{
  "data": {"url": "data/cars.json"},
  "mark": "bar",
  "encoding": {
    "x": {"field": "Origin", "type": "nominal"},
    "y": {"field": "Acceleration", "type": "quantitative", "aggregate": "mean"},
    "column": {"field": "Cylinders", "type": "ordinal"},
    "color": {"field": "Origin", "type": "nominal"}
  }
}

{
  "data": {"url": "data/cars.json"},
  "mark": "bar",
  "encoding": {
    "x": {
      "field": "Origin",
      "type": "nominal",
      "axis": {"labels": false,"title": "","tickSize": 0}
    },
    "y": {
      "field": "Acceleration",
      "type": "quantitative",
      "aggregate": "mean"
    },
    "column": {"field": "Cylinders","type": "ordinal"},
    "color": {"field": "Origin","type": "nominal"}
  }
}

Use labels: false in grouped bar chart example
Use labels: false in grouped bar chart example