HYDRAULIC POWER BRAKE SYSTEM AND METHOD FOR ABS CONTROL

Abstract

A hydraulic power brake system (1) of a wheeled vehicle or for a vehicle unit has a main brake line (20, 21), in which a setpoint brake pressure can be controlled via a brake valve (4) that is operated via a brake pedal (7), and from which an axle brake line or a wheel brake line (46, 49, 50) branches off. Inlet valves and outlet valves and a pilot control valve of the ABS control system for the vehicle unit or for each vehicle axle are respectively disposed together in an ABS modulator block (69), which also includes a temperature sensor (70, 71, 72) for detecting the oil temperature (T) and a heating element (73, 74, 75) for locally heating the hydraulic oil are disposed in each ABS modulator block (69).

Claims

1. A hydraulic power brake system (1) for a wheeled vehicle unit, comprising: a main brake line (20, 21), configured to provide a setpoint brake pressure controlled via a brake valve (4) that is operated via a brake pedal (7), and from which an axle brake line or wheel brake line (46, 49, 50) leading to an actuating unit (13, 15, 17, 19) of a wheel brake (12, 14, 16, 18) branches off, a valve arrangement (8) of an ABS control system, which comprises respectively a hydraulic pressure-controlled inlet valve (28, 34, 40) disposed between the main brake line (20, 21) and a respective axle brake line or wheel brake line (46, 49, 50), and a hydraulic pressure-controlled outlet valve (30, 36, 42) disposed between the respective axle brake line or wheel brake line (46, 49, 50) and an unpressurised return line (51, 52, 53), and a electromagnetically operated pilot control valve (32, 33, 38, 39, 44, 45) connected upstream of each inlet valve and outlet valve (28, 30, 34, 36, 40, 42), wherein the inlet valves and outlet valves (28, 30, 34, 36, 40, 42) and the pilot control valves (32, 33, 38, 39, 44, 45) of the ABS control system for the vehicle unit or for each vehicle axle respectively are disposed together in a respective ABS modulator block (69), wherein a temperature sensor (70, 71, 72) for detecting a local oil temperature T and a heating element (73, 74, 75) for locally heating the hydraulic oil are disposed in each respective ABS modulator block (69).

2. The hydraulic power brake system as claimed in claim 1, wherein the temperature sensor (70, 71, 72) and the heating element (73, 74, 75) are disposed close to the pilot control valves (32, 33, 38, 39, 44, 45) within the respective ABS modulator block (69).

3. The hydraulic power brake system as claimed in claim 2, wherein in at least one of the respective ABS modulator blocks (69), at the temperature sensor (70, 71, 72) and the heating element (73, 74, 75) are disposed close to the pilot control valves (32, 33, 38, 39, 44, 45) for each pair of inlet valves and outlet valves (28, 30, 34, 36, 40, 42) of the axle brake lines or wheel brake lines (46, 49, 50).

4. The hydraulic power brake system as claimed in claim 1, wherein the respective ABS modulator block (69) is shielded by a thermal insulation against the surroundings, at least in the vicinity of the pilot control valves (32, 33, 38, 39, 44, 45).

5. The hydraulic power brake system as claimed in any one of claim 1, wherein the heating element (73, 74, 75) is embodied as an electrical heating body configured to be alternately connected to or disconnected from an electrical power supply of the wheeled vehicle unit via an actuatable electrical switch.

6. The hydraulic power brake system as claimed in claim 1, wherein the heating element (73, 74, 75) is embodied as an electrical heating body that is configured to be alternately connected to or disconnected from an electrical power supply of the wheeled vehicle unit in a self-controlling manner via a bimetallic switch that is integrated within the heating element or on a pilot control valve (32, 33; 38, 39; 44, 45) depending on a prevailing temperature.

7. The hydraulic power brake system as claimed in claim 1, wherein the heating element (73, 74, 75) is embodied as an oil heat exchanger that is alternately connected to or disconnected from a cooling oil circuit of an oil pump of a hydraulic pressure supply system or a combustion engine or a driving gearbox or a working gearbox of the wheeled vehicle unit via an actuatable solenoid valve that is disposed in a feed line or return line of the oil heat exchanger.

8. The hydraulic power brake system as claimed in claim 1, wherein the heating element (73, 74, 75) is embodied as a water heat exchanger that is alternately connected to or disconnected from a cooling water circuit of a combustion engine associated with the wheeled vehicle unit via an actuatable solenoid valve that is disposed in a feed line or return line of the water heat exchanger.

9. A method for ABS control of a hydraulic power brake system (1) of a wheeled vehicle unit according to claim 1, the method comprising the steps of locally measuring the temperature (T) of the hydraulic oil via the temperature sensor (73, 74, 75), and activating the heating element (73, 74, 75) when the measured oil temperature (T) has reached or fallen below a specified switch-on limit value T.sub.H.sub._.sub.on, and deactivating the heating element when the detected oil temperature (T) has reached or exceeded a specified switch-off limit value T.sub.H.sub._.sub.off that is greater than the switch-on limit value T.sub.H.sub._.sub.on.

10. The method for ABS control as claimed in claim 9, comprising the further step of deactivating the ABS control system when the detected oil temperature (T) has reached or fallen below a specified operating limit value T.sub.ABS.sub._.sub.on that is greater than a minimum limit value T.sub.ABS.sub._.sub.min for satisfying predetermined minimum requirements on the ABS control system (T.sub.ABS.sub._.sub.on>T.sub.ABS.sub._.sub.min), the minimum limit value T.sub.ABS.sub._.sub.min being less than the switch-on limit value T.sub.H.sub._.sub.on of the heating element (T.sub.ABS.sub._.sub.on<T.sub.H.sub._.sub.on), (TT.sub.ABS.sub._.sub.on).

11. The method for ABS control system as claimed in claim 10, comprising the further step of outputting a warning signal in a driver's cab associated with the wheeled vehicle unit upon deactivation of the ABS control system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] For further clarification of the disclosure, the description is accompanied by a drawing with an exemplary embodiment and with diagrams. In the figures

[0025] FIG. 1 shows a hydraulic power brake system with an ABS control system according to a first aspect of the present invention in a schematic view,

[0026] FIG. 2 shows a brake pressure profile of an ABS control system of the hydraulic power brake system according to FIG. 1 in the form of a diagram,

[0027] FIG. 3a shows the temperature-dependent viscosity of some hydraulic oils in the form of a diagram, and

[0028] FIG. 3b shows the temperature-dependent viscosity of some hydraulic oils in an enlarged section of the diagram according to FIG. 3a.

DETAILED DESCRIPTION OF THE DRAWINGS

[0029] From the diagram of FIG. 3a and the diagram according to FIG. 3b representing the enlarged section of the diagram of FIG. 3a, it can be seen that the hydraulic oils Agrishift GA 12 and Agrihyd HVLP-D 46 that are often used as brake fluid, gearbox oil and servo oil in agricultural machinery, such as tractor vehicles and harvesting machines, have a large rise in kinematic viscosity at oil temperatures T below 20 C. With the use of the hydraulic oils as brake fluid in hydraulic power brake systems, in which the pilot control valves and the inlet valves and outlet valves of an ABS control system are actuated hydraulically, it is therefore useful to heat the hydraulic oil at least in the vicinity of the pilot control valves when required, i.e. in the presence of a low oil temperature. This reduces the kinematic viscosity of the hydraulic oil that is used for actuation of the inlet valves and outlet valves, which results in shorter switching times of the inlet valves and outlet valves and thus enables a higher ABS control system frequency.

[0030] In the diagrams of FIG. 3a and FIG. 3b, the temperature-dependent viscosity profile of the hydraulic oil Total LHM Plus is shown for comparison. The hydraulic oil, which was specially developed for use in in hydropneumatic suspension systems and brake systems of certain models of passenger vehicles, has a markedly smaller rise in kinematic viscosity at oil temperatures T below 20 C. However, it is not yet used in agricultural machinery.

[0031] In the schematic overview representation of FIG. 1, a hydraulic power brake system 1 of a wheeled vehicle is shown, in which a device according to the invention is provided for detecting the oil temperature T and for heating the hydraulic oil that is used for control when needed.

[0032] The hydraulic power brake system 1 comprises two brake circuits 2, 3 and comprises a brake valve 4, a valve arrangement 8 of an ABS control system comprising three functional groups 9, 10, 11 and a plurality of actuating units 13, 15, 17, 19 of wheel brakes 12, 14, 16, 18 of two vehicle axles of the wheeled vehicle. The wheel brakes 12, 14, 16, 18 are implemented as drum brakes in the present case by way of example, and the actuating units 13, 15, 17, 19 are accordingly embodied as wheel brake cylinders. Via the brake valve 4, which contains two 3/3-way proportional valves 5, 6 and which is operated by a driver via brake pedal 7, a first main brake line 20 of the first brake circuit 2 and a second main brake line 21 of the second brake circuit 3 can each be connected for metered control of a brake pressure with more or less throttling to a pressurized main pressure line 25 of a pressure oil source 24 and an unpressurised return line 26 leading into an oil sump or a reservoir container 27.

[0033] The three functional groups 9, 10, 11 of the ABS control system each comprise an inlet valve 28, 34, 40 and an outlet valve 30, 36, 42, which are embodied as hydraulic pressure-controlled 2/2-way switching valves, and each comprises a pilot control valve 32, 33; 38, 39; 44, 45 embodied as a 3/2-way magnetic switching valve for each inlet valve or outlet valve 28, 30, 34, 36, 40, 42.

[0034] An axle brake line 46 of the first brake circuit 2, from which two wheel brake lines 47, 48 leading to the wheel brake cylinders 13, 15 of the front axle branch off, can be alternately connected to the main brake line 20 of the first brake circuit 2 or an unpressurised return line 51 via the inlet valve 28 and the outlet valve 30 of the first functional group 9 of the ABS control system. The return line 51 is connected to a collecting return line 54 that leads into an oil sump or a reservoir container 55.

[0035] Via the pilot control valves 32, 33, the control inputs 29, 31 of the associated inlet valves and outlet valves 28, 30 can each be alternately connected to a pressurized control pressure line 57, 58, which is respectively connected to a main control pressure line 56 that is connected to the main pressure line 25, or to an unpressurised return line 63, 64 that is connected to the collecting return line 54.

[0036] The main brake line 21 of the second brake circuit 3 branches into a first main brake line branch 22 and a second main brake line branch 23. A first wheel brake line 49 of the second brake circuit 3, which leads to the wheel brake cylinder 17 of the wheel brake 16 of the right vehicle wheel of the rear axle, can be alternately connected to the first main brake line branch 22 of the second main brake line 21, or to an unpressurised return line 52 that is connected to the collecting return line 54, via the inlet valve 34 and the outlet valve 36 of the second functional group 10 of the ABS control system.

[0037] Via the pilot control valves 38, 39, the control inputs 35, 37 of the associated inlet valves and outlet valves 34, 36 can each be alternately connected to a pressurized control pressure line 59, 60, which is respectively connected to the main control pressure line 56 or to an unpressurised return line 65, 66 that is connected to the collecting return line 54.

[0038] A second wheel brake line 50 of the second brake circuit 3, which leads to the wheel brake cylinders 19 of the wheel brake 18 of the left vehicle wheel of the rear axle, can be alternately connected to the second main brake line branch 23 of the second main brake line 21 or to an unpressurised return line 53 that is connected to the collecting return line 54, via the inlet valve 40 and the outlet valve 42 of the third functional group 11 of the ABS control system.

[0039] Via the pilot control valves 44, 45, the control inputs 41, 43 of the associated inlet valves and outlet valves 40, 42 can each be alternately connected to a pressurized control pressure line 61, 62, each of which is connected to the main control pressure line 56, or to an unpressurised return line 67, 68 that is connected to the collecting return line 54.

[0040] In the non-actuated state of the respective inlet valve 28, 34, 40, i.e. the state with zero control pressure, the respective axle brake line or wheel brake line 46, 49, 50 is connected to the associated main brake line 20, 21, and the respective wheel brakes 12, 14 or the respective wheel brake 16, 18 is or are actuated with the setpoint brake pressure. In the actuated state of a control input 29, 35, 41, i.e. the state with a control pressure applied, of the respective inlet valve 28, 34, 40, the respective axle brake line or wheel brake line 46, 49, 50 is shut off from the associated main brake line 20, 21. However, via a non-return valve that is integrated within the respective inlet valve 28, 34, 40, a decrease in pressure in the respective axle brake line or wheel brake line 46, 49, 50 is then possible via the associated main brake line 20, 21 and the brake valve 4, which comes into effect in the event of a temporary release of the brake pedal 7 and a resulting reduced setpoint brake pressure.

[0041] With the respective outlet valve 30, 36, 42 in the non-actuated state, i.e. with zero control pressure, the respective axle brake line or wheel brake line 46, 49, 50 is shut off from the associated return line 51, 52, 53. With the respective outlet valve 30, 36, 42 in the actuated state, i.e. with a control input 31, 37, 43 subjected to a control pressure, the respective axle brake line or wheel brake line 46, 49, 50 is connected to the associated return line 51, 52, 53 so that the associated wheel brake cylinders 13, 15 are pressureless and the respective wheel brakes 12, 14 are released or the associated wheel brake cylinder 17, 19 is pressureless and the respective wheel brake 16, 18 is released.

[0042] During an ABS control operation, in which the pilot control valves 32, 33; 38, 39; 44, 45 are controlled, via electrical control lines, by an electronic ABS control unit 76, by alternately opening and closing the respective inlet valves 28, 34, 40 and outlet valves 30, 36, 42, the brake pressure prevailing in the respective axle brake line or wheel brake line 46, 49, 50 and acting in the wheel brake cylinders 13, 15 of the wheel brakes 12, 14 or in the wheel brake cylinder 17, 19 of the wheel brake 16, 18 is modulated in such a way that locking of the respective vehicle wheels or the respective vehicle wheel is prevented, and as a result the wheeled vehicle remains able to be braked and steered. Because the control pressure is tapped via the main control pressure line 56 on the main pressure line 25, which is at a constantly high oil pressure, the changeover of the inlet valves and outlet valves 28, 30; 34, 36; 40, 42 during ABS control system is always carried out at the same rate independently of the setpoint brake pressure that is controlled via the brake valve 4 in the two main pressure lines 20, 21.

[0043] In the present case, the inlet valves and outlet valves 28, 30; 34, 36; 40, 42 and the pilot control valves 32, 33; 38, 39; 44, 45 of the three functional groups 9, 10, 11 of the ABS control system are disposed together in an ABS modulator block 69 that is mounted remotely from the pressure oil source 24 at a suitable point on the vehicle frame of the wheeled vehicle. In order to enable switching times of the inlet valves and outlet valves 28, 30; 34, 36; 40, 42 of essentially the same rate, and thus an equally ABS control system frequency regardless of current weather conditions, especially at low ambient temperature, a device is provided for detecting the oil temperature T and for heating the hydraulic oil that is used for control when needed.

[0044] For detecting the oil temperature T of the hydraulic oil used for actuation of the inlet valves and outlet valves 28, 30; 34, 36; 40, 42, a temperature sensor 70, 71, 72 is disposed close to the respective pilot control valves 32, 33; 38, 39; 44, 45 in each functional group 9, 10, 11 of the ABS control system. For heating the hydraulic oil that is used for actuation of the inlet valves and outlet valves 28, 30; 34, 36; 40, 42 when needed, in addition a heating element 73, 74, 75 that can be switched on and switched off is disposed close to the respective pilot control valves 32, 33; 38, 39; 44, 45 in each functional group 9, 10, 11 of the ABS control system. Instead of a temperature sensor 70, 71, 72 and a heating element 73, 74, 75 for each functional group 9, 10, 11 of the ABS control system, only one temperature sensor 71 and a heating element 74 could also be disposed centrally in the ABS modulator block 69 close to the pilot control valves 32, 33; 38, 39; 44, 45, as long as the pilot control valves 32, 33; 38, 39; 44, 45 are disposed structurally close to each other.

[0045] The temperature sensors 70, 71, 72 are connected via sensor lines to the electronic ABS control unit 76 for analyzing the detected oil temperature values T. The heating elements 73, 74, 75 preferably embodied as an electrical heating body are for example connected via a relay to an electrical voltage source, which can be actuated by the electronic ABS control unit 76, so as to be able to be switched on and off. The actuation is carried out depending on the temperatures determined by the temperature sensors 70, 71, 72. If the mentioned relay is not available, the heating elements 73, 74, 75 can also be actuated in a self-controlling manner via a bimetallic switch that is integrated within or on a pilot control valve 32, 33; 38, 39; 44, 45 depending on the temperature prevailing there.

[0046] The temperature-dependent switching on and off of the heating elements 73, 74, 75 is described below using the temperature diagram of FIG. 2.

[0047] On starting the wheeled vehicle at time t=0, the heating elements 73, 74, 75 are switched on because the oil temperature T detected via the temperature sensors 70, 71, 72 of the hydraulic oil that is used for control is less than a specified switch-on limit value T.sub.H.sub._.sub.on (T<T.sub.H.sub._.sub.on). The ABS control system is initially deactivated because the detected oil temperature T is also below a specified operating limit value T.sub.ABS.sub._.sub.on. The operating limit value T.sub.ABS.sub._.sub.on of the ABS control system is greater than a minimum limit value T.sub.ABS.sub._.sub.min for satisfying the legal requirements and below the switch-on limit value T.sub.H.sub._.sub.on of the heating elements 73, 74, 75 (T.sub.ABS.sub._.sub.min<T.sub.ABS.sub._.sub.on<T.sub.H.sub._.sub.on). Owing to the separation of the operating limit value T.sub.ABS.sub._.sub.on from the minimum limit value T.sub.ABS.sub._.sub.min, possible measuring inaccuracies in the sensor detection of the oil temperature T and a possible unequal temperature distribution within the ABS modulator block 69 are taken into account, so that in the activated state the ABS control system reliably meets the legal requirements.

[0048] If the oil temperature T of the hydraulic oil has reached or exceeded the operating limit value T.sub.ABS.sub._.sub.on of the ABS control system, the ABS control system is activated, whereby the braking and steering capability of the wheeled vehicle is markedly improved. Once the oil temperature T of the hydraulic oil has reached or exceeded a specified switch-off limit value T.sub.H.sub._.sub.off of the heating elements 73, 74, 75, which is greater than the switch-on limit value T.sub.H.sub._.sub.on (T.sub.H.sub._.sub.off>T.sub.H.sub._.sub.on), (TT.sub.H.sub._.sub.off), the heating elements 73, 74, 75 are switched off, so that the oil temperature T of the hydraulic oil reduces again. If the oil temperature T of the hydraulic oil has then reached or fallen below the switch-on limit value T.sub.H.sub._.sub.on of the heating elements 73, 74, 75 (TT.sub.H.sub._.sub.on), the heating elements 73, 74, 75 are switched on again. Subsequently, owing to the switching off and on of the heating elements 73, 74, 75 a sawtooth-like profile of the oil temperature T results that lies between the switch-on limit value T.sub.H.sub._.sub.on and the switch-off limit value T.sub.H.sub._.sub.off of the heating elements 73, 74, 75.

[0049] Owing to the described heating of the hydraulic oil that is used for control, when starting the wheeled vehicle in cold weather conditions a high switching speed of the inlet valves and outlet valves 28, 30; 34, 36; 40, 42 of the ABS control system and hence a high ABS control frequency is reached relatively rapidly and is subsequently held at a uniformly high level.

[0050] While the above description constitutes the preferred embodiments of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.