GB2128718A - Drive unit consisting of an internal combustion engine and a steplessly adjustable hydrostatic transmission - Google Patents

Abstract

A reversible variable displacement pump (3) is controlled by a servomotor (10) coupled to forward and reverse control valves (16, 18) operated by common controller (19) the control pressure also being applied via shuttle valve (21) and valve (42) to a servomotor (28) controlling fuel supply to an engine driving the pump (31). If the pump delivery pressure exceeds a given value during normal drive, valve (42) vents line (23) and isolates line (24), but during braking this valve isolates line (23) from line (24) and vents the latter to provide hydrostatic braking. Engine speed sensor (53) also causes valve (42) to vent line (23) to relieve any overload. Comparator (58) compares the pressure at (24) with a control pressure from valve (57) and closes throttle (35) when the latter pressure is the higher, this pressure then acting on servomotor (28). A vehicle driven by the engine and hydrostatic transmission also includes a lifting device controlled by element (63) and lever (64) which also closes throttle (35) and actuates servomotor (28) via control valve (65) during operation of the lifting device. <IMAGE>

Description

SPECIFICATION Driveunitconsisting of an internal combustion engine and a Steplessly adjustable hydrostatic trans mi,sçion, This invention relates to a drive unit consisting of an internal combustion engine and a steplessly adjustable hydrostatic,,transmission.

Such a driveunir,whosesetting element is operatively connected to a piston which is adjustable in a control cylinder and which on the one hand abuts against a spring and on the other hand is supplied with a control pressure medium, wherein the pressure of this control pressure medium can be adjusted by means of a control pressure generator either aribitrarily or in dependence upon another parameter, has been disclosed in German Patent Specification No.20 01 701. In such known drive units, the operator on the one hand adjusts the hydrostatic transmission means ofthe control pressure generator and on the other hand adjusts the internal combustion engine by means ofotheractuating elements.However, it is also already known to provide only one actuating element and to adjust both the internal combustion engine and the hydrostaticgear by means of mechanical linkage (German Patent Specification No.1526528). The installation and adjustment of this linkage is often extremelyelaborate and complicated in particular if the internal combustion engineandthe hydrostatic gear, or at least a part thereof, are considerably spaced from one another and from the operating position of the operator (for example, in the case of a vehicle, from the driving seat thereof).Even when the mechanical linkage consists of cables of Bowden cables or similar actuating devices, the shortcomings are not avoided since the necessarily large radius of curvature, the sensitivity to dust, and the danger of breakage during operating limitthe possible uses of traction-transmission elements of thins kind. A further problem consists in that a mechanical linkage of this kind must be reconstructed wheneverthe drive system is to be used for an engine of different dimensions or different spatiat correlations between the internal combustion engine, the hydrostatic transmission and the operating postion.

The present invention is concerned with a drive unit which is incorporated in a motor vehicle, which includes a further energy consuming device driven by the internal combustion engine. It is a particular aim of the invention to enable the further device to be driven at a relatively high speed even if the hydrostatic transmission to the vehiclawheels absorbs only a little power, or is so setthatthe vehicle moves only slowly.

The cha racteristics of the power consu mption of hydrostatic transmissions, and in fact not only of transmissions regulated only on the primary side but also oftransmissions regulated on the primary and th e:secondry side, areknown (see for example "Grund lagen: hyd hydrostatischer Getriebe-Aufbau, Wir kungsvveise und spezielle Anwendugen" in "Linde Berichte ausTechnik und Wissenschaft" No.42, November1977, page 29, in particular pages 47,51 and 59, published in the English language as "Linde Reports on Science and Technology" No.27, 1978, page 29 onwards), and it is also already known to design the mechanical linkage which connects the setting elements of internal combustion engine and hydrostatic transmission accordingly (see German Patent Specification No. 1526528, column 4).A particularly expedienttransmission function can be achieved by means of a device corresponding to the present invention if is further developed in that the stiffness or rigidity ofthe spring in the control cylinder which is assigned to the setting element of the hydrostatic transmission and that of the spring in the control cylinder which is assinged to the setting element of the internal combustion engine are contrived to be such that the piston which is connected to the setting element ofthe internal combustion engine reaches its end position when the control pressure has reached a level at which the piston connected to the setting element of the pump of the hydrostatic transmission has reached a central position at which said setting elementofthe pump assumes that the settingatwhichthe pumpabsorbsthefullpower emitted from the internal combustion engine, so that atthis level of the control pressurethe internal combustion engine is able to deliver its maximum power and the hydro-gear is able to absorb this power when, in the event of a further increase in the control pressure, whilstthe power remains constant, the speed of the driven side ofthe hydrostatictransmission increases and consequentlythe driven torque is reduced in accordance with a hyperboliocharacteris- tic. In a vehicle drive system, an optimum transformation in the hydrostatic transmission in accordance with the traction hyperbola exists which is governed by the lawwhich statesthat"the product of delivery flow and delivery pressure is constant".Full motor power is possible in this hyperbolic range but not at low speeds. On the one hand, the delivery pressure in the hydrostatic transmission is limited by a pressure limiting valve and, on the other hand, when the vehicle is correctly designed, beneath this limit a further limit is provided in that at this torque the vehicle wheels skid. If efficiency is disregarded, the drive power obsorbed by the hydrostatic transmission falls linearly to zero in the lower driving speed range. On the other hand, the internal combustion engine must always operate at a minimum speed in orderto be able to emit any torque at all. If an expedient compromise is made between.

maximum acceleration lowest fuel consumption low noise development it is expedientto ensure that the curve ofthe drive power overthe driven speed differs from the ideal motor power which starts at the zero point, rises steeply and linearlyto the maximum motor power and then remains constant. On the one hand, this is possible by curving the rising graph line with regard to the skid limit ofthe vehicle wheels, and on the other hand by providing that, with regard to the internal combustion engine,thesteeply rising graph line does not pass through said zero point, i.e. does not emanate from the speed-zero, power-zero point.With regard to the dependency of the efficiency of the hydrostatic transmission upon the drive speed, it can furthermore be advantageous to ensure that the steep part of the power-driven speed curve does not reach the maximum motor power butto attach to the latter an arr, which rises in a flat fashion until it reaches the maximum motor power. In a hydrostatic transmission in which both the pump and the motor/motors are adjustable, the hydraulic motor is expediently returned when the internal combustion engine is atfull orat leastapproximatelyfuII speed.

As already stated, the present invention is concerned with the case in which the drive unit is incorporated in a vehicle which comprises a further energy consumer which is arbitrarily actuable and is likewise driven by the internal combustion engine which drives the hydrostatic transmission. Thus, for example in the case of a fork lift truck, in addition to the vehicle drive which is driven by the hydrostatic transmission, a hydraulic lifting device is also provided whose pump is likewise driven by the internal combustion engine; moreover, by way of example, a fork lift truck either moves slowly or is stationary when the hydraulic lifting system is actuated.This means thatthefirst-mentioned control pressure generator is set at a low control pressure and thus the internal combustion engine is set at idling, orat leastthe control pressure generator is set at a low control pressure and consequently the internal combustion engine is set to produce lower power. If the hydraulic lifting system is now operated, so thatthe lifting hydraulic pump absorbs energy, the internal combustion engine must produce power. However, the setting provided by the first-mentioned control pressure generator does not allowthisto happen.Therefore, in accordance with the invention, it is provided that the actuating element connected to this further energy consumer (for example, the lifting mechanism drive) is connected to an additional control pressure generator whose control pressure line is connected to the control pressure line which leads to the control cylinder of the internal combustion engine at the rear ofthe position at which the latter can be closed off, for example at the rear of the restrictorwhich can be set at zero, and the actuating element is connected to this closing element (for example the restrictorwhich can be set at zero) in such mannerthat when this additional control pressure generator is actuated the control pressure line is blocked between the hydrostatic transmission and the control cylinder of the internal combustion engine.

The present invention will now be more particularly described with reference to the accompanying diagrammatic drawing, in which:- Figure 1 illustrates the circuit diagram of an exemplaryembodiment of a drive unit according to the invention; and Figure 2 illustrates an alternative development of one individual part thereof.

Via a shaft 2, an internal combustion engine 1 of a vehicle drives a pump 3 of a hydrostatic transmission whose hydraulic motor 4 is connected to the pump 3 via the two lines 5 and 6 in a closed circuit. The driven shaft7 of the motor 4 is connected to the motion drive of a vehicle. A setting element 8 ofthe pump 3 is connected to a piston 9 which is displaceable in a control or operating cylinder 10 in which a pressure chamber 11 is formed on one side ofthe piston 9 and a pressure chamber 12 is formed on the other side ofthe piston 9, a compression spring 13 being contained in the pressure chamber 11 and a compression spring 14 being contained in the pressure chamber 12. The pressure chamber 11 is supplied via a control pressure line 15 from a control pressure generator 16.The pressure chamber 12 is supplied via a control pressure line 17 from a control pressure generator 18. The two control pressure generators 16 and 18 can be controlled by an arbitrarily actuable actuating element 19 and, in fact, in such mannerthat one ofthetwo control pressure generators 16 and 18 is selectively actuated.

The control pressure line 15 is connected by a branch line 20 to one side of a switch-over valve 21 whose other side is connected to a branch line 22 connected to the control pressure line 17. The switch-overvalve 21 connects the particular one of the two control pressure lines 15 and 17 which carries the higher pressure to a control pressure line 23 which is extended by the control pressure line components 24, 25 and 26, with the resultthatthe control pressure line components 23,24,25,26 form a common part and lead to a pressure chamber 27 of a control or operating cylinder 28 which is assignedtothe internal combustion engine 1 and in which a piston 29 can be displaced against the force of a long spring 30 and a short spring 31.The piston 29 is connected to a piston rod 32 which is articulated to a lever33which acts upon a power regulating element 34 of the internal combustion engine 1.

Between the line components 24 and 25 there is connected a restictor-non-return-valve-element 74 which contains a variable restrictor35 and a nonreturn valve 36 connected in parallel therewith.

This provides the basic form ofthe control device for a drive unit corresponding to the invention, whose mode of operation isasfollows:- When the vehicle is at a halt, the power regulating element34 of the engine 1 is adjusted to its idling setting and the pump 3 occupies the zero delivery position, the actuating element 19 is in the neutral position, and the tappets of the two control pressure generators 16 and 18 are each in contact with a zero stop means.If the actuating element 19 is now operated towards the right (namely, in a clock-wise direction as shown in the drawing) the control pressure generator 16 is operated with the result that the control pressure medium conveyed by a pump 37 flows via the conrol pressure generator 16 at a preselected pressure through the control pressure line 15 into the pressure chamber 11 ofthe control cylinder 10 which is ancillary to the pump 3; this causes the pump to be set at an increased working (stroke) volume per rotation. Afurther outcome is that the pump 3 delivers to the hydraulic motor 4 whose driven shaft 7 now starts to rotate at a rotation speed corresponding to the delivery rate. Simultaneously with the rise in pressure in the control pressure line 15, the pressure also rises inthe branch line 20 and,via the valve 21, rises also in the control pressure line 23, 24,25, 26,the non-return valve 36 being open. Thus, the control pressure from the line 15 continues into the pressure chamber 27 so thatthe piston 29 is displaced againstthe force of the spring 30. If the spring 30 were to become compressed to such an extent that the piston 29 also contacted the spring 31, the displacementofthe piston 29 by one millimetrewouldthen require a greater increase in the control pressure than would be needed to displace said piston 29 when the latter is merely in contact with the spring 30.When the springs 30 and 31 are entirely compressed, the internal combustion engine 1 is set at its maximum power output, whereas the pump 3 has reached the setting in which it is able to accommodate the full power ofthe internal combustion engine 1. If a further increase now occurs in the control pressure in the control pressure line 15 due to further actuation of the actuating element 19 and thus of the control pressure generator 16, the swing-out ortraverse ofthe pump 3 is increased so that, whereas the power output of the internal combustion engine 1 remains constant, the delivery ofthe pump 3 is increased although the pressure against which the pump 3 can deliver is reduced.

If, as a result of a decrease in the swing-out of the actuating element 19, the control pressure generator 16 isturned down, the pressure of the control pressure medium in the control line 15 is reduced and this has the resultthatthe spring 14 adjusts the piston 9 in the sense of a smaller swing-out ofthe pump. As a higher pressure still prevails in the branch line 20than in the branch line 22, the switch-over valve 21 continues to connect the branch line 20 to the control pressure line 23 so that the pressure of the control pressure medium is likewise reduced in said line 23.As a result ofthe fall in the pressure in the control pressure line 23,24,25,26, the springs 30 and possibly 31 move the piston 29 back into the pressure chamber 27so that liquid is force from the latter th rough sub-lines 26 and 25; this has the result that the non-return valve 36 closes and the control pressure medium can flow via the restrictor35 into the lines 24,23 and from the latter via the valve 21 and the branch line 20 into the control pressure line 15.

The described active connection between the setting element 8 of the pump 3 and the power regulating element 34 of the internal combusion engine serves to avoid undesired speed changes in the internal combustion engine 1 which could be occasioned by rapid changes of motion of the actuating element 19. This also avoids jerky accelerations or decelerations of the vehicle or improper relative settings ofthe hydrostatic transmission and the internal combusion engine as can occur as a result of misoperation when the internal combustion engine and the hydrostatic transmission are adapted to be set independently of one another.The valve 21 is necessary in view of the fact that the pump 3 can be adjusted beyond the zero stroke or delivery position thereof so asto deliver in both directions; thus, regardless of whetherthe forwards travel direction has been set by the control pressure generator 16 or the backwards travel direction has been set by the control pressure generator 18, the internal combustion engine is always adjusted in or by the same act to the setting of the hydrostatictransmission. However, differently rated springs can be provided on the two sides ofthe piston 9 in order to allow different setting to be produced for the two directions of rotation if thins is expedient in terms of the engine.

The power regulating element 34 can consist of an injection pump or an injection regulator or a throttle valve of a carburetor.

The described device allows the power regulating element 34 ofthe internal combustion engine 1 to be set simu Itaneously with the setting of the stroke volume ofthe pump 3 or, alternatively, allows the setting of the internal combustion engine to take place aftera certain time lag.

In addition, the lineS of the hydrostatictransmission 3,4,5,6 is connected to a branch line 38 and the line 6 of the hydrostatic transmission 3,4,5,6 is connected to a branch line 39, the two branch lines 38,39 leading to a switch-over valve 40 from which a line 41 leads to the outlet valve element 42.The valve 40 connects that one ofthetwo lines 5 and 6 which serves as pressure conveyor lineto the line 41 so that the particular delivery pressure is contained in a corresponding sub-element ofthe outlet valve element 42. the delivery pressure exceeds a predetermined limit value which liesjusta little belowthe maximum permissible delivery pressure which is limited by a conventional pressure limiting valve (not shown in the drawing), the outletvalve element 42 opens up a connection between the control pressure line 23 and a discharge line 44 which leads to a unpressurised container 43 and at the same time at the rear of thins outlet point cuts offthe connection between the control pressure lines 23 and 24. The result of this is that the control pressure in the lines 24,25,26, andthus in the control cylinder 28 assigned to the engine 1, remains unchanged whereas the control pressure in the line 23, and thus in the control cylinder 10 assigned to the pump 3, falls.Thus, the pump is adjusted to a smaller delivery volume per rotation so that the highest permissible pressure is not exceeded, whereas the internal combustion engine 1 remains at its previous setting so that it is able to emit sufficient power to drive the pump 3 which effects deliveryagainsta high pressure.

Howeverthisfunction is only desired when the engine 1 is driving the driven shaft 7 and thus the driven vehicle via the hydrostatic transmission 3,4,5, 6. If braking is effected via the hydrostatictransmis- sion,the outletvalve element42 exertsa different influence; in such circumstances, the outlet valve element 42 closes the line 23 and connects the line 24 to the discharge line 44. This means that the setting of the hydrostatic transmission can still be effected via the control pressure generators 16and 18forthe purpose of controlling the braking action, whereas the control cylinder 28 assigned to the engine 1 is completely relieved of pressure so that the engine 1 is broughtto its idling setting and can thus exertthe maximum possible drag. Ifthe engine 1 were not provided with this setting, in the braking state it would stiil be supplied with fuel so that braking moment would be accompanied by driving moment and as a result impermissible excess speeds would rapidly be reached.

Inorderto beabletoestablishwhetherthe hydrostatic transmission is operating in drive mode or in braking mode, the outletvalve element 42 is connected to a pressure sensing and comparison device 45 which is connected (a) to a line 46 which is itself connected to the line 5, (b) to a line 47 which is itself connected to the line 6, (c) to a line 48 which is itselfconnectedto the control pressure line 15, and (d) to a line 4 < j which is itself connected to the line 177.

When the control pressure generator 16 is actuated, the control pressure line 15 conducts pressure and the setting element 8 ofthe pump 3 is swung is such mannerthat it effects delivery into the line 5 and the motor4drives the driven shaft 7. If the line 5 and thus the line 46 carry a higher pressure than the line 6 and thus the line 47, and if the line 15 and thusthe line 48 also conduct a higher pressurethan the line 17 and thus the line 49,29, the vehicle is being driven in one direction; the same is true, mutatismutandis, when the control pressure generator 18 is actuated and the line 6 andthusthe line 47 carry a higher pressure than the line 5 and thus the line 46, and the line 17 and thus the line 49 carry a higherpressurethan the line 15 and thus the line 48. If, however, the vehicle is involved in a braking operation, the control pressure line 15 is supplied with pressure and at the same time the line 6 carries a higher pressure than the line 5.That isto say that, in this case, together with the line 15, the line 48 carries a big her pressure than the line 17 and thus the line 49, and in addition the line 6 and thus the line 47 carry a higherpressurethan the lines andthusthe line 46. In this operating state, the pressure sensing and comparison device 45 establishes or determines that the braking state prevails and influences the outlet valve element 42 in such manner that it blocks the line 23 and connects the line 24to the discharge line 44.

The same applies when the control pressure gener ator 18 is actuated and as a result the control pressure line 17 conducts pressure but at the same time the line 5 carries a higher pressure than the line 6.

Thus,wheneverthe outlet valve element 42 connects the line 23 to the discharge line 44, and the setting elements of the pump 3 is adjusted in the direction of its zero delivery position, restrictors 50 and 51 operate to ensure that when the control pressure is bled from the line 15 orfrom the line 17 by the control pressure generator 16 or the control pressure generator 18, respectively, control pressure medium immediately flows in at a pressure which is such thatthe pressure remains constant.

The outlet valve element 42 is also connected to an element 52 which is actively connected to a speed sensor 53 which is itself connected to the shaft 2. This element 53 can consist of a mechanical centrifugal r.p.m. sensor or an electrical one controlled by pulses or a motortacho-generator, or else can consist of a constant pump driven by the shaft2 and a line which leads to a restrictor and to which a pressure measuring element is connected. The element 52 is also operatively connected to the power regulating element34 in a mannerwhich is not illustrated in Figure 1. Each setting of the power regulating element 34 corresponds to a specific predetermined speed ofthe internal combustion engine.If overloading caused by an excessively high torque in the shaft 2 leads to a drop in the speed of the engine 1, the elements 52,53 influence the outlet valve element 42 in such manner that the control pressure line 24 becomes blocked again and the control pressure line 23 is connected to the discharge line 44 so that the particular one of the two control pressure lines 15 and 17 which is carrying pressure is relieved of load and thus the pump 3 of the hydrostatic transmission is adjusted in the direction of a smallerdeliveryvolume per rotation.

The function of the outlet valve element 42 to block the control pressure line 24 can be effected by an operative connection 54 (drawn in dot-dash lines in Figure 1) between the outlet valve element 42 and the variable restrictor 35 which can be closed to zero, so that wheneverthe line 24 is to be blocked the restrictor 35 is entirely closed.

If, as a result ofthe actuation ofthe actuating element 19, one ofthe control pressure generators 16 and 18 is actuated and thus it indirectly occursthat the pump 3 is set at a higher delivery volume per rotation and thus at a higher power consumption, and the internal combustion engine 1 is set at a higher power output, it is advantageous to provide said engine 1 with a specific lead, i.e. an increase in the swing-out of the pump 3 is provided with a specific deceleration.

Restrictors 55 and 56 are provided in orderthatthis deceleration may be achieved.

It has already been mentioned thatwheneverthe delivery pressure in the particular line 5 or 6 which is acting as conveyor line exceeds a maximum permissi ble value, the outlet valve element 42 is actuated via the line 41. In addition to this function (or, instead of this function, at least whenever the power regulating element 34 of the engine 1 is not yet set at maximum power output), it is possible to use a device whose main components consist of a further control pressure generator 57 and the comparator element 58. The generator 57 is supplied via a branch line 59 with the pressure in the line 41 and thus with the pressure in that one of the lines 5 and 6 which carries the particular higher pressure. The generator 57 produces a control pressure in the control pressure line 60.If the comparator element 58 establishes or determines that the control pressure operating in the line 60 is higher than that operating in the line 24, said element 58 provides, via an operative connection 61 ,thatthe restrictor35 is blocked; the outcome ofthis is that the higher control pressurewhich prevails in the line 60 acts via the lines 25 and 26 on the control cylinder 28 assigned to the engine 1, and sets said engine to a higher power output so that it is able to emitthe power which is absorbed by the pump 3 at the higher pressure. A non-return valve 62 prevents control pressure medium from being discharged outofthe line 25 when a higher pressure prevails in said line than in the control pressure line 60.

The vehicle which is driven bythe internal combustion engine 1 via the hydrostatic transmission 3,4,5,6 is provided with a lifting device (not shown in the drawings) which is switched on by the device 63 which is itself operated by the hand lever 64. When the hand lever 64 is operated, a further control pressure generator 65 is actuated which conveys control pressure medium via a control pressure line 66 into the control pressure line 26 and thus into the control cylinder 28 assigned to the engine 1.The operative connection 67 between the hand lever 64 and the variable restrictor 35 simultaneously ensures that the restrictor35 is closed offsothatthesetting of the hydrostatictransmission 3,4,5,6 is still dependent only upon the setting of one ofthe generators 16 or 18, whereas the setting ofthe engine 1 is influenced only viathe generator 65 and in fact in such manner that said engine I emitsthe power taken up by the lifting mechanism drive.

In the embodiment illustrated in Figure 2, a piston rod 32a which is connected to the piston 29 and which fundamentally corresponds to the piston rod 32 is connected to a coulisse plate 68 in which is provided a cam recess 69 in which slides a feeler roller 70 which is connected to a setting rod 33awhich moves in a guide (not shown in the drawing). Said setting rod 33a acts upon the power regulating element 34 of the internal combustion engine 1.The cam recess 69 is designed in such mannerthat, in the event of a constantly rising control pressure in the control pressure line 23,24,25, 26, firstly the power regulating element 34 is adjusted from idling operation to maximum power and then, in the event of a further increase in the control pressure and thus a further displacement ofthe piston rod 32a and thus of the coulisse disc 68to the left as viewed in Figure 2, no further change is effected in the setting of the internal combustion engine.

In another embodiment ofthe cam 69 which has not been shown in the drawing, the latter can be selected to be such that, commencing from the idling operation ofthe power regulating element 34, in the event of an increasing pressure, firstly the setting of the power regulating element 34 is greatly increased and from a specific point onwards is increased only very slightly to the maximum power output.

Thefactthatthe power regulating element 34 of the internal combustion engine 1 is also adjusted by means of an operating piston 29 influenced by control pressure facilitates another embodiment wherein the hand lever 64 acts directly mechanically on the setting lever33 in such mannerthat, when the lever 64 is operated, the element34 is adjusted to a higher power. As a result ofthe mechanical transmission force, the spring 30 and possibly also the spring 31 is/are then compressed, although no further affect occurs upon the control system, in particular as regards the transmission.

Reference has been made above to "improper relative settings" of the hydrostatictransmission and the internal combustion engine. For the avoidance of possible doubt, it is pointed outthat (a) the i.c.e. can be run at low r.p.m. and the hydrostatic transmission can be so adjusted that high driven speed is obtained, or (bathe i.c.e. ca be run at high r.p.m. and the hydrostatic transmission can be so adjusted that it gears down to the required relatively low driven speed. The latter mode of operation would involve improper relative settings because, by comparison with mode (a), the engine would use a lot of fuel, would produce a great deal of noise and exhaust gases and the gear efficiency would be poor.

Lastly, it is to be noted that if the hydrostatic transmission operates in a closed cycle and transmission can take place in both directions of rotation (as is the case of the subject ofthe present invention),there is a mid-positionforthe setting element8 ofthe pump, this mid-position being the neutral position; that is to say, is the setting element is in this mid-position, the transmission is set so that the driven side of the shaft is at a standstill. The setting element 8 can swing towards either ofthe two sides from this mid-position.

The gears are so designed that, in the event of swinging of the setting element 8 of the pump from the neutral position, the pump absorbs greater and greater power until it absorbs the maximum power which the internal combustion engine is able to produce. Atthis stage, the setting element 8 ofthe pump has reached the middle of the adjustment range which is meant in, for example, Claim 2. That isto say, the setting element ofthe pump is not completely swung out yet but is no longer in its neutral position either; it is swung out approximately by half (see the form ofthe coulisse or cam recess 69). This applies to both directions of swivel commencing from the neutral position which can be referred to as "the" mid-position. Thus, itwill be seen thatthere is a differentiation to be made between the exact midpositionorneutral positionofthesetting element8on the one hand and a position ofthe setting element 8 which lies between the neutral position and the position of maximum swing-out of said element on the other hand.

Claims (15)

CLAIMS 1. A drive unit incorporated in a motorvehicle and composed of an internal combustion engine and a hydrostatictransmission whose setting element is operatively connected to a piston which is displace- able in afirstcontrolcylinderandwhich ontheone hand abuts against a spring and on the other hand is supplied with a control pressure medium whose pressure is determined by means of a control pressure generator, wherein a setting element of the internal combustion engine is also connected to a piston which is displaceable in a second control cylinder and which on the one hand abuts against a spring and on the other hand is supplied with the control pressure medium whose pressure is determined by said control pressure generator, and wherein said motorvehicle is provided with another power-consuming arrangement having an actuating lever which is operatively connected to an additional control pressure generator, an operational connection being provided between the second control cylinder and the additional control pressure generator which operational connection is such that, when the rotational speed of the internal combustion engine is increased dueto the actuation ofthe additional control pressure generator, the setting of the hydrostatictransmission is modified in such mannerthatthe rotational speed of the driven shaftofsaid hydrostatictransmission remains constant either atthe value which was set prior to the actuation of the additional control pressure generator or atthe value set bythefirst-mentioned control pressure generator. 2. Adrive unit as claimed in Claim 1,wherein a restrictor is arranged in the control pressure line from the first control pressure generator between the first control cylinderandthe branch pointfromwhich a part of said control pressure line leads to the second control cylinder. 3. A drive unit as claimed in Claim 1 or Claim 2, wherein the stiffness or rigidity ofthethe springs in the first and second control cylinders are such that the piston which is connected to the setting element of the internal combustion engine reaches its end position at a pressure ofthe control pressure medium atwhich the setting element ofthe hydrostatic transmission has reached a position in the middle of its adjustment range, at which position the hydrostatictransmission absorbs the full power produced by the internal combustion engine. 4. A drive unit as claimed in any ofthe preceding Claims, wherein the spring against which abuts the piston which is connected to the setting element ofthe internal combustion engine consists of a stack of springs of different lengths in orderto produce a non-linear characteristic curve. 5. Adrive unitasclaimed in Claim 4, wherein the springs of different lengths have different degrees of stiffness or rigidity. 6. Adrive unit as claimed in Claim 1, wherein a mechanical transmission unit which performs a nonuniform transmission is arranged between the piston ofthe second control cylinder and the setting element ofthe internal combustion engine. 7. A drive unit as claimed in Claim 6, wherein said mechanical transmission unitconsists of a cam with a feeler pin. 8. A drive unit as claimed in Claim 1, wherein the hydrostatictransmission operates in a closed circuit and comprises a pump which can be setto deliver in one of two directions of delivery at a time, the piston in the first control cylinder being connected to said pump, wherein two control pressure lines are provided to supply control pressure medium to said first cylinderon respective opposite sides of said piston, and wherein said two control pressure lines are also connected to a switch-over valve, another line which emanates from the switch-over valve being connected to the second control cylinder. 9. Adrive unit as claimed in Claim 8,wherein a restrictor is arranged in said other line between said switch-over valve and said second control cylinder. 10. A drive unit as claimed in Claim 9, wherein said restrictor is adjustable. 11. A drive unit as claimed in Claim 10, wherein the restrictorcan be adjusted so that a part of said other line is completely closed. 12. Adrive unit as claimed in any of Claims 9to 11, wherein, parallel to the restrictor,there is arranged a non-return valve which opens to the second control cylinder. Newclaimsfiled on 7 Dec 1983 Superseded claims 1-12

1. A motor vehicle propelled by an internal combustion engine through a hydrostatictransmission whose setting element is operatively connected to a piston which is displaceable in a first control cylinder and which on the one hand abuts against a spring and on the other hand is supplied with a control pressure medium whose pressure is determined by means of a control pressure generator, wherein a setting element of the internal combustion engine is also connected to a piston which is displaceable in a second control cylinder and which on the one hand abuts against a spring and on the other hand is supplied with the control pressure medium whose pressure is deter mined by said control pressure generator, and wherein said motorvehicle is provided with a further power-consuming arrangement driven by the internal combustion engine and having an actuating lever which is operatively connected to the setting element ofthe internal combustion engine in such a way that the rotational speed ofthe internal combustion engine can be increased by actuation ofthe actuating lever, whereasthe pressure of the control pressure medium supplied to the first control cylinder continues to be determined bythefirst-mentioned control pressure generator.

2. A motorvehicle as claimed in Claim 1,wherein the actuating lever is operatively connected to an additional control pressure generator, and wherein the control pressure system is arranged in such a way that when the further power-consuming arrangement is brought into operation due to the actuation of the actuating lever, the pressure ofthe control pressure medium supplied to the second control cylinderis determined bytheadditional control pressuregenerator instead ofthe first-mentioned control pressure generator.

3. A motorvehicle as claimed in Claim 2, wherein a restictor is arranged in the control pressure line which leads from the first control pressure generatorto said second control cylinder.

4. A A motorvehicle as claimed in Claim 3,wherein said restrictor is adjustable.

5. A motor vehicle as claimed in Claim 4, wherein the restrictor can be adjusted so that it is completely closed.

6. A motorvehicle as claimed in Claim 5, wherein said restrictor is controlled by said actuating lever in such a waythat,whenthefurlher power-consuming arrangementisbroughtinto operation,the restrictor isclosed.

7. Adrive unitasclaimed in any of Claims3to6,ofClaims3to 6, wherein, parallel to the restrictor, there is arranged a non-return valvewhich opens to the second control cylinder.

8. A motor vehicle as claimed in Claim 1, wherein a mechanical connection is provided between the actuating leverandthe setting elementofthe intemal combustion engine, so that, when the actuating lever is actuated, the power delivered bythe internal combustion engine is increased.

9. A motorvehicle as claimed in Claim 1 wherein a restrictor is arranged in the control pressure line from the first control pressure generator between the first control cylinder and the branch pointfrom which a part of said control pressure line leads to the second control cylinder.

10. A motorvehicle as claimed in anyofthe preceding Claims, wherein the stiffness or rigidity of the springs in the first and second control cylinders are such that the piston which is connected to the setting elementofthe internal combustion engine reaches its end position ata pressure ofthe control pressure medium atwhich the setting elementofthe hydrostatictransmission has reached a position in the middle of its adjustment range, atwhich position the hyd rostatictransmission absorbs the full power produced by the intemal combustion engine.

11. A motor vehicle as claimed in any ofthe preceding Claims,whereinthe spring againstwhich abutsthe piston which is connected to the setting element ofthe internal combustion engine consists of a stackofspring of different lengths in order to produce a non-linear characteristic curve.

12. A motorvehicle as claimed in Claim 11, wherein the springs of different lengths have different degrees of stiffness or rigidity.

13. Adrive unit as claimed in Claim 1,wherein a mechanicaltransmission unitwhich performs a nonuniform transmission is arranged between the piston ofthe second control cylinderand the setting element ofthe internal combustion engine.

14. AmotorvehicleasclaimedinClaim 13, wherein said mechanical transmission unit consists of a cam with a feeler pin.

15. A motor vehicle as claimed in Claim 1, wherein the hydrostatic transmission operates in a closed circuit and comprises a pump which can be setto deliver in one of two directions of delivery at a time, the piston in the first control cylinder being connected to said pump, wherein two control pressure lines are provided to supply control pressure medium to said first cylinder on respective opposite sides of said piston, and wherein said two control pressure lines are also connected to a switch-over valve, another line which emanates from the switch-over valve being connected to the second control cylinder.