Method for starting a vehicle with hydrostatic auxiliary drive

Abstract

Method for starting a vehicle having a vehicle drive with an internal combustion engine (4) for driving a first wheel (2) or a first axle and a hydrostatic auxiliary drive (10) for driving a second wheel (12) or a second axle, wherein the hydrostatic auxiliary drive (10) has an adjustable hydraulic pump (34) driven by the internal combustion engine (4) and at least one hydraulic motor (14), characterized by the steps: - firstly regulating a supply pressure of the at least one hydraulic motor (14) as a function of an accelerator pedal (45); - Determining a rotational speed other than zero of the first wheel (2) or the first axle; and - Synchronizing a rotational speed of the second wheel (12) or the second axle with the rotational speed of the first wheel (2) or the first axle only after the vehicle has started moving.

Description

[0001] The invention relates to a method for starting a vehicle with a hydrostatic auxiliary drive according to the preamble of patent claim 1 or 2.

[0002] For vehicles that are used on surfaces with low traction and / or with steep gradients, e.g. trucks on construction sites, it is known from the state of the art to connect a hydrostatically driven front axle to a conventionally mechanically driven rear axle of the vehicle.

[0003] The publications US 6 644 429 B2, DE 41 10 161 A1, US 2006 / 0 065 465 A1, US 4 444 286 A, DE 42 12 983 C1, and DE 41 10 161 C2 each show such a drive concept, in which an internal combustion engine mechanically drives a rear axle and also a variable displacement pump. The variable displacement pump can drive hydraulic motors for the respective front wheels.

[0004] Document DE 41 10 161 C2 further discloses that the pressure control of the hydrostatic auxiliary drive and thus the torque control of the front wheels, together with the torque control of the rear wheels, is carried out via a vehicle accelerator pedal. This control is carried out simultaneously for the rear wheels via the combustion engine and for the front wheels via a pressure control valve of the hydrostatic auxiliary drive. Pressure medium can only be supplied to the hydraulic motors when a transmission output shaft rotates. This can cause the rear axle to "lead" when moving off, which can lead to a loss of lateral stability and an unstable driving condition. Furthermore, it is possible that if the rear wheels are already spinning, the vehicle can no longer move off despite the additional drive torque built up by the front wheels.

[0005] In contrast, the invention is based on the object of creating a method for starting a vehicle with a hydrostatic auxiliary drive, the starting behavior of which is stabilized.

[0006] This object is achieved by a method for starting a vehicle with a hydrostatic auxiliary drive having the features of patent claim 1 or 2.

[0007] A first variant of the method according to the invention for starting—in particular from a standstill—relates to a vehicle having a vehicle drive with an internal combustion engine for driving a first wheel or a first axle and a hydrostatic auxiliary drive for driving a second wheel or a second axle. The hydrostatic auxiliary drive has an adjustable hydraulic pump driven by the internal combustion engine and at least one hydraulic motor hydraulically coupled thereto. The first variant of the method according to the invention comprises the following steps: - especially first increase and then - regulating a supply pressure of the at least one hydraulic motor as a function of an accelerator pedal; - Determining a non-zero speed of the first wheel or axle - in particular the rear -; and - Synchronizing a speed of the second wheel or the second axle - especially at the front - with the determined speed of the first wheel or the first axle.

[0008] A second variant of the method according to the invention for starting - in particular from a standstill - with a vehicle described above has the steps: - especially first increase and then - regulating a supply pressure of the at least one hydraulic motor as a function of an accelerator pedal; - Determining a speed of the vehicle other than zero; and - Adjusting the speed of the second wheel or axle - especially the front - to the determined speed.

[0009] With both variants of the method according to the invention, a torque specification for the second wheel or the second axle is initially determined upon starting off, and the second wheel is driven without paying attention to the drive of the first wheel or the first axle. This stabilizes the vehicle's starting behavior in this first operating state. It is determined whether the vehicle has started moving. Only after the vehicle has started moving are the drives of the two wheels or the two axles adjusted to one another in a second operating state.

[0010] Further advantageous embodiments of the invention are described in the dependent patent claims.

[0011] The determination of the speed in the second variant of the method according to the invention is preferably carried out via an anti-lock braking system (ABS) on the first wheel.

[0012] The increase or regulation of the supply pressure is preferably carried out depending on the angle of the accelerator pedal. Increasing or regulating the supply pressure is preferably done by adjusting a swivel angle of the hydraulic pump.

[0013] In order to achieve the later target speed as accurately as possible, it is preferred for vehicles with automatic transmission if the swivel angle of the hydraulic pump is pre-controlled or adjusted in accordance with a set gear of the automatic transmission.

[0014] A vehicle for carrying out the method according to the invention has a vehicle drive with an internal combustion engine for driving a first wheel or a first axle and a hydrostatic auxiliary drive for driving a second wheel or a second axle. The hydrostatic auxiliary drive has an adjustable hydraulic pump driven by the internal combustion engine and a hydraulic motor hydraulically coupled to it. A supply pressure of the hydraulic pump can be regulated as a function of an accelerator pedal and also as a function of a rotational speed sensor or speed sensor arranged on the first wheel or on the first axle - in particular at the rear. This allows a torque specification for the second wheel or the second axle to be determined initially when the vehicle starts moving, without paying attention to the first wheel or the first axle.In this way, the vehicle's starting behavior is stabilized in an initial operating state until a speed is determined at the first wheel or axle.

[0015] In a particularly preferred development of the vehicle with anti-lock braking system (ABS), the rotational speed sensor or the speed sensor of the anti-lock braking system is used to minimize the device.

[0016] In a particularly preferred application, the vehicle is a heavy goods vehicle (HGV).

[0017] An embodiment of the invention is described in detail below with reference to the figures. They show: Fig. 1 a schematic diagram of a truck with a hydrostatic auxiliary drive for carrying out the method according to the invention; and Fig. 2 a circuit diagram of the hydrostatic auxiliary drive according to Fig. 1.

[0018] Fig. Figure 1 shows a highly schematic representation of a truck 1 whose rear wheels 2 are driven via a conventional mechanical drivetrain with an internal combustion engine 4, transmission 6, propshaft 8, differential, etc. The truck 1 is equipped with a hydrostatic auxiliary drive 10, which can be optionally activated, for example, in difficult terrain. This hydrostatic auxiliary drive 10 has a hydraulic motor 14 for each of the front wheels 12, which is supplied with pressure fluid via a pump unit 16 driven by the internal combustion engine 4.

[0019] According to the enlarged section of one of the two hydraulic motors 14 in Fig. 1, these are designed as inverse radial piston engines, with a plurality of pistons 18 being supported on a cam ring 20.

[0020] The pistons 18 are radially adjustable and guided in cylinder bores of a cylinder drum 22 and each define a working chamber 24, with each of these multiple working chambers 24 being successively connected to high and low pressure. Due to the resulting piston stroke, the cylinder drum 22 rotates, with the pistons 18 rolling over rollers 26 on the cam ring 20. The cylinder drum 22 is connected in a rotationally fixed manner to a drive shaft 28, which essentially forms the wheel axle of the respective front wheel 12. The hydraulic motor 14 forms a kind of "wheel bearing" for the respective front wheel 12.

[0021] In the position shown, the pistons 18 rest against the cam ring 20, so that when the hydrostatic auxiliary drive 10 is not activated or switched on and the hydraulic motors 14 are running "idly," considerable friction losses can occur. To minimize these friction losses, the hydraulic motors 14 can be operated in a free-wheel mode. For this purpose, a motor housing 30 supporting the cam ring 20 is subjected to pressure, for example a feed pressure, while the working chambers 24 are pressurized or relieved of the tank pressure or another lower pressure. Due to the pressure difference, the pistons 18 are retracted towards the drive shaft 28 and thus lifted off the cam ring 20 - the friction losses are accordingly significantly reduced.

[0022] Fig. 2 shows the circuit diagram of the hydrostatic auxiliary drive 10 optimized according to the invention from Fig. 1. The two front wheels 12 can be seen, each driven by a hydraulic motor 14. The pressure medium is supplied via the pump unit 16, which is hydraulically connected to the hydraulic motors 14 via two working connections A, B and a valve arrangement 32.

[0023] The pump unit 16 has a hydraulic pump 34 which can be pivoted above zero and is driven by the internal combustion engine 4 via a drive shaft 36 representing a power take-off. The power take-off can be operated at the speed of the crankshaft or at the speed of the camshaft of the internal combustion engine. In the following explanations, it is assumed that a (in Fig. 2) The upper pressure line is a low-pressure line 38, while another pressure line connected to a connection of the adjustable hydraulic pump 34 is a high-pressure line 40. Depending on the control of the adjustable hydraulic pump 34, the high-pressure and low-pressure branches can switch for braking or reversing the direction of travel.

[0024] Furthermore, a feed pump is arranged on the drive shaft 36, via which pressure medium can be sucked from a tank T and fed into the low-pressure branch of the auxiliary drive 10 with a feed pressure of, for example, 20 to 30 bar.

[0025] The swivel angle of the adjustable hydraulic pump 34 is adjusted by means of an actuating cylinder 42, whose actuating piston is connected to a pump control valve 44. The pump unit 16 is connected to a control oil supply via control oil connections X1, X2.

[0026] The swivel angle of the adjustable hydraulic pump 34 is used to adjust the supply pressure of the two hydraulic motors 14 and thus to adjust the torque at the front wheels 12. According to the invention, when starting off in a first operating state, a driver of the truck Fig. 1, a command variable for controlling the adjustable hydraulic pump 34 is initially specified. According to the above explanations, the pressure medium is pumped into the high-pressure line 40 and flows back from the consumer, in this case from the hydraulic motors 14, in a closed circuit via the low-pressure line 38 to the low-pressure connection of the hydraulic pump 34.

[0027] As soon as the truck starts moving and a speed is measured at a speed sensor (not shown in detail) of the anti-lock braking system 46 (see Fig.1) of the rear wheels 2 is detected, the system switches to a second operating state. This can occur, for example, at a speed of 3 km / h. In the second operating state, the rear wheels 2 are controlled synchronously with the front wheels 12. The speed of the rear wheels 2 detected by the speed sensor serves as the target value.

[0028] Deviating from the described exemplary embodiment of the method, a speed of the truck 1, which is detected via the anti-lock braking system 46 or via a speedometer or via a global positioning system (GPS), can also serve as the target value. According to the invention, the system then switches to the second operating state when the truck 1 starts moving and a speed is detected.

[0029] Disclosed are two variants of a method for starting—in particular from a standstill—a vehicle having a vehicle drive with an internal combustion engine for driving a first wheel or a first axle and a hydrostatic auxiliary drive for driving a second wheel or a second axle. The hydrostatic auxiliary drive has an adjustable hydraulic pump driven by the internal combustion engine and at least one hydraulic motor hydraulically coupled thereto.

[0030] The first variant of the method according to the invention has the steps: - especially first increase and then - regulating a supply pressure of the at least one hydraulic motor as a function of an accelerator pedal; - Determining a non-zero speed of the first wheel or axle - in particular the rear -; and - Synchronizing a speed of the second wheel or the second axle - especially at the front - with the determined speed of the first wheel or the first axle.

[0031] A second variant of the method according to the invention relates to the same vehicle described above and has the steps: - especially first increase and then - regulating a supply pressure of the at least one hydraulic motor as a function of an accelerator pedal; - Determining a speed of the vehicle other than zero; and - Adjusting the speed of the second wheel or axle - especially the front - to the determined speed.

[0032] Also disclosed is the corresponding vehicle, which has a vehicle drive with an internal combustion engine for driving a first wheel or a first axle and a hydrostatic auxiliary drive for driving a second wheel or a second axle. The hydrostatic auxiliary drive has an adjustable hydraulic pump driven by the internal combustion engine and a hydraulic motor hydraulically coupled thereto. A supply pressure of the hydraulic pump can be regulated as a function of an accelerator pedal and also as a function of a rotational speed sensor or speed sensor arranged on the first wheel or on the first axle—in particular at the rear.

Claims

[1] Method for starting a vehicle having a vehicle drive with an internal combustion engine (4) for driving a first wheel (2) or a first axle and a hydrostatic auxiliary drive (10) for driving a second wheel (12) or a second axle, wherein the hydrostatic auxiliary drive (10) has an adjustable hydraulic pump (34) driven by the internal combustion engine (4) and at least one hydraulic motor (14), characterized by the steps: - firstly regulating a supply pressure of the at least one hydraulic motor (14) as a function of an accelerator pedal (45); - Determining a rotational speed other than zero of the first wheel (2) or the first axle; and - Synchronizing a speed of the second wheel (12) or the second axle with the speed of the first wheel (2) or the first axle only after the vehicle has started moving. [2] Method for starting a vehicle having a vehicle drive with an internal combustion engine (4) for driving a first wheel (2) or a first axle and a hydrostatic auxiliary drive (10) for driving a second wheel (12) or a second axle, wherein the hydrostatic auxiliary drive (10) has an adjustable hydraulic pump (34) driven by the internal combustion engine (4) and at least one hydraulic motor (14), characterized by the steps: - firstly regulating a supply pressure of the at least one hydraulic motor (14) as a function of an accelerator pedal (45); - Determining a speed of the vehicle other than zero; and - Adjusting the speed of the second wheel (12) or the second axle to the speed only after the vehicle has started moving. [3] Method according to claim 2, wherein the speed is determined via an anti-lock braking system (46) on the first wheel (2). [4] Method according to one of the preceding claims, wherein the control of the supply pressure takes place as a function of an angle of the accelerator pedal (45). [5] Method according to one of the preceding claims, wherein the control of the supply pressure is carried out by adjusting a pivoting angle of the hydraulic pump (34). [6] Method according to claim 5, comprising the preceding step: - Pre-controlling or adjusting the swivel angle of the hydraulic pump (34) depending on a set gear of an automatic transmission.

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