Dual-power tractor permanent magnet system emergency stop control method, device and vehicle

Abstract

The present invention belongs to the technical field of tractors, and provides an emergency stop control method, device and vehicle for the permanent magnet system of a dual-power tractor. The method of the present invention includes: information collection: obtaining the status information of the emergency stop button on the operating console; emergency stop status determination: when the emergency stop button is valid, enter the emergency stop control, and the air brake flag is valid at this time; rapid braking torque execution: sending the target speed and target limit torque to the motor controller, and controlling the braking system at the same time; stop torque execution: when the motor speed is less than the speed threshold, the dual-power motor executes the stop torque until the vehicle stops. The emergency stop control method for the permanent magnet system of a dual-power tractor provided by the present invention directly sends the target speed and target torque to the motor controller, and by controlling the brakes, the vehicle stops in a short time, reducing the braking distance, and the stopping distance is shorter, further improving the safety of the vehicle.

Description

Technical Field

[0001] The present invention relates to the technical field of tractor control systems, and in particular to an emergency stop control method, a device and a vehicle for a permanent magnet system of a dual-power tractor. Background Art

[0002] At present, the asynchronous system of subway traction vehicles occupies the main market. In the case of emergency braking, the asynchronous system generally sends the emergency stop button on the console to the inverter for deceleration and parking, resulting in a long braking distance and poor safety. In order to solve the problem of low efficiency of asynchronous motors, permanent magnet synchronous motors are used as power output. Therefore, how to control permanent magnet synchronous motors during emergency stops to ensure safety and braking effect is urgently needed. Summary of the invention

[0003] In view of the defects in the prior art, the present invention provides a method, a device and a vehicle for emergency stop control of a permanent magnet system of a dual-power tractor, so as to solve the emergency stop control problem of a permanent magnet system of a dual-power tractor.

[0004] In a first aspect, the present invention provides a method for controlling an emergency stop of a permanent magnet system of a dual-power tractor, comprising:

[0005] Information collection: obtain the status information of the emergency stop button on the operating console;

[0006] Emergency stop state determination: when the emergency stop button is valid, the emergency stop control is entered, and the air brake mark is valid at this time;

[0007] Fast braking torque execution: Send the target speed and target limit torque to the motor controller and control the braking system at the same time;

[0008] Optionally, after the emergency stop state is determined and before the rapid braking torque is executed, the method further includes detecting motor fault information, including:

[0009] Check whether motor A and motor B are faulty;

[0010] When a fault occurs in motor A and / or motor B and the fault level reaches a preset level threshold, the target limit torque of the faulty motor is sent to the motor controller as 0.

[0011] Optionally, when neither motor A nor motor B has a fault, or the fault levels of motor A and motor B do not reach a preset level threshold, the method for determining the target torque limit includes:

[0012] Get the speed n1 of motor A and the speed n2 of motor B;

[0013] Get the speed difference Δn=|n1-n2| between motor A and motor B;

[0014] The target limit torques of motor A and motor B are determined according to the relationship between the speed difference Δn and the speed difference threshold.

[0015] Optionally, determining the target torque limit of the motor A and the motor B according to the relationship between the speed difference Δn and the speed difference threshold includes:

[0016] When the speed difference Δn≤speed difference threshold, motor A and motor B execute braking torques Ts1 and Ts2; Ts1 and Ts2 are obtained by looking up the table according to the speeds n1 and n2 of motor A and motor B respectively.

[0017] Optionally, determining the target torque limit of motor A and motor B according to the relationship between the speed difference Δn and the speed difference threshold value further includes, when the speed difference Δn>the speed difference threshold value, determining the target torque limit of motor A and motor B according to the relationship between the speed of motor A and the speed threshold value, specifically including:

[0018] If the speed of motor A is less than the speed threshold, the target limit torque of motor A is controlled to be 0, and the air brake flag is invalid at this time;

[0019] If the speed of motor A is ≥ the speed threshold and the speed of motor B is < the speed threshold, the target limit torque of motor B is controlled to be 0, and the air brake flag is invalid at this time; otherwise, the emergency stop control is re-entered.

[0020] Optionally, the rotational speed difference threshold is greater than the rotational speed threshold.

[0021] Optionally, when the speed difference Δn≤the speed difference threshold, after the motor A and the motor B perform the braking torques Ts1 and Ts2, the method further includes:

[0022] When the motor speeds are both less than the speed threshold, motor A and motor B execute the stop torque until the vehicle stops; otherwise, the emergency stop state determination step is re-entered.

[0023] In a second aspect, the present invention provides a dual-power tractor permanent magnet system emergency stop control device, comprising:

[0024] Information collection module, used to obtain the status information of the emergency stop button on the operating console;

[0025] An emergency stop state determination module is used to enter emergency stop control when the emergency stop button is valid, and the air brake flag is valid at this time;

[0026] The fast braking torque execution module is used to send the target speed and target limit torque to the motor controller and control the braking system at the same time.

[0027] Optionally, after the emergency stop state is determined and before the rapid braking torque is executed, a motor fault information detection module is also included, which is specifically used to:

[0028] Check whether motor A and motor B are faulty;

[0029] When a fault occurs in motor A and / or motor B and the fault level reaches a preset level threshold, the target limit torque of the faulty motor is sent to the motor controller as 0.

[0030] Optionally, when neither motor A nor motor B has a fault, or the fault levels of motor A and motor B do not reach a preset level threshold, the rapid braking torque execution module is specifically used to:

[0031] Get the speed n1 of motor A and the speed n2 of motor B;

[0032] Get the speed difference Δn=|n1-n2| between motor A and motor B;

[0033] The target limit torques of motor A and motor B are determined according to the relationship between the speed difference Δn and the speed difference threshold.

[0034] Optionally, the rapid braking torque execution module is further used to:

[0035] When the speed difference Δn≤speed difference threshold, motor A and motor B execute braking torques Ts1 and Ts2; Ts1 and Ts2 are obtained by looking up the table according to the speeds n1 and n2 of motor A and motor B respectively.

[0036] Optionally, the determining the target limit torque of the motor A and the motor B according to the relationship between the speed difference Δn and the speed difference threshold further includes when the speed difference Δn>the speed difference threshold, the rapid braking torque execution module is further specifically used to:

[0037] If the speed of motor A is less than the speed threshold, the target limit torque of motor A is controlled to be 0, and the air brake flag is invalid at this time;

[0038] If the speed of motor A is ≥ the speed threshold and the speed of motor B is < the speed threshold, the target limit torque of motor B is controlled to be 0, and the air brake flag is invalid at this time; otherwise, the emergency stop control is re-entered.

[0039] Optionally, in the rapid braking torque execution module, the speed difference threshold is greater than the speed threshold.

[0040] Optionally, when the speed difference Δn≤the speed difference threshold, after the motor A and the motor B execute the braking torques Ts1 and Ts2, the device further includes a stop torque execution module, which is specifically used to:

[0041] When the motor speeds are both less than the speed threshold, motor A and motor B execute the stop torque until the vehicle stops; otherwise, the emergency stop state determination step is re-entered.

[0042] In a third aspect, an embodiment of the present invention provides a vehicle, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of any of the above methods when executing the computer program.

[0043] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium having computer program instructions stored thereon, which implement the steps of any of the above methods when executed by a processor.

[0044] By adopting the above technical solution, the present application has the following beneficial effects:

[0045] The emergency stop control method of the permanent magnet system of a dual-power tractor provided by the present invention directly sends the target speed and target torque to the motor controller, and stops the vehicle in a short time by controlling the brakes, thereby reducing the braking distance, shortening the parking distance, and further improving the vehicle safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0047] Figure 1 A flow chart of an emergency stop control method for a permanent magnet system of a dual-power tractor provided by an embodiment of the present invention is shown;

[0048] Figure 2 Another flow chart of an emergency stop control method for a permanent magnet system of a dual-power tractor provided by an embodiment of the present invention is shown;

[0049] Figure 3 Another flow chart of an emergency stop control method of a permanent magnet system of a dual-power tractor provided by an embodiment of the present invention is shown;

[0050] Figure 4 A structural block diagram of a permanent magnet system emergency stop control device for a dual-power tractor provided by an embodiment of the present invention is shown;

[0051] Figure 5 A structural block diagram of a vehicle provided by an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0052] The following embodiments of the technical solution of the present invention are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.

[0053] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0054] For subway tractors, in the process of vehicle driving, emergency stopping is required to deal with emergency braking situations and the braking distance must be reduced as much as possible. The existing one-step system generally sends the emergency stop button on the console to the frequency converter for deceleration and stopping, while the permanent magnet system directly sends the target speed and target limit torque to the motor controller, and controls the brakes to stop the vehicle in a short time. In the dual-power scenario, how to control the two motors to achieve a short braking distance and ensure vehicle safety needs to be solved urgently. This embodiment provides an emergency stop control method for a permanent magnet system of a dual-power tractor to solve the above problems.

[0055] This embodiment provides a method for controlling the emergency stop of a permanent magnet system of a dual-power tractor. Figure 1 As shown, including:

[0056] S1. Information acquisition: Get the status information of the emergency stop button on the operating console.

[0057] First, the acquisition module is used to collect the emergency stop button signal on the operating console, as well as the speed signal of each motor controller, the torque signal of each motor, the temperature signal of each motor and the temperature signal of the motor controller, the fault signal of each motor, etc. The above signals can be obtained based on the sensors and other measuring equipment installed on the existing tractor.

[0058] S2. Emergency stop status determination: When the emergency stop button is valid, enter emergency stop control.

[0059] When the emergency stop button signal on the console is valid, the driver should have determined that the vehicle needs to stop urgently and pressed the emergency stop button to make the emergency stop button signal valid. At this time, the vehicle enters the emergency stop state.

[0060] S3, fast braking torque execution: send the target speed and target limit torque to the motor controller, and control the braking system to brake at the same time.

[0061] When the emergency stop button is valid, the braking system works and the air brake flag is valid. At the same time, the target speed of 0 is sent to the motor controller to control motor A and motor B to slow down. Under normal operation, the motor controller controls the target speed of motor A and motor B to 0. However, there may be a motor failure. In this case, before executing step S3, it is necessary to detect the motor failure information to determine whether motor A and motor B have a failure that is sufficient to affect the braking effect of the tractor. The specific steps include:

[0062] Check whether motor A and motor B are faulty;

[0063] When a fault occurs in motor A and / or motor B and the fault level reaches a preset level threshold, the target limit torque of the faulty motor is sent to the motor controller as 0.

[0064] According to the collected fault signals, including but not limited to the motor fault signals, if the motor A has a fault and it is a serious fault, the target limit torque of the motor A is controlled to be 0, and the braking output of the motor A or the motor B is stopped. In this embodiment, it is first determined whether the motor A has a serious fault, if so, the target limit torque of the motor A is controlled to be 0; if not, it is determined whether the motor B has a serious fault, if motor B has a serious fault, the target limit torque of the motor B is controlled to be 0, if not, step S3 is entered.

[0065] When neither motor A nor motor B has a fault, or the fault levels of motor A and motor B do not reach the preset level threshold, the method for determining the target limit torque is as follows: Figure 2 As shown, including:

[0066] S301 , obtaining the rotation speed n1 of motor A and the rotation speed n2 of motor B.

[0067] S302 , obtaining the speed difference Δn=|n1-n2| between motor A and motor B.

[0068] The speed difference Δn is determined according to the speeds n1 and n of the motor A and the motor B acquired by the acquisition module.

[0069] S303 : Control the target limit torque of motor A and motor B according to the relationship between the speed difference Δn and the speed difference threshold.

[0070] The step of determining the target torque limit of the motor A and the motor B according to the relationship between the speed difference Δn and the speed difference threshold comprises:

[0071] When the speed difference Δn≤speed difference threshold, motor A and motor B are controlled to respectively execute braking torques Ts1 and Ts2; Ts1 and Ts2 are obtained by looking up the table according to the speeds n1 and n2 of motor A and motor B respectively.

[0072] Among them, corresponding to different relationships between the speed difference and the speed difference threshold, motor A and motor B perform different braking torques, specifically including the following two situations:

[0073] In the first case, when the speed difference Δn> the speed difference threshold, it is necessary to determine the relationship between the speed of motor A and the speed threshold, which is divided into the following two numerical relationships.

[0074] If the speed of motor A is less than the speed threshold, the target limit torque of motor A is controlled to be 0, and the air brake flag is invalid. If the speed of motor A is less than the speed threshold, the wheel of motor A is locked, the target limit torque of motor A is sent to the motor controller as 0, and the air brake is turned on.

[0075] If the speed of motor A is ≥ the speed threshold and the speed of motor B is < the speed threshold, the target limit torque of motor B is controlled to be 0, and the air brake flag is invalid at this time; otherwise, the emergency stop control is re-entered. When the speed of motor A is ≥ the speed threshold, it is determined whether the speed of motor B is < the speed threshold. If so, the wheel of motor B is locked, the target limit torque of motor B is sent to 0, and the air brake is turned on.

[0076] It should be noted that the rotation speed difference threshold value>the rotation speed threshold value.

[0077] In the second case, when the speed difference Δn≤speed difference threshold, the target limit torques of motor A and motor B are respectively the execution braking torques Ts1 and Ts2; Ts1 and Ts2 are obtained by looking up the table according to the speeds n1 and n2 of motor A and motor B, respectively.

[0078] In order to obtain the brake torque Ts1 and Ts2 of motor A and motor B, the table looked up in this step is a pre-established relationship table of motor speeds corresponding to brake torques. By inputting the speed of motor 1 and the speed of motor 2, the brake torque Ts1 corresponding to the current motor 1 and the brake torque Ts2 corresponding to motor 2 are found out respectively.

[0079] When the speed difference Δn ≤ the speed difference threshold, after motor A and motor B execute the braking torques Ts1 and Ts2, as shown in FIG. Figure 3 As shown, the method also includes:

[0080] S4, stop torque execution: when the motor speeds are both less than the speed threshold, motor A and motor B execute the stop torque until the vehicle stops; otherwise, re-enter the emergency stop state determination step.

[0081] When the speeds of motor A and motor B are both less than the speed threshold, the parking torque is sent to the motor controller; otherwise, the speeds of motor A and motor B are still too fast, and the emergency stop state determination process is re-entered to eliminate control errors and avoid the impact of faults.

[0082] The stopping torque of motor A and motor B is greater than the braking torque. When the vehicle stops, there is no need to consider the braking feedback current. After a delay of y count cycles, the vehicle stops on the rail.

[0083] In one embodiment, a dual-power tractor permanent magnet system emergency stop control device 50 is provided, such as Figure 4 As shown, including:

[0084] Information collection module 501, used to obtain the status information of the emergency stop button on the operating console;

[0085] The emergency stop state determination module 502 is used to enter the emergency stop control when the emergency stop button is valid, and the air brake flag is valid at this time;

[0086] The fast braking torque execution module 503 is used to send the target speed and the target limit torque to the motor controller and control the braking system to brake.

[0087] The dual-power tractor permanent magnet system emergency stop control device 50 provided in the embodiment of the present application and the above-mentioned dual-power tractor permanent magnet system emergency stop control method adopt the same inventive concept and can achieve the same beneficial effects, which will not be repeated here.

[0088] Optionally, after the emergency stop state is determined and before the rapid braking torque is executed, a motor fault information detection module is also included, which is specifically used to:

[0089] Check whether motor A and motor B are faulty;

[0090] When a fault occurs in motor A and / or motor B and the fault level reaches a preset level threshold, the target limit torque of the faulty motor is sent to the motor controller as 0.

[0091] Optionally, when neither motor A nor motor B has a fault, or the fault levels of motor A and motor B do not reach a preset level threshold, the rapid braking torque execution module is specifically used to:

[0092] Get the speed n1 of motor A and the speed n2 of motor B;

[0093] Get the speed difference Δn=|n1-n2| between motor A and motor B;

[0094] The target limit torques of motor A and motor B are determined according to the relationship between the speed difference Δn and the speed difference threshold.

[0095] Optionally, the rapid braking torque execution module is further used to:

[0096] When the speed difference Δn≤speed difference threshold, motor A and motor B execute braking torques Ts1 and Ts2; Ts1 and Ts2 are obtained by looking up the table according to the speeds n1 and n2 of motor A and motor B respectively.

[0097] Optionally, the determining the target limit torque of the motor A and the motor B according to the relationship between the speed difference Δn and the speed difference threshold further includes when the speed difference Δn>the speed difference threshold, the rapid braking torque execution module is further specifically used to:

[0098] If the speed of motor A is less than the speed threshold, the target limit torque of motor A is controlled to be 0, and the air brake flag is invalid at this time;

[0099] If the speed of motor A is ≥ the speed threshold and the speed of motor B is < the speed threshold, the target limit torque of motor B is controlled to be 0, and the air brake flag is invalid at this time; otherwise, the emergency stop control is re-entered.

[0100] Optionally, in the rapid braking torque execution module, the speed difference threshold is greater than the speed threshold.

[0101] Optionally, when the speed difference Δn≤the speed difference threshold, after the motor A and the motor B execute the braking torques Ts1 and Ts2, the device further includes a stop torque execution module, which is specifically used to:

[0102] When the motor speeds are both less than the speed threshold, motor A and motor B execute the stop torque until the vehicle stops; otherwise, the emergency stop state determination step is re-entered.

[0103] Based on the same inventive concept as the above-mentioned dual-power tractor permanent magnet system emergency stop control method, the embodiment of the present application also provides a vehicle 60, such as Figure 5 As shown, the vehicle 60 may include a processor 601 and a memory 602 .

[0104] The processor 601 may be a general-purpose processor, such as a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, and may implement or execute the methods, steps and logic block diagrams disclosed in the embodiments of the present invention. A general-purpose processor may be a microprocessor or any conventional processor, etc. The steps of the method disclosed in the embodiments of the present invention may be directly embodied as being executed by a hardware processor, or may be executed by a combination of hardware and software modules in the processor.

[0105] The memory 602 is a non-volatile computer-readable storage medium that can be used to store non-volatile software programs, non-volatile computer executable programs and modules. The memory may include at least one type of storage medium, such as flash memory, hard disk, multimedia card, card-type memory, random access memory (Random Access Memory, RAM), static random access memory (Static Random Access Memory, SRAM), programmable read-only memory (Programmable Read Only Memory, PROM), read-only memory (Read Only Memory, ROM), electrically erasable programmable read-only memory (Electrically Erasable Programmable Read-Only Memory, EEPROM), magnetic memory, disk, optical disk, etc. The memory is any other medium that can be used to carry or store the desired program code in the form of instructions or data structures and can be accessed by a computer, but is not limited to this. The memory 1202 in the embodiment of the present invention can also be a circuit or any other device that can realize the storage function, which is used to store program instructions and / or data.

[0106] An embodiment of the present invention provides a computer-readable storage medium for storing computer program instructions for the above-mentioned vehicle, which includes a program for executing the above-mentioned page broadcast control method.

[0107] The above-mentioned computer storage media can be any available media or data storage devices that can be accessed by a computer, including but not limited to magnetic storage (such as floppy disks, hard disks, magnetic tapes, magneto-optical disks (MO), etc.), optical storage (such as CD, DVD, BD, HVD, etc.), and semiconductor storage (such as ROM, EPROM, EEPROM, non-volatile memory (NAND FLASH), solid-state drive (SSD)), etc.

[0108] The above embodiments are only used to introduce the technical solutions of the present application in detail, but the description of the above embodiments is only used to help understand the methods of the embodiments of the present invention and should not be understood as limiting the embodiments of the present invention. Any changes or substitutions that can be easily thought of by technicians in this technical field should be included in the protection scope of the embodiments of the present invention.

Claims

1. A method for emergency stop control of a permanent magnet system of a dual-power tractor, characterized in that: include: Information collection: obtain the status information of the emergency stop button on the operating console; Emergency stop state determination: when the emergency stop button is valid, the emergency stop control is entered, and the air brake mark is valid at this time; Fast braking torque execution: Send the target speed and target limit torque to the motor controller and control the braking system at the same time; After the emergency stop state is determined and before the rapid braking torque is executed, the method further includes detecting motor fault information, including: Check whether motor A and motor B are faulty; When motor A and / or motor B has a fault and the fault level reaches a preset level threshold, a target limit torque of the faulty motor is sent to the motor controller as 0; When neither motor A nor motor B has a fault, or the fault levels of motor A and motor B do not reach a preset level threshold, the method for determining the target torque limit includes: Get the speed n1 of motor A and the speed n2 of motor B; Get the speed difference Δn=|n1-n2| between motor A and motor B; Determine the target limit torque of motor A and motor B according to the relationship between the speed difference Δn and the speed difference threshold; The target torque limit of motor A and motor B is determined according to the relationship between the speed difference Δn and the speed difference threshold, including when the speed difference Δn> the speed difference threshold, according to the relationship between the speed of motor A and the speed threshold, specifically including: If the speed of motor A is less than the speed threshold, the target limit torque of motor A is controlled to be 0, and the air brake flag is invalid at this time; If the speed of motor A is greater than or equal to the speed threshold and the speed of motor B is less than the speed threshold, the target limit torque of motor B is controlled to be 0, and the air brake flag is invalid at this time; otherwise, the emergency stop control is re-entered; The rotation speed difference threshold is greater than the rotation speed threshold.

2. The method according to claim 1, characterized in that: The step of determining the target torque limit of the motor A and the motor B according to the relationship between the speed difference Δn and the speed difference threshold comprises: When the speed difference Δn≤speed difference threshold, motor A and motor B execute braking torques Ts1 and Ts2; Ts1 and Ts2 are obtained by looking up the table according to the speeds n1 and n2 of motor A and motor B respectively.

3. The method according to claim 2, characterized in that When the speed difference Δn is less than or equal to the speed difference threshold, after the motor A and the motor B execute the braking torques Ts1 and Ts2, the method further includes: Stop torque execution: When the motor speeds are both less than the speed threshold, motor A and motor B execute the stop torque until the vehicle stops; otherwise, re-enter the emergency stop state determination step.

4. A dual-power tractor permanent magnet system emergency stop control device, characterized in that: include: Information collection module, used to obtain the status information of the emergency stop button on the operating console; An emergency stop state determination module is used to enter emergency stop control when the emergency stop button is valid, and the air brake flag is valid at this time; A fast braking torque execution module is used to send the target speed and target limit torque to the motor controller and control the braking system at the same time; After the emergency stop state is determined and before the rapid braking torque is executed, a motor fault information detection module is also included, which is specifically used to: Check whether motor A and motor B are faulty; When motor A and / or motor B has a fault and the fault level reaches a preset level threshold, a target limit torque of the faulty motor is sent to the motor controller as 0; When neither motor A nor motor B has a fault, or the fault levels of motor A and motor B do not reach a preset level threshold, the rapid braking torque execution module is specifically used to: Get the speed n1 of motor A and the speed n2 of motor B; Get the speed difference Δn=|n1-n2| between motor A and motor B; Determine the target limit torque of motor A and motor B according to the relationship between the speed difference Δn and the speed difference threshold; The method of determining the target torque limit of the motor A and the motor B according to the relationship between the speed difference Δn and the speed difference threshold value further includes the method of executing the fast braking torque when the speed difference Δn> the speed difference threshold value, which is further used to: If the speed of motor A is less than the speed threshold, the target limit torque of motor A is controlled to be 0, and the air brake flag is invalid at this time; If the speed of motor A is greater than or equal to the speed threshold and the speed of motor B is less than the speed threshold, the target limit torque of motor B is controlled to be 0, and the air brake flag is invalid at this time; Otherwise, re-enter emergency stop control; The rotation speed difference threshold is greater than the rotation speed threshold.

5. A vehicle comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 3 are implemented.

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