JP2014503042A - Method for diagnosing catalytic converter and / or exhaust gas sensor of vehicle internal combustion engine - Google Patents

Abstract

The invention relates to a method for diagnosing an exhaust gas sensor (5; 6) arranged downstream and / or upstream of a catalytic converter in a vehicle internal combustion engine (1) catalytic converter (4) and / or an exhaust system (3). About.
According to the invention, the following method steps are provided:
(A) the internal combustion engine (1) is operated with an air / fuel mixture having an air / fuel ratio (λ) below the stoichiometric air / fuel ratio;
(B) the internal combustion engine (1) is stopped;
(C) After the internal combustion engine (1) is stopped, a traction mode in which ignition is not performed is performed in a state where fuel supply is stopped. At that time, the internal combustion engine (1) passes intake air through the exhaust system (3) and the catalytic converter. (4) and sending to the exhaust gas sensor (5; 6);
(D) igniting and starting self-running of the internal combustion engine (1) with an air-fuel ratio (λ) below the stoichiometric air-fuel ratio;
(E) A step of evaluating a signal of the exhaust gas sensor (5; 6) prepared in a time range from at least after the stop until the self-running of the internal combustion engine (1) following a predetermined evaluation criterion.
[Selection] Figure 1

Description

  The present invention relates to an exhaust gas sensor disposed downstream and / or upstream of a catalytic converter of an internal combustion engine for a vehicle and / or a catalytic converter in an exhaust system in such a manner that a signal of the exhaust gas sensor is evaluated according to a predetermined evaluation standard. It relates to a method of diagnosis.

  A number of diagnostic methods have already been proposed for the diagnostic method of a three-way catalyst having oxygen storage capacity. According to this method, the influence of a sudden change in the air-fuel ratio during operation of the vehicle internal combustion engine is evaluated, in particular according to various signal parameters of an exhaust probe installed behind the catalytic converter.

  For example, in Patent Document 1, the engine is suddenly changed from a lean air-fuel ratio operation to a rich air-fuel ratio operation, and the deviation of the signal profile of the lambda probe installed before and after the catalytic converter is verified and evaluated. ing. In Patent Document 2, a proposal has been made to evaluate the time required as a whole to reach a specific signal value when the probe behind the catalytic converter changes the engine from lean operation to rich operation to further lean operation. .

  The disadvantages of these methods are that the exhaust gas purification performance of the catalytic converter is generally reduced at both the lean and rich operation points, and that harmful substances that have not been converted enter the environment.

  Abrupt changes in the air-fuel ratio are often caused when coasting or when recovering from that state. In Patent Document 3, for example, the signal profile of the lambda probe is evaluated while returning from coasting operation to traction operation at a predetermined air-fuel ratio. The drawback here is that coasting is often undesirable or cannot be expressed properly.

DE102006010769A1 DE102005028001A1 DE102004061603A1

  It is an object of the present invention to clearly describe a method for diagnosing exhaust gas sensors located downstream and / or upstream of a catalytic converter in a vehicle internal combustion engine and / or a catalytic converter in an exhaust system. Thereby, the disadvantages faced by the prior art can be avoided as much as possible.

  This object is achieved by a method having the features set forth in claim 1.

  Applying the method according to the invention, the internal combustion engine is operated with an air / fuel mixture with an air / fuel ratio (lambda) below the stoichiometric air / fuel ratio, ie a rich air / fuel mixture. Starting from the rich operation of the internal combustion engine, the engine is eventually switched off, ie stopped. Once the internal combustion engine is stopped, the internal combustion engine enters a towing mode as the fuel supply stops. In this case, the air taken into the internal combustion engine is conveyed to the catalytic converter and the exhaust gas sensor through the exhaust system. The self-running of the internal combustion engine will eventually start at an air / fuel ratio below the stoichiometric air / fuel ratio by ignition. Here, the self-running of the internal combustion engine is started after a predetermined period from the end of the towing mode to the stop state. In order to diagnose the catalytic converter and / or the exhaust gas sensor, the signal of the exhaust gas sensor is evaluated according to a predetermined evaluation criterion at least for a period of time when the engine of the internal combustion engine is turned off. Based on the evaluation criteria, it is determined whether the exhaust gas sensor or the catalytic converter is in a normal state or has an incomplete function or a defect.

  As a result of switching from the engine operation below the stoichiometric air-fuel ratio to the traction mode in which air is fed into the exhaust gas sensor, a sudden change is applied to the air in the exhaust gas sensor, and the state changes from reduction to oxidation. Subsequent changes occur when the internal combustion engine moves to a self-running state. After entering the traction mode state, the fuel supply to the internal combustion engine is stopped, and only air is sent from the intake side of the internal combustion engine to the exhaust system. This operation phase is performed emission-free. If the internal combustion engine is operated at an air / fuel ratio slightly below the stoichiometric air / fuel ratio slightly before and after it stops, harmful emissions are also low in these operating stages, which is desirable. In general, the diagnostic method according to the invention is carried out at a very low emission level of harmful substances.

  In addition, the diagnostic method is preferably implemented in connection with the internal combustion engine or the start / stop mode of the vehicle, so that any problems with driving the vehicle do not cause two setting lambda changes. In particular, there is no need to wait or trigger a state of coasting.

  According to the present invention, the towing mode is implemented by starting the operation of the internal combustion engine with an electric starter, for example. This starter is preferably formed as a starter generator.

  In some embodiments of the method, the method is performed on a vehicle that includes an electric motor drive. The vehicle is therefore designed as a so-called hybrid vehicle driven by both an internal combustion engine and an electric motor. Here, in the towing mode of the diagnostic process, it is particularly desirable that the towing of the internal combustion engine is performed by an electric motor. The method according to the invention is particularly advantageous when using hybrid vehicles since there is no undesirable coasting due to a force fit between the engine power and the transmission caused by the braking effect.

  In another embodiment of the method, a lambda probe type exhaust gas sensor having a jump characteristic (so-called jump probe or binary probe) is diagnosed. The sensor is preferably located downstream of the catalytic converter in the exhaust system, but may be located upstream of the catalytic converter. A lambda-dependent signal profile with a lambda value of 1.0 (λ = 1.0) has jump discontinuities with rapidly changing output signals, which is commonly found in lambda probes. . For jump probe diagnosis, the signal profile is preferably evaluated by comparison with the signal profile of an additional lambda probe placed in front of the catalytic converter. In particular, the additional lambda probe is designed as a so-called broadband lambda probe with an output signal that continually emits according to the lambda value. Such system designs are widely used in automotive engineering, especially in combination with catalytic converters designed as three-way catalysts. In other embodiments of the invention, it is particularly advantageous when designed as a continuous lambda probe, especially when an exhaust gas sensor located upstream of the catalytic converter of the exhaust system is additionally or alternatively diagnosed. . Needless to say, diagnosis of a broadband lambda probe located downstream of the catalytic converter of the exhaust system is also possible. Exhaust sensors and / or catalytic converters designed as jump probes, in particular arranged downstream of the catalytic converter and / or designed as broadband probes, especially arranged upstream of the catalytic converter, are also calculated or memorized. Diagnosis can be made by comparative evaluation using a reference signal profile or a lambda profile.

  Another embodiment of the method is the diagnosis of a catalytic converter with oxygen storage capacity. This catalytic converter is preferably formed as an oxidation catalyst or a three-way catalytic converter having oxygen storage capacity. Here, it is desirable that the signal profile downstream of the exhaust gas sensor is evaluated according to an evaluation standard that depends on the degree of oxygen storage capacity.

  In another embodiment of the invention, the internal combustion engine is operating with an air / fuel mixture having a lambda value of about 0.98 in step (a) of the method. That is, it means that the internal combustion engine is operating at an air-fuel ratio below the stoichiometric air-fuel ratio before turning off the engine. Thereby, it becomes possible to suppress discharge | emission of a harmful substance low.

  In another embodiment of the present invention, the internal combustion engine is operated in a reduced manner using an air / fuel mixture in the range of about 0.98 to about 0.90 in step (d) of the method. ing. That is, self-propelled after the towing stage of the internal combustion engine is performed. Therefore, pollutant emissions are low during this operating phase.

  In another embodiment of the invention, the exhaust sensor signal is evaluated according to at least one of the following criteria: signal slope, dead time, settling time and symmetry. Here, the slope of the signal is defined by the rising or falling of the signal with the signal parameter characterizing the lambda change. The dead time is the signal holding time after lambda change. Settling time is determined by the time it takes for a stable final value to be achieved simultaneously with the signal change and especially the lambda change. In the case of a symmetry-related assessment, it is compared to rising and / or falling lambda changes.

  Other advantages, features, and details of the present invention will become apparent from the following description of the preferred embodiments and the description of the drawings. The features and combinations of features mentioned in the above description, and the features cited and / or shown in the following description of the drawings, are not limited to each specific combination, Combinations or alone can be used without departing from the scope of the invention.

1 is a schematic view of a vehicle internal combustion engine equipped with an exhaust system for carrying out the method according to the invention. It is a graph which shows the signal curve which followed the time passage of the driving | running parameter of the setting shown by FIG. FIG. 6 is a graph showing a typical example of a signal profile over time of a reference signal R of a hypothetical input variable and a hypothetical response signal A as a typical response of an arbitrary sensor.

  The system embodiment conceptually illustrated in FIG. 1 below is a typical advantageous but non-limiting embodiment designed as a spark ignition engine for driving a vehicle (not shown). 1 shows an internal combustion engine 1. Combustion air is taken in through the intake passage 2 and fuel is sent in through the fuel supply path. Although direct fuel injection is not shown in detail, it is desirable that the fuel be injected through the injection valve in such a way that the combusted air / fuel mixture is directed to the combustion chamber of the engine 1.

  Combustion gas generated by the combustion of the air / fuel mixture flows out of the exhaust system 3 via the catalytic converter 4 for exhaust gas purification. Catalytic converter 4 which is provided as a good example as a three-way catalytic converter having oxygen storage capacity forms part of an exhaust purification system capable of holding an exhaust purification component. This includes a downstream nitrogen oxide storage catalytic converter and / or an SCR catalytic converter. Note that this is not shown separately in the drawing because it is clear.

  The first exhaust gas sensor 6 is disposed in the exhaust system 3 on the inlet side of the catalytic converter 4. The second exhaust gas sensor 5 is disposed on the outlet side of the catalytic converter 4. Further, a temperature sensor 9 is provided upstream of the catalytic converter 4 in order to measure the exhaust gas temperature. Without limiting the general principle, it is assumed in the following that the exhaust gas sensors 5, 6 are designed as lambda probes that emit an output signal that correlates to the air-fuel ratio λ or oxygen partial pressure.

  In this example, it is assumed that the first lambda probe 6 is designed to continuously output a detection signal. A broadband probe or a so-called LSU also corresponds to this type of probe, and always outputs a detection signal according to a lambda value. In the current example, the second lambda probe 5 is designed as a jump probe. A so-called two-point probe or binary probe similarly corresponds to this type of probe, and has a jump discontinuity when a lambda value of 1.0 is reached and outputs a detection signal. Those skilled in the art will be familiar with the function of such an exhaust gas sensor and its typical lambda-dependent output signal profile and will not be described in detail here. It goes without saying that other types of sensors and probes can be used to generate output signals that vary in particular according to the lambda value. For example, a nitrogen oxide sensor can be used in place of the first and / or second lambda probes 5, 6.

  The lambda probes 5 and 6 and the temperature sensor 9 are connected to the electronic control unit 7 via a signal line 8. The controller 7 is connected to the engine 1 via one or more additional data lines 10 and can control the operation of the engine according to the connected probes or sensors 5, 6, 9. Here, the control device 7 also receives information on the state variables of the internal combustion engine 1 and the exhaust gas purification system, such as the rotational speed, temperature, pressure corresponding to each sensor or transducer. For example, an air flow rate measuring device (not shown) in the intake passage 2 and a control signal for setting a variable to, for example, an EGR valve, an exhaust gas turbocharger (not shown), and an additional control device may be transmitted. is there. The control device 7 can also adjust the fuel injection as required or in a predesignated manner. For this purpose, the control device 7 may refer to an accumulated characteristic diagram or a calculation and / or management routine. To perform these functions, the controller 7 can communicate via data lines 8, 10 as shown by way of example here, can be connected to the respective components, and can be unidirectional or both It can also be designed as a directional signal or control line.

  In this example, an electric motor (not shown) capable of towing the internal combustion engine 1 is provided. The electric motor can be designed as a conventional starter or as a so-called starter generator. In a particularly desirable embodiment, the electric motor is designed and integrated into a vehicle drive system (also not shown) so that the vehicle can be operated alone or at least temporarily alone with the internal combustion engine. A vehicle equipped with a so-called hybrid drive is preferably provided with a start / stop mode, and the operation of the internal combustion engine 1 is switched off as necessary, especially in a stop phase where it does not move forward.

  In the following, the method according to the invention will be explained in more detail on the basis of the graph shown in FIG.

In FIG. 2, the signal profile and the course of the various manipulated variables are shown in graphs I, II, III and IV along a common time axis t. According to the situation according to the curve 23 shown in the graph II, at the vehicle speed v at which the vehicle decelerates, it is operated until it stops and remains stopped for the further time interval considered here. Initially is performed operated by the internal combustion engine up to the point of t _1, the fuel supply to the internal combustion engine is stopped at the speed point close to the low speed or zero. In the graph III, the control signal _Kaus indicating the stop of the internal combustion engine 1 or the fuel supply is illustrated by a locus 24.

after the fuel supply is stopped at a time point t _1, a short time i.e. a second or power of the electric motor of the vehicle at the time of t ₂ after a few seconds is placed in the trajectory 25 by the signal EM _ein In this graph IV It is shown. Here, the electric motor is operated in such a manner that the internal combustion engine 1 is towed, and air is recirculated to the exhaust system 3 via the intake passage 2 accordingly. In this case, the fuel supply remains stopped as can be inferred from the locus 24 of the graph III. The towing mode of the internal combustion engine 1 is desirably performed at a predetermined rotational speed such as an idling rotational speed, and a method that does not use a throttle when inhaling air is desirable. traction mode of the internal combustion engine 1 is started at a time point t ₂ is up to the time of t _5, it is maintained constant in the period from about 10 seconds to 30 seconds. Here, the second lambda probe 5 by reaching a predetermined signal output value, the time point of t ₅ the traction mode is electric motor and at the same time terminated is stopped is determined is preferred.

In more elapses from about 30 seconds to 120 seconds, the internal combustion engine 1 is short-term traction by an electric motor, the result is ready again fuel supply, self induction of the internal combustion engine 1 with the operation by the ignition at the time of t ₆ Is done. In this case, it is desirable that the internal combustion engine 1 is driven at idling rotational speed while the vehicle is stopped.

The signal profile of the lambda probe 5, 6 described in detail below based on the graph I is examined or evaluated together with the diagnostic method of the first lambda probe 6 and / or the second lambda probe 5 and / or the catalytic converter 4 described above. Is done. Here, the curved line 20 represented by a dotted line represents the output signal of the first lambda probe 6 designed in this case as a broadband probe, and the left ordinate λ _LSU represents this output value. The output signal of the second lambda probe 5 designed as a jump probe in this example is represented as a curve 21, and the right ordinate U _LSF represents this output value.

By the time of stopping t _1, the internal combustion engine 1, lambda value of approximately 0.98 fuel to correspond to a slightly rich air-fuel ratio, it is ignited operation. Accordingly, the lambda probes 5 and 6 first output substantially stable output signals 20 and 21 corresponding thereto. At the air-fuel ratio λ _LSU , as the vehicle speed v approaches zero, the signal 20 of the first lambda probe 6 first rises slowly, at time t ₁ due to the stop of fuel supply, or at t ₂ after the electric motor is switched on. It rises steeply at that time. This increase is a reaction to the reduced or stopped exhaust gas supply and to the subsequent supply to the exhaust system 3 due to the traction mode using an electric motor, whereby in the first lambda probe 6 Ideally, the lambda value suddenly increases from λ≈0.98 to λ = ∞.

  Similarly, however, the signal 21 of the second lambda probe 5 drops in a complementary manner to the rise of the signal 20 of the first lambda probe 6 due to the characteristic of the characteristic curve. What should be noted here is the time delay due to the occlusion of oxygen, usually carried by air, into the catalytic converter 4, which will be described in detail below.

A stop state internal combustion engine and an electric motor, as a base point to the point of t ₆ to the exhaust system 3 is a state in which air is filled, the internal combustion engine 1 is about lambda value corresponding to the air-fuel ratio below the stoichiometric air-fuel ratio When self-propelled from λ = 0.90 to about λ = 0.98, the signal profiles of the lambda probes 5 and 6 in the opposite directions can be appropriately observed.

Due to the influence of the gas transit time, in particular the functional quality of the lambda probes 5, 6, the rise or fall of the λ _LSU and U _LSF signals are ideally rectangular, respectively, or t ₁ to compared with the sudden lambda jump at the time of t _6, but there is a difference of degree, it becomes smooth. This is used according to the invention for the diagnosis of the first lambda probe 6 and / or the second lambda probe 5, which will be explained subsequently.

  In the following, the evaluation criteria that can be derived from the signal profiles of the lambda probes 5, 6 are described using FIG. The graph of FIG. 3 shows in this regard, by way of example only, the reference signal R of the hypothetical input variable and the temporal signal profile of the hypothetical response signal A as a typical response of any sensor in sensitivity to the input variable. Has been. In the present embodiment, the reference signal R is formed in a rectangular jump shape having a sharp rise from zero to 100 and a sharp falling edge in the opposite direction.

Compared with the reference signal R, the response signal A is gentle. On the other hand, the rise at time t _u is delayed compared to the rise of reference signal R at time t ₀ . The reaction time t _u -t ₀ can be used as a delay or dead time until the response signal A clearly rises to a predetermined value W ₁ or as an evaluation of the functional capability or quality of the attached sensor. If the dead time t _u -t ₀ exceeds a predetermined or pre-settable value, the sensor is diagnosed as defective. Further, the rise of the response signal A has a gentler slope than the reference signal R. For example, the maximum ascending slope is used as a functional capability or an associated sensor quality criterion, which is given by the slope of the tangent T at the point where the response signal A has the greatest slope. Furthermore, it can be confirmed that the response signal A is close to the final value of the reference signal for a given slight difference for the first time at time t _o . The corresponding settling time or response time t _o -t ₀ indicates another preferred measure of functional capability until the response signal A reaches a predetermined maximum value W ₂ . If the settling time t _o -t ₀ exceeds a predetermined or presettable value, the sensor is diagnosed as defective.

  Obviously, other criteria based on signal analysis can be used if desired. For example, frequency analysis or spectral analysis using Fourier transform in particular is used for the output signal A, or signal filtering by operation may be performed on the output signal. By these, an evaluation standard can be obtained.

  Evaluation dead time, signal slope and settling time, and evaluation criteria added as needed, are used in a corresponding manner in the falling edge of the response signal A and the reference signal. Diagnosis values are not individually entered in the graph of FIG. 3, but can be obtained by applying the described method listed for the corresponding rising edge. From the comparison of the criteria used with respect to the response to the rising and falling edges, in particular the dead time, the signal slope and the settling time, a symmetrical relationship is calculated for sensor diagnosis as another criterion. Degradation or sensor failure diagnosed when dead time, signal slope and settling time, and if necessary, other signal parameters of output signal A exceed preset maximum deviations for rising and falling edges Is done.

  For practical sensor diagnosis, in an application similar to the above-described method according to the invention, preferably the actual lambda increase or the lambda increase as close as possible to the actual lambda increase is As a result of the transition from traction mode to traction mode, it is used as a reference signal for the response signals of the lambda probes 5 and 6. Similarly, preferably, the actual lambda descent, or the lambda descent as close as possible to the actual lambda descent, is followed by a lambda probe in the transition from the stop of the internal combustion engine 1 and the electric motor to the free running of the internal combustion engine 1. It is intended to be used as a reference signal for 5, 6 response signals. In doing so, it may be contemplated to detect the air-fuel ratio λ of the air / fuel mixture on the basis of known operating variables such as gas transit times, each by actual lambda profile calculation. Similarly, it may be contemplated that the reference signal corresponding to the actual lambda profile at the lambda probes 5, 6 is kept in the form of a characteristic curve stored as a value. For the signal of the second lambda probe 5, the signal of the first lambda probe 6 is also used as a reference signal in order to obtain the quantitative parameters of the aforementioned evaluation criteria.

  For diagnosis of the catalytic converter 4, the signal of the second lambda probe 5 is preferably evaluated. In particular, it is contemplated that the dead time of the second lambda probe 5 or the delay time of the output signal can be used as a basis for a corresponding evaluation criterion for a sudden lambda change caused by the method according to the invention. Is done. To illustrate the preferred method, reference is again made to graph I of FIG. 2 below.

As can be read from graph I, and further as described above, the output signal 21 of the second lambda probe 5 is somewhat different from the lambda jump caused at the time t ₁ by the transition to the traction mode. Clearly shows the delay. The main cause of the time delay is occlusion in the catalytic converter 4 of oxygen carried by air. Occlusion of oxygen to the catalytic converter 4 limits the sudden lambda rise caused by the transition to the traction mode and occurring at the inlet of the catalytic converter 4 so that it cannot immediately operate efficiently on the outlet side of the catalytic converter 4. The At that time, the magnitude of the delay, that is, the period until the lambda rise on the inlet side of the catalytic converter 4 passes to the outlet side of the catalytic converter 4 is a measure of the oxygen storage capacity of the catalytic converter 4. When the oxygen storage capacity is reduced as compared with a new catalytic converter 4, the function of the catalytic converter 4 is impaired. For this reason, the oxygen storage capacity represents a quality standard or measure of the functional capacity of the catalytic converter 4.

From the dead time or reaction time of the signal 21 of the second lambda sensor 5 for a sudden lambda rise caused by the transition to the traction mode, a measure for the oxygen storage capacity of the catalytic converter 4 is preferably as follows: Is calculated. The output signal 21 of the second exhaust gas sensor 5 starts at time t ₃ , at which time the signal 20 of the first exhaust gas sensor 6 reaches the lambda value λ _LSU = 1.0 and is integrated. This integration preferably ends at time t ₄ when the signal 21 of the second exhaust gas sensor 5 falls below a pre-settable value in U _LSF . The integral thus obtained is schematically shown in the graph I by the locus 22. For the diagnosis of the catalytic converter 4, the obtained integrated value is compared with a predetermined or presettable reference value. In this case, the reference value can be set in advance according to the air flow rate carried in the towing mode, for example. Furthermore, temperature dependence can be taken into account, in which case the signal of the temperature sensor 9 can be used to detect the temperature. If the integrated value falls below the reference value, it is evaluated that the catalytic converter 4 has deteriorated unacceptably, and a corresponding failure message is issued.

Claims (8)

A method for diagnosing an exhaust gas sensor (5; 6) arranged downstream and / or upstream of a catalytic converter (4) of a vehicle internal combustion engine (1) and / or a catalytic converter in an exhaust system (3). ,
(A) the internal combustion engine (1) is operated with an air / fuel mixture having an air / fuel ratio (λ) below the stoichiometric air / fuel ratio;
(B) the internal combustion engine (1) is stopped;
(C) After the internal combustion engine (1) is stopped, a traction mode in which ignition is not performed is performed in a fuel supply stop state, in which the internal combustion engine (1) passes air through the exhaust system (3) and the catalytic converter. (4) and sending to the exhaust gas sensor (5; 6);
(D) igniting and starting self-running of the internal combustion engine (1) with an air-fuel ratio (λ) below the stoichiometric air-fuel ratio;
(E) a step in which a signal of the exhaust gas sensor (5; 6) prepared in a time range from at least after the stop until the self-running of the internal combustion engine (1) is evaluated according to a predetermined evaluation criterion;
A method comprising the steps of:   The method according to claim 1, wherein the method is implemented in a vehicle with an electric motor drive.   2. The exhaust gas sensor (5) formed as a lambda probe with jump characteristics, in particular arranged downstream of the catalytic converter (4) of the exhaust system (3), is diagnosed. Or the method of 2.   4. The exhaust gas sensor (6), which is formed as a continuous lambda probe, in particular arranged upstream of the catalytic converter (4) of the exhaust system (3), is diagnosed. A method according to any one of the above.   5. The method according to claim 1, wherein a catalytic converter (4) having an oxygen storage capacity is diagnosed.   6. In step (a), the internal combustion engine (1) is operated with an air / fuel mixture having a lambda value of about 0.98. The method described.   6. In step (d), the internal combustion engine (1) is supplied with an air / fuel mixture having a lambda value in the range of about 0.90 to about 0.98. A method according to any one of the above.   The signal of the exhaust gas sensor (5; 6) is evaluated with respect to at least one of the slope, dead time, settling time and left-right symmetry of the evaluation reference signal. The method according to one item.

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