DK147968B - HYDROSTATIC AID DRIVE SYSTEM FOR A VEHICLE - Google Patents

Description

in 147958

The invention relates to a hydrostatic auxiliary drive system for a vehicle, the system having two auxiliary drive wheels and hydraulically actuated couplings, mutually interposed hydraulic motors, a pump and a directional control valve, in which system the couplings exist between the auxiliary drive wheels and the hydraulic motors in dependence on that between the pump and the hydraulic motors prevailing pressure can be entered and exited and where the vehicle has a main transmission.

In this auxiliary drive system for a vehicle known from United States Patent No. 3,865,207, and designed for a forklift stacker, the pump driving the hydraulic motors is driven around with the engine rpm so that its delivery rate varies depending on the engine rpm. The amount of delivery is thus not dependent on the pressure prevailing in the system, and since the pump always delivers, even with the standing vehicle and the engine running, there is still a pressure in the hydraulic motors, although no auxiliary thrust is required. This pressure must be reduced, namely via a pressure control valve. In the immediate absence of the speed of the vehicle auxiliary drive system, as a rule of the front wheels, and. the speed of the drive motor can only be achieved for the vehicle auxiliary drive system with a low speed range and thus a limited operating final speed.

This may well be fully sufficient for fork stacker because with the known device they can only operate slowly. However, this scope is too small for use with other vehicles, especially in fast-moving vehicles.

The object of the invention is to provide a vehicle with a reliable auxiliary drive system which at all times is accurately and simply adapted to the operating conditions of the main transmission and which according to the given conditions are adjusted accordingly.

This is achieved by the hydrostatic auxiliary drive system according to the invention, which is characterized in that between the main transmission and the directional control valve there is a control device which records the ratio of the main transmission speed to the hydraulic motors and which regulates the delivery rate of the pump depending on the this relationship. This new and very simple and very reliable design ensures that the auxiliary drive system of the vehicle can be connected to the main transmission at any maximum speed of the vehicle in question, whereby the pump only builds up the pressure required for that particular thrust as its delivery volume is controlled in dependence on the parameters provided to the control device.

When using a variable-performance pump and reversible direction of rotation, the direction of rotation of the vehicle auxiliary drive system can be reversed in a very simple and accurate way without the need for additional valves.

A hydraulic connection between a tumble disc included in the pump and directional control valve ensures that the conditions of the vehicle auxiliary drive system in terms of driving speed and direction are adapted to the driving conditions of the main transmission.

The features of claim 4 provide a synchronization between the vehicle auxiliary drive system and the main transmission, as the control device, when the direction of travel of the vehicle is changed, gives a signal to the directional control valve in order to effect a reversal of the direction of rotation of the vehicle through the pivotal turn of the vehicle.

By means of the solenoid valves interposed between the pump and the couplings, both for forward travel and also for reverse travel according to claims 5 and 6, it is possible at all times to prevent a pressure build-up in the couplings, the solenoid valves being moved from the position where they allow flow of hydraulic oil , to the position where they block the flow and thereby the auxiliary drive wheels are cut off from the vehicle auxiliary drive system.

Conveniently, the solenoid valves of claims 7-9 are connected to the associated power circuit and control device in such a way that they are first pushed into the position where they release the flow and thus also enable the auxiliary drive wheels to be engaged when the power current in the main transmission is closed. As a result, there is always a temporal synchronization between the auxiliary drive wheels and the wheels driven from the main transmission, which firstly prevent them from turning in opposite directions when the vehicle's driving direction e.g. gets changed very quickly to bring it out of a swamp hole. In addition, in case of use, the vehicle's auxiliary drive system is not ensured until the wheels driven by the main transmission are already turning and possibly already buried in the ground.

According to Claim 10, for adjusting the time of entry into force of the vehicle auxiliary drive system and thus also of the permissible gap in the rear wheels, a control switch is provided with which a driving speed of the hydraulic motors can be set below or above the speed of the rear wheels derived from the main transmission according to the given operating conditions.

The dividing / joining valve proposed according to claim 11 and its connection with the motors and the pump continuously provide a supply of the hydraulic motors with the amount of pressure oil which, due to the operating conditions of the vehicle, e.g. when cornering, it is necessary to achieve the optimum drag effect of the auxiliary drive wheels.

At the throttle connection according to claim 12, after the split / feed valve in the two forward / return feed lines, a partial differential lock is obtained which reduces the wear on the tires during the curve run. In addition, the throttle opening acts as an equalizer for the pressure between the hydraulic motors so that the dividing / joining valve can resume its un-biased centered divider position when a curve is traversed so that it re-transmits idling wheels during the curve run. a torque. This prevents the split / merging valve from remaining in the position in which it throttles the flow path to the hydraulic motors.

The use of pressure lines leading from the electrically serviceable solenoid valves to the couplings, according to claim 13, enables the couplings to be inserted as soon as the solenoid valves have established the connection to the supply / return lines.

In the use of the shuttle valves specified in claim 14, the pressure oil is simply fed in the desired direction to the hydraulic motors during a low consumption of valves.

The invention will be explained in more detail below with reference to the drawing, in which. FIG. 1a is a perspective view of the right side of the front portion of a motorway grader according to the invention; FIG. 1b, in perspective, the right side of the rear of the gradient of FIG. 1a, FIG. 2 is a side view of the left front wheel and the hydraulic motor for operating it; FIG. 3 shows the hydraulic motor in the direction of arrows 3-3 in FIG. 2; FIG. 4 is a sectional view taken along line 4-4 of FIG. 3 and showing a conventional digital magnetic sensor for sensing the left front wheel motor.

FIG. 5 is a perspective view showing a portion of the differential in the main drive transmission with a conventional digital magnetic sensor for sensing the speed of the main drive wheels; and FIG. 6 is a schematic view of the front wheel drive system.

In FIG. 1a and 1b are shown a highway 10 with front and rear frame sections 12 and 14. The front end of the frame section 12 is supported by a right and left front wheel 16 and 18, respectively, and the rear part of the frame section 12 is supported by the rear frame section 14, with which is connected by a pivot joint 20 with substantially vertical axis of rotation about which the frame sections can be pivoted relative to each other by means of a pair of double acting hydraulic cylinders. Part of one of these hydraulic cylinders is shown at 22. The rear frame section 14 is supported by a right and left set of main drive wheels 24 and 26 respectively mounted in bogie-like manner.

A driver platform 28 is located on the rear end of the frame section 12 of a housing 30 and has a plurality of motor grader steering means. The only controls shown are master drive transmission controls including a gear selector rod 32, a direction selector lever 34, and a clutch pedal 36.

The rear frame section 14 carries a motor 40 in a housing 42. To the output shaft at the rear end of the motor 40 is coupled a set of transmission gear wheels 44 which pull an input shaft 46 for a main drive transmission. The principles of the present invention are applicable in vehicles with different types of main drive transmissions. However, as specifically illustrated herein, the invention is well suited for use with an interchangeable planetary gear, so as to achieve eight forward and four backward speeds. The gear unit has a plurality of hydraulically controlled clutches and brakes (Fig. 6) including a main drive clutch 47 which disengages the transmission when the pedal 36 is depressed, a front drive clutch 48 which is actuated when the direction selector lever 34 is moved from neutral to put the drive transmission into a neutral position. selected mode during forward travel, and a reversing drive brake 49 which is actuated when the direction selector is moved from neutral position to reverse the transmission. An example of such transmission is shown in U.S. Patent No. 3,298,252.

The main drive transmission 46 has an output shaft coupled to a differential gear 50, which is again coupled to the rear set of wheels 24,26 by means of respective output drive gears including planetary gears (not shown). As best seen in FIG.

5, a parking brake disc 51 is also coupled to the gear 50, the connection including a shaft 52, on the upper end of which the disc 51 is attached, and on the lower end of which is a sprocket 54, which engages a differential ring gear 56 On the circumference of the disc 51 are a plurality of teeth 58 and a digital magnetic sensor 60 is mounted near the path passed by the teeth 58 and is adapted to emit electrical impulses corresponding to the speed of rotation of the disc 51, which again corresponds to the average rotation speed. of the rear set of drive wheels 24 and 26. The purpose of this sensor 60 is explained in more detail below.

An auxiliary drive system 62 (Fig. 6) for operating the front wheels is adapted to increase the drag effect of the main drive system of the grader 10 and includes a right and a left motor 64 and 66 respectively housed in housings 68.70 (Fig. 1a). which are attached to the rims of the wheels 16 and 18 and which can be selectively engaged so that they are pulled by the motors by means of planetary gears (not shown) after the thrust of normally coupled right and left clutches 72 and 74, respectively (Fig. 6). In FIG. 2-4, it is seen that the left housing 70 has a removable inner member 76 which covers the inner end of a rotor 78 in the engine.

66. A toothed member 80 is attached to the rotor 78 and mounted near the path through the teeth of the member 80, a digital magnetic sensor 82 is provided which is capable of generating an electrical impulse proportional to the rotational speed of the rotor 78. rotor 78. The purpose of this sensor 72 is explained in more detail below.

147968 7

In FIG. 6, it is seen that the front drive auxiliary drive system 62 includes a reversible variable displacement pump 84 having an upper aperture connected to an aperture on the side of a conventional power sharing and junction valve 86 through a return supply line 88. The valve 86 has opposite pages two openings connected to the associated first working openings in the wheel motors 64 and 66 through feed return lines 90 and 92 interconnected by a throttle line 93. Between a lower opening in the pump 84 and a second set of working openings in the motors 64 and 66 are located a branched feed return line 94. It will be seen that a closed hydraulic circuit exists between the pump 84 and the motors 64 and 66 and is connected in parallel with each other.

The pump 84 is a conventional axial piston tape having an angularly adjustable tumbler 96. To this is hinged single-acting hydraulic movement mechanisms 98 and 100, respectively, at a lower and an upper location of the disc. These hydraulic actuators or servomotors are pressurized to move the tumbler from a centered position, as shown to induce pumping in the forward or backward direction in the pump 84 so that the working fluid from line 94 is pressed into line 88 or vice versa.

A remote-controlled control valve 102 is connected to the hydraulic movement mechanisms 98 and 100 and to a pump 104 and includes a valve slider 106 which can be selectively moved to the right and left from the neutral position shown, thereby depressing either the movement mechanism 98 or the mechanism 100. The movement of the valve slider 106 is controlled by a linear electro-hydraulic servo motor 108 having a reciprocating output member 110 which is connected to the valve slider 106. The servo motor 108 is a commercially available device having the property that the output member with respect to direction and magnitude, is displaced in accordance with the direction and magnitude of electrical control signals transmitted to servo motor 108 in a manner as explained below, for automatic control of servo motor 108 and thus of magnitude 147968 8 and direction of shear movement. or the setting of the pump 84. A feedback rod system 112 is disposed between the thumb washer 96 and the valve slider 106 and acts in the usual manner to return the slider 106 to neutral position when the thumb washer 96 is moved to a new position under control from the servo motor 108.

A hydraulic circuit puts the working fluid of the motors 64 and 66 in connection with the couplings 72 and 74 to operate them, so that the respective drive connections between the motor 64 and the wheel 16 and between the motor 66 and the wheel 18 are established. More specifically explained, the working fluid is led to pull the right wheel motor 64 forward from the feed return line 90 to the clutch 72 through a line 114 which connects line 90 to one side of a right forward coil controlled valve 116, which valve at its The opposite side is connected to a return line 118 and an opening at one end of a reciprocating valve 120 through a line 122. The valve 120 has a central opening which is connected to the coupling 72 through a line 124.

Similarly, the working fluid is driven to drive the left wheel motor 66 forward from the feed return line 92 to the clutch 74 through a line 126 which connects line 92 to one side of a left forward power coil controlled valve 128 which is at its opposite side. connected to a return line 130 and to an opening at one end of a reciprocating valve 132 through a line 134. The valve 132 has a central opening which is connected to the coupling 74 through a line 134 and has at its other end an opening connected to an opening at the other end of the valve 120 through a conduit 136.

The working medium for driving the right and left wheel motors 64 and 66, respectively, is fed backward from the feed return line 94 to the couplings 72 and 74 through a line 138 which connects the line 94 to one side of a power coil controlled valve 140 for rearward travel, which valve at its the opposite side is connected to the return line 130 and to the line 136 between the two reciprocating valves 120 and 132 over a line 144.

The power coil controlled valves 116, 128 and 140 are all shown in disengaged (non-power fed) positions where they connect the couplings to a sump through the return lines 118 and 130. In the following detailed description, the power coil controlled valves 116 and 128 for Forward driving is powered as a result of the main drive transmission being fully engaged for forward driving under certain speed conditions. Power supply to valve 116 causes it to be shifted to the left of the drawing to connect conduit 114 to conduit 122. The valve ball in reciprocating valve 120 changes position and blocks flow to conduit 136 while allowing working fluid to flow to coupling 72 through the conduit 124. Similarly, the power supply of the valve 128 causes it to be displaced to the left of the drawing and connects the conduit 126 to the conduit 134. The valve ball in the reciprocating valve 132 is displaced to block flow to conduit 136 while allowing working medium to flow to the coupling 74 through the conduit 134. It is seen that the fluid pressure to operate the coupling 72 is isolated from the pressure to operate the coupling 74 except by the connection through the throttle conduit 93. This isolation is an important feature because the wheels 16 and 18 can run faster than the wheel motors 64 and 66 either together, thus so m it happens when the gradient runs straight out, or individually, as it will happen when the gradient travels through a bend. The throttle conduit 93. acts in such a turn that a partial differential blocking action is developed to reduce tire wear, and it also acts as a pressure equalizer between conduits 90 and 92 to return the valve slider to the flow divider and collector conduit 86 from a position in which it restricts the flow path to the freewheel wheel while driving in curves to a centered unaffected part position after the running of the waveguide is completed, so that while driving the swivel freewheel motor, it again develops a torque.

147968 ίο

Activation of the reverse coil controlled valve 140 is performed in the manner described below, depending on the main transmission being fully engaged for reverse travel. Activation of valve 140 causes it to move to the left of the drawing to connect conduit 138 to conduit 144, so conduit 136 is pressurized, and thus both reciprocating valves 120 and 132. Valve balls in valves 120 and 132 are thereby engaged. positions where they prevent the flow of working fluid through the disengaged valves 116 and 128 while allowing fluid flow to the couplings 72 and 74 through the lines 124 and 134.

The operation of the above described portion of the front wheel drive system 62 is selectively controlled automatically by an electric circuit 150 which forms part of the system 62. The circuit 150 includes an electronic control box 152 which contains a control circuit (not shown) for processing various electrical input signals , which is described in greater detail below, and for transmitting control signals to linear electro-hydraulic servomotor 108 through signal lines 154 and 156, respectively, for forward travel and reversing, which wires connect box 152 with servomotor 108. Energy for the signal processing circuitry in control box 152 is supplied from a battery 158, which is connected to the box 152 through a supply line 160 having an ignition switch 162 which is connected in series to a contact 164 which is arranged to be connected to a cam (not shown) when the gear selector arm 32 is moved for shifting of transmission 46 for gears 1-4. The supply line is connected to a line 166 within the control box 152 and has an on-off contact 168. It will be seen that no electrical energy will be supplied to the box unless all contacts 162, 164 and 168 are closed.

A line 170 is connected to the control box 152 so as to be connected to line 166 and it branches at 172 into a forward drive 174, which is connected to the right and left current coil-controlled valve 116 and 128, respectively, to a return line 176, which is routed to the power coil U7968 11 controlled valve 140 for chopping. The line 170 has a pressure operated contact 178 which opens when the main clutch pedal 36 is depressed to release the clutch 47. In the wires 174 and 176, normally open forward and reverse contacts 180 and 182 are provided, each of which can be closed by means of not shown bosses. which is moved in dependence on the movement of the directional control arm 34 of the drive transmission as it is moved forward and backward. Also provided in conduit 174 is a normally open pressure operated contact 184 which closes when the forward drive coupling 48 of drive transmission 46 is fully engaged. Similarly, line 176 has a normally open pressure operated contact 186 which is actuated when the reverse reverse acting brake 49 of transmission 46 is fully engaged.

The sensors 60 and 82 are each connected over the control and feedback input signal lines 188 and 190 to the control box 152 for delivering signals for processing in the circuit of the control box to determine the magnitude of the signals supplied to the linear electro-hydraulic servomotor. Sensors 60 and 82 are not directional, but true polarity of the signals applied to servomotor 108 is ensured as follows.

An input signal line 192 is connected to the control box 152 and to the forward drive conduit 174 so that it is energized only when the forward contact 180 is closed. Similarly, a reverse drive input signal line 194 is connected to the control box 152 and to the reverse drive lead line 176 / so that it is energized only when the reverse switch 182 is closed.

The auxiliary drive system 62 has been found to work extremely effectively when applied to a motor gradient so that the front wheel motors 64 and 66 are controlled to develop only torque after the groups of main drive wheels 24 and 26 operate with a slip of '2 , 5%. Accordingly, the current circuit in the control box 152 is set to control the front wheel motors in this way.

Under certain working conditions, e.g. however, when the grader 26 is operating on a slope, it may be desirable for front wheels to operate to maintain the grader safely. operation on the slope, and for such conditions, the steering box may include an "aggressive circuit" which by choice can be engaged in the steering circuit by means of a control switch 196 on the steering box 152. When the steering circuit is in this aggressive state, the wheel motors 64 and 66 are controlled to operate at a speed 1% greater than the speed of the rear wheels 24 and 26.

Although the circuit in control box 152 is described herein as being designed to induce only one sub-speed mode and only one super-speed mode, it will be appreciated that the circuit can be modified to set an unlimited number of modes of operation with a desired workspace.

The auxiliary drive system 62 for operation of the front wheels of the highway 10 operates as follows.

To activate the auxiliary drive system 62 to produce an auxiliary drive operation, the battery 158 must be connected to the control circuit in the control box 152. The driver of the machine induces this activation by sliding the ignition switch 162 and closing the contact. the stroke 164, shifting the gear lever 32 into one of the positions for selecting the gears 1-4 in the drive transmission, and by moving the auxiliary selector switch 168 to its "on" position. With the energy supply to the control box 152, the sensors 60 and 82 are activated to transmit signals representative of the average speed of the rear wheel sets 24 and 26, respectively, and of the rotor 78 in the left wheel motor 66.

If the driver has activated the drive system 62 in the manner just described, but the right-hand selector lever 34 is in its neutral position, the highway rider will still hold and the sensors 60 and §2 will therefore not send signals for processing in the circuit of the control box 152, and no output signals will will be sent to control the linear electro-hydraulic servo motor 108, and the tumbler 96 of the pump 84 will therefore remain in its centered position where no displacement occurs in the pump.

When the driver wants the gradient 10 to move forward, he simply needs to move the direction selector lever 34 to the front position for the drive transverse 46 to enter the forward position. This movement of the arm 34 closes directly the forward contact 180, and assuming that the main drive clutch is fully engaged as it will be when the clutch pedal 36 is released, then the contact 178 actuated by the main clutch pressure is also closed, so that the circuit between the battery 158 and the forward drive lead 174 and the forward input signal lead 192 are closed. When the feed coupling is fully indented, the contact 184 actuated by the pressure in the feed coupling will then close and feed the right and left power coil controlled valve 116 and 128, respectively, so that these valves are shifted to the left of the drawing, thereby connecting the feed return line 90 so that the pressure in the working fluid can actuate the coupling 72 and the feed return line 92 is engaged to supply the working fluid pressure to the coupling 74.

Thus, when the drive transmission 46 is set in its forward mode, a forward torque will be transmitted from the transmission to the rear set of drive wheels 24 and 26 through the differential gear 50, which also pulls the parking brake disc 51 at a rate corresponding to the average rotational speed of the wheelsets 24 and 26. Upon beginning rotation of the disc 51, the sensor 60 begins to send electric pulses in the form of control input signals representative of the rotational speed for processing in the control box 152. It is noted that at this point the control box 152 will receive no feed. back input signals from sensor 82, since left wheel motor 66 does not yet drive its rotor 78. It is assumed that the driver has selected the state of the steering circuit in control box 152 in such a way that it controls left wheel motor 66 to run at a speed; there is 2.5% less than the speed represented by the signal sent from the sensor 60. Sty the circuit processes the control and feed back input signals received from sensors 60 and 82, respectively, and sends an output signal to the hydraulic linear servomotor 108 through the forward drive line 154. Output 147968 14 has such magnitude to affect servomotor 108 that it sets the control valve to move the tumbler disc 96 of the pump 84 to a position corresponding to displacement of working fluid from line 94 to line 88 of a length sufficient to cause rotor 78 of wheel motor 66 to rotate at a speed equal to 2; 5% less than the average speed of the rear wheel sets 24 and 26. When the remote control valve slider is displaced and the servo motor begins to adjust the angular position of the tumbler 96, the feed back link acts to reset the valve slider to neutral. The working fluid supplied to line 88 with pump 84 is divided into the flow splitting and connecting valve to flow to lines 90 and 92 so that motors 64 and 66 are drawn at equal speeds and the pressure in lines 90 and 92 is also transferred to the couplings 72 and 74, the current coil controlled valves 116 and 128 being actuated as previously described.

As soon as the left wheel motor 66 begins to pull, the sensor 82 will begin to send a feed back input signal in the electrically closed circuit to the control box 152 for processing along with the control signals from the sensor 60.

Assuming that the motorway 10 is driving straight ahead and that. the rear wheelsets 24 and 26 do not spin, so the front wheels 16 and. 18 rotate at the same speed as the rear wheel sets, and this speed will exceed that at which the motors 64 and 66 are set, by approx. 2.5%. While the pressure required in lines 90 and 92 to overcome internal resistances in motors 64 and 66 and drive their rotors is sufficient to induce coupling of couplings 72 and 74 to establish drive connections between motor 64 and wheel. 16 and between the motor 66 and the wheel 18, it will be understood that as soon as the connections are established, the wheels pull the motors with the result that the pressure in the wires 90 and 92 is reduced below what is necessary to engage the couplings so that the wheels can run faster than the engines. This means that the pressure in conduits 90 and 92 is automatically modulated in the region 15 U7968 above and below the pressure necessary to engage couplings 72 and 74 so that wheels 16 and 18 can run faster than motors 64 and 66, thereby avoiding , that interferences occur between the main torque and the auxiliary drive torque.

It is then assumed that the motorway 10 continues to run straight out as before, but that the right wheelsets 24 and 26 now spin around with at least 2.5% slip. The wheels 16 and 18 no longer operate at speeds faster than the speeds of motors 64 and 66, and consequently the pressure in lines 90 and 92 will be sufficient to keep the couplings 72 and 74 engaged. If the highway 10 is then made to turn sharply, e.g. to the left, the outer right wheel 16 will be made to rotate faster than the motor 64 and will therefore pull the motor 64 so that the pressure in the conduit 90 decreases below the pressure required to engage the clutch 72. The wheel 16 then runs faster than the engine 64 without any torque interference. Similarly, the wheel 18 will run faster than the engine 16 as the motor jaw 10 turns sharply to the right.

It is noted that during the rotation, the flow splitting and connecting valve 86 will operate to throttle the flow path to the outer wheel, and the throttle passage 93, when the run in a curve is completed, will act to equalize the pressures in lines 90 and 92 to ensure that valve 86 is reset to voltage-free part position. Also, when turning, when both motors 64 and 66 pull the wheels 16 and 18, the throttle passage 93 will act to divert the driving pressure from that of the lines 90 and 92, which is connected to the motor pulling the inner wheel, to the second line, thus that a partial differential locking condition is established which causes reduced tire wear.

From the forward position, the motor gradient 10 can be switched to reverse by moving the direction selector lever 34 from its forward position to its reverse position, so that the main drive transmission 46 is put into reverse. At the same time, the auxiliary drive system 62 is prepared for reverse travel. Moving arm 34 to reverse causes opening of forward travel switch 180 and closing rear drive contact 182. Hereby, the battery 158 is connected to the rear drive line 176 and the rear drive input signal line 194. The movement of the arm 34 also causes the hydraulic control pressure to be cut off from the forward drive clutch. 48 and causing the control pressure to act on the rear drive brake 49 in the transmission. The forward pressure switch 184 opens by reducing the forward pressure coupling pressure so that right and left current coil controlled valves 116 and 128, respectively, are no longer energized but release the couplings 72 and 74. When the rear drive brake 49 in the main transmission 46 is fully engaged, the reverse drive pressure switch will 186 close and power supply the reverse coil controlled valve 140, which leads it to the left of the drawing and fluidly feeds 94 to the couplings 72 and 74. At this point, motors 64 and 66 can drive wheels 16 and 18 to increase the main drive, if the rear wheelsets 24 and 26 spin around with a slip of at least 2.5%; It will be seen that the contacts 180 and 182 operated by the direction selector arm 34 cooperate with the pressurized contacts 184 and 186 to immediately shut off the auxiliary drive motors 64 and 66 from the wheels 16 and 18 as the direction selector arm 34 is passed from one to the other. its working positions and then to reconnect the auxiliary drive motors to the front wheels to pull these in the opposite direction, but only after the main drive transmission pulls the rear wheel sets 24 and 26 in the opposite direction. In this way, switching on and off the main and auxiliary drive systems are synchronized so that one drive system does not counteract the other. This is especially important when the direction selector arm 34 is moved rapidly between forward and reverse positions to cause the motor jaw 10 to rock when it is, e.g. must work free of a mud puddle.

When the gear selector lever 32 is moved to the neutral position or to one of positions 5-8 to produce a corresponding gear exchange in the transmission 46, the contact 164

Claims (10)

147968 mathematically opens and shuts down the battery 158 from the control box 152 to disable the auxiliary drive 62 and consequently drive the tumbler disk of the pump 84 to the O position so that the motors 64 and 66 are no longer operated and the couplings 72 and 74 no longer is in action. Setting the auxiliary drive system 62 in the neutral position when the drive transmission 46 is neutral is a precaution, while disabling the auxiliary drive transmission when the drive transmission is switched to one of the gear exchanges 5-8, where an auxiliary drive drive is normally required, allows wheels 16 and 18 to run. freely around, interrupting unnecessary fluid flow through the auxiliary drive system 62 hydraulic circuits. While working on the grader 10, fast stopping may be necessary. This is usually done by operating the brakes after depressing the clutch pedal 36 to release the clutch 47. Release of the clutch 47 automatically disables the front wheel drive system 62 by inducing opening of the pressure-sensitive contact 178 and blocking the battery 158 from the directional input line 192 or 194 and from the power coil-controlled valves 116 and 128 or 140 for immediate release of the connection between the wheels and the wheel motors to ensure that the gradient 10 can be brought to a safe stop. Another case in which the clutch pedal 36 is depressed to disable the auxiliary drive system occurs during very slow or jerky driving. The pressure at which the switch 178 ends is such that the auxiliary drive system 62 does not affect the slow travel. Claims. A hydrostatic auxiliary drive system for a vehicle, said system having two auxiliary drive wheels (16,18) and hydraulically actuated clutches (72,74), hydraulically driven hydraulic motors (64,66) in parallel, a pump (84) and a directional control valve (102), in which the system the couplings which exist between the auxiliary drive wheels and the hydraulic motors, can, depending on the pressure prevailing between the pump and the hydraulic motors, and which the vehicle (10) has a main transmission (46), characterized in that between the main transmission (46) and the directional bypass valve (102) there is a control device (150, 152) which records the ratio of the speed of the main transmission (46) to the speed of the hydraulic motors (64, 66) and which regulates the pump (84) amount of delivery depending on this ratio. Hydrostatic auxiliary drive system according to claim 1, characterized in that the pump (84) is designed with variable performance and reversible direction of rotation. Hydrostatic auxiliary drive system according to claim 1 or 2, characterized in that the pump (84) has a tumble disc (96) which is adjustable via a control device (98,100), which is hydraulically connected to the directional control valve (102). Hydrostatic auxiliary drive system according to one or more of the preceding claims, characterized in that the directional control valve (102) is connected to the control device (150,152) and is adjustable through it, whereby it operates in response to the direction of rotation of the main transmission (46). . Hydrostatic auxiliary drive system according to one or more of the preceding claims, characterized in that it has an electrically actuated solenoid valve (116,122) for forward operation via a current circuit (174,192), which solenoid valve (116,128) can be displaced between a position allowing the pump for the couplings (72,74) and a position in which it cuts off the pump (84) the disconnections (72,74). U7963 Hydrostatic auxiliary drive system according to one or more of the preceding claims, characterized in that it has an electrically actuated solenoid valve (140) for reversing, which can be displaced between a position enabling inlet from a reverse circuit (176,194). the pump (84) for the couplings (72,74), and a position in which it cuts off the pump (84) from the couplings (72,74). Hydrostatic auxiliary drive system according to one or more of the preceding claims, characterized in that in the current circuit (174,192) of the solenoid valve (116,128) for forward operation there is a contactable contact (178) of a main drive coupling (47), depending on the position of the a directional gear (34) movable forward travel contact (180) and a contact (184) operating at the activation pressure of a forward drive clutch (48). Hydrostatic auxiliary drive system according to one or more of the preceding claims, characterized in that in the current circuit (176,194) of the reversing solenoid valve (140) there is a contact (178) activatable from the main drive coupling (47), depending on the position of the directional gear (34) a movable reversing contact (182) and a contacting actuator (186) acting at the actuating pressure of a brake (49) which causes a reverse drive. Hydrostatic auxiliary drive system according to one or more of the preceding claims, characterized in that the forward circuits (174,192) and for reverse (176,194) are connected to the control device (150, 152) via input signal lines respectively (192, 194). Hydrostatic auxiliary drive system according to one or more of the preceding claims, characterized in that the ratio between the rpm of the main transmission (46) and the rpm of the hydraulic motors (64,66) can be set by means of a control switch (196).