Method of operating a road roller

Abstract: The invention relates to a method for operating a hydraulically driven road roller, primarily for compacting bitumen, with which repeated passes are made over a bitumen coating and in which the roller's speed, acceleration, retardation and direction of travel, forward or in reverse, are selected with an operating lever (1) which, via a control panel (8), electrically acts on hydraulic valves (10, 11, 13) controlling a servo (14) which acts on a hydraulic pump (15) driving the roller's propulsion motors, the operating lever being moveable from a neutral position to full lever deflection and equipped with a forward/reverse switch (2) for selecting the roller's driving direction, and the roller's speed decreases at a programmed retardation rate, when this switch is actuated, until the roller stops, followed by acceleration at a programmed rate to a programmed driving speed in the opposite direction, the roller being brought to a standstill at the maximum permissible retardation rate when the lever is pulled back.

Description: The present invention relates to a method of operating road rollers, primarily bitumen rollers, by means of an operating lever, at an adjustable maximum speed achieved with adjustable acceleration and with which the forward or reverse driving direction is selected with a switch arranged so the roller is automatically brought to a standstill, at an adjustable retardation rate, when the driving direction is switched from forward to reverse, whereupon the driving direction reverses, and the speed automatically increases at the preset acceleration rate until the preset maximum speed is reached. The corresponding procedure is employed for changing roller from reverse to forward drive. The operating lever is moveable from a neutral position to a position for maximum speed, and the change in direction - forward/reverse - is selected with the switch. When necessary, the roller can be stopped by moving the lever to the neutral position. After a 20 to 100 metre stretch of road has been coated with bitumen, a bitumen roller drives back and forth over the coating 2 to 8 times. This procedure requires frequent changes in the roller's driving direction. Here, maintaining an even speed plus braking and accelerating at slow rates are essential to satisfactory compaction. Rapid retardation and acceleration rates increase the risk of bitumen shearing with persistent cracks and impressions in the bitumen as a result. As is previously known (see document US-A-3 412 659), construction vehicles are equipped with operating levers, to control a vehicle's steering to the right or to the left, the lever being equipped with a switch for selecting steering to the right or to the left, and the lever operates within a deflection range in which lever deflection is proportional to the vehicle's speed. The change from forward to reverse is made with a switch integrated into the lever. These prior art operating levers depend on the vehicle operator's judgement and skill, and the vehicle's acceleration, retardation and maximum speed depend on the speed at which the lever is moved to its maximum deflection. In bitumen rolling, it is especially important, as previously noted, for the road roller to accelerate and brake at slow rates and at an even speed. The driving speed of the roller must also be kept constant at a rate selected for the operation to yield satisfactory compaction. The object of the present invention is to achieve a method for operating a roller by means of an operating lever which can be moved from a neutral position to a maximum deflection position, the forward or reverse driving direction being set with a switch integrated into the operating lever, the desired acceleration, retardation and maximum speed being easily programmable with pushbuttons on an electronics unit built into the operating lever, the roller accelerating when the operating lever is moved from its neutral position to its maximum deflection position, at a rate proportional to the speed with which the lever is moved forward, until the preset maximum speed is reached. This preset maximum speed is maintained until the forward/reverse switch is actuated. The roller is then automatically brought to a standstill at the preset rate. The roller thereafter accelerates in the opposite direction at the preset rate until the preset maximum speed is attained. The operator can stop the vehicle completely at any time by moving the lever to the neutral position. The vehicle will then come to a halt at the maximum permissible retardation rate, which normally greatly differs from the slower retardation rate produced when the forward/reverse switch is operated. In an emergency situation, the driver can accordingly stop the vehicle quickly, using a natural lever movement, with no need to disable the automatic operation mode first. The electronics unit also incorporates an emergency stop to bring the vehicle to an immediate halt. To prevent vehicle movement if the operating lever is inadvertently actuated, or when the lever is not in the neutral position, the forward/reverse switch must first be moved to an additional, non-locking position for intentional vehicle operation to be achieved. The invention will now be described below with the aid of attached FIGURES in which FIGURE 1 is a block diagram showing the operating lever and the various functions of the electronics unit connected to same, FIGURE 2 is a diagram showing one example of the relationship between operating lever deflection and current, and FIGURE 3 is a diagram showing an example of acceleration/retardation slopes. FIGURE 4 is a diagram of the hydraulics for the roller's propulsion. In FIG. 1, the operating lever 1 is moveable between a neutral position 0 and a maximum deflection position MAX. A forward/reverse switch 2, offering two fixed positions, i.e. forward (F) and reverse (R), is integrated into the operating lever's handle. The switch is also provided with an additional non-locking position, for each position, which must first be selected when the lever is moved from its neutral position before either forward or reverse drive can be selected. This is to prevent the vehicle from moving if the operating lever is inadvertently actuated. The switch 2 determines which of the hydraulic valves, 10, 11 (FIG. 4), is to supply hydraulic pressure to set the hydraulic valve 13 which, in turn, allows the passage of fluid to operate the pump servo 14. When the operating lever 1 is moved forward, current to the valve 10, 11 increases according to a time slope. The setting of the valve 10, 11 and the fluid pressure after them cause an increase in proportion to the strength of the current. The valve 13 is set, and the fluid pressure then acts on the servo 14 which sets the hydraulic pump 15. Increased pressure increases the angle of the pump which increases its flow of fluid to the roller's propulsion motors which, accordingly, increase the roller's speed. The driving speed, which is adjustable from 2 km/h up the roller's maximum speed, is adjusted with the control buttons 3 on the electronics unit 6, i.e. current can be adjusted from 0.6 to 1.2 Ampere. The MEMO button 7 is used to program the driving speed. When the vehicle reaches the desired driving speed, activation of the MEMO button 7 stores the current speed in a memory. This memory is activated when the LIMITER switch 4 is switched during roller operation to the ON position, causing the roller to assume the programmed speed when the operating lever is fully deflected. If the switch 4 is in the OFF position, however, full lever deflection causes the roller to operate at its maximum speed. If the operator switches from the OFF to the ON position while the roller is in motion, the roller will be retarded according to the preset slope at a speed proportional to lever deflection and the stored driving speed. The corresponding events will occur if the operator switches from the ON to the OFF position while the roller is in motion, i.e. the roller will accelerate according to the preset slope at a speed proportional to lever deflection. The rate of acceleration/retardation (slope) can be increased or reduced with the 5+ and 5- buttons respectively. The rate is shown on a display 12 if the display has been set to mode A with the button 6. This rate determines how rapidly current to valve 10, 11 increases or decreases. When the display is not in mode A but the switch is in the ON position, an L is shown on the display, indicating that the programmed driving speed has been enabled. FIGURE 2 is a diagram showing how current to the valves 10, 11 increases with increasing lever deflection. The upper curve represents the increase in current when the switch 4 is in the OFF position, and the lower curve is an example of the slope when the switch is in the ON position. When the lever is fully deflected, current can be limited between 0.6 and 1.2 A. FIGURE 3 is a diagram showing the increase in current over time, i.e. slopes for acceleration/retardation, the upper curve representing the fastest possible rate for acceleration/retardation and the lower curve showing a restricted rate. FIGURE 4 is a hydraulic circuit diagram of the roller's propulsion in which the hydraulic valve 10 acts on valve 13 for forward drive and on valve 11 for reverse drive. Hydraulic pressure from the valve 13 acts on the servo 14 which sets the pump 15 as previously noted. The invention is not restricted to the above-described version shown in the FIGURES but can be modified within the scope of the following patent claims. The technique is therefore also applicable to other types of pump control and servos, e.g. a proportional valve on a mechanical servo or the like. Naturally, controls of other types than those noted above, e.g. handles, knobs or potentiometers, can also be used.

Claims: A method of operating a hydraulically driven road roller, primarily for compacting bitumen, with which repeated passes are made over a bitumen coating and in which the roller's speed, acceleration, retardation and direction of travel, forward or in reverse, are selected with an operating lever (1) which, via a control panel (8), electrically acts on hydraulic valves (10, 11, 13) controlling a servo (14) which acts on a hydraulic pump (15) which drives the roller's propulsion motors, characterised in that the operating lever (1) can be moved from a neutral position to a position with maximum lever deflection; a forward/reverse switch (2) for selecting the driving direction is integrated into the operating lever's handle section; the roller accelerates at a speed proportional to lever deflection when the lever (1) is moved from the neutral position to maximum lever deflection; when the roller is driven forward at a programmed driving speed, with the operating lever in maximum deflection and the forward/reverse switch (2) in the reverse position, the roller is brought to a standstill at a programmed rate and then accelerates at a programmed rate to the programmed speed in the opposite driving direction; the roller responds as above, when the roller is driven forward, without maximum lever deflection and with the forward/reverse switch (2) in the reverse position, but the speed it achieves in relation to the programmed driving speed is limited in proportion to lever deflection; the roller operator can stop the roller at any time by moving the operating lever (1) to the neutral position, bringing the roller to a standstill at the maximum permissible retardation rate; the operating lever's various functions are controlled by and adjusted with pushbuttons (3, 4, 5, 6, 7) on a control panel (8) equipped with the requisite electronics and a display (12) showing programmed rates and the current speed. A method according to claim 1, characterised in that each of the forward/reverse switch's (2) two positions has an additional, non-locking contact position which must first be manually engaged when the operating lever (1) is moved from its neutral position for forward drive of the roller to start. A method according to claim 1, characterised in that a control switch (4) has two positions, ON and OFF, in which the ON position permits the setting of the driving speed with two symbol-designated buttons (3), one marked with a hare for increasing speed and the other marked with a tortoise for reducing speed, the speed being set with them can be stored in a memory with a MEMO button (7). A method according to claims 1 and 3, characterised in that the ON position of control switch (4) causes the programmed driving speed to be achieved when the operating lever (1) is fully deflected, and the OFF position enables the roller operator to drive the roller at up to its maximum speed without being affected by programmed rates, the letter L being shown in the display (12) to indicate that the ON position has been enabled. A method according to claim 1, characterised in that a rate for roller acceleration or retardation can be set with a button (6), whereby an increase or decrease in acceleration/retardation is made with two buttons (5+ and 5-), the rates being shown on a display (12). A method according to claim 2, characterised in that the forward/ reverse switch (2) is located on the control panel (8) or in its vicinity. A method according to claim 1, characterised in that a switch in the cab must be actuated by the driver's weight before the operating lever can be activated.

Inventors: SAMUELSSON SVEN-ERIK, SAMUELSSON, SVEN-ERIK
Applicants: SVEDALA COMPACTION EQUIPMENT A, SVEDALA COMPACTION EQUIPMENT AKTIEBOLAG
Application year: 1995
Main classification: E01C19
IPC codes: B60K31, E01C19, B62D1