EP1960227A1

EP1960227A1 - A brake system for industrial truck and a method for controlling retardation of an industrial truck

Info

Publication number: EP1960227A1
Application number: EP06824628A
Authority: EP
Inventors: Göran Valfridsson; Andreas Balsner
Original assignee: BT Industries AB
Current assignee: Toyota Industries Europe AB
Priority date: 2005-12-14
Filing date: 2006-12-11
Publication date: 2008-08-27
Also published as: SE0502766L; SE529401C2; EP1960227A4; DE06824628T1; WO2007070000A1

Abstract

The present invention relates to a brake system (1) for an industrial truck. The brake system comprises a control unit (2) arranged to receive at least one electrical signal corresponding to required retardation, to calculate at least one desired value related to required motor speed, at least partially on the basis of the said at least one signal, and to feed the said at least one desired value to a unit for motor control (3) that is arranged to control a driving motor (4) for propulsion of the truck on the basis of the received desired value. The brake system is characterized in that, in addition, the unit for motor control (3) is arranged to send back to the control unit (2) at least one obtained actual value related to the motor speed and in that the control unit (2) is arranged to calculate the next desired value, at least partially on the basis of a relationship between the supplied desired value and the obtained actual value.

Description

A brake system for industrial truck and a method for controlling retardation of an industrial truck

TECHNICAL FIELD The present invention relates to a brake system for an industrial truck according to the preamble to Claim 1.

The invention also comprises a method for controlling retardation of an industrial truck according to the preamble to Claim 9.

BACKGROUND ART

Industrial trucks have normally a driving wheel driven by an electrical motor and free-wheeling, load-bearing wheels. Mounting brakes both on the driving wheel and on the load-bearing wheels is already known. The brake for the driving wheel can either be mounted on the wheel or directly on the driving motor. In addition, utilizing the driving motor as a motor brake is also known.

US 2004/0195911 describes a known brake system for battery-driven industrial trucks. The brake system comprises a three-phase driving motor that drives a driving wheel, a first brake device arranged on the driving wheel and a brake pedal. The brake pedal is connected to a brake signal generator, that creates a brake signal corresponding to the depression of the brake pedal. The brake system comprises, in addition, a control unit including a first conversion unit, that converts the brake signal to a required torque of the driving motor, a second conversion unit that converts the actual torque in the driving motor to an actual braking force, a comparator, in which the required braking force is compared with the actual braking force in order to create a second required braking force for wheel brakes mounted on the truck. In the published patent application, the brake action is principally used for retarding the truck that is obtained via the driving motor together with brakes on the load-bearing wheels. However, the document does not deal with the problems that can arise, for example in the form of too high a torque in the drive shaft or locking of the driving wheel when the motor brake device is used together with the brake device for the driving wheel.

The present invention is intended to solve the abovementioned problem when the motor brake is used in combination with the brake for the driving wheel.

DISCLOSURE OF INVENTION

According to an embodiment of the present invention, a brake system for an industrial truck is obtained, comprising a control unit arranged to - receive at least one electrical signal corresponding to required retardation, calculate, at least partially on the basis of the said at least one signal, at least one desired value related to required motor speed and supply the said at least one desired value to a unit for motor control arranged to control a driving motor for driving the truck on the basis of the received desired values.

The brake system is characterized in that the unit for motor control is, in addition, arranged to send back to the control unit at least one obtained actual value related to the motor speed and in that the control unit is arranged to calculate the next desired value at least partially on the basis of a relationship between the supplied desired value and the obtained actual value.

Due to the fact that the next desired value is calculated at least partially on the basis of a relationship between the supplied desired value and the obtained actual value, it is ensured that the desired value does not deviate in relation to the actual value. By this means, the risk is minimized of problems arising, for example in the form of locking of the driving wheel, in situations where the input signal corresponding to the required retardation is suddenly changed. The input signal is changed, for example, when the driver of the truck suddenly decides to make a strong retardation.

At least in an initial stage of the retardation, the control unit is arranged to calculate desired values that relate to a predetermined deceleration, for example determined by the truck's physical conditions in an unloaded state and the fact that the retardation should not be experienced as unpleasant by the driver of the truck. Thereafter, the control unit can be arranged to calculate desired values that provide a smaller deceleration, taking as a starting point the relationship between the supplied desired value and the obtained actual value. The control unit can thus comprise a function that decrements the next desired value by a decrement value determined at least partially by the relationship between the supplied desired value and the obtained actual value. In addition, when calculating the next desired value, the control unit can be arranged to create a difference value that relates to the difference between the supplied desired value and the obtained actual value and to reduce the decrement value in relation to the preceding calculation if the difference value exceeds a predetermined value. However, other ways of determining the relationship between the actual value and the desired value can be possible. For example, a quotient between the relevant actual value and desired value can be calculated. In addition, when determining the relationship, a preferably weighted sequence of previous relevant actual values and/or desired values can be used instead of only the current actual value and/or desired value. The driving motor is preferably driven by electricity, for example by a battery. The driving motor can either be an alternating current motor or a direct current motor. The driving motor is preferably speed-controlled.

According to an advantageous embodiment, the control unit is, in addition, arranged to control a mechanical brake device arranged to retard the driving motor mechanically. In this case, when calculating the next desired value, the control unit is arranged to compensate for the effect of the mechanical brake device in association with connecting in of the mechanical brake device. The mechanical brake device is, for example, mounted directly on the driving motor or on the driving wheel connected to the drive shaft of the driving motor via a gear. As the desired values are reduced in order to compensate for the torque that acts on the drive shaft, the gear and/or the driving wheel, the increased torque is prevented from acting on the drive shaft/gear/driving wheel when the mechanical brake device is connected in.

The control unit can be arranged to wait a period of time essentially corresponding to the time it takes for the mechanical brake device to take full effect before it compensates for the effect of the mechanical brake device.

In a preferred embodiment, a brake control is operatively connected to the brake system, with a first of the said electrical signals originating from the said brake control. The control system can then be arranged to activate the mechanical brake device when the first electrical signal, and thus the effect on the brake control, exceeds a predetermined value.

In an additional preferred embodiment, the unit for controlling the motor is arranged to send back information to the control unit concerning the current in the driving motor. The control unit is then arranged to increase the decrement value in relation to the decrement value in the preceding desired value calculation when the currents are less than a predetermined value. However, the decrement value may not exceed the initial decrement value determined by, among other things, the braking capabilities of the truck and the comfort of the driver. By monitoring the currents in the motor in this way and increasing the decrement values when the current is so low that additional torque can be applied to the driving motor/gear/driving wheel without the risk arising of excessive wear or locking of the wheels, the retardation sequence will not be longer than it would have been without the brake system according to the present invention.

In addition, the present invention relates to a method for controlling retardation of an industrial truck, comprising

- receiving at least one electrical signal corresponding to the required retardation,

- calculating a desired value related to the required deceleration, at least partially on the basis of the said signal,

- controlling a driving motor for propulsion of the truck on the basis of the desired value, and - determining the current actual value for the motor speed.

The method is characterized in that a relationship is determined between the determined actual value and the calculated desired value and in that the next desired value is calculated at least partially on the basis of the determined relationship.

According to an embodiment, the relationship is determined in the form of a difference value that relates to the difference between the supplied desired value and the obtained actual value. In accordance with this embodiment, when the difference value exceeds a predetermined value, the next desired value is decremented by a decrement value, which decrement value is lower than a decrement value used in the preceding desired value calculation.

In a preferred embodiment, the next desired value is calculated, in addition, on the basis of the measured current in the driving motor in order to ensure maximal retardation.

In yet another preferred embodiment, the next desired value is calculated, in addition, on the basis of the connecting in of a mechanical brake device arranged to retard the driving motor mechanically, in order to compensate for the effect of the mechanical brake device. According to an embodiment, the compensating for the effect of the mechanical brake device can commence a period of time after the connecting in of the mechanical brake device, which period of time essentially corresponds to the time it takes for the mechanical brake device to take full effect after it is connected in.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 shows a block diagram of an example of a brake system according to the present invention.

Figure 2 shows schematically the construction of a brake according to an example of the present invention.

Figure 3a shows a graph of the retardation in an embodiment according to current technology in a case where the mechanical brake device has been applied during an early phase of the retardation sequence. Figure 3b shows a graph of the retardation in an embodiment according to current technology in a case where the mechanical brake device has been applied during a late phase of the retardation sequence.

Figure 4a shows a graph of the retardation with the system according to Figure 1 in a case where the mechanical brake device has been applied during an early phase of the retardation sequence.

Figure 4b shows a graph of the retardation with the system according to Figure 1 in a case where the mechanical brake device has been applied during a late phase of the retardation sequence.

Figure 5 shows a flow chart of how the brakes operate in an example according to the present invention.

MODES FOR CARRYING OUT THE INVENTION

In Figure 1, a brake system 1 for an industrial truck comprises a control unit 2, a unit for motor control 3, a driving motor 4 and a mechanical brake device 5 arranged to retard the driving motor mechanically. The movement of a brake control 6, for example in the form of a lever, a handle or a pedal, is converted to an electrical signal in a converter (not shown), after which the electrical signal is fed to the control unit 2. In the same way, the movement of an accelerator 7 is converted to an electrical signal and is fed to the control unit 2. The accelerator 7 is, for example, a lever, a handle or a pedal.

In order to provide motor braking, a desired value calculation unit 8 comprised in the control unit 2 is arranged to calculate a sequence of desired values associated with a required retardation sequence. The desired values relate to the motor speed and relate, for example, to the rotation speed. In a very simple embodiment, the same retardation sequence is selected each time the brake control 6 is activated, irrespective of how much the brake control 6 is activated. In an alternative embodiment, the desired value calculation unit 8 is arranged to calculate a desired value sequence, in which the degree of the activation of the brake control 6 indicates the required retardation sequence. The desired value sequence forms, for example, a linear curve, for example in the form of an incline. According to an embodiment, the gradient of the curve represents a suitable retardation sequence for an unloaded truck.

According to an embodiment, the calculated desired values are fed in real time to the unit for motor control 3, which unit 3 supplies the motor with a corresponding current on the basis of the respective desired values. The rate of updating is, for example, 10-100 desired values per second. Precisely how the currents are calculated on the basis of the obtained desired values will not be described in detail here. This involves measures taken by experts in the field to determine, on the basis of the selected driving motor, what supply currents are required in order to obtain a required motor speed. The driving motor is preferably an electrical motor. In one embodiment, the motor is an alternating current motor, and in an alternative embodiment, the motor is a direct current motor.

In addition, the unit for motor control 3 sends back to the control unit 2 an obtained actual value for the motor speed for each supplied desired value.

A comparing unit 9 in the control unit 2 continuously receives the obtained actual values and compares each obtained actual value with the associated supplied desired value in order to create a difference value. As long as the difference value is less than a predetermined value, the comparing unit will not carry out any additional measures. When it is detected that the difference value exceeds the predetermined value, this information is fed to the desired value calculation unit.

In the desired value calculation unit 8, the function for decrementing the desired values is updated so that the supplied desired values now correspond to a longer retardation sequence in relation to previously supplied desired values. The new desired values form, for example, a linear curve, for example in the form of an incline. According to an embodiment, the gradient of the curve indicates a suitable retardation sequence for a truck loaded to half of its capacity. The desired values determined according to the updated function are fed to the unit for motor control 3. While the motor is provided with currents related to the desired values, current actual values are fed back to the control unit 2 as described above. If, after a predetermined delay, the comparing unit 9 indicates that the difference value still exceeds the predetermined value, it feeds this information to the desired value calculation unit 8, that again updates the function for decrementing the desired values on the basis of an even slower retardation sequence, after which the desired values calculated according to the additionally updated function are supplied to the unit for motor control 3. The desired values now indicate a curve gradient that, for example, reflects a retardation sequence for a truck with the maximum permitted load.

In addition, the unit for motor control 3 is arranged to send back the relevant current to a current control unit 10 in the control unit 2. The size of the current indicates the brake action of the motor. In order for the braking distance of the truck to be as short as possible, it is ensured that the current is not less than a limit current value. In one example, the current must be at least 85% of the maximum value, in another example, it must be at least 90% of the maximum value and, in yet another example, at least 95% of the maximum value. The current control unit 10 is arranged to compare the obtained current values with the limit current value. As long as the current exceeds the limit current value, equally good retardation is obtained as if the decrementing values had not been changed. If, however, the current is less than the limit current value, this indicates that the brake system is not retarding the truck maximally. The current control unit 10 supplies the information about the fact that the truck is not being retarded maximally to the desired value calculation unit 8, that updates the function for decrementing the desired values so that the supplied desired values now correspond to a shorter retardation sequence in relation to previously supplied desired values. In a simple embodiment, the desired value calculation unit 8 is arranged to go back to using the immediately preceding decrementing values that had been used.

As a result of the comparing unit 9 ensuring that the difference between the relevant desired value and actual value for the motor speed is never larger than a predetermined value, the risk is minimized of too high a torque being applied to the motor in the event of changed conditions, for example when the effect of the brake control increases so that the mechanical brake device is connected in. Too high torques can lead to increased wear and locking of the truck's driving wheel.

In one example, the mechanical brake device 5 is arranged on the driving motor (see Figure 2) and is arranged to act by friction on the motor's drive shaft in order to retard this. This, of course, supplies an additional torque to the motor, as the torque that acts on the motor comes both from the mechanical brake device 5 and from the motor brake. Accordingly, the torque from the motor should decrease during the time that the mechanical brake device 5 is connected in. A unit that is comprised in the control unit 2 for controlling the manual brake device 1 1 is supplied with electrical signals from at least the brake control. The unit for controlling the mechanical brake device 11 is arranged to activate the mechanical brake device 5 on the basis of the movement of the brake control 6 and hence the size of the brake control signal. According to one example, the unit for controlling the mechanical brake device 1 1 is arranged in such a way that it does not connect in the mechanical brake device when the movement is less than 90% of the maximal movement and in such way that it connects in the mechanical brake device as long as the movement exceeds 90% of the maximal movement. In the event of connecting in of the mechanical brake device 5, the unit for controlling the mechanical brake device 11 is arranged to supply information concerning the connecting in of the mechanical brake device 5 to the desired value calculation unit 8. The desired value calculation unit 8 then updates the decrementing values in order to compensate for the effect from the mechanical brake device. According to one example, the decrementing values are updated in such a way that the torque that acts on the motor is essentially the same, irrespective of whether the mechanical brake device is connected in or not. In an alternative embodiment, the torque that acts on the motor is allowed to increase somewhat, whereby the connecting in of the mechanical brake device is not fully compensated for by reduced desired values. According to one example, a time delay is inserted, corresponding to the time it takes for the mechanical brake device to take full effect from the time that it is connected in. By this means, the lower currents are not applied to the driving motor before full torque has been obtained from the mechanical brake device 5. The time delay can depend upon which type of mechanical brake device is used, but is characteristically in the range 10ms to 500ms.

In addition, the unit for controlling the mechanical brake device 11 is arranged to supply information to the comparing unit 9 and to the current control unit 10 concerning the fact that the mechanical brake device 5 is connected in. As long as the mechanical brake device 5 is connected in, the predetermined value with which the comparing unit 9 compares the difference value is adjusted downwards, corresponding to the degree of connecting in of the mechanical brake device 5. In the same way, as long as the mechanical brake device 5 is connected in, the value with which the current control unit 10 compares the relevant current is adjusted downwards, corresponding to the degree of connecting in of the mechanical brake device 5.

In the event of disconnection of the mechanical brake device 5, for example by the action on the brake control 6 being reduced, the desired value calculation unit 8 is arranged to go back to the uncompensated desired value sequence, the comparing unit 9 is arranged to restore the predetermined value with which the difference value is compared and the current control unit 10 is arranged to restore the value with which the relevant current is compared. In a simple embodiment, the mechanical brake device 5 is either connected in or disconnected. In a more advanced embodiment, the mechanical brake device can be partially connected in. In this case, the desired value calculation unit 8, the comparing unit 9 and the current control unit 10 are arranged to compensate to a corresponding degree.

The different parts in the control unit 2 do not necessarily need to be separate physical units, but can also symbolize functions in the control unit that are implemented in hardware and/or software, in one or more physical units.

In Figure 2, the driving motor 4 is, for example, an alternating current motor with the drive shaft 12. The mechanical brake device 5 is mounted above the motor 4 so that it presses against the drive shaft when it is activated. A gear 13 transfers the force from the drive shaft 12 to the truck^'s driving wheel 14, that 69

13

is driven via an axle 15. In this embodiment, the truck is only driven by one wheel. The remaining wheels do not drive. Embodiments are also possible that have driving on several wheels. Wheels without driving can also be provided with brakes, that, for example, are connected in in accordance with the same criteria as the connecting in of the mechanical brake device.

In Figures 3a, 3b, 4a, 4b, the x-axis represents the time, while the y-axis represents the speed of the motor. In Figures 3a, 3b, according to current technology, adjustment of the desired values has been carried out neither on the basis of the connecting in of the brake device 5 nor on the basis of large differences between actual values and desired values. The upper curve represents actual values and the lower curve represents desired values. In Figure 3a, the mechanical brake device 5 has been connected in at an early stage during the retardation sequence at the time ti . In Figure 3b, the mechanical brake device has been connected in at a late stage during the retardation sequence at the time t₂. Figure 4 shows the retardation sequence with the same conditions as in Figure 3, but with the difference that the control unit according to the invention is connected in. Thus, both in the case with early mechanical retardation in Figure 4a and in the case with late mechanical retardation in Figure 4b, the actual value curve lies closer to its associated desired value curve. At the same time, the whole retardation sequence is no longer in Figure 4a and 4b than in 3a and 3b respectively.

In Figure 5, the retardation sequence for an industrial truck is controlled by the control unit receiving 16 a signal that indicates required brake action. At least partially on the basis of the said signal, a desired value bj related to the required motor speed, or deceleration, is then created 17. After this, it is checked 18 whether the mechanical brake has been connected in since a predetermined time Δtl, that is if the time in question exceeds tO+Δtl, where tO represents the time of the connecting in of the mechanical brake. In the diagram in Figure 7, t3 marks the time tO+Δtl . If the time t3 has not been passed, the calculated desired value is compared 19 with an actual value from the motor, which actual value represents the motor's actual speed. If a difference between the actual value and the desired value does not exceed a predetermined value vmax, the calculated desired value is fed 20 to a function for controlling the driving motor. If, on the other hand, the difference exceeds the predetermined value vmax, it is checked 22 that the braking current in the driving motor is sufficiently high, that is that the braking current exceeds a predetermined limit value. If this is the case, the desired value is compensated 23 so that the difference between the actual value and the desired value does not exceed the predetermined value vmax., whereupon the compensated desired value is fed 20 to the function for controlling the driving motor. If, on the other hand, the checking 22 of the current shows that the braking current is less than the determined limit value, this indicates that the brake action could be greater, for which reason the desired value is fed 20 to the function for controlling the driving motor without first being compensated.

If the checking 18 of whether the mechanical brake has been connected in since a predetermined time Δtl shows that the predetermined time has passed, the desired values that are fed to the function for controlling the driving motor will be kept constant during a second, predetermined period of time Δt2, that is until the time in question exceeds t3+Δt2. In the diagram in Figure 7, t4 marks the time t3+Δt2. In practice, the fact that the desired values are kept constant during the second, predetermined period of time Δt2 means that the desired value that was relevant when determining that the time t3 has been passed will be fed 20 to the function for controlling the driving motor during this period of time Δt2, so long as the mechanical brake is connected in. Accordingly, the desired values calculated 17 during this second period of time Δt2 are rejected.

Each time a desired value is fed 20 to the function for controlling the driving motor, the process starts from the beginning with the receiving 16 of a new brake signal.

Claims

1. Brake system (1) for an industrial truck comprising a control unit (2) arranged to receive at least one electrical signal corresponding to required retardation, to calculate at least one desired value related to required motor speed, at least partially on the basis of the said at least one signal, and to feed the said at least one desired value to a unit for motor control (3) that is arranged to control a driving motor (4) for propulsion of the truck on the basis of the received desired value, characterized in that, in addition, the unit for motor control (3) is arranged to send back to the control unit (2) at least one obtained actual value related to the motor speed and in that the control unit (2) is arranged to calculate the next desired value, at least partially on the basis of a relationship between the supplied desired value and the obtained actual value.

Brake system (1) according to Claim 1, characterized in that, in addition, the control unit (2) is arranged to control a mechanical brake device (5) arranged to retard the driving motor (4) mechanically and in that, in the event of connecting in of the mechanical brake device (5), the control unit (2) is arranged to compensate for the effect of the mechanical brake device when carrying out the calculation of the next desired value.

Brake system (1) according to Claim 2, characterized in that the control unit is arranged to wait a period of time essentially corresponding to the time it takes for the mechanical brake device to take full effect before it compensates for the effect of the mechanical brake device.

Brake system according to Claim 2, characterized in that a brake control (6) is connected to the said brake system, with a first of the said electrical signals originating from the said brake control (6).

Brake system according to Claim 4, characterized in that the control unit (2) is arranged to activate the mechanical brake device (5) when the first electrical signal exceeds a predetermined value.

Brake system according to Claim 1 , characterized in that the control unit comprises a function that decrements the next desired value by a decrement value at least partially determined by the relationship between the supplied desired value and the obtained actual value.

Brake system according to Claim 6, characterized in that the control unit is arranged to calculate a difference value that relates to the difference between the supplied desired value and the obtained actual value, when carrying out the calculation of the next desired value, and to reduce the decrement value in relation to the preceding desired value calculation if the difference value exceeds a predetermined value.

Brake system according to Claim 6, characterized in that the unit for motor control (3) is arranged to send back information to the control unit (2) concerning the current in the driving motor (4) and in that the control unit (2) is arranged to increase the decrement value in relation to the preceding desired value calculation when the current is less than a predetermined value.

Method for controlling retardation of an industrial truck, comprising - receiving (16) at least one electrical signal corresponding to required retardation,

- calculating (17) a desired value related to the relevant required motor speed in a retardation sequence, at least partially on the basis of the said signal,

- controlling ( 18) a driving motor for propulsion of the truck on the basis of the desired value, and

- determining a relevant actual value for the motor speed, characterized in that - a relationship (19) is determined between the determined actual value and the calculated desired value,

- the next desired value is calculated (23) at least partially on the basis of the determined relationship.

10. Method according to Claim 9, characterized in that the relationship (19) is determined in the form of a difference value that relates to the difference between the supplied desired value and the obtained actual value, and in that, when the difference value exceeds a predetermined value, the next desired value is decremented by a decrement value, which decrement value is lower than a decrement value used in the preceding desired value calculation.

1 1. Method according to Claim 9, characterized in that, in addition, the next desired value is calculated on the basis of the measured current in the driving motor in order to ensure maximal retardation.

12. Control method according to Claim 9, characterized in that, in addition, the next desired value is calculated on the basis of the connecting in of a mechanical brake device arranged to retard the driving motor mechanically, in order to compensate for the effect of the mechanical brake device.

13. Control method according to Claim 12, characterized in that the compensating for the effect of the mechanical brake device is started a period of time after the connecting in of the mechanical brake device, which period of time essentially corresponds to the time it takes for the mechanical brake device to take full effect after it is connected in.