The present invention relates to a unit and a method for controlling a construction vehicle mainly for loading work such as a wheel loader, etc.

A conventional control system of a unit for controlling a wheel loader mainly for loading work is illustrated in Fig. 7. With reference to the figure, the engine E is controlled by way of a governor gv through a linkage li by operating an accelerating pedal ap. The output of the engine E is transmitted to a torque converter T and a gear G and the output transmitted to the gear G drives a variable capacity hydraulic pump P. The variable capacity hydraulic pump P controls a variable capacity hydraulic pump control valve pc by way of a servo cylinder SC so as to control the amount of oil under pressure. When a bucket operation pilot valve AL is operated to actuate a bucket main operation valve AV to thereby turn a bucket A by way of a bucket cylinder AC, so that the bucket A tilts rearward or dumps forward. When a boom operation pilot valve BL is operated to actuate a boom main operation valve BV to thereby turn a boom B by way of a boom cylinder BC, the boom B lifts upward or lowers downward. Designated at PP is a pilot pump.

The pressure versus flow rate characteristic diagram of the variable capacity hydraulic pump in the conventional control system of a loading machine is illustrated in Fig. 8. As is obvious from the figure, the hydraulic pump torque at high pressure can be limited to a necessary and sufficient amount by varying the flow rate Q according to the pump discharge hydraulic pressure P corresponding to the maximum hydraulic pump torque T_X1 or T_X2. However, in a vehicle in which the output of the engine E is distributed to the hydraulic pump PV and the power transmission device of the driving mechanism (torque converter T) as illustrated in Figs. 7 and 8, there was a serious problem that the reduced amount of power consumed by the hydraulic pump PV was absorbed by the driving mechanism so that the driving power was increased by the reduced amount and the ratio of the output to the driving mechanism relative to that to the loading machine was increased, which deteriorated the operability of a vehicle for earth-sand scoop-up working, etc. as illustrated in Fig. 9. That is, referring to Figs. 8 and 9;

• (1) when the hydraulic torque characteristic of the loading machine pump is reduced from T_X1 to T_X2, contrariwise the absorption torque of the torque converter is increased from T_tx1 to T_tx2, so that the distribution between the hydraulic output and the driving output is inverted.
• (2) When the hydraulic pressure in the loading machine gets high, the hydraulic pump torques are decreased from T_X1 and T_X2 corresponding to the points X₁ and X₂ to T_Y corresponding to the point Y, so that the absorption torques of the torque converter are increased from T_tx1 and T_tx2 to T_ty and the driving force becomes excessive.

It is the object of the present invention to solve the aforementioned problems.

To achieve the above object, the present invention provides a unit for controlling a vehicle for loading operation which carries a variable capacity hydraulic pump for operating a loading machine and a torque converter for driving itself, the control unit comprising an engine provided with an electronically controlled governor capable of selecting stepwise the output characteristic of the engine, electromagnetic changeover valves for setting stepwise the maximum capacity and the output torque of the variable capacity hydraulic pump, a pump capacity detector, an hydraulic pressure detector, a switch for selecting the output characteristics of the engine and the variable capacity hydraulic pump (hereinafter referred to M mode control switch), an electronic governor controller for controlling engine output characteristics and a variable capacity pump controller for selectively setting the maximum capacity and the output torque characteristics of the variable capacity hydraulic pump, so as to control the amounts and distribution of the hydraulic output and the driving output by selecting the M mode control switch for the improvement of operability. Furthermore, the control unit is equipped with a selective switch capable of selecting stepwise the cut-off pressure of the discharge flow of the variable capacity pump (hereinafter referred to L mode control switch). As a result, it is possible to select the distribution of power to the loading machine and driving mechanism by a matrix, i.e., the combination of the steps of the L mode control switch and the steps of the M mode control switch.

Fig. 1 is a view showing the control system of a vehicle for loading work according to an embodiment of the present invention, Fig. 2 is a view for explaining the pressure versus flow rate characteristic curve of a variable capacity pump PV, Figs. 3(a), 3(b) and 3(c) are diagrams for explaining the distributions of power by a combination of M₁ mode and L₁ mode, by a combination of M₂ mode and L₂ mode and by a combination of M₃ mode and L₃ mode respectively, Figs. 4(a) and 4(b) respectively shows flowcharts of the control method of loading machine according to the present invention, Fig. 5 is a diagram for explaining a control method for reducing the setting of an engine torque in response to a hydraulic torque, Figs 6(a) and 6(b) are views for explaining the power distribution matrix of the loading machine hydraulic pressure L and the driving force M and Figs. 7, 8 and 9 are diagrams for explaining a conventional control unit.

An embodiment of the present invention will be described with reference to drawings.

Fig. 1 is a block diagram showing the control system of a vehicle for loading work according to an embodiment of present invention wherein elements which operate in the same way as the conventional system as explained in Fig. 7 are denoted at the same numerals.

An engine E has an electronically controlled governor 10 which is mounted thereon and is capable of optionally selecting output characteristics stepwise and an electronic governor controller 11 is provided for controlling the electronically controlled governor 10 in response to input signals (1) to (4) set forth hereunder.

• (1) a signal representing an engine speed N_E issued by a rotary sensor 12 provided on the gear G
• (2) a control signal of the variable capacity pump PV issued by a variable capacity pump controller 41 (the electronic governor controller 11 receives the control signal as an input signal and issues information signals to the variable capacity pump controller 41)
• (3) a stepping amount signal θ_A issued by an accelerator pedal 14
• (4) M mode selection signal issued by the M mode control switch 42

The variable capacity pump controller 41 receives signals from and sends signals to the electronic governor controller 11 and outputs a signal to an electromagnetic pilot valve 46 to thereby selectively switch the electromagnetic pilot valve 46.

• (5) M mode selection signals issued by the M mode control switch 42
• (6) L mode selection signals issued by the L mode control switch 43
• (7) hydraulic pressure signal issued by a pump capacity detector 44 provided at the discharge side of the variable capacity pump PV for detecting the hydraulic pressure
• (8) a signal representing the discharged amount of oil under pressure issued by a pump capacity detector 45 for detecting the capacity of the variable capacity pump PV

An operation of the embodiment will be described hereinafter. (A) Fig. 2 shows the hydraulic pressure versus flow rate characteristic curves of the variable capacity pump PV according to an embodiment of the present invention. It is possible to set stepwise a plurality of M modes such as M1 mode, M2 mode and M3 mode by operating the M mode control switch 42 thereby to set the torque characteristics of the engine E as indicated by the engine torque curves at M1 mode, M2 mode and M3 mode by way of the electronically controlled governor 10, and it is possible to set stepwise the maximum hydraulic pressure of the loading machine in a plurality of L modes such as L1 mode, L2 mode and L3 mode by selectively setting the torque characteristic of the engine E in accordance with the setting of the M mode control switch 42 among those indicated by the engine torque curves of M1, M2 and M3 modes illustrated respectively in Figs. 3(a), 3(b) and 3(c) by way of the electronically controlled governor 10 and by operating the L mode control switch 43.

As a result, for example, in cases that M1 mode is combined with L1 mode, M2 mode is combined with L2 mode and L3 mode is combined with L3 mode respectively, the maximum torque points are B₁, B₂ and B₃, the hydraulic torques at the maximum torque points are T_B1, T_B2 and T_B3 respectively and the absorption torque points of the torque converters at the maximum torque points are B₁', B₂' and B₃' respectively as illustrated in Figs. 3(a), 3(b) and 3(c), so that it is possible to conform the order in strength of hydraulic torques, i.e., T_B1 > T_B2 > T_B3 to the order in strength of driving forces (absorption torques of the torque converter), i. e., (torque at B₁') > (torque at B₂') > (torque at B₃'). (B) When the pressure of the variable capacity pump PV is high (more than P_A according to this embodiment) and the hydraulic torque is not proportional to the hydraulic pressure as illustrated in Fig. 2, the maximum engine speeds of the engine E (the regulation of an all-speed governor) are changed from N_C1, N_C2 and N_C3 to N_C1', N_C2' and N_C3' by the electronically controlled governor 10 so as to reduce the variation of the absorption torque of the torque converter as illustrated in Figs. 3(a), 3(b) and 3(c). For example, in the embodiment illustrated in Fig. 2 and Figs. 3(a), 3(b) and 3(c), the maximum engine speeds are changed when the hydraulic torques of the hydraulic pressure P_A are around T_A1, T_A2 and T_A3, and the absorption torques of the torque converter are A₁', A₂ 'and A₃' respectively when the hydraulic torques are T_A1, T_A2 and T_A3. The absorption torques of the torque converter at the points A₄, A₅, A₆, B₄, B₅ and B₆ on a curve having a same hydraulic pressure in Fig. 2 are respectively changed to those at the points A₄' A₅' A₆', B₄', B₅' and B₆' in Figs. 3(a), 3(b) and 3(c). In this way, it is possible to suppress the variation of the absorption torque of the torque converter as represented by B₄', B₅' and B₆' in Figs. 3(a), 3(b) and 3(c) even if the hydraulic torque is varied when the pressure of the variable capacity hydraulic pump PV is high, so that it is possible to prevent the excessive increase of driving force in earth-sand scoop-up work.

An operation of the control method will be described with reference to the flowcharts illustrated in Figs. 4(a) and 4(b). Fig. 4(a) shows a control flowchart of the electronically controlled governor 10 for reducing the set maximum engine speed when the loading machine hydraulic pressure is more than P_A1 (or P_A2 or P_A3 ), the capacity of the pump is cut off and the hydraulic torques are under T_A1 (or T_A2 or T_A3), while Fig. 4(b) shows a control flowchart for controlling the target engine speed according to the loading machine hydraulic pressure when the hydraulic pressure of the loading machine is more than P_B1 (or P_B2 or P_B3 ),the capacity of the pump is cut off and the hydraulic torques are under T_B1 (or T_B2 or T_B3).

The same effect can be obtained by reducing the engine torque in accordance with the hydraulic torque of the variable capacity hydraulic pump PV.

It will be described with reference to Fig. 5. When the discharge hydraulic pressure of the pump is more than P_A and the hydraulic torque is reduced under T_A1, for example, when the engine torque is reduced by k(T_A1 - T_B4) in case of the hydraulic torque T_B4 ( = T_A4) of the point B₄ in Fig. 2, the point A₄' can be moved to the point B₄'. (C) Since the variation of absorption torque of the torque converter under the high hydraulic pressure of the loading machine is reduced, the order in strength of the hydraulic torque is conformed to that of the driving torque by way of the engine output selection means and the cut-off pressure of the discharged flow rate of the variable capacity pump PV is stepwise selectable, it is possible to select the distribution of power by a matrix, i.e., the combination of the hydraulic pressures of the loading machine L1, L2 and L3 which are selected by way of loading machine hydraulic pressure selection means and the driving forces M1, M2 and M3 which are stably selected by way of engine output selection means as illustrated in Fig. 6(a). Fig. 6(b) is a view for explaining the operation of the loading machine hydraulic pressure L and the driving force M.

With the arrangement as set forth above in detail, even if the hydraulic torque varies when the pressure of the variable capacity hydraulic pump is high the fluctuation range of absorption torque of the torque converter can be suppressed, thereby preventing the excessive increase of the driving force in earth-sand scoop-up work and enabling to perform the scoop-up working with ease and efficiency.

The present invention has also a great effect that it can correspond to various working conditions with ease since the distribution of power between the loading machine and driving mechanism can be selected by matrix, i.e., a combination of two variables.