Patent Description:
<CIT> discloses a work vehicle according to the preamble of claim <NUM>. A work vehicle such as a wheel loader equipped with a continuously variable transmission is known. Examples of the continuously variable transmission include a hydraulic static transmission (HST) and a hydraulic mechanical transmission (HMT). Patent Document <NUM> discloses the following technique. When the work vehicle equipped with the continuously variable transmission is braked, a braking force is obtained by rotation of a hydraulic pump connected to a power take off (PTO). In this manner, an excessive rotation speed of an engine is prevented.

According to the technique disclosed in Patent Document <NUM>, a control device accurately controls a braking force in an electric motor. On the other hand, regenerative power is absorbed by driving the hydraulic pump connected to the engine to prevent overspeed when engine rotation increases due to regeneration to the engine. However, in order to properly brake the work vehicle by using the technique disclosed in Patent Document <NUM>, it is necessary to provide electrical hardware such as an electric motor capable of properly controlling torques and an inverter for driving the electric motor. Therefore, when a power system includes a hydraulic component, it is difficult to accurately control braking of the work vehicle.

An object of the present invention is to provide a work vehicle, and a control device and a control method for a power machine, which are capable of accurately controlling a braking force regardless of the presence or absence of electrical hardware.

According to a first aspect of the present invention, there is provided a control device for a power machine including a drive source, a hydraulic pump driven by a driving force of the drive source, a power take off device that transmits a portion of the driving force of the drive source to the hydraulic pump, a power transmission device including a hydrostatic continuously variable transmission, in which an input shaft is connected to the power take off device, an output shaft is connected to a load, and the driving force input to the input shaft is transmitted to the output shaft, and an operation device that provides an instruction regarding a magnitude of the driving force of the drive source. The control device includes a target circuit pressure specifying unit configured to specify a target circuit pressure which is a target pressure of the hydrostatic continuously variable transmission, a measurement value acquisition unit configured to acquire an actual circuit pressure which is a measurement value of a pressure of the hydrostatic continuously variable transmission, a brake torque determination unit configured to determine a brake torque based on the target circuit pressure and the actual circuit pressure, the brake torque which is a torque consumed by the hydraulic pump, and a pump control unit configured to control the hydraulic pump based on the brake torque.

According to at least one of the above-described aspects, the control device can accurately control a braking force of a power device regardless of whether or not the power device includes electrical hardware.

Hereinafter, embodiments will be described in detail with reference to the drawings.

<FIG> is a side view of a work vehicle according to a first embodiment.

A work vehicle <NUM> according to the first embodiment is a wheel loader. The work vehicle <NUM> includes a vehicle body <NUM>, a work machine <NUM>, a front wheel part <NUM>, a rear wheel part <NUM>, and an operator cab <NUM>. The work vehicle <NUM> is an example of a power machine.

The vehicle body <NUM> includes a front vehicle body <NUM>, a rear vehicle body <NUM>, and a steering cylinder <NUM>. The front vehicle body <NUM> and the rear vehicle body <NUM> are attached to be pivotable around a steering shaft extending in an upward-downward direction of the vehicle body <NUM>. The front wheel part <NUM> is provided in a lower part of the front vehicle body <NUM>, and the rear wheel part <NUM> is provided in a lower part of the rear vehicle body <NUM>.

The steering cylinder <NUM> is a hydraulic cylinder. A base end portion of the steering cylinder <NUM> is attached to the rear vehicle body <NUM>, and a tip portion is attached to the front vehicle body <NUM>. The steering cylinder <NUM> is expanded and contracted by hydraulic oil, thereby defining an angle between the front vehicle body <NUM> and the rear vehicle body <NUM>. That is, a steering angle of the front wheel part <NUM> is defined by expansion and contraction of the steering cylinder <NUM>.

The work machine <NUM> is used for excavating and transporting a work object such as earth and sand. The work machine <NUM> is provided in a front part of the vehicle body <NUM>. The work machine <NUM> includes a boom <NUM>, a bucket <NUM>, a bell crank <NUM>, a lift cylinder <NUM>, and a bucket cylinder <NUM>.

A base end portion of the boom <NUM> is attached to a front part of the front vehicle body <NUM> via a pin.

The bucket <NUM> includes a blade for excavating the work object and a container for carrying the excavated work object. A base end portion of the bucket <NUM> is attached to a tip portion of the boom <NUM> via a pin.

The bell crank <NUM> transmits power of the bucket cylinder <NUM> to the bucket <NUM>. A first end of the bell crank <NUM> is attached to a bottom portion of the bucket <NUM> via a link mechanism. A second end of the bell crank <NUM> is attached to a tip portion of the bucket cylinder <NUM> via a pin.

The lift cylinder <NUM> is a hydraulic cylinder. A base end portion of the lift cylinder <NUM> is attached to a front part of the front vehicle body <NUM>. A tip portion of the lift cylinder <NUM> is attached to the boom <NUM>. As the lift cylinder <NUM> is expanded and contracted by hydraulic oil, the boom <NUM> is driven in an upward direction or a downward direction.

The bucket cylinder <NUM> is a hydraulic cylinder. A base end portion of the bucket cylinder <NUM> is attached to a front part of the front vehicle body <NUM>. A tip portion of the bucket cylinder <NUM> is attached to the bucket <NUM> via the bell crank <NUM>. As the bucket cylinder <NUM> is expanded and contracted by the hydraulic oil, the bucket <NUM> swings in a tilt direction or a dump direction.

The operator cab <NUM> is a space for an operator who rides in the space to operate the work vehicle <NUM>. The operator cab <NUM> is provided in an upper part of the rear vehicle body <NUM>.

<FIG> is a diagram showing an internal configuration of the operator cab according to the first embodiment. The operator cab <NUM> is internally provided with a seat <NUM>, an accelerator pedal <NUM>, a brake pedal <NUM>, a steering wheel <NUM>, a front/rear selection switch <NUM>, a shift switch <NUM>, a boom lever <NUM>, and a bucket lever <NUM>.

The accelerator pedal <NUM> is operated to set a driving force (traction force) for traveling which is generated by the work vehicle <NUM>. As an operation amount of the bucket lever <NUM> increases, a target driving force (target traction force) is set to be stronger.

The brake pedal <NUM> is operated to set a braking force for traveling which is generated by the work vehicle <NUM>. As an operation amount of the brake pedal <NUM> increases, the braking force is set to be stronger.

The steering wheel <NUM> is operated to set a steering angle of the work vehicle <NUM>.

The front/rear selection switch <NUM> is operated to set a traveling direction of the work vehicle <NUM>. The traveling direction of the work vehicle is either forward (F), rearward (R), or neutral (N).

The shift switch <NUM> is operated to set a speed range of the power transmission device. For example, the shift switch <NUM> is operated to select one speed range from a first speed, a second speed, a third speed, and a fourth speed.

The boom lever <NUM> is operated to set a movement amount of a raising operation or a lowering operation of the boom <NUM>. The boom lever <NUM> receives the lowering operation when tilted forward, and receives the raising operation when tilted rearward.

The bucket lever <NUM> is operated to set a movement amount of a dump operation or a tilt operation of the bucket <NUM>. The bucket lever <NUM> receives the dump operation when tilted forward, and receives the tilt operation when tilted rearward.

<FIG> is a schematic diagram showing a power system of the work vehicle according to the first embodiment.

The work vehicle <NUM> includes an engine <NUM>, a power take off <NUM> (PTO: power take off device), a transmission <NUM>, a front axle <NUM>, a rear axle <NUM>, a variable capacity pump <NUM>, and a fixed capacity pump <NUM>.

For example, the engine <NUM> is a diesel engine. The engine <NUM> is provided with a fuel injection device <NUM> and an engine tachometer <NUM>. The fuel injection device <NUM> controls a driving force of the engine <NUM> by adjusting the amount of fuel injected into a cylinder of the engine <NUM>. The engine tachometer <NUM> measures a rotation speed of the engine <NUM>.

The PTO <NUM> transmits a portion of the driving force of the engine <NUM> to the variable capacity pump <NUM> and the fixed capacity pump <NUM>. That is, the PTO <NUM> distributes the driving force of the engine <NUM> to the transmission <NUM>, the variable capacity pump <NUM>, and the fixed capacity pump <NUM>.

The transmission <NUM> is a continuously variable transmission including a hydrostatic continuously variable transmission (HST) <NUM>. The transmission <NUM> may perform shift control by using only the HST <NUM>, or may be a hydraulic mechanical continuously variable transmission (HMT) that performs shift control by using a combination of the HST <NUM> and a planetary gear mechanism. The transmission <NUM> shifts the driving force input to an input shaft, and outputs the driving force from an output shaft. The input shaft of the transmission <NUM> is connected to the PTO <NUM>, and the output shaft is connected to the front axle <NUM> and the rear axle <NUM>. That is, the transmission <NUM> transmits the driving force of the engine <NUM> which is distributed by the PTO <NUM> to the front axle <NUM> and the rear axle <NUM>. The transmission <NUM> is provided with an input shaft tachometer <NUM> and an output shaft tachometer <NUM>. The input shaft tachometer <NUM> measures a rotation speed of the input shaft of the transmission <NUM>. The output shaft tachometer <NUM> measures a rotation speed of the output shaft of the transmission <NUM>. The HST <NUM> of the transmission <NUM> is provided with an HST pressure gauge <NUM>. The HST pressure gauge <NUM> measures a pressure of the HST <NUM>.

The front axle <NUM> transmits the driving force output by the transmission <NUM> to the front wheel part <NUM>. In this manner, the front wheel part <NUM> is rotated.

The rear axle <NUM> transmits the driving force output by the transmission <NUM> to the rear wheel part <NUM>. In this manner, the rear wheel part <NUM> is rotated.

The front axle <NUM> and the rear axle <NUM> are examples of a traveling device.

The variable capacity pump <NUM> is driven by a driving force transmitted from the engine <NUM>. For example, discharge capacity of the variable capacity pump <NUM> is changed by controlling a tilt angle of a swash plate provided inside the variable capacity pump <NUM>. Hydraulic oil discharged from the variable capacity pump <NUM> is supplied to the steering cylinder <NUM>, the lift cylinder <NUM>, and the bucket cylinder <NUM> via a control valve <NUM>. In addition, the hydraulic oil discharged from the variable capacity pump <NUM> is discharged via a brake valve <NUM> and a relief valve <NUM>.

The control valve <NUM> controls a flow rate of the hydraulic oil discharged from the variable capacity pump <NUM>, and distributes the hydraulic oil to the steering cylinder <NUM>, the lift cylinder <NUM>, and the bucket cylinder <NUM>. The brake valve <NUM> controls the flow rate of the hydraulic oil to be supplied to the relief valve <NUM>. The relief valve <NUM> releases the pressure when the pressure of the hydraulic oil exceeds a predetermined relief pressure, and discharges the hydraulic oil.

The variable capacity pump <NUM> is provided with a first pump pressure gauge <NUM> and a pump capacity meter <NUM>. The first pump pressure gauge <NUM> measures a discharge pressure of the hydraulic oil discharged from the variable capacity pump <NUM>. The pump capacity meter <NUM> measures capacity of the variable capacity pump <NUM> based on a swash plate angle of the variable capacity pump <NUM>.

The lift cylinder <NUM> is provided with a cylinder pressure gauge <NUM>. The cylinder pressure gauge <NUM> measures the pressure of the lift cylinder <NUM>.

The variable capacity pump <NUM> is an example of a device to which the power is distributed from the PTO <NUM>. In another embodiment, the variable capacity pump <NUM> may be configured to include a plurality of pumps, or may include other destinations such as hydraulically driven fans (not shown), instead of or in addition to the variable capacity pump <NUM>.

The fixed capacity pump <NUM> is driven by a driving force transmitted from the engine <NUM>. The hydraulic oil discharged from the fixed capacity pump <NUM> is supplied to a clutch (not shown) inside the transmission <NUM>. The fixed capacity pump <NUM> is provided with a second pump pressure gauge <NUM>. The second pump pressure gauge <NUM> measures the discharge pressure of the hydraulic oil discharged from the fixed capacity pump <NUM>. The fixed capacity pump <NUM> is an example of a device to which the power is distributed from the PTO <NUM>. The fixed capacity pump <NUM> may be configured to include a plurality of pumps, or may have a supply destination such as a lubrication circuit (not shown).

The work vehicle <NUM> includes a control device <NUM> for controlling the work vehicle <NUM>.

The control device <NUM> outputs a control signal to the fuel injection device <NUM>, the transmission <NUM>, the variable capacity pump <NUM>, the control valve <NUM> and the brake valve <NUM> in response to an operation amount of each operation device (accelerator pedal <NUM>, brake pedal <NUM>, steering wheel <NUM>, front/rear selection switch <NUM>, shift switch <NUM>, boom lever <NUM>, and bucket lever <NUM>) inside the operator cab <NUM>.

<FIG> is a schematic block diagram showing a configuration of the control device of the work vehicle according to the first embodiment. The control device <NUM> is a computer including a processor <NUM>, a main memory <NUM>, a storage <NUM>, and an interface <NUM>.

The storage <NUM> is a non-temporary tangible storage medium. Examples of the storage <NUM> include a hard disk drive (HDD), a solid state drive (SSD), a magnetic disk, a magneto-optical disc, a compact disc read only memory (CD-ROM), and a digital versatile disc read only memory (DVD-ROM), and a semiconductor memory. The storage <NUM> may be an internal medium directly connected to a bus of the control device <NUM>, or may be an external medium connected to the control device <NUM> via the interface <NUM> or a communication line. The storage <NUM> stores a program for controlling the work vehicle <NUM>.

The program may partially realize functions of the control device <NUM>. For example, the program may fulfill a function in combination with another program previously stored in the storage or in combination with another program installed in another device. In another embodiment, the computer may include a custom large scale integrated circuit (LSI) such as a programmable logic device (PLD) in addition to the above-described configuration or instead of the above-described configuration. Examples of the PLD include a programmable array logic (PAL), a generic array logic (GAL), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA). In this case, functions realized by the processor may be partially or entirely realized by the integrated circuit.

In a case where the program is distributed to the control device <NUM> via a communication line, the control device <NUM> receiving the distribution may deploy the program in the main memory <NUM>, and may execute the above-described process.

In addition, the program may partially realize the above-described function. Furthermore, the program may be a so-called difference file (difference program) that realizes the above-described function in combination with another program previously stored in the storage <NUM>.

In order to execute the program, the processor <NUM> includes an operation amount acquisition unit <NUM>, a measurement value acquisition unit <NUM>, a vehicle state calculation unit <NUM>, a required PTO torque determination unit <NUM>, a required output torque determination unit <NUM>, a traveling load estimation unit <NUM>, a target rotation speed determination unit <NUM>, an acceleration torque specifying unit <NUM>, a target engine torque determination unit <NUM>, an engine control unit <NUM>, a brake control determination unit <NUM>, a target HST pressure specifying unit <NUM> (target circuit pressure specifying unit), an offset torque determination unit <NUM>, a compensation torque determination unit <NUM>, an assist torque determination unit <NUM>, a brake torque determination unit <NUM>, a target speed ratio determination unit <NUM>, a transmission control unit <NUM>, and a pump control unit <NUM>.

The operation amount acquisition unit <NUM> acquires the operation amount from each of the accelerator pedal <NUM>, the brake pedal <NUM>, the steering wheel <NUM>, the front/rear selection switch <NUM>, the shift switch <NUM>, the boom lever <NUM>, and the bucket lever <NUM>. Hereinafter, the operation amount of the accelerator pedal <NUM> will be referred to as an accelerator operation amount, the operation amount of the brake pedal <NUM> will be referred to as a brake operation amount, the operation amount of the steering wheel <NUM> will be referred to as a steering operation amount, a value corresponding to an operation position of the front/rear selection switch <NUM> will be referred to as an FNR operation amount, a value corresponding to an operation position of the shift switch <NUM> will be referred to as a shift operation amount, the operation amount of the boom lever <NUM> will be referred to as a boom operation amount, and the operation amount of the bucket lever <NUM> will be referred to as a bucket operation amount.

The measurement value acquisition unit <NUM> acquires measurement values from the fuel injection device <NUM>, the engine tachometer <NUM>, the input shaft tachometer <NUM>, the output shaft tachometer <NUM>, the HST pressure gauge <NUM>, the first pump pressure gauge <NUM>, the pump capacity meter <NUM>, the cylinder pressure gauge <NUM>, and the second pump pressure gauge <NUM>. That is, the measurement value acquisition unit <NUM> acquires each measurement value of a fuel injection amount of the engine <NUM>, a rotation speed of the engine <NUM>, a rotation speed of the input shaft of the transmission <NUM>, a rotation speed of the output shaft of the transmission <NUM>, a pressure of the HST <NUM>, a pump pressure of the variable capacity pump <NUM>, capacity of the variable capacity pump <NUM>, a pressure of the lift cylinder <NUM>, and a pump pressure of the fixed capacity pump <NUM>.

Based on the measurement values acquired by the measurement value acquisition unit <NUM>, the vehicle state calculation unit <NUM> calculates an output torque of the engine <NUM>, an upper limit torque of the engine <NUM>, angular acceleration of the engine <NUM>, torques (PTO torques) distributed to the variable capacity pump <NUM> and the fixed capacity pump <NUM> by the PTO <NUM>, an input/output speed ratio of the transmission <NUM>, angular acceleration of the output shaft of the transmission <NUM>, and a traveling speed of the work vehicle <NUM>. The output torque of the engine <NUM> is a torque actually achieved by the engine <NUM> which is calculated based on the fuel injection amount. The upper limit torque of the engine <NUM> is a maximum torque which can be achieved by the engine <NUM>.

The required PTO torque determination unit <NUM> determines a required value (required PTO torque) of the torques distributed from the PTO <NUM> to the variable capacity pump <NUM> and the fixed capacity pump <NUM>, based on the steering operation amount, the boom operation amount, and the bucket operation amount which are acquired by the operation amount acquisition unit <NUM>, and the measurement values of the pump pressure of the variable capacity pump <NUM>, the capacity of the variable capacity pump <NUM>, and the pump pressure of the fixed capacity pump <NUM> which are acquired by the measurement value acquisition unit <NUM>. For example, the required PTO torque determination unit <NUM> obtains a required flow rate of the variable capacity pump <NUM> from the steering operation amount, based on a PTO conversion function that defines a relationship between the operation amount and the required flow rate. Further, for example, the required PTO torque determination unit <NUM> obtains the required flow rate of the variable capacity pump <NUM> from the boom operation amount and the bucket operation amount based on the PTO conversion function. Then, the required PTO torque determination unit <NUM> determines the required PTO torque, based on the measurement values of the pump pressure of the variable capacity pump <NUM>, the capacity of the variable capacity pump <NUM>, the pump pressure of the fixed capacity pump <NUM>, and the required flow rate of the specified variable capacity pump <NUM>.

The required output torque determination unit <NUM> determines the required value (required output torque) of the torque of the output shaft of the transmission <NUM>, based on the accelerator operation amount, the brake operation amount, the shift operation amount, and the FNR operation amount which are acquired by the operation amount acquisition unit <NUM>, and the traveling speed calculated by the vehicle state calculation unit <NUM>. For example, the required output torque determination unit <NUM> determines the required output torque from the traveling speed calculated by the vehicle state calculation unit <NUM>, based on a traveling conversion function that defines a relationship between the traveling speed and the required output torque. In this case, the required output torque determination unit <NUM> determines characteristics of the traveling conversion function, based on the accelerator operation amount, the brake operation amount, the shift operation amount, and the FNR operation amount.

Specifically, the required output torque determination unit <NUM> specifies the traveling conversion function corresponding to a speed range specified by the shift operation amount, out of a plurality of the traveling conversion functions corresponding to a plurality of the speed ranges. When there is an accelerator operation, the required output torque determination unit <NUM> transforms the specified traveling conversion function, based on a magnification relating to the accelerator operation amount. When there is a brake operation, the required output torque determination unit <NUM> transforms the specified traveling conversion function, based on the magnification relating to the brake operation amount. The required output torque determination unit <NUM> determines a code of the required output torque, based on the FNR operation amount. When codes of the required output torque and the traveling speed do not coincide with each other (when the code of a product of the required output torque and the traveling speed is negative), the torque on the braking side is achieved by the transmission <NUM>.

According to the traveling conversion function, when the traveling speed exceeds a predetermined speed, the required output torque has a value on the braking side. Therefore, in the required output torque determination unit <NUM>, when the traveling speed calculated by the vehicle state calculation unit <NUM> exceeds an upper limit of the speed range specified by the shift operation amount, the accelerator operation amount, and the brake operation amount, the required output torque has a value on the braking side (code opposite to the traveling speed).

The traveling load estimation unit <NUM> estimates a traveling load torque Tload relating to the traveling based on the output torque Teng of the engine <NUM>, angular acceleration αeng of the engine <NUM>, a PTO torque TPTO, an input/output speed ratio i of the transmission <NUM>, and angular acceleration αout of the output shaft of the transmission <NUM> which are calculated by the vehicle state calculation unit <NUM>.

The traveling load torque Tload can be calculated based on Equation (<NUM>) below. [Equation <NUM>] <MAT>.

Ieng is a moment of inertia of the engine <NUM>. Iv is a moment of inertia of the work vehicle <NUM>. ηt is torque efficiency of the transmission <NUM>. N is an axle reduction ratio from the output shaft of the transmission <NUM> to the front wheel part <NUM> and the rear wheel part <NUM>. The moment of inertia Ieng, the moment of inertia Iv, the torque efficiency ηt, and the axle reduction ratio N are constants.

Equation (<NUM>) can be derived from Equation (<NUM>) showing a relationship between the output torque Teng of the engine <NUM> and the output torque Tout of the transmission <NUM>, and Equation (<NUM>) showing a relationship between the output torque Tout of the transmission <NUM>, and the acceleration α out of the work vehicle <NUM>. In another embodiment, the traveling load torque Tload may be calculated based on an equation other than Equation (<NUM>). For example, instead of Equation (<NUM>), an equation for specifying the traveling load torque Tload may be derived by using an equation showing a relationship among the pressure of the HST <NUM> which is measured by the HST <NUM>, a capacity command of the variable capacity pump of the HST <NUM> or the pump capacity measured by the pump capacity meter provided in the variable capacity pump, and the output torque Tout In addition, in another embodiment, when the transmission <NUM> includes an electric motor, an equation for specifying the traveling load torque Tload may be derived by using a torque command of the electric motor or an electric motor output torque estimated from a voltage/current. [Equation <NUM>] <MAT>
[Equation <NUM>] <MAT>.

The target rotation speed determination unit <NUM> determines a target engine rotation speed used for controlling the engine <NUM>, based on a required engine output which is a sum of required traveling power calculated from the required output torque and the traveling speed, and the required PTO output calculated from the required PTO torque and the measurement value of the rotation speed of the engine <NUM>. The target rotation speed determination unit <NUM> determines a target engine rotation speed based on a rotation speed conversion function that defines a relationship between the required engine output and the engine rotation speed which are determined in advance by design. For example, the rotation speed conversion function may be designed to suppress the rotation of the engine <NUM> to the low rotation speed side as much as possible within a range in which the required engine output can be achieved and the engine acceleration is not hindered.

In addition, the target rotation speed determination unit <NUM> determines the engine rotation speed (required PTO rotation speed) required for realizing the required flow rate of the variable capacity pump <NUM> which is calculated by the required PTO torque determination unit <NUM>. The target rotation speed determination unit <NUM> determines the required PTO rotation speed based on a rotation speed conversion function that defines a relationship between the required flow rate of the variable capacity pump <NUM> and the engine rotation speed which are determined in advance by design. When the target engine rotation speed falls below the required PTO rotation speed, the target rotation speed determination unit <NUM> determines the target engine rotation speed as the required PTO rotation speed.

The acceleration torque specifying unit <NUM> calculates a target acceleration torque required for rotating the engine <NUM> at a target engine rotation speed based on the measurement value of the rotation speed of the engine <NUM> which is acquired by the measurement value acquisition unit <NUM> and the target engine rotation speed determined by the target rotation speed determination unit <NUM>. That is, the acceleration torque specifying unit <NUM> determines target engine acceleration from the rotation speed of a difference between the measurement value of the rotation speed of the engine <NUM> and the target engine rotation speed, and multiplies the target engine acceleration by the moment of inertia of the engine <NUM>, thereby calculating the target acceleration torque.

The target engine torque determination unit <NUM> determines a target engine torque which is a torque to be output by the engine <NUM>, based on the PTO torque calculated by the vehicle state calculation unit <NUM>, the upper limit torque of the engine <NUM>, the input/output speed ratio of the transmission <NUM>, the required output torque determined by the required output torque determination unit <NUM>, and the measurement value of the rotation speed of the engine <NUM>. The target engine torque determination unit <NUM> calculates a required input torque which is a torque of the engine <NUM> required for obtaining the required output torque by multiplying the required output torque by the input/output speed ratio of the transmission <NUM>. The target engine torque determination unit <NUM> determines the smaller one of the sum of the PTO torque and the required input torque and the maximum value of the engine torque as the target engine torque.

The engine control unit <NUM> outputs an engine torque command to the fuel injection device <NUM>. Specifically, the engine control unit <NUM> outputs the engine torque command indicating the target engine torque determined by the target engine torque determination unit <NUM>. The engine control unit <NUM> is an example of a drive source control unit.

The brake control determination unit <NUM> determines whether or not to perform PTO brake control for obtaining a braking force by driving the variable capacity pump <NUM>. Specifically, the brake control determination unit <NUM> determines to perform the PTO brake control when the required output torque determined by the required output torque determination unit <NUM> has a value on the braking side.

In another embodiment, the brake control determination unit <NUM> may determine to perform the PTO brake control when the code of the required output torque on the braking side and an absolute value exceed a certain threshold value.

The target HST pressure specifying unit <NUM> determines the pressure of the HST <NUM> corresponding to the required output torque determined by the required output torque determination unit <NUM> as a target HST pressure (target circuit pressure) which is a control target of the HST <NUM>. A relationship between the output torque of the transmission <NUM> and the pressure of the HST <NUM> is determined by a relationship of a gear ratio between the output shaft and the HST motor which are determined by the design of the transmission <NUM>, and the capacity of the HST motor at that time.

The offset torque determination unit <NUM> determines the offset torque used for the PTO brake control by multiplying the required input torque by a predetermined coefficient. The required input torque is calculated by multiplying the required output torque determined by the required output torque determination unit <NUM> by the input/output speed ratio of the transmission <NUM>. The offset torque determination unit <NUM> may determine the offset torque by using the required input torque calculated by the target engine torque determination unit <NUM>. The coefficient used for determining the offset torque is a value greater than -<NUM> and equal to or smaller than <NUM>. The PTO brake control is performed when the required output torque is a negative value. Accordingly, the offset torque is a positive value. The offset torque is a feedforward correction factor for estimating the PTO brake torque that is expected to be required empirically or experimentally.

The compensation torque determination unit <NUM> determines a compensation torque used for the PTO brake control by performing proportional integral (PI) control based on a difference between an actual HST pressure (actual circuit pressure) which is the measurement value of the pressure of the HST <NUM> acquired by the measurement value acquisition unit <NUM> and a target HST pressure specified by the target HST pressure specifying unit. The compensation torque determination unit <NUM> according to another embodiment may determine the compensation torque by performing other feedback control based on the actual HST pressure and the target HST pressure. The compensation torque is a feedback correction factor for accurately controlling the braking force in accordance with the target.

The assist torque determination unit <NUM> determines an assist torque for assisting the rotation acceleration of the engine <NUM>, based on the measurement value of the rotation speed of the engine <NUM> which is acquired by the measurement value acquisition unit <NUM>. For example, the assist torque determination unit <NUM> performs P control based on a difference between the smaller of the target rotation speed of the engine and an assist guaranteed rotation speed and the measurement value of the rotation speed of the engine <NUM>. In this manner, the assist torque determination unit <NUM> determines a low rotation assist torque for assisting the rotation acceleration of the engine <NUM> when the rotation speed of the engine <NUM> is lower than the assist guaranteed rotation speed. In order to secure the power for the traveling or the work machine, the assist guaranteed rotation speed is set so that the engine rotation speed does not fall below a prescribed rotation speed.

In addition, the assist torque determination unit <NUM> performs the P control based on a difference between the rotation speed of the engine required for realizing the required flow rate of the variable capacity pump <NUM> calculated by the required PTO torque determination unit <NUM> and the measurement value of the rotation speed of the engine <NUM>. In this manner, the assist torque determination unit <NUM> determines a work machine assist torque for assisting the rotation acceleration of the engine <NUM> when the hydraulic oil is required for driving the work machine <NUM>. The assist torque determined by the assist torque determination unit <NUM> is a value equal to or greater than <NUM>. The assist torque is a correction factor for assisting the engine rotation acceleration when it is necessary to quickly increase the engine rotation.

The brake torque determination unit <NUM> determines the brake torque consumed by the variable capacity pump <NUM> in the PTO brake control, based on the offset torque, the compensation torque, and the assist torque. Specifically, the brake torque determination unit <NUM> determines the brake torque by adding the offset torque and the compensation torque and subtracting the assist torque.

The target speed ratio determination unit <NUM> determines a target input/output speed ratio of the transmission <NUM> based on the measurement value of the rotation speed of the input shaft of the transmission <NUM>, the measurement value of the rotation speed of the output shaft of the transmission <NUM>, the traveling load torque estimated by the traveling load estimation unit <NUM>, the target output torque determined by the required output torque determination unit <NUM>, and the target engine acceleration specified by the acceleration torque specifying unit <NUM>. Specifically, the target speed ratio determination unit <NUM> estimates the rotation speed of the output shaft of the transmission <NUM> after the lapse of time relating to a predetermined control cycle, and sets the rotation speed of the output shaft of the transmission <NUM> as the target rotation speed, based on the rotation speed of the output shaft of the transmission <NUM>, the traveling load torque, and the target output torque. The target speed ratio determination unit <NUM> estimates the rotation speed of the input shaft of the transmission <NUM> after the lapse of time relating to a predetermined control cycle, and sets the rotation speed of the input shaft of the transmission <NUM> as the target rotation speed of the input shaft, based on the rotation speed of the input shaft of the transmission <NUM> and the target engine acceleration. The target speed ratio determination unit <NUM> determines a target input/output speed ratio by dividing the target rotation speed of the output shaft by the target rotation speed of the input shaft.

The transmission control unit <NUM> outputs a control command of the transmission <NUM> in order to realize the target input/output speed ratio determined by the target speed ratio determination unit <NUM>. For example, the transmission control unit <NUM> outputs a capacity command of the HST <NUM> included in the transmission <NUM>.

The pump control unit <NUM> outputs a control command of the variable capacity pump <NUM> in order to realize an absorption torque which is a sum of the required PTO torque determined by the required PTO torque determination unit <NUM> and the brake torque determined by the brake torque determination unit <NUM>. In addition, when the PTO brake control is performed, the pump control unit <NUM> outputs a control command of the brake valve <NUM> in order to realize the brake torque.

<FIG> is a flowchart showing a control method for the work vehicle according to the first embodiment.

First, the operation amount acquisition unit <NUM> acquires the operation amount from each of the accelerator pedal <NUM>, the brake pedal <NUM>, the steering wheel <NUM>, the front/rear selection switch <NUM>, the shift switch <NUM>, the boom lever <NUM>, and the bucket lever <NUM> (Step S1). In addition, the measurement value acquisition unit <NUM> acquires the measurement values from the fuel injection device <NUM>, the engine tachometer <NUM>, the input shaft tachometer <NUM>, the output shaft tachometer <NUM>, the HST pressure gauge <NUM>, the first pump pressure gauge <NUM>, the pump capacity meter <NUM>, the cylinder pressure gauge <NUM>, and the second pump pressure gauge <NUM> (Step S2).

Next, based on the measurement values acquired in Step S2, the vehicle state calculation unit <NUM> calculates the output torque of the engine <NUM>, the upper limit torque of the engine <NUM>, the angular acceleration of the engine <NUM>, the PTO torque, the input/output speed ratio of the transmission <NUM>, the angular acceleration of the output shaft of the transmission <NUM>, and the traveling speed of the work vehicle <NUM> (Step S3).

The required PTO torque determination unit <NUM> determines the required PTO torque based on the measurement values of the steering operation amount, the boom operation amount, and the bucket operation amount which are acquired in Step S1, the pump pressure and the capacity of the variable capacity pump <NUM> which are acquired in Step S2, and the pump pressure of the fixed capacity pump <NUM> (Step S4). The required output torque determination unit <NUM> determines the required output torque based on the operation amount relating to the traveling acquired in Step S1 and the traveling speed calculated in Step S3 (Step S5). The traveling load estimation unit <NUM> estimates the traveling load torque based on the value of the vehicle state calculated in Step S3 (Step S6).

The target rotation speed determination unit <NUM> determines the target engine rotation speed based on the required engine output which is a sum of the required traveling power calculated from the required output torque and the traveling speed, and the required PTO output calculated from the required PTO torque and the measurement value of the rotation speed of the engine <NUM> (Step S7). The acceleration torque specifying unit <NUM> calculates the target acceleration torque based on the measurement value of the rotation speed of the engine <NUM> and the target engine rotation speed determined in Step S7 (Step S8). The target engine torque determination unit <NUM> determines the target engine torque based on the measurement values of the required output torque, the PTO torque calculated in Step S3, the upper limit torque of the engine, the input/output speed ratio of the transmission <NUM>, and the rotation speed of the engine <NUM> acquired in Step S2 (Step S9). The engine control unit <NUM> outputs an engine torque command indicating the target engine torque determined in Step S9 (Step S10).

Next, the brake control determination unit <NUM> determines whether or not the required output torque determined in Step S5 has a value on the braking side (Step S11). When the required output torque has a value on the drive side (Step S11: NO), the brake control determination unit <NUM> determines that it is not necessary to perform the PTO brake control.

When the required output torque has a value on the braking side (Step S11: YES), the brake control determination unit <NUM> determines that it is necessary to perform the PTO brake control. When the required output torque has a value on the braking side (Step S11: YES), the target HST pressure specifying unit <NUM> determines the target HST pressure which is the control target of the HST <NUM>, based on the required output torque determined in Step S5 (Step S12). The offset torque determination unit <NUM> determines the offset torque by multiplying the required input torque by a predetermined coefficient (Step S13).

The compensation torque determination unit <NUM> determines the compensation torque by performing the PI control based on a difference between the actual HST pressure which is the measurement value of the pressure of the HST <NUM> acquired by the measurement value acquisition unit <NUM>, and the target HST pressure specified by the target HST pressure specifying unit (Step S14). When the actual HST pressure is lower than the target HST pressure, the compensation torque has a positive value. When the actual HST pressure is higher than the target HST pressure, the compensation torque has a negative value.

The assist torque determination unit <NUM> determines the low rotation assist torque by performing the P control based on a difference between the smaller of the target rotation speed of the engine and the assist guaranteed rotation speed and the measurement value of the rotation speed of the engine <NUM> (Step S15). In addition, the assist torque determination unit <NUM> determines the work machine assist torque by performing the P control based on a difference between the rotation speed of the engine required for an operator to quickly realize the work machine speed, and the measurement value of the rotation speed of the engine <NUM> (Step S16).

The brake torque determination unit <NUM> determines the brake torque by subtracting the low rotation assist torque and the work machine assist torque from the torque value obtained by adding the offset torque and the compensation torque (Step S17).

The target speed ratio determination unit <NUM> determines the target input/output speed ratio based on the measurement value of the rotation speed of the input shaft of the transmission <NUM>, the measurement value of the rotation speed of the output shaft of the transmission <NUM>, the load torque, the target output torque, and the target engine acceleration (Step S18). The transmission control unit <NUM> outputs a control command of the transmission <NUM> for achieving the target input/output speed ratio (Step S19).

The pump control unit <NUM> specifies the capacity of the variable capacity pump <NUM> required for realizing the absorption torque which is a sum of the required PTO torque determined in Step S4 and the brake torque determined in Step S17, and outputs a control command indicating the capacity to the variable capacity pump <NUM> (Step S20).

In addition, the pump control unit <NUM> determines whether or not to perform the PTO brake control based on a determination result in Step S11 (Step S21). In Step S11, the brake control determination unit <NUM> determines to perform the PTO brake control when the required output torque has a value on the braking side.

When the PTO brake control is performed (Step S21: YES), the pump control unit <NUM> outputs a control command instructing the brake valve <NUM> to open in accordance with the brake torque (Step S22). In this manner, the hydraulic oil is discharged from the relief valve <NUM> when the work vehicle <NUM> is braked. Therefore, out of the torques distributed from the PTO <NUM> to the variable capacity pump <NUM>, the torque which is not used for controlling the work machine <NUM> and controlling the steering is consumed as heat.

The control device <NUM> performs the above-described control processes at every predetermined control cycle.

As described above, according to the control device <NUM> of the first embodiment, the brake torque which is the torque consumed by the variable capacity pump <NUM> is determined based on the target HST pressure and the actual HST pressure of the HST <NUM>, and the variable capacity pump <NUM> is controlled based on the brake torque. In this manner, the control device <NUM> feeds back the torque of the output shaft of the transmission <NUM> by the HST pressure. Accordingly, the control device <NUM> can accurately control the braking force of the work vehicle <NUM> even when the power system of the work vehicle <NUM> does not include the electrical hardware.

In addition, according to the control device <NUM> of the first embodiment, the required output torque is specified based on the operation amount of the operation device and the traveling speed of the work vehicle <NUM>, and the target HST pressure is determined based on the required output torque. In this manner, the control device <NUM> enables the work vehicle <NUM> to achieve the braking force in accordance with the operation amount of the operator.

In addition, according to the control device <NUM> of the first embodiment, the brake torque is determined based on the sum of the offset torque obtained by multiplying the required output torque by the speed ratio and the predetermined coefficient, and the compensation torque obtained by performing the feedback control based on the difference between the target HST pressure and the actual HST pressure. The control device <NUM> can improve followability of the braking immediately after the braking starts by using the offset torque, or can achieve both high responsiveness and stability of the braking force. Therefore, the control device <NUM> can improve accuracy in a final braking force by using the compensation torque. Furthermore, the control device <NUM> according to the first embodiment determines the assist torque based on the rotation speed of the drive source, and determines the brake torque by subtracting the assist torque from the sum of the offset torque and the compensation torque. In this manner, the control device <NUM> can further use a portion of the braking force to assist the rotation acceleration of the engine <NUM>.

In another embodiment, the control device <NUM> may determine the brake torque without using at least any one of the offset torque and the assist torque.

The embodiment has been described above in detail with reference to the drawings. However, the specific configuration is not limited to the above-described embodiment, and various design changes can be made.

In addition, the work vehicle <NUM> according to the first embodiment is the wheel loader. However, the configuration is not limited thereto. For example, the work vehicle <NUM> according to another embodiment may be another work vehicle <NUM> such as a bulldozer or a tractor. In addition, in another embodiment, the control device <NUM> may be applied to a power machine other than a work vehicle.

Claim 1:
A control device (<NUM>) for a power machine (<NUM>) including
a drive source (<NUM>),
a hydraulic pump (<NUM>) driven by a driving force of the drive source (<NUM>),
a power take off device (<NUM>) configured to transmit a portion of the driving force of the drive source (<NUM>) to the hydraulic pump (<NUM>),
a power transmission device (<NUM>) including a hydrostatic continuously variable transmission (<NUM>), an input shaft connected to the power take off device (<NUM>), and an output shaft connected to a load (<NUM>, <NUM>), and configured to transmit the driving force input to the input shaft to the output shaft, and
an operation device (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) that is configured to provide an instruction regarding a magnitude of the driving force of the drive source (<NUM>),
the control device (<NUM>) characterized by comprising:
a target circuit pressure specifying unit (<NUM>) configured to specify a target circuit pressure which is a target pressure of the hydrostatic continuously variable transmission (<NUM>);
a measurement value acquisition unit (<NUM>) configured to acquire an actual circuit pressure which is a measurement value of a pressure of the hydrostatic continuously variable transmission (<NUM>);
a brake torque determination unit (<NUM>) configured to determine a brake torque based on the target circuit pressure and the actual circuit pressure, the brake torque which is a torque consumed by the hydraulic pump (<NUM>); and
a pump control unit (<NUM>) configured to control the hydraulic pump based on the brake torque.