actual or imminent operation of the exhaust gas turbocharger compressor at a surge limit is detected, an additional volume flow is supplied to a compressor inlet of the compressor, wherein the additional volume flow is diverted from a region downstream of the exhaust gas turbocharger compressor. In particular, the additional volume flow is diverted from a region downstream of the compressor and upstream to a turbine of the exhaust gas turbocharger coupled to the compressor. Preferably, the additional volume flow is cooled before being supplied to the compressor inlet of the compressor.

[0008] When a vehicle's internal combustion engine is only required to deliver low power, it also needs correspondingly little fresh air. In this case, a throttle valve regulating the fresh air flow can be set to allow only a small amount of fresh air to be drawn in. However, this can cause problems in the exhaust gas turbocharger, as the exhaust gas has a comparatively high energy content, which is used to drive a mechanically and / or electrically coupled compressor with a correspondingly high energy input. Due to the low fresh air flow supplied to the compressor, this can lead to flow separation within the compressor, a phenomenon also known as "pumping."During turbocharger pumping, fresh air already charged by the compressor can flow backward into the compressor to establish a stable pressure ratio with a positive fresh air volume flow flowing in the designated direction. This leads to high mechanical stress on the compressor and ultimately to its destruction.

[0009] It was recognized that a surge in the compressor's operating range can be prevented not only by reducing the pressure in a supply line connected to a compressor outlet using a surge protection valve, but also by increasing the volume flow supplied to the compressor. However, this is not achieved by controlling the fresh air volume flow through a throttle valve to avoid unpredictable vehicle behavior for the driver. Instead, air—that is, fresh air and / or exhaust gas—is recirculated from the already charged subsystem located downstream of the compressor and upstream of the exhaust gas turbocharger turbine to the compressor inlet.Preferably, the diverted additional volume flow is returned downstream of a charge air cooler provided for cooling the air charged by the compressor, thus preventing or at least reducing unnecessary heating of the compressor by the supplied additional volume flow. Since already compressed air is diverted, it is possible to reduce the back pressure generated at the compressor outlet by the compressor's charging process. In any case, the total volume flow at the compressor inlet, composed of the fresh air volume flow and the additional volume flow, can be increased, thereby achieving or even exceeding a minimum volume flow known from the compressor's performance map. By returning charged air to the compressor inlet, compressor pumping can be avoided simply and effectively, thus enabling reliable and efficient operation of the exhaust gas turbocharger.

[0010] The exhaust gas turbocharger (“ATL”) comprises a compressor and, in particular, a turbine coupled to the compressor. The coupling of the compressor to the turbine can be mechanical, for example, by means of a connecting shaft, wherein the coupling of the connecting shaft can preferably be mechanically engaged and / or disengaged by means of a clutch. In particular, the coupling of the compressor to the turbine can be achieved electrically, for example, by generating electrical energy with the turbine using an electric machine operating in generator mode, which can then be used to drive the compressor. For this purpose, the compressor can include an electric machine operating in motor mode. The exhaust gas turbocharger is thus designed as an electric exhaust gas turbocharger (“eATL”).

[0011] The surge line is generally known as the left edge of the compressor's operating curve and can be read from the curve. This curve may depict the pressure ratio at the compressor outlet to the pressure at the compressor inlet as a function of the total volume flow rate through the compressor. The corresponding pressures and the total volume flow rate can be measured by suitable sensors and evaluated in a control unit. In particular, the control unit can calculate whether the current operating point of the compressor is so close to, or has even exceeded, the surge line that compressor surge is occurring or imminent. The control unit can specifically consider the temporal evolution of the operating point and / or the rate of change of this temporal evolution.

[0012] According to the invention, a vehicle's operating condition is determined, and an impending compressor operation at the surge limit is detected, when low-speed LET (low end torque) operation is identified. In particular, the method is only carried out when low-speed LET operation has been identified. In LET operation, the engine speed is low, significantly below the speed for the optimal operating point, for example, below 1000 rpm or 2000 rpm. In particular, low-speed LET operation occurs when the internal combustion engine is operated slightly above idle speed.Although power is being requested from the internal combustion engine and the vehicle is operating in tow, the requested power is so low that the engine has a very small demand for fresh air, and the exhaust gas turbocharger compressor is supplied with a correspondingly small volume flow of fresh air. In such a situation, it can be advantageous to return a portion of the charged air as an additional volume flow to the compressor inlet to reliably prevent compressor surging. The method according to the invention is preferably used only when the vehicle is operating in tow, and particularly preferably only when a low-speed LET (low-speed electric traction) operating mode has also been determined.Unnecessary check routines, which are intended to verify the need for recirculation of the additional volume flow, can be omitted in detected driving conditions of the vehicle in which such a measure is not desired.

[0013] Preferably, the additional flow rate is diverted via at least one valve, which may be either volume-controlled or uncontrolled. If the valve is uncontrolled, it can only switch between an open and a closed state. Such an uncontrolled valve is preferably provided in a section of the EGR system that has a parallel section. If the valve is volume-controlled, it can assume several intermediate positions, allowing only a portion of the flow rate present at the valve inlet to be diverted as an additional flow rate for the compressor. This allows for very precise control of the additional flow rate.This makes it possible to keep the compressor's operating point very close to the surge line with a predefined safety margin, without risking exceeding the surge line, as long as a return flow is provided as an additional volume flow.

[0014] The process can be further developed and refined, particularly as explained in the following aspects.

[0015] Another aspect of the invention relates to an exhaust gas turbocharger for a motor vehicle, comprising a compressor for compressing a fresh air volume flow, a branch line leading from a compressor outlet to a compressor inlet for returning an additional volume flow to the compressor, and a bypass valve for discharging the additional volume flow into the branch line, wherein the bypass valve can be actuated by a control device, the control device being configured to carry out the method, which can be further developed and implemented as described above. By returning charged air to the compressor inlet, compressor pumping can be avoided simply and effectively, thus enabling reliable and efficient operation of an exhaust gas turbocharger in low-speed LET driving mode.

[0016] Another aspect of the invention relates to an EGR system for a motor vehicle, comprising a fresh air line for drawing in a fresh air volume flow, a compressor of an exhaust gas turbocharger, which can be designed and further developed as described above, for compressing the fresh air volume flow, a supply line leading from the compressor to an internal combustion engine, an exhaust line leading from the internal combustion engine to a turbine of the exhaust gas turbocharger, and a branch line leading from the supply line and / or from the exhaust line to a compressor inlet of the compressor for returning an additional volume flow to the compressor. The EGR system can, in particular, be designed and further developed as explained above using the method.Preferably, the additional volume flow is cooled before being fed to the compressor inlet, in particular by being diverted downstream of a charge air cooler provided for cooling the air charged by the compressor. By recirculating charged air to the compressor inlet, compressor pumping can be avoided simply and effectively, thus enabling reliable and efficient operation of an exhaust gas turbocharger and an EGR system.

[0017] Particularly preferably, at least one valve is provided for discharging the additional volume flow into the branch line, wherein the valve can be actuated by a control device, the control device being configured to carry out the method, which can be designed and further developed as described above. The control device can, for example, have an input port through which measurement results of the pressures at the compressor inlet and at the compressor outlet, as well as the total volume flow through the compressor, can be read, in particular to compare the measurement results with a compressor characteristic map of the compressor stored in the control device and to decide whether the compressor's surge limit is imminent or has already been exceeded.In this case, the control unit can actuate the valve via an output port to return charged air from the supply line and / or the exhaust line to the compressor inlet as an additional volume flow. Furthermore, the control unit can preferably ensure that the additional volume flow is only returned when the vehicle is in tow, and in particular only during low-speed LET operation.

[0018] In particular, the branch line, especially the entire branch line, is formed in or directly adjacent to the compressor housing. The branch line can be partially or completely enclosed by the compressor housing, for example, by interconnected bores within the housing. This allows the additional volume flow to be received as close as possible to the compressor outlet and returned to the compressor inlet via the shortest possible pipe run. For example, the branch line, at least partially formed within the compressor housing, can have an outwardly opening that is fitted with a valve. The branch line and the associated valve can thus be integrated into the compressor housing, forming a single unit for the compressor.In particular, it is possible that, in addition to the branch line formed at least partially in the compressor housing, a further branch line for the EGR system is provided, which leads to the compressor inlet independently of the branch line formed in the compressor housing, or is fluidically connected upstream or downstream to the valve with the branch line formed in the compressor housing, or is fluidically connected to the valve itself.

[0019] Preferably, several exhaust manifolds branch off from the internal combustion engine and merge to form a common exhaust manifold, wherein at least one exhaust manifold, preferably all exhaust manifolds, and / or the common exhaust manifold is equipped with a valve for diverting exhaust gas into the branch line. If the valve is located in the exhaust manifold, the exhaust gas in that manifold can be diverted wholly or partially as an additional volume flow to the compressor, while the exhaust gas from the other exhaust manifolds is fed entirely into the common exhaust manifold. If the valve is located in the common exhaust manifold, the valve can, in particular, be configured to divert only a partial volume flow of the exhaust gas as an additional volume flow to the compressor.In particular, it is possible to provide a valve in at least one of the partial exhaust pipes as well as in the common remaining exhaust pipe in order to be able to adjust the total amount of the additional volume flow more precisely.

[0020] A bypass valve for short-circuiting the compressor during overrun of the vehicle is particularly preferred, wherein the bypass valve is additionally designed to divert exhaust gas into the branch line, at least during low-speed LET driving. The bypass valve can be configured to perform the usual function of a bypass valve during overrun of the vehicle by short-circuiting the compressor inlet and outlet, so that the compressor wheel is not slowed down and essentially only rotates. The bypass valve can be switched passively, in particular by an applied vacuum when the throttle valve is closed during overrun.In train operation, a short circuit between the compressor inlet and the compressor outlet can also be created to prevent the compressor from pumping, thereby opening the bypass valve, particularly when actively actuated, and returning the additional volume flow from the compressor outlet to the compressor inlet and passing it through the compressor again. This additional function of the bypass valve in train operation—short-circuiting the compressor outlet and the compressor inlet to return the additional volume flow—may constitute an independent invention.

[0021] Another aspect of the invention relates to the use of a bypass valve, particularly for an EGR system of a motor vehicle, wherein the bypass valve is designed to short-circuit a compressor of an exhaust gas turbocharger during overrun operation of the motor vehicle, for the purpose of supplying charged air and / or exhaust gas from the internal combustion engine as an additional volume flow to a compressor inlet of the compressor during low-speed LET driving operation. By recirculating charged air and / or exhaust gas to the compressor inlet, pumping of the compressor can be avoided simply and effectively, thus enabling reliable and efficient operation of an EGR system.

[0022] In particular, the bypass valve is used in a process that can be designed and further developed as described above, and / or in an EGR system that can be designed and further developed as described above. The bypass valve can, in particular, be designed and further developed as explained above with reference to the process and / or the EGR system.

[0023] The invention is now explained by way of example with reference to the accompanying drawing, using a preferred embodiment as an illustration, wherein the features shown below can represent an aspect of the invention, either individually or in combination, and the scope of protection is defined by the claims. It shows: Fig. 1 A schematic representation of the principle of an application of an exhaust gas turbocharger according to the invention.

[0024] As in Fig.As shown in Figure 1, the exhaust gas turbocharger 14 according to the invention can be used in a motor vehicle. The exhaust gas turbocharger 14 comprises a compressor 16 and a turbine 18, wherein the energy generated in the turbine 18 with the aid of the exhaust gas from an internal combustion engine can be used mechanically and / or electrically to drive the compressor 16. A fresh air volume flow can be supplied to the compressor 16 via a fresh air line 20, which is compressed in the compressor 16 and supplied in a state charged at a higher pressure level to a supply line leading to the internal combustion engine 12. The fresh air can be mixed with fuel and combusted in the internal combustion engine, which emits the combustion products as exhaust gas. The exhaust gas to be emitted to the environment first passes through the turbine 18 of the exhaust gas turbocharger 14 in order to utilize the enthalpy of the exhaust gas for driving the compressor 16.

[0025] In the illustrated embodiment, the compressor 16 of the exhaust gas turbocharger 14 has a bypass valve 30, for example, located in the supply line or in the fresh air line 20. The bypass valve 30 is designed to short-circuit the compressor inlet and outlet of the compressor 16 during overrun operation of the vehicle, thus providing a bypass around the compressor 16. The bypass valve 30 can be switched passively, in particular by a vacuum that is only present during overrun operation.

[0026] During towing operation of the vehicle, the surge line of the compressor 16 can be reached in low-speed LET (electrical conduction velocity) operation. To prevent the compressor 16 from surgeping, a supplementary volume flow of charged fresh air from the supply line is returned to the compressor inlet. This increases the total volume flow through the compressor 16 and preferably also reduces back pressure in the supply line. The compressor 16 can thus be operated at a higher volume flow and a lower compression ratio, thereby preventing the compressor from exceeding the surge line and entering surge mode.

[0027] In one implementation of this concept, the bypass valve 30, in particular through active actuation triggered by a control device, is additionally designed to be fully or partially opened during towing operation of the vehicle if, during low-speed LET operation, the compressor 16's operating point threatens to approach the surge limit too closely. A bypass line 32, already provided for the bypass valve 30, can in this case be used fully or partially as a branch line 34 leading to the compressor inlet in order to direct the diverted additional volume flow into the compressor 16. Additionally or alternatively, exhaust gas can be diverted as an additional volume flow into the branch line 34.

Claims

[1] Method for operating an exhaust gas turbocharger (14) of a motor vehicle, wherein the exhaust gas turbocharger (14) has a compressor (16) for drawing in and compressing a volume flow of fresh air and In the event that actual or imminent operation of the compressor (16) of the exhaust gas turbocharger (14) is detected at a surge limit, an additional volume flow is supplied to a compressor inlet of the compressor (16), wherein the additional volume flow is diverted from a region downstream of the compressor of the exhaust gas turbocharger (14). characterized by , that a driving operating condition of the motor vehicle is determined and an impending operation of the compressor (16) at the pumping limit is detected when a low-speed LET driving operation is determined. [2] Method according to claim 1, wherein the method is only carried out when the low-speed LET driving operation has been determined. [3] Method according to claim 1 or 2, wherein the additional volume flow is diverted via at least one valve (30), wherein the respective valve (30) is volume-controlled or uncontrolled. [4] Exhaust gas turbocharger (14) for a motor vehicle, with a compressor (16) for compressing a fresh air volume flow, a branch line (34) leading from a compressor outlet of the compressor (16) to a compressor inlet of the compressor (16) for returning an additional volume flow to the compressor (16) and a bypass valve (30) for discharging the additional volume flow into the branch line (34), wherein the recirculating air valve (30) can be actuated by a control device, wherein the control device is configured to carry out the method according to one of claims 1 to 3. [5] Use of a recirculating valve (30) of a motor vehicle, wherein the recirculating valve (30) is designed to short-circuit a compressor (16) of an exhaust gas turbocharger (14) during overrun operation of the motor vehicle, for the purpose of supplying charged air and / or exhaust gas of the internal combustion engine (12) as an additional volume flow to a compressor inlet during low-speed LET driving operation. [6] Use according to claim 5, wherein the bypass recirculation valve (30) is used in a method according to any one of claims 1 to 3.

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