METHOD OF PREVENTING SLIP OF A LOADING VEHICLE

Abstract: A method of preventing slip of the wheeled loader intended for reducing slip during the operation using the wheeled loader and for preventing lowering of operability resulting from slip. Said slip preventing method comprises such steps as detecting slip on the basis of the difference between and variations in the number of revolutions of a pair of driving wheels on the right and left sides and controlling a clutch pressure so that the clutch may be engaged partially upon detection of slip.

Description: TECHNICAL FIELD OF THE INVENTION This invention relates to a method for preventing wheel slippage of the drive wheels of a loading vehicle and more particularly to a method for preventing wheel slippage of the drive wheels of a loading vehicle, whereby the amount of slip of the vehicle in operation can be reduced. A method of this kind is disclosed by the JP-A 63 189 535. According to this conventional method, a micro computer judges that slip is caused at the driving wheels of the loading vehicle, when the difference of the rotational speed of the driving wheels exceeds a given value. At the same time, a micro computer calculates a horizontal component and a vertical component of the excavation resistance to be exerted on a bucket during excavation works. The higher the horizontal component of the resistance, the more traction is needed. On the other hand, the vertical component of the excavation resistance improves the traction, since the vertical component increases the weight of the loading vehicle. The micro computer calculates from the before-mentioned values a critical traction coefficient and derives a corresponding pressure control signal supplied to a traction control portion. BACKGROUND ART OF THE INVENTION A prior art method of preventing a wheel loader from slipping is disclosed in the Japanese Laid-Open Patent Application No. SHO 64-4013. According to this prior art method of preventing the loader from slipping, a slip controlling device conducts processing of information on the basis of an input signal from a detector for detecting the load on an implement, and outputs a command signal for controlling the implement and a command signal for controlling the force of traction upon generation of slip of the vehicle so that the output signals permit the implement to effect compensating operation so as to reduce the loading thereon. Besides the above-mentioned prior art method, in general, methods of controlling the output of the engine or controlling the brake when the wheel loader is slipping could be envisaged. Out of the above-mentioned prior art methods, according to the former method, since the load on the implement is automatically reduced when the vehicle is slipping, that is, no-load condition is reached, so that a situation against the intention of the operator will occur if this method is effected. Further, according to the latter method in case wheel loader slips during excavating operation, even if the operator detects the occurrence of slip and takes procedures to control it, it takes about 0.5 to 1.0 second until the slip is restrained. Therefore, in case of the method of controlling the output of the engine, the response is slow, and in case of the method of controlling the brake, the braking action tends to be delayed, so that both the methods have been ineffective. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances in the prior art, and has for its object to provide a method of preventing a wheel loader from slipping so that the amount of slip of the loader during excavating operation using it can be reduced, and also the decline in the operational efficiency due to the slip can be prevented. To achieve the above-mentioned object, the method according to the invention is characterised by the features of claim 1. Further, according to the present invention, there is provided a method of preventing a wheel loader from slipping as set forth in the above-mentioned aspect, wherein said detection of slip is conducted when the force of traction exceeds a preset value. Still further, according to the present invention, there is provided a method of preventing a wheel loader from slipping as set forth in the above-mentioned aspect, wherein said clutch pressure control is released when the implement is in operation and the fluid pressure in the bottom chamber of a boom cylinder is 100 kg/cm 2 or over, or when the number of revolutions of the engine is 1,300 r.p.m or under. Thus, according to the method of preventing a wheel loader from slipping, upon detection of the occurrence of slip from the difference in the number of revolutions between the pair of left and right drive wheels, the clutch pressure is controlled immediately so as to eliminate the slipping condition without having to reduce the load on the implement. Further, the clutch pressure control is released by conducting such operation of the implement as the slip is eliminated when the implement is in operation, thereby returning to the normal operating condition quickly. An effect obtainable by the present invention is that upon generation of slip of a wheel loader in operation the clutch pressure is controlled immediately so that this slipping condition can be eliminated without having to reduce the load on the implement, thereby enabling the amount of slip of the wheel loader in excavating operation to be reduced, and also the operation as intended by the operator to be conducted always without the need for reducing the load on the implement when the wheel loader is slipping. Another effect of the present invention is that the above-mentioned detection of generation of slip can be conducted quickly even when the wheel loader is running on uneven land. The above-mentioned and other objects, aspects and advantages of the present invention will become apparent to those skilled in the art by making reference to the following detailed description and the accompanying drawings in which a preferred embodiment incorporating the principles of the present invention is shown by way of example only. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flowchart showing steps, in the method of preventing a wheel loader from slipping according to the present invention, Fig. 2 shows control in clutch pressure; Fig. 3 is a diagram showing change in the number of revolutions of a pair of left and right drive wheels, respectively; Fig. 4 is a diagram showing change in the force of traction of the wheel loader; Fig. 5 is a diagram showing torque converter characteristics; and Fig. 6 is a schematic, constructional explanatory view showing the wheel loader and sensors. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. In Fig. 6, reference numeral 1 denotes a wheel loader, 2 an engine rotational speed detector for detecting the number of revolutions of an engine 3 of the loader, 4 a speed position detector for detecting the speed change position of a speed change gear 5, 6 an output shaft rotational speed detector for detecting the number of revolutions of the output shaft of the speed change gear 5, 7 an implement operating position detector such as a limit switch, etc. for detecting the operating position of an implement operating device 8, and 9a, 9b left and right drive wheel rotational speed detector for detecting the number of revolutions of left and right drive wheels 10a, 10b, respectively. Reference numeral 11 indicates a CPU (central processing unit) adapted to receive a detection signal from each of the above-mentioned detectors 2, 4, 6, 7, 9a and 9b as input thereof and transmit a predetermined control signal as output thereof to a clutch control unit 12. One embodiment of the method of preventing the above-mentioned wheel loader from slipping will be described according to the flowchart as shown in Fig. 1. In the first place, a speed change position of the wheel loader 1 which is running is detected by the speed change position detector 4, and it is discriminated by the CPU 11 whether the speed change position is the forward first speed (F1). (STEP 1) When it has been discriminated at STEP 1 that the speed change position is the forward first speed, the force of traction at that time is computed by CPU 11 on the basis of the detection signals transmitted by the speed change position detector 4 and the output shaft rotational speed detector 6, and then a comparison is made whether or not the force of traction is more than a reference value which is, for example, 25 tons. (STEP 2) As a result, if it is more than 25 tons, a horizontal resistance is then computed by CPU 11 on the basis of both the above-mentioned signals, and then a comparison is made on whether or not the horizontal resistance is more than a reference value which is, for example, 25 tons (STEP 3) As a result, if it is more than 25 tons, slip of the drive wheels 10a, 10b is sensed. (STEP 4) It is discriminated that the wheel loader is slipping when the average running speed of the loader is more than 1 km/hour and the speed ratio of drive wheels 10a and 10b is more than 2, or the differentiated value of rotational speed difference a km/hour between the left and right drive wheels 10a and 10b is more than |0.2 g|. At each of the above-mentioned steps 1 - 4, if the result of discrimination is NO, then the system is returned to STEP 1. If it is detected at STEP 4 that the wheel loader 1 is slipping, then a control signal for controlling half-clutch is outputted by the CPU 11 to the clutch control unit so that the clutch pressure is controlled to allow the clutch to be put automatically in half-clutch condition. (STEP 5) Subsequently, the operator will reduce the amount of depression of the accelerator pedal by his foot to reduce the number of revolutions of the engine and compare it with 1,300 r.p.m, for example (STEP 6), and release the above-mentioned clutch pressure control if the number of revolutions of the engine becomes less than 1,300 r.p.m. (step 7) In case at the above-mentioned STEP 6 the number of revolutions of the engine does not drop, and is 1,300 r.p.m or more, then the operator operates the implement (STEP 8), and release the clutch pressure control when the fluid pressure in the bottom side chamber of the boom cylinder reaches 100 kg/cm 2 or more, for example. When a predetermined load is applied to the implement, the drive wheels 10a, 10b, which are front wheels, are subjected to a vertical load, so that even in case the number of revolutions of the engine is more than 1,300 r.p.m the slip of the drive wheels is eliminated. In this condition, the above-mentioned clutch pressure control is released. (STEP 7) In case the load on the implement is low at STEP 8, then the system is returned to STEP 5. The clutch pressure control at the above-mentioned STEP 5 is made as shown in Fig. 2. When it is detected that the wheel loader is slipping, the clutch pressure will drop to a value in the range of 25 to 3 kg/cm 2 so that the clutch is put in half-clutch condition, whilst upon release of the clutch pressure control the clutch pressure will be restored to the original value of 25 kg/cm 2 in 0.4 seconds. The conditions required for releasing this clutch pressure control are the operation of the implement and the drop in the number of revolutions of the engine as mentioned above. Further, in the above-mentioned embodiment, it is sometimes impossible for wheel loaders adapted to be driven mainly on uneven land to detect quickly the occurrence of slip from the difference in the number of revolutions between the left and right drive wheels 10a and 10b. This is due to the fact that since both the drive wheels 10a and 10b trace the road surface when the loader runs on the stone, etc. during its running on uneven land, a pseudo-slip signal is generated so that it takes a longer time to detect the occurrence of slip, that is, a time delay for confirmation of the slip occurs. However, in the ordinary earth excavating operations by a wheel loader, since the bucket of the loader is pressed against the ground surface just before the excavation, there is no possibility for the loader to run on to stone, etc. after commencement of the excavation. Therefore, only when the resistance to excavation (that is, force of traction) exceeds a preset value, the detection of slip of the drive wheels is conducted. Fig. 3 shows change in the number of revolutions of the left and right drive wheels relative to time. The difference in the number of revolutions between the drive wheels varies with road surface condition, and there are regions where a big difference in the number of revolutions between the drive wheels occurs, as indicated by reference characters A and B. Whilst, Fig. 4 shows change in the force of traction relative to time, which corresponds to Fig. 3. In this drawing, reference character C denotes a preset value. In both Figs. 3 and 4, it is discriminated that the wheel loader slips in the region B where a big difference in the number of revolutions between the drive wheels occurs when the force of traction exceeds the preset value C. That is to say; it is discriminated that the loader is slipping when the force of traction is more than the preset value and | the difference in the number of revolutions between the left and right drive wheels| / dt becomes more than 0.2 g. Fig. 5 shows the characteristics of a torque converter for use in a wheel loader. In this drawing, reference character "a" denotes torque ratio Tr(e), "b" primary torque coefficient Pr(e), and "c" efficiency. Speed ratio "e" is the ratio of the number of output shafts of the torque converter to the number of revolutions of the engine. The primary torque coefficient Pr(e) is the absorbed torque when the number of revolutions of the input shaft of the torque converter is 1,000 rpm while the speed ratio is kept constant, the absorbed torque being proportional to the square of the number of revolutions when the speed is kept constant. The step for calculating the traction characteristics in the CPO will be described below. (1) To input the number of revolutions Ne of the engine and the number of revolutions Nt of output shafts of the torque converter. (2) To calculate the speed ratio e = Nt / Ne from the values of Ne and Nt. (3) To find the torque ratio Tr(e) and the primary torque coefficient (Pr) from the graph shown in Fig. 5. (4) To calculate the absorbed torque according to the following equation. Te = Pr(e) x ( Ne 1000 ) 2 (5) To calculate the output torque of the torque converter according to the following equation. T T/C = Tr(e) x Te (6) To calculate the rotational speed V of the drive wheel and the force of traction Fve according to the following equation. V = Nt/Fg Fve = Fg x T T/C - I dω T/C dt wherein, Fg is the gear ratio, and I is the inertia of the power line.

Claims: A method for preventing wheel slippage of the drive wheels of a loading vehicle comprising the steps of: detecting the occurrence of wheel slippage, and controlling a clutch pressure for establishing a half-clutch condition upon detection of wheel slippage, the occurrence of wheel slippage being detected in accordance with the difference of rotational speeds at left and right drive wheels and variation thereof when exceeding a given difference criterion or a given variation criterion, respectively. A method as claimed in claim 1, characterized in that said detection of slip is conducted when the force of traction exceeds a preset value. A method as claimed in claim 1, characterized in that the clutch pressure control is released when the number of revolutions of the engine is 1,300 r.p.m or under, or when the implement is in operation and the fluid pressure in the bottom side chamber of a boom cylinder is 100 kg/cm 2 or over.

Inventors: MORI MASAYUKI TECHNICAL INSTIT, TAKASUGI SHINJI, MORI, MASAYUKI TECHNICAL INSTITUTE OF KABUSHIKI, TAKASUGI, SHINJI, TAKASUGI, SHINJI TECHNICAL INSTITUTE OF KABUSHIKI
Applicants: KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Application year: 1990
Main classification: F16D48
IPC codes: B60K28, F16H59, F16D48