JP5439149B2 - Motor warm-up control - Google Patents

Description

  The present invention relates to motor warm-up control.

  Conventionally, electric vehicles and fuel cell vehicles using a motor as a drive source are known. In an automobile using this type of motor as a drive source, generally, lubricating oil is supplied to smoothly rotate the motor and a gear that is a part of the power transmission means.

  However, an electric vehicle or the like generates little heat in a motor room (equivalent to an engine room of a gasoline-powered vehicle), and therefore the temperature of the lubricating oil may be low at the start of driving. When the temperature of the lubricating oil is low, the viscosity increases, and there is a problem that an extra required driving force is required due to the friction caused by this viscosity, and the power consumption increases. Therefore, a technique for controlling the temperature of the lubricating oil to be quickly raised when the temperature of the lubricating oil is low has been proposed (see, for example, Patent Document 1).

  In Patent Document 1, when the temperature of the hydraulic oil / lubricating oil of the power transmission mechanism is equal to or lower than a predetermined threshold, if the battery charge amount is within a predetermined condition range, the operation mode of the motor and generator is changed. The oil temperature is raised by increasing work and accompanying loss.

JP 2002-174328 A

However, in the control method of Patent Document 1, since the work distribution of the power transmission mechanism, the motor and the generator is operated in an operation mode with a distribution different from the optimal distribution when the warm-up operation is originally completed, the power transmission mechanism, There is a problem that the overall operation efficiency of the motor and the generator is lowered. In addition, it is necessary to provide means for monitoring the amount of electricity stored in the battery and means for determining whether or not to execute control based on the amount of electricity stored.
Furthermore, in the past, priority was given to the temperature rise of the lubricating oil without deciding the upper limit of the electric power to be supplied to the motor when raising the temperature of the lubricating oil, so the electric power consumed for raising the temperature of the lubricating oil became excessive, There is a problem that the travel distance of an electric vehicle is reduced.

  Therefore, the present invention has been made in view of the above circumstances, and it is possible to suppress the power consumed for raising the temperature of the lubricating oil without changing the operation mode of the motor and the power transmission means. It provides warm-up control of the motor.

In order to solve the above-described problems, the invention described in claim 1 is a motor for traveling (for example, the motor 23 in the embodiment) and a motor housing for housing the motor (for example, the motor housing 11 in the embodiment). A gear that transmits the driving force of the motor to wheels, a gear housing that houses the gear (for example, the gear housing 12 in the embodiment), and lubricating oil that flows through the motor housing and the gear housing (for example, Lubricating oil 71) in the embodiment, a power storage device that supplies power to the motor (for example, the battery 8 in the embodiment), and an inverter that converts DC power from the power storage device into AC power (for example, the inverter in the embodiment) 2) and traveling by transmitting the driving force of the motor to the wheels via the gear. Temperature detection means (for example, an oil temperature sensor 75 in the embodiment) for controlling the warming of the motor in both (for example, the electric vehicle 1 in the embodiment), and detecting the temperature at a predetermined position of the motor and the gear; Based on the detection results of the rotation speed detection means (for example, the rotation sensor 25 in the embodiment) and the temperature detection means and the rotation speed detection means for detecting the rotation speed of the motor, the friction torque of the gear (for example, implementation) Friction torque estimating means for estimating the friction torque T2) in the embodiment, and the depression torque to the motor (for example, the depression torque T1 in the embodiment) based on the depression amount of the accelerator pedal (for example, the accelerator pedal 61 in the embodiment). A stepping torque calculating means for calculating, and the friction torque And a correction torque calculating means for calculating a correction torque (for example, a correction torque T3 in the embodiment) based on the stepping torque and the stepping torque, and controlling the inverter with the correction torque and supplying a current corresponding to the correction torque to the motor. And a lubricating oil temperature raising means for raising the temperature of the lubricating oil while ensuring the stepping torque, and the lubricating oil temperature raising means is executed when the lubricating oil temperature raising means is executed. In order to set the limit value (for example, the second power P2 in the embodiment) of the output power value of the power storage device based on the correction torque so as to minimize the power loss in the middle and generate the stepping torque Power consumed (for example, power consumption P0 in the embodiment) and power consumed for generating the friction torque (for example, the first power in the embodiment) 1 power P1) is set as a limit value of the output power value of the power storage device .

  In the invention described in claim 2, when the temperature detected by the temperature detecting means is equal to or lower than a predetermined value, the lubricating oil temperature raising means is executed, and while the lubricating oil temperature raising means is being executed, The limit value is increased by the amount of power lost due to an increase in friction.

  According to a third aspect of the present invention, when the friction torque estimated by the friction torque estimating means is larger than a predetermined first threshold value, the lubricating oil temperature raising means is started, and the friction torque is set to a predetermined second value. The lubricating oil temperature raising means is terminated when it becomes smaller than the threshold value.

  According to a fourth aspect of the present invention, when the friction torque estimated by the friction torque estimating means is larger than a predetermined first threshold, the lubricating oil temperature raising means is started, and the lubricating oil temperature raising means is started. Then, the lubricating oil temperature raising means is terminated when a predetermined time has elapsed.

  The invention described in claim 5 further performs loss increase control for increasing at least one of iron loss and copper loss of the motor, and does not change the shaft output of the motor, and only the input power to the motor. It is characterized by increasing.

  According to the first aspect of the present invention, the friction torque is estimated from the temperature at the predetermined position and the rotational speed of the motor, and the correction torque is calculated by adding the friction torque to the stepping torque actually requested by the driver. Thus, the correction torque is supplied to the motor. By comprising in this way, lubricating oil can be heated up, ensuring treading torque. Further, since the value obtained by converting the correction torque into electric power is set as the limit value of the output electric power value of the power storage device, it is possible to warm up while minimizing the power loss during the warming up control of the lubricating oil. In other words, it is possible to perform warm-up without changing the basic operation mode of the motor and gear and while suppressing the power consumed to raise the temperature of the lubricating oil. Operation becomes possible, and the work output by the motor can be kept constant for external devices. Therefore, when performing warm-up control, power ripple can be suppressed, and there is an advantage that the ride comfort does not change for the driver and the occupant.

  According to the second aspect of the present invention, by raising the limit value of the output voltage value of the power storage device by the amount of electric power lost due to an increase in friction, the temperature of the lubricating oil is increased while securing the depression torque. Can do. That is, the temperature of the lubricating oil can be raised without changing the basic operation mode of the motor and gear.

  According to the third aspect of the present invention, the determination as to whether or not to execute the lubricating oil temperature raising means and the determination as to whether or not to end the lubricating oil temperature raising means after the start are determined according to the value of the friction torque. Therefore, the temperature rise control of the lubricating oil can be limited with a simple configuration.

  According to the fourth aspect of the present invention, the determination as to whether or not to execute the lubricating oil temperature raising means is made in accordance with the value of the friction torque, and ends after the start of the lubricating oil temperature raising means. Whether or not is determined at a preset time, the temperature rise control of the lubricating oil can be limited with a simple configuration.

  According to the fifth aspect of the present invention, when the lubricating oil temperature raising means is executed, the loss increasing control having a larger temperature raising effect is more actively executed. The time for raising the temperature of the lubricating oil can be shortened compared with the case where it is executed.

It is a schematic block diagram of the electric vehicle in embodiment of this invention. It is a schematic block diagram which shows the cooling system system of the electric vehicle in embodiment of this invention. It is a schematic structure sectional view of a motor unit in an embodiment of the present invention. It is a front view of the rotor in the embodiment of the present invention. It is a schematic block diagram of the control part in embodiment of this invention. It is a map which calculates | requires the friction torque in embodiment of this invention. It is a map which calculates | requires friction power in embodiment of this invention.

  Next, an embodiment of the present invention will be described with reference to FIGS. In the present embodiment, a motor unit employed in an electric vehicle will be described.

(Electric car)
FIG. 1 is a schematic configuration diagram of an electric vehicle. As shown in FIG. 1, an electric vehicle 1 includes a motor unit 10 that houses a power transmission unit such as a motor 23 and gears, an inverter 2 and a VCU (converter) 3 for driving the motor 23, an inverter 2 and a VCU 3 A pump 4 for circulating a refrigerant for cooling the refrigerant, a radiator 5 for cooling the refrigerant, a downverter (converter) 6 for reducing the voltage output from the drive system and supplying it to the battery 8, and a battery 8 is provided with a charger 7 used as a voltage converter when charging with a plug-in, and a battery 8 arranged on the entire surface under the floor of the vehicle.

  FIG. 2 is a schematic configuration diagram showing a cooling system of an electric vehicle. As shown in FIG. 2, when the electric vehicle 1 travels, each part generates heat and becomes high temperature, and therefore is appropriately cooled by a cooling system. Specifically, a first cooling system 51 for cooling the inverter 2 and the VCU 3 and a second cooling system 52 for cooling various parts in the motor unit 10 are provided. The first cooling system 51 circulates the refrigerant in the cooling pipe 53 at a desired flow rate by the pump 4, absorbs heat when passing through the immediate vicinity of the inverter 2 and the VCU 3, and dissipates the heat absorbed by the radiator 5. It is configured. The second cooling system 52 will be described in detail later.

(Vehicle drive motor unit)
FIG. 3 is a schematic sectional view of the vehicle motor unit. As shown in FIG. 3, a vehicle motor unit (hereinafter referred to as a motor unit) 10 is a motor that houses a motor 23 having a stator 21 around which a coil 20 is wound and a rotor 22 in which a permanent magnet 30 is disposed. A housing 11, a gear housing 12 that is fastened to one side of the motor housing 11, and that houses a power transmission unit (not shown) composed of a gear that transmits power from the shaft 24 of the motor 23, and the motor housing 11 And a sensor housing 13 that is fastened to the other side and accommodates the rotation sensor 25 of the motor 23.

  The motor housing 11 is configured as a motor chamber 36, the gear housing 12 is configured as a gear chamber 37, and the sensor housing 13 is configured as a sensor chamber 38.

  The motor housing 11 is formed in a substantially cylindrical shape so as to cover the entire motor 23. The motor housing 11 in the present embodiment includes a stator housing 15 formed with substantially the same axial length as the stator 21, and transition housings 16 and 17 connected to both sides of the stator housing 15 in the axial direction. .

  A partition wall 41 that partitions the motor chamber 36 and the gear chamber 37 is formed in the transition housing 16. A through hole 40 penetrating in the thickness direction of the partition wall 41 is formed at a central portion in the radial direction of the partition wall 41. The through hole 40 is provided with a bearing 26 that rotatably supports one end side of the shaft 24 of the motor 23.

  A bearing 27 that rotatably supports the other end of the shaft 24 of the motor 23 is provided on the sensor housing 13 side of the boundary between the transition housing 17 and the sensor housing 13. A permanent magnet 30 is attached to the outer peripheral edge of the rotor 22 connected to the shaft 24. Furthermore, a helical gear (oblique gear) 29 that meshes with the gear in the gear housing 12 is formed at an end portion on one end side of the shaft 24.

  A stator core 18 formed by stacking annular thin plates is press-fitted and fixed to the inner peripheral surface of the stator housing 15. A coil 20 is wound around the stator core 18, and the stator core 18 and the coil 20 constitute a stator 21. The coil 20 is wound around the stator core 18 by distributed winding, for example.

  FIG. 4 is a front view of the rotor 22 as viewed from the axial direction. As shown in FIG. 4, the rotor 22 includes a substantially cylindrical rotor core 44 on which magnetic plate materials 33 are stacked. The shaft 24 is fixed to the through hole 42 formed at the radial center of the rotor core 44. In the vicinity of the radially outer end of the rotor core 44, a plurality of accommodation holes 43 that penetrate the rotor core 44 in the axial direction are formed. A permanent magnet 30 made of a rare earth such as neodymium is housed in each housing hole 43. That is, the motor 23 of the present embodiment is a so-called IPM (Interior Permanent Magnet) motor in which the permanent magnet 30 is embedded in the rotor core 44.

  The permanent magnet 30 is magnetized in the radial direction of the rotor core 44. The permanent magnets 30 are arranged at substantially equal intervals along the circumferential direction of the rotor core 44, and the permanent magnets 30 adjacent in the circumferential direction are alternately magnetized in the opposite direction. Further, the rotor core 44 is formed with a plurality of lightening holes 45 in order to reduce the weight. A plurality (eight in this embodiment) of the lightening holes 45 are formed between the through holes 42 and the accommodation holes 43 at substantially equal intervals in the circumferential direction.

  Returning to FIG. 3, in the transition housing 16, the terminals 28 (28 u, 28 v, 28 w) connected to one end of the three-phase windings of the coil 20 are arranged upward, and the other ends of the windings of the respective phases are connected. A neutral point 31, which is bundled and swaged with a bundling fitting, is provided at the tip of the neutral wire 32 at a position corresponding to the lower side of the motor unit 10.

  In addition, an oil cooling mechanism (second cooling system) 52 for cooling the bearings 26 and 27, the motor 23, the power transmission unit, and the like and ensuring lubrication performance is provided inside the motor unit 10. . The oil cooling mechanism 52 includes a lubricating oil 71, an oil pump 72 that circulates the lubricating oil 71, and an oil passage 73 through which the lubricating oil 71 flows. Lubricating oil 71 is stored below the motor chamber 36 and the gear chamber 37, and the lubricating oil 71 is pumped up by an oil pump 72 provided in the gear chamber 37, and circulates in the motor unit 10 through the oil passage 73. It is configured as follows.

  The oil surface 74 of the lubricating oil 71 is set near the boundary between the stator 21 and the rotor 22 below the shaft 24 in a state where the motor unit 10 is held horizontally. That is, the stator 21 is immersed in oil, but the rotor 22 is not immersed in oil.

  Further, the oil surface 74 of the lubricating oil 71 stored in the lower portion of the gear chamber 37 is set to a height at which a part of the gear provided in the gear chamber 37 is immersed. That is, the lubricating oil 71 is scraped up by the gear provided in the gear chamber 37, and the lubricating oil 71 can be supplied to another gear disposed on the upper portion of the gear chamber 37 to ensure the lubricating performance. It is configured. An oil temperature sensor 75 that detects the temperature of the lubricating oil 71 is provided below the oil surface 74 in the gear chamber 37.

Next, control at the start of traveling of the electric vehicle 1 (at the start of motor driving) will be described.
FIG. 5 is a schematic block diagram illustrating control at the start of running of the electric vehicle. As shown in FIG. 5, the control unit 60 of the electric vehicle 1 includes a stepping torque calculation unit 62 that calculates a stepping torque T <b> 1 that is applied to the motor 23 according to the stepping amount of the accelerator pedal 61 of the electric vehicle 1, and an oil temperature sensor 75. The friction torque calculating unit 63 that calculates the friction torque T2 from the temperature of the lubricating oil 71 detected by the rotation sensor 25 and the rotational speed of the shaft 24 (motor 23) detected by the rotation sensor 25, and the stepping torque calculated by the torque calculating unit 62 And a correction torque calculation unit 64 that calculates a correction torque T3 that is actually applied to the motor 23 from the friction torque T2 calculated by the T1 and friction torque calculation unit 63. The friction torque T2 increases as the oil temperature of the lubricating oil 71 decreases. Further, if the rotational speed is large, the friction torque T2 becomes high.

  In the friction torque calculation unit 63, the temperature of the lubricating oil 71 detected by the oil temperature sensor 75 and the rotation speed of the shaft 24 (motor 23) detected by the rotation sensor 25 are input, and these temperatures and rotation speeds are shown in FIG. The friction torque T2 is obtained from a map stored in advance as shown in FIG.

  The correction torque calculation unit 64 calculates a torque having a magnitude that cancels the friction torque T2 while ensuring the depression torque T1 as the correction torque T3. Since the friction torque T2 has a negative value, the correction torque T3 is calculated by setting the correction torque T3 = the depression torque T1−the friction torque T2.

  The inverter 2 converts the current based on the correction torque T3 calculated by the correction torque calculation unit 64 and supplies a desired current to the motor 23. By supplying current to the motor 23 in this way, the lubricating oil 71 can be raised to a desired temperature while ensuring the stepping torque T1 required by the driver.

  Here, if priority is given to the temperature rise of the lubricating oil 71 without determining the upper limit of the warm air power used to raise the temperature of the lubricating oil 71, the power consumption of the battery 8 becomes excessive, and the travel distance of the electric vehicle 1 becomes long. There is a risk of reduction. For this reason, in the present embodiment, the temperature of the lubricating oil 71 can be increased while minimizing the power loss during the temperature increase control of the lubricating oil 71.

  Specifically, the friction increases as the oil temperature of the lubricating oil 71 decreases. The power (first electric power) P1 due to the increase in friction is P1 (W) = rotational speed (rpm) × friction torque T2 ( N · m) × 2 × circumferential ratio / 60. The friction torque T2 may be obtained using FIG. 6 described above.

  The battery power consumption (second power) P2 (W) that is excessively consumed when the temperature of the lubricating oil 71 is actually raised to a desired temperature is due to power loss in the inverter 2, power loss in the motor 23, and the like. Therefore, it becomes larger than P1.

  Therefore, in this embodiment, when the power (power consumption) by the stepping torque T1 is P0, the value of P2, that is, the output power value of the battery 8 is limited and operated so that P2 ≦ P0 + P1. Thus, by providing the limit value for P2, the temperature of the lubricating oil 71 can be raised while minimizing the power loss of the battery 8 during the temperature rise control of the lubricating oil 71.

  It should be noted that the determination as to whether or not to perform the control for raising the temperature of the lubricating oil 71 described above is configured such that the control is executed when the friction torque T2 is greater than a preset first threshold value. The determination as to whether or not to end after the start of the temperature raising control is configured to end the control when the friction torque T2 becomes smaller than a preset second threshold value. Further, when the temperature raising energization for raising the temperature of the lubricating oil 71 is not executed, the motor 23 is energized by normal energization not considering the friction torque T2.

  Further, when the temperature rise control of the lubricating oil 71 described above is performed, the operating efficiency of the motor 23 is temporarily reduced while limiting the maximum value, and only the input power to the motor 23 without changing the shaft output of the motor 23. By executing the loss increase control for increasing the temperature, the control for raising the temperature of the lubricating oil 71 in a short time may be further executed.

  Specifically, a method of decreasing the PWM frequency, a method of increasing the d-axis current (field weakening current) of the motor 23, a method of applying or increasing the harmonic current of the motor 23, or increasing the output voltage of the VCU 3 There are methods.

  First, when the PWM frequency is lowered, the ripple of the phase current flowing through the motor 23 increases, so the iron loss of the motor 23 increases, the stator 21 has heat, and the lubricating oil 71 can be heated.

  Further, when the d-axis current of the motor 23 is increased, the phase current flowing through the motor 23 is increased, so that the copper loss of the motor 23 is increased, the coil 20 has heat, and the lubricating oil 71 can be heated. .

  Further, when the harmonic current of the motor 23 is applied or increased, the harmonic current flowing through the motor 23 increases, so that the copper loss of the motor 23 increases, the coil 20 has heat, and the lubricating oil 71 is heated. be able to. At the same time, since the ripple of the phase current flowing through the motor 23 increases, the iron loss of the motor 23 increases, the stator 21 has heat, and the lubricating oil 71 can be heated.

  When the output voltage of the VCU 3 is increased, the ripple of the phase current flowing through the motor 23 increases, so the iron loss of the motor 23 increases, the stator 21 has heat, and the temperature of the lubricating oil 71 can be raised. .

  According to the present embodiment, the friction torque T2 is estimated from the oil temperature of the lubricating oil 71 detected by the oil temperature sensor 75 and the rotational speed of the motor 23 detected by the rotation sensor 25, and the stepping torque actually requested by the driver. The correction torque T3 is calculated by adding the friction torque T2 to T1, and the correction torque is supplied to the motor 23. By configuring in this way, it is possible to raise the temperature of the lubricating oil 71 while ensuring the depression torque T1. The friction torque T2 is canceled during the temperature rise control of the lubricating oil 71.

  Further, since the value obtained by converting the correction torque T3 into power (first power P1) is set as the limit value of the output power value of the battery 8, the power loss during the temperature rise (warming up) control of the lubricating oil 71 is suppressed to a minimum. Can be warm (warm). That is, since the warm-up can be performed without changing the basic operation mode of the motor 23 and the power transmission unit and suppressing the electric power consumed for the temperature rise of the lubricating oil 71, Operation with increased work is possible, and the work output from the motor 23 can always be constant for external devices. Therefore, when performing temperature rise (warm up) control, electric power ripple can be suppressed, and therefore control can be performed without changing the ride comfort for the driver and the occupant.

  Further, since it is configured to determine whether to execute the temperature rise control of the lubricating oil 71 and to determine whether to end the temperature increase control of the lubricating oil 71 according to the value of the friction torque T2, The temperature rise control of the lubricating oil 71 can be limited with a simple configuration.

  Furthermore, when performing the temperature rise control of the lubricating oil 71, since it is configured to more actively perform the loss increase control with a large temperature rise effect, than when performing only the temperature rise control of the lubricating oil 71, The time for raising the temperature of the lubricating oil 71 can be shortened.

  The present invention is not limited to the above-described embodiment, and includes various modifications made to the above-described embodiment without departing from the spirit of the present invention. That is, the specific structure and shape described in the embodiment are merely examples, and can be changed as appropriate.

  For example, in the present embodiment, when the power (first power) P1 due to the increase in friction is obtained, the friction torque is called from the map of FIG. 6 and then calculated using a mathematical formula. A map that allows the first electric power P1 to be obtained directly from the oil temperature and the rotational speed as shown in FIG. 7 may be stored in the control unit 60 in advance.

  In the present embodiment, the temperature of the lubricating oil 71 is detected by the temperature sensor 75 and the friction torque T2 is obtained. However, as the temperature detection location, the temperature of the gear housing 12 and the motor housing 11, The configuration may be such that the friction torque T2 is obtained by detecting the refrigerant temperature of the one cooling system 51, the temperature of the battery 8, and the like.

  Further, in the present embodiment, the start / end of the temperature rise control of the lubricating oil 71 is performed based on the first threshold value and the second threshold value that are set in advance. You may comprise so that temperature rising control may be performed only for the period.

  DESCRIPTION OF SYMBOLS 1 ... Electric vehicle (vehicle) 23 ... Motor 25 ... Rotation sensor (rotation number detection means) 61 ... Accelerator pedal 71 ... Lubricating oil 75 ... Oil temperature sensor (temperature detection means) P1 ... 1st electric power P2 ... 2nd electric power T1 ... Depression torque T2 ... Friction torque T3 ... Correction torque

Claims (5)

A motor for traveling,
A motor housing that houses the motor;
A gear for transmitting the driving force of the motor to the wheels;
A gear housing that houses the gear;
Lubricating oil flowing through the motor housing and the gear housing;
A power storage device for supplying power to the motor;
An inverter for converting DC power from the power storage device into AC power, and
The warm-up control of the motor in a vehicle that travels by transmitting the driving force of the motor to the wheels via the gear,
Temperature detecting means for detecting temperatures at predetermined positions of the motor and the gear;
A rotational speed detection means for detecting the rotational speed of the motor;
Friction torque estimation means for estimating the friction torque of the gear based on detection results of the temperature detection means and the rotation speed detection means;
A stepping torque calculating means for calculating a stepping torque to the motor based on a depression amount of an accelerator pedal;
Correction torque calculating means for calculating a correction torque based on the friction torque and the depression torque;
Lubricating oil temperature raising means for controlling the inverter with the correction torque and supplying a current corresponding to the correction torque to the motor to increase the temperature of the lubricating oil while ensuring the stepping torque. ,
In performing the lubricating AburaNoboru raising means sets the limit value of the output power value of the electric storage device based on the corrected torque to the power loss is minimized during the execution of the lubricating AburaNoboru raising means ,
The sum of the electric power consumed to generate the stepping torque and the electric power consumed to generate the friction torque is set as a limit value of the output electric power value of the power storage device. control. If the temperature detected by the temperature detection means is below a predetermined value, execute the lubricating oil temperature rise means,
2. The motor warm-up control according to claim 1, wherein the limit value is increased by an amount of electric power lost due to an increase in friction while the lubricating oil temperature raising means is being executed. Starting the lubricating oil temperature raising means when the friction torque estimated by the friction torque estimating means is larger than a predetermined first threshold;
3. The motor warm-up control according to claim 1, wherein when the friction torque becomes smaller than a predetermined second threshold, the lubricating oil temperature raising unit is terminated. Starting the lubricating oil temperature raising means when the friction torque estimated by the friction torque estimating means is larger than a predetermined first threshold;
3. The motor warm-up control according to claim 1, wherein the lubricating oil temperature raising means is terminated when a predetermined time has elapsed since the start of the lubricating oil temperature raising means.   The loss increase control for increasing at least one of the iron loss and the copper loss of the motor is further performed, and only the input power to the motor is increased without changing the shaft output of the motor. Item 5. The warm-up control of the motor according to any one of Items 1 to 4.

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