JPH0552377B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a travel control device for a wheeled hydraulic excavator.

B. Prior Art As shown in FIG. 5, a wheeled hydraulic excavator includes a lower traveling body 2 having running wheels 1, and an upper rotating body 3 connected to the lower traveling body 2 via a swing ring. The upper revolving body 3 includes a boom 7, which is driven by hydraulic cylinders 4 to 6, respectively.
A digging attachment consisting of an arm 8, a bucket 9, etc. is provided.

Unlike crawler-type hydraulic excavators, this type of wheel-type hydraulic excavator is approved for running on general roads, and therefore is required to run faster than crawler-type hydraulic excavators; however, according to current domestic regulations, the maximum Speed is restricted to less than 35km/h. For this reason, it is an absolute requirement for a wheeled hydraulic excavator to be able to travel at a maximum speed of 35 km/h.

Against this background, the travel drive devices for wheeled hydraulic excavators have traditionally been so-called mechanical types, which drive the axles by mechanically decelerating the output of the engine mounted on the upper revolving structure, or engines. There is a hydraulic type in which a hydraulic pump is driven by a hydraulic motor, which turns a hydraulic motor to drive an axle, but both have the problems described below.

C Problems to be Solved by the Invention Mechanical travel drive systems must mechanically transmit the output of the engine mounted on the upper rotating body to the axle of the lower rotating body, and therefore have a large number of components. It is difficult to assemble and is very expensive.

Further, the conventional hydraulic travel drive device has the following problems.

As mentioned earlier, wheeled hydraulic excavators are allowed to run on general roads, not just within specific work sites. However, it is preferable to be able to drive at the legal maximum speed of 35km/h.

However, in the case of a hydraulic travel drive system, the pressure loss in the hydraulic circuit is large, so the energy required to climb a slope of a predetermined slope at a speed of 35 km/h is much greater than that of a mechanical drive system. Therefore, if the engine is set to high horsepower with emphasis on driving performance when climbing hills, it will be disadvantageous in terms of fuel consumption, noise, cost, etc. when working on excavations or driving on flat ground. If the engine is set to a lower horsepower than the former option with emphasis on fuel efficiency, noise, and cost, sufficient running performance will not be obtained when climbing hills. In other words, when running uphill is taken into consideration, the hydraulic drive wheel shovel has poor matching between running uphill and digging as far as engine performance is concerned.

To this end, various approaches have been taken in the past, and one representative approach is to satisfy the legally mandated speed of 35 km/h only when driving on flat roads.

In this case, from the specifications of the traveling hydraulic motor and transmission used, if the required flow rate when traveling on a flat road at 35 km/h is determined to be Q1 and the required pressure to be P1, the required engine horsepower
PS2' is determined, and thereby the maximum engine speed N1 and the displacement volume q1 of the hydraulic pump are determined, and the engine speed-pump discharge amount curve (N-Q
For example, the curve (curve) is as shown in FIG.

If we consider running uphill in a hydraulic drive system having the N-Q curve shown in Figure 7, as shown in Figure 6a, when climbing uphill, the pump discharge pressure increases to P2, causing the pump to tilt. Since the angle of rotation becomes smaller, the pump discharge rate decreases to Q2, and therefore the speed is much lower than 35 km/h (35 km/h).
Km/h x Q2/Q1), and satisfactory driving performance cannot be obtained.

Therefore, when determining the specifications of the engine and hydraulic equipment, we decided to use a 35 km/h slope at a preset slope.
It is conceivable to make it possible to obtain a speed of .
With this setting, it goes without saying that you can reach a speed of 35km/h even when driving on flat roads.

Therefore, as mentioned above, from the specifications of the hydraulic motor and transmission used, the required flow rate when traveling at 35 km/h on an uphill road with a certain slope is Q1,
When the required pressure is determined as P2 (>P1), the required horsepower PS2 of the engine is determined, for example, as shown in FIG. The engine speed-pump discharge amount curve is as shown in FIG.

Here, the performance of the engine in the hydraulic traveling drive system having the N-Q curve shown in FIG.
Assume that it is defined as shown in the figure. As can be seen from the rotation speed-horsepower curve (N-PS curve) in Figure 9,
If PS2 is the pump absorption horsepower required to run on an uphill road at 35 km/h, that horsepower is obtained when the engine speed is N2. The fuel consumption rate [g/PSh] at that time is found to be g2 from the rotation speed-fuel consumption rate curve (Ng curve). However, if the absorbed horsepower of the pump when traveling at 35 km/h on a flat road with such a hydraulic traveling drive system is PS2'(<PS2), then when the engine is running at full throttle, the engine speed at that time is N2'(>N2),
It can be seen that the fuel consumption rate is g2'(>g2). That is, with such settings of the engine and hydraulic system, when traveling on a flat road at 35 km/h, the engine is used in a region with a low fuel consumption rate, which is not preferable. In addition, since the engine is used in a region with good fuel consumption, if you operate the throttle lever to lower the engine speed and drive, the pump discharge volume will decrease and you will not be able to achieve the specified speed (35 km/h). .

The purpose of the present invention is to solve these problems,
An object of the present invention is to provide a travel control device for a wheeled hydraulic excavator that improves the fuel consumption rate when traveling on a flat road even with a prime mover set to a high horsepower.

D Means for Solving the Problems The present invention provides a wheel-type hydraulic pump that includes a variable displacement hydraulic pump driven by a prime mover and a hydraulic motor that is rotationally driven by oil discharged from the hydraulic pump and drives running wheels. Applied to hydraulic excavator travel control devices. and a setting means for setting at least two maximum displacement volumes, and a selection means for selecting one of at least two modes, a first operation mode for obtaining a large output and a second operation mode for obtaining a small output. , when the second operation mode is selected in response to the operation of the rotation speed limiting means for limiting the maximum rotation speed of the prime mover and the selection means,
The problem described above can be solved by including the setting means and the control means for controlling the rotation speed limiting means so that the maximum rotation speed of the prime mover is lower and the maximum displacement is larger than when the first operation mode is selected. is resolved.

E Effect When the load is large, such as when climbing a slope, the control means operates under the action of the selection means to reduce the maximum displacement of the hydraulic pump and limit the maximum rotation speed of the prime mover to a high value. On the other hand, when the load is small, such as during excavation work or driving on a flat road, the control means works under the action of the selection means to increase the maximum displacement of the hydraulic pump and to lower the maximum rotational speed of the prime mover to a low value. limited by.

F. Embodiment FIG. 1 shows an embodiment of the present invention, in which a discharge port of a variable displacement hydraulic pump 13 driven by an engine 11 constituting a prime mover is connected to a travel hydraulic motor 17 via a control valve 15. It is connected to an excavation actuator 19 including excavation cylinders (hydraulic cylinders 4 to 6 in FIG. 5) provided on the upper revolving body 3 and a swing motor.

The variable displacement hydraulic pump 13 has a pump regulator (not shown) that controls its discharge amount based on circuit pressure (for example, as shown in the P-Q diagram in FIG. 4). In connection therewith, a maximum tilting angle setting mechanism 21 constituting a maximum displacement setting means is provided, which is driven and controlled by a maximum tilting angle setting hydraulic cylinder 21a, thereby adjusting the displacement per revolution of the pump. The maximum value can be controlled in two stages. This hydraulic cylinder 21a is connected to a pressure source 24 and a tank 26 via a solenoid valve 23.
It is connected to the.

Further, an engine rotation speed limiting mechanism 25 as a rotation speed limiting means is provided in association with a governor (not shown) of the engine 11, thereby limiting the maximum rotation speed of the engine 11. Referring to FIGS. 2a to 2c, the rotation speed limiting mechanism 25 has a lever 25a pivotally supported at a predetermined portion, and a throttle lever 12 connected to a governor is connected to the lever 25a. There is. A spring 25 is attached to the tip of the lever 25a.
b is hooked, and the other end of the spring 25b is hooked to one end of a lever 25c that is pivotally supported at a predetermined location. The other end of the lever 25c is connected to an engine control lever (not shown) in the driver's seat, for example, by a push-pull cable 14. Furthermore, this engine speed limiting mechanism 25
The engine has a hydraulic cylinder 25d that limits the rotation angle of the lever 25a, and this hydraulic cylinder 25d limits the maximum rotation angle of the lever 25a, thereby limiting the maximum rotational speed of the engine, as shown in FIG. 2c. Hydraulic cylinder 25d is connected to pressure source 24 and tank 26 via electromagnetic valve 27. Furthermore, Figure 2a
shows the idle state, and FIG. 2b shows the full throttle state.

Referring again to FIG. 1, reference numeral 29 is a controller composed of, for example, a microcomputer, and its input port has a mode changeover switch 31 constituting selection means and a running detection sensor 33.
and an excavation detection sensor 35 are connected. The mode changeover switch 31 is a switch that can be switched between a power mode position P and an economy mode position E, and can be a toggle switch, for example. The travel detection sensor 33 is a sensor that detects whether or not a travel operation lever (not shown) provided on the upper revolving structure is operated, and can be constituted by, for example, an on/off switch that is linked to the travel operation lever. The excavation detection sensor 35 is a sensor that detects whether or not an excavation operation lever (not shown) provided on the upper revolving body is operated, and can be constituted by, for example, an on/off switch that is linked to the excavation operation lever. Note that the excavation operation lever is used in a concept that includes a boom, an arm, a bucket operation lever, and a swing operation lever.

When the traveling operation and excavation operation are carried out by a so-called hydraulic pilot system, the detection sensors 33 and 35 are turned on and off in response to the operating pilot pressure.
Can be configured with a pressure switch to turn off.

The output port of the controller 29 includes a solenoid valve 23 connected to a maximum tilt angle setting hydraulic cylinder 21a and an engine rotation speed limiting hydraulic cylinder 25.
The solenoid valve 27 connected to d is connected.
The solenoid valves 23 and 27 respond to the switching position of the mode changeover switch 31 described above, and when the mode changeover switch 31 is switched to the power mode position, the solenoid valve 23 is energized and the solenoid valve 27 is demagnetized. When switched to the mode position, the solenoid valve 23 is demagnetized and the solenoid valve 27
is excited.

The operation of this embodiment configured in this way will be explained below.

(1) Power mode operation When the mode changeover switch 31 is switched to the power mode position, the solenoid valve 23 is energized and the maximum tilt angle setting hydraulic cylinder 21a is switched to the pressure source 2.
4, whereby the maximum tilting angle setting mechanism 21 shown in the figure operates and the maximum tilting angle is set to the displacement volume _qP.
It is set considerably. At this time, the engine speed limiting solenoid valve 27 is demagnetized and the hydraulic cylinder 25d is not driven, so if the engine control lever on the driver's seat is fully pulled, the lever 25a will rotate as shown in Figure 2b. The engine can be rotated up to the maximum rotation speed N _P without restriction.

Therefore, in the low pressure region (pressure P2 or less), the tilting angle of the hydraulic pump 13 reaches its maximum value, and the displacement volume increases.
As long as q _P , the pump discharge amount increases in proportion to the increase in engine speed, as shown by the solid line in Figure 3, and the maximum engine speed increases.
At N _P , the maximum discharge amount Q _P is obtained. In this case, the P-Q diagram of the pump at the engine speed N _P is as shown by the solid line in FIG.

(2) Economy mode operation When the mode changeover switch 31 is switched to the economy mode position, the maximum tilting angle setting solenoid valve 23 is demagnetized, the maximum tilting angle setting hydraulic cylinder 21a is connected to the tank 26, and thereby The illustrated maximum tilting angle setting mechanism 21 operates to set the maximum tilting angle to a displacement equivalent to the displacement volume q _E (>q _P ). At this time, the engine speed limiting solenoid valve 27
is energized, the hydraulic cylinder 25d is driven, and even if the engine control lever on the driver's seat is pulled all the way, the rotation of the lever 25a is restricted by the cylinder as shown in Figure 2c, and the maximum engine speed is N. limited by _E (< _NP ).

Therefore, as long as the tilting angle of the hydraulic pump 13 reaches its maximum value in the low pressure region and the displacement volume becomes q _E , the displacement is proportional to the increase in engine speed, as shown by the dashed line in Fig. 3. The pump discharge amount increases, and the maximum discharge amount Q _E (=Q _P ) is obtained at the maximum engine speed N _E . In this case, the P-Q diagram of the pump at the engine speed N _E becomes as shown by the dashed line in FIG. 4.

In addition, the curve shown by the broken line in FIG. 4 shows a PQ diagram when the maximum engine speed is not limited to N _E when switching to the maximum displacement volume q _E.

In this embodiment, the maximum displacement of the pump is increased to q _E (>q _P ) in the economy mode.
The maximum engine speed is set to N _E (<N _P ), and the pump maximum discharge amount is set to Q _E =Q _P , thereby keeping the working speed including the traveling speed in economy mode the same. Therefore, as shown in Figure 9, the required horsepower at engine speed N _E
PS2' can be obtained and the fuel consumption rate can be reduced to _gE . On the other hand, considering that the maximum speed is 35 km/h when the pump discharge amount is Q _P (=Q _E ), as can be seen from Figure 4, in economy mode the pump discharge pressure is P1 (for example, flat It is possible to travel at 35km/h up to the pressure required when driving on a road, but if the pump discharge pressure exceeds P1, such as when climbing a hill, the vehicle cannot travel at 35km/h.
In power mode, the pump discharge pressure is up to P2 (for example, the pressure required when running uphill at an angle θ) of 35
It is possible to travel Km/h.

Incidentally, in a conventional pump, for example, a pump having an N-Q curve as shown in Fig. 8, the engine speed is lowered to N1 as in this embodiment to reduce pump absorption horsepower and thereby improve fuel efficiency. In this case, since the maximum displacement of the pump is constant, the P-Q curve becomes like the broken line in FIG. 10, and the pump discharge rate decreases to Q1', making it impossible to obtain the predetermined speed.

In the above explanation, the pump maximum discharge amount Q _P (= q _P × N _P ) and Q _E (= q _E ×
Although we set q _P , N _P , q _E , and N _E so that N _E ) are equal, they do not have to be the same as long as they are approximately equal. h to 35 km/h. Further, in the above explanation, the maximum tilt angle setting mechanism of the pump is controlled by the hydraulic cylinder 21a, but an electromagnetic type may be used, and a linear solenoid or a plurality of hydraulic cylinders may be used. The maximum tilt angle may be set in stages or more. In this case, the engine maximum rotational speed is also limited to a plurality of values accordingly, and the engine and hydraulic system are set to be optimal for various climbing slopes, thereby further improving fuel efficiency. Further, the present invention can also be applied when the hydraulic pump 13 is driven by an electric motor instead of an engine.

G Effects of the Invention According to the present invention, the prime mover and the hydraulic pump can be operated in at least two types of modes,
In operating ranges with larger loads, the maximum displacement of the pump is set to a smaller value and the prime mover can be operated at a higher rotational speed. The number of pumps is now limited to a smaller value, so even if you set each device to achieve the desired speed when driving uphill, you can still obtain the pump absorption horsepower required for driving on flat roads in the low rotation range. Improves fuel efficiency compared to

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Figures 2 a to c are front views showing an example of the engine speed limiting mechanism shown in Figure 1, with Figure 2 a showing the throttle lever in the off position, and Figure 2 b showing the throttle lever in the maximum position. , FIG. 2c shows the case where the throttle lever is restricted, FIG. 3 is a graph showing the relationship between the engine rotation speed N and the pump discharge amount Q in this embodiment, and FIG. 4 is a graph showing the relationship between the engine speed N and the pump discharge amount Q in this embodiment. Figure 5 is a side view showing an example of a wheel-type hydraulic excavator; Figure 6a is a diagram showing a P-Q diagram of the pump;
b is a diagram showing two examples of conventional P-Q diagrams, FIGS. 7 and 8 are graphs respectively showing the relationship between engine rotation speed N and pump discharge amount Q in a conventional wheel-type hydraulic excavator, and FIG. 1 is a diagram showing an engine performance curve, and FIG. 10 is a diagram showing a PQ diagram of a pump of a conventional wheel-type hydraulic excavator. 1: Running wheel, 2: Lower traveling body, 3: Upper revolving body, 4 to 9: Excavation attachment, 11: Engine, 13: Variable displacement hydraulic pump, 15: Control valve, 17: Hydraulic motor, 19: Excavation actuator, 21: maximum tilt angle setting mechanism,
21a: Hydraulic cylinder for setting maximum tilt angle, 23,
27: Solenoid valve, 25: Maximum rotation speed limiting mechanism, 25
a, 25c: lever, 25b: spring, 25d: hydraulic cylinder, 29: controller, 31: mode changeover switch, 33: travel detection sensor, 35: excavation detection sensor.

Claims (1)

[Scope of Claims] 1. A travel control device for a wheeled hydraulic excavator that includes a variable displacement hydraulic pump driven by a prime mover and a hydraulic motor that is rotationally driven by oil discharged from the hydraulic pump and drives a traveling wheel. a setting means for setting at least two maximum displacement volumes; and a selection means for selecting one of at least two modes: a first operation mode for obtaining a large output and a second operation mode for obtaining a small output. , rotation speed limiting means for limiting the maximum rotation speed of the prime mover; and in response to the operation of the selection means, when the second operation mode is selected, the rotation speed is lower than when the first operation mode is selected. A travel control device for a wheeled hydraulic excavator, comprising: control means for controlling the setting means and rotation speed limiting means so that the maximum rotation speed of the prime mover is low and the maximum displacement volume is large. 2. In the travel control device according to claim 1, the hydraulic pump discharge flow rate at the maximum rotational speed of the prime mover in the first operation mode and the second
A travel control device for a wheeled hydraulic excavator, characterized in that the maximum displacement volume is set so that the hydraulic pump discharge flow rate at the maximum rotational speed of the prime mover in the operation mode is set to be substantially the same.