JP2011169351A - Hst type construction vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a construction vehicle mounted with a HST, which travels with a travelling hydraulic motor driven by pressure oil discharged from a hydraulic pump driven by an engine, while suppressing driver's footing of an accelerator pedal to improve fuel economy during high-speed travel. <P>SOLUTION: A wheel loader 50 includes the engine 1, the travelling hydraulic pump 4 driven by the engine 1, the travelling hydraulic motor 10 driven by the pressure oil discharged from the travelling hydraulic pump 4, and tires (travelling wheels) 54 to which rotation driving force is imparted by the travelling hydraulic motor 10. A vehicle body controller 12b sets the minimum capacity of the travelling hydraulic motor 10 in accordance with the detection result of an engine revolution sensor 1a. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an HST construction vehicle that travels by driving a traveling hydraulic motor with pressure oil discharged from a traveling hydraulic pump driven by an engine.

In construction vehicles such as wheel loaders, so-called HST (Hydro Static Transmission) is used in which a traveling hydraulic pump is driven by an engine and a traveling hydraulic motor is driven by pressure oil discharged from the traveling hydraulic pump. Some are equipped.
For example, Patent Document 1 discloses a 1-pump 1-motor type HST system. Patent Document 2 discloses a 1-pump 2-motor type HST system.

Such an HST type construction vehicle travels at the maximum vehicle speed when the travel load is the smallest with the accelerator pedal fully depressed.
Construction vehicles that can travel on public roads are designed such that the maximum vehicle speed does not exceed the limit vehicle speed (generally a vehicle speed determined for each country or region, for example, 38 km / h).
Patent Document 1 discloses that the driver can arbitrarily change the maximum vehicle speed by allowing the driver to change the minimum capacity of the traveling hydraulic motor. However, even in this case, it is designed so that the maximum vehicle speed does not exceed the limit vehicle speed.

By the way, in such a construction vehicle, when moving on a flat ground at high speed, the driver often depresses the accelerator pedal to the maximum and travels at the maximum vehicle speed in order to increase productivity. In this case, the engine speed becomes the maximum speed corresponding to the maximum opening of the accelerator.
The load when traveling on a flat ground at the maximum vehicle speed is smaller than the load when performing excavation work using a working machine and the load when traveling on a hill. In the conventional method, even when the load is small as described above, the engine speed is the maximum, so there is room for improvement in terms of fuel efficiency.

  An object of the present invention is to provide an HST-type construction vehicle capable of improving fuel efficiency in a high-speed traveling or the like in a construction vehicle equipped with an HST.

  The HST type construction vehicle according to the first invention includes an engine, a traveling hydraulic pump, a traveling hydraulic motor, traveling wheels, and a control device. The traveling hydraulic pump is driven by the engine. The traveling hydraulic motor is driven by the pressure oil discharged from the traveling hydraulic pump. The traveling wheels are driven by the driving force of the traveling hydraulic motor. The control device controls the capacity of the traveling hydraulic motor. The control device sets the minimum capacity of the traveling hydraulic motor so that the minimum capacity of the traveling hydraulic motor increases as the engine speed increases so that the same vehicle speed can be obtained regardless of the engine speed. It has a capacity setting unit.

  Here, in a construction vehicle such as a wheel loader equipped with a so-called HST that travels by driving a traveling hydraulic pump by an engine and driving a traveling hydraulic motor by pressure oil discharged from the traveling hydraulic pump, The minimum capacity of the travel hydraulic motor is set so that the minimum capacity of the travel hydraulic motor increases as the engine speed increases so that substantially the same vehicle speed can be obtained regardless of the engine speed.

In conventional construction vehicles, the maximum vehicle speed is not reached unless the driver depresses the accelerator pedal to the maximum.
On the other hand, in the present invention, the minimum capacity of the traveling hydraulic motor is set to be small as the engine speed decreases so that the same vehicle speed can be obtained even if the engine speed decreases.
Thus, for example, even when the driver does not depress the accelerator pedal to the maximum, that is, even when the engine speed is kept lower than before, the minimum capacity of the traveling hydraulic motor is reduced according to the decrease in the engine speed. By doing so, the vehicle can travel at the same maximum vehicle speed as the conventional one. Therefore, the driver travels with the amount of depression of the accelerator pedal suppressed, and the driver operates with a lower engine speed than before, so that fuel efficiency can be improved.

The HST type construction vehicle according to the second invention is the HST type construction vehicle according to the first invention, wherein a threshold value of the engine speed is set in the minimum capacity setting unit. The minimum capacity setting unit keeps the minimum capacity of the traveling hydraulic motor constant when the engine speed is less than or equal to the threshold value, and the same vehicle speed regardless of the engine speed when the engine speed exceeds the threshold value. The minimum capacity of the traveling hydraulic motor is set such that the minimum capacity of the traveling hydraulic motor increases as the engine speed increases so that the engine speed can be obtained by the minimum capacity setting unit. In the following cases, the minimum capacity of the traveling hydraulic motor is set to a certain size. On the other hand, when the engine speed exceeds a predetermined threshold, the traveling hydraulic motor has a minimum capacity that increases as the engine speed increases so that the same vehicle speed can be obtained regardless of the engine speed. Set the minimum capacity.

Here, the minimum capacity of the traveling hydraulic motor set by the minimum capacity setting unit is that the vehicle speed does not exceed the legally limited vehicle speed when the engine speed reaches the above threshold even when the traveling load is the smallest. Is set to Therefore, when determining this threshold value, it is sufficient to set the threshold value to a value that can prevent the traveling hydraulic motor capacity from becoming too small and reducing efficiency more than necessary.
Thereby, in the area | region where an engine speed is below a threshold value, it can avoid that the efficiency of the hydraulic motor for driving | running | working falls more than needed, and can aim at a fuel consumption improvement.

  An HST construction vehicle according to a third aspect of the invention includes an engine, a traveling hydraulic pump, a traveling hydraulic motor, a traveling wheel, an accelerator pedal, and a control device. The traveling hydraulic pump is driven by the engine. The traveling hydraulic motor is driven by the pressure oil discharged from the traveling hydraulic pump. The traveling wheels are driven by the driving force of the traveling hydraulic motor. The accelerator pedal adjusts the engine speed according to the accelerator opening. The control device controls the capacity of the traveling hydraulic motor. In addition, the control device sets the minimum capacity of the traveling hydraulic motor so that the minimum capacity of the traveling hydraulic motor increases as the accelerator opening increases so that the same vehicle speed can be obtained regardless of the accelerator opening. It has a capacity setting unit.

  Here, in a construction vehicle such as a wheel loader equipped with a so-called HST that travels by driving a traveling hydraulic pump by an engine and driving a traveling hydraulic motor by pressure oil discharged from the traveling hydraulic pump, The minimum capacity of the traveling hydraulic motor is set so that the minimum capacity of the traveling hydraulic motor increases as the amount of depression of the accelerator pedal increases, so that approximately the same vehicle speed can be obtained regardless of the amount of depression of the accelerator pedal (accelerator opening). Set.

In conventional construction vehicles, the maximum vehicle speed is not reached unless the driver depresses the accelerator pedal to the maximum.
On the other hand, in the present invention, the minimum capacity of the traveling hydraulic motor is set to be small as the accelerator pedal depression amount is reduced so that the same vehicle speed can be obtained even if the accelerator pedal depression amount is reduced.

  Thus, as in the first invention, for example, even when the driver does not depress the accelerator pedal to the maximum, that is, even when the engine speed is kept lower than before, the accelerator opening (that is, the engine speed) By reducing the minimum capacity of the traveling hydraulic motor in accordance with the decrease in (), the vehicle can travel at the maximum vehicle speed equivalent to the conventional one. Therefore, the driver travels with the amount of depression of the accelerator pedal suppressed, and the driver operates with a lower engine speed than before, so that fuel efficiency can be improved.

  An HST type construction vehicle according to a fourth invention is the HST type construction vehicle according to the third invention, wherein a threshold value of an accelerator opening is set in the minimum capacity setting unit. The minimum capacity setting unit keeps the minimum capacity of the traveling hydraulic motor constant when the accelerator opening is less than or equal to the threshold, and the same vehicle speed can be obtained regardless of the accelerator opening when the accelerator opening exceeds the threshold. Thus, the minimum capacity of the traveling hydraulic motor is set such that the minimum capacity of the traveling hydraulic motor increases as the accelerator opening increases.

  Here, when the accelerator opening is equal to or less than a predetermined threshold, the minimum capacity of the traveling hydraulic motor is set to a certain size by the minimum capacity setting unit. On the other hand, when the accelerator opening exceeds a predetermined threshold, the traveling hydraulic motor has a minimum capacity that increases as the accelerator opening increases so that the same vehicle speed can be obtained regardless of the accelerator opening. Set the minimum capacity.

  Here, the minimum capacity of the traveling hydraulic motor set by the minimum capacity setting unit is that the vehicle speed does not exceed the legally limited vehicle speed when the accelerator opening reaches the above threshold even when the traveling load is the smallest. Is set to Therefore, when this threshold value is determined, it may be set as a value that can avoid that the capacity of the traveling hydraulic motor becomes too small and the efficiency is unnecessarily reduced when the threshold value is set lower than the threshold value.

  Thereby, in the area | region where an accelerator opening is below a threshold value, it can avoid that the efficiency of the hydraulic motor for driving | running | working falls more than needed, and can aim at a fuel consumption improvement.

  According to the HST type construction vehicle according to the present invention, in the construction vehicle equipped with the HST, the amount of depression of the driver's accelerator pedal can be suppressed to improve the fuel efficiency during high speed traveling.

The side view which shows the structure of the wheel loader which concerns on one Embodiment of this invention. The hydraulic circuit diagram which shows the HST system of 1 pump 1 motor mounted in the wheel loader of FIG. The graph which shows the torque characteristic of the engine mounted in the wheel loader of FIG. The graph which shows the relationship between the engine speed in the wheel loader of FIG. FIG. 2 is a control diagram showing specific processing contents regarding setting of a capacity of a traveling hydraulic motor in a vehicle body controller mounted on the wheel loader of FIG. 1. The graph which shows the relationship between the command electric current which the vehicle body controller mounted in the wheel loader of FIG. 1 outputs, and the capacity | capacitance of a hydraulic motor for driving | running | working. FIG. 2 is a graph showing the control content for changing the minimum capacity of the traveling hydraulic motor in accordance with the engine speed in the wheel loader of FIG. 1. FIG. The graph which shows the relationship between the vehicle speed and tractive force in the wheel loader of FIG. (A), (b) is a characteristic diagram which shows the relationship between the torque characteristic of an engine and the fuel consumption rate in the wheel loader of FIG. (A), (b) is explanatory drawing which shows an example of the control content which concerns on other embodiment of this invention. The hydraulic circuit diagram which shows the HST system of 1 pump 2 motor mounted in the construction vehicle which concerns on other embodiment of this invention.

An HST type construction vehicle according to an embodiment of the present invention will be described below with reference to FIGS.
[Configuration of Wheel Loader 50]
As shown in FIG. 1, a wheel loader (HST construction vehicle) 50 according to this embodiment includes a vehicle body 51, a lift arm (work machine) 52 attached to the front portion of the vehicle body, and a tip of the lift arm 52. A bucket (working machine) 53 attached to the vehicle body, four tires (running wheels) 54 that rotate while supporting the vehicle body 51 to travel the vehicle body, and a cab 55 mounted on the upper portion of the vehicle body 51. ing.

The lift arm 52 is a member for lifting the bucket 53 attached to the tip, and is driven by a lift cylinder 19 (see FIG. 2) provided side by side.
The bucket 53 is attached to the tip of the lift arm 52 and is dumped and tilted by the bucket cylinder 56.
As shown in FIG. 2, the lift cylinder 19 and the bucket cylinder 56 are driven by pressure oil discharged from the work machine / steering pump 2 driven by the engine 1. A control valve 18 is provided in a hydraulic circuit for work implement control that connects the work implement / steering pump 2 to the lift cylinder 19 and the bucket cylinder 56. The control valve 18 is activated in response to an operation of a work implement lever (not shown), and controls the movement of the lift cylinder 19 and the bucket cylinder 56. The pressure oil discharged from the work machine / steering pump 2 is also supplied to a steering circuit (not shown).

[Overview of HST system]
As shown in FIG. 2, the wheel loader 50 of the present embodiment is used for traveling by pressure oil discharged from a traveling hydraulic pump 4 driven by the engine 1 and supplied to the traveling hydraulic motor 10 through a closed circuit. This is an HST construction vehicle that travels when the hydraulic motor 10 is driven. Hereinafter, the closed circuit connecting the traveling hydraulic pump 4 and the traveling hydraulic motor 10 is referred to as “HST circuit 20”, and the pressure of the HST circuit 20 is referred to as “HST circuit pressure”.

The HST system of this embodiment is a so-called one-pump one-motor type system in which one traveling hydraulic motor 10 is driven by pressure oil discharged from one traveling hydraulic pump 4, as shown in FIG. It is.
The traveling hydraulic pump 4 is a variable displacement swash plate type axial piston pump, and the traveling hydraulic motor 10 is a variable displacement oblique shaft type axial piston motor.

  The angle of the swash plate of the traveling hydraulic pump 4 and the angle of the oblique axis of the traveling hydraulic motor 10 are controlled by the vehicle body controller 12b. That is, the capacity of the traveling hydraulic pump 4 (amount of pressure oil discharged when the pump is rotated once) and the capacity of the traveling hydraulic motor 10 (amount of pressure oil required to rotate the motor once) are It is controlled by the vehicle body controller 12b. Control of the capacity of the traveling hydraulic pump 4 and the traveling hydraulic motor 10 by the vehicle body controller 12b will be described in detail later.

[Control of engine 1]
The engine 1 is a diesel engine, and output torque generated by the engine 1 is transmitted to a work machine / steering pump 2, a charge pump 3, a traveling hydraulic pump 4, and the like. The engine 1 is provided with an engine controller 12a and a fuel injection device 1b. Further, the engine 1 is provided with an engine speed sensor 1a composed of a rotation sensor for detecting the actual speed of the engine 1, and a speed signal from the engine speed sensor 1a is input to the vehicle body controller 12b. The engine controller 12a controls the engine 1 by adjusting the amount of fuel injected by the fuel injection device 1b.

  The accelerator pedal 13 a is means for controlling the rotational speed of the engine 1 by the driver, and is connected to the accelerator opening sensor 13. The accelerator opening sensor 13 is composed of a potentiometer or the like, and transmits an opening signal indicating an operation amount (accelerator opening) of the accelerator pedal 13a to the engine controller 12a. The engine controller 12a receives the opening signal from the accelerator opening sensor 13 and outputs a command signal to the fuel injection device 1b to control the fuel injection amount.

  In FIG. 3, the torque characteristic of the engine 1 in this embodiment is shown with a continuous line. In the engine 1, the target rotational speed when the accelerator opening is the maximum opening (100%) is Nmax. For example, when the accelerator opening is 85% of the maximum opening, the engine controller 12a sets a regulation line indicated by an alternate long and short dash line R85 with a target rotational speed of N85 (= 0.85 · Nmax). Further, the engine controller 12a sets a regulation line indicated by a two-dot chain line R70 having a target rotational speed of N70 (= 0.7 · Nmax) when the accelerator opening is 70% of the maximum opening, for example.

  Thus, although the engine controller 12a sets the target rotation speed according to the accelerator opening, the actual rotation speed of the engine 1 varies depending on the load. For example, as shown in FIG. 3, when the accelerator opening is 100% and there is no load, the actual rotational speed of the engine 1 is Nmax, but when the torque serving as the load is Tx, the rotational speed is When the torque serving as a load is Ty, the rotational speed is reduced to Ny.

[Details of HST system]
As shown in FIG. 2, the hydraulic drive mechanism 30 constituting the HST system mainly includes a charge pump 3, a traveling hydraulic pump 4, a traveling hydraulic motor 10, and a vehicle body controller (corresponding to a control device of the present invention) 12b. Have.
(Charge pump 3)
The charge pump 3 is a fixed displacement pump, and is a pump that is driven by the engine 1 and supplies pressure oil to the HST circuit 20. The charge pump 3 is also a hydraulic pressure source for generating a pilot pressure for the pump control valve 5 to control the pump displacement control cylinder 6. The pump control valve 5 and the pump displacement control cylinder 6 will be described in detail later.

(Travel hydraulic pump 4)
The traveling hydraulic pump 4 is a variable displacement swash plate type axial piston pump. The pressure oil discharged from the traveling hydraulic pump 4 is supplied to the HST circuit 20. The high-pressure relief valves 7 and 8 are provided to protect hydraulic equipment such as a pump and a motor, and the pressure of the HST circuit 20 (HST circuit pressure) is kept below a predetermined pressure. Further, the lowest pressure of the HST circuit 20 is compensated by the low pressure relief valve 9 and the charge pump 4. In addition, since these structures are well-known, detailed description is abbreviate | omitted here.

The traveling hydraulic pump 4 is connected to a pump control valve 5 and a pump displacement control cylinder 6 that control the displacement of the traveling hydraulic pump 4 by controlling the angle of the swash plate of the traveling hydraulic pump 4.
The pump control valve 5 generates a pilot pressure based on a control signal from the vehicle body controller 12b. The angle of the swash plate of the traveling hydraulic pump 4 is controlled by controlling the pump displacement control cylinder 6 with this pilot pressure.

  The vehicle body controller 12b outputs a control signal to the pump control valve 5 such that the capacity of the traveling hydraulic pump (the amount discharged per pump rotation) increases as the engine speed increases. Therefore, if the HST circuit pressure is constant, the displacement of the traveling hydraulic pump 4 increases as the engine speed increases, as shown in FIG. Note that Vpmax in FIG. 4 is the maximum capacity that the traveling hydraulic pump 4 can take.

As described above, the flow rate of the hydraulic oil discharged from the traveling hydraulic pump 4 (the amount flowing through the HST circuit 20 per unit time) increases as the engine speed increases, and the capacity of the traveling hydraulic pump 4 reaches the maximum (Vpmax ) Increases in proportion to the engine speed.
The swash plate of the traveling hydraulic pump 4 can be tilted in either the forward or reverse direction. That is, the direction in which the pressure oil supplied to the HST circuit 20 flows can be reversed by switching the direction in which the swash plate of the traveling hydraulic pump 4 is inclined. The inclination direction of the swash plate is also controlled based on a control signal from the vehicle body controller 12b.

(Travel hydraulic motor 10)
The traveling hydraulic motor 10 is a variable displacement oblique axis type axial piston motor. The traveling hydraulic motor 10 is driven by the pressure oil discharged from the traveling hydraulic pump 4 to generate a driving force for traveling. As shown in FIG. 2, a motor cylinder 11a for controlling the angle of the swash plate of the traveling hydraulic motor 10 and a motor control electronic servo valve 11b for controlling the motor cylinder 11a are connected to the traveling hydraulic motor 10. ing. The motor control electronic servo valve 11b is an electromagnetic control valve that is controlled based on a control signal from the vehicle body controller 12b. By controlling the motor cylinder 11a, the capacity of the travel hydraulic motor 10 (one rotation of the motor) is controlled. (Capacity necessary for making it change) can be arbitrarily changed. The control of the displacement of the traveling hydraulic motor 10 by the vehicle body controller 12b will be described in detail later.

(Car body controller 12b)
The vehicle body controller 12b corresponds to the “control device” in the present invention.
As shown in FIG. 2, the vehicle body controller 12 b receives signals from a forward / reverse switching lever 14, a speed range selection switch 15, a vehicle speed detection sensor (vehicle speed detection unit) 16, and an HST circuit pressure sensor 17.

  A signal input from the forward / reverse switching lever 14 to the vehicle body controller 12b is a signal indicating whether the forward / reverse switching lever 14 is in a forward, neutral or reverse position. The vehicle body controller 12 b controls the pilot pressure sent from the pump control valve 5 to the pump displacement control cylinder 6 based on the signal from the forward / reverse switching lever 14, thereby changing the inclination direction of the swash plate of the traveling hydraulic pump 4. Switch. As a result, the vehicle body controller 12b switches the flow direction of the pressure oil in the HST circuit 20 between when the forward movement is selected and when the reverse movement is selected.

  The speed range selection switch 15 is a switch for the driver to select a speed range. The wheel loader 50 of the present embodiment has a speed range of 1st to 4th speed, and when excavation work or the like is performed using a work machine, the 1st to 3rd speed, which is a work speed range, is increased at a high speed. When it is necessary to move, the fourth speed, which is the speed range for traveling, can be selected. A signal indicating which speed range is selected by the speed range selection switch 15 is input to the vehicle body controller 12b.

The vehicle speed sensor (vehicle speed detection unit) 16 is a sensor that detects the vehicle speed from the rotation speed of the tire drive shaft, and transmits a vehicle speed signal to the vehicle body controller 12b.
The HST circuit pressure sensor 17 detects the pressure (HST circuit pressure) of the HST circuit 20, and transmits a signal indicating the HST circuit pressure to the vehicle body controller 12b. Note that the HST circuit pressure increases as the traveling load increases and decreases as the traveling load decreases if the displacement of the traveling hydraulic motor 10 is constant.

  As shown in FIG. 5, the vehicle body controller 12b includes a command current calculation unit 41, a speed range control unit 42, an overrun prevention control unit 43, a minimum capacity setting unit 44, and a maximum value selection unit 45 as functional blocks. Yes. The command current calculation unit 41, the speed range control unit 42, the overrun prevention control unit 43, and the minimum capacity setting unit 44 obtain the command current based on the signals from the respective sensors described above, and select the obtained command current as the maximum value. To the unit 45. The maximum value selection unit 45 selects the maximum one of these command currents and transmits it to the motor control electronic servo valve 11b. Note that how to obtain the command current in the command current calculation unit 41, the speed range control unit 42, the overrun prevention control unit 43, and the minimum capacity setting unit 44 will be described in detail later.

Here, in this embodiment, as shown in FIG. 6, the capacity of the traveling hydraulic motor 10 increases as the command current transmitted to the motor control electronic servo valve 11b increases, and the travel current decreases as the command current decreases. The capacity of the hydraulic motor 10 is reduced. In FIG. 6, Vmmax is the maximum capacity of the traveling hydraulic motor 10 determined mechanically (the upper limit value of the capacity of the mechanical traveling hydraulic motor 10), and Vmmin is the hydraulic pressure determined mechanically. This is the minimum capacity of the motor 10 (the lower limit value of the capacity of the mechanical traveling hydraulic motor 10).
Therefore, with the above configuration, the vehicle body controller 12b allows the traveling hydraulic motor 10 to have a capacity obtained by the command current calculation unit 41, a capacity obtained by the speed range control unit 42, and an overload within a range from Vmmin to Vmmax. Control is performed by selecting the maximum capacity obtained by the run prevention control unit 43.

(Determination of motor capacity by command current calculation unit 41)
The command current calculation unit 41 controls the capacity of the traveling hydraulic motor 10 according to the magnitude of the load applied to the engine 1.

The command current calculation unit 41 receives the HST circuit pressure from the HST circuit pressure sensor 17 and the engine speed from the engine speed sensor 1a, and performs PID control of the command current so that the HST circuit pressure becomes a target value. . The target value of the HST circuit pressure is set for each engine speed.
Therefore, due to the function of the command current calculation unit 41, the capacity of the traveling hydraulic motor 10 decreases to increase the HST circuit pressure when the HST circuit pressure decreases, and decreases the HST circuit pressure when the HST circuit pressure increases. growing. That is, when the traveling load is reduced by the function of the command current calculation unit 41, the minimum capacity of the traveling hydraulic motor 10 is reduced, and the driving torque of the tire 54 is reduced while the vehicle speed is increased. On the other hand, when the traveling load increases, the minimum capacity of the traveling hydraulic motor 10 increases and the driving torque of the tire 54 increases while the vehicle speed decreases.

  The capacity of the traveling hydraulic motor 10 depends on the command current output from the command current calculation unit 41, and the mechanical minimum capacity (lower limit value of capacity) (Vmin in FIG. 6) and the mechanical maximum capacity (capacity of the capacity). The upper limit value) (Vmmax in FIG. 6).

(Determining the minimum motor capacity by the speed range controller 42)
The speed range control unit 42 defines an upper limit value of the vehicle speed that can be reached in each speed range.
The speed range control unit 42 stores the command current stored in advance according to the detection result of the speed range selection switch 15, that is, which speed range is selected from the four speed ranges of the speed ranges 1, 2, 3, and 4. Select one of I _{1 to} I ₄ and output. The magnitude of the command current I ₁ when selecting the first speed, the command current I ₂ when selecting the second speed, the command current I ₃ when selecting the third speed, and the command current I ₄ when selecting the fourth speed is I ₁ > I ₂ > I ₃ > I ₄ .

  Therefore, when the accelerator pedal 13a is depressed to the maximum while the traveling load, that is, the HST circuit pressure is sufficiently small, the speed range control unit 42 and the maximum value selection unit 45 can be reached when the third speed is selected. The vehicle speed is lower than when the fourth speed is selected, the vehicle speed that can be reached when the second speed is selected is lower than when the third speed is selected, and the vehicle speed that can be reached when the first speed is selected is limited to be lower than when the second speed is selected.

Here, the command current I ₄ output from the speed range control unit 42 in the 4-speed range is obtained when the capacity of the traveling hydraulic motor 10 takes the mechanical minimum capacity (lower limit value of capacity) (Vmin in FIG. 6). It may be less than or equal to the current value (Imin in FIG. 6). For example, when setting the command current to be set to a value equal to or less than Imin, the minimum capacity that can be taken by the traveling hydraulic motor 10 is the mechanical minimum capacity (lower limit value of capacity) Vmmin. On the other hand, when the command current is set as a value larger than Imin, the minimum value that the traveling hydraulic motor 10 can take is the capacity at the time of the command current I ₄ . That is, the capacity at the command current I ₄ becomes a substantial lower limit value, and the capacity of the traveling hydraulic motor 10 does not decrease to Vmin which is the mechanical minimum capacity (lower limit value of the capacity).

(Determination of motor capacity by the overrun prevention control unit 43)
The overrun prevention control unit 43 is provided to prevent excessive speed (overrun) on a steep downhill or the like.
The overrun prevention control unit 43 determines the vehicle speed based on a graph (see III in FIG. 5) in which the designated current value increases when the vehicle speed detected by the vehicle speed sensor 16 exceeds a predetermined overrun vehicle speed. The command current value according to is output. That is, the overrun prevention control unit 43 prevents the vehicle speed from increasing further by increasing the capacity of the traveling hydraulic motor 10 when the vehicle speed becomes equal to or higher than a predetermined overrun vehicle speed. .

Here, the minimum value (Imin in FIG. 6) of the command current output from the overrun prevention control unit 43 is set as a value smaller than the command current I ₄ output from the speed range control unit 42 at least in the 4th speed range. Has been. Therefore, when the vehicle speed is equal to or lower than the overrun vehicle speed, the command current output from the overrun prevention control unit 43 is not selected by the maximum value selection unit 45. That is, the overrun prevention control unit 43 does not substantially control the capacity of the traveling hydraulic motor 10 when the vehicle speed is equal to or lower than the overrun vehicle speed.

(Setting of minimum motor capacity (lower limit value of capacity) by minimum capacity setting unit 44)
The minimum capacity setting unit 44 is one of the characteristic parts of the present invention, and sets the minimum capacity (lower limit value of capacity) that the traveling hydraulic motor 10 can take. The minimum capacity setting unit 44 sets the minimum capacity (lower limit value of capacity) of the traveling hydraulic motor 10 according to the engine speed.
As shown in IV of FIG. 5, the minimum capacity setting unit 44 stores a correspondence relationship between the command current and the engine speed, and a command current value corresponding to the engine speed detected by the engine speed sensor 1a. Is output.

The command current output by the minimum capacity setting unit 44 is always smaller than any of the command currents I _{1 to} I ₃ corresponding to the respective speed ranges 1, 2, and 3 set by the speed range control unit 42 described above. Is set. Therefore, in the present embodiment, in the first speed, the second speed, and the third speed, the capacity of the traveling hydraulic motor 10 does not decrease to the minimum capacity (the lower limit value of the capacity) set by the minimum capacity setting unit 44. In other words, the minimum capacity setting unit 44 does not substantially function except for the fourth speed which is the maximum speed range.

Further, the command current output by the minimum capacity setting unit 44 is set to a value that is always smaller than the minimum value Imin ′ of the command current output from the overrun prevention control unit 43 described above, regardless of the engine speed. Has been.
As shown in IV of FIG. 5, the correspondence between the engine speed stored in the minimum capacity setting unit 44 and the command current is such that the command current is constant when the engine speed is equal to or less than a predetermined threshold value. When the number exceeds a predetermined threshold, the command current is set to increase as the engine speed increases. In the region where the engine speed exceeds the threshold, the command current change rate (inclination of the slope in the graph shown in IV of FIG. 5) is set so that traveling at the same vehicle speed is possible regardless of the engine speed. is doing. In other words, as shown in FIG. 7, the minimum capacity setting unit 44 includes a minimum capacity (lower limit value of capacity) of the traveling hydraulic motor 10 regardless of the engine speed in an area where the engine speed is equal to or less than a predetermined threshold. ) Is constant. Further, in a region where the engine speed exceeds a predetermined threshold value, the rate of change of the minimum capacity (lower limit value of the capacity) of the traveling hydraulic motor 10 is such that traveling at the same vehicle speed is possible regardless of the engine speed. (Inclination of the inclined portion in the graph shown in FIG. 7) is set. In this embodiment, the threshold value is 80% of the maximum rotation speed.

(Minimum motor capacity design based on vehicle speed limit)
By the way, when designing a construction vehicle that can run on a public road such as a wheel loader, the maximum vehicle speed is a limited vehicle speed (generally a vehicle speed determined for each country or region, for example, 38 km / h). It is necessary not to exceed it.
Here, when the flow rate of the pressure oil flowing into the traveling hydraulic motor 10 is the maximum and the capacity of the traveling hydraulic motor 10 is the minimum capacity, the traveling hydraulic motor 10 rotates at the highest speed, and the vehicle speed of the wheel loader 50 is the highest. It becomes the vehicle speed. The engine speed when the accelerator pedal 13a is depressed to the maximum and the flow rate of the pressure oil supplied from the traveling hydraulic pump 4 to the HST circuit 20 at the load when traveling on flat ground can be determined by design. . Therefore, if the maximum vehicle speed is determined, the minimum capacity (lower limit value of capacity) that the traveling hydraulic motor 10 should take can be obtained by calculation. In other words, the minimum capacity (lower limit value of capacity) that can be taken by the traveling hydraulic motor 10 can be appropriately determined in design according to the limit vehicle speed.

In determining the minimum capacity, it is desirable to set a value that can prevent the capacity from becoming too small and reducing the efficiency more than necessary.
In the present embodiment, as described above, the maximum vehicle speed is set to 38 km / h. Moreover, (the lower limit of the capacity) the minimum volume to the hydraulic motor 10 takes traveling based on the flow rate when the engine speed is 80% of the maximum rotation speed (when the mechanical minimum volume Vmmin or command current I ₄ (Capacity) is set. As described above, when the engine rotational speed is between 80% and 100% of the maximum rotational speed, the traveling hydraulic motor 10 is minimum so that traveling at the same vehicle speed is possible regardless of the engine rotational speed. The rate of change of the capacity (lower limit value of capacity) (the slope of the slope portion in the graph shown in FIG. 7) is set.

(Traction characteristics of HST system)
As described above, if the characteristics of individual devices such as the engine 1, the traveling hydraulic pump 4, and the traveling hydraulic motor 10 are determined, the traction force characteristics of the HST system are determined.
FIG. 8 shows the traction force characteristics of the HST system of this embodiment. In FIG. 8, a solid line F100 is a curve indicating the maximum traction force of the present HST system when the engine speed is maximum (100%). A one-dot chain line F90 indicates the traction force when the engine speed is 90% of the maximum speed, and a two-dot chain line F80 indicates the traction force when the engine speed is 80% of the maximum speed. The product of traction force and vehicle speed is horsepower (power), and as is clear from FIG. 8, the smaller the engine speed, the smaller the horsepower. F100, F90, and F80 are all equal horsepower curves (equal power curves).

  As shown in FIG. 8, the traction force decreases as the engine speed decreases to 90% and 80% of the maximum speed, but the maximum vehicle speed is the limit vehicle speed until the engine speed reaches 80% of the maximum speed. It remains 38 km / h.

<Specific examples of control>
The control performed by the HST system of this embodiment will be described below with a specific example.
(When driving on flat ground at maximum vehicle speed)
Here, a description will be given of a case where the driver selects the fourth speed and depresses the accelerator pedal 13a and travels stably while maintaining the maximum vehicle speed of around 38 km / h when traveling on flat ground.
At this time, the traveling load is sufficiently small because the traveling is stable on a flat ground. Therefore, since the HST circuit pressure is also sufficiently small, the vehicle body controller 12b minimizes the minimum capacity of the traveling hydraulic motor 10 (decreases the capacity to the lower limit value).

Here, when the engine speed is between 80% and 100% of the maximum speed, the vehicle speed does not change no matter how much the accelerator pedal 13a is depressed, and the maximum vehicle speed (38 km / h) is maintained. .
Therefore, the driver is urged to travel while suppressing the depression amount of the accelerator pedal 13a to about 80%.

Here, the difference in fuel efficiency between the control of the present embodiment and the conventional control will be described with reference to FIG. In FIG. 9A, Fm indicates fuel efficiency, and the fuel consumption rate is smaller as the center of the ellipse is closer.
A constant horsepower curve (equal work curve) indicated by a one-dot chain line is drawn from the point G, and the point H at which this line intersects with the torque curve when the accelerator opening is 100% is the maximum vehicle speed (38 km / h) according to the conventional control. This is a matching point. That is, conventionally, the minimum capacity (lower limit value of the capacity) of the traveling hydraulic motor 10 is determined so that the maximum vehicle speed becomes the limit vehicle speed (38 km / h) when the engine rotates at the rotational speed at the point H.

  As is clear from FIG. 9A, the fuel consumption rate at point G is smaller than that at point H, and it can be seen that the fuel consumption rate is improved by the present invention.

(If you are going uphill while driving at the maximum speed)
Next, a case will be described in which the driver selects the fourth speed and depresses the accelerator pedal 13a to the maximum and travels near the maximum vehicle speed (38 km / h), and the traveling load increases due to reaching an uphill road.
At this time, since the HST circuit pressure increases, the minimum capacity of the traveling hydraulic motor 10 increases and the vehicle speed increases in order to shift the HST circuit pressure in the direction of decreasing the HST circuit pressure by the function of the command current calculation unit 41 of the vehicle body controller 12b. Will decline.
Here, as shown in FIG. 9B, if the point at which the torque required by the HST system matches the torque curve of the engine 1 at this time is J, the engine 1 generates the torque Tj and the rotational speed Nj. Rotate with.
In the conventional control, matching is performed at the point J under the same conditions, so that the fuel consumption rate is equivalent to the conventional conditions under these conditions.

(When accelerating to the maximum vehicle speed on flat ground)
Here, a case where the driver depresses the accelerator pedal 13a while driving while selecting the fourth speed and accelerates from about 30 km / h to the maximum vehicle speed (38 km / h) will be described.

In this case, first, the traveling load increases in order to accelerate the wheel loader 50. For example, it is assumed that matching is performed at a point J in FIG. 9B in the initial stage of acceleration.
As described above, after reaching the maximum vehicle speed, matching is finally performed at the point G in FIG. 9A, so the matching point is from the point J in FIG. 9B to the point in FIG. 9A. Gradually move towards G.
On the other hand, in the conventional control, the matching point gradually moves from the point J in FIG. 9B toward the point H in FIG. 9A.
From the above, it can be seen that in the process of accelerating to the maximum vehicle speed on a flat ground, the fuel consumption rate is lower in the control according to the present embodiment than in the conventional control.

[Features of wheel loader 50]
(1)
In the wheel loader 50 of this embodiment, the engine 1, the traveling hydraulic pump 4 driven by the engine 1, the traveling hydraulic motor 10 driven by the pressure oil discharged from the traveling hydraulic pump 4, and the traveling And a tire (running wheel) 54 to which a rotational driving force is applied by the hydraulic motor 10. Then, the minimum capacity setting unit 44 of the vehicle body controller 12b performs control to limit the minimum capacity of the traveling hydraulic motor 10 as shown in FIG. 7 based on the detection result of the engine speed sensor 1a.

  Accordingly, even when the vehicle is traveling near the maximum vehicle speed (restricted vehicle speed), even when the amount of depression of the accelerator pedal 13a by the driver is suppressed and the engine speed is reduced, the motor minimum capacity is reduced to reduce the maximum vehicle speed ( It is possible to maintain traveling near the (restricted vehicle speed). Accordingly, the driver can travel at the maximum vehicle speed even when the amount of depression of the accelerator pedal 13a is suppressed during traveling near the maximum vehicle speed (restricted vehicle speed), and therefore the driver does not depress the accelerator pedal 13a to the maximum. Will start to run. As a result, it is possible to improve fuel efficiency during high-speed traveling.

(2)
In the wheel loader 50 of the present embodiment, only when the vehicle is traveling in the maximum speed range (fourth gear in the present embodiment), the vehicle body controller 12b controls the change in the minimum capacity of the traveling hydraulic motor 10 based on the engine speed described above. The command current value corresponding to each speed range is set so as to be performed.

  As a result, for example, a load is applied to the work machine, and the minimum motor capacity is changed in a situation where the work efficiency decreases when the minimum capacity of the traveling hydraulic motor 10 is reduced. Can be avoided. Therefore, even when the engine speed is decreased from the maximum speed by a predetermined ratio, high-speed traveling can be maintained, and fuel efficiency can be improved.

(3)
In the wheel loader 50 of the present embodiment, when changing the set value of the minimum motor capacity in accordance with the engine speed, the vehicle body controller 12b has a maximum engine speed corresponding to the vehicle speed limit as shown in FIG. The engine speed of 80% has a threshold value.
This threshold value is not limited to 80% of the maximum rotation speed. When determining this threshold value, it is desirable that the threshold value be set so as to prevent the capacity from becoming too small and the efficiency from being lowered more than necessary.
As a result, it is possible to avoid that the efficiency of the traveling hydraulic motor 10 decreases more than necessary in a region where the engine speed is less than the threshold value (80% in the present embodiment).

[Other Embodiments]
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the summary of invention.

(A)
In the above embodiment, as illustrated in FIG. 5, an example in which the minimum capacity setting unit 44 controls the minimum capacity of the traveling hydraulic motor 10 according to the engine speed has been described. However, the present invention is not limited to this.
For example, as shown in FIG. 10A, the minimum capacity setting unit 44 outputs a command current for setting the minimum capacity of the traveling hydraulic motor 10 according to the accelerator opening (the amount of depression of the accelerator pedal). You may do it. In this case, as shown in FIG. 10 (b), the minimum capacity setting unit 44 performs control to change the minimum capacity of the traveling hydraulic motor 10 in accordance with the accelerator opening, so that the same as in the above embodiment. The effect of can be obtained.

(B)
In the above embodiment, the wheel loader 50 equipped with the HST system of one pump and one motor including one hydraulic pump and the traveling hydraulic motor 10 has been described as an example. However, the present invention is not limited to this.
For example, as shown in FIG. 11, two traveling hydraulic motors 110a and 110b, first and second motor control valves 111a and 111b, first and second motor cylinders 112a and 112b, a clutch 113, a clutch control valve 114, The present invention may be applied to a construction vehicle including a one-pump two-motor HST system including the drive shaft 115 and the HST circuit 120.

In this case, the minimum capacity of the hydraulic motor described above may be set for the second traveling hydraulic motor 110a for high-speed traveling.
Specifically, the second motor control valve 111a and the second motor cylinder 112a may be controlled so as to change the minimum capacity of the second traveling hydraulic motor 110a.

(C)
In the above embodiment, as shown in FIG. 5, an example is described in which the vehicle body controller 12b determines a command current value for changing the capacity of the traveling hydraulic motor 10 based on the engine speed based on a predetermined map. did. However, the present invention is not limited to this.
For example, instead of determining based on the map, a relational expression for calculating the command current value may be stored, and the command current value may be calculated by calculation.

(D)
In the above-described embodiment, an example in which the minimum capacity of the traveling hydraulic motor 10 described above is set while traveling in the 4-speed range that is the maximum speed range of the wheel loader 50 has been described. However, the present invention is not limited to this.
For example, when the speed change mechanism of the construction vehicle has 3rd speed or less, or 5th speed or more, the same control may be performed during traveling in the maximum speed range.
Alternatively, in addition to running at the maximum speed range, the same control as described above can be performed when running without using the work implement at all or when using the work implement with a low load. You may implement.

(E)
In the said embodiment, the engine controller 12a and the vehicle body controller 12b were demonstrated and demonstrated as an example. However, the present invention is not limited to this.
For example, the engine controller and the vehicle body controller may be combined as one controller.

(F)
In the above embodiment, the wheel loader has been described as an example of the construction vehicle to which the present invention is applied. However, the present invention is not limited to this.
For example, the present invention can be applied to other construction vehicles equipped with HST.

  The construction vehicle according to the present invention is a construction vehicle that travels by driving a traveling hydraulic motor with pressure oil discharged from a hydraulic pump driven by an engine, and suppresses the depression amount of the driver's accelerator pedal during high-speed traveling. Therefore, the present invention can be widely applied to construction vehicles equipped with so-called HST.

DESCRIPTION OF SYMBOLS 1 Engine 1a Engine speed sensor 1b Fuel injection apparatus 2 Work machine / steering pump 3 Charge pump 4 Traveling hydraulic pump 5 Pump control valve 6 Pump capacity control cylinder 7, 8 High pressure relief valve 9 Low pressure relief valve 10 Traveling hydraulic motor 11a Motor cylinder 11b Electronic servo valve for motor control 12a Engine controller 12b Car body controller (control device)
13 Accelerator opening sensor 13a Accelerator pedal 14 Forward / reverse switching lever 15 Speed range selection switch 16 Vehicle speed sensor 17 HST circuit pressure sensor 18 Control valve 19 Lift cylinder 20 HST circuit 30 Hydraulic drive mechanism 41 Command current calculation unit 42 Speed range control unit 43 Overrun prevention control unit 44 Minimum capacity setting unit 45 Maximum value selection unit 50 Wheel loader (HST construction vehicle)
51 Car body 52 Lift arm (work machine)
53 bucket (work machine)
54 tires (running wheels)
55 Cab 56 Bucket cylinders 110a and 110b Traveling hydraulic motors 111a and 111b First and second motor control valves 112a and 112b First and second motor cylinders 113 Clutch 114 Clutch control valve 115 Drive shaft 120 HST circuit

JP 2004-144254 A (published May 20, 2004) Japanese Patent Laid-Open No. 11-230333 (released on August 27, 1999)

Claims (4)

Engine,
A traveling hydraulic pump driven by the engine;
A traveling hydraulic motor driven by pressure oil discharged from the traveling hydraulic pump;
Traveling wheels driven by the driving force of the traveling hydraulic motor;
A control device for controlling a capacity of the traveling hydraulic motor;
With
The control device is configured so that the minimum capacity of the travel hydraulic motor increases as the engine speed increases so that the same vehicle speed can be obtained regardless of the engine speed. Having a minimum capacity setting section for setting the capacity;
HST construction vehicle. In the minimum capacity setting unit, a threshold value of engine speed is set,
The minimum capacity setting unit makes the minimum capacity of the traveling hydraulic motor constant when the engine speed is less than or equal to the threshold value, and sets the engine speed when the engine speed exceeds the threshold value. The minimum capacity of the traveling hydraulic motor is set such that the minimum capacity of the traveling hydraulic motor increases as the rotational speed of the engine increases so that the same vehicle speed can be obtained irrespectively.
The HST type construction vehicle according to claim 1. Engine,
A traveling hydraulic pump driven by the engine;
A traveling hydraulic motor driven by pressure oil discharged from the traveling hydraulic pump;
Traveling wheels driven by the driving force of the traveling hydraulic motor;
An accelerator pedal for adjusting the rotational speed of the engine according to an accelerator opening;
A control device for controlling a capacity of the traveling hydraulic motor;
With
The control device reduces the minimum capacity of the traveling hydraulic motor so that the minimum capacity of the traveling hydraulic motor increases as the accelerator opening increases so that the same vehicle speed can be obtained regardless of the accelerator opening. Having a minimum capacity setting section to set,
HST construction vehicle. In the minimum capacity setting unit, a threshold value of the accelerator opening is set,
The minimum capacity setting unit is configured to keep the minimum capacity of the traveling hydraulic motor constant when the accelerator opening is equal to or less than the threshold, and regardless of the accelerator opening when the accelerator opening exceeds the threshold. Setting the minimum displacement of the traveling hydraulic motor such that the minimum displacement of the traveling hydraulic motor increases as the accelerator opening increases so as to obtain the same vehicle speed;
The HST type construction vehicle according to claim 3.

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