Brake control device for electric vehicle

A variable load calculator calculates a variable load command VL based on AS pressure and a predetermined table. A vehicle deceleration calculator calculates vehicle deceleration α based on a brake notch command BN and a predetermined table. A required braking force calculator calculates required braking force BL by multiplying a weight indicated by the variable load command VL and the vehicle deceleration α. An electric braking controller calculates an electric braking pattern in accordance with the required braking force BL and then transmits the electric braking pattern to an inverter controller. The electric braking controller calculates an electric braking force produced by operation of the electric motor and then transmits to a subtractor as feedback BT the electric braking force adjusted in accordance with a speed of the electric motor. The subtractor transmits to a mechanical brake as a mechanical braking command a result obtained by subtracting the feedback BT from the required braking force BL.

TECHNICAL FIELD

The present disclosure relates to a brake control device for electric vehicle, the brake control device being mounted on a vehicle driven by an electric motor and performing blending control using both an electrical brake and a mechanical brake.

BACKGROUND ART

Electric braking force for braking an electric railway vehicle is obtained by making an electric motor operate as a generator and applying force of reverse rotation of an armature to axle shafts, the rotational force the direction of which is opposite to the rotational direction of the armature occurring in a conversion from kinetic energy of the electric railway vehicle into electrical energy. The electric braking force is not affected by a friction coefficient between a brake shoe and a wheel, the friction coefficient depending on a vehicle speed, and thus approximately constant electric braking force can be obtained over a wide range of speeds of the electric railway vehicle. The use of electric braking for the purpose of decreasing the use of mechanical braking enables great reductions in wheel maintenance and a wear amount of the brake shoe.

In blending control of vehicle braking using both electric braking and mechanical braking, a brake control device calculates a required braking force necessary for obtaining a desired deceleration, in accordance with a braking command and a weight of a vehicle. The electric motor is controlled on the basis of an electric braking command in accordance with the required braking force, and an electric braking force is generated. The brake control device controls an electro-pneumatic conversion valve so that a mechanical brake is used for compensating for shortfall corresponding to braking force calculated by subtracting from the required braking force electric braking force that is actually generated by the electric motor and that is calculated based on current flowing through the electric motor or a speed of the electric motor.

In the case where the speed of the vehicle is low, desired electric braking force cannot be obtained. Therefore, when the speed of the vehicle falls below a given value, control of stopping electric braking is started in order to make total braking force, which is the sum of the electric braking force and the mechanical braking force, match the required braking force, and then mechanical brake is started up. If response of the mechanical brake is slow, a delay of the start-up of the mechanical braking force causes a difference between the total braking force and the required braking force so that constant deceleration cannot be obtained. As a result, there is a problem that the above braking control device causes an uncomfortable ride in the vehicle.

Methods used for making the total braking force equal to the required braking force include a method in which fast start-up of mechanical braking force is achieved by performing precharge control, by application of very low pressure to a brake cylinder while the electric brake is in operation, to reduce a space between the brake shoe and the wheel to improve the response of the mechanical brake.

In order to make the total braking force match the required braking force, in a braking device for a vehicle disclosed in Patent Literature 1, when the vehicle speed is decreased up to a predetermined speed slightly higher than a speed at which electric braking becomes ineffective, an advanced notice signal for notification of loss of effect of electric braking is transmitted from speed control means to precharge control means included in a brake operating device, and supplemental air braking force is applied to a brake cylinder by the air braking device.

CITATION LIST

Patent Literature

Patent Literature 1: Unexamined Japanese Patent Application Kokai Publication No. H08-164857

SUMMARY OF INVENTION

Technical Problem

A pressure of about 40 kPa or less is usually applied to the brake cylinder in the precharge control. However, tolerance allowed in pressure control of the brake cylinder is about 20 kPa. Therefore, the brake shoe may come into contact with the wheel in the precharge control, which worsens maintainability of the wheel and increases an amount of wear of the brake shoe.

There is a problem in that the braking device for a vehicle disclosed in Patent Literature 1 requires a structure in which each of an electric power converter and a braking controller is provided with an interface for receiving and transmitting an advanced notice signal for notification of loss of effectiveness of electric braking, and thus there is a problem in that the braking device disclosed in Patent Literature 1 has a complicated structure.

In order to solve the aforementioned problem, an objective of the present disclosure is to, via a brake control device of simplified structure, obtain the total braking force equal to the required braking force in the case where the vehicle speed is low.

Solution to Problem

In order to achieve the aforementioned objective, a brake control device for electric vehicle of the present disclosure, which is to be mounted on a vehicle driven by an electric motor, includes: a required braking force calculator; an electric braking force calculator; and an adjuster. The required braking force calculator calculates a required braking force on the basis of: a deceleration of a vehicle included in a braking instruction; and a weight of the vehicle, the required braking force being a braking force required for obtaining the deceleration. The electric braking force calculator calculates electric braking force generated by operation of the electric motor. The adjuster: adjusts electric braking force calculated by the electric braking force calculator to a smaller value when the speed of the electric motor is equal to or smaller than a threshold; and outputs the adjusted electric braking force.

Advantageous Effects of Invention

According to the present disclosure, the electric braking force generated by the electric motor is adjusted to a smaller value when the speed of the electric motor is equal to or smaller than the threshold, to use the adjusted electric braking force as feedback of electric braking force, and the mechanical brake is controlled based on a mechanical braking command depending on the feedback of electric braking force, and thus, by use of a simplified structure, total braking force equal to required braking force can be obtained in the case where a vehicle speed is low.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present disclosure is described in detail hereinafter with reference to drawings. Components that are the same or equivalent are assigned the same reference signs throughout the drawings.

FIG. 1is a block diagram illustrating an example configuration of a brake control device according to the embodiment of the present disclosure. A brake control device1is mounted on an electric railway vehicle that is hereinafter referred to as “electric vehicle”. The brake control device1includes: a variable load calculator11to calculate a variable load command VL on the basis of air suspension pressure (AS pressure) from an air suspension of a bogie and a predetermined table; a vehicle deceleration calculator12to calculate a required vehicle deceleration α on the basis of a brake notch command BN and a predetermined table; a required braking force calculator13to calculate a required braking force BL based on the variable load command VL and the vehicle deceleration α, the required braking force BL being a braking force required for obtaining the vehicle deceleration α; an electric braking controller14to output an electric braking pattern according to the required braking force BL and to calculate and output feedback BT of electric braking force (which is hereinafter referred to as “feedback”); and a subtractor15to output, to a mechanical brake, a result obtained by subtracting the feedback BT from the required braking force BL, the result obtained by the subtraction being used as a mechanical braking command. The subtractor15operates as a mechanical braking controller.

FIG. 2is a drawing illustrating an example of how to mount the brake control device according to the embodiment on an electric railway vehicle. An inverter controller6controls a switching element included in an electric power converter4. The inverter controller6executes pulse width modulation (PWM) control. The electric power converter4is a commonly used inverter circuit. Silicon (Si) may be used for the switching element. Alternatively, a compound semiconductor such as silicon carbide (SiC) or gallium nitride (GaN) may be used for the switching element. By control of the electric power converter4by the inverter controller6, the electric power converter4converts electric power obtained from an overhead line2via an electric power collector3to supply the converted electric power to an electric motor5, and thus driving power for the electric vehicle can be obtained. Also, the inverter controller6controls the electric power converter4in accordance with an electric braking pattern transmitted from the electric braking controller14, and thus the electric motor5operates as an electric power generator, and electric braking force can be obtained. The number of electric motors5to which the electric power converter4supplies electric power is optional. Any electric motor, such as an induction motor or a synchronous motor, may be used as the electric motor5.

The brake control device1starts up the mechanical brake before a start of control for stopping electric braking due to decrease in a vehicle speed, and thus the brake control device1makes a total braking force match the required braking force, the total braking force being the sum of the electric braking force and a mechanical braking force. The phrase, “making the total braking force match the required braking force”, means “keeping a difference between the total braking force and the required braking force within a certain range in which such a difference does not cause uncomfortable ride in the vehicle”.

Operation of each component of the brake control device1is described below. The variable load calculator11calculates a variable load command VL on the basis of AS pressure and a predetermined table and then transmits the variable load command VL to the required braking calculator13and the electric braking controller14. The vehicle deceleration calculator12calculates vehicle deceleration α on the basis of a brake notch command BN and a predetermined table and then transmits the vehicle deceleration α to the required braking force calculator13. The required braking force calculator13calculates required braking force BL by multiplying a load indicated by the variable load command VL and the vehicle deceleration α together, and then transmits the required braking force BL to the electric braking controller14and the subtractor15.

The electric braking controller14calculates an electric braking pattern in accordance with the required braking force BL and then transmits the electric braking pattern to the inverter controller6. The electric braking controller14calculates an electric braking force generated by operation of the electric motor5on the basis of current flowing through the electric motor5and then transmits, to the subtractor15as a feedback BT, the electric braking force adjusted in accordance with a speed of the electric motor5. The subtractor15transmits, as a mechanical braking command to a mechanical brake, a result obtained by subtracting the feedback BT from the required braking force BL.

FIG. 3is a block diagram illustrating an example configuration of an electric braking controller according to the embodiment. The electric braking controller14includes: a first pattern calculator21to calculate a first pattern indicating a relation between a speed of the electric motor5and the electric braking force in accordance with the required braking force BL; a comparison pattern calculator22to output a pattern for comparison indicating a relation between a predetermined speed of the electric motor5and the electric braking force; a minimum value calculator23to calculate an electric braking pattern on the basis of the first pattern and the pattern for comparison; a second pattern calculator24to calculate a second pattern indicating a relation between the speed of the electric motor5and the electric braking force on the basis of the required braking force BL, the variable load command VL and the first pattern; an electric braking force calculator25to calculate the electric braking force generated by operation of the electric motor5; and an adjuster26to adjust the electric braking force in accordance with the first pattern, the second pattern and a speed FM of the electric motor5and output the adjusted electric braking force as the feedback BT.

The adjuster26includes: a switch28, a comparator27to perform switching operation using the switch28in accordance with the speed FM of the electric motor5, the first pattern and the second pattern; and a multiplier29to output, as the feedback BT, a result obtained by multiplying the electric braking force calculated by the electric braking force calculator25by1or γ inputted via the switch28.

Calculation of the feedback BT by the electric braking controller14is next described. The comparison pattern calculator22outputs a pattern for comparison indicating a change in electric braking force in a range of speeds of the electric motor5in which electric braking becomes ineffective due to decrease in a speed of the electric motor5.FIG. 4is a chart illustrating an example of a pattern for comparison in the embodiment. In the chart illustrated inFIG. 4, the horizontal axis indicates the speed of the electric motor5and the vertical axis indicates the electric braking force. The speed of the electric motor5is expressed in “Hz” units, and the electric braking force is expressed in “Nm” units. Decrease in a speed of the electric motor5results in decrease in electric braking force, and, inFIG. 4, electric braking becomes completely ineffective when the speed of the electric motor5reaches fm0. That is to say, electric braking force cannot be obtained at all when the speed of the electric motor5is equal to or lower than fm0. The pattern for comparison is expressed by formula (1) described below. The symbols, “a” and “b” in formula (1) described below are constant numbers and are determined in accordance with characteristics of the electric motor5.
[Formula 1]
T=α·FM+b(1)

The minimum value calculator23outputs to the inverter controller6the electric braking pattern that is found using the first pattern and the pattern for comparison, includes minimum values of electric braking force for speeds of the electric motor5, and represents a relation between a speed of the electric motor5and the electric braking force. The inverter controller6controls the electric power converter4in accordance with the electric braking pattern calculated with the first pattern and the pattern for comparison, and thus control for stopping electric braking can be started in accordance with the time at which the electric braking starts becoming ineffective.

FIG. 5is a block diagram illustrating an example configuration of a second pattern calculator according to the embodiment. The second pattern calculator24includes: an electric motor deceleration calculator31to calculate a deceleration β of the electric motor based on the required braking force BL and the variable load command VL; a shift amount calculator32to calculate a shift amount for the electric braking force in accordance with the deceleration β of the electric motor; and a subtractor33to subtract the shift amount from the pattern for comparison. The second pattern calculator24outputs as the second pattern a result obtained by subtracting the shift amount from the pattern for comparison.

The required braking force BL inputted to the electric motor deceleration calculator31is expressed by formula (2) described below. The symbol “c” in formula (2) is a conversion constant. The required braking force BL is proportional to the product of the variable load command VL and the vehicle deceleration α. When the vehicle deceleration α is expressed by the formula α=k·β, where the symbol “k” denotes a conversion constant, formula (3) described below is obtained. Formula (4) described below is obtained by transformation of formula (3). By setting K=1/(c·k), formula (5) described below is obtained from formula (4).
[Formula 2]
BL=c·VL·α(2)
[Formula 3]
BL=c·VL·k·β(3)
[Formula 4]
β=BL/(c·k·VL)  (4)
[Formula 5]
β=K·BL/VL(5)

The electric motor deceleration calculator31calculates the deceleration β of the electric motor from the required braking force BL and the variable load command VL using formula (5) and then transmits the deceleration β of the electric motor to the shift amount calculator32.

The time required for a BC pressure to change from zero to a pressure corresponding to a precharge pressure is assumed to be t (seconds), where the BC pressure is the pressure in the brake cylinder of the mechanical brake. The precharge pressure is a minimum pressure required for starting up the mechanical brake without delay when the electric braking starts becoming ineffective. The precharge pressure does not produce the mechanical braking force. The precharge pressure and time t are determined in accordance with characteristics of the mechanical brake. An electric motor speed variation ΔFM that is an amount of the change in the speed of the electric motor5during time t (seconds) is expressed by formula (6) described below.
[Formula 6]
ΔFM=/β·t(6)

By starting up the mechanical brake t (seconds) earlier than the time at which the electric braking starts becoming ineffective, the total braking force can be made to match the required braking force even at low vehicle speed. The electric braking controller14calculates the feedback BT based on the first pattern and the second pattern calculated by shifting the pattern for comparison illustrated inFIG. 4by ΔFM in the direction in which the variable on the axis describing a speed of the electric motor5increases. When electric braking force indicated by the second pattern is expressed by a symbol “T′”, this electric braking force T′ is expressed by formula (7) described below. A shift amount S is expressed by formula (8) described below.

FIG. 6is a chart illustrating a relation between the deceleration of the electric motor and the shift amount in the embodiment. In the chart illustrated inFIG. 6, the horizontal axis indicates deceleration of the electric motor5, and the vertical axis indicates the shift amount. The deceleration of the electric motor5is expressed in “Hz/s” units, and the shift amount is expressed in Nm units. The shift amount calculator32calculates the shift amount S using the electric motor deceleration β, as illustrated inFIG. 6and described in formula (8). The subtractor33subtracts the shift amount S from the pattern for comparison illustrated inFIG. 4and outputs a result of the subtraction. The second pattern calculator24outputs the output from the subtractor33as the second pattern.

The electric braking force calculator25may find the electric braking force by calculating torque generated by the electric motor5based on current flowing in the electric motor5or by sensing the braking force generated by the electric motor5via a brake torque sensor. The comparator27included in the adjuster26acquires the electric motor speed FM that is the speed of the electric motor5from a non-illustrated speed sensor attached to the electric motor5. A first braking force that is the electric braking force calculated from the first pattern on the basis of the electric motor speed FM is compared with a second braking force that is the electric braking force calculated from the second pattern on the basis of the electric motor speed FM. When the first braking force is larger than the second braking force, the comparator27controls the switch28so that “1” is inputted into the multiplier29. When the first braking force is equal to or smaller than the second braking force, the comparator27controls the switch28so that “γ” is inputted into the multiplier29. The value γ is a freely selected positive number less than 1 and is determined by characteristics of the mechanical brake including time required for starting up the mechanical brake.

When the first braking force is equal to or smaller than the second braking force, the electric braking controller14outputs as feedback BT a calculation result obtained by multiplying the electric braking force by γ having a value less than 1. The mechanical brake is controlled based on the mechanical braking command calculated based on electric braking force smaller than actually-occurring electric braking force, and thus the mechanical brake starts up before the electric braking force starts becoming ineffective, and the BC pressure is set to the precharge pressure.

FIG. 7is a chart illustrating the timing of a start-up of the mechanical brake in the embodiment. In the chart illustrated inFIG. 7, the horizontal axis indicates speed of the electric motor5, and the vertical axis indicates electric braking force. The speed of the electric motor5is expressed in Hz units, and the electric braking force is expressed in Nm units. Thick solid lines illustrated inFIG. 7indicate a first pattern outputted by the first pattern calculator21in the case where the variable load command VL is equal to VL1 and a first pattern outputted by the first pattern calculator21in the case where the variable load command VL is equal to VL2. A brake notch command BN in the case where VL=VL1 is equal to a brake notch command BN in the case where VL=VL2. InFIG. 7, the dot-and-dash line indicates a pattern for comparison outputted by the comparison pattern calculator22and the narrow solid line indicates a second pattern outputted by the second pattern calculator24. When deceleration of the electric motor is expressed by the symbol, “β0”, a second pattern is found by subtracting a shift amount, “a t·β0”, from a first pattern. That is to say, the second pattern is obtained by shifting the first pattern by β0·t in the direction of increasing speed of the electric motor5.

In the case where VL=VL1, the electric braking starts becoming ineffective when the speed of the electric motor5reaches fm1, and the electric brake becomes completely ineffective when the speed of the electric motor5reaches fm0. When a speed of the electric motor5is larger than fm1′ that is larger than fm1, the electric braking controller14outputs as feedback BT the electric braking force calculated by the electric braking force calculator25, and a mechanical braking command calculated based on the feedback BT is transmitted to the mechanical brake. When a speed of the electric motor5is equal to or smaller than fm1′, the electric braking controller14outputs as the feedback BT a calculation result obtained by multiplying together the electric braking force calculated by the electric braking force calculator25and γ. That is to say, when the speed of the electric motor5becomes fm1′, the mechanical brake is started up.

In the case where VL=VL2, electric braking starts becoming ineffective when the speed of the electric motor5reaches fm2, and the electric braking becomes completely ineffective when the speed of the electric motor5reaches fm0. When the speed of the electric motor5is larger than fm2′ that is larger than fm2, the electric braking controller14outputs as feedback BT electric braking force calculated by the electric braking force calculator25, and a mechanical braking command calculated based on the feedback BT is transmitted to the mechanical brake. When a speed of the electric motor5is equal to or smaller than fm2′, the electric braking controller14outputs as feedback BT a calculation result obtained by multiplying together the electric braking force calculated by the electric braking force calculator25and γ. That is to say, when the speed of the electric motor5becomes fm2′, the mechanical brake is started up.

Both the difference between fm1 and fm1′ and the difference between fm2 and fm2′ are β0·t. That is to say, independently of variable load commands VL, the mechanical brake is started up t (seconds) earlier than the time at which the electric braking starts becoming ineffective, and BC pressure reaches the precharge pressure at the time at which the electric braking starts becoming ineffective.

FIG. 8is a chart illustrating the timing of a start-up of the mechanical brake in the embodiment.FIG. 8is to be regarded similarly toFIG. 7. Thick solid lines illustrated inFIG. 8indicate a first pattern outputted by the first pattern calculator21in the case where the brake notch command BN is equal to BN1 and a first pattern outputted by the first pattern calculator21in the case where the brake notch command BN is equal to BN2. InFIG. 8, the dot-and-dash line indicates a pattern for comparison outputted by the comparison pattern calculator22, the narrow solid line indicates a second pattern outputted by the second pattern calculator24in the case where BN=BN1 and the dashed line indicates a second pattern outputted by the second pattern calculator24in the case where BN=BN2.

In the case where BN=BN1, when deceleration of the electric motor5is expressed by the symbol “β1”, the second pattern is calculated by subtracting a shift amount a·t·β1from the first pattern. That is to say, the second pattern is obtained by shifting the first pattern by β1·t in the direction of increasing speed of the electric motor5. The electric braking starts becoming ineffective when the speed of the electric motor5reaches fm1, and the electric braking completely becomes ineffective when the speed of the electric motor5reaches fm0. When a speed of the electric motor5is larger than fm1′, the electric braking controller14outputs as feedback BT the electric braking force calculated by the electric braking force calculator25, and a mechanical braking command calculated based on the feedback BT is transmitted to the mechanical brake. When a speed of the electric motor5is equal to or smaller than fm1′, the electric braking controller14outputs as feedback BT a calculation result obtained by multiplying together the electric braking force calculated by the electric braking force calculator25and γ. That is to say, when the speed of the electric motor5becomes fm1′, the mechanical brake is started up.

In the case where BN=BN2, when deceleration of the electric motor5is expressed by the symbol “β2”, a second pattern is calculated by subtracting a shift amount a·t·β2from the first pattern. That is to say, the second pattern is obtained by shifting the first pattern by β2·t in the direction of increasing speed of the electric motor5. Electric braking starts becoming ineffective when the speed of the electric motor5reaches fm2, and, the electric braking becomes completely ineffective when the speed of the electric motor5reaches fm0. When a speed of the electric motor5is larger than fm2′, the electric braking controller14outputs as feedback BT the electric braking force calculated by the electric braking force calculator25, and a mechanical braking command calculated based on the feedback BT is transmitted to the mechanical brake. When a speed of the electric motor5is equal to or smaller than fm2′, the electric braking controller14outputs as feedback BT a calculation result obtained by multiplying together the electric braking force calculated by the electric braking force calculator25and γ. That is to say, when the speed of the electric motor5becomes fm2′, the mechanical brake is started up.

In the case where the speed of the electric motor5is β1, the difference between fm1 and fm1′ is β2·t, and in the case where the speed of the electric motor5is β2, the difference between fm2 and fm2′ is β2·t. That is to say, independently of brake notch, the mechanical brake is started up t (seconds) earlier than the time at which the electric braking starts becoming ineffective, and BC pressure reaches the precharge pressure at the time at which the electric braking starts becoming ineffective.

FIG. 9is a timing chart illustrating an example of adjustment of electric braking force in the embodiment. InFIG. 9, the brake notch is steady. In order to obtain a steady required braking force BL, the electric braking controller14outputs a steady electric braking pattern at the start of braking control. The electric braking controller14outputs an electric braking pattern decreasing at a constant rate after time T2in accordance with the loss of effectiveness of the electric braking in the case of low speed running. The comparator27determines until time T1that the first braking force is larger than the second braking force, and then the comparator27outputs a signal of a low level (L-level). When the signal outputted by the comparator27is of the L-level, the value “1” is inputted into the multiplier29via the switch28. The comparator27determines at time T1that the first braking force is equal to or smaller than the second braking force, and then the comparator27outputs a signal of a high level (H-level). When the signal outputted by the comparator27is of the H-level, the value “γ” is inputted into the multiplier29via the switch28.

When the magnitude of electric braking force outputted by the electric braking force calculator25is expressed by the symbol “A”, the feedback BT outputted by the electric braking controller14at time T1is γA. Occurrence of a difference between required braking force BL and the feedback BT at time T1results in start-up of the mechanical brake, and thus the BC pressure starts increasing. The BC pressure becomes the precharge pressure at time T2, and thus mechanical braking force starts increasing. Since the mechanical braking force starts increasing at time T2at which the electric braking force starts decreasing, an actual deceleration of the vehicle can be kept constant.

When the speed of the electric motor5is equal to or smaller than a threshold, the mechanical brake is started up before the start of control for stopping electric braking by adjusting feedback BT to a value smaller than actual electric braking force, and thus mechanical braking force can be increased without delay from the start of control for stopping electric braking. As a result, total braking force equal to the required braking force can be obtained even though the speed of the electric motor5is low. Also, a configuration of a conventional brake control device may be used as that of a brake control device1other than the electric braking controller14for adjusting feedback BT.

As described above, in the brake control device1according to the present embodiment, electric braking force calculated by the electric braking force calculator25is adjusted to a smaller value and the adjusted electric braking force is used as feedback BT when the first braking force is equal to or smaller than the second braking force, and then the mechanical brake is controlled by a mechanical braking command calculated based on the feedback BT, thereby total braking force equal to required braking force can be obtained with a simple structure that does not requires an interface for receiving and transmitting an advanced notice signal for notifying loss of an effect of electric braking without deterioration of ride quality in the case of a low vehicle speed.

Embodiments according to the present disclosure are not limited to the aforementioned embodiment.FIG. 10is a block diagram illustrating another example configuration of the second pattern calculator according to the embodiment. As illustrated inFIG. 10, the electric motor deceleration calculator31may calculate deceleration β of the electric motor based on only the required braking force BL. Also, the method for calculating the timing of performing switching operation using the switch28is not limited to that of the above-described example.

REFERENCE SIGNS LIST